Location

University of Leeds

Keywords

Compressive strength, Expansion, Shrinkage, Expansive concrete, Fly ash

Abstract

This study is aimed to investigate effect of fly ash on compressive strength, free expansion and shrinkage of expansive concrete. High CaO and low CaO fly ashes are used in this study. The replacement percentages of total binders by fly ash are 0 and 30% by weight. The replacements of expansive additive are 0, 20 and 30 kg/m3 of concrete. The test results revealed that the use of fly ash especially the high CaO fly ash can enhance expansion of expansive concrete at early age. The use of fly ash also reduces shrinkage at long term of the expansive concrete when compared with that of the expansive concrete without fly ash. Therefore, dosage of expansive additive in concrete can be reduced when fly ash is incorporated in the expansive concrete. An enhanced expansion of the expansive concrete is mainly due to a formation of ettringite which is verified by XRD/Rietveld analysis. The compressive strength is tested in conditions of unconfinement and confinement. The results revealed that the compressive strength of expansive concrete treated under confined condition is improved. The expansive concrete containing fly ash with a superior expansion is more effective to improve the confined compressive strength. This is because the restricted expansion under confinement leads to an improvement of microstructure, so making denser paste structure and gaining more strength.

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Compressive Strength, Free Expansion and Shrinkage of Expansive Concrete containing Fly Ash

University of Leeds

This study is aimed to investigate effect of fly ash on compressive strength, free expansion and shrinkage of expansive concrete. High CaO and low CaO fly ashes are used in this study. The replacement percentages of total binders by fly ash are 0 and 30% by weight. The replacements of expansive additive are 0, 20 and 30 kg/m3 of concrete. The test results revealed that the use of fly ash especially the high CaO fly ash can enhance expansion of expansive concrete at early age. The use of fly ash also reduces shrinkage at long term of the expansive concrete when compared with that of the expansive concrete without fly ash. Therefore, dosage of expansive additive in concrete can be reduced when fly ash is incorporated in the expansive concrete. An enhanced expansion of the expansive concrete is mainly due to a formation of ettringite which is verified by XRD/Rietveld analysis. The compressive strength is tested in conditions of unconfinement and confinement. The results revealed that the compressive strength of expansive concrete treated under confined condition is improved. The expansive concrete containing fly ash with a superior expansion is more effective to improve the confined compressive strength. This is because the restricted expansion under confinement leads to an improvement of microstructure, so making denser paste structure and gaining more strength.