Plastic shrinkage cracking refers to cracks that form in freshly placed concrete before it has hardened, caused by rapid evaporation of surface moisture.
Explanation
These cracks typically occur within the first few hours after placement, while the concrete is still in its plastic state. When the rate of moisture evaporation exceeds the rate at which bleed water rises to the surface, tensile stresses develop, leading to cracking.
Plastic shrinkage cracks are usually shallow and appear as parallel or irregular lines, often spaced at regular intervals. They are most common in conditions involving high temperatures, low humidity, strong winds, or direct sunlight.
Large surface areas such as slabs, pavements, and screeds are particularly vulnerable. Poor curing practices, lack of wind protection, and delayed finishing can further increase the risk.
Preventative measures include proper curing methods, use of evaporation retardants, windbreaks, and timing concrete placement to avoid extreme environmental conditions.
Why It Matters
Although typically non-structural, plastic shrinkage cracking can significantly reduce surface durability. These early cracks provide pathways for water and contaminants, increasing the likelihood of long-term issues such as reinforcement corrosion or freeze–thaw damage.
In repair and construction projects, controlling plastic shrinkage is essential for ensuring durability, performance, and compliance with quality standards.