Composition

Aggregates are sand and gravel. They are the “skeleton” of concrete and:

• they provide strength and stiffness
• they counteract the shrinkage of cement during hardening, avoiding cracking
• they reduce the overall cost of concrete

Cement Paste is formed by the mixing of cement, water and possibly chemical admixtures. Cement paste has the role of binding the aggregates, but has also a primary influence on

• workability, strength, durability of final concrete.

Concrete can be seen as a composite material: a dispersed phase (aggregates) bound by a matrix (the cement paste). The roles of aggregates and cement paste within concrete are different.