Enhanced Shrinkage Model Based on Early Age Hydration and Moisture Status in Pore Structure

Abstract

In this research, an existing multi-scale model for shrinkage behavior is enhanced to improve its applicability and precision. The enhancement work focuses on the initial autogenous shrinkage and intrinsic driving forces of the shrinkage at the microscale. The existing model underestimates the rapid development of the autogenous shrinkage of cement with a low water/cement (w/c) ratio. Hence, combined with self-desiccation, the autogenous shrinkage at an early age is first discussed. As an approximation, a portion of the autogenous shrinkage at an early age is quantitatively calculated using the chemical volume change and distance between cement particles, and that portion is added to compensate for the underestimation in the existing model. Furthermore, in the existing model, capillary tension is assumed to be the principal driving force in all of the pores with various sizes, which would cause an overestimation of the long-term shrinkage in the analysis. Therefore in the enhanced model, the driving forces are discussed and modified. The capillary tension is assumed to only be active in relatively coarse pores, whereas the disjoining pressure dominates in fine pores on the nanoscale. These two driving forces are quantified by the water status in the pores using the proposed formulas. With the above enhancements, the autogenous and drying shrinkage behaviors with various w/c ratios and relative humidity can be simulated reasonably.