Which factors can lead to differential settlement in concrete flatwork?

Differential settlement in concrete flatwork occurs when different sections of a slab settle at different rates, leading to potential cracking, uneven surfaces, and structural issues. The correct answer highlights several critical factors that can contribute to this phenomenon, namely inconsistent subgrade support, moisture variation, and improper soil compaction.

Inconsistent subgrade support means that the foundation beneath the concrete slab is not uniform. Variations in density or composition of the soil can lead to areas that are either more stable or less stable. This variation causes differential rates of settlement.

Moisture variation refers to the differences in water content within the soil subgrade. Areas that retain more moisture compared to drier sections can expand and contract, influencing how much they settle over time. Such fluctuations in moisture can lead to uneven support levels beneath the slab.

Improper soil compaction means that the soil was not adequately compressed before placing the concrete. This can create voids or weak spots within the subgrade, which can allow parts of the slab to sink more than others as loads are applied, leading to uneven settling.

Collectively, these factors illustrate how crucial proper preparation of the subgrade is to ensure even support for concrete flatwork, thereby minimizing the risk of differential settlement.