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Volume 2 Number 1 . June 1992 ISSN 1012-9812

UNITED NATIONS CENTRE FOR HUMAN SETTLEMENTS (Habitat)

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JOURNAL OF THE

NETWORKof African countries on local

building materials and technologies

United Nations Centre for Human Settlements (Habitat)

Nairobi, 1992

Women contribute significantly in shelter constuction.

Nigeria:

Mauritius:

Malawi:

CONTENTS

Page

Foreword .iii

Significance of information exchange inpromoting the local building-materials sectorin developing countries , .

Pozzolana-the cheap alternative to Portland cement 8

A study of the potential use of Mauritian bagasse ashin concrete 13

The use of rice-husk and bagasse ash as building material 21

Technology profiles:

· Mini-cement production 29· Production of lime 35· Hydrated lime 37

Publications review 40

Events 42

THE AIM OF THE NETWORK AND ITS JOURNAL

The Network of African Countries on Local Building Malerialsand Technologies has the objective of strengthening localtechnological capacity through facilitating infonnation flow,regional cooperation and the transfer of appropriatetechnologies in lowcost and innovative building-materialssector among African counnies.

The Journal of the Network, currently published biannually,seeks to provide a channel for information that is available andcould be of use by professionals, technicians, researchers and

CONTRIBUTIONS TO THE JOURNAL

This Journul welcomes infonnation or articles on lowcostinnovations in building materials technology. Information inthe form of technical and policy papers, illustrations, newsitems lmd announcements of events can be sent fromindividuals or institutions in the private or public sectors, fromwithin lmd outside the African region. An correspondence onthe Journal should be addressed to the Chief, Building andInfrastructure Technology Section, Research andDevelopment Division, UNCHS (Habitat), P.O. Box 30030,Nairobi, Kenya.

The views expressed in this Journal do not necessarily reflectthose of the United Nations. Mention of fIrm names andcommercial products do not imply the endorsement ofUNCHS (Habitat). The reprinting ofany ofthe material in thispublication is welcome, provided that the source is mentionedand one copy sent to UNCHS (Habitat).

National network institutions

Cyprus Organization of Standards and Control of QualityMinistry of Commerce and IndustryCyprus

Department of Civil EngineeringUniversity of Addis AbabaEthiopia

Building and Road Research Institute (BRRI)Kumasi UniversityGhana

Housing and Building Rese:lfCh Institute (HABRI)College of Architecture and Engineering

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scientists, as well as policy and decision makers. It is a mediumfor information exchange and facilitator for acquisition ofsuitable technologies and know-how by needy countries.

Efforts are made to compile, process and publish articles andtechnical papers originating, mainly, in the African region.However, as deemed appropriate and subject to availability,research findings and technological information from countriesoutside the African region are also included to stimulateinterregional cooperation as well.

University of NairobiKenya

Department of Civil EngineeringThe PolytechnicUniversity of MalawiMalawi

Department of Architecture and Civil EngineeringUniversity of MaltaMalta

School of Industrial TechnologyUniversity of MaoritiusMauritius

Nigerian Building and Road Research Institute (NBRRI)LagosNigeria

Faculty of EngineeringFourah Bay CollegeUniversity of Sierra LeoneFreetownSierra Leone

Geological Survey Mines DepartmentMinistry of Lands and MinesEntebbeUganda

Building Research UnitDar-es-SalaamUnited Republic of Tanzania

Ministry of Public Construction and National HousingHamre

Zimbabwe

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FOREWORD

One of the importnnt factors that hinder the development of the local building materi<'l1s sector in most developing countries isthe inability of research institutions to tmnslate their research fmdings into commercial production. One way of tackling thisconstmint is through effective information exchange. Information exchange is an important tool for the development of any sec­tor. It increases awareness among various actors involved in the sector, facilitates transfer and diffusion of technology andstimulates intercountry or interinstitutional cooperation in a variety of areas.

In the past few decades, quite a number of research institutions and universities have been established in Africa and consider­able research work is being carried out in them. However, in the absence of effective information exchange mechanisms, mostresearch results and innovations in the building materi<'l1s sector have remained inaccessible to many African countries. Prospec­tive entrepreneurs or industrial promotion agencies looking for new technologies will need all the available technical informa­tion about a production process and its output. They would also be interested in knowing whether the technology has proved acommercial success elsewhere, particularly, under similar conditions of application.

A major reason for the present unsatisfactory situation is that building research institutions in many developing countries re­main preoccupied with basic research work and the important task of disseminating research information to the industry is notgiven requisite priority. Consequently, the industry, as a whole, has very little access to information on new and innovativetechnologies appropriate to its needs. The limited information available from equipment suppliers are also often biased in fa­vour of large-scale technologies, of little relevance to the vast majority of small-scale producers of building materials.

The Network of African Countries on Local Building Materials and Technologies, through this Journal, is attempting to bridgethis informntion gap by collecting, processing and disseminating information on appropriate technologies and materials amongAfrican countries. The previous two issues of the Journal focused on roofmg and walling materials. The theme selected for thisissue is binding materials. There is no doubt that both waIling and roofing materials are crucial for the construction of a low­cost house, however, none of them could be produced without the use of appropriate binding materials. Binders are essentialcomponents in the production of mortars for masonry, in plastering walls, in stabilizing soil and in making concrete. Amongthe different types of binding materials, Portland cement, with its proved suitability in all types of construction work, has re­mained practically inaccessible to many low-income house builders in developing countries because of its scarcity and highcost. M1my research institutions, in the recent past, have devoted efforts to finding solutions to replace cement with such alter­native binders as lime and natural pozzolanas, and binders produced from agricultural and industrial wastes, and other materi­als. What remains now is to stimu1'lte the industrial sector to make use of such research findings, mincrease cOlTunerciaJproduction, and, by innovative marketing programmes, to increase the acceptability of such lowcost binders among individualhouse builders and contractors.

In this issue of the Journal a number of technical articles on research fmdings and innovations for the production and use oflowcost binders have been compiled, and I hope that they will be of interest and use to the readers. In this connection, I wouldlike to acknowledge and thnnk all the authors and institutions in the countries whose papers are included in this issue and hopethat all these efforts will assist in meeting our common objective: to facilitate better shelter for all.

. .Dr. Arcat RamachandranUnder-Secretary-GeneralExecutive Director

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A gnod foundation is important fix ensuring durability of low-cost houseS"

Side view of a lime kiln

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SIGNIFICANCE OF INFORMATIONEXCHANGE IN PROMOTING THE LOCAL

BUILDING-MATERIALS SECTOR INDEVELOPING COUNTRIES

Introduction

One of the main barriers in technology transfer amongdeveloping countries is related to the limited amount ofinformation exchange. The absence of any systematicinformation flow between developing countries has led to atrend of wasting scarce resources and agenerallack ofprogressin the area of local building materials. Information exchange isa vital component and sometimes the backbone to technologytransfer, a process which has proved to be viable in attainingself-sufficiency in many developing countries in thebuilding-materials and construction sectors.

In both developing and developed countries, there is abundantinformation on low-cost building-materials technologies whichshould be sufficient enough to promote the wide adoption of thebuilding materials. However, in most cases, the bulk of theinformation originating from developing countries is notprocessed or published. The dissemination of the informationis yet another key problem. Even when the information isprocessed and published, there are defiCiencies in the eventualdissemination. This problem is common to information onlow-cost building materials originating from all sources,developing countries, developed countries and relevantinternational organizations. The information is hardly everdisseminated to the target groups: those who would ultimatelymake practical use of the information such as site supervisors,technicians in charge of machine-fabricating workshops,small-scale entrepreneurs and practitioners who are actuallyinvolved in the day-to-day opemtions in the production and useof building materillls. There is also the question of how torepackage information to a comprehensible level for artisans inrural areas who may not understand the rather complextechnical publications which characterize most availableinformation on low-cost building materials.

This article is meant to exllmine the major shortcomings in andsolutions to information exchange. Section A analysesinformation needs. Section B describes the various sources ofinformation relevantto the building-materials sector. Section C

. gives a briefoverview on the services which should be renderedto users. Sections D and E exllmine the current situation and theobstacles to the flow of information and give some solutions onhow to overcome the barriers.

A. Analysis ofinfonnation needs

Generally, there exists a direct relationship betweeninformation needs and the ultimate use of information, i.e.,information needs derme exactly the type of infonnationrequired by a specific user-group or individual. Information hasvalue only when it is osed. No infonnntion can be processed orused effectively, if it does not satisfy the needs of the user, ifthe user does not trust the source of informntion, or if theprocessor of information does not know who would be theultimate user of informntion. The informntion flow, therefore,will not succeed if these prerequisites are not satisfied.

The mnjor user-groups could be cntegorized as follows.

1. Decision/policy-makers

The infonnation requirements of decision- and policy-makersinvolve the directions and priorities of plnnning ~md

progranuning. Decision-mnkers need to dmw on many sourcesof concise, authoritative and up-to-date information which canbe fed with confidence into planning models with dueconsideration to sociological, economic and envirolUnen~tl

factors which are often very complex.

The mnjor types of specific information required are:

(a) State-of-the-mt of available technological capacity inthe country; the performance ofthe industry, its adap~~bility andapplication characteristics;

(b) Data on geological surveys of available and potentialnaturnl resources suitable for production of building mllterials;

(c) Data on current and projected demand of buildingmaterials and forecasting;

(d) Studies on the compatibility of the use of innovativelocal building materials with existing social and cultural pat­terns and on the envirorunen~lI impact of their use.

2. Researchers

Most research institutions in developing countries areconcerned with applied research which might lead to industrialapplication. The bulk ofresearchers need infonnation on resultsachieved atotherresearch institutions which have had an impacton the commercial production ofbuilding materials. Up-to-dateand accurate infonnation on research activities world-wide

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could be of considerable help to research institutions indeveloping countries in selecting the most relevant researchproject, even tho~gh, the selecti?n proc~d~~ for researchprojects normally IS based on a polley of pnonnes.

The specific information requirements are:

(a) Types of research being carried out world-wide and, inpmticular, in developing countries. In view ,of ~e geogm~hic

and climatic resemblances of some countnes ill one regIOn,regional information is more relevant and useful;

(b) Existing research experience and fmdings; laboratorytest results, physical and chemical properties of raw materials~U1d end-products; machinery design, efficiency and perform­~U1ce; costing and cost-benefit ~U1alysis'reports;

(c) Proceedings of conferences, seminars, workshops andother similar events.

Research institutions need infonnation for their activities

3. Trainers

Training and education are the backbone of any type ofdevelopment; training at the.grass-roots level is crucial, becausethe skilled labourers are the ones who are directly involved inthe day-to-day work of production. Universities and high-leveltechnical and vocational training centres are in existence inmany developing countries; however, the training of artisansand other craftspeople has unfortunately not yet reached thelevel of expectatic;m. Trainers in this category are always in needof information related to the various methods of training andskill upgrading.

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The specific needs of those involved in training are:

(a) Basic textbooks; manuals on the production of buildingmaterials; simple and illustrative technical notes; fact sheets;etc.;

(b) Current awareness buUetins/joWllals reporting sourcesas well as trends ~U1d developments in various applications;

(c) Literature surveys; conference and seminar proceed­ings and periodical journals;

(d) Audio-visual aids;

(e) Evaluated data on sources, material tmd methods,

Audio-visual materials are important infonnation sources for trainers

4. Entrepreneurs and professionals

Building-materials production phmts, construction finns andprofessionals and technicians working in such facilities areindeed the main actors directly involved in the manufacture anduse of building materials. These groups are the largest amongthe others mentioned earlier, and in a broad sense, theirexperience, endeavours and achievements very often establishthe basis for a number of peripheral activities such as researchand training, among others. Therefore, furnishing suitabletechnical information to these user-groups would significantlyimprove their operations. In fact, these groups are usually themain sources ofinfonnation generation, which, ifprocessed anddisseminated among, and used by different groups, would helpconsiderably in the promotion of the building-materials andconstruction industries in every country. The major informationrequirements of these groups are:

(a) Directories of institutions and fIrms involved in researchand in the design of buildings, in the production of buildingmaterials and in construction;

1(b) Directories of /inns and workshops involved in the

manufacture of machinery and equipment for the production ofbuilding materials;

(c) Periodical journals, technical reports ,md other types ofpublications covering innovations, case-studies and appliedresearch results in the building materials and construction sec­tor;

(d) Standards and specifications for building-materials pro­duction ,md application.

B. Survey o/sources olin/ormation

The diversity of various institutions and individuals concernedwith low-cost building materials and construction technologiesis reflected in the pattern of information provision, both throughinfonnal exchange and fonnal information service provision.This institutional diversity and the very rapid growth of interestand activity have resulted in a situation where mechanisms forinformation exchange currently available are widelyrecognized as being inadequate.

Among the major information sources, the following areconsidered as the most relevant ones.

Conferences and workshops [lrc important for intcrpcrsonalcomm unication

1. Conferences, meetings alld workshops

Among the various means of information transfer, interpersonalconununication through participation in meetings, conferencesor workshops is preferred. Over the past few decades theincrease in the number of conferences and different types ofmeetings of international and regional scope, in all areas ofbuilding materials and technologies, has been large, and thepublished proceedings of such events are heavily cited in thereview of literature. In fact, such events are good sources ofinfonnation, because they establish forums for the excrumge of

views, provide exhibits, pennit site visits, ,md facilitate personalconta.cts among different groups having mutual interests.

Even though interpersoJkll conullunication through meetings isregarded as being very effective, there is clearly a limit to theextent to which this kind of information tnmsfer can begeneralized and extended, if only for the timmcial burden, bothfor the orgmrizers and the participants.

Meetings lire important for exchange of vicws

2. Directories

The import,mce of identifying institutions and individuals aspotential sources of infonnation on building materials ,mdconstruction is well recognized. Collection and disseminationof such infonnation is usually org,mized through publisheddirectories or databases developed in relevmlt libraries ,md!ordocumentation centres.

Directories are meant not only to provide a roster of llfunes andcontact addresses, but also 10 stimulate intercountrycooperation. Recognizing the need for better knowledge of, .mdcloser links between institutions dealing with humansettlements issues, UNCHS (Habitat) undertook, as early as1978, the preparation of a series of directories ,md guides 1.0infonnation sources on institutions, organizations andindividuals involved in the field of hum,m settlements. Eachdirectory ,md infonnation source deals with a different aspectof human settlements such as: training, financing, andconstruction materials, among others. The most comprehensiveand up-to-date directory published by UNCHS (Habitat) is theHabitat Directory (HS/106/86) *which lists 1784 llfunes oforg,mizations de,t.ling with human settlements, in threelanguages.

