Rigid plastic foams were developed by BASF in 1950 which have been consistently used in building construction (BASF, 1990) and in various geotechnical applications such as pavements (BASF, 1991; 1993), embankments (BASF, 1995) since 1960s. However, it has been proposed to consider as a geosynthetics material under a new product category called “Geofoam? (Horvath, 1991). Other names used previously in geotechnical literature when referring to such materials include geoblock, geoboard, geoinclusion and geosolid. In India, the application of such material in various fields was introduced by BASF (2004).
EPS geofoam material
Expanded polystyrene (EPS) geofoam is a cellular geosynthetic material used worldwide due to its large number of applications. Here is a brief outline about EPS geofoam material.
Since the early 1990?s, geofoam has been generic term for any synthetic geomaterial created in expansion process using a gas (blowing agent) and resulting in a texture of numerous closed cells. Therefore, geofoam is not just one material or product but a very diverse family of many different kinds of materials and products. Expanded Polystyrene (EPS) geofoam is a cellular plastic material. It is a lightweight material usually in the form of block. The commonly used parameter for EPS geofoam is density. The density of EPS geofoam is very less compared to other conventional fill materials used in the foundation practice.
Materials – Several proven geofoam materials exist. There are additional materials which have been tried over the years but were found to be technically unacceptable. Geofoam materials can be divided into three major categories:
Cementitious (typically using Portland cement) and
The polymeric category is further subdivided depending on the polymer chemistry and specific manufacturing process used:
Rigid cellular polystyrene (RCPS), which can be either expanded polystyrene (EPS) or extruded polystyrene (XPS)
Polyethylene-polystyrene (PE-PS) blend and
Despite the relatively large number and variety of geofoam materials, as a result of more than 40 years of in-ground experience EPS geofoam has emerged worldwide as a material of choice in most applications.
Product – Geofoam that can only be manufactured in a factory (which includes the dominant EPS) are typically moulded or cut into the final block or panel shape required for the particular application. However, field cutting of a block or panel to accommodate a particular construction situation can easily be done using a variety of tools. Geofoams such as PUR or FPCC that are foamed in place simply fill the shape of the volume that panel is to be filled.
1 Compared to conventional fill materials EPS geofoam is almost 100 times lighter.
Any shape of required dimension can be prepared.
It is moisture resistant, possesses negligible capillarity.
Excellent compatibility with other construction materials such as concrete and steel.
EPS geofoam blocks are easy to assemble, placed and do not require skilled labour which leads to saving in cost as well as time.
It has high resistance against growth of bacteria, fungus and insects.
It does not interfere with ground water table.
1.5 Organization of the report
The material contained in this thesis is presented as six chapters. A review of the previous literature published on fly ash in combination with other material and its uses in geotechnical application and the research needs in present in Chapter (2).
The various materials and their characteristics used in the proposed work for the development of EPGM material for sustainable construction are described in Chapter (3).
The basic consideration in the planning of experimental program and detailed scheme of proposed investigation are presented in Chapter (4).
Development and characteristics of EPGM material is demonstrated in Chapter (3).
The data obtained from the experimental investigation is analyzed and interpreted in Chapter (5).
The dissertation concludes with Chapter (6), which highlights the importance of the work and enlists the broad conclusions derived from the study conducted. This is followed by the presentation of topics for future research.
Construction of roadway or railway embankments on soft foundation soil such as marine clay is always a major issue due to poor load carrying capacity and excessive settlements. In such conditions, two major remedies are available. One is ground improvement technique by enhancing the engineering properties of foundation soil and second is reduction in the overburden pressure of structure on foundation soil this kind of study can overcome such kind of problems.
Considering first remedial measure as a ground improvement technique, enhancing the engineering properties of foundation soil and its strengthening may be very difficult due to certain reasons such as differing in soil strata or soil strata may not be known accurately. However, second remedial measure is to reduce the overburden pressure on foundation soil by using expanded polystyrene (EPS) geomaterial having well defined properties and it can noticeably reduce the overburden pressure on foundation soil due to its very low density.
The application of EPS geofoam in geotechnical engineering structures have been given by several researchers, especially in the construction of embankments and pavements (e.g. Frydenlund and Aaboe, 1994; Chang, 1994; Duskov, 1997a; 1997b; Beinbrench and Hillmann, 1997; Duskov and Scarps, 1997; Perrier, 1997; Zou et al., 2000; Stark et al., 2004;; Horvath, 2008; Arellano and Stark, 2009; Newman et al., 2010), centrifuge modeling of EPS geofoam embankments Mandal and Nimbalkar (2000), slope stability analysis (e.g. Jutkofsky et al., 2000; Mandal and Nimbalkar, 2004; Akay et al., 2013).
From the available literature, it is found that most of the work has been carried out in the direction of actual application of EPS geofoam in the field and a very little attention has been given towards experimental investigation especially towards EPS geomaterial in roadway embankments, filling material behind retaining walls and bridge abutments, for backfilling of pipeline trenches and for irregular areas. Therefore, an initiative has been taken to study the small scale model testing of EPS geomaterial for roadway embankments, filling material behind retaining walls and bridge abutments, for backfilling of pipeline trenches and for irregular area fillings.
chapter – 2
This chapter presents the overview of various constraints associated with the disposal Fly-ash and its uses in civil engineering are hereby identified. Also the fly ash, its physical properties and general uses in various applications is viewed. However, this lightweight geomaterial technology has not yet found its place in geotechnical construction practice in our country. In order to make this technology more relevant and use to, technically sound and cost effective in the present scenario in India, an effort is made to develop a new EPS beads based lightweight geomaterial (LWGM) of desired characteristics for its use in embankments over compressible soils, for reduction in earth pressures in soil retention structures and as backfilling material. The paper presents the investigations carried out in this respect and the outcome thereof.
Keeping in view the above objective, this study represents the information regarding use and application of fly ash based light weight material, stabilized with small percentage of cement, their properties and uses in a most concise, compact and to the point manner. Waste materials utilization is not only the promising solutions for disposal problem, but also saves construction cost of the project to a limit.
