Abstract:According to the technical requirements such as good fluidity, deformation ability, short setting time for concrete bridge crack grouting material, superfine Portland cement and sulphur aluminate cement mortar was composite modified by, styrene acrylic emulsion and ultrafine nano - SiO2, and the effects of the dosage of styrene-acrylic emulsion on the workability and mechanical properties of ultrafine cement slurry were studied systematically. Finally, the reasonable ratio of ultrafine cement slurry was determined. The test results show that although the styrene-acrylic emulsion has a certain adverse effect on the compressive strength of the ultrafine cement slurry, it can significantly improve the construction performance of the ultrafine cement slurry, and improve its flexure strength, tensile deformation ability and flexure ratio, so as to enhance the toughness of the ultrafine cement slurry.The superfine cement slurry modified by styrene-acrylic emulsion and nano-SiO2 is expected to be widely used in the repair of cracks in the floor of concrete Bridges.