Concrete

Concrete is a composite material, which is made of cement as a binder, water and aggregates. The binder (cement paste) "glues" the aggregates (sand and gravel up to 16 – 32 mm in diameter) together to form a synthetic conglomerate. In concretes of higher strengths, the maximum diameter of aggregate is smaller. Its compressive resistance is about an order higher than tensile resistance. Usually concrete is classified according to compressive strength after 28 days. The ranges are changing along the time and depending on source, but a rough classification is:

• Ordinary concrete: fck < 50 MPa
• High Strength concrete: 50 MPa < fck < 100 MPa
• Very High Strength concrete: > 100 MPa