Cement compositions and processes for reducing air entrainment in a cement composition generally include mixing a hydraulic cement with a defoamer composition including an organic acid ester of a polyoxyethylene-polyoxypropylene block copolymer.

For measuring the stress history in a simple form, which is widely applicable to various types of structural materials which the elastic modulus is different from each other, a large number of calcite particles is embedded as a stress sensor in a cement-based composite material that can be elastically deformed after receiving an external. A twin-crystal density of the calcite particles is measured after an external force is applied to the composite material, to convert the twin-crystal density to a strain by an approximate formula set in terms of a strain (%) generated in the composite material and a twin-crystal density Dtw (lines/mm) of the calcite particles, and further to convert this strain to a stress by the elastic modulus of the composite material, whereby to estimate the history of stress and strain. The approximate formula between strain and twin-crystal density is independent of the modulus of the composite material and is used in a common form.