Hindawi Publishing Corporation International Interna tional Journal o Polymer Science Volume ����, Article ID ������, �� ������, �� pages pages http://dx.doi.org/��.����/����/������
Research Article Ultrasonic, Molecular and Mechanical Testing Diagnostics in Natural Fibre Reinforced, Polymer-Stabilized Earth Blocks C. Galán-Marín,1 C. Rivera-Gómez, 1 and F. Bradley 2 �
Departamento Construcciones Arquitect onicas o´ nicas I, Escuela ecnica e´cnica Superior de Arq Arquitectur uitectura, a, University of Sev ille, Avda. Reina Mercedes, �, ����� Seville, Spain Avda. � Department of Architecture, Faculty of Engineering, University of Strathclyde, �� Richmond Street, Glasgow G��XQ, UK Correspondence should be addressed to C. Gal an-Mar´ a´n-Mar´ın; ın;
[email protected] Received �� March ����; Revised �� July ����; Accepted �� July ���� Academic Editor: Gonzalo Mart´ Mart´ınez-Barrera ınez-Barrera Copyright © ���� C. Gal´an-Mar an-Mar´´ın ın et al. Tis is an open acce access ss artic article le distri distribute buted d underthe Crea Creative tive Commo Commons ns At Attribu tribution tion Licen License, se, which permits unrestricted use, distribution, and reproduction reproduction in any medium, provided the original work 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 assesss their pote asses potentialor ntialor use in build building ing app applica lication tions. s. Mixtu Mixtures res were stab stabilized ilized with a nat natural ural polym polymer er (algi (alginate nate)) and rein reinorc orced ed with 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 manuactured 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 mechanical resistance o the samples to varying degrees, depending on the plasticity 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 �uorescence spectroscopy spectroscopy (XRF), and energy dispersive X-ray �uorescence (EDXRF) (EDX RF) tech technique niquess were all used in con conjunct junction ion with qual qualitat itative ive iden identi�ca ti�cation tion o the aggr aggregat egates. es. Ultr Ultrasoni asonicc wave pro propaga pagation tion was ound to be a useul technique or assisting in the determination o soil shrinkage characteristics and �bre-soil adherence capacity and UPV results correlated well with the measured mechanical properties.
1. Introduction Te development o building systems has been inextricably linked throughout history with the evolution o construction materials mate rials and the techn technologic ological al adva advanceme ncements nts rela related ted to harvesting harves ting and explo exploitin itingg our plane planet’ t’s nat natural ural reso resource urcess [ �].In recent years, the construction sector has b een under increasing pressure to reduce its CO 2 emissions and the volume o natural resources which it is responsible or consuming. Environmental concerns relating to the speci�cation o contemporary tempo rary mate materials rials which ofen invo involve lve ener energy-int gy-intensiv ensivee and oil-d oil-depende ependent nt proc processeshave esseshave becomeincreasin becomeincreasingly gly recog recog-nised [� [�] and wit with h bui buildi ldings ngs,, cit cities ies,, and the their ir ass associa ociated ted inrastructure playing such a signi�cant role in depleting our global resources, it is vital that material utilisation within buildings is speci�ed with care in order to reduce the impact on our planet’s resources and delicate ecosystems. Te purpose o this research was to explore the potential ordevelopi ordevel oping ng a lo low w emb embodi odied ed ene energy rgy con constr structi uction on ma mater terial ialss
obtained where possible rom natural, renewable resources. Te main barrier to the use o natural materials at present, particularl particu larlyy in devel developed oped countries, countries, is their perceived perceived poor mechanical mecha nical properties properties and durability durability in compa comparison rison with synthetic materials such as steel, concrete, and other ceramics. Tis study thereore explores the mechanical properties o an innovative, natural, un�red, composite brick designed to reduce both embodied energy values and CO 2 emissions. Earth construction is not only cost effective, as a result o the inclusion o low-cost raw materials, but it also uses locally sourced, benign materials. As a building system, it is considered to be highly energy efficient due to the excellent thermalprope the rmalpropertie rtiess whic which h ear earthe then n ma mater terial ialss exh exhibi ibitt andit als also o possesses a low embodied energy when raw clay is utilised [�]. Adobe blocks, or example, do not undergo any energyintens int ensiv ivee �rin �ringg pro proces cesses ses sin since ce the theyy ar aree sim simply ply sun sun-dr -dried ied and there the reor oree har harnes nesss sol solar ar ene energy rgy dir directl ectlyy. o pu putt thi thiss in con contex text, t, the energy require required d to pr produ oduce ce an ado adobe be blo block ck is onl only y � (kWh (kWh)/cub )/cubic ic meter compa compared red to abou aboutt ���� (kWh (kWh)/cub )/cubic ic
� metre or a �red brick and ���–��� (kWh)/cubic metre or concrete [�]. Earth construction is thereore 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 progressively recognised [�]. With regards to un�red earth construction, Heath et al. [�] have recently shown that there is structural potential or utilizing commercially manuactured un�red bricks but concluded that additional research needs to be carried out into structural behaviour and methods or minimizing moisture susceptibility. Tis project thereore examines an innovative, sustainable, natural earth product to assess its initial perormance against an extensive series o mechanical and analytical laboratory tests [ �]. Chemical soil stabilization involves changing the properties 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 beore compaction improves the characteristics o the material, particularly its resistance to water [�–��]. A proportion o at least �-�% o cement is generally needed to obtain satisactory results [ ��]. When compaction o moist soil is used in combination with cement stabilisation, it not only improves compressive strength and water resistance compared to earth construction techniques such as “adobe,” but also improves dimensional stability and tolerances 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 manuacture 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
International Journal o Polymer Science ���� �: Physical characteristics, grain size, and Atterberg limits o the three soils. Physical characteristics Sand content Silt content Clay content Classi�cation I.S.S.S. Liquid limit Plastic limit Plasticity index
Errol ��.��% ��.��% ��.��% Silty clay loam ��.�% ��.�% ��.�%
Ibstock ��.��% ��.��% ��.��% Silt loam ��.�% ��.�% �.�%
Raeburn ��.��% ��.��% ��.��% Loam ��.�% ��.�% �.�%
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), ultrasonic 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 manuacturers; 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
International Journal o Polymer Science 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 Xray diffraction (XRD) and 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 thereore 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 environmental 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 characteristics. 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 materials 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 reinorcement where available, to improve certain engineering 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 reinorcing materials not only or soils, but also within various 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 reinorcement. 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 reerred 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 reinorcement within earth blocks, totally 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 manuactured with the addition randomly oriented o a small amount (�.�–�.��%) o this raw, unprocessed wool according to recommendations rom previous
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International Journal o Polymer Science ���� �: Mixes used (by weight).
Soil mix no. � � � � �
Proportions Unstabilized soil Soil + alginate Soil + �.��% wool Soil + alginate + �.��% wool Soil + alginate + �.��% wool
Soil ��.�% ��.�% ��.�% ��.�% ��.�%
Alginate — ��.��% — ��.�% ��.�%
Lignum �.�% �.�% �.�% �.�% �.�%
Wool — — �.��% �.��% �.��%
Water ��.�% �.��% ��.��% �.��% �.��%
���� �: Mass percentages o each mineral and clay proportions. Soil Errol Ibstock Raeburn
Calcite
