Strength development in hardened cement paste: examination of some empirical equations

A number of empirical expressions are frequently used to describe or predict the strength of normal hardened cement paste. The more well-known expressions of Balshin, Hasselman and Ryshkewitch relate strength and porosity. The Bolomey formula relates strength and water/cement ratio. All these expressions are shown to be theoretically well justified. They are pore-specific versions of a more general expression presented in this paper. The Balshin expression is suggested to be in general the better strength-porosity relation. Bolomey’s formula is shown to be a logical numerical consequence of this statement. Parameters are given for both these relations which depend on degree of hydration. The Ryshkewitch expression applies strictly only at vanishing porosity. Low-porosity strengths are overestimated by the Ryshkewitch expression when calibrated (fitted) to experimental data at finite porosities.