Abstract:
This research was carried out to investigate the effect of using recycled concrete aggregate as
a partial replacement for coarse aggregate blended with wood ash on the properties of concrete.
Different studies have conducted research on improving the quality of recycled aggregate with
purpose to diminish cost and implement friendly environment. Concrete waste products when
crushed to the required nominal sizes such as 10mm, 14mm, 20mm, etc. provide a rough and
irregular surface which aids in blending cement paste and the aggregate.
Response Surface Methodology with central composite design (CCD) was used in the
experimental design to obtain the possible different percentage partial replacement of WA and
RCA for cement and NA respectively to observe careful accuracy requirement for experiment.
Flexural strength and compressive strength of concrete were evaluated by conducting
laboratory experimentation. RSM-CCD was also used in the analysis of results obtained from
the laboratory test for flexural and compressive strengths.
It was observed that flexural strength 2.9 MPa at 28 days yielded better results from the mix of
10% WA and 20% RCA increased from 2.2 MPa at 7 days to 2.9 MPa at 28 days. Compressive
strength had highest value of 33.2 MPa at 28 days indicating good results with other result
values ranging from 26.4 MPa to 33.2 MPa at 28 days showing better increased in the
compressive strength of concrete. For both flexural strength and compressive strength, there
was increased in water absorption with the increased in percentage replacement of WA and
RCA. The optimized values for flexural strength and compressive strength were 2.9MPa and
30.8MPa at 28 days of curing and setting.
This project encourages the recovery and utilization of waste products from concrete and wood
ash to be used in the production of concrete hence conserving the environment from quarrying
and pollution arising from dumping. This will in turn reduce the overconsumption of natural
aggregate from quarrying as well as reduce for landfills where the demolished concrete waste
products are deposited.
