Characterisation of Reject Red Clay Bricks in Khartoum as a Pozzolan

Material

Dissertation for a partial fulfilment of BSc in Civil Engineering

Civil Engineering Department

Faculty of Engineering

Academic Year 2010-2011

Student Names:

Ashraf Osman Rahama

Khalid Adam Habeeb

Magdi Mohammed Khatir

Mohammad Alhassan Mohammed Osman AlKhalifa

Suprvisor: Dr Yousif Hummaida Ahmed

1

ABSTRACT

Due to the poor quality control in traditional Sudanese bricks industry, the percentage

of product rejected for sale mounts up to about 25%. This is about 0.7 billion bricks

that represent a potential reserve for producing pozzolans in the Sudan.

In this study, random samples of reject red bricks were collected from various

traditional brick kilns at Elgerief-Umdoum and Shambat in the Khartoum estate. The

reject red bricks were crushed and sieved on #200 sieve (75µm). The amount passed

through the sieve was further pulverised using ball mill until more than ⅔ passed

through #325 sieve (45µm). The powdered materials for reject bricks collected from

Elgerief-Umdoum specimens were denoted as red brick powder (RBP)-G-U, while

those from Shambat specimens were denoted as RBP-SH.

The properties of the RBPs, namely fineness, strength activity indices of blended

binders containing 20%RBP and 80% Portland cement (OPC) (by mass) and water

requirement using methods described in with ASTM C311-02. In addition chemical

compositions the RBPs were measured using methods described in BS EN 196-2 and

BS EN 196-21. The values of these properties were compared with specifications in

ASTM C 618-05, which classifies pozzolans in categories of class F, Class C and

Class N.

This study found that according to ASTM C618-05 specifications, RBPs in Khartoum

estate were of Class F, producing more than 75% of the strength of control OPC

mortar. Also, unlike OPC, that there was a significant increase in the strength

between 28days and 91 days (more than 20%) for blended binders containing up to

30% gain. The gain for OPC mix was about 10% between 28 and 91days.

The study also investigated blended binders containing 30%RBP and 70%OPC (by

mass) and found that the strength dropped with increasing the RBP dosage from 20%

to 30%.

2

ACKNOWLEDGEMENT

الرحيم الرحمن الله بسم

( والمؤمنون ورسوله عملكم الله فسيرى إعملوا (قلالعظيم الله صدق

والتطيب .. بطاعتك إلى النهار واليطيب بشكرك إال الليل اليطيب إلهيإال .. .. الجنة تطيب وال بعفوك إال اآلخرة تطيب وال بذكرك إال اللحظات

جالله جل الله برؤيتكونور .. .. الرحمة نبي إلى األمة ونصح األمانة وأدى الرسالة بلغ من إلى

العالمين ..وسلم عليه الله صلى محمد سيدنا

واما بعد...البد لنا ونحن نخطو خطواتنا األخيرة في الحيFFاة الجامعيFFة من وقفة نعود إلى أعوام قضيناها في رحFFاب الجامعFFة مFFع أسFFاتذتنا الكFFرام الذين قدموا لنا الكثير باذلين بذلك جهودا كبيرة في بناء جيل الغFFد لتبعثاألمFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFة من جديFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFد ... وقبل أن نمضي تقدم أسمى آيFFات الشFFكر واالمتنFFان والتقFFدير والمحبFFةإلى الFFFFFFFFذين حملFFFFFFFFوا أقFFFFFFFFدس رسFFFFFFFFالة في الحيFFFFFFFFاة ...إلى الFFFFFFFFذين مهFFFFFFFFدوا لنFFFFFFFFا طريFFFFFFFFق العلم والمعرفFFFFFFFFة ...

إلى جميع أساتذتنا األفاضل.......

كن عالما. فإن لم تستطع فكن متعلما ، فإن لم تستطع فأحب""العلماء ،فإن لم تستطع فال تبغضهم

وأخص بالتقدير والشكر مشرف هذا المشروع:

أحمد : حميدة يوسف الدكتورالFFذي نقFFول لFFه بشFFراك قFFول رسFFول اللFFه صFFلى اللFFه عليFFه وسFFلم: "إن الحوت في البحر ، والطFير في السFماء ، ليصFلون على معلم النFاسالخFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFير" وكذلك نشكر كل من ساعد على إتمام هذا البحث وقدم لنا العون ومد لنايد المساعدة وزودنا بالمعلومات الالزمة إلتمام هذا البحث ونخص بالذكر:

جامعة: الهندسة بكلية والتربة الطرق شعبة رئيس زمراوي مجدي الدكتورالخرطوم

( لهذا: المعملية التجارب على مشرف يوسف محمد الرحيم عبد االستاذالمشروع(

( امدرمان: بجامعة الخرسانة معمل مشرف آدم يحيى علي االستاذاالسالمية(

الخرطوم جامعة الهندسة بكلية البيئية و الصحية الهندسة معمل اسرة

ولكل الذين كانوا عونا لنا في بحثنا هذا ونورا يضيء الظلمة الFFتي كFFانتتقف أحيانا في طريقنا.

إلى من زرعوا التفFFاؤل في دربنFFا وقFFدموا لنFFا المسFFاعدات والتسFFهيالت

3

واألفكار والمعلومFFات، ربمFFا دون يشFFعروا بFFدورهم بFFذلك فلهم منFFا كFFلالشكر،:

.

4

Title……………………………………………………………………………………1

Abstract………………………………………………………………………………..2

Acknowledgement……………………………………………………………….…….3

Table of content…………………………………………………………….………….4

1. Background

1.1. Portland Cement

1.1.1. Introduction

1.1.2. Hydration of Portland Cement:

1.2. Pozzolans

1.2.1. Introduction

1.2.2. Chemical Process for the Pozzolanic Reaction

1.2.3. Types of Pozzolans

1.3. Utilization of Pozzolans in Sudanese Construction Industry

2. Aims and Objectives

3. Experimental Program

3.1. Materials

3.1.1. Reject Red Bricks:

3.1.2. Graded Standard Sand

3.1.3. Ordinary Portland Cement (OPC)

3.2. Test Methods & Results

3.2.1. Fineness

3.2.2. Water Requirement

3.2.3. Strength Activity Index (SAI) with Portland Cement

3.2.4. Chemical Composition

4. Discussion

5. Conclusions

6. Recommendations for further studies

7. References

8. Appendices

8.1. Appendix 1: ASTM C311 02 Standard Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans for Use in Portland-Cement Concrete

8.2. Appendix 2: ASTM C 618 05 Standard Specification for Coal Fly Ash and Raw or Calcined Natural-pozzolan for Use as a Mineral Admixture in Concrete.

8.3. Appendix 3: Standard Sand adapted from Table 4 of BS 882:1992

5

1. BACKGROUND

1.1. Portland Cement

1.1.1. Introduction

Portland Cement (PC) is the binder used to make concrete, mortars and grouts for all

types of building and construction. Unlike gypsum plaster, Portland cement is a

hydraulic cement; i.e., it sets and hardens when mixed with water. The year 1824 is

considered the beginning of modern Portland cements when the name ‘‘Portland’’

was used in a patent by Joseph Aspdin. This term was used to reflect the similarity of

concrete made with patented cement to Portland limestone. By the 1860s the

Portland-cement industry was flourishing in the UK and Europe. The first patent in

the US was filed by David Saylor in 1870.

The Portland cement is manufactured by mixing and crushing raw materials which are

mainly limestone and siliceous clays. After the crushing process, which can be wet or

dry, the mixture is fed through a rotating kiln with variable temperature zones, where

the decomposition the raw material and fusing to produce what is known as Portland

cement clinker.

Portland cement clinker consists mainly of four oxides: CaO (lime), denoted by

cement chemists as C, SiO2 (silica), denoted as S, Al2O3 (alumina), denoted as A and

Fe2O3 (iron oxide) denoted as F. Moreover, H2O is denoted as H and represents

SO3.

The levels of the four clinker minerals can be estimated using Bogue’s equation. The

method assumes that all the F is combined as C4AF. The remaining A (i.e. after

deducting that combined in C4AF) is combined as C3A. The C combined in the

calculated levels of C3A and C4AF and any free lime are deducted from the total C

and the level of S determines the proportions of C3S and C2S. The procedure is

expressed mathematically (in mass %) as follows (Moir 2003):

6

C3S = 4.071(C – free lime) – 7.600S – 6.718A – 1.430F

C2S = 2.867S – 0.7544C3S

C3A = 2.65A – 1.692F

C4AF = 3.043F

In general when calculating the compound composition of cements (rather than

clinkers) the normal convention is to assume that all the SO3 present is combined with

Ca+2 (i.e. is present as calcium sulphate). The total CaO content is reduced by the free

lime level and by 0.7×SO3 (Moir 2003)

There are different types of Portland cements including Ordinary Portland Cement

(OPC), rapid hardening PC (RHPC), low heat PC, sulphate resisting cements (SRPC),

pozzolan cement, etc..

