Use of zeolite, coal bottom ash and fly ash as replacement materials in cement production

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Abstract

In this research, the effects of zeolite, coal bottom ash and fly ash as Portland cement replacement materials on the properties of cement are investigated through three different combinations of tests. These materials are substituted for Portland cement in different proportions, and physical properties such as setting time, volume expansion, compressive strength and water consistency of the mortar are determined. Then, these physical properties are compared with those of PC 42.5. The results showed that replacement materials have some effects on the mechanical properties of the cement. The inclusion of zeolite up to the level of 15% resulted in an increase in compressive strength at early ages, but resulted in a decrease in compressive strength when used in combination with fly ash. Also, setting time was decreased when zeolite was substituted. The results obtained were compared with Turkish Standards (TS), and it was found that they are above the minimum requirements.

Introduction

In recent studies, various types of materials such as silica fumes, fly ash and coal bottom ash have been investigated as Portland cement replacement materials [1], [2], [3]. Their substitution in Portland cement has been an interesting subject for research due to environmental and technical reasons. Clearly, different substitution materials will have different effects on the properties of the cement due to their chemical, physical and mineralogical characteristics [4], [5].

The previous research has concluded that fly ash lowers the early heat of hydration and gives better durability compared to plain Portland cement due to alkali–silica reaction [6]. Low-quality fly ash is adequate for cement mixes because it has sufficient resistance to sulfate corrosion [7]. Addition of alkali-activated fly ash to the blended cement mixes improves the mechanical strength of the concrete [8]. Compressive strength of the concrete decreases with increasing silica, alumina and iron(III) oxide content [9]. With adequate grinding, coal bottom ash with pozzolanic activity can be used as a replacement material in Portland cement production [10].

Natural zeolite contains large quantities of reactive SiO2 and Al2O3[11]. Similar to other pozzolanic materials such as silica fumes and fly ash, zeolite substitution can improve the strength of concrete by the pozzolanic reaction with Ca(OH)2. In general, natural zeolite, like other pozzolanic materials, contributes to the strength of concrete better than the strength of cement [12]. Natural zeolite also prevents the undesirable expansion due to alkali–aggregate reaction. In this study, the physical properties of zeolite (Z), coal bottom ash (BA) and fly ash (FA) and their effects on the mechanical properties of cement were examined. The objective of this research is to compare the chemical and physical properties of the cement mixes.

Section snippets

Materials

The zeolite used was obtained from natural deposits in Manisa while the fly ash and the coal bottom ash were obtained from the Soma and the Etibank Soma thermal plants in Manisa, Turkey, respectively. The chemical compositions of zeolite and fly ash were determined by an X-ray fluorescence spectrometer. The chemical compositions and physical characteristics of the materials are given in Table 1.

Cement mixtures

Three series of mixtures and reference mixtures were prepared according to Turkish Standards (TS) [13]

Results and discussion

This study was conducted to examine the effects of zeolite, zeolite+fly ash and zeolite+coal bottom ash on the properties of the cement. The properties of the materials used are given in Table 1. In this table, the SiO2, Fe2O3, Al2O3, MgO and SO3 contents of ash samples are reasonable with TS.

The results of the physical analysis of the cement mixtures, which are fineness, specific surface, specific weight and grinding time, are given in Table 2. As shown in Table 2, when fineness of the cement

Conclusion

Cement mixtures obtained in this study by the substitution of zeolite, fly ash and coal bottom ash require less amount of clinker, which results in increases in production and savings in energy, thereby reducing air pollution by decreasing the emission of CO2 and other gases. Mineral-substituted cement mixtures can have a big market share in the future since the emission limits on CO2 and other gases are being applied in the cement industry. This shows that an investment on mineral-substituted

Acknowledgements

The authors would like to thank Cimentas Co. for providing the facilities needed to carry out the experiments mentioned in this paper.

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