earth block.pdf

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http://dx.doi.org/��.��/��/�� http://dx.doi.org/��.��/��/��

Research Article

Ultrasonic, Molecular and Mechanical Testing Diagnostics in

Natural Fibre Reinforced, Polymer-Stabilized Earth Blocks

C. Galán-Marín,

11

C. Rivera-Gómez,

11

and F. Bradley

22

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�_{Departamento Construcciones Arquitect}_{Departamento Construcciones Arquitect ´}_´_{onicas I, Escuela }_{onicas I, Escuela }_{ecnica Superior de}_{ecnica Superior de}_´_´ _Arq_Arq_uitectur_{uitectura, University of Sev}_{a, University of Sev}_ille,_ille,

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Avda. Reina Mercedes, �, �� Seville, Spainvda. Reina Mercedes, �, �� Seville, Spain

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�_{Department of Architecture, Faculty of Engineering, University of Strathclyde, �� Richmond Street, Glasgow G��XQ, UK}_{Department of Architecture, Faculty of Engineering, University of Strathclyde, �� Richmond Street, Glasgow G��XQ, UK}

Correspondence should be addressed to C. Gal

Correspondence should be addressed to C. Gal´´an-Maran-Mar´´ın; [email protected]ın; [email protected] Received �� March ��; Revised �� July ��; Accepted �� July �� Received �� March ��; Revised �� July ��; Accepted �� July �� Academic Editor: Gonzalo Mart

Copyright © �� C. Gal´an-Man-Marar´´ın et al.ın et al.TisTisisisananopenopenacceaccessssarticarticleledistridistributebuteddundertheundertheCreaCreativetiveCommoCommonsnsAtAttributributiontionLicenLicense,se, which permits unrestricted use,

which permits unrestricted use, distribution, and reproductiodistribution, and reproduction in n in any medium, provided the original work any medium, provided the original work is properly cited.is properly cited. Te aim o this research study was to evaluate the in�uence o utilising natural polymers as a orm o soil stabilization, in order to Te aim o this research study was to evaluate the in�uence o utilising natural polymers as a orm o soil stabilization, in order to asses

assessstheirtheirpotepotentialorntialoruseuseininbuildbuildingingappapplicalicationtions.s.MixtuMixturesreswerewerestabilizedstabilizedwithwithaanatnaturaluralpolympolymerer(algi(alginatenate))andandreinreinorcorcededwithwith wool �bres in order to improve the overall compressive and �exural strength o a series o composite materials. Ultrasonic pulse wool �bres in order to improve the overall compressive and �exural strength o a series o composite materials. Ultrasonic pulse velocity (UPV) and mechanical strength testing techniques were then used to measure the porous properties o the manuactured velocity (UPV) and mechanical strength testing techniques were then used to measure the porous properties o the manuactured natural polymer-soil composites, which were ormed into earth blocks. Mechanical tests were carried out or three diﬀerent clays natural polymer-soil composites, which were ormed into earth blocks. Mechanical tests were carried out or three diﬀerent clays which showed that the polymer increased the

which showed that the polymer increased the mechanical resistance o the samples to varying degrees, depending on the mechanical resistance o the samples to varying degrees, depending on the plasticity plasticity index o each soil. Variation in soil grain size distributions and Atterberg limits were assessed and chemical compositions were index o each soil. Variation in soil grain size distributions and Atterberg limits were assessed and chemical compositions were studied and compared. X-ray diﬀraction (XRD), X-ray

studied and compared. X-ray diﬀraction (XRD), X-ray �uorescence spectrosco�uorescence spectroscopy (XRF), and py (XRF), and energy dispersive X-ray �uorescenceenergy dispersive X-ray �uorescence (EDX

(EDXRF)RF)techtechniqueniquesswerewereallallusedusedininconconjunctjunctionionwithwithqualqualitatitativeiveidenidenti�cati�cationtionoothetheaggraggregategates.es.UltrUltrasoniasoniccwavewavepropropagapagationtionwaswas ound to be a

ound to be a useul technique or assisting in useul technique or assisting in the determination o soil shrinkage characteristics and �bre-soil adherence capacity the determination o soil shrinkage characteristics and �bre-soil adherence capacity and UPV results correlated well with

and UPV results correlated well with the measured mechanical properties.the measured mechanical properties.

