# Experimental Evaluation of the Durability of Concrete Repair Materials
## 3 Results and Discussion  
### Compressive and Flexural Strength  
Table 2 and Figures 4 and 5 show the compressive and flexural strength results. The specimens were divided into intact (no notch), notched (unrepaired), epoxy, impregnant, and epoxy/impregnant groups. After 28 days, the compressive strengths of the intact samples with target strengths of 20 and 40 MPa were 21.3 and 39.1 MPa, respectively. For the specimens with a target strength of 20 MPa, those with 2 and 5 mm notches had strengths of 20.1 and 18.8 MPa, approximately 5% and 15% lower than the intact specimen, respectively. Among the repaired specimens, those repaired with epoxy or epoxy/impregnant were approximately 2-5% stronger than those repaired with impregnant. In addition, the difference between the strength of the impregnant and epoxy specimens was greater when the notches were wider. For the specimens with a target strength of 40 MPa, those with 2 and 5 mm notches were approximately 10% and 17% weaker than the intact specimen, respectively. Among the repaired specimens, the epoxy and epoxy/impregnant specimens were approximately 2-5% stronger than the impregnant specimens. When the cracks were narrower, the difference between the strength of the impregnant and epoxy specimens increased [30; 31]. When cracks occur in such a way, the concrete performance is degraded, and the epoxy material that serves as the filling has an eminent adhesive strength, so it behaves integrally with the concrete. However, the impregnant material is a coating type and has a lower concrete strength performance than epoxy.  
Figure 4: _Cont._  
Figure 4: Compressive strengths of specimens with target compressive strength of **(a)** 20 MPa and **(b)** 40 MPa.  
Figure 5: Flexural strengths of specimens with target compressive strength of **(a)** 20 MPa and **(b)** 40 MPa.  
The flexural strengths of the intact specimens with target strengths of 20 and 40 MPa were 3.7 and 5.3 MPa, respectively. For a target strength of 20 MPa, the unrepaired notched specimens were approximately 50% weaker than the intact specimen. Among the repaired specimens with 2 and 5 mm notches, the epoxy specimens were approximately 2 and 1.5 times stronger than the impregnant specimens, respectively. For a target strength of 40 MPa, the unrepaired notched specimens were more than 60% weaker than the intact specimen. Among all the repaired specimens, the epoxy specimens were approximately 1.5 times stronger than the impregnant specimens.  
These results show that the compressive and flexural strengths of the concrete decreased when there were cracks, and that the epoxy and epoxy/impregnant had clear repair effects. However, the impregnant did not have a significant effect on the strength. Furthermore, the epoxy/impregnant repair had an insignificant effect on the specimen with a target strength of 20 MPa and a 5 mm notch. It is likely that this is because just three specimens were used; such errors may be expected to be reduced if more specimens are used.  
As for the strength, the epoxy repair is more effective than impregnant repair and is expected to be effectively applicable to infrastructure such as bridges, roads, and dams on which high loads act.