enhancing durability of adobe by natural reinforcement for ... · on social, economic and...

International Journal of Sustainable Built Environment (2016) 5, 141–155

HO ST E D BYGulf Organisation for Research and Development

International Journal of Sustainable Built Environment

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Original Article/Research

Enhancing durability of adobe by natural reinforcementfor propagating sustainable mud housing

Vandna Sharma a,⇑, Bhanu M. Marwaha a, Hemant K. Vinayak b

aDepartment of Architecture, NIT Hamirpur, IndiabDepartment of Civil Engineering, NIT Hamirpur, India

Received 25 July 2015; accepted 15 March 2016

Abstract

Low durability and compressive strength of adobe blocks leads to frequent maintenance problem associated with rural house wall con-struction. This forms the main reason of abandonment of vernacular mud housing building technology in rural areas today. The presentpaper presents an attempt to improve upon the low durability of adobe blocks by addition of natural reinforcement of Grewia Optiva andPinus Roxburghii which otherwise are treated as waste material in rural areas. Experimental investigations were carried out for cylindricaland cubical stabilized and unstabilized soil samples. Durability tests conducted included wetting and drying test, water absorption andexpansion test, sponge water absorption test, spray test, total absorption test, and water strength coefficient tests carried out as per Indianstandards and international research. Results indicated that durability of stabilized soil samples increases by 72% and 68% for fibers ofGrewia Optiva and Pinus Roxburghii as compared with unstabilized soil samples. The results recommend that fibers of Grewia Optivaand Pinus Roxburghii can be advantageously added in adobe blocks for improving durability. This would propagate durable mud housingon a large scale thereby reducing housing shortage especially in developing countries, economizing use of natural resources, reducingenergy consumption during manufacturing of modern construction materials and most importantly provide sustainable way of living.� 2016 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V. All rights reserved.

Keywords: Adobe; Durability; Fibers; Grewia Optiva; Pinus Roxburghii

1. Introduction

1.1. Earth: most economical and user-friendly local building

material

Earth is the oldest building material which is mostcommonly used for making shelter. Dethier (1986) and

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Coffman et al. (1990) discuss that nearly 30% of total pop-ulation of world still resides in mud houses. It is one of themost popularly used building construction materials inEurope. Singh and Singh (2007) discuss that 55% of housesin India are constructed with mud walls. Earth is the mostpreferred building material for providing shelter for peopleespecially in less economically developed countries as dis-cussed by Danso et al. (2015). Research studies byCiancio et al. (2013) regarding soil suitability test forrammed earth highlighted financial and environmentalaspects of earth as construction material. The discussion

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142 V. Sharma et al. / International Journal of Sustainable Built Environment 5 (2016) 141–155

on social, economic and environmental benefits associatedwith use of earth reveals that when soil is used as raw mate-rial on site both financial and environmental impact of theconstruction are significantly reduced. Ease of use of earthand associated building techniques can help employ eventhe unskilled labor. This would enhance self-help technol-ogy among rural people eliminating the need for costlytransportation of labor, material and equipment fromother places. This would also act as a boon for the areaswhere other construction materials and technologies arenot available (Ngowi, 1997). Earth is used in varied formsfor construction of shelters such as adobe, rammed earth,cob, wattle and daub, compressed soil blocks etc.(Delgado and Guerrero, 2006; Falceto et al., 2012).Thisvaried use of earth depends upon climatic factors, topogra-phy and living requirements of inhabitants of the area.While use of compressed earth blocks have seen popularityover past few years as reported by Reddy et al. (2007), useof unbaked earth in shelter construction dates back to overthousand years as discussed by Minke (2001). Research byFalceto et al. (2012) discusses international durability testsin Spain regarding compressed earth blocks. The study dis-cusses that different terminologies used in literature in thiscontext like earth blocks as compressed earth blocks,cement stabilized earth blocks, compressed stabilized earthblocks, soil–cement blocks all refer to use of same product,that is earth blocks (without reinforcement). Similarly doc-ument by CRATerre (CRATerre-EAGC, 1998) states thatcompressed earth blocks comprise of different varietieswith or without stabilization. AENOR (2008) discussescompressed earth blocks used for the construction of wallsand partitions highlighting their benefits over use of rawearth blocks as adobe. Standards of New Zealand regard-ing earth buildings (NZS 4297, 1998; NZS 4298, 1998;NZS 4299, 1999) also state use of pressed bricks in con-struction of buildings. Similarly ASTM standards providea set of guidelines for design of buildings involving use ofvaried forms of earth (ASTM. Standard guide, 2010). Mid-dleton discusses use of pressed blocks in earth wall con-struction (Middleton, 1987). Standards of Sri Lanka (SLS1382-1, 2009; SLS 1382-2, 2009; SLS 1382-3, 2009) regard-ing compressed stabilized earth blocks (CSEB) discuss atlength the requirements, test methods and guidelines forproduction, design and construction with CSEB blocks.Use of soil–cement blocks either in a compressed form asCSEB or pressed blocks is considered beneficial and sus-tainable over other modern construction materials likeburnt bricks, cement, glass etc. A similar idea is supportedby standards of Brazil (ABNT.NBR 8491, 1986; ABNT.NBR 8492, 1986; ABNT.NBR 10832, 1989; ABNT.NBR10833, 1989; ABNT.NBR 12023, 1992; ABNT.NBR12025, 1990; ABNT.NBR 12024, 1992; ABNT.NBR10834, 1994; ABNT.NBR 10835, 1994; ABNT.NBR10836, 1994; ABNT.NBR 13554, 1996; ABNT.NBR13555, 1996). These standards give specifications regardinguse of soil–cement blocks. In India; standards give specifi-cations regarding soil based blocks for general building

