Publication: Improving the performance of concrete containing locust bean pod ash with the incorporation of metakaolin
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Date
2024-12-01
Authors
Isa Felix, Nkapheeyan
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Abstract
The extensive use of cement and other non-renewable materials in global
infrastructure development contributes to environmental degradation. This has shifted
building industry research towards using abundant natural raw and waste materials.
This study evaluated the performance of locust bean pod ash (LBPA) and Metakaolin
(MK) as supplementary cementitious materials (SCMs) in concrete. The LBPA and
MK were obtained from the calcination of locust bean pod and Kaolin at temperatures
of 600˚C and 800˚C for 2 hours, respectively. The properties of the LBPA and MK
were evaluated and ordinary Portland cement (OPC) was replaced with LBPA and
LBPA-MK by mass at 0, 5, 10, 15, 20, 25 and 30% LBPA and 15% MK. The
workability of the normal strength concrete (NSC) and high strength concrete (HSC)
as well as the setting times of the HSC were determined. The compressive, flexural
and tensile strengths of NSC and HSC were determined and at 3, 7, 14, 28, 56, 90 and
180 days of curing using cubes, beams and cylinders, respectively. Also, the resistance
of the NSC subjected to 5% HCl and H2SO4, as well as 10% Na2SO4 was investigated.
Additionally, the HSC’s performance against water absorption and elevated
temperatures of 100˚C to 600˚C, and MgSO4 was assessed, as well as the
microstructural analysis of the HSC using Sanning Electron Microscope (SEM).
Moreover, mechanical properties of the concrete were statistically analysed and
optimized using response surface methodology (RSM) and linear regression for the
NSC and HSC, respectively. Results showed that LPBA was of low reactivity, with 76.16% strength activity index (SAI) and having a combined SiO2, Al2O3 and Fe2O3
content of 42.81% while the MK was more reactive with 85.54% SAI and having a
combined SiO2, Al2O3 and Fe2O3 content of 89.96 %. For NSC, as the LBPA content
increased, the workability was reduced. Further, the 5% LPBA replacement showed
the greatest improvement for the binary system while the combined 20% (5% LBPA
and 15% MK) replacement level gave the best performance for the ternary system at
90 days. Additionally, both blends improved the performance of concrete against HCl,
H2SO4 and Na2SO4. The optimized model of 5% LBPA had the highest accuracy with
percentage errors of 0.02%, 0.04% and 0.05% for compressive strength in HCl, H2SO4
and Na2SO4 respectively. Similarly, LBPA improved the performance of HSC against
water absorption, sulphate attack, and elevated temperatures, in addition to the
mechanical properties. The performance of HSC improved much better for the OPC-
LBPA-MK HSC. The prediction model of concrete with 10% LBPA shows the best
accuracy for compressive and tensile strengths, while that with 5% LBPA had the best
accuracy for flexural strength, with errors of 0.72%, 0.00% and 4.06%, respectively.
The study concludes that for the binary concrete, 10% is the optimum replacement
level, while up to 35% OPC (20%LBPA and 15%MK) could be replaced in ternary
system for NSC and 30% (15% LBPA and 15%MK) for HSC. Thus, LBPA and MK
can be successfully used as SCMs to improve the performance of concrete, and
ensuring a safe environment.