Preparation of TiO2/epoxy resin composite and its effect on mechanical and bonding properties of OPC mortars

Abstract

Bisphenol A-type epoxy resin reinforced by TiO2 with different dosages (0, 1%, 3%, 5%) was for the first time used as a polymeric admixture to prepare ordinary Portland cement (OPC) mortars in this study. Tensile strength of the TiO2/epoxy resin composite, and flowability, compressive strength and flexural strength as well as the bonding strength of OPC mortars were measured. Scanning electron microscopy (SEM) was also carried out to observe the interfacial transition zone (ITZ) between sand and OPC paste, and the bonding interfacial transition zone (BITZ) between OPC mortar (either modified by the epoxy resin or not) and a substrate material. Results showed the tensile strength of the TiO2/epoxy resin composite was enhanced to a greater extent with a higher content of TiO2 nanoparticles. A lower flowability of mortar samples when modified by the epoxy resin was observed compared to the pure OPC counterpart. The compressive, flexural strength, flexural toughness indicated by the flexural-to-compressive strength ratio and bonding strengths of TiO2/epoxy resin-modified mortars quantified by the interface tensile strength were noted to be the highest for mortars modified by the epoxy resin containing 5% TiO2. For interface tensile strength, it was found that the increment was 7.3% and 14.6% for the mortar specimen modified by the epoxy resin with 5% TiO2 compared to the mortar modified by the same amount of epoxy resin but without TiO2 and the control with no epoxy resin respectively. SEM results showed that both ITZ and BITZ were denser when epoxy resin was added into the OPC mortar systems, leading to an improved flexural toughness and bonding strength. Several enhancing mechanisms are proposed including epoxy resin bridging effect, pore-filling effect, claw-like adhesion and delayed water loss and rigid TiO2 particles with good adhesion towards epoxy resin polymer molecules.