construction purposes. Research works in CBRI Roorkee(India) regarding development of low cost sustainablebuilding materials especially cement stabilized mud blocksand non-erodable mud plaster (REHSI, 1958; BRN12) givean idea of practical ways of use of improved earth materialin building construction activity at minimal environmentaland financial costs. Experimental investigation shows thatnon-erodable mud plaster is not only water repellent anderosion resistant but also provides safety to walls duringrainfall. ICONTEC (ICONTEC.NTC 5324, 2004), KEBS(KEBS, 1993) and Lunt (1980) discuss in detail the specifi-cations regarding ground block cements and stabilized soilblocks used for construction of walls and otherwise. Simi-larly New Mexico earthen buildings materials Code (CID,2009) and African Regional Standards (ARSO.ARS 670,ARSO.ARS 671, ARSO.ARS 672, ARSO.ARS 673)regarding varied aspects of compressed earth blocks givean idea about the importance of earth as building materialin the construction industry in varied and improved forms.

1.2. Thermal and mechanical properties of earth

Literature studies (Galan et al., 2010; Ogunye andBoussabaine, 2002; Hall, 2007; Ola, 1990; Walker, 2004)involving different experimental investigations give a com-parative analysis of properties of earth products before andafter modifications. Studies by Ogunye and Boussabaine(2002), Mbumbia and Tirlocq (2000), Ola (1990), Obonyoand Baskaran (2010), Donkor and Obonyo (2015),Villamizar et al. (2012), Prasad et al. (2012), Yetimogluet al. (2005) all ascertain considerable improvement inmechanical and physical properties of soil after treatment.Table 1 gives a literary review of comparative improvementin properties of soil after treatment (stabilization andreinforcement).

Given the advantages of thermal comfort (Taylor andLuther, 2004), heat and sound insulation (Binici et al.,2009; Binici et al., 2005, 2007; Acosta et al., 2010), localmaterial availability, local employment criteria (Morelet al., 2001), minimal impact on environment (John et al.,2005) and easy repair and maintenance of adobe structures(Turanli and Erdogan, 1996) earth has remained a fre-quently used building and construction material. Researchstudies (Goodhew and Griffiths, 2005; Hall and Djerbib,2004) have shown that thermal, acoustic and fire resistantproperties of earth materials are very high and additionof fibrous material to adobe further enhances its thermalconductivity thereby increasing heat savings in the build-ings. Research studies by Reddy (2012), Quagliarini et al.(2015) and Kinuthia (2015) discuss the energy efficiencyand low embodied energy aspects of earth as buildingmaterial.

Considering all these advantages and popularity of earthmaterial for construction of shelter many countries haveframed legal regulations and codes dictating use of earthin varied forms as discussed by Torgal and Jalali (2012).Research discusses at length codes and regulations of

Table 1Improvement in properties of soil after treatment.

Reference Property improvement Treatment Results

Stabilizer Reinforcement

Vilane (Vilane, 2010) Compressive strength Ordinary Portland Cement Molasses, cow-dung,sawdust

Soil samples with molasses and Ordinary Portland Cement shown improvedcompressive strength

Ngowi Strength of earth construction Cement, lime, bitumen Fibers, cow-dung Specimen of lime and cement show improved strengthHeathcote Durability of adobe Cement; different proportions

(2.5%, 5%, 7.5%)– Specimens of 7.5% cement show improved durability

Ren Durability of adobe Sodium silicate solution,silioxane and siliconeemulsion

– Treated specimens show better durability than untreated samples

Turnali and Erdogan Structural behavior of adobe – Straw, fly ash, plasterreinforcement

Load carrying capacity increased by addition of straw, fly-ash and plasterreinforced mesh

Binci et al. Compressive strength, heatconductivity, earthquake resistance

Cement, gypsum, basalticpumice

Plastic fibers, straw,polystyrene fabric

Specimens reinforced with plastic fibers showed increased compressivestrength, thermal insulation, elasticity and earthquake resistance

Ramırez et al. Durability, compressive strength,flexural strength

Lime Sugarcane bagasseash (SCBA)

Specimens with 10% lime + 10% SCBA showed improved properties

Muntohar(Muntohar, 2011)

Compressive strength Lime Rice husk ash Specimens with 1:1; lime : rice hush addition showed improved compressiveand flexural strength

Kumar et al. Compressive strength – Plain and crimpedpolyester fiber

Fibers reinforced samples showed improved compressive strength

Ghavami et al.(Ghavami et al.,1999)

Compressive strength Coconut and sisalfibers

Fibers reinforced samples showed improved compressive strength

Guettala et al. Durability, strength Cement, lime, resin – Samples stabilized with 5% cement and resin showed better durabilityDanso et al. Compressive and tensile strength Coconut, bagasse, oil

palm fibersAddition of coconut and oil palm fibers showed increase in strength

Taallah et al. Mechanical properties andhygroscopicity of compressed earthblocks

Cement Date palm fibers Specimen with .05% fiber + 8% cement showed improved properties

Tang et al. (Tanget al., 2007)

Compressive strength andmechanical properties

Cement Discrete shortpolypropylene fiber

Reinforced Specimens both cemented and uncemented showed increasedcompressive strength, shear strength, decrease in stiffness and loss in post-peak strength

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countries like New Zealand, Australia, Zimbabwe, NewMexico, Germany, Spain, Brazil, and France regardinguse of earth. These regulations also give design and plan-ning guidelines involving use of earth for various construc-tion purposes for maximizing benefits from earth shelters.