1. Introduction

Te development o building systems has been inextricably Te development o building systems has been inextricably linked throughout history with the evolution o construction linked throughout history with the evolution o construction mate

materials rials and and the the techntechnologicological al advaadvancemencements nts relarelated ted toto harves

harvestingtingandandexploexploitinitinggourourplaneplanet’t’ssnatnaturaluralresoresourceurcess[[��].In].In recent years, the construction sector has b

recent years, the construction sector has been under increas-een under increas-ing pressure to reduce its CO

ing pressure to reduce its CO22 emissions and the volumeemissions and the volume o natural resources which it is responsible or consuming. o natural resources which it is responsible or consuming. Environmental concerns relating to the speci�cation o Environmental concerns relating to the speci�cation o con-tempo

temporary rary matematerials rials which which ofen ofen invoinvolve lve enerenergy-intgy-intensivensivee and

andoil-doil-dependeependentntprocprocesseshaveesseshavebecomeincreasinbecomeincreasinglyglyrecogrecog- -nised [

nised [��] ] and and witwith h buibuildildingsngs, , citcitiesies, , and and thetheir ir assassociaociatedted inrastructure playing such a signi�cant role in depleting our inrastructure playing such a signi�cant role in depleting our global resources, it is vital that material utilisation within global resources, it is vital that material utilisation within buildings is speci�ed with care in order to reduce the impact buildings is speci�ed with care in order to reduce the impact on our

on our planet’planet’s resources and s resources and delicate ecosystems.delicate ecosystems.

Te purpose o this research was to explore the potential Te purpose o this research was to explore the potential ordevel

ordevelopiopingngaalolowwembembodiodiededeneenergyrgyconconstrstructiuctiononmamaterterialialss

obtained where possible rom natural, renewable resources. obtained where possible rom natural, renewable resources. Te main barrier to the use o natural materials at present, Te main barrier to the use o natural materials at present, particu

particularllarly y in in develdeveloped countriesoped countries, , is is their perceivetheir perceived d poorpoor mecha

mechanical propertienical properties s and durabiliand durability ty in in compacomparison withrison with synthetic materials such as steel, concrete, and other synthetic materials such as steel, concrete, and other ceram-ics. Tis study thereore explores the mechanical properties ics. Tis study thereore explores the mechanical properties o an innovative, natural, un�red, composite brick designed o an innovative, natural, un�red, composite brick designed to reduce both embodied energy values and CO

to reduce both embodied energy values and CO22emissions.emissions. Earth construction is not only cost effective, as a result Earth construction is not only cost effective, as a result o the inclusion o low-cost raw materials, but it also uses o the inclusion o low-cost raw materials, but it also uses locally sourced, benign materials. As a building system, it is locally sourced, benign materials. As a building system, it is considered to be highly energy efficient due to the excellent considered to be highly energy efficient due to the excellent the

thermalpropermalpropertiertiesswhicwhichhearearthethennmamaterterialialssexhexhibiibittanditanditalsalsoo possesses a low embodied energy when raw clay is utilised possesses a low embodied energy when raw clay is utilised [

[��]. Adobe blocks, or example, do not undergo any energy-]. Adobe blocks, or example, do not undergo any energy-int

intensensivivee�rin�ringgproprocescessessessinsincecethetheyyarareesimsimplyplysunsun-dr-driediedandand the

therereororeeharharnesnessssolsolarareneenergyrgydirdirectlectlyy..oopuputtthithissininconcontextext,t, the energy requ

the energy requireired d to to prproduoduce ce an an adoadobe be bloblock ck is is onlonly y �

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metre or a �red brick and ��–�� (kWh)/cubic metre or concrete [�].

Earth construction is thereore becoming an increasingly valued natural building material and its durability bene�ts

and minimization o pollution and waste characteristics— particularly in industrial countries—are also being progres-sively recognised [�]. With regards to un�red earth con-struction, Heath et al. [�] have recently shown that there is structural potential or utilizing commercially manuactured un�red bricks but concluded that additional research needs to be carried out into structural behaviour and methods or minimizing moisture susceptibility. Tis project thereore examines an innovative, sustainable, natural earth product to assess its initial perormance against an extensive series o mechanical and analytical laboratory tests [ �].

Chemical soil stabilization involves changing the proper-ties o a soil by adding chemicals or additives. Tis occurs either by creating a matrix, which binds or coats the grains, or by means o a physiochemical reaction between the grains and the additive materials. Cement is one o the most widely used chemical stabilizers or compressed earth blocks (CEBs) and adding it beore compaction improves the chara-cteristics o the material, particularly its resistance to water [�–��]. A proportion o at least �-�% o cement is generally needed to obtain satisactory results [ ��]. When compaction o moist soil is used in combination with cement stabilisa-tion, it not only improves compressive strength and water resistance compared to earth construction techniques such as “adobe,” but also improves dimensional stability and toler-ances improving construction quality and integrity [ ��].

