What can cause plastic shrinkage cracking in concrete?

Plastic shrinkage cracking in concrete is primarily caused by moisture loss occurring early or rapidly during the setting process. When freshly placed concrete begins to lose moisture too quickly, particularly in warm or windy conditions, it can lead to the formation of cracks before the concrete has sufficiently hardened.

The hydration process is critical for developing strength in concrete, and if this process is interrupted by rapid evaporation, the concrete surface can create tensile stresses that exceed its capacity, resulting in cracks. This phenomenon is particularly prevalent if the surface dries faster than the underlying layers, leading to differential shrinkage.

While other factors listed, such as low temperatures, excessive vibration, and using unsuitable aggregates, can affect concrete's overall quality and performance, they are not the primary triggers for immediate plastic shrinkage cracking. The key factor in causing these types of cracks remains the rapid loss of moisture right after the concrete has been placed.