'" Symbols in parentheses are the salcs numbers ufthe publicatiun.

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Bibliographies and directories are important sources of information

3. Referral services

Referral services are meant to supply appropriate informationto other dissemination centres or individuals. The majorfunctions of a referral service are:

(a) To collect, on a world-wide basis, information aboutdalll and information resources on a specific subject:;

(b) To prepare a comprehensive inventory of the kinds ofdatHfmformation/services available from these sources with adetIliled subject index for access;

(c) To guide users to the appropriate sources of the requireddata or information.

4. BibLiographic references

Bibliographies are considered as being among the most relevantinformation sources for all those who, in one way or another,are involved in a specific sector of the building indusby.Undoubtedly, all actors involved in the building sector, whowant to keep abreast of developments in the building-JTh1.terialsand construction industries, need up-to-date reference materialin their day-to-day work.

UNCHS (Habitat), in its endeavour to achieve its objective offostering technology exchange and information dissemination,has produced a series of bibliographies on topics related tohum,ffi settlements. Among these bibliographies which relate tothe building indusby are:

-Bibliography 011 Local Building Materials. PLants andEquipment (HS/22/82E)

-Bibliography 011 Small-scale BuiLding Materials Production(HS/154/89E)

-Bibliography on Earth COJlstruction (HS/169/89E)

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-Bibliography 011 Passive Solar Systems in Buildings(HS/173/89E)

5. Periodicals and other technical publications

During the past few decades, a numberofinternational, nationaland non-government.1l organizations, in an attempt to collectand disseminate information, have launched programmes forpublishing periodicals, such as journals, news bulletins, andbooks, which are considered quite satisfactory and effective forthe user-communities. .

Exhibitions could be good sources of information

Even though, publishing specialized periodicals has a very longhistory in developed countries, the process, particularly in the

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may exist in the memory or notebook of a personal source.Information services are usually composed of primary sourcesas well as compendia ;md a variety of traditional retrievalguides. As no document collection is self-sufficient, it mustidentify other sources of infonnation through catalogues anddirectories. Between infonnation ,md its user there are theoperations of the infonnation service, such as disseminationwhich is initiated by the infonnation services, and searches lmdretrieval, which C,ill be initiated by the user. The main categoriesof user groups, in this regard, could be defmed as: thoseexpressing individual qu~ries and those expressing wider ,mdmore pennanent interests that are to be regularly matchedagainst new acquisition~ in the documentation services. Eithertype of group consists ofa set ofkeys which should be comparedwith document profiles. The simplest fonn of matching is torequire that all user keys must be present in the profile of adocument before the latter's location is reported.

Another important function that an infonnation service shouldcarry out in order to render services to users is reviewingpublications upon their receipt for the purpose of selectinginfonnation pertinent to the progrmnme ofa specific user-groupand to note individual items to be brought to the attention ofusers. This is generally known as "current-awareness" service.A refmement of the current-awareness idea is the selectivedissemination of infonnation that is designed to serve theindividuals directly.

6" Technical assistance programmes as information sources

An exmnination of technical assistance progrmnmes, bothinternational ,md bilateral, indicates that the experience gainedin them provides a potentially valuable source of infonnationto and about developing countries. The extent to which theinfonnation generated might be generally available is hardlyknown. However, much of it warrants systematic and widerdissemination, especially at the regional level and in tenns ofteclmical cooperation among developing countries (TCDC).

In the context of technical assistance progrrunmes initiated bythe United Nations system, the establishment of regional andglobal networks in specialized areas, as a means for collectinginfonnation ,md establishing databases, is considered as one ofthe most effective methods, and if operated on a sustainablebasis, could become a vital source of infonnation in a specificsubject area. These networks, in order to function effectively,would obviously need various types of means such as:equipment ,md hardware; software; personnel; and premises. Itis difficult, however, to estimate in quantifiable tenns the extentof the means necessary for the operation of a network or one ofthe documentation centres in the network. This would dependon the number ;md characteristics of the USers to be served, thevolume of documentation to be processed, the documentationmethod used, the services to be provided etc. Therefore, as apreliminary step to each case, these various elements must bethe subject of a detailed assessment and analysis making itpossible to estimate in qmmtitative tenns what means arerequired.

field of low-cost building materials and technologies, is in itsinfancy in most developing countries and the number ofpublications dealing only with the problems of developingcountries in this subject is very limited. Commercial publishers,in recent years, are showing ,ill increased interest in textsrelevant to developing countries, but much of their outputs tendto consist of case-studies which attract limited interest outsidethe country concerned. Moreover, by their very volume,journals being published world-wide may be presumed tocontain much infonnation on specialized topics, yet, there isoften a considerable amount of duplication and of publicationfor the sake of doing so. Therefore, in order to improve thequality of the journals specializing in the low-costbuilding-materials sector, there is need for increasedcooperation between the relevant institutions in developingcountries and the publishing organizations.

** In the" prepaIlltion of this section, the use of the Handbook forInfortfwtion Systems and Services (ISBN 92-3-101457-9), publishedi~ "1977 by the United Nations Education"aI, Scientific and Cultural Technical co-operation projects are potentiIII sources of infonnationOrganization, as reference and source, is acknowledged.

If a successful flow of infonnation has to be realized, thenservices such as searching ,md retrieval, dissemination,notification, translation and document reproduction, to mentiononly a few, have to be rendered to the users. !nfonnation maybe recorded in a document whether public or confidential, or it

c. Services to the users **

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Translation and document-reproduction services are alsoconsidered imporUUlt services that should be provided to theuser communities. Translation of documents, very often,imposes great baniers to the transfer of information. Whetherthe actual translation occurs in the processing or disseminationplmse, the information service may be expected to provide fulldocument translations or vernacular summaries of foreignlanguage material. Document reproduction, similarly, carmotbe considered as a purely technical matter. Therefore, the levelof reproduction facilities and capabilities has a direct bearingon the effective service that a documentation service canprovide to its users.

For almost every conceivable building ffillterial which is likelyto have an impact on low-income housing, there is a proved andappropriate technology. Despite this, and in view of a generallack of a sySteffilltiC flow of information, the majority ofdeveloping countries are still stuck with huge resource outlayson the fundamentals of research into innovations in low-costbuilding materials and often achieving results of noconsequence at all to the worsening shelter crisis. The logicalstep, following the few correct approaches to the promotion oflow-cost building materials should obviously be a process ofinformation exchange among these countries to preclude thiswasteful trend.

The figure shown below is a chart of the flow of information toa scientific and professional user.

D. Examination of the present situation and theobstacles to the flow of infonnation

In the context ofdeveloping countries, even though informationexchange in the building-materials sector is not the soleprerequisite for intercountry cooperation for promoting thesector, it is a vital input to the complex and resource-demandingprocess oftechnology transfer. Some developing countries haveover the years been engaged in various levels of activity topromote low-cost building materials, sometimes involvingprojects which are complementllry to one another, at other timesinvolving straightforward duplication of projects. The issueworth emphasizing is thllt the remaining developing countrieswould not need to invest in any primary research but to buildupon existing experiences and innovations.

The process of information collection and disseminationthrough specialized information services and duta centres indeveloping countries is undergoing gradual development.Special libraries and documentation centres are alreadyestablished in most countries and are usually attached togovernment ministries or universities. The specializedinformation and duta centres are organized in different waysaccording to the system chosen and local conditions. State-runcentres and non-governmental centres play different roles inspecific conditions. However, the assignments of these centresare often not closely linked to each other and in the process ofcollecting and disseminating information, each centre usesresources from abroad. Moreover, the availability anddissemination of information via data centres are, in general,handicapped by the isolated location of these centres and theirlocal production of national duta. Therefore, most scientists areobliged to semch for their information needs personally, whichis a time-consuming effort.

II INFORMATION I

PERSONALSOURCES

Othercollectionsondinfonno.tionservices

IGUIDES

Bibliographies,indexes,abstracts,

~l-"'_V_i,_w_'__-J

Journals,reports,patents,theses,standards,monographs

PUBLICATIONS

r-----t I Inronnation

L---j service 1- CATALOGUE ------'

I 1-----_ ~D1~R~EC~TO~R~Y~~=t===:=:.----~IS~EA~R~C~H~Il ...JL..r D1SSEMINATtON

Ju Clrculalion,announcement,

____J:~r~'p;r;Dd~D;";;D;n==::!_ [~~JSEARCI:I _1 USER I

COMPENDIA

Treatises,encyclopnedio.,handbooks,do.lntables

A model of flow of information to a scientific and technical user. This figure is a reproduction of figure 5.6.1. from UNESCO, Handbook forInformation Systems i2nd Services (Paris, 1977).

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In the past few decades a number of information anddocumentation centres in the areas of building-materials andconstruction induslry have been set up and are in operation inseveral developed countries. The mandate accorded to theseinformation centres are, in many cases, very similar which is tocollect, process and store systematically research activities andtheir fmdings and retrieve and supply them to the interestedparties upon request Some of them are also established merelyto provide technical advice on innovative technologies relevantto developing countries.

These information centres, even though, having contributedconsiderably in collecting and disseminating information, andwhile possessing sophisticated and computerized facilities toprocess information, have, unfortunately, not been able tosatisfy fully and effectively the information needs of manydeveloping countries, and, in particular many countries of theAfrican region. Although digital linkages and communicationexchange have been successfully implemented, the transfer oftechnical and scientific research information into practice hasnot yet been implemented successfully and systematically inmany developing countries, and in some cases the existence ofsuccessful research results is seldom brought to the attention ofusers. There are a several reasons for these problems, the mainones being the almost non-existence of well-organized and-equipped information centres at both the national and regionallevels, a scarcity of trained and experienced professional staffin developing countries to manage these centres, a lack ofadequate policies and strategies to promote the informationflow, and, obviously, the existence of finlUlcial constraintsprevailing in many countries.

Also, there are non-coherent patterns of building-materialsproduction between the formal and informal sectors, the lattergenerally being characterized by small- and medium-scaleproducers. However, considering the induslry as a whole, thereis a lack of appropriate mechanisms for infonnation flow so asto promote the linkages between these two sectors leading tobalanced growth, and to bridge the gap between the demand forand supply of building materials. Therefore, national andsub-regional information centres, to facilitate increasedawareness among professionals llild decision-makers, areconsidered to be equally important as international or regionalinformation centres.

E. Solutions to the barriers in informationexchange

In the preceding sections, a brief analysis of information needs,information sources and obstacles to the flow of information

. relevant to developing countries Ims been presented. In view ofthe multidisciplinary character of information exchange and itsimportance in the promotion ofthe low-cost building- materialssector, tackling the obstacles confronting systematicinformation flow, and devising precise guidelines and solutions,would require a more comprehensive examination of the sectorwhich should be carried out, possibly, in conjunction with somecase studies. However, in the context and limits of this article,some proposed solutions may be summarized as follows:

(a) National, regional and international infonnation cen­tres/networks should be established, and, if in existence, theircapabilities to coordinate and to work in liaison with researchinstitutions and successful entrepreneurs in the area ofbuildingmaterials and technologies, should be strengthened.

(b) All national research institutions, universities and anyestablishment involved in the building-materials industryshould be aware of the existence ofrelevlUlt information centresand should be committed to cooperate with them in regullrrlysupplying relevant inf0iffiation on their activities lmd workprogress.

(c) The infonnation.centres should have professional com­petence and should be in a position to process the informationgathered from vatious institutions and to store it properly foreasy retrieval.

(d) Governments of developing countries, donor countries,and non-governmental and international organizations shouldsupport the information centres during their initial stages andup to the time when they Clm become self-supportive in theiroperations.

(e) The information centres should devise guidelines lmdevaluation procedures for the institutions and/or individualswho are suppliers of information, so that wasteful efforts incompiling and processing of information could be mini­mized/eliminated.

(f) In view of the poor communication systems prevalentin many developing countries for the efficient flow of informa­tion from information centres to the user-communities, it is thevital role of the information centres to ensure a systematic flowof information between the suppliers and users of infonnation.In this regard, information needs must be examined from thefollowing aspects:

(i) The aim of the information (for what use, by whom, inwhich type of institutions):

(il) The nature of the infonnation needed;

(iii) The form in which information is, or might be,delivered.

(g) The information centres/networks should endeavour topublish and disseminate periodicals, journals, technical notes,audio-visual material and any other suitable publications withthe aim of infonning the user-communities on research results,innovations, case studies etc.

(h) The information, technical data and case studies pub­lished must include relevant and useful material. They shouldavoid duplication and should be simple and able to be under­stood by specific categories of user-communities.

(i) Conferences, seminars, workshops, exhibitions andsimilarevents are important tools for the purpose of informationexchange. Therefore, efforts should be made to encourage theirorganizers and increase the number of such events.

(j) Referral material such as bibliographies, directories,compendia etc. needs to be published and disseminated, and ifalready in existence should be updated as appropriate.

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F. Conclusions

Infonnation exchange is a vital component of technologytransfer and an important input to the process of promoting thebuilding-materials industry.

Existence of national infonnation services, in order to facilitatetranslation of research findings into industrial production, andcreate necessary linkages between research and developmentinstitutions on the one hand, and entrepreneurs, on the other, areconsidered as important as the regional and internationalinfonnation centres.

In the process of collecting and disseminating infonnation, theneeds of specific categories of the user-communities should betaken into consideration, e.g., the type of infonnation neededby professionals or researchers should be different from theinformation needed by policy-makers. Likewise, theuser-commurtities must be made aware of the sources ofinfonnation. They must be furnished with such infonnation ascould be deemed useful and relevant to their area ofspecialization.

Organization of conferences, workshops and similar events asa medium for infonnation exchange, as well as publication ofdirectories, bibliographies, journals and the like, on specificaspects of building rnaterials and related technologies, are veryuseful tools in facilitating increased awareness among variouscategories of user-communities.