The main objective is to investigate the potential of using light weight materials in the field of geotechnical engineering. While studying various relevant literatures, various important facts about Fly ash are realized but various important information about the light weight material is not realized. There is lack of information about the use and behavior of fly ash as a backfill material. This study, therefore, seeks to fill this gap.
The present Chapter reviews the attempts made by several researchers to understand the behavior of expanded polystyrene (EPS) material as a construction material to minimize the degradation to a level consistent with sustainable development is reviewed; its procedures and design technologies adopted are studied. Literature reviewed in the present Chapter reveals many studies on the application of geomaterial in various Civil engineering projects which are important to contribute the gain of experience and accuracy in framing the future work.
2.2 Advantages of EPGM material as a sustainable backfill material
Nowadays, EPGM is an atypical backfill material, but has a number of qualities that makes it stand out from other material. Here are its main attributes.
It is very good fire resistant.
Light in weight, easily manageable on site.
Has comparative high strength.
Can be used in Construction over the soft soil having low bearing capacity.
Can be used in low lying areas.
Can be used to reduce the over burden pressure and to economize structures like retaining wall and embankments, for reduction in earth pressures in soil retention structures and as backfilling material.
It can be used as a substitute of EPS block geofoams.
2.3 Literature Review
Lightweight geomaterials using EPS beads
Tsuchida et al. (2001) carried out a series of unconfined compression tests on geomaterial prepared with expanded polystyrene beads, dredged bay mud and cement. The engineering properties of geomaterial developed mainly include modulus of elasticity, compressive strength, and deformation characteristics were studied. The experimental investigation showed that the secant modulus of geomaterial increases 150-400 times the shear strength obtained from unconfined compression test (qu/2). The stress reaches to a well defined point and then to the residual state in the direct shear test. Direct shear tests were also performed on the geomaterial to gain the correlation between two parameters such as compressive strength test and shear strength.
Yoonz et al. (2004) studied the mechanical characteristics of the light-weighed soil (LWS) made up of EPS, water, dredged clay and cement through a series of triaxial compression tests and unconfined compressive test . The test specimens were prepared in the ratio of EPS, water and cement to dredged clay by percent weight. The stress-strain characteristics, along with the different parameters affecting the strength of the light-weight soil such as initial water content in dredged clay, EPS ratio effect, cement ratio effect, curing pressure effect were studied. The experimental study revealed that the compressive strength of the LWS does not depend upon effective confining pressure. The secant modulus obtained at 50% failure strain is about 20-40 times triaxial compressive strength. The influence of initial water content in the dredged soil is also important as the axial strain in triaxial test decreases significantly with decrease in initial water content in dredged soil.
Stark et al. (2004b) has discussed the advantages of lightweight fill materials for embankment by using EPS. These lightweight fill materials have a density less than soil which reduces the overburden pressure over poor foundation soil such as marine clay thereby reduces the excessive settlements. It was also reported and observed that the magnitude of secondary compression of soft soils can be considerably reduced by using the lightweight materials.
Liu et al. (2006) conducted compressive strength tests to study the effect of different mixing ratios of EPS beads, cement and water with respect to soil on the compressive strength, density, modulus of elasticity of the lightweight fill material. From the experimental investigation, it was observed that, the density of lightweight material is highly dependent on percentage of EPS beads added in the mix; however the effect of percentage of cement and water added is insignificant compared less to EPS beads. The compressive strength of the lightweight material depends on all the three mixing ratio and it increases with increase in the percentage of cement whereas decreases with increase in EPS beads and water. The lightweight material produced has higher density but high compressive strength compared to EPS geofoam block and can be used as an optional material when high strength fill materials are required.
Kim et al. (2008) developed a lightweight soil consisting of dredged clayey soil, cement, and air-foam with waste fishing net as reinforcement for the material. A series of unconfined compression tests and one dimensional compression tests were conducted to investigate the strength characteristics of unreinforced and reinforced lightweight soil with fishing net. The lightweight soil specimens were prepared with different composition of cement, water, air-foam and fishing net contents. The results showed that the compressive strength increases with increase in cement content but decreases with increase in water and air-foam content. Inclusion of waste fishing net increases the compressive strength of lightweight soil due to the friction and the bond strength at the interface between waste fishing net and soil mixtures; however increase in the compressive strength was not directly proportional to the percentage of waste fishing net. The air-foam content affected the bulk unit weight of lightweight soil.
Zhu Wei et al.(2008)developed a new geo technical material, sand EPS beads mixture (SEM).Direct shear tests, density test and compression test were performed to study the density and strength properties of the SEM. The results showed and revealed that i) water is necessary for preparation of specimen, but has no different effect on shear strength and dry density of the SEM, ii) dry density of the SEM decreases linearly with volumetric EPS beads content, but increases with preload pressure, and iii) the shear strength of the SEM changes little with volumetric EPS beads content and gravimetric water content but increases with preload pressure.
Wang and Miao (2009) performed laboratory experimental to study the effectiveness of fill material made from different mixtures of river sand, cement and expanded polystyrene beads. The proportion of sand and EPS beads was measured by volume, while the proportions of sand, water and cement were determined by weight. The compaction test was conducted with different water content proportion to obtain the optimum water content. The test specimens of cubical shape were prepared using the density and water content determined already. The unit weight of lightweight fill material produced was 10 kN/m3. These specimens were tested for unconsolidated undrained triaxial test, consolidated undrained test, unconfined compression test. The outcomes showed that the unconfined compressive strength of proposed material increases with the increase in curing time and cement content. In unconsolidated undrained triaxial test, it was observed that the cohesion of lightweight material has strong influence of cement content; whereas angle of internal friction was not affected much when tested for 7 days and 14 day cured specimen. In consolidated undrained test, with increase in cement content increases the cohesion value whereas the angle of internal friction of soil was found to almost the same compared to UU test. The performance of lightweight fill material was also studied by construction of embankment over soft soil by using 2 dimensional finite element analysis package PLAXIS 2D. The results obtained from FEA were then compared with similar soil embankment stabilized with lime. The results indicated and revealed that there is considerable reduction in the settlement of soft soil with better strength of embankment with lightweight material when compared with the lime stabilized soil embankments.
