Showing papers in "Cement and Concrete Research in 2005"

The coexistence of geopolymeric gel and calcium silicate hydrate at the early stage of alkaline activation

Abstract: Scanning electron microscopy was used to study the effects of the addition of ground granulated blast furnace slag (GGBFS) on the microstructure and mechanical properties of metakaolin (MK) based geopolymers. It was found that it is possible to have geopolymeric gel and calcium silicate hydrate (CSH) gel forming simultaneously within a single binder. The coexistence of these two phases is dependent on the alkalinity of the alkali activator and the MK / GGBFS mass ratio. It has been found that the formation of CSH gel together with the geopolymeric gel occurs only in a system at low alkalinity. In the presence of high concentrations of NaOH (> 7.5 M), the geopolymeric gel is the predominant phase formed with small calcium precipitates scattered within the binder. The coexistence of the two phases is not observed unless a substantial amount of a reactive calcium source is present initially. It is thought that voids and pores within the geopolymeric binder become filled with the CSH gel. This helps to bridge the gaps between the different hydrated phases and unreacted particles; thereby resulting in the observed increase in mechanical strength for these binders.

Composition and Microstructure of Alkali Activated Fly Ash Binder: Effect of the Activator

Abstract: The alkali activation of fly ashes is a chemical process by which the glassy component of these powdered materials is transformed into very well-compacted cement. In the present work the relationship between the mineralogical and microstructural characteristics of alkaline activated fly ash mortars (activated with NaOH, Na2CO3 and waterglass solutions) and its mechanical properties has been established. The results of the investigation show that in all cases (whatever the activator used) the main reaction product formed is an alkaline aluminosilicate gel, with low-ordered crystalline structure. This product is responsible for the excellent mechanical-cementitious properties of the activated fly ash. However the microstructure as well as the Si/Al and Na/Al ratios of the aluminosilicate gel change as a function of the activator type used in the system. As a secondary reaction product some zeolites are formed. The nature and composition of these zeolites also depend on the type of activator used.

Resistance of geopolymer materials to acid attack

Abstract: This article presents an investigation into durability of geopolymer materials manufactured using a class F fly ash (FA) and alkaline activators when exposed to 5% solutions of acetic and sulfuric acids. The main parameters studied were the evolution of weight, compressive strength, products of degradation and microstructural changes. The degradation was studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The performance of geopolymer materials when exposed to acid solutions was superior to ordinary Portland cement (OPC) paste. However, significant degradation of strength was observed in some geopolymer materials prepared with sodium silicate and with a mixture of sodium hydroxide and potassium hydroxide as activators. The deterioration observed was connected to depolymerisation of the aluminosilicate polymers in acidic media and formation of zeolites, which in some cases lead to a significant loss of strength. The best performance was observed in the geopolymer material prepared with sodium hydroxide and cured at elevated temperature, which was attributed to a more stable cross-linked aluminosilicate polymer structure formed in this material.

Mechanical Properties of Recycled Aggregate Concrete Under Uniaxial Loading

Abstract: In this paper, the compressive strength and the stress–strain curve (SSC) of recycled aggregate concrete (RAC) with different replacement percentages of recycled coarse aggregate (RCA) are investigated experimentally. Concrete specimens were fabricated and tested with different RCA replacement percentages of 0%, 30%, 50%, 70% and 100%, respectively. Uniaxial compression loading is applied in the experiments. Special attention of the analysis is devoted to the failure behaviour and the influences of the RCA contents on the compressive strength, the elastic modulus, the peak and the ultimate strains of RAC. Analytical expressions for the peak strain and the stress–strain relationship of RAC are given, which can be directly used in theoretical and numerical analysis as well as practical engineering design of RAC structures.

Geopolymeric materials prepared using Class F fly ash and elevated temperature curing

Abstract: This paper reports the results of the study of the influence of elevated temperature curing on phase composition, microstructure and strength development in geopolymer materials prepared using Class F fly ash and sodium silicate and sodium hydroxide solutions. In particular, the effect of storage at room temperature before the application of heat on strength development and phase composition was studied. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and SEM were utilised in this study. Long precuring at room temperature before application of heat was beneficial for strength development in all studied materials, as strength comparable to 1 month of curing at elevated temperature can develop in this case only after 24 h of heat curing. The main product of reaction in the geopolymeric materials was amorphous alkali aluminosilicate gel. However, in the case of sodium hydroxide activator in addition to it, traces of chabazite, Linde Type A, Na-P1 (gismondine) zeolites and hydroxysodalite were also present. The type of zeolite present and composition of aluminosilicate gel were dependent on the curing history.