1.1.2. Hydration of Portland Cement:

The hydration of the PC is described briefly as the sum of the hydration process of its

four main crystallized compounds. Both C3S and C2S react with water to produce an

amorphous calcium silicate hydrate known as C–S–H gel. This gel is the main

‘cementing compound’ that binds the sand and aggregate particles together in

concrete. The process is simplified in the following equations:

C3S + 4.3H ⇒ C1.7SH 3 + 1.3CH

C2S + 3.3H ⇒ C1.7SH3 + 0.3CH

C3S is much more reactive than C2S and under ‘standard’ temperature conditions. At

20°C approximately half of the C3S in PC cement will hydrate by 3 days and 80% by

28 days. In contrast to C3S, C2S hydration proceeds to a noticeable extent after 14

days. Both C3S and C2S has a typical Ca to Si ratio around 1.7. This is noticeably

lower than the 3:1 ratio in C3S. The excess Ca is precipitated as calcium hydroxide

(CH) crystals. C2S hydration also produces some CH formation albeit in lower

quantity.

7

The hydration reactions of C3A with water, in absence of gypsum is very violent and

causes flash setting. When mixed with water, in absence of gypsum, C3A and (to a

lower extent C4AF) reacts rapidly in a highly exothermic reaction to form the phases

C2AH8 and C4AH19. These hydration phases subsequently convert to C2AH6.

However, the rate of reaction of the aluminate phases is significantly reduced by

addition of finely ground gypsum (CaSO4·2H2O) or hemihydrate (CaSO4·0.5H2O)

prior to mixing with water. This reduction in rate of reaction is due to the formation

of a protective layer of ettringite (denoted in cement chemistry notation as AFt) on the

surface of the C3A crystals. The reaction can be summarized as C3A + dissolved

calcium (Ca2+) + dissolved sulfate (SO4-2) + water ⇒ ettringite which is written in

cement chemistry notation as:

1.2. Pozzolans

1.2.1. Introduction

The term “pozzolan” was derived from volcanic ash firstly used by the Romans from

deposits close to the village of Pozzuoli, near nowadays Naples, Italy. Pozzolans are

primarily vitreous siliceous materials which react with calcium hydroxide to form

calcium silicates and other cementitious products formed depending on the chemical

composition of the pozzolan.

A pozzolan is a siliceous or aluminosiliceous material, which is not crystallized, i.e.

highly vitreous or glassy. By its own, it has no cementitious properties, however

when mixed with CH or a lime rich medium such as OPC, it exhibits cementitious

properties. These cementitious properties are due to the reaction of silicates with lime

to form calcium silicate hydrates with a low C/S ratio that gain gradual strength

usually after 7 days. Pozzolans are commonly used as cement replacement material.

The rate of pozzolanic reaction is slower than OPC hydration reaction; this is

normally reflected as lower short-term strength of concrete made with pozzolans,

compared to the pure OPC concrete. This difference between the strengths of blended

cement concrete and OPC concrete is reduced in long-term. However, highly reactive

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pozzolans, such as silica fume (SF) and high reactivity metakaolin can produce "high

early strength" concrete that may match or exceed the strength of OPC concrete.

The rate of gaining strength depends upon the chemical composition of the pozzolan

and its degree of fineness as well the percentage of replacing OPC. The greater the

percentage of vitrious alumina and silica, the better the pozzolanic reaction and the

higher the strength development.

The replacement of Portland cement by pozzolans imparts many beneficial

characteristics to the produced concrete. They increase the long-term strength and

durability. Also they reduce the overall cost besides reducing the CO2 emission

which will reduce the impact on global warming. Pozzolans have potential to make a

significant contribution towards provision of low-cost building materials and

consequently affordable houses for the poor masses.

It has been known for more than a century that several benefits can be derived by

admixture of a suitable pozzolan with Portland cement, particularly for use in

hydraulic structures. The optimum proportion of pozzolan is usually between 10 and

30 % by weight of the blended cement, however, ground granulated slag (GGBS) can

be added to a much higher levels up to 85% (Calcrete 2008).

In general, the benefits of using pozzolans may be summarised as:

1. Reducing heat generation in massive structures concreting.

2. Reducing cost of construction by saving in Portland cement constituent.

3. Increasing concrete tensile strength.

4. Reducing concrete permeability.

5. Improving some properties of plastic concrete, such as improving workability

and lowering the tendency to segregation and water gain.

6. Increasing the resistance of concrete to sulphate attack.

7. Reducing the risk of alkali aggregate reaction (AAR).

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1.2.2. Chemical Process for the Pozzolanic Reaction

Pozzolanic reaction can simply be classified as simple acid-base reaction between

CH, also known as Portlandite, and silicic acid (H4SiO4, or Si(OH)4). as follows:

Ca(OH)2 + H4SiO4 → Ca2+ + H2SiO42- + 2 H2O → CaH2SiO4 2 H2O

or summarized as CH + SH → CSH

The ratio Ca/Si, or C/S of the CSH as well as the number of water molecules may

differ depending on the stoichiometry and the chemical composition of the pozzolans.

The density of CSH is lower than that of CH and pure silica, resulting in a swelling of

the reaction products.

1.2.3. Types of Pozzolans

Historically the two most abundant and widely used pozzolans are calcined clays (see

section 1.2.3.1) and volcanic ash (1.2.3.2). Calcined clay in form of crushed fired

clay bricks, tiles or pottery has traditionally been used for improving properties of

lime mortars and renders. The most commonly used pozzolans today are artificial

such as fly ash (by product of burning coal in power-generating stations see section

1.2.3.3), ground granulated blast furnace slag (see section 1.2.3.4) and silica fume

(see section 1.2.3.5). Other less common types are: high-reactive metakaolin and

ashes of agricultural wastes including rice husk ash (RHA) & baggase ash which is a

bye product of sugar industry.

Many pozzolans available for use in construction today were previously viewed as

waste products. The use of pozzolans reduces the demand for Portland cement in

producing concrete. This is more environmentally friendly and current practice may

permit up to a 40% reduction of Portland cement. Also an optimisation of the mix

design may permit utilization of pozzolans without significantly reducing the final

compressive strength or other durability performance criteria.

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1.2.3.1. Calcined Clays and Shales

Clays or shales suitable for use as pozzolan are widespread and are readily available

worldwide. They have been utilized as cement replacement materials on large scale

construction programmes in the US, Brazil, Egypt and India. For example, in Egypt,

a lime-calcined clay mortar was used in the core of the first Aswan dam built in 1902.

Also OPC-calcined clay mixture was used in the construction of the Sennar dam in

Sudan in 1919 to 1925 (Salih et al. 1999, Practical Action Technical Brief 2011). The

blended calcined clay & lime mixture is known as surkhi in India, homra in Egypt and

semen merah in Indonesia. Shales are harder than clays and have similar mineral

contents resulting in similar pozzolanic properties.

However, this large-scale utilization has declined in the last three decades, due to the

availability of pozzolan such as ground granulated blastfurnace slag (GGBFS) and

pulverized fuel ash (PFA). In areas these where artificial pozzolans are not available,

for example in Sudan, the use of calcined clay still has considerable potential.

Sandy-clays are often used as a pozzolan, frequently in the form of crushed fired clay

bricks. It is worth mentioning that the coarser sand is not reactive. The pozzolanic

activity is imparted by the finer clay mineral fraction, and sandy clays may not

produce the best pozzolan.

Despite their variable pozzolanic reactivity, the use of ground underfired or reject

bricks and tiles as a pozzolan is likely to continue on a small scale due to the low cost

of these waste materials. Plastic clays, used in tile manufacture or pottery, may

produce better pozzolan, although the composition of good pozzolanic clays is

variable. Table 1 shows chemical composition (on an oven-dry basis) of some raw

clays in India that are suitable for producing pozzolans conforming to the Indian

Standard for calcined clay pozzolan (IS 1344.1981).

Fineness similar or slightly greater than that of OPC is usually recommended for

pozzolans although some have been ground considerably finer. The minimum

fineness recommended by the Indian standards for pozzolan (IS 1344. 1981. Calcined

11

clays) is 320 and 250m2/kg for grade 1 and 2 pozzolans respectively, measured by the

Blaine air permeability test (Practical action 2011).

