What is 'aggregate base course'?

The term 'aggregate base course' refers to a layer of mixed gravel or stone that is placed on top of the subgrade to provide structural support for pavement. This layer is critical in highway construction and plays a vital role in distributing loads from the pavement to the underlying soil, improving overall stability and performance.

By utilizing a mix of various sizes of aggregate, this layer helps to create a strong foundation that can withstand the stresses imposed by traffic and environmental conditions. The proper compaction and grading of the aggregate base course are essential to prevent issues such as settlement, cracking, and other forms of distress in the overlying pavement.

While other options describe different aspects of road construction, they do not accurately define the function or characteristics of an aggregate base course. For example, a layer of asphalt placed on top of existing pavement pertains to surface treatments rather than foundational support, and paving methods with concrete involve different processes altogether. Therefore, the identification of the aggregate base course as a structural support layer is crucial in understanding its purpose and importance in highway construction.