The use of thermal analysis in assessing the effect of temperature on a cement paste

Abstract: Upon heating, the cement paste undergoes a continuous sequence of more or less irreversible decomposition reactions. This paper reports studies on a cement paste fired to various temperature regimes up to 800 °C in steps of 100 °C for a constant period of 24 h. This work has been carried out using thermal analysis technique to study the effect of temperature in the mineralogical composition of cement hydration products. The thermal decomposition of the cement paste is analysed with the thermogravimetric analysis (TGA) and the derivative thermogravimetric analysis (DTG) curves. Such techniques can be used to determine fire conditions and the consequent deterioration expected in the cement paste. Therefore, the aim of this work is to have a better knowledge of the reactions that take place in a cement paste during a fire and thus to be able to determine the temperature history of concrete after a fire exposure. The results show that even if the dehydroxylation reaction is reversible, the portlandite formed during the cooling has an onset temperature of decomposition lower than the original portlandite and can thus be considered as a tracer for determining the temperature history of concrete after a fire exposure.

Microstructural analysis of recycled aggregate concrete produced from two-stage mixing approach

Abstract: Owing to the shortage of space for land reclamation in Hong Kong, it is difficult to dispose of tons of masonry waste generated daily from construction activities. Adoption of recycled aggregate from concrete waste thus becomes a burning issue. The Hong Kong SAR Government has set-up a recycling plant in Tuen Mun Area 38 aiming at turning concrete waste into recycled aggregate with a practice note and specifications issued for controlling the quality of recycled aggregate. However, the use of recycled aggregate concrete to high-grade applications is rarely reported because of its poorer compressive strength and high variability in mechanical behavior. This paper proposes a new approach in mixing concrete, namely, “two-stage mixing approach (TSMA),” intended to improve the compressive strength for recycled aggregate concrete and hence lower its strength variability. Based upon experimental works, improvements in strength to recycled aggregate concrete were achieved. The effect can be attributable to the porous nature of the recycled aggregate, and hence, the premix process can fill up some pores and cracks, resulting in a denser concrete, an improved interfacial zone around recycled aggregate and thus a higher strength when compared with the traditional mixing approach.

Properties of concrete incorporating fine recycled aggregate

Abstract: The properties of concrete containing fine recycled aggregate are investigated. Recycled aggregate consisted of crushed concrete (CC) or crushed brick (CB) with particles less than 5 mm in diameter. The free water/cement ratio was kept constant for all mixes. The fine aggregate in concrete was replaced with 0%, 25%, 50% and 100% CC or CB. Generally, there is strength reduction of 15–30% for concrete containing CC. However, concrete incorporating up to 50% CB exhibits similar long-term strength to that of the control. Even at 100% replacement of fine aggregate with CB, the reduction in strength is only 10%. Beyond 28 days of curing, the rate of strength development in concrete containing either CC or CB is higher than that of the control indicating further cementing action in the presence of fine recycled aggregate. More shrinkage and expansion occur in concrete containing CC or CB.

Microstructure Development of Alkali-Activated Fly Ash Cement: A Descriptive Model

Abstract: The microscopic study of a set of alkali-activated and thermally cured fly ash samples enabled the authors to establish a descriptive model for the microstructural development of fly ash-based cementitious geopolymers. The morphology of most fly ash particles (perfect spheres) not only makes microscopic research highly productive but facilitates the formulation of hypothesis explaining the fly ash activation over time through a series of consecutive steps that can be successfully fitted to real situations.

Preliminary study on the water permeability and microstructure of concrete incorporating nano-SiO2

Abstract: Water permeability resistant behavior and microstructure of concrete with nano-SiO2 were experimentally studied. A water permeability test shows that, for concretes of similar 28-day strength, the incorporation of nano-SiO2 can improve the resistance of water penetration of concrete. An ESEM test reveals that the microstructure of concrete with nano-SiO2 is more uniform and compact than that of normal concrete. Mechanism about the effect of nano-SiO2 on concrete is described.