Once the pozzolan has been ground, it must be blended with lime and/or OPC to

produce a pozzolanic cement. The grinding can be accomplished by human or

animal-powered methods but full homogeneity is unlikely to be achieved. The

strength and consistency of cements blended in this manner will vary considerably.

Mechanical techniques, preferably intergrading in a ball mill or, as a second option,

dry blending in a pan or concrete mixer, may give better results in terms of both

strength and consistency.

Pozzolans can be used with either lime and/or OPC for non-structural purposes

replacement of up to 50% can be used. A larger percentage of OPC may be required

if only poor quality pozzolan as are available. The exact ratio of the ingredients will

depend upon the quality of the respective raw materials and on the required

characteristics of the concrete or mortar made from the cement.

With lime pozzolan cements mixtures of 1:1 to 1:4 (lime : pozzolan) by weight are

used. A good calcined clay pozzolan may produce a cement, when mixed with a good

quality lime to produce concretes and mortars with 7 and 28 days strengths exceeding

2 and 4 MPa respectively.

Pozzolan : lime mixture strength development is slow and long-term strengths should

be considerably higher, as much as 15Mpa by 2 years. The addition of 5-10% of OPC

to lime : pozzolans mixtures will improve strength and decrease setting times.

Strength development can be accelerated if up to 4 per cent of fine gypsum is added to

the lime-pozzolan mix (Practical Action Technical Brief).

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Table 1: Indian Standard IS 1344 1981 specification for chemical composition for clays (on oven dry basis) that are suitable for producing pozzolan upon calcination.

Constituent Content by weight (%)

Silica + Alumina + Iron oxide ≥ 70.0

Silica ≥ 49.0

Calcium Oxide ≤10.0

Magnesium Oxide ≤3.0

Sulpher Trioxide ≤3.0

Water Soluble Alkalis ≤0.1

Water soluble materials ≤1.0

Loss On Ignition (LOI) ≤10.0

IS 1344.1981 states that raw materials for calcined clay pozzolan should be free from

coarse sand or gravel larger than about 0.6mm in diameter.

In tropical climates, such as in Sudan, clay deposits are often subjected to a form of

chemical weathering that leaches out the silica and alkalis. This leaves a soil rich in

ferric (e.g. lateritic i.e. iron bearing) and aluminium hydroxides (e.g. bauxitic i.e.

aluminium bearing). However, despite their low silica content, both soils may exhibit

some pozzolanic reactivity after calcination. The reactivity of laterite is lower than

bauxite. The latter exhibits reasonable results and can be used as pozzolan in lack of

silica-bearing clays.

Several researchers reported that the utilization of crushed clay bricks in construction

industry. The use of rejects from these industries have been researched as

construction materials in Argentina, Spain and Thailand (Araceli et al. 2009, Sanchez

de Rojas et al. 2006 and Torkittikul & Chaipanich 2010). For example, Monteiro et

al. 2003 (cited by Ummi Kalsum et al. 2008) investigated the effect of ground clay

brick to replace cement mass and found it effective in suppressing the alkali-silica

reaction (ASR) expansion in mortar.

Other use for crushed bricks and tiles in construction industry have been investigated

by several researchers, e.g. Poon et al. 2006 cited by Ummi Kalsum et al. 2008

investigated the use of crushed clay bricks as unbound road sub-base. Also, the

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recycled clay bricks were also used as aggregates in asphalt concrete (Khalaf et al.,

2005 cited by Ummi Kalsum et al. 2008). Gutovic et al. 2005 (cited by Ummi

Kalsum et al. 2008) later reported the strength development of autoclaved OPC-clay

brick blends, where different varieties of claybrick were used. The optimum

compressive strengths were achieved at 50 mass % clay brick additions. Poon et al.

2006 (cited by Ummi Kalsum et al. 2008) presented a study on the investigation of

blending recycled concrete aggregate and crushed clay brick as aggregates on the

production of paving blocks. The results indicated that the incorporation of crushed

clay brick reduced the density, compressive strength and tensile strength of the paving

blocks. Recently, Kenai et al. 2007 (cited by Ummi Kalsum et al. 2008) investigated

the use of crushed brick as coarse and fine aggregate for a new concrete. Results

showed that it is possible to manufacture good concrete containing crushed bricks

provided that the percentage of recycled aggregates is limited to 25% and 50% for the

coarse and fine aggregates, respectively.

In Sudan, Hamid (2002) researched the use of several local calcined clays and reject

red bricks (grog). The calcined clays sources were from the Blue Nile banks, kaolin

and black cotton soil. He studied the mixtures hydrated lime (CH) from three

different resources namely Rabak, El-fao and Atbara. He tested various levels of

replacing OPC by grog namely 10%, 20% and 30%. He found that for replacing OPC

by 20% grog in a mortar, the strength was 19.59, 25.79, 38.78 & 39.78 N/mm2 for 3,

7, 28 and 60 days respectively. For 1:2:4 concrete containing 20% proportion of

grog, the strength was 13.30, 23.23, 36.70 & 43.90 N/mm2 for 3, 7, 28 and 60 days

respectively.

The calcination process of calcined clay pozzolans is similar to the moulding and

firing process of clay bricks, tiles or pottery. The optimum calcination temperatures

for clay pozzolans are slightly below those for clay bricks or tiles. It is much better to

design specific moulding and firing process for producing pozzolans. The Indian

Standard (IS1344 1981) gives the following range of temperatures for different types

of clays: Montmorillonite type 600° to 800°C, Kaolinite type700° to 800°C and Illite

type 900 to 1000°C. In practice, most clay soils consist of a mixture of minerals, and

a calcination temperature of 700-800°C is normally considered suitable. The

14

optimum period of calcination depends on the clay type but is normally about one

hour or less.

Rotary kilns have been the most common means of calcining clays and have been

extensively used in the US and Brazil. Natural gas or oil is normally used as a fuel

and outputs vary from 12.5 to 100 tonnes per day. Several Indian institutions,

including the Central Road Research Institute and the National Building Organization,

have researched designs on kilns specifically for clay pozzolan production with

production rates between 5 and 20 tonnes per day.

Calcined clays are ground to produce fine powder. This grinding can be performed

with human or, more commonly, animal-powered methods. Ball mills are more

suited to large-scale applications. Some calcined clays, such as kaolin, are softer than

others and require less grinding in order to achieve the desired fineness.

The majority of brick making industries in the Sudan are operating along the banks of

the rivers descending from the Ethiopian Rift. They operate during the dry season

between October and July of the year. Fired clay bricks are mainly produced by

conventional methods using biomass fuels such as fuelwood and dung cake (zibalaa).

The modern brick industries produce less than 2% of the total annual brick production

where fuel oil is used.

In 2006, the total annual production of fired clay bricks in the Sudan was estimated to

be about 2.8 billion bricks (Alam 2006). About 88.5% of this amount was produced

in Khartoum and Central States (Gezira, Sinnar, White Nile and Blue Nile). The

brick industries located on the Blue Nile banks produced about 82.4% and those on

the River Nile bank produced about 9.5%.

Alam (2006) estimated the total annual consumption of wood by the brick making

industries of the Northern Sates of Sudan to be about 549,000 stacked m3 equivalent

to 183,000 tonnes of fuelwood. From this total, the brick making industries of

Khartoum and Central States consumed 46.2% and 42.3% respectively. Wood

consumption per 1000 bricks varied widely from 0.117 m3 to 1.6 m3. wood

consumption per 1000 bricks in Kassala and Kordofan States is approximately more

15

than 10 times those consumed in Khartoum and Central States. The total number of

workers employed in this sector was about 35,000; of which 50% were employed in

Khartoum and 38% in Central States.

Due to the poor quality control in traditional Sudanese bricks industry, the percentage

of product rejected for sale mounts up to about 25%. This is about 0.7 billion bricks

that represent a potential reserve for producing pozzolans in the Sudan. These rejects

are usually broken to smaller sizes up to 50mm aggregate size and mixed with quick

lime & OPC and used as a lightweight waterproof layer on building roofs. The

mixture is known locally as Khafja.

1.2.3.2. Volcanic Ash

Deposits of volcanic ash exist wherever there are active or recently active volcanos,

e.g in the Mediterranean, the Pacific region, and central and eastern Africa. The form

of volcanic ashes may range from loose fine material to coarse deposits containing

quite large particles. Deposits may be loose, with an appearance and texture similar

to a compacted coal or wood ash. Other deposits are cemented, sometimes with

appearance and properties similar to stone, and in this form they are normally referred

to as tuffs or trassy. The colour of deposits can vary from off-white to dark grey.

