The Research Of Preparation And Gelling Properties Of Polyurethane/Cement Mortar

At present, the research for modification of cement mortar by polymer focuses on poly(acrylic-acid), epoxy resin, styrene-butadiene emulsion, and so on. However, there are little reports of the modification of cement mortar by waterborne polyurethane in the literature. The research that the preparation and properties of waterborne polyurethane, the preparation and mechanical properties of waterborne polyurethane/cement mortar and the hydration reaction and gel properties of polyurethane cement paste, were developed in this paper.Two kinds of waterborne polyurethane with water-soluble and water-dispersible were designed and prepared in this paper. The chemical structures of water-borne polyurethanes prepared were characterized respectively by FTIR and1H-NMR, The effect of temperature and synthesis technology on synthetic reaction of water-soluble polyurethane was investigated. The intrinsic viscosity of water-soluble polyurethane, the solid content and surface tension of water-dispersible polyurethane were measured. The intermiscibility of polyurethane and cement mortar was observed, the results showed that water-soluble polyurethane that can be uniformly dispersed in cement paste. The hydration of cement mortar was stop, and the compressive and rupture strength were almost zero when the added content of water-soluble polyurethane was30%while the largest added content of water-dispersible polyurethane in mortar was38%, and Non-uniform phase, such as flocculent deposit and spheroidal would appeared in Mortar paste when the content exceeded8%.The waterborne/cement mortar was prepared with waterborne polyurethanes as modifier of cement mortar. The effects on polyurethane/cement mortar key factor in the mechanical properties were studied by the L16(45) of the orthogonal table (the elastic modulus of cement mortar as the evaluation point), the optimal ratio A3B1C1D3E1was obtained by optimization analysis. The mechanical properties of water-soluble polyurethane(with different molecular weight)/cement mortar and water-dispersed polyurethane/cement mortar were studied by contrast test, the results showed that compression strength and Rupture strength of cement mortar increases with an increase of water-borne polyurethane content in a low range, and decrease when water-borne polyurethane content is larger than a certain percentage. It has been found that there exists maximum compression strength and rupture strength occurs at0.8%waterborne polyurethane content. The compression strength and rupture strength of water-dispersed polyurethane/cement mortar were higher than the water-soluble polyurethanes/cement mortar prepared at the same prescription and the value of the maximum compression strength and rupture strength were38.6MPa and7.5MPa respectively.The effect of water-borne polyurethane on the release of heat of hydration during cement hydration reaction was analyzed; the structure of surface, pore, and crystal of the cement hydration products were analyzed by Nitrogen adsorption、SEM、XRD etc,. The results showed that the waterborne polyurethane has retarded effect on hydrated reaction of cement, but it led to the cement particles homogeneous dispersed in the mortar paste, promote more complete hydration of cement particles, hinder the formation of ettringite, promote the formation of C-S-H gel and calcium silicate, crystallization of hydration are more structured. Amount of the polyurethane can reduce the distribution and radius of pore reduced, increase micro-porous surface area of products of cement hydration. The specific area of BET of cement hydration products reached to29.231m2/g and the average pore diameter was64.6[A0].