Fracture mechanism in cement-based materials subjected to compression

The fracture processes in cement-based materials (cement paste, mortar, and concrete) subjected to compressive loads are examined. The use of friction-reducing materials reduced the end constraints and eliminated the barrel effect. The material composition as well as the end-shear confinement was found to affect the nonuniform deformations observed at the early stages of loading. Primarily, cracks propagated parallel to the loading direction for all tested material compositions. A nondestructive measuring system utilizing digital image correlation was developed for the fracture study of quasi-brittle materials. Theoretical predictions on crack growth were made based on fracture mechanics approaches in conjunction with experimental observations. Two different approaches for the computation of the stress intensity factors were made; one (for cement paste) was based on discrete cracks in a three-dimensional body, and the other (for concrete) was based on multiple sliding cracks relying on a damage mechanics concept.