Table 2: Composition of volcanic ash suitable for use as a pozzolan

Constituent Content by weight (%)

Alumina + Iron oxide 15-30

Silica 45-65

Calcium Oxide + Magnesium Oxide +

Alkalis

Up to 15

Loss On Ignition (LOI) Up to 12%

The pozzolanic reactivity of ash deposits can vary considerably. The quality of

material may also vary within a single deposit or a single geologically consistent

stratum, with variations in depth being common. Regular testing is therefore required

if volcanic ash is to be used as a pozzolan and this has been a constraint to its

16

commercial exploitation. However, volcanic ash is, or has recently been, successfully

used as a pozzolan in many countries including the US, Germany, Japan, Italy, Kenya

and Indonesia, with pilot plants tested in Tanzania and Rwanda. For example, 200,000

tonnes of volcanic pozzolan were used in the construction of the Glen Canyon dam in

the US, completed in 1964.

In Sudan, resources of natural pozzolans material in form of volcanic tuffs and

pumice are reported in Bayouda deserrt, Jebbel Marra and other volcanic fields.

Sulieman (2008) reported several quarry sites of Bayouda Desert natural pozzolans,

hereinafter denoted as BDNP, located in the Northern State, some 63Km South of

Merowe city. The area of the pozzolan raw material occurs in Jebel Hebeish and Jebel

Mazrub, and bounded by Latitudes 18º 29Z 01″. & 18º 29Z 26″ N and Longitudes 32º

26 28″. & 32º 28 50″.1 E. The amount of reserve are estimated to be 10 million

tonnes at the former and 33 million tonnes at the latter. These reserves are accessible

from Khartoum by Shrian Al Shimal paved road to Merowe and 63Km by unpaved

road or from Atbara to Merowe by paved road across Bayouda Desert and 46km

towards the north by unpaved road. The area is permanently accessible by trucks

during all season of the year. Other potential pockets of NP exists in Elgeili

(Sabaloga), Jabel , Jabbel Katool in Kurdofan and Jabbel Marra in Darfur (Sulieman

2008).

Once the deposits of natural pozzolans are excavated most volcanic ashes will require

only minor processing before use as a pozzolan. Many ashes are only loosely

cemented and can easily be excavated by hand, although others may need mechanical

or pneumatic equipment. Some lithic tuffs may require blasting with explosives. The

ash may require drying, and in dry sunny climates this can simply be achieved by

spreading the ash in a thin layer on a specially prepared drying floor, similar to those

commonly used to dry crops. Alternatively, in wet climates, and for large quantities,

inclined rotary driers are normally used (Practical Action 2011).

If the ash is cemented it will need to be crushed before entering the dryer. Some

volcanic ashes may be in form of very fine and loose powders that may not require

crushing or grinding. Other ashes may be of sufficient fineness but be cemented

together. These will require milling or crushing. Coarse ashes and lithic tuffs will

17

need to be ground in a ball mill or similar pulverising apparatus (Practical Action

2011).

1.2.3.3. Pulverised Fly Ash (PFA)

Fly ash from a coal-fired power station is a pozzolan that results in low-permeability

concrete, which is more durable capable of resisting ingress of deleterious chemicals.

When coal burns in a power station furnace between 1250°C and 1600°C, the

incombustible materials combine to form spherical glassy droplets of silica (S),

alumina (A), iron oxide (F) and other minor constituents.

The first reference to the idea of utilizing coal fly ash in concrete was by McMillan

and Powers in 1934 and in subsequently researched by others research. These

researches were culminated by the construction of the Lednock, Clatworthy and

Lubreoch Dams during the 1950s with fly ash as a partial cementitious material.

These structures are still in excellent condition, after some 50 years (Lewis et al.

2003).

In Sudan, recently in 2005, the power generation at Gerri Power Stations started to

produce fly ash. Unfortunately due to the use of petroleum coke as fuel, the generated

fly ash is not suitable for using in construction. This is attributed to its very high

carbon content. Further research and optimisation of the burning process and the fuel

type are required in this field.

1.2.3.4. Ground Granulated Blastfurnace Slag (GGBS)

Blastfurnace slag is a by-product of manufacturing iron in a blastfurnace. It results

from the fusion of a limestone flux with ash from coke. The slag is composed of the

siliceous and aluminous residue remaining after the reduction and separation of the

iron from the ore.

Two alternative processes, namely granulation or pelletization can be utilized to

convert molten slag into a form suitable for use as a cementitious material. Either

process requires that the molten slag to be rapidly cooled to form a glassy disordered

18

structure. If the slag is allowed to cool too slowly this allows a crystalline well-

ordered structure to form which is stable and non-reactive.

In the granulation process the stream of molten slag is forced over a weir into high-

pressure water jets of below about 50°C. The water slag ratio is normally between ten

and twenty to one. This process produces glassy granules of cooled slag no larger

than about 5 mm in temperature diameter. Following the granulation the granulate is

dried and ground to cement fineness in a conventional cement clinker grinding mill.

In the pelletization process, the molten slag is poured onto a water-cooled steel-

rotating drum of approximately 1m diameter. The drum has fins projecting from it,

which the slag is thrown through the air inside a building where water is sprayed onto

it. This results in rapid cooling and produces pelletized particles from about 100 mm

down to dust. However, large particles tend to be crystalline in nature and have little

or no cementitious value. Particles larger than about 6 mm are therefore screened off

and used as a lightweight aggregate in concrete and only the finer fraction (< 6 mm)

used for the manufacture of GGBS.

Granulation is produces materials with a high glass content, but the capital costs of a

granulator are about six times greater than that of a pelletizer. Both materials can be

used as raw feed for GGBSs and most Standards do not differentiate between them.

The hydraulic potential of ground granulated blastfurnace slag (GGBS) was first

discovered in 1862 in Germany by Emil Langen. Commercial production of lime-

activated GGBS was started in 1865 and around 1880 GGBS was first used in

combination with Portland cement (PC). It has been used extensively in many

European countries, such as Holland, France and Germany. In the UK the first British

Standard for Portland Blastfurnace Cement (PBFC) was produced in 1923 (Lewis et

al. 2003)

The chemical composition of slag depends on the source of the raw materials and the

blastfurnace conditions. The major oxides exist within the slag glass (formed as the

result of rapid cooling) in the form of a network of calcium, silicon, aluminium and

19

magnesium ions in disordered combination with oxygen. The oxide composition of

GGBS is shown in Table 3 compared to the Portland cement.

Table 3: Comparison between oxide composition of European Portland Cements and

GGBS (after Lewis et al. 2003)

1.2.3.5. Silica Fume (SF)

Various names including silica fume, microsilica and volatilized silica are often used

to describe by-products extracted from the exhaust gases of silicon, ferrosilicon and

other metal alloy smelting furnaces. The terms microsilica and silica fume (SF) are

used to describe those condensed silica fumes that are of high quality, for use in the

cement and concrete industry. The latter term, SF is adopted in the European Standard

– prEN 13263-1 (Lewis et al. 2003).

SF was first produced in Norway, in 1947, when environmental policy made the

filtering of the exhaust gases from the furnaces compulsory. The major portion of

these fumes was a very fine powder containing high percentage of silicon dioxide.

Large-scale filtering of gases began in the 1970s and the first standard, NS 3050, for

use in a factory-produced cement, was granted in 1976. As the pozzolanic reactivity

for SiO2 was well known, extensive research was carried out at the Norwegian

Institute of Technology. There is extensive research 3000 papers now available that

detail work on silica fume and silica fume concrete (Lewis et al. 2003).

Due to the high S content of SF, the dosage of SF that would consume all the CH

produced by PC hydration is not exceeding 10% (Lewis et al. 2003)

20

1.3. Utilization of Pozzolans in Sudanese Construction

Industry

A workshop held in 1999 on pozzolan utilization in the construction industry in

Sudan, jointly organized by the Sudanese Organization of Economic Alternatives, the

Building & Road Research Institute of University of Khartoum and Sudan

Engineering Society estimated that pozzolan alone, as an alternative for OPC have a

capital business share of around 6,000,000USD per annum (Salih et al. 1999).

