Why do we cure concrete? We cure concrete to maximise its strength. i.e. increase structural integrity and reduce the likelihood of cracks. Put simply, concrete is a mixture of sand, cement and aggregate. It is the chemical reaction between water and the cement that causes the concrete to set. Water is a critical factor in the strength of concrete. Think of cement particles like pool balls, round and smooth. Once water is added they start to grow out capillary type arms that intertwine with the arms of surrounding cement particles. This is the process that makes concrete go stiff as the particles join up. Too much water and the particles are too far apart to bond strongly. Too little water and the capillary arms do not grow long enough to bond strongly. The trick is to have the correct amount of water in the mix. The concrete companies are on to this. The longer the water remains in the concrete, the longer this chemical reaction will occur, meaning that the concrete will continue to grow in strength. This is a process that we can control on site, and is known as CURING. Whenever we can see that a slab is drying out too fast (absence of bleed water) we apply anti-vap to the surface of the concrete after each time it is worked. We are preventing the slab, especially the top layer, from drying out too fast and becoming weak. At the completion of the pour we spray anti-sol A on the slab to “seal” the surface and prevent rapid moisture loss. We may also cover the slab with polythene to prevent rapid moisture loss. In the old days, slabs were “ponded” for a few days. It is said that some of the concrete in the Hoover dam is so thick that the curing process will take literally decades, and that enormous strength will be achieved.
Posted on: Mon, 06 Oct 2014 08:40:53 +0000
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