1.3. Limitations in use of earth

Use of earth suffers from certain drawbacks as well asdiscussed by Heathcote (1995), Guettala et al. (2006) andRen and Kagi (1995). These have been identified mainlyas with less durability and low compressive strength ofwhich low durability has been seen as a very prominent fac-tor affecting the use of earth. Study by Degirmenci (2008)show that adobe has poor mechanical properties in termsof compressive strength and durability in addition to poorresistance to moisture and water attack. Adverse climaticconditions produce deteriorating effects on mud sheltersas reported by Bengtsson and Whitaker (1986) andReman (2004). Rainwater erodes mud walls and severityof rainfall even leads to their collapse. Frequent exposureof mud walls to water leads to absorption of water in thewalls which results in their swelling and upon evaporationduring drying, shrinkage occurs. It produces structural andsurface cracks in mud walls in addition to surface erosionas discussed by Heathcote (1995) and Frencham (1982).

1.4. Need for stabilization of earth for improvement of

properties

Studies (Ngowi, 1997; Frencham, 1982; Walker, 1995)have shown that stabilization of earth with suitable stabi-lizer and reinforcing material either natural or man-madenot only improves its durability but also compressivestrength. Study by Sharma et al. (2015a,b) shows that com-pressive strength of soil increases considerably by additionof fibers. Study by Egenti et al. (2014) discussed that earthis a sustainable low cost construction material and its usefor building purposes is very old in Nigeria. Research workfurther discusses planning, quality control and soil stabiliza-tion ways associated with earth and recommends ShelledCompressed Earth Block as an effectively durable buildingmaterial for propagating cost effective housing in Nigeria.

Different stabilizers produce different impacts on dura-bility of mud bricks. Most frequently used natural stabiliz-ers are jute, sisal, straw, rice-husk, sugarcane bagasse(Ramırez et al., 2012; Khosrow et al., 1999) and soluble sil-icate silanes or siloxanes, isocyanates (Consoli et al., 2002),lime, cement, gypsum, basaltic pumice (Smith, 1996) aresome of the frequently used man-made stabilizers. Studiesby Parisi et al. (2015), Demir (2006), Achenza and Fenu(2006), Kolop et al. (2010), Juarez et al.(2010), Chan(2011), Villamizar et al. (2012) and Millogo et al. (2014)regarding stabilization of soil using natural fibers of straw,processed waste tea, vegetal, oil palm empty fruit bunches,lechuguilla, pineapple leaves, cassava peel and hibiscuscannabinus respectively prove that mechanical properties

of unstabilized earth can be considerably improved uponby use of natural stabilizers (Danso et al., 2015). Recentstudies by Taallah et al. (2014), Quagliarini et al. (2015)and Kinuthia (2015) discuss improvement in weatherabilityof modified earth blocks in addition to their improvementin thermal properties. Most commonly adopted durabilitytests employed are spray erosion test, drip test, wet todry strength ratio test (Heathcote, 1995; Ogunye andBoussabaine, 2002), wetting and drying cycling, UV-condensation weathering test (Ngowi, 1997; Ren andKagi, 1995), capillary water absorption test, total waterabsorption test and freezing and thawing test (Guettalaet al., 2006)

1.5. Utilization of forest and fodder waste

Processes involved in the production of soil blocks areless energy intensive than for cement and burnt brick man-ufacturing processes (Fitzmaurice, 1958). Due to this, soilblocks have less impact on environment and are more sus-tainable (Danso et al., 2015). Moreover, soil is locallyavailable therefore its abundance makes it an easy andaffordable construction material especially for mass hous-ing in rural areas of less economically developed countries(Chan, 2011). Furthermore, study area comprises largePinus Roxburghii forest area that requires prescribed firesin controlled area by local forest department every yearto counteract spread of natural fire during every summerseason. Prescribed fires are most common practice globallyin Pine forests that result in harmful emissions. Thereforein order to minimize negative impacts associated, fibersof Pinus Roxburghii have been proposed for manufactur-ing of improved soil blocks to advantageously use this for-est waste product (ENVIS Centre of Forestry). Similarlyuse of fibers of Grewia Optiva is limited to rope makingthat has diminished nowadays due to use of plastic rope.Moreover after use of leaves of Grewia Optiva as fodderfor animals, its fibrous stem and branches are thrown awayas waste material. Hence fibers of Grewia Optiva can be alucrative option to be used for producing improved soilblocks. Therefore understanding of how these waste fiberscan be used to enhance adobe block properties is importantto practitioners of earth construction technology to maxi-mize benefits of this sustainable material.

