Optimum design of alkali activated slag concretes for the low oxygen/chloride ion permeability and thermal conductivity

In this research, individual and interactional effect of curing temperature (CT), curing time (CTime), sodium concentration (SC) and silicate modulus (SM) on the compressive strength, chloride ion permeability, oxygen permeability and thermal conductivity of alkali activated slag (AAS) concretes were investigated and the best possible combination of CT, CTime, SC and SM for the maximization of compressive strength while for the minimization of chloride ion permeability, oxygen permeability and thermal conductivity of AAS concretes were determined. An experimental program that contains 21 different combinations of independent parameters (CT, CTime, SC and SM) was conducted by using the central composite design method. Alkali solution-slag ratio was kept constant at 0.53 in all production. The effects of the independent parameters were characterized and analyzed by using statistically significant quadratic regression models on the measured properties (dependent parameters). Optimum values of the independent parameters were determined by solving a multi-objective optimization problem obtained by using the proposed regression models for dependent parameters. The results of test and the analysis indicate that the independent parameters affect the dependent parameters considerably; however, the most effective parameter for the compressive strength, chloride ion permeability, oxygen permeability and thermal conductivity is the sodium concentration. The optimum combination of CT, CTime, SC and SM is 46.8 °C, 8.3 h, 5.5% and 2.0, respectively, for the minimization of chloride ion permeability, oxygen permeability and thermal conductivity and the maximization of compressive strength of AAS concretes.