Which factor can lead to plastic shrinkage cracking during concrete placement?

Plastic shrinkage cracking occurs when the surface of newly placed concrete loses moisture quickly, leading to localized shrinkage. Rapid evaporation of moisture can be exacerbated by environmental conditions such as high wind speeds, high temperatures, and low humidity. When the water on the surface of the concrete evaporates faster than it can be replaced from the underlying concrete, it creates tension in the outer layer. If this tension exceeds the tensile capacity of the concrete at that stage, cracks will develop.

In contrast, low ambient temperatures can slow down the evaporation rate of moisture, reducing the risk of plastic shrinkage cracking. High humidity levels generally help to retain moisture in the atmosphere, thus lowering the likelihood of rapid evaporation. Excessive compaction, while it can affect concrete density and strength, does not directly lead to plastic shrinkage cracking. Therefore, the rapid evaporation of moisture is the critical factor that increases the likelihood of cracks forming during the early stages of concrete curing.