| The effect of styrene-acrylic emulsion modified resistance to sulfate attack and impermeability of sulphoaluminate cement has been studied in this paper. Styrene-acrylic emulsion was synthesized by pre-emulsification and semi-continuous emulsion polymerization, with styrene and butyl acrylate as monomers. Different kinds of styrene-acrylic emulsion have been synthesized by changing initiator dosage, emulsifiers dosage, the ratio of styrene and butyl acrylate. The properties, such as monomer conversion, solid content, particle size and distribution of later particles, stability, viscosity and MFT have been tested. It can be find the best composing of styrene-acrylic emulsion. Mix the different kinds of styrene-acrylic emulsion into sulphoaluminate cement, test the mechanical property, impermeability and resistance to sulfate attack of the polymer cement. In order to clear about the mechanism of styrene-acrylic emulsion modified cement, X-ray, SEM-EDS, infrared analysis and pore structure analysis are studied.The results show that styrene-acrylic emulsion has perfect property, such as little aggregates, high solid content and monomer conversion, big viscosity and particle size, low MFT and so on. At this time initiator dosage is 5‰of the total amount of monomers , emulsifiers dosage is 3.0% of the total amount of monomers, the ratio of styrene to butyl acrylate is 1.5:1.The mechanical properties of sulphoaluminate cement modified by styrene-acrylic emulsion are not as good as that without styrene-acrylic emulsion. Sulphoaluminate cement modified by styrene-acrylic emulsion can be used in non-load-bearing type structure, such as surface repair of bridge. Compressive strength and flexural strength of the polymer cement mortar are relatively high when initiator dosage is 5‰of the total amount of monomers, emulsifiers dosage is 3.0% of the total amount of monomers, the ratio of styrene to butyl acrylate is 1.5:1, the ratio of polymer to cement is 7.5%, and it can be arrived at 4.9MPa and 28.0 MPa.Durability of sulphoaluminate cement has been impro??after entering styrene-acrylic emulsion. The infiltration height reduces greatly after entering styrene-acrylic emulsion. The flexural strength increases greatly after entering styrene-acrylic emulsion. The impermeability and resistance to sulfate attack of sulphoaluminate cement are best when initiator dosage is 5‰of the total amount of monomers , emulsifiers dosage is 3.0% of the total amount of monomers, the ratio of styrene to butyl acrylate is 1.5:1, the ratio of polymer to cement is 7.5%. Excessive amount of emulsifier can bring a mass of bubble. It makes a lot of pores in the cement paste. So the impermeability and resistance to sulfate attack decrease. MFT becomes higher and higher with the increase of styrene dosage. MFT are all above 32℃when the ratio of styrene to butyl acrylate is bigger than 1.5:1. So the film-forming property can not fully exert when the cement mortar is molded at room temperature.The micro-structure of materials decides the macro-behavior. Pore structure analysis shows that the proportion of harmful pores of sulphoaluminate cement significantly reduce after entering styrene-acrylic emulsion, and innocuous pores increase significantly. The total porosity reduces after entering styrene-acrylic emulsion. Styrene-acrylic emulsion modified the internal structure of sulphoaluminate cement. The cement paste has been hardened. SEM-EDS can farther explain that sulphoaluminate cement paste could modified by styrene-acrylic emulsion. It is also can be seen that a mass of membranous substance stride over the pores and play the role of bridge and tamping. The results show that the pore volume has been smaller and network structure has been formed. Infrared analysis shows that some active groups of polymer molecule make chemical reaction with hydration products, and new materials are formed. There are carboxyl and ester bond in styrene-acrylic emulsion. Ester bond may hydrolyze at alkaline conditions and form carboxyl. Carboxyl group and Ca2+ can form electrovalent bond. Different polymer chain can cross with each other by electrovalent bond. XRD analysis shows that the main hydration products of cement paste are AFt, aluminium-joints and iron gum. AFt in the polymer cement is reduced. It can be said that styrene-acrylic emulsion may postponed hydration of the cement paste.
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