1.6. Research objectives

With the aforementioned issues in mind, the presentresearch study was undertaken to fulfill the followingobjectives:

1. Check for possible improvement in durability of soilafter reinforcement with natural fibers of Grewia Optivaand Pinus Roxburghii (as reinforced adobe blocks)comparative with durability of raw soil (as unreinforcedraw adobe blocks) through planned experimentalinvestigation. This would therefore check the feasibility

Table 2Soil characteristics.

Property Value

Classification as per Indian Standard SCSpecific gravity of soil solids, G 2.67Liquid limit % 23.29Plastic limit % 17.79Plasticity index, PI 5.512Water content % 12.5

Figure 1. Particle size distribution of the experiment soil.

V. Sharma et al. / International Journal of Sustainable Built Environment 5 (2016) 141–155 145

of stabilization of adobe using natural fibers as anattempt to enhance the weatherability of soil at minimalfinancial and environmental impacts.

2. To provide for sustainable use of otherwise waste forestproduct (Pinus Roxburghii) and animal fodder waste(Grewia Optiva) posing disposal problems.

The present study has been undertaken as follow upwork of compressive strength improvement of low com-pressive soil using local natural fibers as reported in earlierwork (Sharma et al., 2015a). The main aim of the presentwork is to provide a sustainable way to address rural hous-ing problem due to construction material constraints.Adobe is a frequently used building material for wall con-struction in rural areas of Indian state of Himachal Pra-desh and nearly 60% of rural houses are made of adobe(Revised Development Plan, 2012). Today, however peopleare shifting more toward use of modern building construc-tion materials like cement, glass, burnt bricks and similarothers due to low durability and strength constraints asso-ciated with vernacular building materials and technology.This has pushed this indigenous and self-help constructiontechnology into the state of abandonment. The presentresearch work tries to address the problem of low durabil-ity associated with vernacular building material adobe. Forthis purpose material modification of adobe using naturalfiber reinforcement has been undertaken. Enhancement ofdurability of soil in natural and sustainable manner wouldalso enhance the use of adobe on a wider scale for masshousing which otherwise is restricted due to problems offrequent repair and maintenance associated with it. Exper-imental framework comprises weatherability testing ofadobe blocks stabilized with natural fibers of Pinus Rox-burghii and Grewia Optiva in different proportions offibers randomly distributed in the samples comparativewith non-stabilized adobe blocks through a series of dura-bility tests as per IS codes (IS: 2720-4, 1985; IS: 2720-5,1985; IS: 2720-7, 1980; IS: 2720-10, 1991; IS: 1725, 1982;IS: 4332-1, 1967; IS: 4332-4, 1968; IS: 4332-10, 1969) andinternational research works (Heathcote, 1995; Guettalaet al., 2006; Ren and Kagi, 1995; Degirmenci, 2008;Bengtsson and Whitaker, 1986; Reman, 2004; Frencham,1982; Walker, 1995). Checking of the detailed thermalcomfort performance of stabilized adobe bricks for ruralhouses has been identified as follow up work.

2. Experimental program

2.1. Materials used

2.1.1. Soil

The soil used in this investigation was sourced from NITHamirpur (near gate 1) located in District Hamirpur of theIndian state Himachal Pradesh. Atterberg limits and phys-ical properties of soil were tested (IS: 2720-4, 1985; IS:2720-5, 1985; IS: 2720-7, 1980; IS: 2720-10, 1991) andreported in the Table 2 (Sharma et al., 2015a). The particle

size distribution curve is shown in Fig. 1. From the curve itcan be interpreted that the soil was Sand Clay designatedby SC as per Indian Standard classification (IS: 1498,1970) given in codal provision IS: 2720-4 (1985) and wasclassified as clay of low compressive strength. Other prop-erties include maximum dry density of 18.8 kN/m3, opti-mum moisture content of the soil as 12.5%, and specificgravity of soil as 2.67. Soil composition consists of coarsegrain particles as .0756 for sand and .0005 for clay (IS:1498, 1970). The cement used was of standard M43 gradewith specific gravity 3.10. The study involves use of cementfor stabilization of earth for the reasons of: (1) poor dura-bility of unstabilized raw adobe bocks (based on both fieldobservation and experimental investigation) due to highsurface erosion demanding repair and maintenance eventwo times in a year and (2) easy availability and knowledgeof use of cement (over selection of other stabilizers) since itis one of the most common modern building constructionmaterials. However the proportion has been selected asminimum as possible and stated by Indian codes (IS:1725, 1982) so that it may not affect the sustainability ofthe resultant adobe block to a significant extent.

Study by Kumar et al. (2006) and Casagrande et al.(2006) show that the peak strength value of soil increasesafter stabilization of soil matrix with fiber reinforcement.Babu and Vasudevan (2008) discuss that strength and stiff-ness of tropical soil increases by addition of discrete coirfibers by 1–2% by weight in the soil. Similarly variationsin length and content of fibers also affect the strength char-acteristics of soil.

2.1.2. Fibers

Fibers used were natural indigenous fibers of Pinus Rox-burghii (Chir Pine) and Grewia Optiva (Beul). Only natural


vernacular fibers were selected on the basis of (1) easyavailability and good abundance as both are locally avail-able natural vernacular materials, (2) both materials posedisposal problems and need an alternative use. Moreover,preliminary pilot survey and case study of vernacularhouses conducted during research pointed out the problemof frequent repair and maintenance in adobe walls becauseof surface erosion owing to poor durability. This promptedthe need to find some sustainable natural fibrousmaterial which is not only cost-effective but also is easyto procure and use by rural people. This fibrous materialwhen mixed with soil matrix would increase the weather-ability of adobe. Therefore fibers of Pinus Roxburghiiand Grewia Optiva were selected for use as reinforcementin soil matrix.

