# Effect of Injecting Epoxy Resin Adhesive into Cement Mortar on Tile Adhesion Performance
## 3 Results and Discussion
### Adhesive Strength of Tile with Epoxy Resin Injection Reinforcement  
Figure 13 shows the adhesion strength based on the curing conditions. As seen in Figure 13a, under standard air curing conditions, the specimens with the epoxy resin adhesive exhibited the highest adhesion strength, regardless of the type of tile. This may be because the formation and dispersion of a polymer film based on the penetration of the epoxy resin into the cement matrix improves the bonding strength [19; 20]. The adhesion strengths of the porcelain and polished tiles were lower because of their small pore sizes and absorption rates, making it difficult for the mortar to penetrate and mechanically adhere to the tiles. Figure 13b shows the adhesion strength under water curing conditions. In comparison to air curing, the adhesion strength of DM and AM improved significantly with water curing, owing to the reduced moisture evaporation and stable hydration reaction. However, ERM demonstrated a lower adhesion strength than the other specimens when air-cured. This is presumably due to the mechanical degradation of the epoxy as it absorbs water, which also reduces the adhesion strength. Previous reports have also confirmed the degradation of the mechanical properties of epoxy, such as the tensile strength and elastic modulus, due to water absorption and the plasticization effect [21; 22; 23]. Figure 13c shows the adhesion strength under freezing-thawing conditions. Overall, the adhesion strength under freezing-thawing conditions was lower than that under water curing conditions. In particular, the adhesion strength of ERM was reduced as a result of the water curing performed prior to freezing-thawing and the stress caused by the different linear expansion coefficients of the epoxy resin adhesive and mortar. Figure 13: _Cont._Figure 14 shows the effect of salt immersion on the adhesion strength of porcelain tiles. The adhesion strengths of the tiles after salt immersion were 51, 24, and 16% lower for DM, AM, and ERM, respectively. The penetration of chlorides supposedly reduced the durability of the DM and AM specimens and impacted the adhesion performance. Conversely, in the case of ERM, the epoxy resin functioned as a coating agent for the mortar, thus minimizing the loss of durability due to chloride penetration; however, the adhesion strength still decreased as a result of the moisture degradation of the epoxy itself. Figure 14: Adhesive strength of porcelain tile by salt immersion. Figure 13: Adhesive strength based on different curing conditions: (**a**) air, (**b**) water, and (**c**) freezing-thawing. Figure 15 shows the adhesion strength of the porcelain tiles before and after the removal of laitance. The adhesion strength before the removal of laitance was lower than that after the removal, regardless of the type of mortar. The use of ERM improved the adhesion strength by approximately 96 and 49% compared to that of DM and AM, respectively, prior to laitance removal. The adhesion strength of ERM prior to laitance removal still exceeded those of the DM and AM specimens following laitance removal. This is attributed to the direct effect of the epoxy reinforcement after penetrating the mortar and reaching the cement interface. The results of the laitance removal indicated that ERM improved the adhesion strength by \(\sim\)65 and 27% relative to DM and AM, respectively. ERM produced excellent adhesion strength, regardless of whether laitance was removed, thus demonstrating its superior adhesion. Details of the adhesive strength based on curing conditions, salt immersion and laitance are shown in Table 3.  
Figure 15: Adhesive strength of the porcelain tiles based on the laitance of concrete.