Homogenization Model Examining the Effect of Nanosilica on Concrete Strength and Stiffness

Composite homogenization is a numerical simulation method that allows determination of the effect of microstructure constituents on the mechanical properties of composite materials. This homogenization technique allows cement paste to be modeled as a composite material in which microparticles are randomly dispersed in the cement paste matrix. By using microstructural homogenization, a representative volume element (RVE) can be developed and used to simulate the constitutive model of the composite cement paste by considering its constituent phases. A four-phase cement paste model is considered to describe cement paste incorporating nanosilica. Cement paste microstructures are divided into Phase I, hydrated cement paste; Phase II, unhydrated cement paste; Phase III, nonreacted nanosilica; and Phase IV, capillary porosity. Cement hydration models are used to predict the volume fraction of the four phases on the basis of the mixture proportion of the cement paste mix. Constitutive models for Phases I, III, and IV are assumed on the basis the literature. A constitutive model for Phase II is identified with the RVE model by matching the stress–strain curves of the cement paste extracted from nanoindentation experiments. The validated RVE model is then used to examine the effect of changing the nanosilica content in the cement paste on the stress–strain curve of the composite cement paste. It is evident computationally that increasing the nanosilica content will increase the strength and stiffness of the cement paste and therefore will increase the ability of the cement paste to absorb energy represented by the area under the stress–strain curve.