Another method o stabilizing soil is with nonhydraulic lime (quicklime or slaked lime). Tis technique is commonly used or road construction, although it is mainly adopted in temporary roads. Te use o this type o stabilizer is not recommended, however, or the manuacture o CEBs as these bricks require a airly low moisture content and a soil with a relatively high sand content. For stabilization purposes the amounts generally used range rom � to ��% that is equivalent to the proportion o cement used [ ��]. Te disadvantage o using lime alone is its negative impact on durability as described in [ ��].

Cementing and waterproo�ng cohesive soils can be achieved with small amounts o natural or synthetic polymers proportionally less than �% by dry weight o soil. ypical polymers used in soils comprise cement-resin mixes such as polymer cements or organic resins. Tese range rom epoxy, acrylic, polyacrylate, polyurethane, polymers derived rom tomato pulp to alginate, which is an extract rom seaweed [��]. Tere are other recently researched methods relating to the stabilization o clay bricks described in [ ��] and a variety o techniques and compositions currently under investigation relating to �red and un�red bricks. Tis research work, however, ocuses on ��% natural material ingredients, namely, clay, lignin, wool, and alginate.

2. Materials and Methods

Te main objectives o this research were to analyse the eﬀect on the mechanical properties o alginate added to

�� : Physical characteristics, grain size, and Atterberg limits o the three soils.

Physical characteristics Errol Ibstock Raeburn Sand content ��.��% ��.��% ��.��% Silt content ��.��% ��.��% ��.��% Clay content ��.��% ��.��% ��.��% Classi�cation I.S.S.S. Silty clay loam Silt loam Loam Liquid limit ��.�% ��.�% ��.�% Plastic limit ��.�% ��.�% ��.�% Plasticity index ��.�% �.�% �.�%

F�� : Photograph o the three soil types used.

hand-moulded bricks stabilized with natural �bre and to determine an optimal ratio or wool and alginate within three diﬀerent soil types. Te samples and methods that were selected are described in this section. X-ray diﬀraction (XRD), energy dispersive X-ray �uorescence (EDXRF), ultra-sonic pulse velocity (UPV), and compression and bending tests were all conducted to provide a wide spectrum o data or analysis.

�.�. Soil. Te materials used in these experiments were three different types o clay soils, alginate, wool, and lignin. Te physical properties and Atterberg limits o the three different types o alluvial soils used in this experimental investigation are described in able �. All the soils were supplied by Scottish brick manuacturers; Errol (rom the East Coast o Scotland) and Ibstock and Raeburn rom Glasgow (see Figure �). All three soils had different colours and textures but importantly their particle-size distributions were all within the maximum limits speci�ed or utilisation within CEBs.

Te moisture content (in mass percentage) at which clays and silts pass rom semisolid into plastic states and then into a liquid state is de�ned by the Atterberg limits, which are empirical divisions between the solid, plastic, and liquid limits o a clay. Te upper and lower limits o the range o water content over which soils exhibit plastic behaviour are de�ned by liquid and plastic limits and the water content range between these values is termed the plasticity index [��]. Te Errol soil has a much higher liquid limit compared to the other soils as can be seen in able �. Te clay in each soil sample acts like cement in concrete, binding all the larger

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particles in the soil whereas the silt and sand particles behave as �lters in the soil matrix in a similar manner to aggregates. Errol soil is described as a silty clay loam and contains a signi�cantly higher proportion o clay compared to either an Ibstock or Raeburn soil. Te Ibstock soil is classi�ed as a silt loam and the Raeburn soil is classi�ed as a loam [ ��]. With regards to their plasticity indexes, it is interesting to note the quite remarkable variation (see able �). All soils were additionally analysed and characterized by utilizing X-ray diffraction (XRD) and X-X-ray �uorescence (EDXRF) tests. �.�. Alginate. Seaweed is abundant within the coastal waters o countries acrossthe globe and during the last two centuries has been used or a wide variety o products rom ood and medical products to soda ash production or soap and glass production. In terms o its chemical composition, alginic acid, also called algin or alginate, is a polysaccharide or carbohydrate molecule and it is obtained by extracting alginate salts rom the cell walls o brown seaweeds. Tese alginate salts make up between �� and ��% o the dry matter o the algae and take the orm o different compounds including sodium alginate, calcium alginate, and magnesium alginate.Te physical andchemical properties o alginatesare nowadays being increasingly investigated and the polymer composition o this natural molecule is increasingly being understood to have a structural unction within the cell walls and intercellular mucilage o seaweed [ ��]. Te alginate matrix thereore contributes to the �exibility and mechanical strength o algae [��] in a similar manner to the way that cellulose and pectin components affect land-based plants [��]. Different algal species as well as geographical and envi-ronmental conditions in�uence alginate matrices which gives rise to the variations in properties that different alginates can exhibit.

