Key properties of hardened concrete
The following physical properties of normal strength Portland cement concrete has led to its widespread use in the construction industry.
Density (2,240 to 2,400 kg/m3 [140 to 150 lb/cf])
Density is the concrete’s mass per unit volume. For example, 1 m3 (35 cf) of concrete weighs approximately 2,240 to 2,400 kg (4,900 to 5,300 lbs).
Compressive strength (20 to 40 MPa [3,000 to 6,000 psi])
Compressive strength is one of the most common performance measures used by engineers in designing buildings and other structures. It is measured by breaking concrete cylinders in a testing machine by applying compressive force on the cylinder until failure. The failure load divided by the cross-sectional area of the cylinder is the compressive strength. This is an important property in the design of structural elements such as columns, piers, or footings.
Flexural strength (3 to 5 MPa [400 to 700 psi])
The flexural strength (modulus of rupture) of unreinforced concrete is calculated by testing a rectangular ‘beam’ of concrete by applying loads at right angles to its axis. It is a measure of tensile strength. Concrete is weak in tension (approximately 10 to 20 per cent of the compressive strength). Flexural strength is important in the design of floor slabs, pavements, and beams. Due to its low flexural (tensile) strength, concrete is usually reinforced with steel in areas where flexural or tensile stresses are expected.
Tensile strength (2 to 5 MPa [(300 to 700 psi])
The tensile strength is similar to concrete’s flexural strength. It is determined by subjecting a concrete cylinder to forces that are perpendicular to its long axis in such a way that it splits in tension. The ultimate breaking force divided by the surface area is the tensile strength.
Modulus of elasticity (14,000 to 41,000 MPa [2,030,528 to 5,946,547 psi])
This is the ratio of the stress to strain of concrete. The modulus of elasticity can be used to predict how concrete will react (stretch/shrink) when subjected to forces. This is important to calculate a structure’s elongation under various loads.
Permeability
The permeability of concrete is the property that governs the rate of flow of fluid (e.g. water) through a porous solid. Water travels slowly through concrete (1 x 10-10 cm/sec), thus making it a good barrier to water flow. It does not stop the flow of water, but slows it down considerably.