In the past few decades some non-governmental andinternational agencies in developed countries have establisheddatabases and infonnation systems on the general building andconstruction industries, with very few of them specializing inthe areas of low-cost building materials and relatedtechnologies. Even though their achievements are highlyappreciated and accepted by different categories ofuser-communities, their efforts have not yet been effective instimulating and improving the process of infonnation exchangein many developing countries, in particular, in the countries ofthe African region. This is, mainly, because of the poorcommunication systems in many developing countries, a lackof coherent and sustainable links among various institutions indifferent countries and a h~ck ofsound management on the partof the infonnation centres.

NIGERIA: POZZOLANA - THE CHEAPALTERNATIVE TO PORTLAND CEMENT*

Abstract

The paper is aimed at introducing new entrants into researcheson pozzolanas. Reference is made to the past efforts of theindustrial countries in research work leading to the developmentand commercialization of local pozzolanas in their environs,and how Africa, albeit having abundant potential forpozzoh1l1as, has not yet succeeded in making effective use ofthe only known cheap alternative to Portland cement. The paperenumerates the physical and chemical characteristics of apresumed pozzolanic material. It. gives the state-of-the-art ofresearch methods in the area of pozzolanic materials withoututilizing sophisticated laboratory equipment. With the help ofthe test results, new methods for the physical and the chemicalcombination of pozzolanas, to produce the best blend, areintroduced. The methods could be used in laboratories andindustry, especially when there is need to improve pozzoh'lrticactivity or produce blended cement. Emphasis is laid on the

* By Dotun Adepegba, Professor ofSturcturnl Engineering, Universityof Lagos, Nigeria.

This paper was presented to the Seminar on Local Materials forHousing, Third International Seminar of the African Network ofScientific and Technological Institutions (ANSTI), Civil EngineeringSubnetwork, held at the University of Mauritius. Reduit, March 1990.ANSTI is a UNESCO-sponsored Network

8

need for African Governments to persuade the existing Portlandcement factories in Africa to undertake pozzoh1l1a productionas anew line. The examples ofRwanda and the United Republicof Tanzania are highlighted with a view to encouraging otherAfrican countries to adopt the experiences of developedcountries in the production of pozzolana as an alternative toPortland cement for masonry work.

Illtroduction

Pozzolana is a natural or artificial material which contains silicaand alumina or ferruginous materials in a reactive form. Thenatural pozzolanas are of volcanic origin, such as volcanicashes, tuffs and other diatomaceous earths, and agricultural andmine wastes. Pozzolanic materials are not cementitious inthemselves but, when finely ground, contain some propertieswhich at ordinary temperatures will combine with lime andshale in the presence of water to fonn compounds which havea low solubility character and possess cementitious properties.

There are various types of pozzolanas depending on theircomposition. Portland pozzoh1l1a is a blend of Portland cementand pure pozzolana such as volcanic ashes or rice-husk ash.Lime pozzolana is a blend of natural pozzolana with lime. Ch~ypozzotana is a blend ofshale or clay with pure pozzolana. Therehas not been a report yet on whether pure pozzolanas arecombined to fonn pozzolana cement. There are already a

1

number of pOZZOIan,1S of AfriCffil origin apart from those whichderived their sources from volcffiloes. The mine wastes, such asbauxite wastes, riget cake, riget stone, magnetite, ash of drystalks of palm bunch, coal ash ffild ibnonite are new additionsto the family of pozzolffila of African origin. They are mainlyfrom tin, aluminium ffild coal mines.

Pozzolfma is not a new binder. It was used by the earlyEgyptiffilS, centuries ago. The Greeks used the volcanic tufffrom the islffild ofThem ffild the Romffils used the red volcanictuff found in the Bay of Naples. The best variety of the tuff wasfound around Pozzuoli, hence it was called pozzolan,~.

The high cost ofproduction ofPortlffild cementffild the resultinghigh cost of construction, led some countries in Europe ffildAmerica to mffilufacture pozzolana cements so as to reduce thedemffild on Portlffild cement. Countries that use pozzol= areAustralia, Greece, India, the Russiffil Fedemtion, Spain, theUnited States of America ffild Yugoslavia, However, there areinherent problems in the mffilufacture of pozzolffila cementswhich could raise the cost oftheirproduction to almost the samelevel as POrtlffild cements. Some of the problems are: the refusalof the existing Portlffild-cement factories to adopt pozzolanacement as one of their lines of production; a lack of sufficientqUffiltity of pozzolanic materials; the high tempemture demffildby some pozzolmric materials to improve pozzolanic activity;and the extremely low rate of strength developmentcharacteristic of some pozzohmas due to a deficiency ofessential elements.

In Africa however, RWffilda ffild the United Republic ofTanzffilia have gone into trial production of pozzolffila.Organization of a small pilot plffilt for the mffilufacture oflime-pozzolffila was reported by Apers ffild others (I). The basematerial is volcffilic ash, found in north-western Rwanda. Thelime deposit was found near the site for the factory atRunhengeri. The production cost of lime pozzolffila was aboutRwF6000 (RwFIOO =US$I) per ton, whereas the productioncost of Portlffild cement was about RwF30,OOO per ton. The

lime-pozzolana cement costs about one fifth the cost ofPortlffildcement. This is possible because pozzolana formed about 60 percent of the content, 20 per cent was lime ffild the remnining 20per cent was Portland cement.

Kawiche (2) reported the efforts of the Government of theUnited Republic ofTffilZania in persuading the Mbeya PortlffildCement Factory to produce pozzolan,~cement as one of its linesof production. There is not a single African country thm isdevoid of pozzolanic mnterials. The most common pozzolanicmnterials in Africa are IHterite, limestones, clay ffild shales.Evidence is also nvnilitble that agricultuml wastes withpozzo1Hnic chamcteristics are availnble in large qUffiltities inAfrica,

Comparison ofpozzolanas with Portland cemelll

Pozzol= do not develop strength nt the same high mte nsPortland cement. The strength which ffil ordinary Portlffildcement will attain in 14 days may not be nttained by untreatedpozzo1Hnas in 60 days. The problem is that all pozzolffilas havea low content of calcium oxide ffild a high content of silicondioxide. This imbalance is responsible for the low mte strengthdevelopment.

Tables I and 2 show the efforts of Lea (3) who an,'t1ysed somepozzolan,1S that were found in Europe ffild the United States ofAmerica It is pertinent. therefore, to collate pozzolffilas ofAfriCffil origin with a view to combining one or two of them ifnecessHry, for the improvement of pozzolanic activity or forvolumetric purposes. The Africa Pozzolana ResearchDepository (APRD) which is located in the Civil EngineeringDepartment of the University of Lagos, could be a focal pointfor tlris purpose. APRD hns been involved in research,. since1985, on the explomtion of local pozzokwa, ffild is prepnred toprovide information and help, ffild carry out tests ffild ffilalysisofffily presumed POZZOkWC material thntis nvailnble in fmy pnrtof Africn. In tlris regard, communicntions Cffil be nddressed tothe nuthor.

MgO Nn20 K20 S03

3.9 0.4

3.8 0.1

1.5 0.2

2.6 0.7

4.2

3.1

0.3

0.3

0.2

Table 1. Percentage composition of volcanic ash pozzolanas

Pozzolana Ignition SiOl Ah03 F",03 Ti02 CnO

loss

Rhenish truss 10.1 54.6 16.4 3.8 0.6 3.8

Rhenish lrass 8.5 54.8 17.2 4.4 0.6 2.3

Bavarian truss 14.0 57.0 10.9 5.6 0.5 6.0

Santorian earth 4.9 63.2 13.2 4.9 1.0 4.0

Santarian earth 3.1 65.2 12.9 6.3 3.2

Rome Segni 9.6 44.1 17.3 10.7 1.2

Rome Segni 5.3 48.2 21.9 9.6 7.5

Sao Paolo 4.1 45.2 2.0 10.7 9.8

Naples: Bacoli 4.8 55.7 19.0 4.6 5

Baia 14.4 59.5 t9.3 3.3 2.1

Romanian truss 13.9 62.5 11.6 1.8 6.6

Crimean tuff 11.7 70.1 10.7 1.0 2.5

United States Rhyolithic 3.4 65.7 15.9 2.5 3.4

Pumicite 4.2 72.3 13.3 t.4 0.7

1.9

0.9

2.2

2.1

1.9

2.0

3.2

3.8

1.3

0.2

0.7

0.3

1.3

4.0

5.1

7.0

1.8

3.9

2.6

1.4

3.4

51.6

1.9

5.4 Trace

9

Table 2. Percentage composition of some artificial pozzolanas

Pozzolana Ignition Si02 AhO, Fe2o, eaO MgO Na20+ SO,

loss K20

Burnt clay 1.6 58.2 18.6 9.3 3.3 3.9 3.9 1.1

1.3 60.2 17.7 7.6 2.7 2.5 4.2 2.5Spent oil shale 3.2 51.7 22.4 11.2 4.3 1.1 3.6 2.1

Raw gaize 5.9 79.6 7.1 3.2 2.4 1.0 0.9

Burnt gaize 88 6.4 3.3 1.2 0.8 Trace

Rawmoler 5.6 66.7 11.1 7.8 2.2 2.1 1.4Burnt moler 70.7 12.1 8.2 2.3 2.2 1.5Raw diatomite 8.3 86 2.3 1.8 Trace 0.6 0.4

Burnt diatomite 0.4 69.7 14.7 8.1 1.5 2.2 3.2

Fly ash (United States) 1.2 47.1 18.2 19.2 7.0 1.1 3.95 2.8

7.5 44.0 18.4 11.2 11.6 1.1 3.14 2.0

Fly ash (United Kingdom) 0.9 47.4 27.5 10.3 2.1 2.0 5.7 1.8.. .. .. 4.1 45.9 24.4 12.3 3.6 2.5 4.2 0.9

Rice-husk ash 85.6 2.5 0.3 1.0 1.0 2.5 1.5

Simple methodfor measurement ofpozzolanic activity.

In order to detennine whether or not a material is pozzolanic,the fIrst test to be carried out is the standard constistency test ona paste made from finely ground powder of the material. Thistest is used to detennine the standard consistency of the pastefor use in the tests for the initial and the final setting times ofthe paste. The standard consistency test gives the indication ofthe quantity of water to be added to the dry powder of thematerial being tested to produce the type of paste to be used inthe VICAT apparatus. The quantity of water required for aconsistent paste is an indirect measure of the degree of finenessof the powder. The fmer the powder, the more water it willrequire to produce a consistent paste.

The initial and the fmal setting times of the consistent paste isalso an indication of pozzolanic activity. The nearer the initialand the final selling times of a pozzolanic material to that ofPortland cement, the greater the pozzolanic activity. Twotypical brands of Portland cement were tested, one at the CivilEngineering Department, University of Lagos, and the other atthe Civil Engineering Department, City University, London.The two brands were ordinary Portland cement manufacturedto the specifIcations of BS 12. The test in London was carriedout in the winter and the test in Lagos in the dry season whenthe temperature was about the highest The initial setting timefor the test in London was 3.40 hours and the test in Lagos was2.30 hours. The fJnaI setting time for the test in London was4.27 hours whereas, the test in Lagos gave 3.95 hours. The weD­known behaviourofcement, setting slower in cold weather thanin hot is clearly demonstrated. The same phenomenon isexpected from pozzolanic materials. Therefore, if a test onpozzolanic material is carried out in the cold period the resultcarmot be comparable with the test carried out in the hot period,

10

if, setting time is the detenninant. However, setting times arejust one of the factors that detennine the degree of pozzolanicactivity of materials.

The chemical composition of finely ground powder is the nextstep in the test to identify a pozzolana, whether ornot the settingtimes are suspicious. The need to examine the chemicalcomposition is to find out if the principal elements whichnonnaUy exist in pozzolanas are present. There are severalmethods to detennine the composition of materials. The majorconstituents expected in a pozzolana are silica, lime, aluminaand iron oxide, although others like magnesia, calciumsulphate, potassium, titanium, sulphur and copper have beenfound to be present, depending on the source of materials.GeneraUy, most pozzolanas have a very high content of silicaas is evidenced in tables I and 2. The second highest is alumina.In most cases, untreated pozzolanas are defIcient in calciumwhich is needed to promote pozzolanic activity in combinationwith silica and alumina.

Physical state - new method to combine pozzolanas for maxi­mum activity

The degree ofpozzolanic activity can be increased by two majormethods, viz., the physical method and the chemical/calcinationmethod. The chemical and physical mechanisms by whichpozzolanas develop cementitious properties are complex. In thephysical method of increasing pozzolanic action, one or two, oreven more pozzolanas can be combined to produce an entirelynew pozzolana. The combination may be as a result of thenon-availability of a suffIcient quantity of one or twopozzolanas. A combination of these pozzolanas may produceincreased quantity but not necessarily increased pozzolanicactivity. The combination may, otherwise, be due to a balancingof elements having found that the element that is low or absent

in one pozzolana is abundantly present in the other. Forexample, if the fly ash, with 11.6 per cent of calcium oxide, iscombined with the rice-husk ash with 1 per cent calcium oxide(see table 2) a material with higher pozzolanic activity than thefly ash and the rice-husk ash may result There is a graphicalmethod of scientifically combining any number of pozzolanasto produce a single pozzolana, having a property, very close to,ID ideal composition which is !:he Portland cement. Suppose,there are I:hree pozzolanic materials A, B and C with !:hefollowing chemical compositions:

Pozwlanic material Percentage composition

Fe:!03 Ah03 Si02 CaG

A 14 26 48 5B 11 18 44 12C 3 18 30 30

Portland cement 3 5 22 65

Plot the points as shown in figure 1, with the elements arrangedin the ascending order of the percentage content of the elementin the ideal material, which in this case is !:he Portland cement.The curve with the lowest percentage content of calcium oxideis for material A. The curve with the next percentage content ofcalcium is material B and the curve next to !:hat is for materialC. The highest content of calcium oxide occurs in !:he idealmaterial which is always !:he Portland cement for any exerciseof combining pozzolanas.

Join the foot of curve A to the head of curve B with a dash­and-dot line. Join the foot ofcurve B to the head ofcurve C witha dash-and-dot line. The dash-and-dot line which joins !:he footofcurve A to the head ofcurve B intersects !:he Portland cementcurve at 13 per cent which means that material A will fonn 13per cent of the new material produced by combining materialsA, B and C. Similarly the dash-and-dot line which joins the footofcurve B to the head ofcurve C intersects the Portland cementcurve at 24 per cent which means thnt material B will fonn 24per cent of the new 11k1terial produced by combining materialsA, B and C. Therefore, material C will fonn the balance whichis 63 per cent. This arrangement will produce the bestcombination of the I:hr~e materials for !:he best pozzolanicactivity.