Alginates are extremely versatile and exhibit important gelling properties as well as high water holding characteris-tics. Importantly in this research, they have the ability to act as a natural binding matrix within composite systems. Teir natural propensity or improving viscosity and stabilizing emulsions has acilitated their widespread use today within the medical, pharmaceutical, and ood industries where they are widely used as dental impression materials and gelling agents. Teir colours range rom white to yellowish brown and they are sold in a variety o orms including �lamentous, granular, powdered, or gel orms.

Within the geotechnical engineering sector it, patents have been approved or the use o alginates within in situ stabilization o contaminated and non-contaminated soils [��] and a ew previous tests such as those o Friedemann et al. [��] and Gal´an-Mar´ın et al. [��, ��] have also been carried out incorporating alginate into building materials.

Te initial selected proportions o the composite mate-rials was derived rom work previously carried out at the Laboratory o the Building Construction Department at the University o Seville and has been the subject o a patent [��]. Te alginate used in our research was supplied by FMC Biopolymer, Girvan, Scotland (UK), under the name o seaweed extract and contained sodium alginate, sodium carbonate, and inorganic salt. In these experiments, we used

an alginate paste (gluey, brown liquid), which is a product o the �rst stage o alginate extraction rom seaweed.

�.�. Fibre. raditionally, natural �bres have been used as soil reinorcement where available, to improve certain engineer-ing properties o the soil. Vegetal �bres, derived rom plants such as coir, jute, sisal, bamboo, wood, palm lea, coconut lea truck, cotton, hemp, and grass, have been tested as rein-orcing materials not only or soils, but also within vari-ous polymer matrix composites [��] or utilisation within various industries.

Vegetal �bres such as coir can come in diﬀerent varieties and the individual �bre cells are narrow and hollow, with thick walls made o cellulose. Coir is a relatively waterproo �breand isone o the ew natural �bers resistant to damageby salt water. Jute, in contrast, is a long, sof, shiny vegetable �bre similar to industrial hemp and �ax (linen) and can be spun into coarse, strong threads and when woven is called hessian or burlap [��]. Another natural �bre that has recently been utilised in CEB research has been produced rom cassava peels [��] and sugarcane bagasse ash [ ��] so there are a wide variety o vegetal �bres currently being examined in clay

composites with regards to strength and �exural properties. Organic products containing cellulose �bres do however have several drawbacks such as an incompatibility with hydrophobic polymer matrices [��] and a propensity to show little resistance to prolonged moisture. For this reason this project has examined the behaviour o animal �bres which to date have tended to be overlooked as a constituent in un�red brick reinorcement.

Wool �bre is composed o a protein known as keratin. Generally, wool �bres measure ��–�� mm in length and ��– �� in width. Teir cross-sectional shape is oval in orm and the �bregrows in the orm o a wavewith a certain amount o twist. Its mechanical properties include a tensile strength ��– �� MPa, an elasticity component o ��–��% elongation at break and Young’s modulus o �.�–�.� MPa [��]. Alternative �gureslisted in CESEdupak (��) [��] give a tensile strength o between �� Mpa and �� Mpa and Young’s modulus values between �.�MPa and �.� Mpa. Different species o sheep produce quite different types o wool with varied �bre length, diameter, and other differing physical characteristics. Te molecular structure o wool �bres is interesting in that they comprise two different types o cell. Internal cells are reerred to as the cortex and then outside these cells are external cuticle cells (or scales) that orm a sheath around the �bre, overlapping like roo tiles. Tis structure gives wool its uniqueness compared to the variety o other �bres being used within natural composites today.

For the tests carried out in this project, wool �bre was added as the natural reinorcement within earth blocks, tot-ally untreated and taken straight rom the animal �eece so that no arti�cial additives were introduced. In addition, the wool was hand-cut, by trimming the top �� mm strand o �bre, as longer �bres would have been too long to create a homogenous mix. All the specimens or this study were prepared and manuactured with the addition randomly oriented o a small amount (�.�–�.��%) o this raw, unpro-cessed wool according to recommendations rom previous

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�� : Mixes used (by weight).

