Optimum Utilization of Coal Ash in Cement Concrete Production
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Date
2019-09
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Addis Ababa University
Abstract
Coal ash is the waste that is left after coal is combusted (burned). It includes fly ash (fine powdery
particles that are carried up the smokestack and captured by pollution control devices) as well as
coarser materials that fall to the bottom of the furnace. Coal ash used as Portland cement constitutes
or as ingredient of concrete will help in more sustainable cement production by lowering energy
and raw material consumption.
This study aims to investigate the suitability of coal ashes produced in different factories of
Ethiopia (AYKA Addis Textile factory and Dongfang Spinning and printing) as supplementary
cementitious material in Cement Concrete production. The physical and chemical characteristics
of coal ash and concrete raw materials were investigated to check their compliance with the
requirements of standards and specifications.
Coal ashes taken from the factories were pulverized and sieved with 300µm sieve and fineness
determined by air-permeability test, results 3385.57 cm
/g for FA-1 and FA-2
respectively. X-ray examination has shown that the fly ashes are mainly amorphous but there are
also present crystal phases like feldspar, melilite, hematite, very little anhydrite, and quartz.
2
/g and 3788.9 cm
2
The substitution portions of fly ashes were made 10%, 15%, 20% and 25% by volume of cement
for FA1 and 5%, 10%, 15% and 20% by volume of cement for FA2. Furthermore, two classes of
concrete with a water-binder ratio of 0.4 and 0.6 were made to investigate the effect of coal ashes
on the strength of concrete.
The performance of the concrete was evaluated by conducting compressive strength, flexural
strength and water penetration tests. The results showed that both coal ashes possess sufficient
pozzolanic characteristics to be used in the production of cement concrete, and the optimum
cement replacement level by these ashes can range between 5-15% by volume.
Description
Keywords
Coal ash, fly ash, bottom ash, pozzolanic, compressive strength, flexural strength, water penetration, cost-benefit analysis, Green House Gas