Calcined clays were used in 1920s to construct Sennar dam. Khafja , a local term for

a mixture of wasted bricks aggregate plus lime and/or cement is normally used for

roofing in traditional Sudanese building industry. Chinese PFA was imported for

constructing Merewe dam, despite the presence of Bayouda Dessert Natural

Pozzolans (BDNP) vicinity of 50Km. Apart from these cases, there are neither sound

engineering practice nor a drive and will to utilize pozzolans in domestic construction

industry. Also due to the existence of large sugar industry in Sudan, there is a

potential of using baggase ashes as pozzolanic material in Sudan (Salih et al. 1999)

The lack of using pozzolans as cement replacement material may be attributed to

scarce information on engineering properties of pozzolans blended cements. This

trend is common almost in all African countries, apart from limited experiments in

Egypt, Rwanda, Tanzania and Kenya (Salih et al. 1999). Also, it may be due to the

industry’s ignorance of benefits imparted by blended pozzolans cement. However,

Mamoun & Zamzami (2010) recently published a paper characterizing samples of

BDNP using Indian standard. Their study was carried out from a geological

perspective and involved chemical analysis, x-ray diffraction and compressive

strength of lime and BDNP mixes.

The need for cement in the Sudanese construction industry has increased significantly

in the last few years. This increase is due to the initiation of a vast public work

construction programme. Thus large quantities of cement have been imported to

cover the specific needs of the construction sector. Despite the recent openings of

21

several new cement factories, the cost of Sudanese cement per tonne is still far higher

than its average international cost. International average cost per tonne is 70USD

while producing Sudanese cement costs about 100USD and about 130USD to the end

consumer in Khartoum (Assalam Cement Factory Management, Personal

communication 2010).

Moreover, one of the challenges facing the Sudanese cement and concrete industry is

production of durable concrete especially in coastal areas and economical concrete

nationwide. The utilization of Bayouda desert volcanic ash and other similar

resources may be the key for addressing these challenges. Bearing in mind the

vicinity of Bayouda dessert to the Port-Sudan and the accessibility to Khartoum, there

is a potential market for using this material in coastal area for resisting chloride and

sulphate attacks.

22

2. AIMS AND OBJECTIVES

As mentioned in Section 1.2.3.1, it is estimated that about 0.7 billion bricks are

rejected annually due to the poor quality control in traditional Sudanese bricks

industry. These reject bricks represent a potential reserve for producing pozzolans in

the Sudan.

This aim of this study is investigating the potential of using ground reject fired clay

bricks in Khartoum as pozzolan for replacing cement. The objectives of this research

are:

1. Collection of samples of reject bricks from different traditional red brick

industries located at Elgerief-Umdoam and Shambat in Khartoum, Sudan.

2. Crushing and pulverising samples collected in Paragraph 1 to produce fine

Red Brick Powder (RBP).

3. Measuring the properties of RBP, as pozzolanic material, according to the

scope of Standard Test Methods for Sampling and Testing Fly Ash or Natural

Pozzolans for Use in Portland-Cement Concrete ASTM C311-02 (See

Appendix 1). Namely, Chemical composition, water requirement, fineness

and strength activity index with OPC will be assessed.

4. Interpreting the test results determined in Paragraph 3 using Specifications in

ASTM C 618-05 (see Appendix 2) to characterise RBP as pozzolanic material.

The ASTM C 618-05 provides specification for Coal Fly Ash and Raw or

Calcined Natural-pozzolan for Use as a Mineral Admixture in Concrete.

23

3. EXPERIMENTAL PROGRAM

3.1.Materials

3.1.1. Reject Red Bricks:

Random samples of reject red bircks (weighing about 50Kg) were collected from

various Brick kilns located on the east bank of the Blue Nile river, namely El-gerief

east & Umdoum. These samples, hereinafter, bear the suffix G-U (short for El-gerief

east & Umdoum). Also other 50Kg samples were collected randomly from various

bricks kilns located on the east bank of the river Nile, namely in Shambat in

Khartoum North. These samples bear the suffix SH (short for Shambat). Photographs

1 to 8 document for trips to collect reject brick samples.

The reject red bricks were firstly crushed using a crusher at Building and Road

Research Institute (BRRI), University of Khartoum. Then they were sieved on # 200

sieve (75µm). The amount passed through the sieve was further pulverised using ball

mill crusher at the Corporation of Geological Researches Laboratory, Ministry of

Mining located at El-neel Avenue Khartoum. The powdered materials for the El-

gerief-Umdoum specimens are denoted as RBP-G-U, while those from Shambat

specimens are denoted as RBP-SH.

Clause 5.2 of ASTM C 311-05 (see Appendix 1) recommends that the hydrated lime

used in the tests shall be reagent-grade calcium hydroxide, 95 % minimum calculated

as Ca(OH)2, and have a minimum fineness of 2500 m2/kg as determined in accordance

with Test Method C 204. However, in this study, quick lime was used, purchased

form Al-gamieer on the west bank of the River Nile at Umdurman. The quick lime

was dissolved in water at 23oC to produce hydrated lime. This reaction is exothermic

and was carried out using protective eye and hand gear.

24

Photograph 1: A platform for moulding green bricks (front) and a yard for sun drying of the green bricks. (back).

Photograph 2: Stacking of dried bricks for firing.

25

Photograph 3: Start of firing the bricks after covering the stacked bricks with broken bricks cemented with cow dung (Zibala).

Photograph 4: Cooling down of a fired brick kiln.

26

Photograph 5: A finished fired brick kiln at El-gerief East, Khartoum.

Photograph 6: Firing holes for feeding fuelwood at the bottom of a red brick kiln.

27

Photograph 7: Unloading the fired bricks from a kiln -1

Photograph 8: Unloading the fired brick from the kiln-2

28

3.1.2. Graded Standard Sand

The ASTM C311 requires that “The sand used for making test specimens for the

activity index with Portland cement shall be natural silica sand conforming to the

requirements for graded standard sand in Specification ASTM C 778”. However, in

this study, the standard sand was prepared according to BS 882:1992, the grading was

conforming to the specifications of BS 882:1992 as described in Appendix 3

3.1.3. Ordinary Portland Cement (OPC)

Ordinary Portland Cement (OPC) of class 42.5N produced by Atbara Cement

(http://www.atbaracement.sd). The chemical composition of the cement is listed in

Table 4.

Table 4: Chemical Composition of OPC

Oxide % by Weight

Al2O3 7.17

CaO 62.5

CL content 0.004

Fe2O3 3.28

Insoluble Residue (IR) 2.12

Loss on Ignition (LOI) 0.88

MgO 1.10

SiO2 20.16

SO3 2.75

Alkaline (Na2O & K2O) 00

Total 99.96

29

3.2. Test Methods & Results

3.2.1. Fineness

RBP G-U and RBP-SH specimens were wet-sieved in accordance with ASTM 593-69

through sieve #325 (45µm) as required. The results are shown in Table 5

Table 5: Fineness Results for RBP-G-U and RBP-SH

Specimen

Ref

Weight

(gm)

Weight retained on sieve #325

(45µm)

%retained %passed

RBP-G-U 50 15.67 34.33 68.66

RBP-SH 50 16.00 34.00 68.00

3.2.2. Water Requirement

The ASTM C 1437, the Standard Test Method for Flow of Hydraulic-Cement Mortar,

determines how much a mortar sample flows when it is unconfined and consolidated.

The mortar flow is similar to a slump test is a relative measure of workability.

Changes in flow indicate variability in the materials and/or the batching process that

may not be observed from slump testing alone. Mortar flow is most sensitive to water

content and air content. It is also more sensitive than the slump test for stiff concrete

mixtures. Mortar flow is a process control test procedure and should not be

considered as an acceptance criteria. The test is sensitive to several parameters

including water content, fine aggregate gradation, cementitious chemistry, mixing

time, air content, and concrete temperature all interact to affect mortar flow.

The apparatus for the flow test is shown in Photograph 9. The apparatus consists of

flow table, flow mould, clipper, tamper, trowel, and ruler. The apparatus is Model ZI

1007 made by ZEAL International:1, Netaji Subhash Marg, Daryaganj, New Delhi,

INDIA. The flow table consists of a 30 cm diameter polish steel plate with 3

engraved annular circles 7, 11 and 19cm diameter. The table top is arranged for a free

fall of 12.5mm by a cam action. A brass conical mould with the following

dimensions: 65mm internal diameter. at base and 40mm internal diameter at top,

30

height of 90mm. The test was carried out at the Civil Engineering Laboratory of

Umdurman Islamic University.

Photograph 9: Flow Table apparatus for testing mortar flow

Photograph 10: Transformation of the conical mould of mortar to a pancake shape

after manual vibration.

