The important physical properties of building materials are as follows:
Bulk Density
Bulk density is the mass per unit volume of a material in its natural state. This is obtained by finding the ratio of the mass of the material to the volume of the material. Most of the technical properties such as strength, conductivity, etc., depend on the bulk density of the material. It is represented by the unit kN/m3. Bulk densities of some of naturally available materials are granite: 25 to 27 kN/m3, limestone: 18 to 24 kN/m3, pinewood: 5 to 6 kN/m3.
Mass per unit volume of a homogeneous material is termed as density. Density of steel is 78.5 kN/m3. Density index is the ratio of bulk density to its density. Evidently the density index of most of the building materials is less than one.
Chemical Resistance
It is the ability of a material to withstand the action of chemicals like acids, alkalis, salt solutions and gaseous substances.
Fire Resistance
Fire resistance is the capacity of a material to sustain the action of high temperature without loosing strength and change in the original shape of the structure. Wood, one of the building materials, is highly affected by fire. Such materials should be treated so as to resist high temperature and fire.
Frost Resistance
When voids of a building material are filled with water and subjected to sub-zero temperature, it is affected by a process known as freezing. Thus, the ability of water-saturated material to resist freezing and thawing is known as frost resistance. It depends on the density of the material and its degree of water saturation. Generally, dense materials are frost resistant.
Spalling Resistance
Materials that could sustain repeated temperature changes is said to be of high spalling resistance. This mainly depends on the coefficient of linear expansion of the material.
Weathering Resistance
It is the capacity of a material to resist alternate wet and dry conditions without getting affected. Weathering causes a change in shape and decrease in mechanical strength.
Porosity
Porosity of a material is the ratio of volume of voids or pores to the total volume of the material. Denser the material, lesser will be its porosity. Bulk density, water absorption, thermal conductivity, strength, durability, etc., depend on the porosity of the material.
Water Absorption
The ability of a material to absorb and retain water is called water absorption. It depends on the porosity of the material, the size and shape of the pores.
Water Permeability
It is the capacity of a material to allow water to pass through it under pressure. For example, wood may have high water permeability compared to steel.
Hygroscopicity
It is the property of a material to absorb water vapour from the air. It is governed by the porosity of the material, air temperature and the nature of the substance involved.
Coefficient of Softening
It is the ratio of compressive strength of a fully saturated material to that of the same material when dry. Materials that have a coefficient of softening more than 0.8 are said to be water-resistant material.
Durability
The property of a material to resist the action of atmospheric and other factors continuously is called the durability of the material. For example, the durability of a building depends on the resistance offered by various materials used to construct it under different conditions.
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