Improve the structural performance of GFRP longitudinally reinforced concrete beams have a cold joint using CFRP sheets

This research aims to assess the structural efficiency of reinforced concrete beams with casting joints made of GFRP bars that are longitudinally reinforced and CFRP sheets added to the system. The focus is mainly on the effects of casting discontinuities at strategic locations, such as the shear and flexural regions, that may significantly affect the structural strength. To determine the initial hardening time, the effect of retarding plasticizers on hardening on the initial setting time and mechanical properties of concrete was studied. Then, seven beams made of high-strength concrete were cast and subjected to failure testing in the initial phase of the study, two beams reinforced with GFRP bars and three with conventional steel reinforcements have a cold joint. The third stage involved casting two more beams with GFRP and having cold joints at the flexural zone, representing the most critical scenario similar to previous beams reinforced with CFRP sheets placed in different configurations. The results show risks in concrete beam have joint at flexure or shear zone due to delayed casting that the lowest failure value for beam reinforced longitudinally with GFRP bars have cast-joint was 23.6 kN a decreasing till 46% due to weak efficacy GFRP bars at joint. So, for these beams must be strengthened by the CFRP layers. The effect of the CFRP layers was improved a behavior of these beams. The strengthened of these beams reinforced longitudinally with GFRP bars have joint at mid by using CFRP sheets was increased a load capacity about 111% to 118%. This paper provides new information about CFRP sheets debonding at the casting joint was after concrete crushing in the compression zone. According to the results, CFRP strengthening is a good way to increase load capacity and reduce the flaws that casting joints introduce. Generally, this study endeavors to yield novel insights into the behavior of such composite systems to enhance concrete beams have cold joints.