Effect of Using Bottom Ash as Fine Aggregate Replacement in Concrete (The Case of Reppie Waste to Energy Power Plant)

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Addis Ababa University


Thousands of tons of municipal solid waste are generated each year in Addis Ababa, necessitating a large area for disposal and negatively impacting the area's echo system. This urban solid waste is currently used to generate electricity at the Reppie waste-to-energy power plant. Reppie waste to energy power plant used this municipal solid waste to generate electric energy with a waste processing capacity of (394.7 kt/year). Even if this power plant uses municipal solid waste to generate usable electricity, it produces waste (bi-product) that has an effect on the echo system and necessitates a wide disposal area. The wastes produced from this power plant are of two types, namely, fly ash (15.21 kt/year) and bottom ash (BA) (100.4 kt/year). On the other hand, fine aggregate (FA) has been used extensively as a key component of concrete production in the building industry. The over-exploitation of natural sand as a source of FA has resulted in depletion and environmental degradation. This research is conducted to determine the effect of using Reppie waste to energy power plant bi-product BA as partial replacement of FA for production of concrete. The test result showed that BA is a class C ash, light in weight material with more pores particles. When using it in concrete, the increase in percentage substitution of BA reduces the workability and slump value. On hardened concrete, the compressive strength rises up to 35% substitution and then start to decline beyond that, however up to 50% substitution, also gives a better result than the controlled result. The splitting tensile strength and flexural strength increase up to 50% substitution which has the value nearly similar with the control and starts to decrease at 65% substitution. The water penetration constantly decreases for all substitution of FA with BA. Furthermore, an ultrasonic pulse velocity test result indicated that all percentage substitution has a good concrete quality grading. Based on the results, this BA can replace FA up to 50%, but the maximum results are obtained at 35% substitution, and this maximum result is obtained after 28 days of curing.



Bottom Ash, Fine Aggregate, Concrete