Effects of chemical and mineral admixtures on the foam indexes of cement-based materials

Air in cement-based materials is one of the important parameters affecting its properties in fresh and hardened states. Various types of chemical and mineral admixtures have been combined and used in cement-based materials. This makes the formation and stability of air bubble in fresh cement-based materials very complicated, and the control of air void in cement-based materials difficult. In this paper, air-related issues of cement-based materials were evaluated by foam indexes and surface tension test. The effects of mineral admixtures, including slag, fly ash and silica fume, and chemical admixtures, including superplasticizers, viscosity-modified admixtures and air-entraining admixtures on the foam indexes were studied. Results showed that surface tension is one of the factors affecting foam ability and foam stability, but not decisive one. Foam ability and foam stability of cement-based materials depend on many factors, such as types of chemical admixtures, compatibility of chemical admixtures, fineness and its chemical compositions of mineral admixtures.