Concrete Curing and Strength Gain

Study Notes

Curing of Concrete

Strength of concrete increases with age under favorable curing conditions.
Early-age strength gain is rapid; slowing down as time progresses.
At 28 days, concrete reaches about 60% of its maximum compressive strength.
By 3 months, compressive strength can reach approximately 80%.
Curing keeps concrete from drying out too quickly, essential for strength.
Effective curing methods include:
- Covering with wetted paper sacking, burlap, sand, or earth.
- Removing forms only after the specified time has elapsed.
- Sprinkling or spraying surfaces with water immediately after form removal.
- Using curing compounds to retain moisture.

Admixtures

Substances added to improve specific properties of cements, mortars, and concrete.
Types of admixtures include:
- Hydrated lime for improved workability.
- Air-entraining agents to enhance durability.
- Calcium chloride as an accelerator for quick setting.
- Retarders to slow the setting process.
- Additives for wear resistance and waterproof qualities; e.g., kaolin, celite.
- Pigments for color enhancement.
Dropped concrete should not exceed 5 ft for unexposed work and 3 ft for exposed work to prevent damage.

Shrinkage and Temperature Changes

Concrete shrinkage occurs due to hardening and temperature contraction, leading to cracks.
Crack size is influenced by the volume of concrete; large cracks can often be subdivided with reinforcement.
Use of shrinkage or contraction joints is advisable in long continuous concrete placements.
Shrinkage cracks typically occur at joints between fresh and set concrete; proper joint placement is crucial.

Hardening Process

Curing allows concrete to harden, as cement and water unite to form strong durable compounds.
Hardening is influenced by three main factors:
- Age of the concrete.
- Temperature during the curing process.
- Availability of moisture.
Protect fresh concrete from excessive vibration, loads, extreme temperatures, rapid drying, and contamination during the first 7 days of curing to ensure optimal strength development.

Description

Learn about how the strength of concrete increases with age under favorable curing conditions. Discover the process of curing concrete to prevent rapid drying, aiding in the development of compressive strength over time.