Frost building materials shows how a particular sample was able to maintain its properties after several successive cycles of freezing and thawing.In the case of concrete, the main cause of destruction during these processes becomes water in the solid state, which exerts considerable pressure on the walls of the microcracks and pores in the material.
In turn, the greater hardness of the concrete does not give water to expand freely, so the test of frost resistance of concrete are high voltages.The destruction begins with the protruding portions, and then continuing in the upper layers and finally it penetrates.
factor that accelerates the destruction of concrete, it is also a different coefficient of thermal expansion of the elements that make up a building material.This creates additional stress.
Frost Concrete is measured using methods that control the procedure of freezing and thawing.Performance of the test parameters depend on the following factors: the temperature of the freezing cycle time, the size of the test sample, the method of water saturation.For example, the process of destruction of concrete is faster if the produce at the lowest possible freezing temperatures in salt solutions.
Frost Concrete is calculated up to the moment when a certain number of repetitions of the cycle does not reduce the weight of the sample by 5 percent and reduce its strength by 25 percent.That's the number of procedures that have stood the building material determines its brand.Degree of hardiness is appointed as depending on where in the area of the concrete will be applied.
Frost Concrete has a special structure.His character does not allow the porosity volume of ice to create too much pressure and slows the process of destruction.
frost resistance of concrete depends on the number of macropores as water in small pores does not freeze even at the lowest possible temperatures, so it does not create additional tension.Thus, greatly influenced by the nature, shape and volume of large pores.
frost resistance of concrete can be improved in the following ways:
- Decrease increase in the density of large pores of the concrete.
- creating additional air pores in concrete by introducing certain additives.If the volume of these pores will be a quarter of the frozen water, it will not be filled during normal water saturation.In the space leak unfrozen water, ice shifted, and then the pressure will weaken.
internal volume of air in the frost resistance of concrete must be between four and six percent.The amount of air is dependent not only on the flow of cement and water, but also from the coarse aggregate.The volume of air in the internal pores of the concrete is increased when the water flow increases and cement, and aggregate size fractions, on the contrary, reduced.
