Mechanical Strength Optimization of Alkali-Activated MK/GBFS Binary Cements Through the Response Surface Methodology

The present article shows the compressive strength modeling and optimization for a non-conventional binder free of clinker, which was produced by the alkali activation of a binary mixture of metakaolin (MK) and a granulated blast furnace slag (GBFS). AGBFS/(GBFS+MK) ratio between 0,0 and 0,8; and the overall SiO2=Al2O3 molar ratio from 2,8 to 4,2 were considered as the main factor of this study. Sodium hydroxide and sodium silicate were used as alkali activator. The overall SiO2=Al2O3 molar ratio corresponds to the silica and alumina contribution from the precursor (MK+GBFS), as well as the alkali activator used. The statistical assessment through response surface methodology (MSR) showed a considerable effect between the SiO2=Al2O3 molar ratio, GBFS content and the compressive strength. Complementary, a microstructural characterization of the materials produced through X-ray diffraction (XRD) and scanning electron microscopy (SEM) was performed. The GBFS inclusion leads to an increasing of reaction kinetic and the formation of a more compact structure. These new reaction products gives to the material a higher mechanical performance than those based on a 100% of MK. The study shows the performance prediction in materials with 7 days of curing through the adjustment of some design criteria in order to obtain a binder with a particular mechanical performance