Chemical state

The chemical conversion of pozzolana is highly technical andrequires experience. Care must be taken not to introducechemicals which are strange to !:he chemistry of cement andwhich are likely to be deleterious to pozzolana cement when inuse. The chemical process cannot be complete withoutcalcination. But calcination involves cIinkerization which c,mput extra cost in the production process. The chemical processmust essentia11y be followed by two tests: (a) determination ofthe free lime, which is the same thing as !:he soundness test forcement by Le Chatelier; (b) determination of the sulphatecontent. The chemical process and calcination can be appliedto the physical state, Le., after the combination of one or twopozzolanns, if the result is still not satisfactory. In most casescarbonates of metals are recommended for the chemicalconversion of pozzolanas for improved pozzolanic activity.

100,.-------,-----------r--------,

CliO

_. - - --..:----,~8

Sin2

~e.t,SC<l.l 11'" 0' pOllolana A::.J...<l.l

of BCo 24% pOllDlana... 50c 63% of pozzoJlIna C<l.l

5:;;;...c...E...~

Major Elemenls

Figure 1. Combination of three types of pOlZolana

11

Amorphous silica was reported by Malquori(4) to react muchmore mpidly than the crystalline form because its structuralbonds are weak and unstable, thus, making it vulnerable tocalcium hydroxide. For exrunple, in clay materials, annihilationof the bonds between silica and alumina, due to calcination, hasmade silica and alumina more reactive with calcium hydroxide.This process may not achieve good results in materials formedfrom crystallization in which silica and alumina are slronglyheld in their lattices. A good and easily improved pozzolanicmaterial must have a great percentage of its silica in theamorphous form.

Mecllanical state

Mechanical tests invQlve the determination of the compressiveand the tensile slrengths on a short- and long-term basis. It isadvisable to test the paste as well as the concrete made from thepresumed pozzolanic material. In order to avoid results that arenot reproducible the following points are important and mustbe noted:

(a) Temperature and humidity at the time of casting of thespecimens must be recorded in order to quantify the effect ofthese variables on the test results.

(b) Test specimens prepared from pozzolanic materiaJ.sshould be cured under wet sacks and not immersed in water.Concrete, mortar or paste made from pozzolanas must be keptdamp for a mirtirnum of60 days during which time it must havedeveloped the full slrength of an ordinary Portland cement. Ifpozzolanic specimens are immersed in water, especially at theearly ages, there is a tendency to absorb water, which mayincrease the water of hydration and therehy reduce the Slrengthof the specimen.

(c) Curing under wet sacks may continue for 90 daysbecause some pozzolanas give compressive Slrengths which arehigher than those ofordinary Portland cement at about that age.

12

Pozzolanas set slowly and, therefore, develop very low heat ofhydrution. This makes them very useful for non-structuralconstruction in hot countries. Pozzolanas are more suitable foruse in hot countries th.w in cold because higher pozzoh"Ulicactivity can be developed in hot countries th.w in cold by thesame materials.

References

(I) Apers, J., Pletinck, M., and Verschure, H., "A pozzo-limeindustry in Rwanda", in Proceedings of Symposium all

Appropriate Buildinl{ Materialsfor Low-cost HOIlSillg, Kenya,1983, vol. 2, pp. 86-92.

(2) Kawiche, G. M., "Production ofPortland-pozzolana cementin Tanzania", in Proceedings of Symposillm all AppropriateBuilding Materialsfor Low-cost Housing, Kellya, 1983, vol. 2,pp.95-104.

(3) Lea, F. M., The Chemistry ofCement and Concrete (London,Edward Arnold Limited, 1938), p. 141.

(4) Malquori, G., "Portland-pozzolana cement", in Proceedingsof 4th International Symposium, Washington, vol. II, pp.983-1006.

Acknowledgement

Acknowledgment is due to the University of Lagos CentralResearch Committee, for providing the funds for this researchwhich is part of the exploration of pozzolanas in Nigeria for thepurpose of finding a cheap alternative to expensive ordinaryPortland cement

MAURITIUS: A STUDY OF THE POTENTIALUSE OF MAURITIAN BAGASSE ASH IN

CONCRETE*

Abstract

Bagasse is the fibrous residue of sugarcane after crushing andextraction of juice. Bagasse ash is the waste product of thecombustion of bagasse for energy in sugar factories. Anestimated 20.000 tons of bagasse ash are produced every yearin Mauritius, of which about 11,000 tons are potentially usable.

This paper investigates the technical feasibility ofusing bagasseash as a pmtial replacement of cement in concrete (i.e., as apozzolana), and as a fme aggregate in concrete. The lowchemical reactivity of the ash is demonstrated. Its use as sandin concrete shows no adverse effects on strength or strengthdevelopment up to one year. However, the longer-termproperties ofthe concrete, such as shrinkage and durability needto be further investigated.

Introductioll

The economy of Mauritius, a small, 1800 km2, Indian Ocean

island, has been and is still very much dependent on thecultivation of sugarcane. The production of sugarcane variesfrom year to year, the main factor for such variations beingclimatic conditions, the average annual yield being about 5.6million tons (I). Bagasse, the residue of sugarcane aftercrushing and extraction ofjuice, consists of water (about 50 percent), fibres (above 48 per cent) and relatively small amountsof soluble solids. Nearly all bagasse produced in Mauritius isburnt for energy needed for sugar processing. The surplusenergy is converted into electricity. Only a very small amount(about 3750 tons per year) is used for making resin-bondedboards.

Bagasse ash is at present considered to be a waste product withlittle or no use. It has negative value, in that, the sugar factorieshave to spend money to dispose ofit. Moreover, it is a potentialenviromnental pollutant. It is estimated that about 20,000 tonsof bagasse ash are produced every year. This represents about0.3 per cent of cane crushed or about 2.8 per cent of the dryweight of bagasse.

Since all cement used in Mauritius is imported, the prime use

. • By B. K. Baguant and G.T.G. Mohamedbhai, Department of CivilEngineering, University of MauritiusThis paper was presented to the seminer on Local Building Materialsfor Housing, Third International seminar of the African Network ofScientific and Technological Institutions (ANSm, civil engineeringsubnetwork. held at the university ofMauritius,Reduit, March 1990.ANS~ is aUNESCO-sponsored Network.

of bagasse ash in concrete would be as pozzolana, that is, as a

pmtia1 replacement for cement. Another possibility is its use asa fine aggregate, even though the quantities available are smallcompared with the national annual consumption of about 1.2million tons of fine aggregate. The latter requirement iscurrently being satisfied by crushing basalt rock and quarryingin dwindling reserves of natural coral sand.

Although Mauritius is sparing little effort in developing itsindustrial sector, its economy will continue to depend heavilyon sugar production for many years to come. The sugar factorieson their side, will continue to depend entirely on bagasseburning for energy. The supply of bagasse ash is, therefore,ensured for years ahead.

Characteristics ofbagosse ash

Types and availability

The sugar factories in Mauritius use two types of bagasse-firedwater-tube boilers: a hearth-type and a suspension-burning type(2). In the former, bagasse fed in at the top of the furnace fallsin a pile on the floor of the hearth, while cold or hot air is blownon to the burrting bagasse. This type of burning produces threetypes of ash:

(a) Furnace bottom ash, which accumulates on the floor ofthe hemth and is removed manually at every weekend shut­down.

(b) Hopper ash, which is blown by horizontal air blasts intohoppers situated at the back of the furnace.

(c) Fly ash, which is carried by the exhaust gases up thecltimney and is partially removed by sprays of water.

In the suspension-burrting type, bagasse fed in from the sides isdistributed by a spreader-stoker on to the plan area of thecombustion chmnber, while primary air is blown upwardsthrough a grate enabling the bagasse to burn in suspension inair without heaps forming on the grate. This type of furnace alsoproduces three types of ash:

(a) Grate ash, which accumulates on the grate and is re­moved by tilting the grate every six to eight hours.

(b) Hopper ash, which is blown into hoppers by second,uyair fed in from the sides of the furnace.

(c) Fly ash, which is carried up the cltimney.

Of the estimated 20,000 tons of bagasse ash produced everyyear, about 4000 tons are fly ash (2). The remainder consistsmainly of grate ash (about 11,000 tons).

13

l' '

Table I. Chemical composition of bagasse ash (excluding fly ash) from different sources

Constituents Percentage composition

Ref.9 Ref. 10 Ref. 11 Ref. 2 Dundee, Dundee

Hopper grate

ash ash

Si02 74.2 75.0 71.4 73.07 50.19 57.61Ah03 12.12 3.6 1.6 12.00 10.12 10.11Fe203 12.12 2.7 1.9 12.00 15.75 10.79CaO 3.93 3.9 4.3 4.3 4.94 4.58MgO 0.32 4.1 3.8 2.66 8.14 5.31K20 1.67 7.1 11.0 2.65 5.56 6.22Na,O 0.36 0.2 0.8 0.16 0.41 0.29P,Os 5.58 2.3 3.4 2.57 2.09 2.38803 0.20 0.3 0.23Ch 0.07 0.01MoO 0.26 0.29TiO, 1.57 1.46L.O.!' 1.63 1.65 1.30 1.23 1.24

* Loss-an-ignition

Chemical composition

Results of chemical tests on grate and hopper ashes canied outin Mauritius and at the University of Dundee are shown in tableI. The local data were obtained using classical laboratorytechniques whereas the Dundee results were obtained by al\X-ray fluorescence (XRF) method of oxide analysis.

The results indicate a fairly high degree of variability inchemical composition of the ashes, with the Dundee datashowing marked departures from typical results. But, ingeneral, the grate and hopper ashes have a high silica content,which, if present in an amorphous chemically reactive form,

could enable the ashes to exhibit pozzolanic properties. Also,being alkaline, the ashes are compatible for mixing withPortland cement

The grate and hopper ashes have reasonably lowloss-on-ignition values (see table 2), with the exception of ashesfrom fuel where the factory bums pulverized coal in addition tobagasse for energy production. Fly ash has a high carboncontent. It is also soft, compressible and highly absorptive. Itis, therefore, not suitable for inclusion in concrete.

Physical properties

Table 2. Loss-on-ignition (L.a.I) values of bagasse ashes from various sources

Type of ash

Factory Grate Hopper Fly

Man Desert Alma 3±0.5 1±0.3 71±3Belle Vue 4±0.3 1±0.2F.U.E.L. 14± 1 4±0.3 80±2Rose-Belle ·3±0.5 1±0.2 7 ±0.5

14

Table 3. Specifications of BS 3892 for pulverized fuel ash (pfa) for use in concrete

Property

Fineness (expressed as themass proportion retained on a45 micron sieve)

Loss-on-ignitionWater requirement of nmixture of pfa and ordinaryPortland cement (OPe)PozzoIanic activity index

The grate and hopper ashes are granular, TOugh, vasicularparticles whose maximum sizes can vary extensively as thematerial forms lumps in the furnace. The relative density of theashes on a saturated surface dry basis range between 1.90 and2.12. The ashes also have very high absorption values of 10 ±2 per cent.

The grading of the ashes can be extremely variable, thepercentage passing 600 urn sieve ranging from 14 per cent to80 per cent. But, in general, the ashes tend to be rather coarse,with 15-25 per cent passing the 600 )llTI sieve (2,3).

Pozz%llie activity

There is no national or international standard for testing bagasseash. The specifications of BS 3892 (4) for pulverized fuel ash(pfa) for use in concrete (see table 3) were therefore, used toestablish whether bagasse ash could be an effective pozzolanicmaterial for use in concrete.

Samples of grate ash and hopper ash obtained from one factorywere used in all the tests. Fly ash was excluded because of itshigh carbon content. The ash samples were oven-dried, groundin a ball-mill and sieved through a45,urn test sieve. The samples

Limit (percentage)

Not greater than 12.5

Not greater than 7Not greater than 95 of that ofOPe

Not less than 85

thus automatically satisfied the fineness requirement. Theloss-on-ignition values for grate ash varied between 1.4 and 1.7per cent and those for hopper ash between 0 and 0.2 per cent.These values are well below the 7 percent specified in BS 3892.

The water requirement of grate ash (110 per cent) and hopperash (104 per cent) were greater than the 95 per cent specified inBS 3892, probably because of greater friction between theparticles of ash compared with pfa (5). The greater angularityof grate ash particles compared with hopper ash is reflected inits higher water requirement to give the same flowcharacteristics as that of hopper-ash mortar.

The pozzolanic activity index values for grate-ash andhopper-ash mortars were found to be 68 per cent and 65 percent, respectively, which are much lower than the specifiedminimum of85 per cent in BS 3892, showing the relatively poorreactivities of the ashes. This is not too surprising in view of therelative absence of cenospheres revealed by the scanningelectron microscope (SEM) photographs. However, manypozzolanas are known to exhibit low reactivities at early agesand yet develop significantly higher strengths at later ages. Itwas therefore, decided to investigate the strength development

Table 4. Mix proportion of normal, hopper- and grate-ash concrete

Concrete mix Normal Hopper ash Grate ash

Cement (kg/m3) 320 320 32020 mm gravel (kg/m3) 744 744 74410 mm gravel (kg/m3) 372 372 372

. Natural sand (kg/m3) 744 558 558Ash (kg/m3

) 95 60Water (kg/m3) 200 200 200Total (kg/m3) 2380 2289 2254Slump (mm) 85 50 70

15

Table 5. Strength development with time

Compressive strength

Age Normal Hopper-ash Grate-ash(days) concrete concrete concrete

N/mm2 Percentage N/mm2 Percentage N/mm2 Percentage

3 19.9 48.3 21.5 48.5 20.4 46.9

7 30.3 73.5 30.9 69.7 29.9 68.728 41.2 100.0 44.3 100.0 43.5 100.0

90 45.4 110.2 50.1 113.1 47.8 109.9

180 45.2 109.7 50.7 114.4 48.4 111.3

365 45.9 111.4 51.5 116.2 51.5 118.4

tbe ground. Also, because grate ash is available in largerquantities than hopper ash, it was decided to use grate ash inthis series of investigations.

