Expansive Cement Concrete-Micromechanical Models for Free and Restrained Expansion.

摘要

A micromechanical model of the expansive process in sulfoaluminate expansive cement has been developed. An example of the calculation of free expansion based on the model is given for a Type K shrinkage-compensating cement. Parameters used in the calculation include the chemical composition of the unhydrated cement,its particle size distribution,and the water-cement ratio of the cement paste. The calculated expansion has been verified by experimental measurements. The model has been extended to the case of restrained expansion,based on the assumption of a limiting stress,above which ettringite formation is effectively prevented. From the geometry of the model an equation is developed which relates the unit expansion to the fractional area of restraining steel. The form of the equation compares favorably with experimental data on restrained expansion. Further analysis suggests that there is an upper limit to the magnitude of stress that can be developed by a given cement.