Effects of alkalinity on early age shrinkage characteristic of cement-based materials

Initial cracking time, electrical resistivity and rate of heat evolution of cement-based materials with different alkalinities were measured by an ellipsis-ring cracking apparatus with an automatic monitoring system, non-contact resistivity instrument and JAF calorimeter, respectively. Results show that the alkali accelerates the hydration process of portland cement but shortens greatly the initial cracking time of mortar, especially at a lower water-cement ratio. Moreover, there is an interactive effect between the initial cracking time and resistivity inflexion, as well as maximum heat peak. A ratio of resistivity step/heat step (as K value) indicates a relation between early-age deformation and alkali content of cement-based materials.