Fly Ash Lightweight Aggregate Research Articles

Pelletized fly ash lightweight aggregate concrete: A promising material

Pelletized fly ash lightweight aggregate concrete: A promising material

Optimization of properties of fly ash aggregates for high-strength lightweight concrete production

The optimization of properties of lightweight fly ash aggregates for suitability in high-strength lightweight fly ash concrete production was investigated using response surface methodology (RSM). Design-Expert software was used to establish the design matrix and to analyze the experimental data. The relationships between the sintering parameters (temperature, binder content and binder type) and experimentally obtained three responses (specific gravity, water absorption and crushing strength) were established. Also, the optimization capabilities in Design-Expert software were used to optimize the sintering process. Historical data design technique under RSM was performed to optimize the input parameter interactions which showed the best conditions for preparation of fly ash pellets. According to the obtained results, the developed models are statistically accurate and can be used for further analysis. The experimental values agreed with the predicted ones, thus indicating suitability of the model employed and the success of RSM in optimizing the sintering conditions.

Strength and elastic properties of structural lightweight concretes

The study presents the influence of characteristics of four aggregate types (two sintered lightweight fly ash aggregates, cold-bonded lightweight fly ash aggregate and normalweight crushed limestone aggregate) on the strength and elastic properties of concrete mixtures. Different models were also used in order to predict the strength and modulus of elasticity values of concretes. The results of this study revealed the achievement of manufacturing high-strength air-entrained lightweight aggregate concretes using sintered and cold-bonded fly ash aggregates. In order to reach target slump and air content, less amount of chemical admixtures was used in lightweight concretes than in normal-weight concrete, leading to reduction in production cost. The use of lightweight aggregates (LWA) instead of normalweight aggregates in concrete production slightly decreased the strength. The models given by codes, standards and software and equation derived in this study gave close estimated values to the experimental results.

On the Testing Strength Curve of Clay and Fly Ash Lightweight Aggregate Concrete by Rebound Method

Testing strength curve of 1400~1900 density grade and LC15~LC50 strength grade lightweight aggregate concrete by rebound method was studied systematically. Results show that, adopting the Chinese national unified testing strength curve, specified by JGJ/T 23-2001 of Technical Specification for Detection of Concrete Compressive Strength by Rebound Method, to detect the lightweight aggregate concrete strength, the strength scaled value obtained is higher, which would reduce the structure assurance coefficient. The special testing strength curve of 1400~1900 density grade and LC15~LC50 strength grade lightweight aggregate concrete were built, and the computed mean relative error and relative standard error are less than 12.0% and 14.0% respectively, meet the error requirement of special curve that specified by JGJ/T 23-2001 of Technical Specification for Detection of Concrete Compressive Strength by Rebound Method.

Durability of lightweight concretes with lightweight fly ash aggregates

This paper presents the effects of aggregate properties such as strength, porosity, water absorption, bulk density and specific gravity on the strength and durability of lightweight fly ash aggregate concrete (LWAC). The influence of properties of four aggregates (sintered lightweight fly ash aggregates, cold-bonded lightweight fly ash aggregate and normalweight aggregate) on mechanical and durability properties of concrete is discussed. Experimental results revealed that durable high-strength air-entrained lightweight concretes could be produced using sintered or cold-bonded lightweight fly ash aggregates, having comparable performance with the normalweight concretes. The use of lightweight aggregates (LWA) instead of normalweight aggregates in concrete production decreased the strength and stiffness due to the higher porosity and lower strength of the aggregate included in the concrete. However, permeability of sintered fly ash aggregate lightweight concretes was comparable and slightly lower than normalweight concrete whereas permeability of cold-bonded fly ash lightweight concrete was greater than the others. All concretes had a durability factor greater than 85, which met the requirements by showing quite perfect resistance to freeze–thaw.

Characteristics of lightweight fly ash aggregates produced with different binders and heat treatments

This study investigated characteristics of lightweight fly ash aggregates with various binders produced by different heat treatments. Different amounts of binders were mixed with fly ash and put into the pelletization disc. Bentonite and glass powder were used as binders at 0%, 5% and 10%, individually, and in combination at 7.5% each, by weight of fly ash. The pellets thus produced were then sintered at temperatures of 1100, 1150 and 1200 °C. Specific gravity, water absorption, porosity and crushing strength of these aggregates were determined. The properties and microstructure of aggregates were modified by different sintering agents and heat treatments. The strength and specific gravity of all aggregates decreased with increasing the binder content (disregarding binder type) at the highest temperature. Aggregates with low water absorption and high strength and specific gravity can be attributed to the dense structure with discontinuous and small size pores. Increasing binder content reduced water absorption at all temperatures.

