Concrete

Concrete is a composite material consisting of a binding cement paste that coats and binds together aggregates such as sand and gravel, plus water and often additives. The cement paste hardens through hydration, creating a rigid matrix that surrounds the aggregates.

The most common binder is Portland cement; admixtures modify setting time, workability, and durability. The water-to-cement ratio controls strength and porosity; lower ratio yields higher strength but more difficult placement. Workability, curing conditions, and aggregate quality all influence the final properties.

Concrete comes in many forms: plain or unreinforced concrete, reinforced concrete with steel rebar or fibers, prestressed concrete, and lightweight or high-strength variants. Self-consolidating concrete flows under its own weight, reducing the need for vibration during placement. Fibers and other additives can enhance toughness, crack resistance, or thermal properties.

History and production: Roman concrete using lime and pozzolanic ash influenced later developments, and modern Portland cement was developed in the 19th century. Today concrete is produced worldwide in large volumes for a wide range of applications, from foundations to infrastructure and precast elements.

Durability and maintenance: concrete is susceptible to cracking, freeze–thaw damage, corrosion of embedded reinforcement, and alkali–silica reaction. Proper curing, adequate cover for reinforcement, and appropriate mix design improve longevity and performance.

Environmental considerations: cement production is energy-intensive and emits significant CO2. Practices to reduce impact include using supplementary cementitious materials, recycled aggregates, efficient curing, and optimized mix designs. Concrete remains a versatile, widely used material in construction and civil engineering.