Figure 1. Strength development as a percentage of 28-day strength

with time of concrete specimens incorpomting ground grate-and hopper-ashes. The mix proportions of the nonnal, grate-and hopper-ash concretes (see tnble 4) were such that the

"0 cement content was kept constnnt and the natural sand was

"t!. reduced by an amount equal to the volume of ash added. The"

" strength results of the specimens tested over a period ofone years 100

are shown in figure 1 and in tnble 5.~;;

The strengths of both gmte- and hopper-ash mixes were~

'"' IlQ compamble with those of the normal mix at all corresponding•~

I!l ages. There was no evidence of any significant additionalt 00 strength development due to pozzolanic activity. These results

~ o Normal cone-rele confirm the poor reactivity of the ashes and make it most

"" l!I. Gnlle-ll5h.concreleunlikely that bagasse ash in Mauritius will ever be used HS

pozzolana in concrete.E Hopper-ash concrele

20Bagasse as" as sand replacemelll ill COllcrete

0 3 7 '" '" 120 360Characteristics ofash selected

Age (Days)

Gmte ash is granular requiring no grinding for use as sand,whereas hopper ashusually cont.1ins clinkery lumps which mus

Table 6. Series 1: Concrete mixes with basalt sand

Mix Free water! Cement Basalt sand content Course aggregate

cement ratio content content

(kg/m3) (kg/m3) (kg/m3)

1.1 0.41 561 747 912

1.2 0.48 480 800 9401.3 0.59 390 878 9521.4 0.67 343 939 939

1.5 0.84 274 1031 915

16

Table 7. Series 2: Concrete mixes with grate ash

Mix Free water! Cement Grate ash Coarsecement ratio content content aggregate

content

(kg/m3) (kg/m3

) (Kg/m3)

2.1 0.41 561 498 9122.2 0.48 480 553 9402.3 059 390 585 9522.4 0.67 343 626 9392.5 0.84 274 688 915

The ash was oven-dried for 24 hours and then passed through aBS 4.75 mm standard test sieve to remove the coarser particles.Tests were carried out on grate ash and crushed basalt sand todetermine their gmding, relative density, and water absorptionin accordance with BS 812 (6).

The grading of grate ash was coarser (20 per cent passing a 600um sieve) limn tlmt of basalt sand (41 per cent passing a 600um sieve). The relative density of the ash (2.00) was about twothirds that of basalt sand and the replacement of the sand by theash was carried out by volume mther than by weight in ordernot to affect the volume stability ofthe concrete. The absorptionvalue of the ash (10 ± 2 per cent) was very high compared withthat of basalt sand (0040 ± 0.01 per cent).

Compressive strength tests

Three series of tests were carried out.

Series J: These tests consisted of five concrete mixes preparedwith ordinary Portland cement, basalt sand and 12 mmmaximum size basalt aggregate. These mixes were designed inaccordance with the United Kingdom Department of theEnvironment (DOE) (7) design procedure for normal concretemixes so as to obtain a range of 28-day strengths varyingbetween 20 and 60 N/mm2 and a slump of 30-60 mm. Theaggregates used were oven-dried and the actual amount of wateradded to each of the five mixes was the sum of the free waterand the absorption of the aggregates. The cement content of themixes ranged from 274 kg/mJ to 561 kg/mJ and the

Table 8. Series 3: Concrete mixes with gmte ash and superplasticizer

Mix

3.13.23.33.435

Free water!Cement ratio

0.290.340.410.470.58

cementcontent(kg/m3)

561480390343274

Grnle ashcontent(kg/m3)

498533585626688

Coarse aggregatecontent(kg/m3

)

912940952939915

Superplnsti-cizercontent(kg/m3)

171412108

T3ble 9. Compressive strength results of mixes in the three series, 28-day cube strength (N/mm2)

Mix Series 1 Series 2 Series 3• (basalt sand) (grate ash) (grate ash + plasticizer)I

1 (0.41) 62 (0.41) 33 (0.29) 702 (0.48) 53 (0.48) 28 (0.34) 653 (0.59) 42 (0.59) 21 (0.41) 554 (0.67) 34 (0.67) 14 (0.47) 455 (0.84) 24 (0.84) 8 (058) 35

(Figures in brackets indicate the free water/cement ratios)

17

Table 10. Average initial absorption

Time Average initial surface absorption (ml/m2{s)

(Minutes) Series 1(basalt sand)

Series 2(grate ash)

Series 3(grate ash + plasticizer)

103060

120

0.1500.1170.0700.067

0.1430.0730.0580.033

0.0450.0220.0150.010

corresponding free water/cement ratio varied from 0.84 to 0.41(see table 6).

Series 2: In these test specimens, basalt sand in each of the fivemixes was totally replaced, by volume, by grate ash (see table7). The free water/cement ratios were kept the same but the totalamount of water for each mix was adjusted to take into accountthe higher absorption value of grate ash. Nevertheless, areduced slump of 0-10 nun was obtained.

Series 3: A water-reducing superplasticizer (Melment LlO - amodified condensate product of melamine and fonnaJdehyde)was added to the mixes of series 2. The cement, ash and coarseaggregate contents ofseries 2 and series 3 mixes were, thus, the

same (see table 8). Preliminary tests were carried out todetennine the optimum dosage of superplasticizer to be used,that is, the amount of superplasticizer for which no furthersignificant waterreduction was observed. This was found to beabout 3 per cent by weight ofcement, and this was the amountused in each of the five mixes ofseries 3, causing a 22 per centreduction in the total amount of water used, but again giving aslump of 0-10 mm. Three 1oo-nun cubes were prepared fromeach of the five mixes in each of the three series. The cubes werestored in water and tested in compression at the age of28 days.The results are shown in table 9 and figure 2.

Shrinkage

nasaU-sand concrete--- lJasalt·Simd c(]m:rele

...... - ...---- {~liIte·ll5hconcrete

20

Totill ",Bier mntent

10

350

3110

.r 250S~

tl.~ 200c1:...on

150

100

50

_. A. (;nate-Ilsh-plastici:ter c:onrrele

-- - - ... __ (irute·a.sh. concrete80

I/' I

,.,0' I/ I

150 IN /

IE / ,~ I

rIJI~

;., 50 /,

"""" I'" .6r' I;;,I' I

~ 40 / 1c/ 1~ r1 --I

" ..0,,.-- I~ ~ Ie JO

.r;t'" I...1; ... ...... 1:: .-... I

20 e 1/.- 1.- I" I"0.- I10 .- I...

Jr;f

200 JOO 400 500 llOO 700

C.",.nt Lunl.nl (klll",21

Figure 2. Change of strength with change in cement content Figure 3. Shrinkage - time graph

18

)

J

)

)

Shrinkage tests were carried out using standard 300 x 75 x 75mm prisms, in accordance with BS 1881 (8), on mix 3 of thethree series of concrete described earlier. After storing thespecimens in water for seven days, they were removed andshrinkage readings were started. Shrinkage was recorded overa period of 49 days during which the specimens werecontinuously stored in air.

The results (see figure 3) showed that shrinkage increased withage in all the three series but the increase was more marked ingrate-ash concrete (with or without superph1Sticizer) (3).

Although both concrete mixes had the same free water contents,the to~1.l water contents in the mixes were significantly differentbecause of the higher absorption of the grate ash. This couldhave been responsible for the greater drying shrinkage in theash concrete. The superplasticizer caused only a slightreduction (about 12.5 per cent) in the shrinkage of the ashconcrete.

Permeability

Penneability of concrete, that is the measure of the ability ofliquids or gases to penetrate the material, is an indirect measureof its durability.

There are various methods of measuring penneability and theone used in this study was the initial surface absorption test(ISAT) described in BS 1881. The test measures the rate of flowof water, under a small consk1nt head, into oven-dried concreteper unit surface area after a s~~ted interval of time from thebeginning of the test. The initi.1.l surface absorption ofconcretedecreases with time until no more water is absorbed and thesurface has reached saturation.

Tests were carried out on concrete cubes of mix 3 in each of thethree series of concrete. Three cubes, at the age of 28 days, weretested in each series. The average initial surface absorptionvalues of the three series are shown in table 10. (3)

Discussion

The variability in the chemical and physical characteristics ofbagasse ash is an impoffiwt consideration in the evaluation ofthe material for potential use in concrete. Hopper ash and grateash are fairly similar in chemical composition, whereas fly ashIt.1S a very high carbon content. Grate ash is fairly granular,which makes it quite sui~~ble for use as a fine aggregate inconcrete. Hopper ash tends to fonn clinkery lumps whichwould need grinding or crushing before incorporation in aconcrete mix. Fly ash is soft, compressible and highlyabsorptive, which makes it quite unsui~~ble for mixing into

. concrete. Quantities also favour the useaf grate ash in concretein preference to the other ashes.

Although both grate ash and hopper ash satisfy the requirementsof BS 3892 for loss-an-ignition, silica, magnesia and sulphuricanhydride contents, they fail to meet the specification for waterrequirement and pozzolanic activity index. Moreover, the ashes",quire grinding before they can comply with the finenessrequirements.

There appears to be no adverse effect on the strength or strengthdevelopment of concrete incorporating bagasse ash over aperiod of up to one year. Further tests are required to assess thelonger-tenn effects, in particular the shrinkage and durabilityproperties.

Grate-ash concrete has significlmtly lower strength th.w thecorresponding basalt sand concrete. The 28-day strength of theash concrete varies from about hIM to one third ofthe equivalentcontrol mix. However, the addition of a superplasticizer to thegrate-ash concrete caus~s a considemble increase in strength.With the h~tter concrete, strengths about three times those ofunplasticized ash concrete and about 35 per cent higher thanthose of basalt-sand concrete are ob~wed. Also, the plasticizedgrate-ash concrete appears to reach a strength limit at about 70N/mm2

.

In the fresh state, the ash-concrete mixes show lowerworkability. The slump decreases from 30-60 nun in thebasalt-sand concrete to 0-10 mm in the grate-ash concrete (withor without superplasticizer). This is due to the coarse gradingof the ash and to the rough angular nature of the grate-ashparticles which increase aggregate friction and interlock. Thisresults in poor cohesion of the fresh concrete, the workabilityof which hardly improves even with further addition of water.

Conclusions

Bagasse ash in Mauritius shows too poor reactivity withPortland cement to make it an effective pozzolana in concrete.

Bagasse ash can be effectively used as a fme aggregate inconcrete to produce a range of compressive strengths up toabout 70 N/mm2. However, genemlly reduced workability isobserved in the fresh concrete;uue to the coarse grading andangular texture of the ash particles.

The shrinkage of bagasse-ash concrete is not excessively higherth.w that of nonnal concrete. However more data are requiredto assess this property of the concrete.

The initial surface absorption characteristics of bagasse-ashconcrete do not give any indication of low durability incomparison with basalt-sand concrete.

The addition of a superplasticizer significantly reduces theinitial absorption capacity of bagasse-ash concrete.

Acknowledgement

The invaluable contribution of Dr. R.K. Dhir, Reader in CivilEngineering, Deparunent of Civil Engineering, University ofDundee, in connection with this project is gratefullyacknowledged.

References

I. MohamedbIt.'ti, G.T.G., and Baguan\, B.K., "Possibility ofusing bagasse ash and other furnace residues as partialsubstitute for cement in Mauritius". Revue agricole et sucrierede I'lle Maurice, vol. 64, no. 3, September-December 1985.

19

2. Li Pin Yuen, L.Y.N.G., "Availability of bagasse ash and itscharacteristics in Mauritius", B.Tech. final year project (Redui~University of Mauritius, 1986).

3. Kim CUITUn, G.S., "The effects of plasticizer on bagasse ashconcrete", B.Tech. fInal year project (Reduit, University ofMauritius, 1988).

4. British Standard, BS 3892: 1982, Pulverised fuel ash.

5. Choollun, V.K., "Pozzolanic activity of bagasse ash and alaterite", B.Tech. fmal year project (University of Mauritius,1988).

6. British Standard, BS 812: 1975, Methods for sampling andtesting of mineral aggregates, sands and fIllers.

20

7. Department of the Envirorunent,Design ofNarmal ConcreteMues (Garston, Building Research Establislunenl, Transportand Road Research Laboratory, 1975).

8. British Standard, BS 1881: 1990, Methods of testingconcrete.

9. Uteene, A.F., "Investigation into the properties of bagasseash cement", B.Tech. final year project (Reduil, University ofMauritius, 1980).

10. Cementia Engineering and Consulting Ltd., A Report onTests Carried out on Bagasse Ash from Mauritius, 1978.

11. Paturau, I.M., By-products ofthe Cane Sugar Industry. AnIntroduction to Their Industrial Utilisation, Sugar Series, 3(Elsevier Scientific Publishing Company).

MALAWI: THE USE OF RICE-HUSK ANDBAGASSE ASH AS BUILDING MATERIAL*

In Ma.lawi, about 45,000 tons of rice are milled every seasonbut on.ly a sma.l.l proportion of the remaining husks is used bysome of the large industrial concerns as fuel energy, and,thereafter, the rice-husk ash is usually discarded as a wasteproduct. It is already common knowledge that rice-husk ashcontains the highest proportion of silica compared with thatderived from any other ashed natural plant material, and it isthus, an inunediately available asset and under-developedsource of wealth.

Approximately 8500 tons of high-silica rice husks areobminable each year from three ricemilJs, namely Blantyre,processing 13,000 tons of milled rice, Karonga, 6000 tons, andNkhotakota, a further 6000 tons. Yet this potentia.l source, foruse in building-materials industry, has received very littleattention within the economy. In Malawi, a continuing studyof this naturally occurring waste material has been carried outover several years, and a low-cost plant capable ofmanufacturing sodium silicate (waterglass) solution fromrice-husk ash was designed and built in the laboratory. One ofthe prototype installations is at present being used inconjunction with work on a large low-cost housing projectfinancially supported by the Danchurchaid and the GermanDevelopment Assistance Association for Social Housing(DESWOS). Sodium silicate (waterglass) solution cnn beshown to have a considerable number of advantages whenapplied to building materials, and may eventua.l.ly help toincrease durability and lower the costs of low-cost housingconstruction throughout the country.

Cement

Cement has proved to be a very expensive commodity for usein many recent low-cost housing programmes in Malawi, 50 kgis priced at MK 29.00 (1992 price). It is estimated that 1800tons of ash could be produced annually in relation to the presentmilling capacity of approximately 45,000 tons of rice, as 1 tonof rice yields about 40 kg of ash as a by-product. However,because of the limited quantities which would be readilyavailable, it was decided that any ash that was produced shouldbe used for the manufacture of sodium-silicate (waterglass)solution rather than dealt with as an extender for cement, owingto the fact that the former product could have a much moreextensive application in the construction industry.