Fibers were used in raw and dry states without any priortreatment as shown in Fig. 2. Fibers of Pinus Roxburghiiwere procured as needle leaves of the tree and used in nat-ural dry state. Fibers of Grewia Optiva were obtained fromthe branches of the tree after leaves were used as animalfodder. Fibers were obtained from the tree branches asper the procedure given in CSWCRTI (CSWCRTI)(http://www.cswcrtiweb.org/technology/english/m.pdf). Thefibers obtained in this way were used in raw state withoutany chemical or other prior treatment. Same literature alsosupports that earlier fibers of Grewia Optiva were also usedin rope making for packaging of vegetables like jute ropestill the fiber rope was replaced by synthetic ropes. Thefibers were cut into pieces of length 30 mm. Properties offibers were examined and have been reported. Table 3(Sharma et al., 2015a) and Table 4 show the mechanicaland physical properties of fibers.

Life of pine needles has been estimated up to three years(when lying in open) as indicated by ENVIS Center for for-estry (ENVIS. Chir Pine http://www.frienvis.nic.in/) andShuaib et al. (2013). However similar studies and fieldexperience also indicate that when mixed with earth theycan exist in soil matrix without decomposition or changein state for more than a period of three years. Similarlyfor fiber Grewia Optiva, field experience of local villagersand study by Singha and Thakur (2009) reveal that fibershave longevity of over 10 years. There are, however notenough experimental evidence to confirm the exact ageand more research work can be undertaken in this regard.

2.2. Testing method and mix proportions

For experimental investigation two different types ofsamples were prepared: 90 cylindrical samples (38 mmdiameter and 76 mm height) and 162 cubical samples(modular brick of size 190 mm � 90 mm � 90 mm) as perIndian standards (IS: 1725, 1982; IS: 4332-1, 1967). Thesoil–fiber matrix was prepared as per Indian codal provi-sions (IS: 2110, 1980 for cylindrical samples and IS: 1725,1982 for cubical samples).The soil–fiber matrix was firstmixed in dry state and then kneaded properly with handsafter addition of water to achieve randomly distributed

yet approximately even mix of fibers in soil. Fiber–soilmatrix was compacted mechanically as per the codal provi-sions (IS: 2110, 1980; IS: 4332-1, 1967; IS: 4332-3, 1967).Fiber–soil moist matrix was compacted into three equallayers in the mold. The mold was lubricated from insidebefore compacting the matrix in order to reduce thechances of sample fracturing during removal. Mold wasfilled in three layers and each layer was compacted beforefilling in subsequent layers. The surface of each layer wasscoured after compaction and filling of subsequent layersin order to provide good bond between different layers.After the mold was filled to the desired height and com-pacted the specimen was trimmed off with scissors forany fiber striking out of the sample. The untreated andtreated specimens were subjected to different laboratorytests as per Indian standards (IS: 1725, 1982; IS: 4332-1,1967, 51-54) and international research (Heathcote, 1995;Guettala et al., 2006; Ren and Kagi, 1995) and are men-tioned in subsequent subsections. Four sample tests weretaken for each type of specimen for all durability tests asper codal provisions (IS: 4332-4, 1968). Overall test resultswere found as the average of the four test results for eachexperimental investigation. Individual variations of morethan ±5% of the average were not considered in calculatingthe average values. Verification tests were also performedso that the repeatability of the experimental investigationcan be established. Durability tests like wetting and dryingcycling test, water absorption and expansion test, spongewater absorption test, spray test, total absorption test,and ‘wet’ to ‘dry’ strength ratio test were conducted forall samples of both types (cylindrical and cubical). The pre-sent paper discusses test values of cubical samples (modu-lar brick: 190 mm � 90 mm � 90 mm). Soil samples wereprepared at maximum dry unit weight which was deter-mined using the standard Proctor test and optimum mois-ture content and tested (IS: 2720-7, 1980). The studycomprised preparation and testing of unstabilized unrein-forced samples (0% cement + 0% fibers), stabilized unrein-forced samples (2.5% cement + 0% fiber) and stabilizedreinforced samples prepared with 2.5% cement and 0.5%,1%, 1.5% and 2% (by weight of dry soil) of fibers of bothPinus Roxburghii (Chir Pine) and Grewia Optiva (Beul).Samples were classified as per different compositions aslisted in Table 5. The samples were taken out from themolds, dried and cured for a period of four weeks (IS:1725, 1982). Then they were tested for different durabilitytests.

2.3. Tests conducted

Durability tests conducted included wetting and dryingtest (IS: 4332-4, 1968), water absorption and expansion test(IS: 4332-10, 1969), sponge water absorption test (Ren andKagi, 1995), spray test (IS: 1725, 1982), total absorptiontest (IS: 1725, 1982; IS: 3495-1 to 4, 1992), water strengthcoefficient (Houben et al., 1989 and AFNOR) and theirresults have been reported in Table 6.

http://www.cswcrtiweb.org/technology/english/m.pdf

http://www.frienvis.nic.in/

(1) Pinus Roxburghii

(2) Grewia Optiva

(3) Bricks made of fibers

Figure 2. Natural vernacular fibers of (1) Pinus Roxburghii and (2) Grewia Optiva (3) Bricks made of fibers.