Deng and Xiao (2010) conducted and performed consolidated drained triaxial tests on EPS sand mixtures to observe the stress-strain characteristic under different confining pressures. The EPS-sand mixtures were produced by adding 0.5, 1.5 and 2.5% of EPS beads by weight of sand which was found to be 26 to 63% lighter than the conventional fill materials. The triaxial specimens were loaded under confining pressures of 100, 200, 300 and 400 kPa. The results of the investigation showed and revealed that the EPS content and confining pressures were found to be major influencing parameters to the stress-strain and volumetric strain behavior of the mixtures. Increase in EPS content increases volumetric strain and decreases the shear strength. Increase in confining pressures enhances the strength of the mixture. EPS content dependent strain increment equations were also derived by compromising Cam-clay and modified Cam-clay, and used to model the stress-strain characteristics of EPS-sand mixtures. The established equations were verified being able to depict the stress-strain observations of EPS-sand specimens, at least for the ranges of EPS contents and confinements.
Onishi et al. (2010) carried out series of triaxial compression tests on cement stabilized sand with EPS beads. The change in strength and deformation properties with increase in EPS beads content is studied and observed. The findings reported that the unit weight of the geomaterial produced can be reduced to a greater extent by addition of EPS beads but on the other hand mixing of such material can degrade the strength and deformation properties of the geomaterial. However, this degradation can be effectively controlled by addition of appropriate amount of cement. Based on the outcomes from the study, the practical implications of designs of these types of lightweight geomaterials are also discussed in terms of unit weight, strength and deformation characteristics.
Gao et al. (2011a) discussed the geotechnical properties of lightweight geomaterial called EPS composite soil (EPSCS) made up of clay, cement, water and EPS. The properties such as unit weight, compressive strength and modulus, deformation behavior, permeability, dynamic property using creep behavior, cyclic triaxial test and water absorbability. The advantages of the lightweight geomaterial in the geotechnical applications are discussed with some case histories. Based on this study, some future scope of research is also suggested and projected.
Gao et al. (2011b) carried out a series of cyclic triaxial tests to understand the strength and deformation characteristics of lightweight sand EPS soil (LSES). A united framework was suggested for LSES for setting up deformation and strength characteristics by failure cyclic number that corresponds to complete degradation of LSES structure. Cylindrical shaped test specimens with diameter 61.8 mm and height 140 mm were prepared using different mix ratios. The cyclic stress-strain relationship along with Modulus Reduction Curves for LSES was studied. The experimental investigation showed that LSES possesses good resilient- elasticity recovery ability due to presence of EPS beads which play an important role in energy consumption, affected by which, the cyclic stress–strain curves of LSES under low confining pressures show remarkably linear type. The behavior of LSES under cyclic loading was found to be clearly different from those of sand or cemented sand or EPS. The LSES specimens exhibit brittle failure.
Gao et al. (2012) performed 2D finite element simulation of the embankment constructed with lightweight geomaterial (EPSCS already mentioned in Gao, 2011a) having unit weight 11 kN/m3 over soft clay to determine and study the settlement, soil pressure and pore water pressure and to improve the safety of the ground. The comparison was made between EPSCS and embankment with conventional fill material having unit weight of 18 kN/m3. Compared with the conventional embankment, EPSCS embankment can effectively reduce the settlement problems, soil pressure and excess pore water pressure and so as to improve and safe guard the safety of the ground.
Miao et al. (2013) proposed a new lightweight fill material consisting of EPS beads, cement and the hydraulic sand from the Yangtze River, for its application in settlement problems associated with bridge approach embankments over soft soil. The experimental investigation and study was carried out to understand the mechanical properties of lightweight material such as standard Proctor tests, unconfined compression tests, unconsolidated-undrained tests, California Bearing Ratio (CBR) tests, and consolidated-undrained tests. The test results showed that proposed lightweight fill material possess consentient properties which suit as a backfill material in highway embankment projects. A field study was also performed to verify the performance of the embankment backfilled with this lightweight material, which resulted in a smaller settlement than the embankment backfilled with lime-stabilized soil.
Qi et al. (2013) conducted permeability tests on geomaterial prepared with EPS beads, sand and cement. The effect of different mixing ratios, curing age and applied consolidation pressure on permeability of the geomaterial produced was studied through laboratory experimental tests using consolidation parameter. The test results indicated that the permeability of EPS beads-mixed lightweight soil decreases with the increasing of curing age and cement ratio, and decreasing of EPS beads ratio and particle size. The coefficient of permeability of EPS beads-mixed lightweight soil decreases with the increase of consolidation pressure and the decreasing trend is slow down under large consolidation pressure. The extent of reduction of permeability coefficient with the increase of consolidation pressure is comparatively larger under large EPS beads ratio or small cement ratio.
Padade and Mandal (2014) conducted a study of Expanded Polystyrene-Based Geomaterial with Fly Ash. This paper reports the engineering behavior of proposed expanded polystyrene-based geomaterial (EPGM) with ?y ash through a laboratory experimental study. The proposed geomaterial is prepared by blending ?y ash with expanded polystyrene (EPS) beads and a binder such as cement. The effects of different compositions and different mix ratios between EPS beads and ?y ash (0.5–2.5%), cement and ?y ash (10–20%), and water and ?y ash (50 and 60%) on density, compressive strength, and initial tangent modulus of the geomaterial formed were studied for 7 days and 28 days duration. The authors observe that the density of EPGM can be effectively controlled by the quantity of EPS beads added in making the material. With the inclusion of merely 0.5–2.5% of EPS beads to ?y ash (by weight), the density of the geomaterial formed can be reduced from1,320 to 725 kg/m3. The compressive strength of EPGM increases considerably if cement-to-?y ash ratios of 10, 15, and 20% are used. Compared with EPS block geofoam, EPS beads mixed geomaterial has higher density but higher compressive strength and higher stiffness. Thus the geomaterial developed in the current study can be used as a substitute for EPS geofoam block when strong ?ll materials with high strengths are required.
