A review on the modification mechanism of polymer on cement-based materials

Abstract

This paper conducted a comprehensive investigation into the role of polymers in cement-based materials. First, the modification mechanism of polymers on cement-based materials based on physical and chemical effects are analyzed. The polymers are adsorbed on the surface of cement particles and cement hydration products through electrostatic attraction or hydrogen bonding, and filled in the pores or interfacial areas, and then transformed into a three-dimensional interpenetrating network structure, so as to densify the matrix materials. Then, the effects of polymers on the cement hydration reaction were introduced. It is mainly attributed to the adsorption behavior between polymer particles, and polymer films with cement causes them to cover the surfaces of cement particles and hydration products, which to some extent restricts the effective diffusion of various ions, such as Ca2+, AlO2−, SiO42−, SO42−, etc., as well as water in the system. And the complexation of functional groups in the polymer with Ca2+ hinders the nucleation and precipitation of calcium-containing hydration products, which in turn delays the hydration reaction process. In terms of strength, as it can be due to the agglomeration of polymer chains, increased porosity arised from generated CO2 gas and entrained air during preparation, the improvement effect of the polymers on cement-based material's compressive strength is not apparent or it shows a decreasing trend. As the role of “microfibers” and “bridge”, many filamentous or network structures composed of flexible polymer membranes dramatically improve the flexural strength and toughness, and also enhance the bonding property of the matrix material. It is expected that the polymers containing designed specific structures according to target property will be applied in cement-based materials, and the universal guidelines and regulations will be provide for expanded application of polymer modified cement-based materials (PMCBMs) in the construction industry.