Table 3Mechanical properties of fibers.

Property Pinus Roxburghii (value) Grewia Optiva (value)

Tensile strength (N) 11.15 15.35Length (mm) 324 730Elongation at break % 10.68 10.28Aspect ratio (l/d) .00148 .000041

Table 4Physical properties of fibers.

Property Pinus Roxburghii (value) Grewia Optivia (value)

Cross-section Triangular CircularDiameter (mm) .48 .03Natural water content % 1.4% .25%Water absorption % (after 05 min) 66.23 121.64Water absorption % (after 24 h) 189.08 220Water absorption % (after 48 h) 157.9 165Water absorption to saturation % 127.6 144.2


3. Result and discussion

3.1. Effect of addition of fiber on properties of soil

3.1.1. Wetting and drying cycling test

Almost all mud bricks either treated or untreated absorbwater when completely immersed in water and during dry-ing shrink and crack due to evaporation. The results asreported in Table 6 and Fig. 5 indicate that minimumweight loss was shown by sample M9 reinforced with fiber:2% Grewia Optiva followed by sample M4 reinforced withfiber: 1% Pinus Roxburghii. Untreated unstabilized sam-ples of mix M1 and stabilized and unreinforced samplesof mix M2 broke after just after 1st cycle and 4th cyclerespectively. It can be interpreted from the curves that sam-ples of mixes M9, M4, M8, M7, M5, M3 and M6 showed95.42%, 95.38%, 95.25%, 95.16%, 93.16%, 90.32% and87.97% reduced weight loss respectively and hence therewas proportionate improvement in durability (with basecase M1).The test results showed that addition of stabilizerand fiber reinforcement improves durability of soil matrix.

3.1.2. Water absorption and expansion test

The test was conducted to imitate moist conditions whichare generally seen after and during rainfall during monsoonseason in the study area (refer Fig. 3). The water absorptionvalues of all samples have been reported in Table 6. Resultsclearly indicate that samples of mix M9 reinforced with 2%Grewia Optiva showed minimum water absorption values.Treated (stabilized and fiber reinforced) adobe bricksabsorb less moisture than untreated adobe bricks. Fig. 6shows reduction in water absorption values with additionof fiber content and thus there was corresponding improve-ment in durability. It can be interpreted from the values thatthe samples of mixes M9, M8, M4, M6, M7 andM2 showed58%, 54%, 50.4%, 48%, 45% reduced water absorption(with base case M1) respectively and hence there was

proportionate improvement in durability. This implies thatstabilization of soil with cement and fibers of Grewia Optivaleads to maximum improvement in durability.

3.1.3. Sponge water test

This test was conducted to imitate moderate and lowrainfall conditions accompanied by occasional sunshinein the study area which results in alternate wetting and dry-ing of adobe in real life conditions. According to Indianstandards (IS: 1725, 1982), weight loss limit is 5%. Weightloss (in percentage) values of all the specimens correspond-ing to 14 cycles over a period of 28 days are represented inTable 6 and Fig. 7. From the curves it can be interpretedthat minimum weight loss is shown by sample M9 followedby samples M4 and M6 corresponding to soil matrix rein-forced with 2% Grewia Optiva, 1% Pinus Roxburghii and2% Pinus Roxburghii respectively. The values give theinterpretation that samples of mixes M9, M4, M6, M8and M7 showed 48%, 42%, 37%, 34.5% and 30% reducedwater absorption respectively (with base case M1) andhence proportionate improvement in durability. Thisimplies that stabilization of soil with cement and fibers ofGrewia Optiva leads to maximum improvement in durabil-ity followed by stabilization with cement and fibers ofPinus Roxburghii.

3.1.4. Spray testThis test was conducted to imitate average to heavy

rainfall conditions in real life conditions (refer Fig. 4).According to Indian standards (IS: 1725, 1982), maximumpermissible pit depth for surface erosion is 10 mm. Erosionvalues of all samples are reported in Table 6 and Fig. 8. Itcan be interpreted from the figure that sample M9 showedno erosion while sample M8 and sample M6 showed aver-age erosion effect. Here samples M9, M8 and M6 corre-spond to soil matrix reinforced with fibers of 2% GrewiaOptiva, 1% Grewia Optiva and 2% Pinus Roxburghii

Table 5Designation of mix compositions.

Mix designation Mix specification

M1 Soil (0% Cement, 0% Fiber)M2 Soil (2.5% Cement, 0% Fiber)M3 Soil (2.5% Cement 0.5% Fiber: Pinus Roxburghii)M4 Soil (2.5% Cement 1.0% Fiber: Pinus Roxburghii)M5 Soil (2.5% Cement 1.5% Fiber: Pinus Roxburghii)M6 Soil (2.5% Cement 2.0% Fiber: Pinus Roxburghii)M7 Soil (2.5% Cement 0.5% Fiber: Grewia Optiva)M8 Soil (2.5% Cement 1.0% Fiber: Grewia Optiva)M9 Soil (2.5% Cement 2.0% Fiber: Grewia Optiva)

Figure 3. Water absorption test.

