Experimental investigation on flexural shear capacity of beams cast in two phases

Abstract

The aim of this research is to investigate on flexural shear capacity of RC Beams which are cast in two phases. Suitability of using epoxy as bonding agent under one point loading was investigated and compared with two phases of concrete joined without any bonding agent. To achieve the objectives, total thirty half scale specimens were constructed and tested. Ten of them, Group A, were constructed to obtain concrete strength 3ksi with and without using bonding agent. Similarly for Group B and C target strength were respectively 4ksi and 5ksi. All the specimens were constructed in two phases except the control specimen of each group. At first phase, for three groups total three beams were fully cast and twenty seven beams were half cast. At second phase, after one day nine half cast beams (from each group three beams) were cast fully with and without using bonding agent. Same procedures were followed after three days and seven days. So, total twenty seven half cast beams were fully cast at phase two. Specimens were tested under incremental one point loading. The load was applied by Universal Testing Machine at midspan of the beam. A constant strain-controlled loading was applied with the movement rate of the platform being 5mm/min. Time vs load was continuously monitored and data was saved automatically. Deflections of the beams were also monitored with a video extensometer and time versus deflection data was stored continuously. These data are then combined to prepare load versus deflection curves which are the basis of analysis for beam strength. Load-deflection curves of beams were plotted to study their behavior under one point loading. Behavior of the beams such as ultimate load, deflection and failure pattern are compared with that of fully cast beams and beams cast in two phases by using bonding agents. By means of constructing beams in two phases with using bonding agent 50MPa Epoxy and 75MPa Epoxy, the flexural shear capacity of the beams can be increased. The beams cast in two phases with using bonding agent 75MPa Epoxy have higher values of ultimate load than using 50MPa Epoxy. So, 75MPa Epoxy is more effective as a bonding agent. The effect of age of concrete after which the second phase of construction is started on ultimate load with using bonding agent 50MPa Epoxy and 75MPa Epoxy is very less. So, the effect of applying epoxy as a bonding agent with the variation of days is insignificant once the concrete is set. For concrete strength of 3ksi, the increase in ultimate load for beams cast in two phases after one day respectively by using 75MPa Epoxy and using 50MPa Epoxy are almost 18.4% and 3.9% than compared to that of fully cast beam. For concrete strength of 4ksi, it was 11.72% for beams cast in two phases after one day by using 75MPa Epoxy than compared to that of fully cast beam but for the beam cast in two phases after one day by using 50MPa Epoxy, ultimate load did not increase than the fully cast beam. Again for concrete strength of 5ksi, the ultimate load increases almost 7.82% and 5.97% respectively for beams cast in two phases after one day by using 75MPa Epoxy and using 50MPa Epoxy than compared to that of fully cast beam. Similarly for concrete strength of 5ksi, ultimate load increases almost 8.2% and 4.2% respectively for beams cast in two phases after three days by using 75MPa Epoxy and using 50MPa Epoxy than compared to that of fully cast beam. Again for concrete strength of 5ksi, increase in ultimate load for beams cast in two phases after seven days respectively by using 75MPa Epoxy and using 50MPa Epoxy are almost 6.5% and 1.2% than compared to that of fully cast beam.