One of the main issues associated with fly ash is the variation in the fineness of fly ash produced within a plant and between thermal power plants, due to the variation in the quality of coal used and the production technique adopted in which pelletization of fly ash becomes complex. In this paper, the influence of fineness of fly ash is studied by collecting typical samples of fly ash from two thermal power plants. Significance of the factors influencing the pelletization of fly ash was statistically determined by adopting 24 with eight run and 25 with sixteen run fractional factorial design for fly ash with fineness of 414 m2/kg and 257 m2/kg, respectively. Finer fly ash exhibits higher pelletization efficiency as compared to coarser fly ash. Addition of clay binders like bentonite and kaolinite enhanced the pelletization efficiency of coarser fly ash. Amount of binder content and moisture content varies with type of binder used (with fly ash having a fineness of 257 m2/kg), which is attributed to the difference in plasticity index. Addition of clay binder changes the relative influence of pelletization factors. © 2007 Elsevier Ltd. All rights reserved.

K. Ramamurthy

Department Of Civil Engineering

Aggregates

Binders

Clay

Coal

Electric power plants

Moisture

Pelletizing

Statistical methods

FINENESS

Pelletization

Thermal power plants

Fly ash

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Cement and Concrete Composites

Statistically designed experiments using Response Surface Methodology have been undertaken to identify the parameters influencing manufacturing process and properties of aggregate using coal pond ash (generated from bituminous and lignite coal sources). Based on the preliminary studies, Ca(OH)2 and borax have been identified as pelletization and strength enhancing admixture respectively. Pelletization efficiency of bituminous and lignite pond ash increased with an increase in binder and Ca(OH)2 dosage to 20-98% and 50-98% respectively, with proportionate quantity of water. Sintering has been used as a hardening method with temperature range of 900°C and 1100°C for a duration range of 45-120min. Phase composition and sintered microstructure of aggregate has been reported using X-ray diffraction and scanning electron microscopy respectively. The ten percent fines value of aggregate with clay binder was 5.5tonne as against a value of 4.5tonne with aggregate with bentonite binder. Among the binders studied, bentonite resulted in high volume utilization of pond ash, i.e. up to 88%. © 2014 Elsevier Ltd.

Materials and Design

Identification of admixture for pelletization and strength enhancement of sintered coal pond ash aggregate through statistically designed experiments

This paper explores the feasibility and the process of converting of pond ashes - a waste material into artificial aggregates - a value added product. As a first step, identification of the parameters influencing manufacture and properties of artificial aggregate with pond ash has been carried out. Pond ash of both bituminous and lignite type have been chosen to make aggregate through pelletization and cold-bonding. The parameters identified are moisture content, binder dosage, pelletization enhancer and strength enhancer dosage. The range of parameters are varied and the designed experimental runs are carried out by adopting statistical technique known as central composite design of Response Surface Methodology. The physical properties of aggregate like bulk density, water absorption and open porosity and the strength property of aggregate represented through 10% fines value have been determined for the influence of parameters thus identified. Microstructure and phase composition of aggregate are represented by SEM and XRD respectively. Ordinary Portland cement, locally available hydrated lime, and hardening admixture are used as binders at varying amounts from 10% to 20% by weight. Calcium hydroxide and sodium sulphate are used as pelletization and strength enhancing admixture respectively. It is observed that the dosage of binder, strength and pelletization enhancing admixture improved the properties of aggregate. The results indicated, potentially exposes a new avenue to convert pond ash - a waste material into a value added product. © 2013 Elsevier Ltd.

Identification of design parameters influencing manufacture and properties of cold-bonded pond ash aggregate

A comprehensive research has been conducted to explore the influence of sintering on the properties of fly ash aggregate containing clay binders (bentonite and kaolinite). Fly ash aggregate containing clay binders, have been subjected to various sintering temperatures at different durations of 700-1400 °C and 15-120 min, respectively. The variation in aggregate properties, viz strength, water absorption, density and shrinkage during sintering, have been determined and discussed. In addition to these, the uniformity of sintering and rate of water absorption of sintered aggregate were also determined. No significant changes in aggregate properties were observed for aggregate sintered up to 900 °C, due to the insufficient sintering temperature range. However, the aggregate properties substantially enhanced for temperature above 1000 °C, which is attributed to the activation of liquid phase sintering. For temperatures between 1000 and 1300 °C, the aggregate with bentonite shows significant increase in shrinkage (30 %), density (density ratio 0.70), higher ten percent fines value (TPFV) (6.13 tonne), reduction in porosity (35 %), and water absorption of 4 %. However, at 1400 °C, the aggregate properties degraded due to the decomposition of mineral phases in bentonite. For aggregates with kaolinite, highest TPFV of 8.5 tonne with lowest water absorption of 2 % have been observed at 1400 °C. The presence of a higher amount of interconnected pores for aggregates sintered between 700 and 1000 °C leads to a higher rate of water absorption and then reduces to 30 % for temperatures between 1200 and 1300 and 1200 to 1400 °C for bentonite and kaolinite aggregates, respectively. This reduction is due to the reduced interconnected pores. Duration of sintering has no impact on the aggregate properties for temperatures up to 800 and 1000 °C for aggregates with bentonite and kaolinite, respectively. However, between 1000 and 1400 °C, there has been considerable improvement in the aggregate properties for increasing duration up to 60 min. In comparison, during sintering, aggregates with bentonite possessed better properties for temperature less than 1000 °C, whereas aggregates with kaolinite exhibited superior properties between 1100 and 1400 °C. © 2012 Springer.