Durability of Geopolymer Materials in Sodium and Magnesium Sulfate Solutions

Abstract: This paper presents an investigation into the durability of geopolymer materials manufactured using class F fly ash and alkaline activators when exposed to a sulfate environment. Three tests were used to determine resistance of geopolymer materials. The tests involved immersions for a period of 5 months into 5% solutions of sodium sulfate and magnesium sulfate, and a solution of 5% sodium sulfate+5% magnesium sulfate. The evolution of weight, compressive strength, products of degradation and microstructural changes were studied. In the sodium sulfate solution, significant fluctuations of strength occurred with strength reduction 18% in the 8FASS material prepared with sodium silicate and 65% in the 8FAK material prepared with a mixture of sodium hydroxide and potassium hydroxide as activators, while 4% strength increase was measured in the 8FA specimens activated by sodium hydroxide. In the magnesium sulfate solution, 12% and 35% strength increase was measured in the 8FA and 8FAK specimens, respectively; and 24% strength decline was measured in the 8FASS samples. The most significant deterioration was observed in the sodium sulfate solution and it appeared to be connected to migration of alkalies into solution. In the magnesium sulfate solution, migration of alkalies into the solution and diffusion of magnesium and calcium to the subsurface areas was observed in the specimens prepared using sodium silicate and a mixture of sodium and potassium hydroxides as activators. The least strength changes were found in the solution of 5% sodium sulfate+5% magnesium sulfate. The material prepared using sodium hydroxide had the best performance, which was attributed to its stable cross-linked aluminosilicate polymer structure.

Investigation of blended cement hydration by isothermal calorimetry and thermal analysis

Abstract: Hydration of portland cement pastes containing three types of mineral additive; fly ash, ground-granulated slag, and silica fume was investigated using differential thermal analysis, thermogravimetric analysis (DTA/TGA) and isothermal calorimetry. It was shown that the chemically bound water obtained using DTA/TGA was proportional to heat of hydration and could be used as a measure of hydration. The weight loss due to Ca(OH) 2 decomposition of hydration products by DTA/TGA could be used to quantify the pozzolan reaction. A new method based on the composition of a hydrating cement was proposed and used to determine the degree of hydration of blended cements and the degree of pozzolan reaction. The results obtained suggested that the reactions of blended cements were slower than portland cement, and that silica fume reacted earlier than fly ash and slag.

Characteristics and pozzolanic reactivity of glass powders

Abstract: This paper deals with the morphology, fineness and pozzolanic activity of four glass powders: one (GP-fine) from the screening of crushed waste glasses, one (GP-dust) from a dust collector for the glass crushing process and two (GP-4000 and GP-6000) from further grinding of the powder from the dust collector in a ball mill. GP-fine and GP-dust consist mainly of large flaky particles, while GP-4000 and GP-6000 consist mainly of small angular particles. The finenesses of these glass powders are measured by particle size distribution and Blaine fineness method. For a similar particle size distribution, ground glass powder has a higher Blaine specific surface area than Portland cement due to the angular morphology of glass particles. Finely ground glass powders exhibited very high pozzolanic activity. The finer the glass powder is, the higher its pozzolanic reactivity is. An increase in curing temperature accelerates the activation of pozzolanic reactivity of both glass powder and coal fly ash in terms of strength development rate. Mortar cube strength results (ASTM C109) indicated that curing temperature has a greater influence on the glass powder than on fly ash. The rapid mortar bar expansion test (ASTM C1260) results indicate that the replacement of Portland cement with ground glass powder also reduces the expansion due to alkali–aggregate reactions, although it is not as effective as coal fly ash.

Strength properties of nylon- and polypropylene-fiber-reinforced concretes

Abstract: The strength potential of nylon-fiber-reinforced concrete was investigated versus that of the polypropylene-fiber-reinforced concrete, at a fiber content of 0.6 kg/m 3 . The compressive and splitting tensile strengths and modulus of rupture (MOR) of the nylon fiber concrete improved by 6.3%, 6.7%, and 4.3%, respectively, over those of the polypropylene fiber concrete. On the impact resistance, the first-crack and failure strengths and the percentage increase in the postfirst-crack blows improved more for the nylon fiber concrete than for its polypropylene counterpart. In addition, the shrinkage crack reduction potential also improved more for the nylon-fiber-reinforced mortar. The above-listed improvements stemmed from the nylon fibers registering a higher tensile strength and possibly due to its better distribution in concrete.

