Performance of crystalline forming additive materials in concrete

Crystalline forming materials have shown a considerable reduction in permeability of concrete structures under severe environment. This paper addresses the performance of crystalline forming additive materials in terms of morphology characterization and water Sorptivity. Three different water-cement ratios of concrete; namely, 0.6, 0.5 and 0.387 have been considered to cover the range of concrete mixtures from highly to low permeable concrete. Test methods include scanning electron microscopy (SEM), coupled with energy-dispersive X-ray spectroscopy (EDX), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and sorptivity test. The results indicate that, the potential of crystalline materials to reduce permeability of concrete depends on available pore space in concrete mixtures. Thus, the effectiveness of these materials appears in high water cement ratio mixtures. The crystals have been found to be calcium silicate hydrate C-S-H of different phases ranging from round to needle form with high Ca/Si ratio. (C) 2019 Elsevier Ltd. All rights reserved.