31-07-2013, 03:06 PM
Strength Properties of Corn Cob Ash Concrete
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Abstract
The objective of this paper is to enhance the reduction of corn cob wastes and reduce the cost of concrete
production by using locally available materials. Physical and mechanical properties of varying percentage of
CCA cement concrete and 100% cement concrete of mix 1:2:4 and 0.5 water-cement ratios were examined and
compared. A total of 72 concrete cubes of size 150 × 150 × 150 mm3 and 12 concrete cylinders of size 100mm
(diameter) x 200mm (height) with different percentages by volume of CCA to Portland cement in the order
0:100, 10:90 and 20:80 were cast, tested and their physical and mechanical properties determined. A high
strength (35MPa) concrete was further designed using CCA as a partial replacement for cement with a total of
32 concrete cubes (16 samples each for 0% and 10% partial replacements) and 8 concrete cylinders (4 samples
each of 0% and 10% partial replacements). The specific gravity of the CCA was 1.15, while the mechanical
properties which included compressive strength tests showed that 10% of the CCA in replacement for cement
was quite satisfactory with no compromise in compressive strength requirements for concrete mix ratios 1:2:4
at 7days, but did not meet the standard strength at 14, 21 and 28 days. The 20% CCA replacement for cement
did not meet the satisfactory strength requirements at all. While the split tensile test revealed that concrete
tensile strength is about 11-12 times lower than its compressive strength. The high strength concrete designed
was adequate in compressive and split tensile strength requirement, but did not reach the designed compressive
strength of 35MPa at 28days. However, test results showed that the use of CCA as a partial replacement for
cement in concrete, particularly in plain concrete works and non-load bearing structures; will enhance waste to
wealth initiative. Though CCA could be used as a partial replacement for cement in high strength concrete, but
the CCA concrete would take longer time to achieve its designed strength and the CCA concrete would require
water/cement ratio less than 0.40. Hence, the use of superplasticizers is required to enhance workability. This
research was carried out at the University of Ibadan, Ibadan, igeria.
EXPERIMETAL STUDIES
Compressive strength tests were carried out on
concrete cubes (150mm × 150mm × 150mm) while
split tensile strength tests were carried out on
concrete cylinders 100mm (diameter) x 200mm
(height) having varying composition of corn cob ash
as a replacement for cement in concrete. Batching
operation by volume approach was used adopting a
mix of 1:2:4 (cement: fines: coarse aggregates) with
water/cement ratio of 0.50. Grade 35 MPa concrete
was also designed using the ACI method of mix
proportioning with water/cementitious material ratio
of 0.45. The following samples were tested in the
study
RESULTS
1) Concrete batching by volume of mix 1:2:4
The results of the physical and mechanical properties
of the varied corn cob ash concrete are presented in
Tables 2-5 as obtained from the study. Table-2 gives
the average density of the concrete cubes; Table-3
gives the average compressive strengths of the
concrete cubes; Table-4 gives the average density of
the concrete cylinders; while Table-5 gives the
average tensile strength of the concrete cylinders
examined.
Physical and Mechanical Properties
The physical properties of the high strength concrete
were the same as the ones observed in the previous
specimens except for the reduced workability and the
specific gravity of the ash was 1.15.
CONCLUSION
Based on the findings from this study, the following
conclusions can be arrived at;
1. Concrete strengths increases with curing age
and decreases with increasing percentage of
corn cob ash.
2. Corn cob ash concretes do not attain their
design strengths at 28days. The strengths of
corn cob ash concrete are dependent on its
pozzolanic activities.