Journal of Material Cycles and Waste Management

Physical characteristics of sintered fly ash aggregate containing clay binders

Autogenous curing behavior of cold-bonded fly-ash-aggregate concrete for a range of cement and aggregate contents is studied by subjecting concrete to three different curing regimes, viz, mist curing, sealed condition and air curing. The moisture movement from the aggregate to concrete at various ages is estimated and correlated to the paste-aggregate proximity. The degree of hydration is evaluated through nonevaporable water content. Thermal gravimetric analysis (TGA) has been employed to identify hydration products with age of concrete. The results suggest that the degree of hydration and strength of cold-bonded aggregate concrete are almost insensitive to curing conditions. The autogenous curing of cold-bonded aggregate concrete could be effectively utilized with no variation in compressive strength or porosity as compared with mist curing, if it is properly covered to minimize the evaporation loss. © 2011 American Society of Civil Engineers.

Journal of Materials in Civil Engineering

Autogenous curing of cold-bonded fly-ash-aggregate concrete

Cold bonding facilitates production of aggregate with minimum energy consumption compared to the sintered aggregate, which requires a heat treatment in the range of 1000-1200 °C. The strengthening of pelletized bottom ash in cold bonding at ambient temperature is due to the formation of CSH gel during the hydration from the chemical reaction between CaO, water and the pozzolanic character of the bottom ash. Chemical activation is done using Na 2SO4 to enhance the strength of the cold-bonded aggregate by accelerating the pozzolanic reaction and formation of more ettringite. Experimental runs were designed using Central Composite Design and the properties of cold-bonded aggregate like bulk density, ten percent fines value (TPFV), porosity and water absorption were studied. It was observed that increase in binder and Na2SO4 dosages increased the strength and decreased the open porosity thereby reducing the water absorption. © 2010 Elsevier Ltd. All rights reserved.

Journal of Cleaner Production

Environmental friendly technology of cold-bonded bottom ash aggregate manufacture through chemical activation

A pelletization process is used to manufacture artificial lightweight coarse aggregate using fly ash. Pelletization depends on the size of particles and their distribution, the wettability of particles and moisture content, along with the process related parameters. A review indicates that only limited studies have been reported on the pelletization of fly ash aggregates. The influence of the following parameters has been studied: (i) speed of revolution of pelletizer disc, (ii) angle of pelletizer disc, (iii) moisture content, and (iv) duration of pelletization. Fractional factorial experiments using the concept of Taguchi's orthogonal array is used in this study, which uses an orthogonal array table to arrange multifactor experiments and uses statistical methods to analyze the experimental results. The relative influence of the factors above and their interaction effects on the strength, water absorption and size growth of fly ash aggregates are discussed. © 2005 Elsevier Ltd. All rights reserved.

Waste Management

Influence of pelletization process on the properties of fly ash aggregates

Sustained research and development work on the utilization of fly ash for various productive uses have been carried out in the past. In the construction industry, major attention has been devoted to the use of fly ash in concrete as a cement replacement. The production of artificial lightweight coarse aggregate using fly ash has potential for its large-scale utilization in the construction industry and this is an area that merits attention in many parts of the world, bearing in mind the rapid dwindling of sources of natural aggregates. As only limited details on manufacture and parameters influencing properties of sintered fly ash aggregates have been reported in the literature, a systematic study was undertaken. In this paper, the relative performance of three binders, viz., cement, lime and bentonite, on the properties of sintered fly ash aggregate is reported. The salient observations are (i) the characterization studies on sintered fly ash aggregates show that the properties of aggregates depend on the type of binder and its dosage, (ii) the significant improvement in strength and reduction in water absorption of sintered fly ash aggregate is observed when bentonite is added with fly ash, (iii) the binders used did not alter the chemical composition, while they influence the microstructure of the aggregate, which results in enhancement in the properties of aggregates. © 2005 Elsevier Ltd. All rights reserved.

Journal	Cement and Concrete Composites
ISSN	09589465
Open Access	No