Performance of millet husk ash in self compacting concrete

Abstract

In a quest to mitigate the negative effects associated with the use of high cement content in self-compacting concrete (SCC), mineral additive from agricultural waste of millet husk ash (MHA) was explored with a view to partially replace cement in SCC without loss of quality. Several trial mixes were carried out with the aim of achieving grade 40 SCC, using water to binder ratio of 0.35 and plasticizer at 1.05 litre per 100 kg of cement. The adopted mix proportion satisfying the desired strength was used in production of MHA concrete (SCC – MHA) containing 5, 10, 15, 20, 25 and 30 percentages by weight of MHA as a replacement of cement respectively. Slump flow, L-box height ratio and segregation resistance were used to evaluate the fresh properties of the SCC – MHA mixes and compressive, splitting tensile and flexural strengths of the SCC – MHA evaluated at 3, 7, 28, 56 and 90 days curing ages were used to study the effects of the MHA in SCC. The result from the study shows that the slump flow and passing ability of the fresh SCC – MHA reduces with increase in MHA content in SCC but with improvement in the resistance against segregation. In addition, the increase in MHA content in SCC from 10 to 30 % reduces the compressive, splitting tensile and flexural strengths of the SCC – MHA. A microstructure study conducted on some selected specimen using X-Ray diffraction and scanning electron microscopy revealed that the available portlandite in the SCC were gradually consumed in the presence of MHA as the curing age increases. However, the result from the study showed that the MHA is class N pozzolanic material with optimum usage dose of 5 % for improvement of the hardened properties of SCC.