Concretes

Concrete is a composite material composed of a cementitious binder, usually Portland cement, aggregates, and water. The binder hydrates to bind the aggregates into a rigid matrix, and admixtures may modify setting time, workability, or durability. When cured, concrete develops compressive strength and dimensional stability; its tensile strength is typically enhanced through reinforcement.

Concrete mixes vary: normal-weight concrete uses standard aggregates; lightweight concrete substitutes part of the aggregate with low-density materials; high-density concretes use dense fillers for shielding; specialty concretes include high-strength, self-consolidating, fiber-reinforced, and early-strength formulations designed for rapid construction.

Production and curing: concrete is manufactured by batching cement, water, and aggregates, adding admixtures as needed, and placing the mixture before it sets. After placement, curing maintains moisture and temperature to enable proper hydration, reducing cracking and improving long-term strength.

Performance and testing: key properties include workability, density, compressive strength, and durability to freeze–thaw cycles, chemical attack, and corrosion of reinforcement. Common tests measure slump (workability), compressive strength, and modulus of elasticity, with standards established by bodies such as ASTM, EN, or ISO.

Durability and sustainability: durability depends on material quality, design, and exposure. Cement production is energy-intensive and a notable source of CO2; mitigation strategies include supplementary cementitious materials, blended cements, and recycling of aggregates. New concretes seek lower heat of hydration, greater longevity, and reduced environmental footprint.

Applications and history: concrete is used in buildings, bridges, highways, dams, and precast elements. Its use dates back to ancient Rome and matured with Portland cement in the 19th century.