Study On The Performance Of Soap-free Emulsion Modified Cement-based Materials

Cement-based material is a kind of typical brittle material. Because of the nature of its larger rigidity and the lack of resilience, its application is limited by a lot. Polymer modified cement-based materials refer to the cement mixed with polymer materials which dispersed in the water or can be dispersed in water. Due to the addition of polymer, the working performances, flexibility, the bonding strength of cement-based materials are improved obviously. At the same time, it makes the resistance to freezing-thawing and permeability resistance of cement-based materials better. In our country, the polymer modified cement-based materials are mainly used in hydraulic structures, the repair of concrete structures and anti-corrosion materials, adhesives, etc.Emulsifier which contains small molecules in ordinary polymer emulsion does harm to modified mortar or concrete and can cause certain pollution to the environment. Soap-free emulsion polymerization which is a kind of new technology based on the conventional emulsion polymerization has great prospects for development in the construction industry, coating and adhesive application.In this paper, soap-free acrylates emulsion with better dispersion is prepared by acrylates monomer and reactive monomers using the soap-free emulsion polymerization technology. It is used to modified cement mortar or concrete, and the influences on the properties of cement mortar or concrete are explored.1. Soap-free acrylates emulsion is prepared by using BA and MMA as monomers, VPEG and SMAS as reactive monomers, KPS as initiator and adopting semi-continuous soap-free emulsion polymerization. Through the 5 factors 4 levels of orthogonal design experiments, the influences of 5 factors(the ratio of monomers, the dosage of VPEG and KPS, polymerization temperature and time) are discussed. And the best polymerization conditions were determined by range analysis. The optimum dosage of SMAS and defoaming agent is determined respectively by single factor analysis. The stabilities of soap-free emulsion are tested, and the results are all qualified. By FTIR analysis of soap-free emulsion, the molecular structure of the polymer is concluded.2. Soap-free emulsion is used for the modification of cement mortar or concrete.(1)The influences of soap-free emulsion on water requirement of normal consistency and the setting time of cement are investigated, and the results indicate that with the increase of polymer cement ratio, water requirement is reduced and the setting time of cement increases slightly;(2)The influences of the two conditions(fixed water cement ratio and fixed fluidity) and the soap-free emulsion containing defoaming agent on mechanical properties of modified cement mortar are discussed, it is indicated that the compressive strength of modified cement mortar is decreased, but when the P/C is 1% under the condition of fixed fluidity, the flexural strength is the highest; When the dosage of soap-free emulsion containing defoaming agent is 5%, the flexural strength of mortar modified is the highest. And three different curing system is adopted to study the properties of the above three kinds of modified mortar, it is found that the properties of modified cement mortar using 7d standard curing and 21 d room temperature curing is the best.(3)The influences of P/C on durability of modified cement mortar or concrete under the condition of fixed fluidity and using soap-free emulsion containing defoaming agent are studied, the results declare that the resistance to chloride ion penetration and the resistance to freezing-thawing of the modified mortar or concrete are improved.3. By FTIR and XRD analysis of cement paste, the interaction between soap-free emulsion and cement is researched. And through the SEM, the microscopic structure of modified cement mortar is observed.