Concrete

The material. Concrete is a composite, and a complex one. The matrix is cement; the reinforcement, a mixture of sand and gravel ("aggregate") occu­pying 60-80% of the volume. The aggregate increases the stiffness and strength and reduces the cost (aggregate is cheap). Concrete is strong in compression but cracks easily in tension. This is countered by adding steel reinforcement in the form of wire, mesh, or bars ("rebar"), often with sur­face contours to key it into the concrete; reinforced concrete can carry useful loads even when the concrete is cracked. Still higher performance is gained by using steel wire reinforcement that is pretensioned before the concrete sets. On relaxing the tension, the wires pull the concrete into compression.

Composition

6:1:2:4 Water:Portland cement:Fine aggregate:Coarse aggregate

General properties

Density

2300

– 2600

kg/m3

Price

0.041

– 0.062

USD/kg

Mechanical properties

Young’s modulus

15

– 25

GPa

Yield strength (elastic limit)

1

– 3

MPa

Tensile strength

1

– 1.5

MPa

Elongation

0

%

Hardness—Vickers

*5.7

– 6.3

HV

Fatigue strength at 107 cycles

*0.54

– 0.84

MPa

Fracture toughness

0.35

– 0.45

MPa. m1/2

Thermal properties

Melting point

972

– 1230

°C

Maximum service temperature

480

– 510

°C

Thermal conductor or insulator?

Poor insulator

Thermal conductivity

0.8

– 2.4

W/m. K

Specific heat capacity

835

– 1050

J/kg. K

Thermal expansion coefficient

6

– 13

p, strain/°C

Electrical properties

Electrical conductor or insulator? Electrical resistivity Dielectric constant Dissipation factor Dielectric strength

Poor insulator

1.8 X 1012 – 1.8 X 1013 pohm. cm

*8 – 12

*0.001 – 0.01

0.8 – 1.8 106 V/m

Reinforced concrete enables large structures and complex shapes.

Ecoproperties: material

Annual world production Reserves

Embodied energy, primary production CO2 footprint, primary production Water usage Eco-indicator

Ecoproperties: processing

Construction energy Construction CO2

Recycling

Embodied energy, recycling CO2 footprint, recycling Recycle fraction in current supply

Typical uses. General civil engineering construction and building.