DOI: 10.14457/tu.the.2016.1724
title: Use of bottom ash as an internal curing and partial fine aggregate replacement material

description: In this study, potential of using bottom ash from coal power plant as a partial fine aggregate replacement material was studied both basic properties of bottom ash and properties of concrete using bottom ash as a partial fine aggregate replacement material. Bottom ash samples were collected from Mae-moh power plant in the northern of Thailand. They were collected from different period of time and power plant unit. Moreover, as bottom ash is porous material and cannot be determined water absorption as normal fine aggregate. Therefore, new standard testing method for water retainability has been proposed.  Firstly, method for testing water retainability of bottom ash is proposed based on modified standard sand sieving machine. The new method is faster and provides a result with more consistent. Results of basic properties of bottom ash showed that gradation of bottom ash has fine particle more than requirements of material to be used as fine aggregate material in concrete. However, when bottom ash is partially replaced sand, gradation is within the requirement. Specific gravity of bottom ash is significantly lower than natural sand because of its high porosity. Due to the same reason, water retainability of bottom ash is also significantly higher than absorption of sand. Chemical composition of bottom ash is similar to that of fly ash and mainly depends on chemical composition of coal. Variation of basic properties has been observed depends on time and unit of power plant. Properties of concrete are significantly affected by bottom ash. Due to high water retainability of bottom ash, water is released during concrete mixing and increase slump of concrete with bottom ash. Therefore, strength and durability of concrete have been affected. However, in case of high water to binder ratio concrete, strength of 10% by volume bottom ash replacement level concrete was higher than that of natural sand concrete. This is due to the formation of hard shell around aggregate. If mixing water content is reduced, slump can be controlled. As a result, compressive strength of 10% by volume bottom ash replacement level concrete was higher than that of natural sand at all cases. Effect of internal curing of bottom ash also clearly observed on compressive strength result not only OPC concrete but also fly ash concrete. Curing sensitivity is significantly reduced. Autogenous shrinkage of bottom ash concrete decrease, due to extra supplied water from bottom ash reduces self-desiccation. However, at early age, autogenous shrinkage of bottom ash concrete increase a little bit due to faster hydration of cement from extra supplied water from bottom ash. High porosity of bottom ash increase drying shrinkage, as a result total shrinkage of bottom ash concrete is slightly lower than that of normal concrete. Regarding to chloride and carbonation resistance, bottom ash concrete showed lower resistance due to high porosity of bottom ash. However, please be noted that testing was conducted on uncontrolled slump concrete specimen. In conclusion, regarding to compressive strength of concrete, 10% by volume replacement level of bottom ash to natural sand has a potential to be used. However, trial mixing must be conducted to adjust the mixing water content. Recommendation for using bottom ash as fine aggregate replacement materials has been provided.