Soil mix no. Proportions Soil Alginate Lignum Wool Water � Unstabilized soil ��.�% — �.�% — ��.�% � Soil + alginate ��.�% ��.��% �.�% — �.��% � Soil + �.��% wool ��.�% — �.�% �.��% ��.��% � Soil + alginate + �.��% wool ��.�% ��.�% �.�% �.��% �.��% � Soil + alginate + �.��% wool ��.�% ��.�% �.�% �.��% �.��%

�� : Mass percentages o each mineral and clay proportions.

Soil Calcite Quartz Phyllosilicates Feldspars Illite Kaolinite Chlorite

Errol <� �� races ��

Ibstock — �� races �� races

Raeburn — �� <� ��

research which looked at the impact o various proportions [��].

�.�. Lignin. Ligninis a treacle-like resin extracted rom wood during the production o cellulose. Lignosulonate and lignin products are thereore derived rom a natural raw material. In all three mixes �.�% o lignin sulonate (under name o Additive A, raﬀaid �� by Borregaard Lignoech) was added to improve the workability o the soil mixture because it greatly acilitates the mixing o clay with low proportions o water. Tis additive is commonly used in the manuacturing processes or un�red bricks.

3. Sample Manufacturing Process

Material preparation was carried out manually in the lab-oratory o the University o Seville. Machine mixing was carried out using hand compaction andno extra compression was added. Te mixtures adopted a proportion o close to �� : �� soil: (water + stabilizer) ratio afer making necessary adjustments to previously carried out corrective dosages [��]. It was decided to choose a water/soil ratio o ��.�/��%(adding �.�% o lignum) to get a normal consistency and low total shrinkage or mixes without the addition o alginate. Ratios o �.��–�.�% o wool were added to mixes, where alginate was added to the mix and �.��% only where no alginate was present (see able �). Soil Mixes numbered �, �, and � were used as contrast dosages to compare the eﬀect o either the �bre or the polymer alone. Soil Mixes numbered � and � were manuactured to detect the appropriate quantity o �bre reinorcement. Reinorcing wool �bres were cut to the required length, soaked in water or �� hours, to improve mixing, and then added randomly, but in a homogeneous way, to the moist soil using a � litre mixer until a completely homogeneous composite was achieved. All the brick samples used in this study were prismatic specimens (160 × 40 × 40 mm) in accordance with the European standards ormat or the mechanical testing o mortar tests or masonry [ ��].

In this research study three diﬀerent soils were tested and �ve diﬀerent mix combinations. For each batch, seven specimens were tested. All specimens were �rst placed in

an oven at ��∘C to dry or �� hours and subsequently dried at room temperature or �� hours beore unmolding. Specimens were cured in the uncontrolled laboratory environment at ��–��∘C and about ��% RH. A diﬀerent consistency and workability was observed during the manuacturing process, or the Errol mixes. Tis was due to the higher percentages o illite within the Errol soil compared to Raeburn or Ibstock, which allowed more water to be absorbed within the crystal matrix.

�.�. X-Ray Diﬀraction (XRD). In order to identiy and quan-tiy the presence o the diﬀerent mineral components within the clays and the phyllosilicates in each soil, the researchers ollowed a standard protocol, set out in a standard prepara-tion protocol procedure, entitled PN��LRX�� [ ��]. Te experiments were carried out in the laboratory within the University o Seville and the protocol determined the per-centage composition o the small illite, kaolinite, and chlorite grains within each sample, using the oriented aggregates method which led to the proportions described in able �.

Te oriented aggregates study included dissolving the samples in ethylene glycol and then subjecting them to a heat treatment between �� degrees and �� degrees. Figures �, �, and � show the phyllosilicate and quartz ractions over the majority o each soil type and the percentage and proportion o each mineral is shown in able �. esting and analysis was perormed in this way relating to all the diﬀerent groups o clays prevailing within each soil.

�.�. X-Ray Fluorescence Spectroscopy (XRF). XRF is mostly a quantitative technique—the peak-height or any element being directly related to the concentration o that element within the sampling volume. However, extreme care must be taken because two or more elements can interact with each other, resulting in contamination and thus skewing results. XRF tests showed (see able �) the chemical composition o three soils (samples dried at ��∘C).

