Synthesis of alkaline cements based on fly ash and metallurgic slag: Optimisation of the SiO_2/Al_2O_3 and Na_2O/SiO_2 molar ratios using the response surface methodology

摘要

During the present work, different binders were synthetized by alkaline activation of fly ash (FA) and a mixture of 75% fly ash and 25% metallurgical slag (FASLG). Two different curing periods, of 7 and 28 days, were considered. A Variance Analysis (ANOVA), conducted to assess the effectiveness of the Response Surface Methodology that was used to structure the study, revealed that this was capable to predict, with satisfactory precision, the maximum compression strength values of the pastes considered. By optimising the independent variables, defined as the SiO2/Al2O3 and Na2O/SiO2 molar ratios, 28-day uniaxial compression strength (UCS) values of 44.3 MPa and 28.5 MPa were predicted, for the FA(28) and FASLG(28), respectively. The experimental results showed UCS values of FA28 = 41.5 MPa and FASLG28 = 22.1 MPa, confirming the validity of each model. R-square values of 85.76% (FA28) and 85.48% (FASLG28) are an effective measure of the experimental variability associated with the estimation of new observations, which can be further reduced if more variables are controlled and included in the model. (C) 2019 Elsevier Ltd. All rights reserved.