Waterproofing liquid

liquid coating ofsodium-silicate (waterglass) solution dries intoa hard vitreous fi.Im with a "varnished" type fmish that is bothprotective of the outward appearance and water-resistant. Anapplication to the stnface of porous concrete, burnt bricks,compressed soil and sun-dried building blocks produces an

'" B'y Uffe Leinum, Architect/planner, building materials and low-cost

additional hardness and renders the material waterproof. Inaddition, this material is suitable for preserving thatched roofsand also gives considerable protection against fire in existingbuildings.

Bricks

It has proved practicable to mix rice husks with clay in order toproduce strong and more resistrmt burnt bricks or blocks, andbricks and blocks containing this mixture have been found tobe very suitable for use in the construction of foumL.1.tions <Uldfloors. As the quality of clay differs considerably from place toplace, a test of the mixture should be carried out at the speciticlocality prior to manufacture, although reasonable results haveusually been obtained when incorporating 10 per cent rice huskby volume. Both burnt bricks and sun-dried blocks are easilymanufactured loca.l.l y, but it must always be borne in mind thata considerable mnount of fIrewood is used for fIring - in fact,approximately 1 cubic metre for every 1000 bricks produced,which puts an additional stress on the economy of a ruralcorrununity, as wood is inevitably used extensively for cooking.Because of the urgent need to conserve these finite resources,the use of burnt bricks is recommended mainly for foundation

Figure 1. When applied as a paint coal, the sodium-silicate sludge hasbeen found to be eXlremely useful fur fuundatiun plinths (Habitat

21

works and where the external walls lend to suffer from extremeexposure to rain. However, they may be considered in smallquantities for decorative purposes, such as below windows, adetail which has been incorporated in existing designs for rurallow-cost houses recently built in Malawi.

Paillt alld adhesive

A sodium-silicate (waterglass) solution can be used as aprotective coating or paint for solid walls, with the addition ofextenders, such as limestone, clay or iron oxide. The decorativefInish achieved by this process has proved to be considerablycheaper than any surface treatments obtained by using importedpaints or waterproofmg. The liquid also has the properties of-ageneral adhesive and can be used as a gluing agent for metal,wood and concrele products, such as roofing tiles, as well asbeing capable of fixing various glass and cenunic materials.

Varnish

Where the groundwater table is very high, the application of asodium-silicate (waterglass) solution on bricks or concrete willquite satisfactorily substitute for a waterproof membrane andinhibit rising drunp. At the same time, it provides a decorativesurface fInish which is both hard-wearing and easy to keepcle~Ul.

Adobe plaster for external walls

As a result of tests, it has been proved that the addition ofbetween 0.5 per cent and I percent sodium-silicate (waterglass)solution in the mixing water used for the preparation of mudplaster produces_a hard surface fmish, but, in order to make thefacing material totally resisrant to driving rain, a further coat ofsolution is required. This also acts as a good undercoat, prior todecoration with a "home-made" product - calciumstearate/cement paint.

Adobe blocks alld stabilized sUIl-dried block walls

For centuries, soil has been used as a basic material for theconstruction of walls throughout the civilized world, and thesewill often last indefmitely, provided they receive propermaintemmce and preservation. In ruml areas of Malawi, the useof adobe blocks for walls is quite common, and these structures,built out of soil in the shape of sun-dried building blocks, haveadequate strength under any conditions and can be very durable,in spite of rain and/or a humid climate, if supported on a goodfoundation. An additional design factor that can beincorporated is the provision ofa generous overhang to the roof.In order to withstand a humid atmosphere, an economicalmeans of giving protection to the sun-dried block is to stabilizethe soil content with a diluted sodium-silicate (waterglass)solution. This process enables ~m unskilled labour force to castsmall and comparatively cheap sun-dried building components,without the conventiona.1 use of either cement or lime additives,both of which are expensive to purchase. The compressivestrength of each block can be doubled by the addition of 0.5 percent sodium-silicate (waterglass) solution to the mixing water.Wails can be either plastered with mud plaster which has hadincorporated between 0.5 and 1 per cent sodium-silicate

22

Figure 2. Application of waterproof cement paint on adobe wall(Chikwawa, Malawi).

solution as a stabilizer, and/or then decomted by means of aprotective coating consisting of calcium stearate/cement paintcombined with a sodium-silicate (waterglass) solution.

The recommended procedure to be adopted prior to decomtionis as follows:

(a) One priming coat consisting of sodium-silicate (water­glass) solution to cover the mud-plaster surface;

(b) One finishing coat (coloured if required) of calciumstearate/cement paint. The cement paint is rendered much moredurable if it is protected with further application of sodiumsilicate.

Calcium stearate/cemellt paillt

Although materials such as waterproof paint are available foruse on mud-brick/block walls, they are usually produced withimported elements. By using materials which are readi.1y athand in the locality and then made up in accordance with theformula developed by Urfe Leinum, consultant architect to theChristian Service Committee of the Churches in Malawi,overall costs can be greatly reduced. A programme consistingof the construction of five demonstration houses wasundertaken, with a recommendation for on-site manufacture ofwaterproof cement painL The water-repellent paint contains thefollowing essential ingredients: Portland cement, hydratedlime, calcium stearate (a fat coated with lime) and rice-husk ash.

Calculations relating to the approximate cost of 10 kg of paintwith 1Ul optimum covering capacity of 20 square metres are asfollows:

A mixture ofhome-made waterproofpaint weighing I kg wouldbe expected to cover 2 square metres of wall surface at anominal thickness of 0.5 mID. However, if an initial applicationof sodimn-silicate (waterglass) solution is used as a priming

coat, coverage of up to 4 square metres of wall surface shouldbe achieved. A compnrison with the cost of equivalentcommercia.l products will show a net saving of80 per cent even

-I

J

Hem

Portland cementHydrated limeCalcium stearaleSilica ashFirewoodRed oxide (colouring agent)

Total cost

Estimated cost of equipment(oil drum, scales and hand tools)

Relative expenditure per square metreexcluding equipment)

"Home-made" red paintRed PYA paint"Home-made" grey paintgrey PYA paintWhite cement

Amount(kg)

7.31.50.50.50.51.0

Cost inMK.

4.350.540.200.000.503.509.09

450.00

MK

0.452.540.282.194.90

when a relatively expensive pigment is incorporated as acolouring agent.

Sugarcane (bagasse) as a waterproofing agellt

Adjacent to one of the selected development areas in theSouthern Region, the Sugar Corporation of Malawi(SUCOMA) has a large plant for the production ofrefined sugm'and sugar by- products. Investigations have already confmnedthat the wax obtainec;l from sugarcane has excellentwaterproofing properties and, if prepared, is suitable forexternal application to walls. Molasses is known to be 1Ul

efficient binder for clay and soil. It also has a comparativelylong-lasting waterproofing effect on these products, as well asendowing the clay/molasses mixture with additionalcompressive strength. Elsewhere, the sugarc,U1e crop is alreadybeing converted into a wide range of products, frommonosodium glutmnate for the food industry to hardboard forfurniture; but the possible diversification of sugarc,U1e wasteinto an increased supply of bagasse (the cane fibre), whichremains after the sugar-extraction process has been completed,appears to be pmticularly advantageous.

Given the escalating costs of fuel and its scarcity, using [Ulylocal asset, such as bagasse, is becoming increasingly relevantand important. The ash produced after burning the bagasse hasa comparatively high silica content, although somewhat lessthan rice-husk ash, but it is equally suitable and C,Ul be usedquite economically in producing sodium-silicate (waterglass)solution for general use in the building industry. Sugarproduction is increasing to an extent that an estimated 480,000tons of bagasse might soon become available. This mnountwould yield between 16,800 and 24,000 tons of ash per annumafter it had been used as fuel/energy.

•

Figure 3. Storage of bagasse for fuel (Sugoma, Malawi)

23

«~

chimnev stack woter wafer water ~u!Otlc:

I2.2.''':I':Z~m,"

tank tank +qnk >odo

filler and PM ~ ~pl""e~sl:lre

Ifillorrwater

1safety pipe +ot'lkmin. ?am

._-

~~

= steam1= cold water main I

::::;rear;tor reedor

- E ves:~1 vess:elhea1er

E boiler nH- E V-470 l V-450l

~.~ stecam in~ctor~

~ or-essure ,.e.lease valve ~U" SuO,.d;w,.,,~··1= V E

E ' ,~

I::

