The phasing of residential asphalt construction is a common practice that is occasionally practiced on retail, commercial and industrial projects. Phased asphalt construction usually means that the base stone and base course of asphalt are placed early in the construction process, while the final asphalt surface is placed near project completion. For residential projects, this can mean that the surface asphalt is placed several months or more after the base stone and base asphalt are installed. For retail or commercial construction, the time between the installation of base and final asphalt is usually much shorter.

What are the implications of the phasing of asphalt? Is this a good idea?

Pavement Design - A Basic Primer

All pavement systems are designed on the basis of three factors: (1) the strength of the subgrade soil, (2) the traffic loading conditions, and (3) the strength of the materials that are combined to create the pavement system. The strength of the soil is usually evaluated empirically, most commonly based on a test known as the California Bearing Ratio (CBR) test. The traffic loading conditions are a function of the in-service use of the site. For residential construction, most jurisdictions will publish an average traffic loading factor per residential unit. For retail or industrial use, the traffic loading conditions are normally determined by a traffic study or provided by the end user of the facility. The strength of the asphalt, usually expressed in terms of a "structural number", is a function of the materials that make up the asphalt system. Commonly, the local department of transportation will publish a structural number factor for the various types of stone, base asphalt and surface asphalt used in an area.

Most pavement systems are supported by native soils, either as they exist in place or after being remolded as compacted engineered fill. Usually, these soils are not subject to substantial modification (there have been earlier Lessons Learned on cement and lime stabilization to modify native soils). Traffic loading conditions, while sometimes subject to much discussion, are also "fixed" in that they are a function of the use of the site. The structural number, then, is the only factor that can be manipulated, generally, by the designer.