Figure 4. Spray test


respectively. The results give the interpretation stabiliza-tion of soil with cement and fibers of Grewia Optiva leadsto maximum improvement in durability followed by stabi-lization with cement and fibers of Pinus Roxburghii. Thetest results also indicated that with increase in fiber contentdurability of soil matrix increases. This may be attributedto better fiber–soil interaction and resultant fiber–soil bondwhich binds soil particles together more firmly unlike in thecase of unreinforced soil samples.

3.1.5. Total water absorption test

The test was conducted to identify maximum waterabsorption capacity of adobe both as untreated and treatedcompositions. The water absorption values of all the sam-ples are reported in Table 6 and Fig. 9. Reinforced stabi-lized samples of soil mixes M3, M4, M7 and M9 showedwater absorption values within maximum permissible limitgiven by Indian standard codes (IS: 1725, 1982) which is15%. The curves give the interpretation that samples ofmixes M7, M8, M4 and M9 showed 72%, 68%, 56% and51% reduced water absorption respectively and hence therewas proportionate improvement in durability (with basecase M1). Comparison of both treated (stabilized and rein-forced) and untreated (unstabilized and unreinforced) sam-ples showed lower water absorption values in the case of

result specimens.

Table 6Test results.

Brick characteristics Values

M1 M2 M3 M4 M5 M6 M7 M8 M9

Wet–dry cycling test (weight loss) % 100.00 70.00 9.68 4.62 6.84 12.03 4.84 4.75 4.58Water absorption test (water absorption) % 4.90 2.70 3.62 2.43 2.73 2.33 2.67 2.26 2.07Sponge water absorption test (weight loss) % 6.51 4.77 5.51 3.78 6.08 4.11 4.58 4.26 3.36Spray test (pit depth, mm) 18 36 47 8 33 6 7 5 0Total absorption test (water absorption)% 23.60 52.29 7.56 10.35 23.68 21.71 6.8 8.73 11.65Compressive strength in dry state, N/mm2 .95 1.2 1.75 2.25 2.05 1.3 1.85 2.35 3Compressive strength in wet state, N/mm2 .10 .19 .62 1.45 1.13 .41 .78 1.39 2.04Water strength coefficient .11 .16 .35 0.64 0.55 .32 .42 0.59 0.68

Figure 5. Wetting and drying cycling test: weight loss (%) over period of24 days.

Figure 6. Water absorption test results: Water absorption (%).

Figure 7. Sponge water test: weight loss (%) over period of 28 days.

Figure 8. Spray test results: pit depth (mm).

Figure 9. Total absorption test results: water absorption (%).


treated samples than untreated samples. This indicatesimprovement in durability with addition of stabilizer andfiber reinforcement in treated samples.

3.1.6. Water strength coefficient

This gives the ratio of ‘wet’ to ‘dry’ compressive strengthfor all samples (treated and untreated). As stated by Cra-Tere specification (Houben et al., 1989) and AFNOR spec-ification, the minimum permissible value for this ratio hasbeen taken as 0.5. Water strength coefficient values for allsamples have been reported in Table 6 and Fig. 10. Itcan be interpreted from the figure that samples of mixM9 reinforced with 2% Grewia Optiva show the highestwater coefficient value. Samples of mixes M4, M8 andM5 reinforced with 1% Pinus Roxburghii, 1% GrewiaOptiva and 1.5% Pinus Roxburghii respectively also showconsiderable values of water strength coefficient whichare well above the permissible limit of 0.5. The tests

Figure 10. Wet to dry strength ratio test results: water strength coefficient.


therefore showed improvement in durability with additionof stabilizer (cement) and fiber reinforcement (GrewiaOptiva and Pinus Roxburghii) as compared with untreatedand unstabilized samples of soil.

An analysis of improvement in durability of differentsamples with respect to different tests is presented inFig. 11. The curves give the interpretation that with addi-tion of fiber content in soil both water absorption andweight loss over a period of cycles have reduced as com-pared with unstabilized soil samples. This implies that trea-ted samples of soil matrix show improvement in durabilityas compared with untreated mix samples. These results arein agreement with previous research works by Ziegler et al.(1998) and Millogo et al. (2014) which state that additionof natural fibers in soil improves the durability andstrength of earth.

3.2. Effect of content proportion of fiber on properties of soil

Experimental investigation also revealed that in the caseof fibers of Grewia Optiva increase in proportion of fibercontent resulted in an increase in durability unlike in the

Figure 11. Analysis of test results:

case of fiber Pinus Roxburghii where durability in generaldecreased with an increase in the proportion of fibercontent in soil matrix. The reason for such varied behaviorof fibers is explained by different structures of both types offiber. Fibers of Grewia Optiva are finer than triangularcross-sectional fibers of Pinus Roxburghii. This results inbetter bonding not only among soil particles and fibersbut also among fibers themselves in the case of GrewiaOptiva unlike slipping of fibers over each other in the caseof Pinus Roxburghii (with increase in proportions of boththe fibers) due to which fibers hold together soil particlesmore firmly in the case of samples of fiber Grewia Optivathan samples of fiber Pinus Roxburghii. This resulted ina better fiber–soil bond interaction in the case of GrewiaOptiva as compared to samples of fiber Pinus Roxburghii.Almost all test result values indicated a better performanceof Grewia Optiva fibers than fibers of Pinus Roxburghii.Factors that influence fiber–soil bond will be examined atthe microscopic level for both types of fibers over the per-iod of time.

