CSLB Class B General Contractor's License Practice Exam

What is a common cause of severe cracks in concrete?

1. Inadequate subsoil compaction

2. Inadequate forms

3. Pouring on a hot day

4. Excessive soil in the concrete

The correct answer is: Inadequate subsoil compaction

Severe cracks in concrete are often a result of inadequate subsoil compaction. Proper subsoil compaction is crucial because it provides a stable foundation for the concrete. When the soil beneath the concrete is not compacted adequately, it can lead to uneven settling over time. As the concrete slab settles unevenly, it can create tension in the material, causing it to crack. This issue is particularly evident in areas where there are significant changes in moisture content or heavy loads applied to the surface of the concrete. In contrast, the other factors mentioned do not typically lead to severe cracking as directly as inadequate subsoil compaction. While inadequate forms can cause issues with shaping or finishing the concrete, and pouring on a hot day can lead to rapid drying and surface scaling, these do not generally result in severe structural cracks. Excessive soil in the concrete can affect its strength and appearance but is not a common cause of severe cracking, as it would usually lead to more cosmetic issues rather than foundational problems. Thus, understanding the importance of good soil compaction is key to preventing severe cracks in concrete structures.