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Published on Jul 27, 2014
This video shows the concreting of the bridge deck of the reconstructed Whitchurch Bridge. It was poured in one go on the hottest day of 2014 so far and required approximately 230 cubic metres of readymix concrete. For clarity, the video has subtitles identifying the eight phases of the pour and these are as follows:
1) Setting up the pipeline. Because of the length of the bridge deck, extension pipes were attached to those on the boom of the Putzmeister Elephant concrete pump. These stretched to the starting point of the pour on the Whitchurch side of the bridge deck. As the pour progressed towards its completion on the Pangbourne side of the bridge deck, these were removed.
2) Readymixed concrete delivery. The concrete was brought in by a fleet of readymix trucks. Here, one truck is seen reversing up to the pump hopper to discharge its load whilst the previous truck is hosed down in the site's designated cleaning area.
3) Priming the pump and pipeline. Before any concrete can be pumped, a slurry consisting of cement and water has to be pumped down the pipeline first to prime or coat it. If this was not done, any concrete being pumped would rapidly lose its moisture into the surface of the pipes and lacking the necessary plasticity for it to flow smoothly would block them.
4) Pumping starts Once the priming is complete, the Putzmaister Elephant pumps the concrete from the trucks onto the deck where it is squeezed out like toothpaste.
5) Poker Vibration The rather phallic looking vibrating poker is inserted into the poured concrete to "chivvy out"as many air bubbles as possible. This is especially important since the presence of excessive quantities of air pockets would significantly weaken the concrete.
6) Tamping This machine stretches across the width of the poured concrete to level and smooth off the surface. Its vibrating action will also help to force air bubbles to the surface of the poured concrete.
7) Quality Control Like all manufactured products, concrete has to be checked for strength and quality. Here a technician from an independent laboratory is testing the concrete's consistency to ensure it is neither too dry nor wet. He also makes test cubes that will be crushed at 8 and 28 days to ensure the concrete has reached the correct strength.
8) Curing Behind the construction crew a fine mist of water can be seen being sprayed over the surface of the concrete that has already been laid and levelled. This water forms the first part of a protective covering over the surface of the concrete to prevent it from hardening too quickly. Plastic sheeting is then laid down over the setting concrete as a longer term protection. If these curing measures were not applied, the concrete would set too quickly causing surface cracks to occur and weaken it.