The purpose of the study is primarily to compare andimprove the durability of existing adobe blocks (whichare basically raw untreated and unreinforced earth blocks)used in mud walls of rural houses with sustainable andmost commonly available stabilizers and reinforcement.Results of the experimental investigation indicate thatdurability of fiber reinforced and cement stabilized mudblocks/adobe is more than that of non-stabilized and unre-inforced adobe (M1) and cement stabilized and unrein-forced adobe (M2) samples. This low cost adobetechnology, therefore can be advantageously used in ruralareas where (1) people have self-help tendency, (2) trans-portation cost of modern construction materials likecement, burnt bricks, and marble is very high, (3) availabil-ity of skilled labor for construction processes is both timeand finance consuming. Fiber reinforced adobe blockswould prove user-friendly for uneducated poor rural

improvement in durability (%).


people for whom use of compressed cement stabilized earthblocks also appears to be a laborious and complicatedconstruction technology. This is due to the reason thatmanufacturing of compressed cement stabilized earthblocks involves pressing of blocks at specific compactionrates demanding specialized mechanical equipment andtrained manpower. This makes it a comparatively compli-cated work making it less user-friendly technology espe-cially in rural areas. Moreover use of cement forstabilization purposes of earth is much more which lessensthe sustainability of compressed cement stabilized earthblocks. Research study, however does not draw compar-isons of this technology with other earth technologies likecompressed earth blocks, or compressed cement stabilizedmud blocks. It has been proposed as complementary sus-tainable technology for poor people and unskilled peopleof rural areas to address the problem of economical masshousing.

4. Conclusion

With the objective to improve weatherability of soil in asustainable manner by stabilization with natural fibers ofGrewia Optiva and Pinus Roxburghii, durability tests wereconducted on untreated and treated adobe compositions inlaboratory as per Indian standard codes. Test results aresummarized as follows:

� All test results indicated that treated soil samples (stabi-lized and reinforced) showed improvement in weather-ability as compared with untreated (unstabilized andunreinforced) samples. Samples reinforced with fibersof Grewia Optiva showed more improvement in durabil-ity than samples reinforced with fibers of PinusRoxburghii.

� In wetting and drying test, results indicated that samplesreinforced with fiber: 2% Grewia Optiva + 2.5% cementshowed least weight loss over a period of 12 cycles fol-lowed by samples reinforced with fiber: 1% Pinus Rox-burghii + 2.5% cement. Both samples showedmaximum improvement in durability as compared withother samples.

� In water absorption and expansion test, results indicatedthat samples reinforced with fiber: 2% Grewia Optiva+ 2.5% cement showed least water absorption over aperiod of 7 days. Samples showed maximum improve-ment in durability.

� In sponge water absorption test, results indicated thatsamples reinforced with fiber: 2% Grewia Optiva+ 2.5% cement showed least weight loss over a periodof 14cycles followed by samples reinforced with 1%Pinus Roxburghii + 2.5% cement. Both samples showedmaximum improvement in durability as compared withother samples.

� In spray erosion test, results indicated that samples rein-forced with fiber: 2% Grewia Optiva + 2.5% cementshowed no erosion and samples reinforced with fiber:

2% Pinus Roxburghii + 2.5% cement showed slight ero-sion values. Both samples showed maximum improve-ment in durability as compared with other samples.

� In total water absorption test, results indicated thatsamples reinforced with fiber: 0.5% Grewia Optiva+ 2.5% cement and 1.0% Grewia Optiva + 2.5% cementshowed least water absorption corresponding toimprovement in durability.

� In the case of water strength coefficient, the maximumvalue was shown by samples reinforced with fiber: 2%Grewia Optiva + 2.5% cement followed by samples rein-forced with fiber: 1% Pinus Roxburghii + 2.5% cement.Both samples showed maximum improvement in dura-bility as compared with other samples.

Therefore sustainable stabilization with recommendedproportion of Grewia Optiva (2% addition by weight)and Pinus Roxburghii fibers (1% addition by weight) isadvantageous for producing improved and durable adobebricks used for rural house wall construction. These testswere performed with the purpose of establishing effective-ness of natural fibers in enhancement of low durabilityproperties of soil. In today’s context especially in ruralareas, vernacular construction techniques and materialsare abandoned due to problems of low durability andcompressive strength of vernacular materials like adobe.The present paper is an attempt to improve upon the ver-nacular material; adobe so that low durability problemassociated with rural house wall construction can beaddressed effectively. This would reduce frequent mainte-nance problems of adobe walls of rural houses owing toweatherability problems. It would also propagate theuse of adobe for sustainable mass housing on a large scaleespecially for people in less economically developedcountries.

5. Limitations of the study

Factors influencing fiber–soil bond would be examinedat the microscopic level over a period of time which hasnot been included in the present study. Moreover the studyof impact of fiber reinforced cement stabilized adobe brickson indoor thermal comfort environment of houses for thearea would be taken up as follow up work. Experimentalinvestigation is required to be carried out to confirm theage of Pinus Roxburghii and Grewia Optiva fiber rein-forced soil matrix which is also not included in the scopeof the study.

Acknowledgement

The authors are thankful to Ar. Aniket Sharma ofArchitecture department and Dr. R.K. Dutta of Civil Engi-neering Department, NIT Hamirpur for providing guid-ance and advice in performance of the variousexperiments and their analysis.


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