What risk is associated with freshly laid concrete block walls when exposed to temperatures at or below 32°F?

Freshly laid concrete block walls are particularly vulnerable to frost damage when exposed to temperatures at or below 32°F. This occurs because the water content in the concrete can freeze, leading to expansion. As the water freezes, it creates internal pressure within the concrete blocks, which can weaken their structure and integrity.

Frost damage can result in various problems, including the formation of ice within the concrete, which disrupts the curing process and can ultimately lead to crumbling or a significant reduction in the material's compressive strength. Because concrete relies heavily on moisture to cure properly, freezing temperatures can severely hinder the curing process, resulting in long-term damage to the walls.

While cracking can occur in concrete due to various factors, it is more commonly associated with drying shrinkage or temperature changes, rather than direct frost exposure. Spalling refers to surface flaking or chipping of concrete, which can also result from freeze-thaw cycles but is not specifically the primary concern with freshly laid walls. Delamination is more relevant to issues with layers in composite materials rather than to concrete blocks.

Thus, frost damage is the most significant risk in this scenario, as it directly affects the integrity and performance of the concrete block walls when they are newly installed and still curing.