Investigation on the effects of acidic environment and accelerated carbonation on concrete admixed with rice straw ash and microsilica

In this research, the effects of the acidic environment and accelerated carbonation curing (ACC) on concrete admixed with rice straw ash (RSA), microsilica (MS) and combination of both were evaluated. The loss of mass and compressive strength of concrete admixed with RSA and MS were observed at 28 and 365 days of water curing followed by 30 days of immersion in two acidic solutions of 2.5% concentration, i.e., hydrochloric (HCl) and sulphuric (H2SO4) acid. The least loss of mass and compressive strength under acidic environment were observed in concrete admixed with a combination of 10% RSA and 5% MS (mix R2M3). The percentage loss of compressive strength (compared to strength at 58 days of water curing) and percentage loss of mass (compared to initial mass before acidic immersion) of mix R2M3 at 28 days of water curing were 3.69% and 2.19% respectively under HCl immersion and 1.81% and 1.27% respectively under H2SO4 immersion. The corrosive impact of HCl on concrete was higher as compared to H2SO4. The characterization of concrete mixtures after acidic immersion was performed using XRD and SEM analysis. The mechanical strength and carbonation depth of concrete admixed with RSA and MS were observed at 28 days of combined curing (14 days of water curing, 14 days of ACC). The maximum increase in the strength of concrete at 28 days of combined curing as compared to 28 days of water curing was found in mix R2M3. Also, the carbonation depth was highest in mix R2M3 (17 mm).