Concrete Composition and Structural Reinforcement Methods

Concrete Composition

Concrete is a mixture of cement, sand, and gravel in varying proportions, to which water is added.

• Cement Content: The amount of cement per cubic meter of concrete directly affects its impermeability and mechanical strength. However, higher cement content increases contraction during curing, which can cause cracks.
• Aggregates: Sands and gravels, known as aggregates, are distinguished by size. They directly influence the tensile strength of the concrete.
• Water Quality: The water used can be non-potable, but carbonated water must be avoided.

Mechanical Properties

Once set, concrete can achieve a compressive strength of up to 650 kg/cm². However, its tensile strength is barely a tenth of this value. To improve this quality, reinforced concrete and prestressed concrete are used.

Reinforced Concrete

Reinforced concrete is obtained by adding properly dimensioned steel rods or rebar to fresh concrete.

• Load Distribution: Compressive stresses are supported by the concrete, while tensile stresses are resisted by the steel reinforcement.
• Construction Process: A shuttering or mold is created in the shape of the desired structure. Steel reinforcement is placed inside, and fresh concrete is poured to cover and wrap the frame. Once hardened, the formwork is removed.
• Structural Application: In a beam, the reinforcement is located at the bottom, which is subject to tension. The concrete coating ensures the impermeability of the structure, protecting the steel from corrosion.
• Grip: It is desirable for reinforcing bars to be twisted or have a textured surface to increase grip and prevent slippage.

Prestressed Concrete

If the tensile stresses are very high, the steel bars may undergo elastic expansion, causing the surrounding concrete to crack. To improve tensile strength, the steel bars are tightened to compensate for potential expansion.

Tensioning Processes

• Prestressed: Tensioning the rods before the concrete sets.
• Post-tensioned: Stretching the rods within pods after the concrete has initiated the setting process.