Early-age cracking in concrete structures poses challenges to durability, strength, and maintenance costs. Beyond aesthetic concerns, these cracks can impact occupant comfort and tarnish a contractor’s reputation. Implementing effective measures from design to construction is essential to mitigate or eliminate early-age crack development.
In the design phase, careful consideration of restraints in concrete elements is crucial. Constraints on concrete movements due to thermal expansion and autogenous shrinkage play a pivotal role. Factors such as concrete cover, non-uniform depth, and reinforcement influence crack development. For instance, a reduction in concrete cover significantly increases the likelihood of cracking.
2.1 Aggregates
The choice of aggregates plays a vital role in early-age cracking. Factors like size, roughness, and thermal expansion coefficient of coarse aggregate affect concrete’s performance. For example, larger aggregate sizes can increase the transition zone in concrete, lowering tensile strength and increasing crack susceptibility.
2.2 Cement Types
Optimizing cement type and content is crucial. Portland cement with specific characteristics can lower cracking temperatures, while careful adjustment of water-cement ratios impacts drying shrinkage. Utilizing different cement types in high-strength concrete doesn’t affect early-age crack development under equal water-cement ratios.
2.3 Supplementary Cementitious Materials and Admixtures
Incorporating additives such as fly ash, slag, and various admixtures can enhance concrete performance. For example, a blend of Portland cement, slag, and fly ash outperforms ordinary Portland cement. Shrinkage reducing admixtures and self-compacting admixtures prove effective in reducing shrinkage and heat of hydration, thus minimizing the risk of early-age cracking.
The temperature of fresh concrete significantly influences crack development. Lowering fresh concrete temperature enhances its tensile strength. Thoughtful planning of the concrete placement procedure, including formwork, insulation, and neighboring structures, can mitigate temperature differences and reduce the risk of early-age cracks.
Factors like surrounding temperature, humidity, wind, and solar radiation impact water evaporation. Dry air and rainfall during concrete placement can affect concrete strength and increase the likelihood of early-age cracking. Understanding and managing these environmental conditions are vital in crack prevention.
Heavy vehicles, especially in the case of high slump concrete, can affect concrete integrity. Restricting heavy traffic during the initial stages of concrete casting is advisable to prevent early-age cracking.