Assessment of determination methods for time-zero of autogenous shrinkage in cement mortars

Determination of time-zero is crucial for standardizing autogenous shrinkage measurement, data processing and cracking risk calculation for cementitious materials. The main objective of this study is to assess mainstream methods of time-zero determination and to provide recommendations based on the underlying mechanism and data reliability. In total, nine kinds of determination methods for time-zero were conducted for mortars with different water-to-cement ratios (w/c) including a simplified measurement for the restraint stress generation. The method of combining penetration resistance and capillary pressure is suggested due to its clear mechanism and ease of operation in different cementitious systems. After classification and statistical evaluation, the final setting, the peak rate time of the temperature, the restraint stress generation time and the newly proposed combined method are considered more suitable among the assessed time-zero determination methods. The recommendation is applicable for cement mortars with the w/c 0.3-0.4 and also expected to be extended to more complex cementitious systems.