Testing concrete beams
Tom Sheldrake
Objective
The objective of this session was to test the strength of concrete using different reinforcements and different curing times. We used the same mix of concrete for all the beams and cubes.
Method
For this experiment we started by making the mix of concrete. This consisted of 75kg ballast, 12kg cement and 5.5kg water. After we added these amounts to the mixer we carried out a slump test. This is a simple test to make sure that the consistency of the concrete was right. You simply pour the mix into a cone making sure that it is compacted, remove the cone and place it next to the pile of concrete. You then lay a steel rod across the top of the metal cone and measure the distance from the rod to the pile of wet concrete. The ideal mixture should have slumped between 30-60mm. Ours measured 40mm. We then used three identical moulds measuring 150x150x750mm to create the concrete beams. One was plain, the second had two 5mm steel R bar reinforcements and the third had two 8mm steel T bar reinforcements. These were placed slightly in from the bottom and sides of the beam to avoid exposure to oxygen and therefore prevent corrosion. When pouring the mixture into the moulds we used a vibrating compactor to ensure that the concrete was compacted sufficiently. This piece of equipment us normally used for basements so was more than required for the job. It made the concrete flow like a liquid and air bubbles rise. We then tested these on a four point bend rig. This was to see how much the reinforcements strengthened the beams.
