Cement was used by the Romans, but modern concrete was invented by Joseph Aspdin in 1824. Concrete beams are increasingly used in homes as opposed to wood or steel alone. This is a function of cost, availability and strength. When building your home you may have considered using concrete beams. Before you make a final decision, you should acquaint yourself with the properties of concrete beams.
Concrete alone does not make for a very good building material, especially as a beam. For this reason, concrete beams often have reinforcing bars or "rebars" in the concrete. This provides the beams with extra tensile strength, keeping them from sagging or cracking under the pressure of the load that they bear. Rebars are placed into the beam mould before the concrete is poured and stressed to 70 per cent of their tensile strength. Concrete is then poured around the reinforcing bars. Once the concrete dries the stress is removed from the rebars.
Post-tensioned beams are the opposite of pre-stressed beams. Manufacturers place ducts in the mould, allowing the concrete to dry around the ducts. After the concrete dries, manufacturers insert threaded cables through the ducts. These cables are then stressed to 70 per cent of their possible tensile strength. The cables are anchored at either end of the ducts before the tensioning force is released. Once the force is released the ducts are filled with grout to protect the cables.
Modern concrete is made of very specific ingredients. These ingredients combine to give the concrete a strength greater than the sum of its parts. Silica, alumina, iron ore and lime are ground up and fired in a kiln. This produces a substance called clinker. The clinker is then ground into a fine powder after drying.
Creep is a deformation that can take place in concrete beams. The concrete becomes warped and bowed after high amounts of stress taking place over long periods of time. Concrete beams can sometimes have twice the amount of curve they were intended to have, resulting in a number of cracks in the beams. This is why many concrete beams have reinforcing beams or rebar inside them. Compression steel is particularly useful as a reinforcing agent for controlling creep.