.~"-1[_t of. ~lLl,"~ "H,al:r ~

;; 0'-

~~~I:: .~

1= Ol.l~~t and, c:;li;~;'/je.Jtihctwater i= so rn SIll te ud

drLlmoutlet '.. ;":;:'0': .§~ ;?mb'i~;on ~omber l

steo m to plonr '\ . droin valve

Figure 4. Diagram of sodium-silicate plant

Productioll ofsodium silicote (waterglass)

Production ofsodium-silicate (waterglass) solution is at presentbeing carried out at a materials-production industries' centreattached to a large low-cost rural housing programme in theChikwawa district of Malawi, where the basic raw materials arewaste rice-husk ash and bagasse. Most of the rice-husk ash forthe project has been obtained from a large industrial plant, afterit had been used with other combustible materials, such as woodand cotton waste, for fuel/energy. This specific mixture ofsubstances prior to firing has resulted, in the presence of blackcarbon, which settles as "sludge" after the manufacturingprocess is completed to provide an extremely useful materialfor applying as a paint coat to brick foundation plinths. It is acompletely satisfactory and cheap alternative to the use ofcement rendering or imported bituminous paint

The whole operation maximizes the use of a surplus materialto advfmtage, as well as eliminating all traces ofwaste, althoughif pure, non-contmninated rice-husk ash is used, the "sludge"left behind has proved to be minimal. Unfortunately, causticsoda is still required for the manufacturing process - an importedraw material costing currently about MK 6.50 per kg (1992price).

1n order to produce a marketable quality of sodium-silicate(waterglass) solution, the various ingredients are introducedinto the reactor vessel (drum): caustic soda, rice-husk ash asindustrial waste, and water, in predetermined and controlledproportions. The production time required for obtaining 200litres of material ·from one reactor vessel, which includespreparation and lighting up the boiler, cooking and coolingperiods, complete with tapping off, is estimated at

24

approximately 24 liours. However, a small-scale plantcombining several production vessels connected to one boiler,could yield up to 1000 litres in a day (see figure 4).

Basic desigllfor processillg plollt

Either rice-husk or bagasse ash is fed into the reactor vessel,where steam from the boiler can be led into the contlliner. Afterthe correct amount of caustic soda and water has been added tothe ash deposit, the reactor vessel is subjected to the boilingprocess for approximately one hour. The resultant'liquid canthen be cooled, filtered and placed in contlliners ready for useon site.

Estimated manufacturing cost of mtered waterglass

Per 200 litre drum Malawi Kwacha

1. Caustic soda 77502. Fibrewood 7503. Labour - two men 5.004. Water - 250 litres 0.405. Transport 25 per cent 24.866. Depreciation of machinery 9.04

10 percent

Total manufncturing costs 124.30

7. Profit at 15 per cent 18.65

Total production costs 142.95

Therefore, the estimated costs for sodium-silicate (waterglass)solution will be:

These calculations are based on the use of a single productionvessel of 200 litres capacity ~md, therefore, present the worstexample fmancially, as normally a multiple unit would beengaged in this operatio!).. Production levels ClUl then quiteeasily be brought up to five times the fanner amount, at the samefixed costs and workforce level. The paint coverage that can beanticipated for concrete floors, sun-dried blocks or burnt brickwalls is about 14 square metres per litre, but a two-coatapplication is recommended for all sun-dried block-work, at anestimated cost of MK 0.10 per square metre.

Safety factors

1. When burning rice husks in large quantities, it is very difficultto detennine ifcombustion is occurring at the centre of the pile.Because of this particular factor, a safety fence should beerected around the bonfIre site, in order to permanently restrictaccess by children playing in the area.

2. Rubber gloves should always be worn for weighing out thecaustic soda, as any contact with the skin is hmmful.

3. The reactor vessel must be filled with a lid, as, during theinitial 20 minutes, the substances are alkaline and should not beallowed contact with the eyes. When the fmal stages of themanufacturing process have been reached, the mixture is onlyas caustic as lime. Soap and water should be used for cleaningskin surfaces.

Figure 5. SodiulT1-~ilicate (walerglass) plant (Chikwawa, Malawi).Patent application has been ftIcd

Volume of drum (litre)

2005I

MK

142.957.881.58

Figure 6. Boiling calcium strcarate for paint (Chikwawa, Malawi).

25

.zedp'efo vesse I

dI'ipevessel

reactor vessel mode q two s1-andard oil drums

fl! led to d.scharqepipe

(885 mm h. " 575" lOrn diGl.)

galvanized sl-eel k I

3/Fu nnel sleeve ---welded toiopof -;qtlinder ordrum In"

\.- %qgalvan'',eed I'iwelded

no 2 oil drumswelded Toqetherand lid removed -

r¥(galvanizedischa"le

._ welded+oInn I

steam injector =:lwelded fo vessel 'uon

0

" ~~

'-", / -- --

"qalvan',zed cone :;:welded fu cylinder ~or drum <-

discharge pipe welded - Q

to cone .:!

'?O rom 9"'te. valve~

Figure 7. Reactor vessel

26

,,,,ff r~e"'Ute <afeiy pipe 2_---'m.:..:;I'-=-'nlmum 7m -.hrgh /;:d ::::,

- ~'===;;=====~IIfrom waier +cmk'to boi er

fi II and pl'essure5 Q fety pi p-e

preS3ure releasevalve

hot water ou11et- I

chi mney stack and roo~made out of 9alvQnizedmefa I ( Qugc. 18)

boiler

.A

c

~~_-~~~~~~~~~_,r-~BOO ----Jl"--,~'u9J..f_l-

l5..2.r;l,-----J.-P LA N

--I--. ----.;:. -:, :

2.4~ rl-II~O--;-I 2,4f- -·1--,-----:--+

I I : 1sleam heater 1 I : I

-r----L : : IA L : :_...1--- I !

L I

Figure 8. Boiler unit

27

~-----------------_ai

Figure 9. Construclion of a chimney stack/boiler ruof (Georgetown,Guyana),

Notc

The sodium-silicate solutions described in this report areinorganic, non-intlanunable, non-explosive, non-toxic and are

28

Figure 10, Steanl heater and boiler unit under construction(Georgetown, Guyana),

not regarded as hazardous chemical substances. It is partly therelatively low environmental risks, which are alreadyassociated with soluble Silicates, that account for theirever-increasing world-wide application.

&

Technology Profile No.1

MINI-CEMENT PRODUCTION*A mini-cement plnnt is one the total installed capacity of whichis not greater than 200 tons per day, including one or more kilnson one site. The case for developing mini-cement plants inIndia has arisen from the high cost of installing viably-sizedconventional cement plants, the large number of small depositsof limestone dispersed at various parts of the country and theversatility of mini-cement plants in matching the limitedavailability of power, water and other inputs. By meeting thedemands of local captive markets, mini-cement plants alsoprovide for participation oflocal small entrepreneurs and, thus,help in building up local economies.

Major advaJlk1ges of mini-cement plants are:

- Less capital-intensive;

- hort gesk1tion period;

- Quick return of investment;

- Utilization of small deposits of limestone;

- Low transport costs, as product can beconsumed locally;

- Attractive to young entrepreneurs with limited [mancialresources.

A mini-cement plant of capacity 20-10,0 tons per day, based onvertical-shaft-kiln (VSK) technology, has been developed byRegional Research Laboratory (RRL), Jorhat. India. Thetechnology package is licensed through the National ResearchDevelopment Corporation of India, and the plant is set up by anumber of conSulklllts, appointed for the purpose, on a turn-keybasis. The product conforms to IS: 269 -1976, the specificationfor ordinary Portland cement. Mini-cement plants, withtechnical know-how from RRL and licence from the NationalResearch Development Corporation, New Delhi, have startedcorrunercial production successfully in several parts of thecountry. Complete dek1iled engineering reports can be offeredfor a25 ton/day VSK plant Basic design and process know-howis available from the RRL, Jorhat.

Figures 1and 2 show outside views of two mini-cement pkllltsin India.

Production processes

Some of the processes on which mini-cement production could.be based, are:

(a) VSK;

(b) Rotary kiln;

(c) Lurgi sinter bed;

(d) ,Belt kiln.

.. Thi~ teclmology has been developed by RegininJ Re~enrch Laboratory (RRL),JOIhllt, Indi n.

Figure 1. Pmg Shiva mini-cement plant in Guwahati Assam, India.

Figure 2. Bhagyanagar mini-cement plant in Nandigram, Hyderabad,India.

29

Processes 1 and 2 are established as commercially viable, whileprocesses 3 and 4 are of theoretical interest. The developmentof the VSK process for cement production can be traced backto 1824. At that time, this process did not receive muchattention, as the operations were highly labour-intensive, theclinkers produced were of non-uniform quality, and the overalleconomics were unfavourable. However, with thedevelopment of the pan-type nodulizer, which ensures auniform-quality product, the situation has radically changed.

The kiln consists of a cylindrical shell with a conical sinteringzone lined with refractory bricks. A rotary discharge grate atthe bottom of the shell coupled with its drives and air sealingdevice takes care of the uniform rate of discharge of clinker.The green nodules thus move down gradually and encounterhott1ue gases. In the sintering zone, nodules are calcined and oxidesrecombine to form the essential cement phases. The clinkersthus formed move further downward, encounter incoming airand become cooled Finally the clinkers exit through therowrydischarge grate and reciprocating discharge gate. The RRLshaft kiln is highly efficient in calorie consumption (l030±50kCal/kg of clinker).

The cementclinkers are th~n pulverized after admixing with therequired amount of gypsum in a cement mill to a minimumfmeness of 2250 sq cm/g.

Figure 3 shows a view of a VSK designed by RRL, and figure4 shows another VSK designed by Cement Rese..1Tch Institute(CRI), India, for a 20 ton/day capacity plant.

The VSK process of cement production which is a semi-dryprocess consists of the following major operational steps:

(a) Prinulry crushing of limestone, clay and other addi­tives, if any, to a fmeness of about 12-15 rom.

(b) Pulverizing of the raw meal (stated in 1 above) andcoke breeze to a fineness of 90 per cent below 170 mesh BSS.

(c) Blending of the pulverized material in suitable propor­tions, to ensure desired uniform-quality product.

(d) Preparation of nodules, by the addition of water to theraw meal in the nodulizer.

(e) Feeding of nodules into the VSK wherein the nodulesundergo drying, calcining, sintering and cooling, resulting inthe formation of cement clinkers.

({) Grinding of clinker and blending of the groundclinker with gypsum, to obtain quaiity Portland cement.

Figure 5 shows a nodulizer of a VSK mini-cement plant andfigure 6 shows a raw material balancing and grinding section.

Vllrdc.ill·shBft kiln

Figure 4. General arrangement of eRI type VSK for Visvakannamini-cement plants.(This figure is reproduced from Monograph on Appropriate IndustrialTechnology, Appropriate Industrial Technology for Construction andBuilding Materials, No.12 (New York, United Nations IndusU'ialDevelopment Organization, 1980), p. 66, fig. 1.)

Chlmn",y

Figure 3. View of a VSK

30

Raw materials, includingfuel

Limestone:

The typical consumption pattern of these raw materials per tonof product is as follows:

A process flow diagram ofa VSK mini-cement plant is shownin figure 7 and a typical layoutof50/100 ton/day-capacity VSKcement plant is shown in figure 8.

6000 kCal/kg minimum30 per cent m.1.Ximum8 per cent maximum

60-66 per cent12-18 per cent5-9 percentMedium plastic

45 per cent minimum12 per cent maximum4 per cent maximum2-4 per cent maximum2.0 per cent maximum

80 per cent minimum

Gypsum:

CaS042HzO

CaOSiOzAh03Fez03MgO

Clay/tly-ash}shale:

SiOzAh03Fez03Plasticity

Coke breeze (fuel):

Calorific valueAshVolatile matter

Figure 5. Nodulizer ofVSK mini-cement plant Pioneer Cement Plant,Ltd. Hyderabad, Andhra Pradesh, India.

The principal equipment in a VSK process for a typical plant of25 tons per day capacity is given in table 1.

Table 1. List of equipment for a 25 ton/day VSKmini-cement plant

(a) Limestone(b) Clay(c) Coke-breeze(d) Gypsum

1.36T0.17TO.25TO.04T

Quality Utilities

Consumption of utilities per ton of product is as follows:

Compressive strength (kg/cmz):(a) 3 days 160 minimum(b) 7 days 220 minimum(c) 28 days 330 minimum

Chemical

About 135 kWhAbout one cubic metre

30 minutes600 minutes

10 mm m.'lXimum0.8 per cent maximum

(a) Power(b) Water

Soundness:

(a) Le Chatelier(b) Autoclave

Product specifications

Physical

Specific surface:Setting time:

(a) Minimum(b) Maximum

6 ton/h6 tan/h6 ton/h6 tan/h3 ton/h2 ton/h

(a) 2 ton/h(b) 120 kg/h(c) 300 kg/h(d) 100 kg/h

4 ton/h4ton/h3 ton/h3 ton/h4 ton/h10 ton/h3 ton/h3 ton/h3 ton/h3 tan/h25 ton/day4 ton/day4 ton/day50 to 150kg/h1-4 ton/h2ton/h4 ton/h4 ton/h0-100 kg

Capacity

1111114

11111211111111

Equipment

Clinker feederCement millCement elevatorScrew feederWeighing machine

Limestone crusherLimestone conveyorHammer millBelt conveyorLimestone elevatorCoke-breeze, clay and additive elevator _Table feeders (1 each)

Belt conveyor for raw material _Raw material elevatorRaw material grinding millScrew cJnveyorRaw meal elevatorHomogenizerRaw meal feederNodulizerNDdule screenNodule elevatDrVertical shaft kilnClinker elevatorClinker and gypsum elevatorGypsum feeder

31

Figure 6. Raw material balancing and grinding section. Bhagyanagar Cement Plant Ltd., Nandigram, Hyderabad, Andhra Pradesh, India.

Loss-of-igni lion 5.00 per cent maximum Le Chatelier expansion:

Insoluhie residue 4.00 per cent maximum 1-2mm 10 mm maximum

S03 content 2.75 max., when C3A <7 per Autoclave test: 0.05-0.2 per cent 0.8 per cent maximum

cent 3.00, when C3A >7 perLabourcent

MgO content 6.00 mnximum 50 ton/day 100 ton/day

Alumina ratio 0.66 minimum Skilled 45 50

Lime saturationUnskilled 75 80

factor Between 0.66 ;md 1.02 Designation

Special requirements:

(a) C3AManaging director 1 1

less than 7 per cent Works manager I I

(b) S03 2.75 per cent maximumShifl-in-charge 4 4Plant operator 8 8

Characteristics ofcemellt IS; 269-1976 limits Nodulizer operator 8 8Raw mill operator 4 4

Specific surface area: Cement mill operator 4 4

'1Minimum 2250 cm2/g

Senior chemist 1 13100-3300 cm~/g Junior chemist ::I ::I

Storekeepcr-cum-uccountant 1 1Setting time (min.): Electrician 2 2

Mechanic fitter 2 2Initial 106-130 minutes Not less than 30 min. Peon 2 2

Driver 2Final 220-260 minutes Not more than 600 min. Guards 4 4

Helper 3Compressive strength: Unskilled labour 35 35

3 days 190-220 kg/cm2 Minimum 160 kg/cm2 Unskilled contract labour 40 45

7 days 280-310 kg/em2 Minimum 220 kg/cm2 Total 120 130

28 days 405-450 kg/cm2 Minimum 330 kg/cm2

32

41I

s

Buck etEI eva tor

Cement~mill J8 uc ket

Elevator

\/ Cementn _ ]1~V Silo

~ \-Screw ConveyorPacking c::J--Bagging Machine

Blender

Screw Conveyor

---- ~04-NOdUlizer----Clinker Storage

rL--L-, D-Gypsum storage

WeighingB a I a nc e

PrImarycrusher

Belt Bucket~~~ ~Conveyor Elevator

6 V 0 r:::::J '\"7 Hopper~ \V ~...... T able feederDisintegralor \.,;."I &..:..I I-l o-.r-- I

o () rffi

lBuc.kel

~I Elevator

Raw meal

.0&- 9l--~ B a II m i \I

Screw conveyor-$

Figure '-,. Process flow diagram of a VSK mini-cement plant.

33

15 SCREW FEEDER

1" KILN

13 VIBRATING SCREEN

12 SK I P HOIST

11 1110 DULIZ ER

10 HOMOGE IIIIZER

9 SCREW CONVEYOR

8 BALL MILL

7 CEMENT SILO

6 TAB LE FEE D E R

5 HOPPER

" ELEVATOR

J 1M PACTOR

2 BE LT CONVEYOR

1 JAW CRUSHER

SL. NAME ;JF E;JUPTNO·

-I

To be shifted 10position 'X' for100 T P D

I I ,.. .. _l-J

.....L-I

55000

COKE BREEZE

,I ,..l ......

NOTE - THE DOTTED LINES INOI CATE FUTURE EX PANSJON

o 0o 0o ~trI

'"

Figure 8. Typical layout of a 50/100 ton/day VSK cement plant.

Technology Profile No.2

PRODUCTION OF LIME*Production of lime is a simple process in which limestone iscalcined at elevated tempemtures. Theoretically. 900°C is asufficiently high temperature to carry out the process. However,in practice, it has been found necessary to maintain thetemperature at a much higher level than this to complete thechemical reaction. In the absence ofadequate tempemture oversufficient time, the lime produced will be of inferior quality: itmight be underburnt or overbumt. The success of the process,therefore, lies in maintaining proper conditions for calcination.

Kiln design

Lime kilns of various designs have been used. However,vertical-shaft types are thermally the most efficient.Consequently, their use results in savings in fuel. In India,different types of kiln have been employed through the ages,but investigations carried out at the Central Building ResearchInstitute (CBRI) have shown that most of the traditional designsproduce an inferior quality of product with a higherconsumption of fuel. CBRI, in recent years, has developed limekilns of several types, which are being offered for exploitationby the industry. The smallest kiln has about a 5 ton/day capacitybelow which hardly any efficiency can be expected. Figure 1shows a lime kiln developed by CBRI.

Some salienl features of the kilns

(a) The kilns are of brick or stone masonry;

(b) The kiln designs ensure smooth running and periodicwithdrawal of lime;

(c) The kilns lend themselves to a fair degree ofinstru­mentation, if required;

