Effect of gel–space ratio and microstructure on strength of hydrating cementitious materials: An engineering micromechanics approach

Strengths of cement pastes with different mixture properties and maturities depend in a very similar overlinear fashion on the gel–space ratio, which is the ratio of the volume of hydration products over the volume of both hydration products and capillary pores. We here investigate the underlying microstructural effects by the experimentally validated micromechanics model of Pichler and Hellmich [CemConRes 41(5), 2011]. This model shows that the macrostrength of cement pastes are not only triggered by the capillary porosity, but also by a strengthening effect of unhydrated clinker “reinforcements” which are embedded as inclusions in the hydrate foam. The analysis is continued with quantifying the strength of the hydrates, in terms of an extended model validation activity. Satisfactory model performance is the motivation to present model predictions for the biaxial compressive failure envelopes of cement pastes, again as a function of gel–space ratio.