Ram Rathan Lal and Badwaik (2015) conducted experimental study on bottom ash and expanded polystyrene beads–based Geomaterial. The increasing production of bottom ash and its disposal in an eco-friendly manner is a matter of concern. This paper concisely describes the suitability of bottom ash to be used in civil engineering applications as a way to minimize the amount of its disposal in the environment and in the direction of sustainable development. The proposed geomaterial was prepared by blending bottom ash with expanded polystyrene (EPS) beads and a binder such as cement. The experiments were conducted by adding EPS beads with different mix proportions. The mix ratio percentages 0.3, 0.6, 0.9, 1.2, and 1.5 were used in this study. The cement to bottom ash (C/BA) ratios of 10 and 20% were used in the study. All the ratios used in the study are with respect to weight of bottom ash. The compressive strength of geomaterial was evaluated for curing periods of 7, 14, and 28 days. The effects of various mix ratios, cement content, and curing periods on the density, compressive strength, and initial tangent modulus was studied and the results were incorporated. Test result indicated that the density of geomaterial reduced from 650 to 360 kg/m3 with addition of EPS beads from 0.3 to 1.5%. For a particular curing period, compressive strength reduced marginally following the inclusion of EPS beads in geomaterial. For each mix ratio, compressive strength increased with increasing curing periods. The initial tangent modulus of the geomaterial decreased with increasing mix ratio values. The prepared geomaterial was light in weight comparatively and it can be used as a substitute to conventional fill materials.
Marjive and Ram Rathan Lal(2016)carried out an experimental study on stone dust and EPS beads based material, a series of compressive strength were performed on newly developed construction material (NDCM) prepared by using stone dust, expanded polystyrene (EPS) beads and binder material such as cement. Two different densities of EPS beads 22 kg/m3 and 16 kg/m3 were used in this study. The mix ratio percentages used in the study are 0.25, 0.75, and 1.25. The compressive strength of material was determined for curing periods of 7, 14, and 28 days. For a particular mix ratio value, compressive strength of material increased with increasing curing period and for a particular curing period value it decreased with increasing mix ratios. The density of NDCM was found to be decreased with increasing mix ratios for both the densities EPS beads. For a particular mix ratio, NDCM prepared using EPS beads of density 16 kg/m3 shows lower density than that of prepared using density 22 kg/m3. For a particular mix ratio and for each curing days, NDCM prepared using EPS beads of density 22 kg/m3 shows higher compressive strength than EPS beads of density 16 kg/m3.
Ashna et al. (2017) carried out an experimental study on stress-strain behavior of EPS beads-sand mixture. In this study, Expanded Polystyrene beads of two sizes, namely 1 mm and 2 mm were mixed with sand at proportions 0.25%, 0.5% and 0.75% by weight to obtain a new geo-material. A Tri-axial compression test was done at three different confining pressures. The results showed that by increasing the EPS content by weight, maximum deviator stress and angle of internal friction decreased. However, bead in the mix contributed to the lightweight aspect which can be used in several geotechnical applications. The stress strain behavior of the mix was found to be dependent on size of bead, bead content and confining pressures. The study concluded with, dry unit weight decreases with the addition of EPS beads into sand which shows that it has the potential characteristic of a lightweight fill, Angle of internal friction decreased with increase in bead content, Deviatoric stress decreased with increase in % by weight of beads for both bead sizes, Smaller sized beads showed greater strength compared to larger sized beads was observed.
From available permanent literature, lightweight geomaterials are prepared by using EPS beads, soil and cement as binder material (Tsuchida et al., 2001; Yoonz et al., 2004; Stark et al., 2004b; Liu et al., 2006; Kim et al, 2008; Wang and Miao, 2009; Deng and Xiao, 2010; Onishi et al., 2010; Gao et al., 2011a; 2011b; 2012; Miao et al., 2013 ; Qi et al., 2013), a few study has been done by using EPS beads, fly ash and cement as binder material (Padade and Mandal 2014, Ram Rathan Lal and Badwaik 2015; Marjive and Ram Rathan Lal 2016; Ashna et al 2017). However, it is observed that some of the aspects of mix ratios are not discussed adequately in the study.
As studied and reported by Liu et al. (2006), the usage of EPS geofoam blocks in infrastructure projects suffer from some disadvantages viz. (i) EPS geofoam blocks are usually of regular shapes, therefore it is not possible to use them to fill in irregular volumes; (ii) shapes EPS geofoam blocks cannot be fabricated on site, hence its transportation is necessary on site and (iii) So as to suit site conditions the basic properties of EPS geofoam blocks cannot be modified.
Several researchers have done experimental and numerical investigations on lightweight fill material prepared by using EPS beads, soil and cement (e.g. Tsuchida et al. 2001, Yoonz et al. 2004; Liu et al. 2006; Kim et al. 2008; Wang and Miao 2009; Deng and Xiao 2010; Onishi et al. 2010; Gao et al. 2011a, 2011b, 2012; Miao et al., 2013 and Qi et al. 2013). A few research by Padade & Mandal 2014; Ram Rathan Lal & Badwaik 2015; Ram Rathan Lal et al. 2016; Ashna et al. 2017 in the light of using fly ash as EPGM material has been done. Shin et al. (2011) proposed application of light soil particles (LSP) made of expanded polystyrene (EPS) material in mortar.
It is well studied from the available literature that numerous studies have been carried out to understand the behavior of lightweight geomaterial (EPGM) prepared by using EPS beads, soil and cement as binder material. However, much attention is not paid to develop geomaterials by using fly ash instead of soil or any other material in combination with EPS beads and cement.
As per the problems mentioned and detailed by Das and Yudbhir (2005) and Gandhi et al. (1999), Padade & Mandal 2014 the present research work was carried out by using fly ash and EPS beads in the light of long term strength gained by the specimens in comparison with specimens prepared without beads.
Fly ash is the finely divided residue that results from the combustion of pulverized coal and is transported from the combustion chamber by exhaust gases. Over 61 million metric tons of fly ash was produced in 2001.The total generation of fly ash in 2010-11 was 131.09 million-tonnes. The data of fly ash generation and utilization for year 2015-16 received from 71 Power Utilities in India was 176.7441 Million- tonne which is 2.6 times more as compared to 2001 report .Therefore with an exponential increase in population of India there has been increasing in power demand and supply. This directly led to increase in production of fly ash. Leading to direct impact on global environment. In India, thermal power plants produce a huge quantity of fly ash. Therefore, an attempt has been made in the direction of using fly ash instead of soil for the preparation of geomaterial along with EPS beads and cement.