�.�. Energy Dispersive X-Ray Fluorescence (EDXRF). Energy dispersive X-ray �uorescence is one o two general types o X-ray �uorescence techniques used or elemental analysis

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0 1000 2000 3000 4000 5000 6000 0 10 20 30 40 L i n ( c o u n t s ) Errol 2-_-scale

Untreated soil Ethylene glycol treated soil 350∘C treated soil 550∘C treated soil

F�� : XRD patterns o the Errol soil oriented aggregates.

Ibstock 0 1000 2000 3000 4000 5000 6000 0 10 20 30 40 L i n ( c o u n t s ) 2-_-scale

F�� : XRD patterns o the Ibstock soil oriented aggregates.

applications. Tese tests show the chemical composition o the three soils (samples dried at ��∘C), their main elements, and traces (see able �).

�.�. Ultrasonic Pulse Velocity esting (UPV). Application o ultrasonic methods or the testing o materials including polymer composites has a long-lasting tradition. In this con-text, ultrasound’s physical nature as a mechanical wave is used and knowledge o sound wave propagation characteristics in a tested medium allows or a theoretical analysis o a phenomenon.

On the basis o wave parameters on the boundary o an area, conclusions can be drawn concerning geometric

0 1000 2000 3000 4000 5000 6000 0 10 20 30 40 L i n ( c o u n t s ) Raeburn 2-_-scale

F�� : XRD patterns o the Raeburn soil oriented aggregates.

�� : Chemical composition o three soils.

Errol Ibstock Raeburn SiO� % ��,�� ,�� ,�� Al�O� % ��,�� ,�� ,�� Fe�O� % �,�� ,�� ,�� MnO % �,�� ,�� ,�� MgO % �,�� ,�� ,�� CaO % �,�� ,�� ,�� Na_�O % �,�� ,�� ,�� K�O % �,�� ,�� ,�� iO� % �,�� ,�� ,�� P�O� % �,�� ,�� ,�� SO� % �,�� ,�� ,�� PC % �,�� ,�� ,�� OAL % ��,�� ,�� ,��

properties and the distribution o physical properties within a medium—in this case un�red natural bricks.

Ultrasonic tests were carried out with the ultrasonic model brand BPV Krautkramer. Tis equipment gives the delay time rom when a transmitted wave leaves the probe until the wave is received back by the probe. It is measured by a liquid crystal �ve digit display which measures the reading timein microseconds. Te accuracy is±0.1s. Measurements were recorded by cylindrical transducers and the emission requency o the probes was �� KHz. A single ultrasonic head was used and the time o a sound wave transition through tested samples (�), wasexpressed in microseconds. Te sound wave velocity (�) through a sample was then calculated using the ollowing ormula:

� = ℎ

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�� : Chemical composition o three soils (m ain elements and traces). Cl Sc V Cr Co Ni Cu Zn Ga Ge As Se Br ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm Errol �� N.D. �� N.D. N.D. Ibstock �� N.D. � � N.D. Raeburn �� N.D. � � N.D. Rb Sr Y Zr Nb Mo Ag Cd Sn Sb e I Cs ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm Errol �� N.D. N.D. � � N.D. N.D. � Ibstock �� N.D. N.D. � � N.D. N.D. � Raeburn �� N.D. N.D. � � N.D. N.D. � Ba La Ce Nd Sm Yb H a l Pb Bi T U ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm Errol �� N.D. � �� N.D. �� Ibstock �� N.D. � �� Raeburn �� N.D. �� N.D. �� F�� : Ultrasonic tests.

where ℎ was the sample thickness. All the UPV tests were carried out on the prism specimens as per the guidelines o UNE-EN ��-�/A� [��]. est pieces with dimensions 160 mm × 40 mm × 40 mm were tested perpendicularly to the 40 mm × 40 mm plane as shown in Figure � and the results are shown in Figure �. A comparison between a series o mechanical and UPV test results or all soils and mixes is shown in able �.

