Role of Early Drying Cracks in the Shrinkage Size Effect of Cement Paste

Abstract

Standardized shrinkage models for concrete incorporate a function which depends on the ratio of volume to sample surface. These empirically calibrated functions are rationalized based on nonuniform moisture distributions during drying. Nonuniform moisture distributions also lead to crack development during early exposure to drying conditions. The role of early crack patterns on the cement drying shrinkage size effect is studied by companion three-dimensional X-ray microscope scans and shrinkage studies of cement paste samples. The scanned internal surface area allows for the incorporation of crack surface area to provide a more accurate representation of the drying surface. It is found that cracks generated during drying shrinkage will accelerate the moisture diffusion and cause additional shrinkage strain, and both effects follow a size effect that becomes more prominent for larger sections. Discussion of the experimentally observed impact of cracking on the shrinkage size effect behavior separates the contributions from diffusion and strain using a finite difference model. Based on these results, insights for concrete construction practice of aggregate arrangement to minimize differential shrinkage strains and cracking in nonuniform sections, such as bridge girders, are also discussed.