Study on the effect of waterborne epoxy resins on the performance and microstructure of cement paste

Concrete repairing, rehabilitation and prolonging the effective service-life of structures plays an important role in building field worldwide. The polymer-modified cementitious material dominated by different resins has been widely applied in repairing and reinforcing, wherein the epoxy resin is a material with excellent comprehensive properties. The waterborne resin gets a better compatibility and coupling effects with the cement hydration. In this paper, the effect of two waterborne epoxy resins on the hydration of cement and the microstructure of paste have been studied. The mechanical properties, mesoscopic morphologies after mixing and curing, the hydration products, chemical bonds and three-dimensional structures of the cement paste with emulsion type epoxy resin (EEP) and non-emulsion type epoxy resin (NEP) (with content of 5%-80% wt.) are studied by optical microscopy, field emission scanning electron microscopy, X-ray diffractometer, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray computed tomography. The results show that EEP and NEP have a significant effect on the formation of portlandite crystals at an early stage. NEP is more effective than EEP on the toughening effect with the content of 40% wt. The stress-strain curve of non-emulsion epoxy cement paste (NEPC) manifests an obvious secondary step, and the fracture strain value rises from 0.6% to 1.2-1.3% which proves the NEP enhances the resistance to cracking. The resin in NEPC mainly consists of a layered network structure with the continuous phase in the transverse direction.