Self-Compacting Concrete: Theoretical and Experimental Study

Abstract: This paper addresses experiments and theories on Self-Compacting Concrete. First, the features of ‘‘Japanese and Chinese Methods’’ are discussed, in which the packing of sand and gravel plays a major role. Here, the grading and packing of all solids in the concrete mix serves as a basis for the development of new concrete mixes. Mixes, consisting of slag blended cement, gravel (4–16 mm), three types of sand (0–1, 0–2 and 0–4 mm) and a polycarboxylic ether type superplasticizer, were developed. These mixes are extensively tested, both in fresh and hardened states, and meet all practical and technical requirements such as medium strength and low cost. It follows that the particle size distribution of all solids in the mix should follow the grading line as presented by Andreasen and Andersen. Furthermore, the packing behaviour of the powders (cement, fly ash, stone powder) and aggregates (three sands and gravel) used are analysed in detail. It follows that their loosely piled void fraction are reduced to the same extent (23%) upon vibration (aggregates) or mixing with water (powders). Finally, the paste lines of the powders are used to derive a linear relation between the deformation coefficient and the product of Blaine value and particle density.

Effects of Waste PET Bottles Aggregate on the Properties of Concrete

Abstract: This paper investigates the surface microstructure of waste polyethylene terephthalate (PET) bottles lightweight aggregate (WPLA) to examine the effect of granulated blast-furnace slag (GBFS) on WPLA. The WPLA was made from the waste PET bottles and GBFS, and experimental tests were conducted on compressive strength, splitting tensile strength, modulus of elasticity, slump, and density of waste PET bottles lightweight aggregate concrete (WPLAC). The 28-day compressive strength of WPLAC with the replacement ratio of 75% reduces about 33% compared to the control concrete in the water–cement ratio of 45%. The density of WPLAC varies from 1940 to 2260 kg/m 3 by the influence of WPLA. The structural efficiency of WPLAC decreases as the replacement ratio increases. The workability of concrete with 75% WPLA improves about 123% compared to that of the normal concrete in the water–cement ratio of 53%. The adhered GBFS is able to strengthen the surface of WPLA and to narrow the transition zone owing to the reaction with calcium hydroxide.

Mechanisms of Air Entrainment in Concrete

Abstract: The advent of air-entraining agents is probably one of the most important technological advances in construction in the last century. It has been widely used to improve the freeze–thaw resistance of concrete, and to a lesser extent, the workability of concrete. Despite the overall successful application of air-entraining agents in concrete, problems in field concrete are not uncommon. The ability to consistently obtain target air-void systems in concrete is not trivial, and changes in raw materials, processing, or construction methods may significantly impact air entrainment. To address these potential problems in the field, a sound understanding of the mechanisms of air entrainment is essential. This paper attempts to synthesize available literature and field experience and provide a framework for understanding the fundamental aspects of air entrainment in concrete. Various parameters and influencing factors, such as concrete temperature, the physical and chemical characteristics of constituent materials, and mixing and placing techniques, are discussed.

Comparison of Methods for Evaluating Bond Strength Between Concrete Substrate and Repair Materials

Abstract: This investigation was aimed at studying the effect of test methods on bond strength between concrete substrate and repair material. Four test methods with cementitious or modified-cementitious repair materials, and two surface roughnesses were studied. The methods used were pull-off, slant shear, splitting prism and a new direct shear named Bi-Surface shear test. While the coefficient of variation (COV) for each type of test was acceptable, the bond strengths from some tests were up to eight times larger than those obtained from others. It is imperative that the bond tests be selected such that they represent the state of stress the structure is subjected to in the field. The new test method was easy to carry out and had reasonable results and can be developed by further investigations.

Use of microorganism to improve the strength of cement mortar

Abstract: This study describes a method of strength improvement of cement–sand mortar by the microbiologically induced mineral precipitation. A thermophilic anaerobic microorganism is incorporated at different cell concentrations with the mixing water. The study showed that a 25% increase in 28 day compressive strength of cement mortar was achieved with the addition of about 105 cell/ml of mixing water. The strength improvement is due to growth of filler material within the pores of the cement–sand matrix as shown by the scanning electron microscopy. The modification in pore size distribution and total pore volume of cement–sand mortar due to such growth is also noted. E. coli microorganisms were also used in the cement mortar for comparison, but no improvement in strength was observed.

