چكيده به لاتين
The crack in concrete pavements is a place for the penetration of corrosive substances, oil, and water into the pavement and reduces its long-term durability and level of service. One of the causes of cracks in concrete pavements is plastic shrinkage cracking, which is caused by the rapid drying of the pavement surface due to the evaporation rate of the surrounding environment, and the formation of negative surface capillary pressures. The environmental evaporation rate is a function of climate factors, and changes in environmental conditions affect the severity of cracking. Also, the use of synthetic fibers is a solution to control and reduce this type of cracking. In this study, using ASTM C1579 method, the temporal and geometric characteristics, including the time of balance of bleeding and evaporation, time of the start of cracking, crack length, mean crack width, and cracking area in 27 different climate conditions were examined. Climate conditions include a combination of three environmental temperature variables, three relative humidity variables, and three different wind flow velocities. The continuous video recording system and the analysis of images taken by the digital microscope were used to measure the characteristics. Also, the effect of adding one type of synthetic fibers based on polypropylene in micro dimensions and two types of these fibers in macro dimensions in both hot and dry climate conditions in controlling and reducing cracking was investigated. The results showed that among the temporal characteristics, balance time, and geometric characteristics, the cracking area had the most significant effect due to the change in environmental conditions. It was also observed that the change in the percentage of relative humidity has the greatest impact on the temporal and geometric characteristics of cracking. Combining mild climate factors with harsh climate factors can significantly reduce the severity of cracking. Also, the results of multivariate linear regression analysis on the crack area showed that the percentage of relative humidity played an essential role in the crack area, the effect of ambient temperature and wind speed is close to each other. Micro polypropylene fibers have the best performance in reducing the mean crack width. Macro polypropylene fibers perform better than micro propylene fibers in reducing cracking length, especially in harsh environmental conditions. It has also been shown that the effect of Forta fibers in controlling and reducing cracking is slightly better than Barchip fibers. But the results of these two fibers are close to each other.