31

The mortar specimen was placed inside 90mm tall conical brass mould in two 45mm.

layers, each layer was tamped 20 times. The mortar on the top of the mould was

stricken off and flushed with the top of the mould. The mould was removed and the

mortar was vibrated manually as the flow table rises and drops 12.5mm., 15 times in

15 seconds. The mortar changed from a conical shape with a 65mmn. base to a

“pancake.”. The diameter of the pancake was measured (see Photograph 10). The

Mortar flow was reported as a percentage of the original diameter based on the change

in diameter from 4 in. to the final diameter of the mortar “pancake.”.

First, the flow for a standard mix containing 500gm OPC, 242mL water

(Water/Cement (W/C) ratio=0.48) and 1:3 cement: standard sand was calculated.

Then water was added (on a trial basis starting from 255gm) to a 1:3 binder : standard

sand mix. The binder is made of 400gm OPC and 100gm pozzolan (i.e. 20% RBP

replacing OPC). The flow was measured targeting a flow level equals to that of the

control OPC mix flow ± 5.

The data and the results for the mortar flow test are shown in Table 6.

32

Table 6: Data and Results of Mortar Flow Test.

Mix Ref.

Mix Constituents (gm) Diameter Flow

Sand

(gm) Cement (gm)

RBP

(gm)

Water

(gm)

Water /Binder ratio

(W/B) Original (cm) Spread (cm) (%)

OPC-Control 1375.00 500.00 0.00 242.00 0.484 6.50 13.00 100.0

RBP-G-U 20% 1375.00 400.00 100.00 255.00 0.510 6.50 14.50 123.1

RBP-G-U 20% 1375.00 400.00 100.00 252.00 0.504 6.50 13.50 107.7

RBP-G-U 20% 1375.00 400.00 100.00 250.00 0.500 6.50 13.00 100.0

RBP-Sh 20% 1375.00 400.00 100.00 250.00 0.500 6.50 13.00 100.0

33

The water requirement, which was later used for the Strength Activity Index with

Portland Cement in Section 3.2.3 was calculated as a percentage of control as follows:

water requirement= Y242

×100

where: Y = water required for the test mixture to be ±5 of control.

As deducted from data in Table 6, the Y value for both RBP-G-U and RBP-SH was

found to be 250gm resulting in water requirement = 103%

3.2.3. Strength Activity Index (SAI) with Portland Cement

The test for strength activity index as described in section 4.1.1 of ASTM C311-05

was carried out to determine whether RBP produced an acceptable level of strength

development when used with hydraulic cement in concrete.

The mix references, curing regime and proportions and shown in Table 7. Nine 70×

70× 70 mm mortar cubes of each mix were cast. The water binder ratios W/B were

0.484 for OPC control mix and 0.50 for OPC + RBP mixes as calculated from the

Water Requirement Section 3.2.2. Clause 26.2 of the ASTM C311-05 requires that

SAIs to be evaluated on 7 or 28 days on 20%RBP:80%OPC mortars cured in

saturated lime. However, in this study extra SAIs for 20%RBP:80%OPC were

evaluated after 91days, as well as for water cured specimens. In addition extra mixes,

containing 30%RBP:70%OPC binder were also cast and cured in water to investigate

the effect of higher RBP dosage on SAIs.

It is worth noting that for charactering RBP only 6 cubes were required. Since ASTM

C 618 specifies that “meeting the 7 day or 28 day Strength Activity Index will indicate

specification compliance” only one age might be required. It is optional for the

producer or the user after preparing six-cube batches to choose only three cubes of

control and test mixtures need to be demoulded for either 7 or 28 day testing.

34

The apparatus for measuring SAIs was 3 sets of triplicate 70mmx70mmx70mm cubes

joint together, mechanical concrete mixer, sensitive platform balance, blade, scoop,

ruler, mechanical vibrator, graduated cylinder, cube crushing machine, water curing

tank and curing cabinet. The curing cabinet model was Control 65-L0013/D

CURACEM Cement Curing Cabinet supplied by CONTROLS S.R.L Via Aosta, 6 –

20063 Cernusco, Italy. The cabinet provides a curing environment between 95% and

100% relative humidity (RH). Its temperature was set to 26±1oC deviating from the

ASTM C311 standard requirement of 23±2oC.

First the mix ingredients were weighed as shown in Table 7, then the dry ingredients

were poured in the mixture and mixed for 1 minute. Then the water was added and

mixed for 4 minutes. Then 3 sets of clean and oiled triplicate moulds were filled with

one 35mm thick layer of mortar and vibrated by the mechanical vibrator for 1 minute.

Another layer of 35mm thick was filled and vibrated for another 1 minute. The cast

cubes were labelled and designated for triplicate testing on 7, 28 and 91 days.

The cast samples were sealed with cling film and placed immediately after vibration

into the curing cabinet for 24 hours. After 24 hours, the specimens were demoulded

and stored in the designated curing regime until testing dates at 7, 28 and 91 days. The

strength activity indices (SAIs) with OPC were calculated using the following

equation:

Strengthactivity index with Portland cement= AB

×100

where:

A = average compressive strength of test RBP mixture cubes (Mpa) and

B = average compressive strength of OPC control mix cubes (Mpa)

The compressive strength of the cast mortars and their relevant strength activity

indices (SAIs) are shown in Table 8.

35

Table 7: Mix References, proportions and curing conditions.

Mix Ref.

Mix Ingredient (gm)Curing solution

(23oC±1)

Number of

70x70x70 mm

cubesSand (gm) Cement (gm) RBP (gm) Water (gm)

Water /Binder ratio1

(W/B)

OPC-Control 2 1800.00 600.00 0.00 288.00 0.484 Water 9

RBP-G-U 20%-W 1800.00 480.00 120.00 300.00 0.500 Water 9

RBP-SH 20%-W 1800.00 480.00 120.00 300.00 0.500 Water 9

RBP-G-U 30%-W 1800.00 420.00 180.00 300.00 0.500 Water 9

RBP-SH 30%-W 1800.00 420.00 180.00 300.00 0.500 Water 9

RBP-G-U 20%-L3 1800.00 480.00 120.00 300.00 0.500 Saturated lime 9

RBP-SH 20%-L4 1800.00 480.00 120.00 300.00 0.500 Saturated lime 9

1 For determining W/B ratios please see Section 3.2.2 for water requirement2 Control OPC Mix cured in water3 El-gerif –Umdoum Red Brick Powder replacing 20% (by weight) of cement and cured in saturated lime for measuring ASTM 618 strength activity index with OPC4 Shambat Red Brick Powder replacing 20% (by weight) of cement and cured in saturated lime for measuring ASTM 618 strength activity index with OPC.

36

Table 8: Strength Activity Indices for various RBP:OPC mixes

Mix Ref. Average 7 Days Strength (N/mm2)

Strength Activity Index (7days)

Average 28 Days Strength (N/mm2)

Strength Activity Index (28 days)

Average 91 Days Strength (N/mm2)

Strength Activity Index (91days)

OPC-Control 33.36 1.00 41.90 1.00 45.83 1.00

RBP-G-U 20% (W) 26.74 0.80 29.99 0.72 40.15 0.88

RBP-SH 20% (W) 24.44 0.73 28.02 0.67 44.59 0.97

RBP-G-U 30% (W) 20.81 0.62 28.85 0.69 35.87 0.78

RBP-SH 30% (W) 19.24 0.58 26.06 0.62 37.97 0.83

RBP-G-U 20% (L) 26.53 0.80 35.25 0.84 43.10 0.94

RBP-SH 20% (L) 27.02 0.81 33.05 0.79 39.27 0.86

37

3.2.4. Chemical Composition

Clause 4.1.2 of ASTM C311 states that “The chemical component determinations and

the limits placed on each do not predict the performance of a fly ash or natural

pozzolan with hydraulic cement in concrete, but collectively help describe

composition and uniformity of the material”. However, in this study the chemical

compositions of RBP-G-U and RBP-SH were, determined using methods described in

BS EN 196-2 and BS EN 196-21. The chemical compositions of RBP-G-U and RBP-

SH are shown in Tables 8 and 9 respectively.