Modeling the linear elastic properties of Portland cement paste

Abstract: The linear elastic moduli of cement paste are key parameters, along with the cement paste compressive and tensile strengths, for characterizing the mechanical response of mortar and concrete. Predicting these moduli is difficult, as these materials are random, complex, multi-scale composites. This paper describes how finite element procedures combined with knowledge of individual phase moduli are used, in combination with a cement paste microstructure development model, to quantitatively predict elastic moduli as a function of degree of hydration, as measured by loss on ignition. Comparison between model predictions and experimental results are good for degrees of hydration of 50% or greater, for a range of water : cement ratios. At early ages, the resolution of the typical 1003 digital microstructure is inadequate to give accurate results for the tenuous cement paste microstructure that exists at low degrees of hydration. Elastic computations were made on higher resolution microstructures, up to 4003, and compared to early age elastic moduli data. Increasing agreement with experiment was seen as the resolution increased, even when ignoring possible viscoelastic effects.

From mini-cone test to Abrams cone test: measurement of cement-based materials yield stress using slump tests

Abstract: Stoppage tests in civil engineering consists in measuring the shape of a fresh material deposit after flow occurred. This measured geometrical value (slump, spread) is linked to the plastic yield value of these yield stress materials. The most famous example is the Abrams cone for concrete. In this work, the flow induced by a smaller cone test for cement pastes and grouts is studied. In a first part, the spread is theoretically linked to the plastic yield value. Experimental results on several cement pastes validate the obtained relation but also shows the necessity to take in account the surface tension effects for low yield stress materials. The modified relation allows the prediction of the plastic yield value from the measured spread. The proposed method is then applied to the Abrams cone and fresh concrete. It is demonstrated that it is only suitable for high slumps (>20 cm).

Rheological Properties of Cementitious Materials Containing Mineral Admixtures

Abstract: The rheological properties of cementitious materials containing fine particles, such as mineral admixtures (MA), were investigated using a Rotovisco RT 20 rheometer (Haake) with a cylindrical spindle. The mineral admixtures were finely ground blast furnace slag, fly ash and silica fume. The cementitious materials were designed as one, two and three components systems by replacement of ordinary portland cement (OPC) with these mineral admixtures. The rheological properties of one-component system (OPC) were improved with increasing the dosage of PNS-based superplasticizer. For two-components systems, yield stress and plastic viscosity decreased with replacing OPC with blast furnace slag (BFS) and fly ash (FA). In the case of OPC-silica fume (SF) system, yield stress and plastic viscosity steeply increased with increasing SF. For three components systems, both OPC-BFS-SF and OPC-FA-SF systems, the rheological properties improved, compared with the sample with SF. In the two and three components systems, the rheological properties of samples containing BFS improved much more than with FA replacement alone.

Hydration of fly ash cement

Abstract: Fly ash, a waste product of coal-fired power plants, can be used as a component of blended cement. Fly ash use results in a low heat of hydration, development of fluidity, and suppression of alkali-aggregate reaction; however, fly ash cement tends to be vulnerable to carbonation. This article reports on a study of the hydration of fly ash cement in which the influences of the glass content and the basicity of the glass phase on the hydration of fly ash cement were clarified and hydration over a long curing time was characterized. Two kinds of fly ash were used, with different glass content: one with 38.2% and another with 76.6%. The hydration ratio of fly ash was increased by increasing the glass content in fly ash in the specimens cured for 270 days. The results show that when the glass content of fly ash is low, the basicity of the glass phase tends to decrease. However, at an age of 360 days, the reaction ratios of fly ash show almost identical values with different glass contents. Fly ash also affected the hydration of cement clinker minerals in fly ash cement. For example, while the hydration of alite was accelerated, that of belite was retarded at a late stage. The authors conclude that, regardless of glass content and composition, fly ash in cement paste cured at 20 deg C did not react in any specimens until 7 days, so the glass content and the composition of fly ash do not need to be taken into consideration for the heat liberation of initial hydration, which is important for mass concrete.

Influence of Silica Fume on the Tensile Strength of Concrete

Abstract: The present paper is directed towards developing a better understanding on the isolated contribution of silica fume on the tensile strengths of high-performance concrete (HPC). Extensive experimentation was carried out over water–binder ratios ranging from 0.26 to 0.42 and silica fume–binder ratios from 0.0 to 0.3. For all the mixes, compressive, flexural and split tensile strengths were determined at 28 days. The compressive, as well as the tensile, strengths increased with silica fume incorporation, and the results indicate that the optimum replacement percentage is not a constant one but depends on the water–cementitious material (w/cm) ratio of the mix. Compared with split tensile strengths, flexural strengths have exhibited greater improvements. Based on the test results, relationships between the 28-day flexural and split tensile strengths with the compressive strength of silica fume concrete have been developed using statistical methods.