(d) They work on natural dmft and have an arrangementfor their control;

(e) They work continuously but can be adapted for dayworking only;

(I) They are thermally efficient, and heat losses are mini­mal;

(g) They produce a unifonn quality lime, by avoidingoverburning or underbuming;

(h) Under standard working conditions, these kilns pro­duce very little core or unburnt material;

(i) They can be operated by trained unskilled labour;

(j) Contamination of lime with fuel is minimal.

Raw material and cllemical composition

The impurities in limestone are primarily Si02, Al203 andFe203. They are non-volatile in nature and remain ascontaminants in the lime produced. Limestone generallycontains some MgC03. also. Calcite stone usually containsCaC03 exceeding 95 per cent, and dolomitic stone has anMgC03 content of35-40 per cent. In the burning operation, thecarbonates are converted to their corresponding oxides.Dolomitic lime is used largely in refractories where a high MgOcontent is essential.

The principal reactions involved in the calcination of calciticand dolomitic limestones are:

CaC03 -> CaO + C02(Calcite)

CaC03 MgC03-> CaO.MgO. + 2C02(Dolomite)

The avemge dissociation temperatures for the above two typesof limestone at atmospheric pressure are 900° and 725°Crespectively. Certain materials, such as sulphur dioxide, presentin the stone or fuel tend to react with lime and oxygen to fonnCaS04 which is unstable at high temperatures. Ah03 and Si02combine with CaO and MgO to fonn various silicates andaluminates at very high temperatures. These compounds arewater-insoluble and are undesirable, as they decrease oxidevalues and also coat the lime particles and so reduce itsreactivity.

The reaction of quicklime is also influenced by high operatingtemperatures and retention times. With an increase intempemture, the reaction rate increases, and, consequently, thereaction time decreases. However, the maintenance of hightempemtures beyond an optimum limit causes overburning ofthe lime.

Production process

Limestone is broken to a size of about 75 to 125 mm, and coalto half this size. These are mixed in mixers near the kiln. Toinitiate fire, a layer of firewood is first laid. Above this, somesteam coal is spread. Thereafter, the kiln is filled withpreviously mixed coal and limestone. Generally, the coalrequirement is 12-15 per cent that of limestone, but this varies,depending upon the type of limestone and the quality of coal.Fire is introduced from the bottom and rises. Charging and

'" This technology hIlS been developed by the C.entml Building Resenrch Institute {eBRO, Roarkee, India

35

Figure 1. Lime kiln.

II ,I IIII

I,I,

IJ, ,I II I,

IIIII,

n I

I (,I, I

1 :,

Figure 2. Production process of quicklime.

36

1. limestone

2. Coal

3. Mixer

4. Belt conveyor

5. Bucket elevator

6. ChaIn conveyor

7. Vertical shaft kiln

B. Belt conveyor9. Storage

disclmrging are so adjusted that the fIring zooe is maintained inthe middle of the kiln.

Scheme for the productioll ofquicklime

(a) The manufacturing process is shown in a flow chartin fIgure 2.

(b) Productioll scale

(i) Rate ofproductioll

10 tons per day of three shifts,3000 tons per year of 300 working days

(ti) [Ilputs

Land 3000 sqm

BuildingShedMachinery andequipmentElectric power

WaterCoal (stearn)LimestoneLabour

20sqm200sqmI lime kilnI feeding device50,000 kWh per year

1000 kl per year900 tons per year6000 tons per yearI manager30pemtors

4 skilled labourers

2700 work days labour

2 guards

Technology Profile No.3

HYDRATED LIME*Lime produced by the calcination of limestone in a kiln isknown as quicklime. Before using it in construction, it needs to

be hydrated. Chemically the process is:

CaO + H20 -> Ca(OHh

Some of the physical properties of hydmted lime are shown intable 2.

Table 2. Physical properties of hydrated lime

The above results show that the hydrator can be used forproducing class B and Climes.

ln this process, if any magnesia is present, it may also behydmted partially or fully as:

MgO + H20 -> Mg(OH)2

Although the conversion of quicklime into hydrated limeappears to be a simple process, the reaction is governed bynumerous factors' which affect the properties of the fInalproduct. It is, therefore, desirable that the manufacture ofhydrated lime is carried out in a factory under controlledconditions, mther than in the fIeld where hardly any control canbe effected.

Constituents

Residue on 2.36 mm sieveResidue on 850 micron sieveResidue on 300 micron sieveResidue on 212 mil.TOn sieveSoundness (Le Chatelier)Workability

Properties

0.01.2 - 1.46 per cent1.6 - 3.97 per cent3.64 - 3.80 per cent05 - J.Omm

40 - 44 per cent

Process ofhydratioll

Lime samples hydrated in the machine during trial runs wereevaluated for their physical and chemical properties.

The chemical properties of hydmted lime are shown in table 1.

Table 1. Chemical properties of hydrated lime

Chemical constituents

SiD:!Ah03CaOMgOC02Loss,-on-ignition (LO!)

Percentage composition

25 -4.60.7 -55

82.0- 96.3056 -5.861.65 - 1.89

23.45 - 25.75

Advalltages ofthe use ofhydrated lime

The use of hydrated lime has the following advantages.

(a) Properly manufactured and carefully packed hydratedlime possesses defmite and uniform properties;

(b) There is hardly any deterioration even after long stor­age, if the material is properly packed;

(c) It is easy to handle, store and transport and can beused without any further processing at the site;

(d) It can be incorpomted in mortars in exact proportions;

"'This tedmology has been developed by the Central Building Research Institule(CBRD, Roorkee, India.

37

Figure 1. Lime hydrator.

riod for the reaction between lime and water can be adjustedto achieve complete hydration;

(d) Steam generated during hydration is used for pre-heat­ing the water used for hydration and thereby speed of the re­action is accelerated;

(e) The smaller model is transportable as one unit and,hence, it is possible to carry it to the site of use;

(f) Lime obtained is in an almost dry state;

(g) The machine is suitable for high-calcium and soft­burnt dolomite lime;

(h) Machines capable of hydrating about three, five andten tons of quicklime per shift of eight hours have been de­signed, fabricated and tested in the laboratory. They havealso been commissioned in the field

Schemefor the production ofhydrated Lime

The manufacturing process is shown in the flowchart (see figure 2).

The production scale is as follows:

Rate a/production

22 tons per day of 2 shifts6600 tons per year of 300 working days

ltI

Land and building

6000 tons per year

100,000 kWh per year10,000 kl per year

(e) The plasticity of lime putty C<ffi be improved, if so de­sired, by soaking it in water.

Hydrated lime, possessing defmite advantages, is fmdingincreasing demand in construction and various other industries,such as paper, sugar, leather tannery <md agriculture, amongothers. TImt is why, there is always a considerable demand fora suitable indigenous machine for hydrating quicklime.

Lime hydrating machine

Based on extensive research work carried out at the CentralBuilding Research Institute (CBRI), Roorkee, a lime hydratingmachine has been developed, which is commercially producedin two different sites. Special features of the CBRI limehydrating machine are:

(a) The machine has three tiers with consequent savingof space;

(b) Each of the three tiers of the machine has a well-de­fmed fu nction:

(i) The frrst tier acts as mixer;

(li) The main process of hydration takes place inthe second tier;

(iii) In the third one the hydration process iscompleted and the fmal product is dried.

(c) The design of the machine has been kept flexible sothat movement of materials and, consequently, the contact pe-

38

LandBuildingShed

Machinery and equipment

Crusher for quick lime

Lime hydrator

Bucket elevator

Vibrating screen

Storage Bins

Belt conveyor for quick lime

Raw materials

Quicklime

Utilities

Electric powerWater

Warl..force requirement

Plant supervisor-cum-manager

Chemist-cum-analyst

Mechanic-cum-operator

Electrician-cum-mechanic

sqm

200020

250

1

1

1

1

2

1

1

1

62

-

Storekeeper

Clerk-cum-typist

I

1

Skilled labour 12

Machinery/equipment

Energy consumption/or a day's production*

Energy

Crusher, lime hydrator,bucket elevator, vibratingScreen, belt conveyor

Electrical

334 kWh

Thennal

.. Requirement for 22 tons of hydrnted lime

4

5

TO STORACiE

1.

2.

J.

4.

LIME KIUI

BELT CONVEYOR

HAMMER KILL

BUCKET ELEVATOR

5.

6.

7.

B.

HYDRATOR

BUCKET ELEVATOR

CURING BIN

VIBRATORY SCREEN

9. PACKING UNIT

Figure 2. Production process of hydrated lime.

39

PUBLICATIONS REVIEWPublished by UNCHS (Habitat)

1IiIi

I

Bibliography Oil Passive Solar Systems ill BuildingsNe~rrly half of the world's commercial energy is consumed inbuildings in order to provide indoor comfort However, thenatural environment can be used to reduce energy requirementsin buildings by making use of passive energy systems whichc~m contribute to indoor comfort In order to promote standardsrmd technologies for the provision of economically efficientinfrastructure, the United Nations Centre for HumanSettlements (Habitat) has prepared this bibliography to provideprofessionals, such as designers, architec;ts and engineersconcerned with construction and rehabilitation of buildings,with information on passive solar systems and allied subjectsfrom the available literature, to encourage them to makemaximum use of energy-conserving devices and systems.

The bibliography lists selected references on passive solarsystems in buildings. It includes information for thoseconcerned with the reconstruction .md retrofitting of buildings,

40

especially in developing countries. The bibliography covers thefollowing parts: (a) general reading list; (b) bibliography bytopics, covering passive solar technology, heating, cooling,building materials and construction techniques and solarradiation and climate; (c) annotated bibliography; and (d)descriptor index to part (b). The list of literature covered is inthe form of books, conference proceedings, journals, reports,papers and articles. There is also an annex which lists referencesof specialist publishers.

68 pp. HS/173/89: ISBN 92-1-131094-8

Corrosi011 Damage to COilcrete Structures ill Western Asia

With the present-day understanding of the problem, it ispossible to prevent corrosion by a proper choice of materialsadmixtures and by following sound construction practices thatwill produce concrete of good quality. It is also possible toprevent corrosion by providing, where the importance of the

CORROSIONDAMAGE

TOCONCRETE

STRUCTURESIN

WESTERNASIA

United Nation. Cent", for HumlUl Seltlements (HobUatl

Nnlrobl, 1990

--structure justifies, cathodic protection which reverses theelectrochemical process that causes corrosion.

This monograph explains the phenomenon of corrosion anddeals with the repair of structures damaged by corrosion,corrosion-monitoring techniques, and the steps to be taken toprevent corrosion.

33 pp. HS/204/90E: ISBN 92-1-131122-5

EXECUTIVE SUMMARYOF THE

()N HlJMAN SETTLEN1ENTS

UNITED NATIONS CENTRE FOR HUMAN SETTLEMENTS (HABITAT)

Executive ,SulJlmary of the Global Report on HumanSettlemellfs

The Global Report all Humall Settlements was prepared byUNCHS (Habitat) ~md published by Oxford University Press in1987. The Global Report was prepared under the GeneralAssembly's m~mdate ~md documents world-wide settlementsconditions ~md trends so as to assist governments in improvingtheir settlements policies, plans and progr.urunes. It is dedicatedto those who, in spite of limited means and the ftrumcial andphysical odds with which they are confronted, are at thismoment building or improving their own habitat, to those whosewisdom and inspiration prompted the world community toembrace the concept of human settlements. ,md to the plarmers,md builders who believe that the world can become a betterplace to live in.

The executive summary highlights the main issues ,md fmdingsof the Global Report 011 Human Settlements ,md is considered{is a synthesis of the main topics covered in the main report

45 pp. HS/129/88E: ISBN 92-1-131055-5

Energy for Building - Improving Ellergy Efficiellcy inCOllStruction and ill the Productioll OfBuilding Materials inDeveloping Coulltries

The link between energy production ,md use ,md the local ,mdglobal envirornnent is causing increasing concern world-wide.There is also a growing demand for envirorunental impactassessments of all building projects which should includeconsideration of embodied energy.

This publication exmnines the question of energy efnciency inbuilding materials from the point of view of product:rs ofbuilding materials, building designers ,md builders. Producerswill want to know how they c~m ch,mge their productionprocesses so as to reduce energy consumption (;md cost), howenergy consumption c,m be reduced by ch~mging tlle rawmaterials ;md the product mix specification used, ~md howenergy costs c,m be reduced by ch,mging to different energysources.

41

Producers fmd builders will also wfmt to know what techniquesare available for application now, and what techniques arecurrently under development or might become available in thenear future. The publication is also intended to be of use topolicy-makers in the field of housing and construction who will

be interested in the conclusions of the report about the mosteffective actions to be k'lken by each group.

104 pp. HS/250/9IE: ISBN 92-1-l3I 174-8

EVENTS

Expert Group Meeting on Appropriate, Intermediate,Cost-effective Building Materials, Technologies and TransferMechanisms for Housing Delivery, Madras, India, 4-7Febmary 1992

The COirunission on Hwmm Settlements, in its decision 13/24of7 May 1991, requested the Executive Director of the UnitedNations Centre for Human Settlements (Habik~t) to prepare atheme paper entitled "Appropriate, intennediate, cost-effecthuilding materials, technologies and transfer mechartisrns forhousing delivery", for its consideration during the fourteenthsession to be held in mid-1993. The purpose of the theme paperis to submit for consideration of the Commission an objectiveappraisal of the perfonmmce of the building materials industryin developing countries, lllcusing on the major problems andconstraints that currently hinder the adequate supply of basicbuilding materi,ds at prices that Cfm be afforded by averagehouse-builders. The paper sbould fdso highlight availablepolicy options fmd submit a framework of action, at bothnational <'Uld international levels.

The Experl Group Meeting, org,mized by UNCHS (Habiwt)hroughllogether more thfm 10 experts and had the objective ofidentifying the suitable structure and fonnat of the draft,produced the preliminmy outline of the paper. It fdso defmedways fmd me,ms on how to acquire ,md anfdyze necessary dawfmd infonnation ,md the type ofinputs which would be requiredfrom member governments.

Workshop on the Second Issue of the Global Report onHuman Settlements, Nairobi, Kenya, 2-6 December 1991

The main objective of the Global Report is "to provide acomplele review ofhwmm settlements conditions, including anfmfctysis of major forces fmd trends accounting for both theirpresent developments and their continuing creation,maintemmcc ~md improvement". The prime purpose is to,m,ctyse world-wide regional development trends ,md futureprospects in the lield of human settlements and, in Utis way,

42

assist governments to implement the recornmendations fornational action made at Habitat: United Nations Conference onHuman Settlements.

The workshop, organized by UNCHS (Habik~t), broughttogether experts from Africa, Asia, North and South Americaand Europe and was intended to provide suggestions to UNCHS(Habik~t) on the contents and format of the second issue of theReport.

IllternationalSeminaron Housing Indicators, Nairobi, Kenya27-30 January 1992

More than 50 participants from 27 countries of Africa, Asia,North America, and Western and Eastern Europe, as well asrepresenk~tives of the World Bank ,md UNCHS (Habik~t)

participated in the four-day seminar which was orgartized byUNCHS (Habitat). The Seminar was organized in response tothe question, which arose after the formal adoption ofthe GlobalStrategy for Shelterto the Year 2000, ofsetting in place suik~ble

mechanisms and guidelines for monitoring progress inachieving the Strategy's goal of adequate shelter for all by theyear 2000 - a k~k which was a fundmnenkll part of the Strategyitself.

Housing indicators were on the agenda of 10 sub-regiorudintergovernmental meetings orgartized by UNCHS (Habik~t) onnational shelter strategy formulation and implemenk~tion.

These meetings revealed the interest of Member Sk~tes inacquiring tools for monitoring their progress in addressing theStrategy's national goals and offered useful suggestions on howUtis k~k could be approached.

The discussions during the Seminar focused mainly on suchtopics as: qmmtity and price indicators, housing quality indica­tors, housing demand indicators, housing supply indicators, theregulatory audit and lessons learned from the extensive survey.Moreover, the participants had the opportunity to discuss ,mddeliberate on the preliminary results of the housing indicatorsprogranune in their respective countries.