Table 9: Chemical Composition of Red Brick Powder (RBP) from Elgerief East &

Umdoum (RBP-G-U)

Oxide % by Weight

Al2O3 9.40

CaO 3.30

CL content Not determined (ND)

Fe2O3 6.50

MgO 0.34

SiO2 78.73

SO3 0.27

Na2O 0.225

K2O 0.292

Equivalent total alkali content to Na2O 0.817

Insoluble Residue (IR) ND

Loss on Ignition (LOI) ND

Total 99.057

38

Table 10: Chemical Composition of Red Brick Powder from Shambat (RBP-SH)

Oxide % by Weight

Al2O3 9.28

CaO 3.44

Fe2O3 4.20

MgO 0.157

SiO2 80.68

SO3 0.216

Na2O 0.615

K2O 0.625

Equivalent Total alkali content to Na2O 0.773

CL content Not determined (ND)

Insoluble Residue (IR) ND

Loss on Ignition (LOI) ND

Total 99.213

39

4. DISCUSSION

The results in Table 8 were plotted in Figures 1 to 12. Figure 1 shows that Red bricks

powders (RBP) produced from reject bricks collected from both El-gerief & Umdoum

(G-U) and Shambat (SH) have strength activity indices (SAIs) with OPC of about

80% higher than 75%. This satisfies the ASTM C 618 criterion of SAI for 7 days.

Figure 2 also shows that both RBPs satisfied the criterion for 28 days. However,

RBP-G-U produced a higher SAI of 84% than RBP-SH which is 79%. Despite not

required by ASTM C618, the SAIs for 91 days still showing that RBP-G-U performed

better than RBP-SH.

Ratio=1

Ratio=0.80 Ratio=0.81

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

OPC-Control RBP-G-U 20% (L) RBP-SH 20% (L)

7 days Strength (N/mm2) and Strength Activity Indices with OPC (expressed as Ratio)

Figure 1: Influence of Red brick powder source on seven days Strength Activity Indices (SAIs)

with OPC.

40

Figure 2: Influence of red brick powder source on 28 days strength activity indices (SAIs) with OPC.

Figure 3: Influence of Red brick powder source on 91 days strength activity indices (SAIs) with OPC. NB the ASTM C618 does not require for 91 days.

Figures 4, 5 and 6 summarise the influence of increasing the RBP dosage from 20% to

30% when cured in water. It is clearly that increasing of RBP dosage lowered the

strength.

41

Ratio=1

Ratio=0.84Ratio=0.79

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

OPC-Control RBP-G-U 20% (L) RBP-SH 20% (L)

28 Days Strength (N/mm2) and Strength Actvity Indices with OPC (expressed as ratio)

Ratio=1

Ratio=0.94

Ratio=0.89

38.00

39.00

40.00

41.00

42.00

43.00

44.00

45.00

46.00

47.00

OPC-Control RBP-G-U 20% (L) RBP-SH 20% (L)

91 Days Strength (N/mm2) and Strength Actvity Indices with OPC (expressed as ratio)

Figure 4: Influence of dosage level of red brick powder (RBP) on 7 days strength of water cured mortars.

Figure 5: Influence of dosage level of red brick powder (RBP) on 28 days strength of water cured mortars.

42

Ratio =1

Ratio = 0.8Ratio =0.73

Ratio=0.62 Ratio=0.58

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

OPC-Control RBP-G-U 20%(W)

RBP-SH 20%(W)

RBP-G-U 30%(W)

RBP-SH 30%(W)

Effect of RBP Dosage on 7 days Strength

Ratio =1

Ratio = 0.72Ratio =0.67 Ratio=0.68

Ratio=0.62

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

OPC-Control RBP-G-U 20%(W)

RBP-SH 20%(W)

RBP-G-U 30%(W)

RBP-SH 30%(W)

Effect of RBP Dosage on 28 days Strength

Figure 6: Influence of dosage level of red brick powder (RBP) on 91 days strength of

water cured mortars.

Figure 7: Influence of curing regime on 7 days strength of 20%RBP:80%OPC mortars.

43

Ratio =1Ratio = 0.88 Ratio =0.91

Ratio=0.78Ratio=0.83

0.005.00

10.0015.0020.0025.0030.0035.0040.0045.0050.00

OPC-Control RBP-G-U 20%(W)

RBP-SH 20%(W)

RBP-G-U 30%(W)

RBP-SH 30%(W)

Effect of RBP Dosage on 91 days Strength

Ratio=1

Ratio=0.80 Ratio=0.80Ratio=0.73

Ratio=0.81

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

OPC-Control RBP-G-U 20% (W) RBP-G-U 20% (L) RBP-SH 20% (W) RBP-SH 20% (L)

Effect of Curing Solution on 7 days Strength & Strength Activity Indices of 20RBP:80OPC Mixes

Figure 8: Influence of curing regime on 28 days strength of 20%RBP:80%OPC mortars.

Figure 9: Influence of curing regime on 91 days strength of 20%RBP:80%OPC

mortars.

Figures 7, 8 and 9 show that curing in saturated lime, produced higher strength than

curing in water. This is attributed by the fact that curing in water will leach out Ca+2,

while curing in saturated lime may preserve or increase the Ca+2 concentration within

44

Ratio=1

Ratio=0.72

Ratio=0.84

Ratio=0.67

Ratio=0.79

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

OPC-Control RBP-G-U 20% (W) RBP-G-U 20% (L) RBP-SH 20% (W) RBP-SH 20% (L)

Effect of Curing Solution on 28 days Strength & Strength Activity Indices of 20RBP:80OPC Mixes

Ratio=1

Ratio=0.88

Ratio=0.94Ratio=0.91

Ratio=0.89

37.0038.0039.0040.0041.0042.0043.0044.0045.0046.0047.00

OPC-Control RBP-G-U 20%(W)

RBP-G-U 20%(L)

RBP-SH 20%(W)

RBP-SH 20% (L)

Effect of Curing Solution on 91 days Strength & Strength Activity Indices of 20RBP:80OPC Mixes

the mortar. As mentioned in Section 1.2.2 that the presence of Ca+2 is essential for the

pozzolanic reaction.

Figure 10 shows that mix containing 20%RBP-G-U (cured in lime) gained 32.86%

extra strength from 7 days to 28 days, however this gain dropped to 22.27% from

28days to 91 days. For mix containing 20%RBP-SH these gains were 22.32% and

18.88%. This shows that the rate of pozzolanic reaction for both RBPs was exceeding

22% and more significant between 7 and 28days.

Figure 11 shows that mix containing 20%RBP-G-U (cured in water) gained 12.15%

extra strength from 7 days to 28 days, however this gain increased significantly to

33.88% from 28days to 91 days. For mix containing 20%RBP-SH these gains were

14.65% and 59.14% respectively. This shows that the rate of pozzolan reaction for

both RBPs was more significant and exceeding 33% between 28 to 91days. Hamid

(2002) found that the strength of 20%RBP from blue Nile (Suba):80%OPC increased

by 50.36% from 7 days to 28 days.

Figure 12 shows that mix containing 30%RBP-G-U (cured in water) gained 38.64%

extra strength between 7 and 28 days. However this gain reduced to 24.33% from

28days to 91 days. For mix containing 30%RBP-SH these gains were 35.54%

between 7 and 28 days and increased to 45.70% between 28days and 91days. This

shows that the rate of pozzolan reaction for both RBPs was more than 24% in the

duration between 28 to 91days.

45

Figure 10: Influence of age on strength gaining of 20%RBP:80%OPC mortars cured in saturated

lime.

Figure 11: Influence of age on strength gaining of 20%RBP:80%OPC mortars cured in water.

46

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

1 10 100

OPC-control

RBP-G-U 20% (L)

RBP-SH 20% (L)

Age (Days) Log Scale

Stre

ngth

(N/m

m2 )

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

1 10 100

OPC-control

RBP-G-U 20% (W)

RBP-SH 20% (W)

Age (Days) Log Scale

Stre

ngth

(N/m

m2 )

Figure 12: Influence of age on strength gaining of 30%RBP:70%OPC mortars cured in water.

47

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

1 10 100

OPC-control

RBP-G-U 30% (W)

RBP-SH 30% (W)

Stre

ngth

(N/m

m2 )

Table 11 summaries ASTM C 618 05 Standard Specification for Coal Fly Ash and

Raw or Calcined Natural-pozzolan for Use as a Mineral Admixture in Concrete. The

assessed physical properties of both RBP, namely fineness, water requirement &

strength activity indices (SAIs) and chemical compositions are compared to Table 11

values and summarised in Table 12. It is clear that both RBPs satisfy the requirement

for class F. However, for full classification of the pozzolans, it is strongly

recommended to investigate other untested properties listed in Table 11.

Table 11: Summary of ASTM C 618 05 Standard Specification for Coal Fly Ash and

Raw or Calcined Natural-pozzolan for Use as a Mineral Admixture in Concrete. (see

Appendix 2)

48

Table 12: Partial characterisation of red brick powders (RBPs) from El-gerief &

Umdoum (G-U) and Shambat (SH) based on tested properties in this

study.

