Concrete is a hard and durable material, however, it is also susceptible to deformation due to large external loads. Therefore, when erecting concrete structures, it is imperative to take into account what kind of force they can withstand. The ability to deformation of a temporary nature, that is, elastic, is expressed through such an indicator as the modulus of elasticity of concrete.
How concrete deforms
To determine the elasticity of concrete, a series of compression and tensile tests are usually performed. However, in construction, the most significant fact is that concrete that does not contain reinforcement is not capable of tension. One of the properties of concrete is creep, it is because of it that deformation increases under force. The first stage of deformation is elastic deformation. This means that after the pressure disappears, the loaded material will return to its original shape. If the force is increased, the deformation becomes irreversible. A further increase in the load leads to the destruction of the object. It is difficult to determine at what moment the elastic deformation becomes irreversible, since the change in the shape of concrete depends on the rate of increase in the load. This value is the initial modulus of elasticity of concrete.
How the modulus of elasticity is calculated
It is difficult to calculate the initial modulus of elasticity, but you can establish its approximate value. In the course of testing a concrete sample for strength, a graph of the dependence of deformation on the impact force is drawn up. Typically, in such graphs, the secant of the strain versus stress graph is parallel to the tangent through the origin. Indirectly, using this graph, you can determine the modulus of elasticity of concrete.
Typically, the modulus of elasticity is directly proportional to the root of its strength. True, this statement is true not for the entire graph, but only for its main part. Much also depends on the conditions in which the tests were carried out and on the environment. For example, water-saturated concrete is more elastic than dry concrete, although their strength is almost the same. The quality of the coarse filler has a great influence on the elasticity index. The relationship is straight - lightweight concrete samples have a lower modulus of elasticity than heavy ones.
This indicator also depends on the age of the material. The older the concrete, the higher its modulus of elasticity.
In practical applications, the modulus of elasticity of concrete is important in construction. At release, all materials are labeled, so an approximate starting module can be determined based on the labeling. For this, a special table has been compiled, according to which the quantitative value of the modulus of elasticity of each grade of concrete is calculated. It is very important to choose the right material so that the structure does not collapse during construction, but remains strong for many years.
