Towards Developing a Concrete Mix Design to Withstand Sulphuric Acid Attack in Concrete Sewer Pipes Using Rice Husks Ash as an Admixture

Abstract

Concrete corrosion from sulphuric acid generated from the sewage content is one of the main causes of infrastructure failure in concrete sewer works in many cities of the world. This has raised the demand for sustainable concrete for such aggressive environments. A number of mitigation interventions have been developed but have not been sustainable given the cost implications.

The effect of incorporating varied quantities of fine burnt rice husk ash (RHA) in cement as a binder system with two water cement ratios for concrete exposed to a simulated acidic sewer environment was investigated. The objective was to evaluate the effect of the two on the strength, mass loss porosity and surface texture of concrete exposed to acidic environment and thus develop a mix design with the right % RHA in cement and W/C that can withstand corrosion.

The experimental study entailed preparation of 150mmx 150mm x 150mm concrete cubes with varying percentages of RHA in cement with two water cement ratios. The cubes were then cured for 28 days, allowed to dry off for 7 days then fully exposed to acidic sulphuric acid solution for 12 weeks.

The effect the acidic solution had on the surface roughness, mass loss, porosity and compressive strength of the cubes was then evaluated. Samples with 0.35 W/C were observed to have slightly more compressive strengths and also performed better in terms of surface texture, mass loss and porosity than those with 0.4 W/C. The highest compressive strengths, for the two water cement ratios, were achieved with 5% RHA in cement and thereafter the strengths reduced with increasing presence RHA. The mass loss and porosities, for both water cement ratios, decreased with increasing presence of RHA in cement an indication that incorporation of RHA in cement lead to a more impermeable concrete. A compressive strength of 35.29N/mm2 slightly higher than the design characteristic strength by 0.8% was achieved with 0.35 W/C and 10% RHA in cement after the specimen were exposed in acidic solution.