Abstract

Fresh concrete exposed to a drying environment is susceptible to plastic shrinkage cracking, which could result in negative impacts on concrete durability. In the current ASTM standard, plastic shrinkage cracking is evaluated by the average crack width measured at 24 hours after concrete placement, considering that the traditional crack measurement tools cannot be used on fresh concrete. In this project, a non-contact strain measurement technique based on digital image correlation (DIC) was applied to study the behavior of plastic shrinkage cracking. In the experimental program, the effects of air temperature, wind velocity, water to cement ratio (w/c), and substrate roughness on plastic shrinkage cracking were investigated. Several cement paste specimens were tested separately in a controlled environmental chamber. A series of digital images was taken above the specimen surface throughout each experiment. DIC analysis was then performed on these images. The crack areas were also determined based on the images using MATLAB functions. It was found that DIC can provide a series of strain contour maps that helped to understand the process of plastic shrinkage cracking. The accumulations of tensile and compressive strains can be used to illustrate the cracking intensity and the overall shrinkage, respectively. The evolutions of the maximum tensile and compressive strains can be used to indicate the time to first crack and the shrinkage capacity, respectively. The effects of air temperature, wind velocity, w/c, and substrate roughness were well explained by both the DIC analysis results and crack areas computed in MATLAB.