Compressive and Splitting Tensile Performance of Rice Husk Ash Concrete Under Hydrochloric Acid and Sodium Sulfate Exposure

The use of agricultural residues as supplementary cementitious materials offers a potential route for reducing Portland cement consumption while valorising waste resources. This study experimentally investigates the influence of rice husk ash (RHA) as a partial replacement for cement on the compressive and splitting tensile strengths of concrete under control curing, hydrochloric acid (HCl), and sodium sulfate (Na₂SO₄) exposure. Five mixtures were investigated, consisting of a control mixture (M0) and mixtures containing 5, 10, 15 and 20% RHA by cement replacement. The reported cement contents ranged from 13.28 kg/m³ for the control to 9.30 kg/m³ at 20% RHA, while the fine and coarse aggregate contents were maintained at 21.58 and 39.85 kg/m³, respectively. Under control curing, the 28-day compressive strength decreased progressively from 25.16 MPa for M0 to 16.74 MPa for M20, corresponding to a maximum reduction of 33.5%. In contrast, the 28-day splitting tensile strength showed a smaller reduction, from 2.74 MPa for M0 to 2.66 MPa for M20, with M5 producing the highest value of 2.77 MPa. Following HCl exposure, 56-day compressive strength decreased from 20.87 MPa for M0 to 11.27 MPa for M20, while the highest splitting tensile strength was recorded at 15% RHA (2.51 MPa). Under Na₂SO₄ exposure, compressive strength declined progressively with increasing RHA content, from 27.96 MPa for M0 to 13.85 MPa for M20. However, tensile strength did not follow the same monotonic trend, reaching 2.31 MPa at 15% RHA. The results demonstrate that increasing RHA replacement reduced compressive strength at the investigated ages, whereas moderate RHA contents, particularly 15%, produced comparatively favourable tensile responses under chemical exposure. The findings highlight the need to optimise RHA dosage according to the governing mechanical and durability requirements rather than considering cement replacement on a single performance indicator.