4. Mechanical Test Results

�.�. Compression ests. Afer breaking samples roughly in hal, three-point bending strength tests were used to deter-mine compressive strength and a total o �� compressive strength tests were carried out (see able � and Figure �). �.�. Flexural ests. Bending strengths were determined by carrying out a three-point bending test on the specimens, in agreement with the speci�cations o UNE-EN ��-��:�� European standards. Tis standard is or the determination o bending strength o mortars used or rough castings and mortarlinings,but it wasdecided to adopt this standard in the absence o otherspeci�c regulations. Several papersincluding

Ultrasonic test (m/s) 0 200 400 600 800 1000 1200 1400 1600 1800 2000 1 2 3 4 5

Soil mix code

U l t r a s o n i c t e s t ( m / s ) Errol soil Ibstock soil Raeburn soil

F�� : Graphical comparison o the UPV results on the �ve diﬀerent mixes o the three types o soils.

the study carried out by Raut et al. [ ��] have illustrated the wide range o testing and curing regimes currently being carried out in diﬀerent laboratories as well as the range o sizes o earth brick samples. Furthemore and Heath et al. [�] have additionally discussed the current limitations in Eurocode �: Design o masonry structures (BS EN ��-�:��) and the act that it does not currently have a section reerring to earth masonry. Within this context, it was elt that UNE-EN��-��:�� was an appropriate standard to adopt.

All the �exural tests were conducted at room temperature (��∘C) on a Codein S.L., MCO-��/�� machine (maximum

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�� : Mechanical and UPV tests results o three soils.

Mix code ��

Unstabilized soil Soil + alginate Soil + �.��% wool Soil + alginate + �.��% wool

Soil + alginate + �.��% wool

Errol soil

Compressive strength (MPa) �,�� ,�� ,�� ,�� ,�� Flexural strength (MPa) �,�� ,�� ,� _�,�� _�,�� Ultrasonic testing (m/s) �� _�� _�� Ibstock soil

Compressive strength (MPa) �,�� ,�� ,�� ,�� ,�� Flexural strength (MPa) �,�� ,�� ,�� _�,�� _�,�� Ultrasonic testing (m/s) �� _�� _�� Raeburn soil

Compressive strength (MPa) �,�� ,�� ,�� ,�� ,�� Flexural strength (MPa) �,�� ,� �,�� _�,�� _�,�� Ultrasonic testing (m/s) �� _�� _��

Compressive strength (Mpa)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 C o m p r e s s i v e s t r e n g t h ( M p a )

Soil mix code Errol soil

Ibstock soil Raeburn soil

1 2 3 4 5

F�� : Graphical comparison o the compressive strength results on the �ve diﬀerent mixes o the three types o soils.

load �� kN) in a three-point bending con�guration. Te support length was adapted to the size o sample, and at least seven specimens were tested or each mix under study. A total o �� tensile tests were thereore conducted both with the �brous and non-�brous samples and the mechanical properties determined rom these tests included the �exural modulus, the ultimate stress, and the ultimate strain (see able � and Figure �).

Flexural strength (Mpa)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 F l e x u r a l t s r e n g t h ( M p a )

Soil mix code Errol soil

Ibstock soil Raeburn soil

1 2 3 4 5

F�� : Graphical comparison o the �exural strength results on the �ve diﬀerent mixes o the three types o soils.

5. Results and Discussion

It is generally accepted that incorporation o �bres increases �exural strength. Our tests have not shown the expected improved �exural strength, indeed sometimes just the oppo-site, as is shown in Figure � or the Ibstock soil. In act the addition o just �bre to soils, without the presence o alginate (as indicated in the comparison between mixes �� and ��), does not increase �exural strength. Additionally, compressive

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strength in samples with no alginate and only �bres is incr-eased only in the soil with the high plasticity index, namely, Errol. Indeed, both the �exural and compressive strengths o the Raeburn and Ibstock soils decreased in the mixture only containing wool �bres without the polymer.

In contrast, adding wool into the soil mixed with alginate always increased �exural resistance, especially i a proportion o �.��% o wool was added. Te incremental strength improvement was particularly signi�cant (��%), or the Ibs-tock soil specimens, where �exural resistance changed rom �.�� MPa (plain soil specimens) to �.�� MPa (0.25% wool + soil + alginate mixes).

As the XRD analytical results show, higher percentages o illite can be ound in the Errol soil (compared to Raeburn or Ibstock). Tis phyllosilicate appears to allow more water to be absorbed within the crystal matrix giving rise to a drier mix and this �nding is consistent with the plasticity indexes obtained or the diﬀerent soils showed in able �. Te consequences o this drier and thereore stiﬀer consistency can be observed in the mechanical results.

