What is aggregate base in construction?

Aggregate base is the structural stone layer of a paving assembly, sitting between the compacted subgrade and the asphalt or concrete surface. It lives on the civil C-sheets: the paving plan shows the limits of each pavement type, and the pavement section details show base depth for each section, with the geotech report recommending the thicknesses. The material is a dense-graded crushed stone whose name changes by state DOT (Class 2 in California, CA-6 in Illinois, ABC in the Carolinas), so estimators price what the local quarry actually sells. The sitework or grading contractor typically owns the scope, sometimes the paving sub. New estimators get three things wrong: they take off only the asphalt footprint and miss base under curb, sidewalk, and dumpster pads; they overlook the detail note extending base beyond the edge of pavement, often 12 inches; and they forget the difference between compacted volume in place and loose volume delivered, which can run 20 to 25 percent.

Aggregate base is measured as area times depth. Pull the area of each pavement section from the paving plan in sf, convert to sy (divide by 9) for the placement and fine grading lines, and compute cy (area times depth in ft, divided by 27) or tons for the material line. Standard duty and heavy duty sections carry different depths, so they are taken off separately. Cost drivers are depth, the specified stone class, haul distance from the quarry, and compaction effort, with proof rolling and density testing sometimes carried as their own lines. Watch the section detail for base extending past the pavement edge and for a geotextile separation layer beneath it.

Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.