Effect of sulfate content on the porosity distribution and resulting performance of composite cements

We investigated the effect of sulfate on the porosity distribution and the resulting mechanical performance of Portland-based composite cements. The porosity was investigated by dynamic vapor sorption and mercury intrusion porosimetry technique. Additional experiments were performed and are recalled from the earlier publication (Adu-Amankwah et al., 2018) to assess the phase assemblage. The micromechanical model for strength upscaling was applied to link the sulfate level, resulting microstructure and the mechanical performance. The results demonstrate that the sulfate content influences the ettringite content and impacts the porosity distribution. The ettringite stabilization by the sulfate added results in a higher solid volume and thus in a lower total pore volume. However, this phenomenon cannot explain the experimental observations of strength loss for high sulfate contents. Dynamic vapor sorption results reveal that there are fewer coarse capillary pores and more fine gel pores as the sulfate content increases. The mechanical model reflecting both aforementioned phenomena enables the reproduction of the strength evolution typical for the sulfate optimization experiments, i.e. the initial increase of the strength with the increasing sulfate content followed by the maximum and strength decrease. (C) 2018 Elsevier Ltd. All rights reserved.