Effects of lightweight fly ash aggregate properties on the behavior of lightweight concretes

Influence of different lightweight fly ash aggregates on the behavior of concrete mixtures was discussed. The performance characteristics of lightweight concretes (LWCs) and normalweight concrete (NWC) were investigated through compressive strength, modulus of elasticity and splitting tensile strength representing the mechanical behavior; through rapid chloride permeability representing the transport properties and through rapid freezing and thawing cycling representing the durability of concrete. In order to investigate the aggregate–cement paste interfacial transition zone (ITZ), SEM observations were performed. Regression and graphical analysis of the experimental data obtained were also performed. An increase in compressive strength was observed with the increase in oven-dry density. The ratios of splitting tensile strength to compressive strength of lightweight aggregate concretes were found to be similar to that of normalweight concrete. All the 28- and 56-day concrete specimens had a durability factor greater than 85 and 90, respectively, which met the requirement for freezing and thawing durability.

Fly ash lightweight aggregates in high performance concrete

Lightweight aggregates have been manufactured by sintering fly ash and crushing the product into suitable sizes. These aggregates possess unique characteristics that make them suitable for high strength and high performance concrete. Concrete produced using these aggregates is around 22% lighter and at the same time 20% stronger than normal weight aggregate concrete. Drying shrinkage is around 33% less than that of normal weight concrete. Moreover, the aggregates possess high durability characteristics required in high performance structures. The importance of the new aggregates lies mostly in the fact that superior qualities are achieved without having to increase the cement content. Thus it is possible to reduce the amount of cement by as much as 20% without affecting the required strength. Weight reduction may reduce precast concrete transportation costs as well as provide slender and spacious construction. Utilising fly ash to produce quality aggregates should yield significant environmental benefits.

Properties of concrete made with alkali-activated fly ash lightweight aggregate (AFLA)

Abstract An experiment was performed to investigate the properties of the hardened paste of fly ash by alkali activation and to determine the possible use of the paste in the production of lightweight aggregates. The highest compressive strength was 33.9 MPa, for paste with 10% NaOH, 15% sodium silicate, and 5% MnO 2 , cured at room temperature after 24 h of moisture curing at 50 °C. The hardened paste of fly ash was granulated to produce AFLA (alkali-activated fly ash lightweight aggregate). AFLA exhibited specific gravity (SSD, OD), water absorption, unit weight, and solid volume percentages of 1.85 (SSD), 1.66 (OD), 11.8%, 972 kg/m 3 , and 58.6%, respectively. The results of the heavy metals leaching test met US EPA regulations. The concrete using AFLA exhibited a compressive strength of 26.47 MPa and good freeze–thaw resistance at 6.0% entrained air content.

Effects of fly ash properties on characteristics of cold-bonded fly ash lightweight aggregates

The study presented herein provides a new insight into the effects of physical and chemical properties of the fly ash on the characteristics of the cold-bonded fly ash lightweight aggregates. LWAs were manufactured through the cold-bonding pelletization of two fly ashes differing in their physical and chemical properties. Moreover, one type of the LWAs was surface treated by water glass. The produced fly ash aggregates were then examined by means of ESEM micrograph, EDX spectrum, and XRD pattern to resolve the microstructural and the mineralogical characteristics of the LWAs. The findings of the study revealed that the fly ash with higher specific surface and with lower CaO content yielded higher strength LWAs. Furthermore, the surface treatment with water glass provided a marked increase in the aggregate strength and a reduction in the water absorption. The LWCs made with such LWAs had a compressive strength of as high as 60 MPa.

Effects of cold-bonded fly ash aggregate properties on the shrinkage cracking of lightweight concretes

Abstract This paper presents an experimental study on the restrained shrinkage cracking of the lightweight concretes made with cold-bonded fly ash lightweight aggregates. Two types of fly ash having different physical and chemical properties were utilized in the production of lightweight aggregates with different strengths. Afterwards, lower strength aggregates were also surface treated by water glass and cement–silica fume slurry to improve physical and mechanical properties of the particles. Therefore, a total of eight concrete mixtures were designed and cast at 0.35 and 0.55 water–cement ratios using four types of lightweight coarse aggregates differing in their surface texture, density, water absorption, and strength. Ring type specimens were used for restrained shrinkage cracking test. Free shrinkage, creep, weight loss, compressive and splitting tensile strengths, and modulus of elasticity of the concretes were also investigated. Results indicated that improvement in the lightweight aggregate properties extended the cracking time of the concretes resulting in finer cracks associated with the lower free shrinkage. Moreover, there was a marked increase in the compressive and splitting tensile strengths, and the modulus of elasticity.

Physical, mechanical and microscopic characterization of cold bonded fly ash lightweight aggregates

This study presents the results of the different tests carried out on fly ash lightweight aggregates produced with three different kinds of binders: Lime, Portland cement and Pozzolan Portland cement. The elaboration process used for the aggregates consisted in an agglomeration system by agitation under cold bonded hardening conditions. The tests carried out were a physical characterization of the aggregates, the determination of mechanical properties with a crushing test and, finally, the study of the microstructure of the aggregates with scanning electron microscopy (SEM) and dispersive energy X ray (EDX). From the point of view of mechanical strength, the results indicate that the best kind of aggregate is the one made with a 5% Pozzolan Portland cement. This result was confirmed by the microstructure analysis, which shows that this kind of aggregate presents the highest hydration speed.

