Effect of fly ash and red mud on strength and electrochemical properties of seawater mixed concrete

The utilisation of seawater (SW) for making concrete appears to be a reasonable alternative to conserve freshwater. This paper investigates the possibility of making seawater mixed concrete (SMC) using cementitious replacement of fly ash (FA) and red mud (RM) to offset the adverse effects of SW in concrete. FA was added by replacing from 10% to 40% by weight of cement and RM from 5% to 20% and compressive strength, split tensile strength and electrochemical properties of concrete were evaluated for different mixes for 7, 28 and 90 days of testing. Analysis of variance method was used to identify the influences of FA, RM and concrete testing age on the SMC properties. The best mix was then finalised using the response surface method (RSM). It was observed that RM and especially FA were very effective in improving SW concrete properties, that is, increasing mechanical strength and controlling corrosion of steel in concrete. The results showed that to successfully utilise SW for making concrete, the best results at the testing age of 90 days were obtained on replacing cement with approximately 40% FA. The novel mix showed approximately 23% increase in compressive strength and 12% increase in tensile strength compared to SWM concrete. In addition, the novel mix electrical resistivity is around 60 k omega cm showing it to be in low corrosion zone.