UPV measurements (see Figure �) demonstrated that Errol specimens, in most o the mixes tested, provided much higher compactness and with regards to mechanical tests, Errol specimens reached higher resistance values in the compression tests compared with the other soils. Flexural tests, however were less conclusive, with Errol providing higher �exural strengths in mix �, Raeburn in mix �, and Ibstock in mixes � and �. Flexural strength values were equal in the Raeburn and Errol soils in mix � and the UPV results showed a pulse velocity increase or mixes � and � compared to mixtures �, �, and �. Specimens o any type o soil tested or mix� (the mixwith the lower quantities o wool reinorcement) showed higher UPV values than mix �. Tis was particularly the case with the Raeburn soil which had the lowest plasticity index. Tis compactness decrease could be caused by the act that the shrinkage values or the �bre were much higher than the soil shrinkage.

Lower compressive and �exural resistance values were obtained when larger quantities o �bre were used in mix �. Tis could be explained as ollows: the development o strength properties in the �bre/soil mixes mostly depends on the ormation o �bre-matrix bonds as has been shown in previous studies [��]. Bonding is aﬀected by �bre dimensions, surace textures, and the number o �bres present in a given volume o material. Increasing wool �bre quantities gives

rise to �bre agglomeration and olding o �bres (balling) and this can result in a decrease in the bond strength within the specimens, which in turn leads to lower compressive strength values. In addition to the XRD, XRF, and EDXRF results, the ultrasonic results were incorporated into this study’s testing regime in order to indicate the prevalence o voids and compare the relative material densities. Te results o these tests within each sample con�rm that mix � had the best overall engineering properties and it is suggested that this was due to the quality o bonding within the composite matrix and the overall homogeneity o the mixture.

Te highest compressive strength, in all three soil types, was obtained with the composite specimens including both alginate and wool reinorcement and better results were

obtained with the reduced quantity o wool, that is, the �.��% mix ��.By adding wool to the mix, theIbstock soil specimens stabilized with alginate improved their compressive strengths by ��% whilst the Raeburn soil specimens improved their compressive strengths by ��%.

Various research papers have shown that hygrometric shrinkage and its associated cracking o earth-basedmaterials can be greatly reduced by introducing �bres into the mixture and this study con�rmed these �ndings by demonstrating that shrinkage due to the drying process was signi�cantly reduced with the inclusion o natural �bres into the soil mix. As would be expected, specimens o plain soil had a very quick (and almost without warning), brittle ailure mode. In contrast, �bre-reinorced mixes deormed, afer the ultimate load was reached and �ne cracks could be seen on the surace giving warning beore ailure.

6. Conclusions

Soil characterization through XRD, XRF, and EDXRF tests has proved to be very important in order to understand the different mechanical behaviour o the differentstabilised soils (with the same �bre and stabilizer content) and thereore the effect o the stabilization itsel.

Mixes �, �, and � (those that included the alginate pol-ymer as a stabilizer) showed better results in UPV tests in every type o soils, especially though the Errol soil and these results are consistent with the compression test results. As would be expected, �exural resistance values generally incre-ased in mixes � and �, where alginate and �bre were used simultaneously.

Te use o UPV, in this study, has added an interesting additional data set with results which closely align with the mechanical compressive strength results. Errol soil, due to its higher content o illite, contains a crystalline structure that acilitates a higher level o water absorption compared to the Raeburn and Ibstock kaolinite crystalline structures. Improved results were thereore obtained with the Errol soil due to the higher plasticity index related to a higher proportion o illite within the clay raction.

Te addition o short wool �bres (�� mm long) randomly orientedto the mixes leads to a decrease in bulk density which correspondingly decreases the compressive strength o the specimens. Tereore UPV measurements were useul in determining the resultant �nalporosity o the dried mix, afer the shrinkage process.

Fibre water adsorption and soil-�bre surace riction, due to the drying shrinkage characteristics o a �bre, depend on the available water and this in turn depends on the characteristics o the soil plasticity or diﬀerent types o clay. Te higher plasticity index obtained or the Errol soil seems to be responsible or its diﬀerent behaviour observed in the various tests compared with the Ibstock and Raeburn soils,

in mixtures with similar water proportions.

As a result o the range o data presented within this paper, it hasthereore beenshown that it is possible to prepare ��% green composites rom natural �bres and natural polymers with mechanical perormance results within ranges compatible with producing un�red bricks. Further research

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is currently under development to investigate methods or improving composite bonding and interaction and ultimately durability.

Acknowledgments

Te authors wish to acknowledge the IUACC “Instituto Uni- versitario de Arquitectura y Ciencias de la Construcci ón” or the necessary support to develop this research. Tey would also wish to acknowledge the CIIUS “Centro de Inve-stigación, ecnolog´ıa e Innovación” o the University o Seville, X-Ray Laboratory, where these tests were carried out.

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