In a slab-on-grade application, concrete is poured over a base of what material?

In a slab-on-grade application, the concrete is poured over a base that can consist of various materials, creating a stable foundation for the slab. Using materials like gravel, sand, or soil helps in properly distributing the weight of the concrete and provides excellent drainage to prevent water accumulation beneath the slab, which can lead to cracking and other structural issues over time.

Gravel is commonly used because it allows for good drainage and provides stability, reducing the risk of future settling. Sand can also serve as a leveling material or base but may not provide the same structural support as gravel. Soil, if properly compacted and stable, can be used as a base as well, although its effectiveness can greatly depend on the type of soil and its moisture content.

Since any of these materials can fulfill the requirements of a base for a slab-on-grade foundation when used appropriately under the right conditions, it's correct that concrete can be poured over any of them, making this option accurate for the question regarding the base material for slab-on-grade applications.