Effect of Waiting Time Before Re-vibration on Flexural Behavior of Reinforced Concrete Beam

Re-vibration, which is the process of repeating the operation of vibration of fresh concrete after a time interval, may be useful to enhance the mechanical properties of concrete (compressive strength, tensile strength, flexural strength, and modulus of elasticity), and also to get the maximum applied load, first crack load, deflection at mid span, stiffness and strain, particularly when successive layers of fresh con[1]rete were placed and the upper layer of fresh concrete was partially hardened. After a period of time, the aggregate particles are rearranged by the re-vibration process, and any trapped water is removed, potentially enhancing the concrete's compressive and tensile strengths. The use of re-vibration can help to remove plastic shrinkage cracks for exposed concrete. The amount of time that re-vibration lasts has a big impact. Using the re-vibration technique in construction of structural members is expected to improve the structural properties of the beams, and cracking. The effect of the waiting time before re-vibration must be investigated and time duration of vibrations on the structural response of flexural reinforced concrete beams to establish and verify the best process to apply this technique. The purpose of this study is to examine the impact of waiting time before re-vibration. and variable time duration for vibration and re-vibration operation of structural response for flexural reinforced concrete beams and using Ordinary Portland Cement-type 1, with w/c ratio of 0.4, and a greater number of re-vibration time lag intervals ranging from half an hour to two hours to evaluate the impact of re-vibration on the mechanical properties of concrete with different time duration of vibrations ranging from 15 to 60 seconds. The experimental schedule includes a total of 28 twenty-eight rectangular rein[1]forced concrete beams of dimension (125 mm x 250 mm) and length of 1500 mm was prepared for this work. Which were classified into seven groups Each group includes four samples. Beams for group (A, B, C, D, E and F) reinforced with longitudinal top reinforcement of (2ø10mm) and bottom reinforcement of (2ø12mm) with transvers reinforcement (Stirrups) ø12mm all over the beams except group F which are without transverse reinforcement and group G is without longitudinal and transverse reinforcement. Additionally, 144 cylinders with dimensions of 300 mm in height and 150 mm in diameter were utilized to evaluate the concrete's compressive and tensile strengths. After 56 days, these samples were analyzed in an attempt to study the impacts of vibration, and the effect of re-vibration delay and vibration duration on the development of concrete strength. The results have shown that the mechanical properties of concrete, ultimate load, first crack load and deflection at mid-point with various time duration and re- vibration techniques was increased for the 1st one hour and re-vibrated for 45 seconds time duration. After that for waiting time 1.5 and 2 hours and re-vibrated for 60 seconds was decreased.