Influence of waste glass powder usage on the properties of alkali-activated slag mortars based on response surface methodology

•RSM was used for the optimisation by maximising strengths.•The optimum combination of 8.31% Na2O and 14.57% GP was attained in AASGP mortar.•The suitable amount of GP is effective in improving the properties of AAS mortar.•Waste GP is an ideal admixture in AAS mortar. In this study, the effect of waste glass powder as a potential cementitious material on the strength, drying shrinkage and sulfate attack resistance of slag mortar activated by the mixture of water glass and sodium hydroxide was evaluated. Also, Central composite design and response surface method were used for the optimisation of the alkali content (sodium oxide equivalent) and replacement ratio of waste glass powder by maximising flexural and compressive strengths. The results of analysis of variance (ANOVA) indicated that the accuracy of the developed strength models based on response surface method was satisfactory. The optimal alkali content and replacement ratio of waste glass powder were found to be 8.31% and 14.57%, respectively. Under this condition, the experimental values of 3-, 7- and 28-day flexural strengths and 3-, 7- and 28-day compressive strengths of alkali-activated slag/glass powder mortar were 6.6 MPa, 7.1 MPa and 8.4 MPa, respectively and 49.2 MPa, 52.9 MPa and 66.4 MPa, respectively, which agreed closely with the predicted values since the percentages of error were negligible in the range of 0–2.38%. When the alkali content was 8.31%, the addition of 14.57% waste glass powder in alkali-activated slag mortar could improve the 3-, 7- and 28-day flexural and compressive strengths, reduce the dry shrinkage by up to 15.8% at 1 day and 20.3% at 120 days, and increase the resistance to sulfate attack.