The present study mainly focuses on mechanical behavior of EPS based geomaterial using fly ash and cement as binding material. Compared with other similar geomaterials like EPS geofoam blocks, and cement-soil-EPS lightweight fills the proposed EPGM has some advantages that includes cement saving, irregular shape filling and indirectly proper utilization of fly ash in geotechnical engineering application which reduces the environmental pollution related problems to disposal of fly ash and finally better to overcome the thermal insulation problems. In comparison with the EPS geofoam block, the lightweight fill that includes EPS beads may be controlled in terms of both density, shear strength, compressive strength .
2.4 Main Aims and Objectives of the Proposed Work
The primary aim of this study was to investigate the feasibility of using a significant proportion of fly-ash for beneficial purpose in civil engineering applications that is sustainable and environmentally friendly. To study strength characteristics of fly ash and EPS beads in combination with cement and water. This study reports the results of an experimental investigation into the engineering properties, such as compressive strength depending on the proportion of beads to fly ash, cement to fly ash, water to fly ash ratio.
The objective is also to promote safe uses of fly ash material along with EPS beads in civil engineering projects. The detailed laboratory investigations were planned and carried out for the determination of the best product and the best mix design. Thus, the main objective of the study undertaken in this dissertation work may be summarized as under:
The primary objective of the present study deals with determination of physical properties of locally available fly ash and its suitability as a construction material.
To evaluate compressive strength of specimen prepared from different composition of EPS beads, cement and water along with fly ash and study its long term strength and stiffness.
Preparation of lightweight material using the proportions mentioned by Padade & Mandal (2014)
Density measurement for light weight material.
Effect of mix ratios on density, compressive strength and stiffness.
Stress-Strain behavior of the material.
The optimal mixture of locally available fly ash stabilized with cement and EPS beads was selected among experiments under consideration to produce the alternative EPGM material mix.
2.5 Scope of Present Work
Considering above stated aims and objectives, the scope of present work is defined as follows,
A new expanded polystyrene (EPS) based geomaterial has been proposed with different mix ratios between the four components (EPS beads, fly ash, cement and water). The mix ratios were based on fly ash as basic material with respect to which mass of EPS beads, cement and water were taken. The geomaterial has been prepared with thirty six different combinations and test results of 144 samples of EPS beads based geomaterial are discussed with respect to the long term effect of these mix ratios on density, stress-strain nature, variation in compressive strength, effect of curing period on strength development and initial tangent modulus is determined and presented in the study.
a. The lightweight geomaterial (LWGM) evolved from the study by using fly ash and expanded polystyrene beads has high potential for its use in several geotechnical constructions in infrastructure development works in India.
b. The composite material of required lightness and strength can be formed by adjusting EPS beads (B) content from 0.5% to 2.5% of weight of fly ash (FA). However, for appropriate strength development 10%, 15%and 20% cement (by weight) is needed.
d. As compared to traditional coarse grained moorum type earth commonly used in embankment construction and backfilling, the suggested LWGM is 50% light and 16.5 times strong.
e. The LWGM developed from the study can be used in the form of blocks of any size pre-casted and cured at casting yard near site or as wet mix to be placed in bulk for the desired construction job.
f. Embankments with very steep slopes can be formed by using LWGM. This results in substantial saving of land area occupied by embankment. Besides, the volume of embankment material is significantly reduced.
3.1 Fly Ash
Flyash, is known as one of the residues generated by coal combustion, and is composed of the fine particles that are driven out of the boiler with the flue gases. The fly ash is continuously produced in unimaginably huge quantity in our country from several thermal power plants. In absence of its timely and effective disposal it creates many environmental hazards. This fly ash forms the main constituent of the proposed geomaterial. Fly ash is an industrial waste product from coal based power station.
The fly ash is slightly alkaline in reaction. Fly ash is a good material for a wide range of applications viz. by geopolymerisation, by preprocessing, by heat treatment process can be utilized for manufacturing of cement, substitute of cement in concrete, manufacture of bricks, blocks, ceramic tiles, paving blocks, self glazed tiles, immobilization, mechanical activation, refractory bricks, synthetic granite etc. Classification of Fly ashes classified by precise particle size requirements, thus assuring a uniform, quality product. In the present study fly ash is collected in wet state from Koradi thermal power plant, Koradi, Nagpur, India having specific gravity 2.18 Class F fly ash is available in the largest quantities. Class F is generally low in lime, usually under 15 percent, and contains a greater combination of silica, alumina and iron (greater than 70 percent) than Class C fly ash. Class C fly ash normally comes from coals which may produce an ash with higher lime content generally more than 15 percent often as high as 30percent. Elevated CaO may give Class C unique self-hardening characteristics.
Fly ash used for the present laboratory study is taken from Koradi power plant, Nagpur which is stored in gunny plastic bags and it is classified as class F. Flyash having following components are summarized below,
The percentage of basic chemical compounds present in fly ash were SiO2 (61.15%), calcium oxide, CaO (3.31%),Magnesium oxide, MgO(0.64%),total Sulphur as Sulphur trioxide ,SO3(0.127%),Silicon dioxide (SiO2) +aluminium oxide(Al2O3)+ iron oxide(Fe2O3) (94.95%),Total loss on ignition was (0.34%). Depending on percentage of chemical compounds present in fly ash, as per ASTM C618-08, it is classified as Class F. The specific gravity of fly ash is 2.18. Fineness by sieving is 9.30%, compressive strength 28 days is 34.50N/mm2, consistency as 27.5%, soundness by Autoclave method as 0.039% respectively.
3.2 Expanded polystyrene beads
Expanded Polystyrene (EPS) is a super lightweight synthetic cellular material that was invented in 1950. This rigid plastic foam type material is being used in geotechnical constructions since 1960’s when a product category ‘Geofoam ‘was discovered. EPS is generally used as packaging material for sensitive appliances and electronic items during transportation. EPS is a polymeric form of its monomer, Styrene. It is white in colour, and is manufactured from a mixture of 5-10% gaseous blowing agent, most commonly pentane or carbon dioxide and 90-95% polystyrene by weight. The solid plastic is expanded into foam by the use of heat; usually steam. EPS can be used in the form of blocks (also called EPS geo-foam) and beads. Expanded polystyrene beads used are spherical and round in shape with diameters ranging between 2 to 3 mm. These highly compressible EPS beads have a density 20 kg/m3. Compared to EPS shreds and strips, EPS beads make the composite material with the lowest unit weight.
