# Influence of Polymer Types on the Mechanical Properties of Polymer-Modified Cement Mortars
## 5 Discussions and Recommendations  
In this study, four different polymers (AC, PVA, SBR, and EVA) with two different dosages (0% and 3%) were employed to prepare polymer-modified cement mortars. The mechanical properties such as compressive strength, flexural strength, and pull-off bond strength were measured and compared with those of control mortars. The measured strengths were generally improved with the addition of polymers, and the results showed good agreement with previous literature. In general, the polymer-modified cement mortars containing EVA showed the best performance, with up to 33% and 63% increases in compressive and flexural strengths after 28 days, respectively, in terms of mechanical properties measured in this study. In comparison, AC, PVA, and SBR produced smaller (16%-46% compared to control) improvements in the flexural strength after 28 days. As shown in Figure 4, Figure 7, and Figure 8, the relationships between measured strength values were investigated and compared to a previous study [28]. Effects of the incorporated polymers were clearly expressed in terms of flexural strength rather than compressive strength. The reason for the better mechanical properties from the sample containing EVA is not clear at this moment, and further experimental studies must be conducted. It should be noted that the findings of this research are limited to the polymer dosage of 3% adopted in this study, and different dosages might significantly change the performance of produced PCMs. Therefore, the ranking of the investigated polymers using the limited dosage in this study should not be regarded as a general ranking for the effect of these polymers on the PCMs. Figure 8: Relationships between averaged flexural and pull-off bond strengths at seven and 28 days. Figure 7: Relationships between averaged compressive and pull-off bond strengths at seven and 28 days. American Concrete Institute (ACI) committee 546 recommends the compressive strength of repair materials to be higher than 28 MPa [32]. In addition, Sprinkel reported that the tensile bond strength of repair materials should be higher than 2.1 MPa for the repair of bridge deck structures [33]. In this regard, it can be seen that the measured properties of control sample prepared in this study satisfy the guidelines and recommendations. However, it is obvious that the repair materials showing higher strength and improved interfacial bonding should be selected for the better repair work for RC structures. Furthermore, it is not appropriate to conclude the best type of polymer based on the results of this study, and further experiments must be conducted to investigate the structural performance of repaired RC members using polymeric repair materials. It is known that the mechanical properties of cement mortar can be improved with the use of polymers due to the development of the polymer film. It is also believed that the polymer film inhibits crack propagation because of its high tensile strength. The effects of polymers on the mechanical properties were confirmed throughout this study, while systematic comparisons between the different commercial polymers were not included in the scope of this study. As mentioned previously, the ranking of polymers verified in this study could not be generalized, and further experimental studies focusing on the microscopic structures and air voids of PCMs might be important. Further research might be necessary for the better use of various polymers in practical applications, including patch repair, coating, floor leveling, and surface protection of concrete structures. Long-term investigations including durability and exposure tests are especially important for the selection and use of polymers. A long-term study might also be useful to determine the optimum replacement ratio of the polymer. It is known that durability performance can be improved with the use of a polymer. However, most of the previous research focused more on short-term behavior ranging between three and 28 days rather than long-term behavior.