Comparison of Break-off and Pull-off test results for determining compressive strength of steel fiber reinforced concrete

Here, the efficiency of the non-destructive Break-Off (BO) and Pull-off tests was investigated for assessing the in-place compressive strength of steel fiber reinforced concrete (SFRC). SFRC was studied due to its advantages in increasing tensile and flexural strength in particular. To provide a through and comprehensive database, 24 mix designs were selected with cement contents of 400, 450 and 500 kg/m3 with constant water/cement ratio of 0.4 for all mixes, two maximum aggregate sizes of 12.5 and 25 mm along with steel fiber volume fractions of 0%, 0.33%, 0.67% and 1% for ages of 14, 28 and 90 days. A total of 360 Break-Off and Pull-off tests and 216 standard cube tests were carried out in this investigation.Then, effective parameters of SFRC and non-destructive tests results were evaluated. The studies showed that volumetric percentage and features of steel fibers had a significant influence on concrete properties as well as Break-Off and Pull-off tests results. According to the experimental results it could be generally concluded that the influencing factors, namely, SFRC properties due to presence of steel fibers and non-destructive tests significantly affect the results as follows:Generally, for a constant W/C ratio, it can be concluded that raising the cement content increase the mean values of Break-Off and Pull-off strengths.
In adition to, conventional numerical regression model was developed in this study. Statistical indices were used to compare the efficiency and accuracy of model. The result of this study has confirmed the accuracy of linear regression model for non-destructive tests.