Cracks in concrete structures can be a concern, but adopting specific design and construction measures can significantly reduce their occurrence. By addressing various factors contributing to crack formation, such as plastic settlement, shrinkage, thermal contraction, and long-term drying, it is possible to enhance the durability of concrete elements.
Concrete cracks can manifest in different forms, including plastic settlement cracks, plastic shrinkage cracks, thermal contraction cracks, long-term drying shrinkage cracks, cracks due to reinforcement corrosion, alkali-aggregate reactions, and crazing. Each type requires specific preventive measures to minimize their impact.
Table-1 provides an overview of the types of cracks and effective preventive measures. Plastic settlement cracks, for instance, can be mitigated by using a high-quality concrete mix with shrinkage-compensating admixture, ensuring adequate concrete cover thickness, and employing rigid forms for slabs. Initiating concrete placement from deep sections further reduces the risk of surface crack development.
To counteract plastic shrinkage cracks, wetting the substrate and formwork before pouring concrete is crucial. Using synthetic steel fibers in the concrete, employing chilled water or ice in hot weather, providing wind barriers, and applying aliphatic alcohol over the concrete surface after screening help control the impact of plastic shrinkage.
Managing early thermal contraction cracks involves reducing the heat of hydration, incorporating expansion joints, insulating concrete to decrease thermal gradients, and placing reinforcements at suitable spacing to control crack width.
For long-term drying shrinkage cracks, practices such as providing suitable spacing between steel bars, decreasing water content, using water-reducing admixtures, avoiding calcium chloride-containing admixtures, utilizing shrinkage compensating admixtures, incorporating rigid aggregates, and introducing expansion joints can contribute to controlling crack width.
Addressing crazing involves starting concrete curing promptly, keeping the concrete surface wet for at least three days, preventing excessive segregation and bleeding by considering low slump or entrained concrete, and avoiding finishing work during bleed water presence.
Cracks resulting from reinforcement corrosion can be minimized by compacting concrete around steel bars, adhering to applicable codes for bar spacings, using clean steel bars for a good bond, reducing concrete permeability through a low water-cement ratio, adequate compaction, and curing, and applying a protective coating system to enhance resistance against harmful substances.
Preventing alkali-aggregate reaction cracks involves using low-alkali Portland cement, avoiding susceptible aggregates, considering pozzolans as cement replacements, and applying protective coating and joint sealing for added safeguarding.
By implementing these preventive measures, the risk of crack development in concrete structures can be significantly minimized, ensuring the longevity and structural integrity of the construction.
