Effect of Finely Ground Coal Bottom Ash as Replacement for Portland Cement on the Properties of Ordinary Concrete

Abstract

Featured Application The COP26 UN climate conference was held from 31 October to 13 November 2021, in Glasgow, Scotland, United Kingdom. The Glasgow Climate Pact was the first climate deal to explicitly address the need for a reduction in unabated coal power, which is a major contributor to climate change. However, substituting coal fly ash for Portland cement is a proven effective method for carbon reduction. In Taiwan, the price of coal fly ash has risen significantly due to the implementation of coal reduction policies. This study focused on finely grinding bottom ash, a byproduct of coal combustion, for use as a substitute for Portland cement. A comparison was made between finely ground bottom ash and coal fly ash from the same power plant. Apart from workability, no discernible differences that would affect structural safety were found. Therefore, utilizing low-cost bottom ash by finely grinding it to replace Portland cement in concrete is feasible, achieving both carbon reduction and economic viability.Abstract This study investigates the use of finely ground coal bottom ash (FGCBA) as a substitute for Portland cement in concrete, comparing it with coal fly ash from the same power plant. The incorporation of this ash necessitates the addition of a superplasticizer to achieve the desired slump at the same replacement rate. The results demonstrate that at an optimal 20% replacement rate, as determined by 91-day compressive strength tests, the maximum strength achieved by FGCBA is 97.7% of the control group with pure cement, whereas coal fly ash reaches 114.0%. Drying shrinkage tests indicate for both materials have similar volume stability, while rapid chloride permeability tests show their effectiveness in reducing chloride ion permeability, with superior performance from FGCBA. Under optimal conditions, the result of the RCPT test was only 559 coulombs, which is significantly better compared to the 4108 coulombs when using fly ash from coal combustion. Our results demonstrate that utilizing low-cost bottom ash by finely grinding it to replace Portland cement in concrete is feasible, achieving both carbon reduction and economic viability.