The formation of ettringite and the expansion associated with it were studied on paste made from Portland cement, two Al-bearing compounds such as calcium aluminate cement and calcium sulphoaluminate cement, and calcium sulfate with different reactivities (anhydrite, α-hemihydrate and gypsum). The hydration process and formation of ettringite in the binders with different content of calcium sulfate was investigated by free expansion testing, isothermal conduction calorimetry, X-ray diffraction (XRD) and environmental scanning electronic microscope (ESEM). Results showed that the reactivity and amount of the calcium sulfate determined the balance between the hydration products of ettringite and monosulfate, and also the early hydration kinetics including the formation content, size and location of ettringite. It was also found that all the ternary systems with higher addition of calcium sulfate expand significantly. When a higher content of α-hemihydrate was added, besides ettringite much secondary gypsum also forms in voids between cement granules, which exerted adverse effects on the properties of ternary systems. However, the formation content of ettringite appeared to have no connection with the expansion value.

Redispersible polymer powders of Vinyl acetate / ethylene copolymer (EVA) and Ethylene/vinyl laurate/vinyl chloride copolymer (E/VL/VC) were applied to modify decorative mortar. Results showed that EVA and E/VL/VC both smoothed the surface of mortar, decreased the leachability of Ca2+, K+, Na+ ions and increased the leachability of SO42- in the surface leaching solution. However, with redispersible EVA and E/VL/VC being the same content, E/VL/VC-modified mortar hydrated for 1d showed lower bulk density, better surface hydrophobicity, higher alkalis leachability and more severe efflorescence. Moreover, EVA and E/VL/VC both had little influence on the components of efflorescence substances on the surface of mortar.

Effect of latex film distributions on flexibility of redispersible polymer powders modified cement mortar were evaluated by scanning electron microscopy (SEM). Latex film distributions such as forming interpenetrated networks embedded in cement pastes, covering cement hydrates locally, bonding cement hydrates together, bridging aggregates were all beneficial for the improvement of flexibility of cement mortar. Latex film distributions such as remaining single particles in cement mortar, completing film formation unsuccessfully, film formation on surfaces of aggregates, bonding cement minerals to surfaces of aggregates may contribute little to the improvement of flexibility of cement mortar.