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There are a few different processes by which a contractor can make concrete stronger. For those who are not in the business of pouring concrete, you may hear such terms as pre-stressing, post-tensioning and pre-tensioning. To better understand what is meant by these terms so that you can understand what your contractor is saying and why he/she is choosing these processes for your concrete project, the following definitions and explanations between the processes are provided.
Pre-Stressing Concrete
The concept behind pre-stressing concrete is to make the concrete feel some stress before it hardens. It is tested to its limits so that it can support the weight of whatever structure you place on it. To pre-stress concrete, it is often poured over a tensioned grid of metal. The metal grid may be tightened either before or after the concrete is poured. The grid acts as both the reinforcement the concrete needs and the stressing mechanism to prevent fracturing.
Pre-Tensioning Concrete
Pre-tensioning concrete involves pouring wet concrete onto a metal grid that has already been set in "tense" mode. The metal grid is pulled tight in all directions. The concrete is poured over the top of this grid to create a concrete slab. Pre-tensioning is often done in a controlled setting, usually in a factory, where all of the steel rods in the metal grid can be held tightly by machines. The benefit to pre-tensioning and creating slabs is that the concrete is then ready for installation and nothing else needs to be done with the concrete slabs.
Post-Tensioning Concrete
Post-tension in concrete is achieved through laying down a steel grid in-situ. The grid is installed in the ground or over the tops of other concrete supports. Then the concrete is poured over the top of the grid until the grid is completely covered. Before the concrete has a chance to full dry and harden, all of the rods that make up the grid are connected to machinery that pulls the rods taut and creates the expected tension and effect on the concrete. Now the concrete is, effectively, stressed. This leaves the concrete able to distribute not only the weight of the structure above it, but any tremors or vibrations that rattle it as well. Post-tensioning is commonly used in the construction of roads and bridges, as well as foundations for buildings in areas of the country that are prone to earthquakes.
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