Statistical study of curing conditions in alkali activation of Portuguese mine tailings

The use of industrial by-products to produce new types of cement-substitute binders is gaining significant momentum, particularly through the alkaline activation technique. However, the exact curing conditions that should be considered with each binder variation have not been fully understood yet. The aim of the present work is thus the statistical analysis of the effects of curing conditions (humidity and temperature) on the mechanical response (uniaxial compression strength and elastic modulus) of different aggregate/binder weight ratios. Five blends of solid mine tailings (as an aggregate) and fly ash (as a precursor), both collected from the Portuguese industry, were activated with sodium hydroxide solution and cured under nine different temperature and humidity combinations. The data analysis was performed using multivariate analysis of variance and analysis of variance, followed by Tukey’s post hoc test, whenever appropriate. Results show that the curing humidity factor showed a lower impact than the curing temperature. Although the increase in temperature and decrease in humidity produced higher compression strengths, the best results were obtained with a specific combination of both (60°C and 50% relative humidity). In general, the increase in tailings’ content produced a reduction in compression strength, but only for values above 20% (by weight of the sum of solids).