Nondestructive Estimation of Cement Content of Hardened Concrete

Abstract

This paper describes a method to estimate the cement content of hardened concrete specimens based on the determination of the water content of ovendried powdered concrete specimens by neutron scattering. The cement content could be computed on the assumption that the percentage of water of hydration is approximately constant for all cements. To justify this assumption, a systematic investigation of hydration value was carried out with cement specimens of various Turkish origin. The method involved dehydration of the hydrated cement specimens at 100 C in an atmosphere of oxygen and absorbing water in calcium chloride. A value of 14.1 was found for the mean percentage of hydration water with a standard deviation of 0.5. Because it is impossible to eliminate capillary water in situ—a requirement for adapting this technique to a nondestructive method—attempts were made to estimate this water by measuring electrical conductance of concrete. The over-all water content, that is, capillary water plus hydration water, is determined by neutron scattering, and the hydration water content is found by substraction. The cement content is then calculated from the mean hydration value of cement.