Abstract
Bottom ash is a coal plant by-product that is abundant and underutilized. There is the potential use of bottom ash as a fine aggregate replacement in concrete mixtures; however, the problems of water absorption and uniformity of quality of the material need to be overcome first. In this study, bottom ash was treated by sieve separation and pounding to smaller particle size for use as a sand substitute. The physical and chemical characteristics of bottom ash were tested after treatment including water absorption, sieve analysis, and fineness modulus. Highvolume fly ash (HVFA) mortar specimens were made and the compressive strength and flowability test using bottom ash after treatment are compared with that of the sand specimen. Low water to cementitious ratio was used to ensure higher strength from the cementitious paste and superplasticizer demand was determined for each treatment. The result showed that bottom ash can be used as fine aggregate replacement material. Sieve separation of the bottom ash could produce 75% of the compressive strength compared with the control sand specimen, whereas pounded bottom ash could have up to 96% of the compressive strength of the control specimen. A 28-day compressive strength of 45 MPa was achievable with 100% replacement of fine aggregate with bottom ash.
Highlights
The large amount of natural materials used in making concrete has been a concern in the construction industry
Coarse bottom ash had a higher absorption value compared with the fine bottom ash because the voids are reduced as the particles become finer
The bulk volume of coarse bottom ash and fine bottom ash is lighter than sand, whereas the bulk volume of pounded bottom ash is 4.75% greater than sand due to a better gradation of the particles such that the gaps between them can be filled
Summary
The large amount of natural materials used in making concrete has been a concern in the construction industry. Concern about the large-volume usage of cement has been raised due to the carbon released during cement production, making concrete a nonenvironmentally friendly material. Concrete developed, manufactured, and used in an environmentally friendly way is called "Green Concrete" [1] and efforts to reduce the use of cement by improving mix composition and replacing natural materials with recycled or waste materials are on-going, with further research needed. Using bottom ash in concrete mixtures reduces concrete strength, increases water absorption, and decreases density [4]. Bottom ash has a larger particle size than fly ash and a rough surface that can interlock which lowers workability of the mixture. Bottom ash can be treated by grinding and sieving to reduce the particle size to reduce water consumption and voids [6]; the grinding process requires a lot of energy and cost
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