An expanded polystyrene bead was used as a mixing component. These closed cell particulates are often called as polystyrene pre-puffs in the manufacturing sector. The lightness of the material is accomplished by adding EPS beads in fly ash.
Expanded polystyrene beads were spherical and round in shape with diameters ranging between 2 to 4 mm and having durable property. It was aimed to develop a composite material containing larger percentage of EPS beads and lesser quantity of cement. The trial mixing and testing revealed that the beads content should be 0.5% to 2.5% of the weight of fly ash. EPS beads having the chemical formula (C8H8) n, density in the range of 0.96 -1.04 gm/cm3, having melting point approximately 240oC (464oF) and decomposes at lower temperature, thermal conductivity 0.033 W/ (m-k), Refractive index (nD) 1.6; dielectric constant 2.6(1KHz-1GHz), was obtained from a regional supplier of EPS material for engineering, packaging, manufacturing industries Thermo Pack Industries, Kalamna market road, Nagpur, India.
An Ordinary Portland cement of 43 grade (IS 8112: 1989) was used as a binding material. Cement is a binder, a substance used for construction that sets, hardens and adheres to other materials, binding them together. Cement is seldom used on its own, but rather to bind sand and gravel together. The density of ordinary Portland cement was 3.15 g/cm³(3150 kg/m3). This type of cement should confirm according to IS: 8112-1989.
Potable water is used to mix these materials. Potable is water safe enough to be consumed by humans or used with low risk of immediate or long term harm. In most India, the water supplied to households, commerce and industry meets drinking water standards, even though only a very small proportion is actually consumed or used in food preparation. Typical uses (for other than potable purposes) include toilet flushing, washing, and landscape irrigation.
Figure 3.1 Photographic view of EPS beads
The experimental program was planned with an objective to understand and investigate the suitability of fly ash. The following chapter discusses the laboratory equipment, method and techniques utilized throughout the testing program.
4.1 Mix proportion
The work plan comprise of mix proportions and preparation of specimens with several different combination of Fly ash, Cement at suitable W.C. (%). In the experimental study three different mix ratios were used to prepare the EPGM. The mix proportion is defined as the proportion of two materials by weight. These ratios are as follows –EPS beads to fly ash (B/FA), cement to fly ash ratio (C/FA), and water to fly ash (W/FA). A pilot project work was also conducted before deciding the range of limits of different mix ratios and specimen of size 100 X 100 X 100 mm was taken into consideration. During the sample preparation it was observed that beyond 2.5% proportion of (B/FA) ratio the sample segregates, due to volumetric increase of beads as compared to fly ash .The cement to fly ash ratio (C/FA) was also fixed between 10% to 20% because C/FA ratio below 10% was insignificant as the components were found to be segregated after curing of one day. And the last component of water to fly ash ratio (W/FA) ratio cannot be formed into homogeneous slurry below water to fly ash of 40%. Table gives the study for preparation of the EPGM.
Table 4.1 Mix ratios used to prepare EPGM
EPS beads to fly ash (B/FA)% Cement to fly ash (C/FA)% Water to fly ash (W/FA)%
0.5, 1.0, 1.5, 2.0, 2.5 10 40
0.5, 1.0, 1.5, 2.0, 2.5 15 40
0.5, 1.0, 1.5, 2.0, 2.5 20 40
0.5, 1.0, 1.5, 2.0, 2.5 10 50
0.5, 1.0, 1.5, 2.0, 2.5 15 50
0.5, 1.0, 1.5, 2.0, 2.5 20 50
NOTE: B/FA = EPS beads to fly ash ratio and C/FA= Cement to fly ash ratio
4.2 Experimental Program
Experimental program consists of determination of
Preparation of lightweight material using the proportions mentioned by Padade ; Mandal (2014)
Density measurement for light weight material.
Compressive strength test for long term of 7/14/28/56 days on cubical specimen.
Effect of mix ratio on density, compressive strength and stiffness.
Stress-strain behavior of the material.
4.3 Preparation of test specimen
The EPS beads mixed geomaterial was prepared as follows. The dried fly ash was weighed and placed into a container. The cement was also added according to C/FA ratio and dry mixing was carried out first. For compound mix, potable water was added slowly according to W/FA ratio specified and the fly ash–cement-water mixture was mixed into homogeneous slurry as shown in Figure 4.1(a). The EPS beads were then slowly added into slurry and mixing continued until the beads were evenly distributed well within the slurry. With some more time of mixing, fresh EPS beads mixed geomaterial was produced in a slurry form as shown in Figure 4.1(b). After a thorough mixing the slurry formed was cast into specimens for compressive strength tests. These compressive strength test specimens were prepared in a cube shape moulds having dimension 100 mm × 100 mm × 100 mm as shown in Figure 4.2. After setting time, all specimens were removed from the moulds and placed in the water tank for curing until the date of testing as shown in Figure 4.3. The EPGM specimens after curing are shown in Figure 4.4. The curing periods used in experimental program were 7 days, 14 days, 28 days and 56 days. 30 tests were conducted on EPGM samples for each curing period. Therefore, the results of 120 tests are reported in the study along with test results of 24 tests obtained from mixing of fly ash along with cement and water without beads for a comparative study.
Fig. 4.1 Preparation of EPGM (a) dry cement and fly ash mix and
(b) slurry after mixing of EPS beads and water
Fig. 4.2 EPGM specimen casting in moulds
Fig. 4.3 EPGM specimens in curing tank
Fig. 4.4 EPGM specimens after curing
4.4 Test procedure
After curing, the specimens were air dried and dimensions of each specimen were measured using a vernier calliper for volume determination (Figure 4.5 a ). The mass of each specimen was measured using an electronic balance having accuracy of 0.01 g. These measurements were used to calculate the density of specimen by dividing mass with volume.