Chemical/Physical Property ASTM C618 F Class RBP-G-U RBP-SH

SiO2+Al2O3+Fe2O3 ≥70% 94.53% 94.16%

SO3 ≤5% 0.27% 0.216%

Moisture Content ND ND

Loss on Ignition ND ND

Available Alkalies ≤1.5% 0.877% 0.773%

Fineness #325 (percentage

retained)

≤34% 31.34% 32.00%

Water Requirement ≤105% 103% 103%

Strength Activity Index with

cement (SAI) -7 days (cured in

lime)

≥75% 80% 81%

Strength Activity Index with

cement (SAI) -28 days (cured

in lime)

≥75% 84% 79%

49

5. CONCLUSIONS

1. Reject brick were collected from Khartoum Estate brick industries, namely El-

gerief East & Umdoum (G-U) and Shambat (SH) areas. Then they were

crushed and pulverised to fine powders denoted as RBP-G-U and RBP-SH

respectively.

2. The physical properties of both RBPs were assessed, namely fineness, water

requirement & strength activity indices (SAIs) with Portland cement in

accordance with ASTM C311.

3. The fineness of RBP-G-U when assessed as percentage passed through #325

(45µm) was found to be 68.66%. For RBP-SH the fineness was 68%.

4. For both RBPs, the water requirement assessed in accordance with clauses

26.1.1 & 30 Of ASTM C311 and ASTM C 1437 was found to be 103%.

5. Both RBPs have strength activity indices (SAIs) with OPC of about 80%

assessed in accordance with clauses 26, 27, 28 and 29 of ASTM 311. This

satisfies the ASTM C 618 criterion of SAI for 7 days, i.e. ≥75%. Also both

RBPs satisfied the criterion for 28 days. However, RBP-G-U produced a

higher SAI of 0.84 than RBP-SH which is 0.79. Despite not required by

ASTM C618, the SAIs for 91 days still showed that RBP-G-U performed

better than RBP-SH.

6. The mix containing 20%RBP-G-U (cured in lime) gained 32.86% extra

strength from 7 days to 28 days, however this gain dropped to 22.27% from

28days to 91 days. For mix containing 20%RBP-SH these corresponding

values were 22.32% and 18.88%. This shows that the rate of pozzolanic

reaction for both RBPs was more significant in duration between 7 and

28days.

50

7. The mix containing 20%RBP-G-U (cured in water) gained 12.15% extra

strength from 7 days to 28 days, however this gain increased significantly to

33.88% from 28days to 91 days. For mix containing 20%RBP-SH these

values were 14.65% and 59.14% respectively. This shows that the rate of

pozzolan reaction for both RBPs was more significant exceeding 33% in the

duration between 28 to 91days.

8. The mix containing 30%RBP-G-U (cured in water) gained 38.64% extra

strength from 7 days to 28 days, however this gain reduced to 24.33% from

28days to 91 days. For mix containing 30%RBP-SH these figures were

35.54% and increased to 45.70% respectively. This shows that the rate of

pozzolan reaction for both RBPs was more than 24% in the duration between

28 to 91days.

9. The chemical composition of both RBPs was assessed in accordance with BS

EN 196-21: 1989. The SiO2+Al2O3+Fe2O3≥70%, namely 94.53% for RBP-G-

U and 94.16% for RBP-SH. The available alkalies were found to be 0.877%

and 0.773% for RBP-G-U and RBP-SH for respectively. The SO3 were found

to be 0.27% and 0.216%. for RBP-G-U and RBP-SH for respectively.

51

6. RECOMMENDATIONS FOR FURTHER STUDIES

1. Full characterisation of red brick powders (RBPs) including all of tests listed

in ASTM C 311-02 and specified in ASTM C 618-05, namely the following:

moisture content, loss on ignition, density, autoclave expansion, drying

shrinkage, air entraining admixture demand, control of alkali silica reaction

(ASR), sulphate resistance in moderate and high exposures.

2. Investigation of samples of reject bricks from other production areas in

Khartoum estates, for example Suba, Algamier, Elgieli, Alkabbashi, etc.

3. Investigation of producing lime:RBPs mixtures in accordance with Indian

Standard IS 1344.1981.

4. Investigation of concretes containing RBPS as cement replacement and also

investigation of using coarse red bricks as aggregates in light concrete

production.

5. Investigation of the economy of mass production of RBPs by preparing a

feasibility study for a typical production unit.

52

7. REFERENCES

Araceli E. Lavat *, Monica A. Trezza, Mónica Poggi. Characterization of ceramic

roof tile wastes as pozzolanic admixture. Waste Management 2009 : 29, pp. 1666–

1674.

Alam, Syed Ashraful. Use of biomass fuels in the brick-m akingindustries of Sudan:

Implications for deforestation and greenhouse gas emission. MSc Thesis submitted

for an M. Sc. Degree in Forest Ecology /Tropical Silviculture, Department of Forest

Ecology, Viikki Tropical Resources Institute (VITRI), University of Helsinki, Finland

2006.

Assalam Cement Factory, Atbara, Sudan, Mr Ahmed Abdaljalil, Deputy General

Manager, November 2010.

Calcrete. Computer based training (CBT) Software for learning about concrete. The

Concrete Centre, Camberley, United Kingdom 2008.

Hamid, Mohammed Hussein (in Arabic). Used of burnt

clays as pozzolanic materials. Journal of Building and Road Research. 2002 : 4, pp.

65-74.

Lewis, R, Sear, L, Wainwright, P and Ryle, R. Cementitious additions. In John

Newman and Ban Seng Choo eds, Advanced Concrete Technology: Constituent

Materials. Oxford: Butterworth-Heinemann, 2003, pp. 99-159.

Mamoun E.E. and Zamzami M.A. Characterization of natural pozzolanic deposits of

Northern Bayouda Northern Sudan. Journal of Building and Road Research. 2010 : 9,

pp. 20-27.

Moir, G (2003). Cements. In John Newman and Ban Seng Choo eds, Advanced

Concrete Technology: Constituent Materials. Oxoford : Butterworth-Heinemann,

2003, pp. 18-62.

53

Practical Action Technical Brief. Pozzolans: Calcined Clays and Shales, and

Volcanic Ash. The Schumacher Centre for Technology & Development, Bourton on

Dunsmore, RUGBY,CV23 9QZ, United Kingdom. Tel.:+44(0)1926634400, Fax:

+44(0)1926634401,email practicalaction@practicalaction.org.uk, website:

http://www.practicalaction.org, 2011.

Salih, et al.: Indicators about the future uses of pozzolans in Sudan, a paper presented

in workshop, held in Khartoum on pozzolans uses in the construction industry in

Sudan. 1999.

Sanchez de Rojas, M. I., Marin, F., Rivera, J. and Frias, M. Morphology and

Properties in Blended Cements with Ceramic Wastes as a Pozzolanic Material. J.

Am. Ceram. Soc., 2006 : 89 [12], pp. 3701–3705.

Suleiman, S. H.. Geological Report on Pozzolan Quarry Sites in the Bayuda Volcanic

Field. Unpublished report Prepared for Nevkarsand for Investment Industry Transport

& Construction Co. Ltd. 2008.

Specification for Calcined Clay Pozzolan (2nd revision), Indian Standard IS 1344:

1981, Bureau of Indian Standards, New Delhi, India, http://www.bis.org.in/

Torkittikul, Pincha and Chaipanich, Arnon. Utilization of ceramic waste as fine

aggregate within Portland cement and fly ash concretes. Cement & Concrete

Composites 2010: 32, pp. 440–449.

Ummi Kalsum, H.M.N, Mashitah, M.D. and Badorul, A.B. Recycling of clay based

demolition wastes for the production of concrete block. International Conference on

Environment 2008 (ICENV 2008).

السودان في البوزوالنا استخدامات مستقبل حول عمل 1999مؤشرات ورشة في قدمت ورقة

قاعة السودانية االقتصادية البدائل منظمة بالسودان البناء صناعة في البوزوالنا استخدامات في

الخرطوم جامعة 1999سبتمبر 21الشارقة

54

8. APPENDICES

55

8.1. Appendix 1: ASTM C311 02 Standard Test Methods for

Sampling and Testing Fly Ash or Natural Pozzolans

for Use in Portland-Cement Concrete

56

57

58

59

60

61

62

63

8.2. Appendix 2: ASTM C 618 05 Standard Specification for Coal

Fly Ash and Raw or Calcined Natural-pozzolan for Use as a

Mineral Admixture in Concrete.

64

27

65

66

28

67

68

8.3. Appendix 3: Standard Sand adapted from Table 4 of BS

882:1992

69