Some characteristics of high strength fiber reinforced lightweight aggregate concrete

The effect of polypropylene and steel fibers on high strength lightweight aggregate concrete is investigated. Sintered fly ash aggregates were used in the lightweight concrete; the fines were partially replaced by fly ash. The effects on compressive strength, indirect tensile strength, modulus of rupture, modulus of elasticity, stress–strain relationship and compression toughness are reported. Compared to plain sintered fly ash lightweight aggregate concrete, polypropylene fiber addition at 0.56% by volume of the concrete, caused a 90% increase in the indirect tensile strength and a 20% increase in the modulus of rupture. Polypropylene fiber addition did not significantly affect the other mechanical properties that were investigated. Steel fibers at 1.7% by volume of the concrete caused an increase in the indirect tensile strength by about 118% and an increase in the modulus of rupture by about 80%. Steel fiber reinforcement also caused a small decrease in the modulus of elasticity and changed the shape of the stress–strain relationship to become more curvilinear. A large increase in the compression toughness was recorded. This indicated a significant gain in ductility when steel fiber reinforcement is used.

Techno-commercial perspective study for sintered fly ash light-weight aggregates in India

Enhanced construction activities, shortage of conventional building materials and abundantly available industrial wastes have promoted the development of new building materials. Annual production of approx. 50 million tonnes of fly ash in India has still limited applications, the large bulk quantity of which remains abandoned as waste. Production of sintered fly ash aggregates has the unique possibility for bulk utilization of fly ash. A techno-commercial feasibility study was undertaken on the production of the light-weight aggregates from fly ash. This paper describes the production method, pilot plant investigations, process engineering of a demonstrative unit, major plant and equipment specifications, cost-economics, etc. The prospects for setting up a commercial unit in the state of West Bengal in the proximity of thermal power plants have been observed to be significantly potential.

97/03781 Effect of lightweight fly ash aggregate microstructure on the strength of concretes

The structure and properties of sintered fly ash lightweight aggregate was modified by heat and polymer treatments to obtain aggregates different in their strength, absorption and pozzolanic activity. These properties of the aggregates were accounted for by changes in their microstructure. The strength of concretes of equal effective water/cement ratio prepared from these aggregates was determined at different ages to resolve the influence of the aggregate properties. It was shown that the strength of the concrete could not be accounted for by the strength of the aggregates only, and it is suggested that the absorption and pozzolanic activity of the aggregates can have an influence on the strength developed.

Effect of lightweight fly ash aggregate microstructure on the strength of concretes

The structure and properties of sintered fly ash lightweight aggregate was modified by heat and polymer treatments to obtain aggregates different in their strength, absorption and pozzolanic activity. These properties of the aggregates were accounted for by changes in their microstructure. The strength of concretes of equal effective water cement ratio prepared from these aggregates was determined at different ages to resolve the influence of the aggregate properties. It was shown that the strength of the concrete could not be accounted for by the strength of the aggregates only, and it is suggested that the absorption and pozzolanic activity of the aggregates can have an influence on the strength developed.

Interfacial interactions in lightweight aggregate concretes and their influence on the concrete strength

The interactions between sintered fly ash lightweight aggregates and the matrix in portland cement concretes was studied to resolve factors other than aggregate strength which influence the concrete strength. Aggregates of variable properties were produced and concretes of equal effective water cement ratio were prepared and tested for strength and microstructure. It was found that differences in concrete strength could not always be accounted for by differences in the aggregate strength. These trends could be related to physical and chemical interfacial processes, which have an influence on the overall strength beyond that of the aggregate strength. The physical process identified was densification of the interfacial transition zone due to absorption of the aggregates; this process has considerable influence already at early age. The chemical processes were associated with pozzolanic activity of the aggregate and deposition of CH in the pores in the shell of the aggregate; these processes became effective only at later age, beyond 28 days. The enhancement in strength due to these influences ranged between 20 and 40%. Such influences should be taken into account when predicting the concrete strength or in the design of lightweight aggregate of optimal properties.

Massive use of pulverised fuel ash in concrete for the construction of a U.K. power station

This paper describes the incorporation and benefits of pulverised fuel ash (PFA) in nearly 620,000 m 2 of concrete used in the construction of the U.K.'s first commercial pressurised light water nuclear reactor power station, Sizewell B, Suffolk. Overall nearly 100,000 t of PFA, 1300 t of sintered fly ash lightweight aggregate, and nearly 137,000 t of Ordinary Portland Cement (OPC) were used in the works. Generally in the construction of the main power station buildings, structural concrete with a characteristic strength of 45 N/mm 2 was placed and included fly ash as 40% of the cementitious component. Also, concrete with fly ash as 50% of the cementitious component was placed as mass fill. The programme of research is reported, including sulphate resistance, heat of hydration, elastic properties, alkali-silica reaction, and long-term strength test results. Test and field results are presented and discussed. Strict quality assurance procedures were enforced and statistical summaries are offered to give an insight into the quality of control exercised. Test work and long-term results are also outlined.