Compression test was performed on EPGM specimens to measure compressive strength and stiffness. Compression tests were conducted Compression testing machine as shown in Figure 4.5(b) having a capacity of 20 tonnes. The maximum load at failure of specimen with corresponding deformation was noted as a compressive strength.
(Fig. 4.5 a) Specimen measured 4.5 b) Compressive strength tests on EPGM
with vernier caliper specimen on CTM.
Compression Testing Machine, Cube specimen.
• After preparing a mix, the cubical test specimens of dimensions 100x100x100 mm is prepared for compressive strength.
• The Compressive Strength test was performed as shown in the figure.
• The specimen is placed between steel plates under loading frame.
• Load is applied axially at uniform rate till failure.
• Maximum load at failure divided by average area of bed face gives compressive strength.
Compressive Strength (kN/m2) =Max.load at failure in kNAverage Area in m2
Fig. 4.6a) Cube Compressive strength test set up
4.4.2 Determination of Density
One of the important parameter for EPGM is its density. The specimens were weighed by using electronic weighing balance. The density of the material block was calculated by dividing weight with volume of the specimen.
Electronic weighing balance.
Density =Weight of speciment in kNVolume of specimen in m34.4.3 Stiffness modulus
22.214.171.124 Initial Tangent Modulus
The initial tangent modulus, Ei , is often used to characterize the stiffness of the geomaterial. It is determined as the slope of the tangent line to the origin of the stress–strain curve. Using the compressive testing results, the initial tangent modulus of the alternative geomaterial were calculated and plotted against the corresponding compressive strengths.
RESULTS AND DISCUSSIONS
The properties of lightweight geomaterial such as density, compressive strength and initial tangent modulus are studied and discussed in this chapter in detail corresponding to different mix ratios used for its preparation.
5.2 Effect of mix ratios on density of lightweight geomaterial
Figures 5.1 and 5.2 represent the variation of density with respect to B/FA ratio. It can be clearly noted that the density of lightweight geomaterial decreases with increase in B/FA ratio. Lightweight geomaterial with B/FA ratios 0 to 2.5% have density in the range of 1665 to 772 kg/m3. This is due to the weight of EPS beads which is very less compared to fly ash. Replacement of nearly 0.5% beads increases its volume significantly which results in dreased density of geomaterial. Increase in B/FA ratio from 0.5 to 2.5% reduces the desnity of geolmaterial in the range of 19 to 51%. However, increse in C/FA ratio does not show any effect on density of lightweight geomaterial. Increase in C/FA ratio from 10 to 20% resulted in density variation within 0.5 to 1%. The change in density of lightweight geomaterial is noticable for B/FA ratio however, it is insignificant for C/FA ratio.
The density of lightweight geomaterial decreases with increase in W/FA ratio but the change is marginal. Increase in W/FA ratio from 40 to 50% decreases the density of lightweight gematerial within the range of 1 to 3%.
From above discussions, it is very clear that B/FA ratio is a governing factor density of geomaterial whereas the other factors (C/FA) and (W/FA) do not have any effect on density.
Figure 5.1 Effect of B/FA ratio on density of geomaterial at C/FA ratio 40% for W/FA ratios (a) 7 days, (b) 14 days, (c) 28 days and (d) 56 days
Figure 5.2 Effect of B/FA ratio on density of geomaterial at C/FA ratio 50% for W/FA ratios (a) 7 days, (b) 14 days, (c) 28 days and (d) 56 days
Considering the above graphical representation given in Figures 5.1 and 5.2 which shows nearly equal values for the density with respect to C/FA ratio as discussed earlier, the average density was calculated considering the curing period and plotted against C/FA ratio as shown in Figures 5.3 (a) and (b). For the specimen cured for 7, 14, 28 and 56 days, the change in density of geomaterial is found to be insignificant.
Figure 5.3 Effect of mix ratio on density of geomaterial with C/FA ratio
for (a) 40% and (b) 50%
5.3 Effect of mix ratios on compressive strength
Figures 5.4 and 5.5 represent the effect of B/FA ratio on compressive strength of geomaterial. It is important to note that the representation of relationship between compressive strength and mix ratios are given on same scale for all the cases. This is done to identify the nature of the geomaterial with respect to beads (B/FA), cement (C/FA), water (W/FA) and curing period.
The compressive strength decreases with increase in B/FA ratio from 0.5 to 2.5%. Within this range the change in compressive strength was found to be 25 to 68%. The decrease in compressive strength was observed due to increase in the proportion of highly compressible beads in the mix. It is important to note that 0.5% increase in beads by weight substantially increases its volume resulted in reduced compressive strength. However, the strength increases with increase in C/FA ratio from 10 to 20% for a particular B/FA ratio having same W/FA ratio.
Increase in W/FA ratio affects the compressive strength of geomaterial which decreases with increase in W/FA ratio from 40 to 50%. Within this range of increase, the decrease in compressive strength is found to be in the range of 7 to 16%. Therefore, it can be referred that the mixing ratios required high precision with respect to W/FA ratio.
It is interesting to observe that specimen without EPS beads have compressive strength less than specimen with 0.5% beads and equal or some times less than 1.0 to 1.5% beads for most of the cases. This has been clearly observed in stress-strain curves and discussed in detail therein. The nature of relationship between compressive strength and B/FA is found to be non-linear for all the cases.
Figure 5.4 Effect of mix ratio on compressive strength of geomaterial with C/FA ratio at W/FA ratio 40% for (a) 7 days, (b) 14 days, (c) 28 days and (d) 56 days
Figure 5.5 Effect of mix ratio on compressive strength of geomaterial with C/FA ratio at W/FA ratio 50% for (a) 7 days, (b) 14 days, (c) 28 days and (d) 56 days
5.4 Effect of curing on compressive strength of geomaterial
Figures 5.6 and 5.7 represent the relationship between compressive strength with age of curing of specimens for W/FA ratios of 40% and 50% respectively. It is observed that the effect of curing decreases with increase in B/FA ratio. This may happen due to increase in volume of beads in mix proportion where the water absorption capacity of EPS material is almost negligible. Increase in beads content The relationship shows increase in value of compressive strength almost linearly upto 28 days curing period however, it decreases from 28 to 56 days. Effect of curing beyong 28 days is found to have very less increase in compressive strength.
