Structural build-up at rest in the induction and acceleration periods of Portland Cement

Structural build-up in fresh cement paste at rest is characterized by time evolutions of storage modulus and yield stress, which both increase linearly in time during the induction period of hydration, followed by an exponential evolution after entering the acceleration period. Here, we investigate structural build-up by coupling calorimetry and oscillatory shear measurements of Portland Cement at different w/c ratios and in the absence of admixtures, capturing how the storage modulus evolves with changes in cumulative heat. This allows the decoupling of hydration kinetics from the mechanisms dictating build-up at rest. We obtain an exponential relation between stiffness and heat, with the same exponent in both the induction and acceleration periods. This suggests that, at least in the absence of admixtures, the same mechanism dictates build-up at rest in both periods. Since it is understood that C-S-H dictates build-up at rest in the acceleration period, we deduce that the same mechanism holds in the induction period.