This paper presents the results of pull-off and twist-off tests on bond strength between fiber reinforced polymer (FRP) and cement-based mortar substrate and is carried out to investigate the effect of moisture and temperature at the time of installation. In the field of fracture mechanics, it is common to classify the pull-off and twist-off tests as mode-I and mode-II fractures, respectively. A total of 27 specimens were prepared and 243 tests were conducted. In order to evaluate the significance of each factor and their interactions, analysis of variance (ANOVA) was performed. Results revealed that surface moisture content and temperature significantly affect the adhesion of the two materials and bond strength. ANOVA confirmed that these two parameters have great influence on bond strength between FRP and cement-based mortar, although compressive strength and total porosity of substrate were not statistically significant. To estimate the bond strength by considering the effective parameters and based on the collected experimental data, new and more accurate relations were proposed using nonlinear regression techniques.

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