The effect of increase in compressive strength is significant with increase in C/FA ratio and W/FA ratio. With increase in C/FA ratio from 10 to 20% almost double increase in value of compressive strength is observed for same configuration. Similarly, increase in value of W/FA ratio decreases the compressive strength. With nearly 10% increase in value of C/FA ratio decreases the compressive strength by 15 – 26% for the same configuration of B/FA ratio.
Therefore, it can be stated that all the three mix ratios affect significantly in terms of curing period on strength.
Figure 5.6 Effect curing period on compressive strength of geomaterial with C/FA ratio at W/FA ratio 40% for B/FA ratios (a) 0.5%, (b) 1.0%, (c) 1.5%, (d) 2.0 % and (e) 2.5%
Figure 5.7 Effect curing period on compressive strength of geomaterial with C/FA ratio at W/FA ratio 50% for B/FA ratios (a) 0.5%, (b) 1.0%, (c) 1.5%, (d) 2.0 % and (e) 2.5%
5.5 Failure pattern
The failure patterns of the lightweight geomaterial are also studied under compressive loading condition. It was observed that the failure patterns of test specimens were highly influenced by all the three mix ratios used for preparation of lightweight geomaterial.
As B/FA ratio increases the failure pattern of test specimen changes from brittle to ductile behavior. This can also be confirmed by stress-strain curves plotted for different test specimen. However, increase in C/FA ratio changes the failure pattern from ductile to brittle behavior. Most of the test specimen were failed along the diagonal of the cube. The ductile and brittle behavior of failure patterns are depicted in Figures 5.8 and 5.9 respectively.
Figure 5.8(a) Test specimen of geomaterial failed under compressive load (Ductile behavior)
Figure 5.8(b) Test specimen of geomaterial failed under compressive load
5.6 Stress-strain behavior
The data obtained from compressive strength test was also used to plot the stress-strain curve and to determine stiffness characteristics of lightweight geomaterial. With increase in C/FA ratio the test specimen becomes more brittle. The specimens of geomaterial failed within a strain range of 1 to 2%. The compressive strength and stress-strain behavior of geomaterial are affected by B/FA ratio. The compressive stress is decreased with increase in B/FA ratio for 7, 14, 28 and 56 days cured specimens. It can also be seen that the compressive strength and stress-strain behavior is significantly affected by W/FA ratio. With increasing W/FA ratio, the compressive strength as well as stiffness of EPGM decreased and the stress-strain curves become more ductile. Therefore, it can be stated that, all three mix ratios have significant effect on compressive strength and stiffness characteristics of geomaterial.
The stress-strain curves for different mix proportions for different curing periods are shown in Figures 5.9 and 5.10.
Figure 5.9 Stress-strain curves for different C/FA ratios for W/FA ratio 40%
Figure 5.10 Stress-strain curves for different C/FA ratios for W/FA ratio 50%
As discussed earlier, the specimen with B/FA as 0.5% have compressive strength values more than specimen without beads. This is due to the presence of highly compressible beads in suitable mix proportion where specimen carried higher load with stain 1.5% compared to specimen without beads which failed with less load having strain 1.0%. With little more strain value geomaterial having beads can solve specific purposes whenever required with higher compressive strength. Figures 5.11 (a) and (b) represents the nature of stress-strain curves observed for such condition.
Figure 5.11 Stress-strain curves for different B/FA ratios for W/FA ratio
(a) 40% and (b) 50%
5.7 Initial tangent modulus
Initial tangent modulus is an important property of lightweight geomaterial which gives an idea about the stiffness of material. The stiffness of geomaterial is determined by calculating initial tangent modulus as the slope of stress-strain curve from origin. This stiffness of geomaterial is highly influenced by C/FA ratio. Higher the compressive strength of test specimen higher is stiffness values. For the specimen tested for different curing period, the values of initial tangent modulus are found to be in the range of 112 -2800 MPa. The relationship between compressive strength and initial tangent modulus is well established by fitting a curve as shown in Figure 5.12. These values of initial tangent modulus are higher as compared with earlier developed geomaterial using EPS beads with nearly same density range.
Figure 5.12 Relationship between compressive strength and initial tangent modulus of geomaterial
The initial tangent modulus values of lightweight geomaterial are much higher as compared to values reported in earlier studies of lightweight geomaterial. The comparison between properties of lightweight geomaterial developed earlier (Liu, et al; 2006, Padade and Mandal 2014) and geomaterial developed in the present study is given in Table 5.1.
Table 5.1 Comparison of geomaterial properties with earlier developed products
Property Lightweight fill material Expanded polystyrene-based geomaterial with fly ash Lightweight geomaterial developed in present study
(Liu et al., 2006) (Padade andMandal,2014) Density
(kg/m3) 700 – 1100 725 – 1320 772 – 1361
Compressive strength (kPa) 100 – 510 158 – 3290 171- 8555
Initial tangent modulus (MPa) 79 – 555 51-500 112 -2800
The engineering properties of proposed expanded polystyrene based geomaterial are investigated through a laboratory experimental study. The lightweight geomaterial prepared with EPS beads, fly ash and cement using different mix ratios between beads to fly ash, cement to fly ash and water to fly ash. The effect of these mix ratios on density, compressive strength and initial tangent modulus of this geomaterial is presented. The following conclusions are drawn from the study and summarized hereunder:
The lightweight geomaterial developed in the present study reveals various properties and its application in various geotechnical engineering applications. The density of lightweight geomaterial decreases with increase in B/FA ratio and W/FA ratio. However, the effect of C/FA rati o is insignificant. Compressive strength of geomaterial decreases with increase in B/FA ratio and W/FA ratio and it increases with increase in C/FA ratio. Effect of curing beyong 28 days is found to have very less increase in compressive strength. Strength and stifness characteristics are well co-related in the study which gives an idea about the material and its application for specific purpose.
6.3 Limitations of the study
Some of the limitations of the present study are given hereunder:
Control of weight of beads is very important in the present study which may not be possible at every place. However, accurate weight is maintained while preparation of test specimen in this study.
Threshold value of the geomaterial developed in the present study cannot be specified.
6.4 Future Scope of work
The study can be repeated for cylindrical samples with varying aspect ratios.