Effect of Superplasticizer and Shrinkage-Reducing Admixtures on Alkali-Activated Slag Pastes and Mortars

Abstract: This paper shows how several superplasticizers (polycarboxylates, vinyl copolymers, melamine and naphthalene-based) and shrinkage-reducing (polypropylenglycol derivatives) admixtures affect the mechanical and rheological properties and setting times of alkali-activated slag pastes and mortars. Two activator solutions, waterglass and NaOH, were used, along with two concentrations—4% and 5% of Na 2 O by mass of slag. All admixtures, with the exception of the naphthalene-based product, lost their fluidifying properties in mortars activated with NaOH as a result of the changes in their chemical structures in high alkaline media. The difference in the behaviour of these admixtures when ordinary Portland cement is used as a binder is also discussed in this paper.

Synthesis and characterisation of magnesium silicate hydrate gels

Abstract: Magnesium silicate hydrate gels (M-S-H) have been prepared by precipitation. The range of gel compositions lie between Mg/Si molar ratios 0.67–1.0. The gels were subject to short cure, approximately 24 h at approximately 22 °C and longer cure, 180 days at 85 °C, following which they were characterised by XRD, FT-IR and solid-state 29 Si NMR. Ageing at longer times and higher temperatures somewhat improves the local ordering. The nature of the partially ordered structures is related to those of M-S-H mineral phases. The structures and compositions of M-S-H gels differ from those of C-S-H gels and partly on that account, C-S-H gels contain little magnesium while M-S-H gels in blended cements coexist with C-S-H but contain little calcium.

Steady and transient flow behaviour of fresh cement pastes

Abstract: Fresh cement pastes behave as non-Newtonian viscous fluids. During steady flow, their apparent viscosity depends on the applied strain rate. During transient flow, the apparent viscosity is a function of time. In this work, a thixotropic model is presented. Its four parameters are identified experimentally for a tested cement paste using coaxial viscometer test. Viscometer flow simulations are then carried out. The model proves to be able to predict the trends of the fresh behaviour of cement pastes in various flow situations.

Contribution Of Hybrid Fibers On The Properties Of The High-Strength Lightweight Concrete Having Good Workability

Abstract: The contribution of hybrid fibers to the workability, mechanical and shrinkage properties of lightweight concrete (LWC) with high strength and workability was investigated. The results show that adding fiber to the lightweight concrete mixture greatly reduces the sedimentation of aggregates during mixing and improves the uniformity of the mix; however, the slump value is reduced. Compared with single type of fibers, hybrid fibers significantly improve the mechanical properties and brittleness of lightweight concrete, and restrain the long-term shrinkage.

Cement Hydration In The Presence Of High Filler Contents

Abstract: To realise self-compacting concrete, high filler contents are often used, and in order to avoid problems with excessive heat development during hardening, inert filler materials can be used. In this research two different filler types, limestone and quartzite, are considered in combination with different Portland cements. Although the filler material has often been considered to be inert, experimental results show that it does influence the hydration processes. On the one hand the reaction rate is influenced due to a modified nucleation possibility, and on the other hand, in some cases, the reaction mechanisms are altered, with a new hydration peak occurring. Based on isothermal conduction calorimetry on different cement-filler systems, an existing hydration model for blended cement is modified for these systems. Within the degree of hydration based hydration model, the cement/powder ratio seems to be an important parameter for the cement-filler systems. The model accurately predicts the heat of hydration during the hardening process.

Properties of lightweight expanded polystyrene aggregate concretes containing fly ash

Abstract: Lightweight concretes can be produced by replacing the normal aggregates in concrete or mortar either partially or fully, depending upon the requirements of density and strength levels. The present study covers the use of expanded polystyrene (EPS) beads as lightweight aggregate, both in concrete and mortar. The main aim of this programme is to study the mechanical properties of EPS concretes containing fly ash and compare the results with these in literature on concretes containing OPC alone as the binder. The effects of EPS aggregate on the green and hardened state characteristics of concretes containing fly ash were evaluated. The compressive strength of the EPS concretes containing fly ash show a continuous gain even up to 90 days, unlike that reported for OPC in literature. It was also found that the failure of these concretes both in compression and split tension was gradual as was observed earlier for the concretes containing plastic shredded aggregates. The stress–strain relations and the corresponding elastic modulus were also investigated.