Concrete is one of the most widely used structural materials in the world and is usually a cheaper alternative to steel. It is made from cement, water and aggregates.
To make the most effective use of concrete, one must understand where its strengths and weaknesses lie. This article will expound upon some of the main mechanical properties of concrete.
Material Behavior
Strictly speaking, concrete is not a homogenous material. However, since the cements and aggregates are randomly distributed, we can idealise concrete as a isotopic material, just like steel.
Density
The unit weight of concrete depends on the concrete strength. In general, we can consider normal reinforced concrete to have a density of 2,400 kg/m3. Lightweight reinforced concrete may be considered to have a density of 2,100 kg/m3.
※ What is the unit weight of concrete? Explained in 1-minute
Compressive Strength
The ability of the concrete to withstand compressive forces, usually measured in megapascals (MPa) or N/mm2.
Tensile Strength
Concrete is much weaker at resisting tensile forces compared to compression. In general, the tensile strength is said to be about 10% of the compressive strength. In reinforced concrete design, the tensile strength of concrete is generally ignored for strength calculations.
Poissons Ratio
Poisson's ratio describes how much a material will deform in the direction perpendicular to the applied load (as a ratio to the deformation in the parallel direction). Although the value varies somewhat, the Poisson's ratio for design is usually taken as 0.2.
For example, if a concrete cube is subjected to a axial compression and compresses by 10 mm, then the expansion in the perpendicular direction may be 10 x 0.2 = 0.2 mm.
Workability
The ease with which concrete can be mixed, placed, and finished, which can be affected by factors such as water-to-cement ratio and aggregate size.
Permeability
The ability of water or other fluids to pass through concrete, which can affect its durability.
Thermal Properties
The ability of concrete to store and transfer heat, which can be affected by factors such as the type of cement used, the water-to-cement ratio, and the aggregate size.
Sound Insulation
The ability of concrete to reduce the transmission of sound, which can be affected by factors such as the thickness of the concrete and the type of aggregate used.