The relationships of cement hydration and concrete compressive strength to maturity

A maturity function was evaluated over a wide range of curing temperatures and curing times for concrete specimens of different water-to-cement (w/c) ratio. The function was developed based on an investigation of hydration, rate kinetics and pore structure of hydrated cement.; The Arrhenius equation for thermal activation was used to study rate kinetics of type I portland cement over a wide hydration range. Two hydration stages were defined. In the first stage, which includes degrees of hydration up to about 60%, hydration is chemically controlled with a constant activation energy of 40 KJ/mole and is independent of the w/c ratio. During this stage temperature has a major effect on the rate of hydration. Hydration kinetics can be accurately predicted by the Arrhenius equation. A second stage, for degrees of hydration greater than 60%, was characterized by a continuous decrease in activation energy. During this stage hydration becomes diffusion controlled; the hydration rate is low and the effect of temperature is negligible compared to the first stage of hydration.; The pore structure (i.e., pore volume and pore size distribution) of hydrated cement was investigated using the mercury intrusion porosimeter method. For a given w/c ratio the pore structure depends on degree of hydration only and is independent of curing temperature in the range of 3-43{dollar}spcirc{dollar}C. Thus degree of hydration is a basic parameter for predicting strength of paste and concrete.; The proposed maturity function was evaluated against the Saul-Nurse and the Freisleben-Hansen and Pedersen functions. It predicts well the effects of curing temperature and time on strength development for the curing times studied. The Saul-Nurse function did not predict well strength results during the first few days of curing. The Freisleben-Hansen and Pedersen function was nearly as good as the proposed function during this period except for curing temperatures below ambient. At later ages this function overestimated the influence of temperature on maturity and strength.