What is Hot In-Place Recycling?

Hot In-Place Recycling Defined

Hot in-place recycling (HIR) is a preventive maintenance technique in which a one- to two-inch layer of surface asphalt is heated, scarified, remixed and placed again to correct a pavement with minor deficiencies before they become major problems. The process can include additives to correct pavement mix deficiencies, and it can produce either a wear course or an intermediate layer for an HMA overlay.

It makes sense . . . when an HMA overlay isn't cost-effective, either because the existing pavement has too many deficiencies, or because the pavement is far removed from asphalt production facilities.

It doesn't make sense . . . when pavement deficiencies are too deep (generally, more than two inches), or when a simple overlay or chip seal will solve the problem for the same or less money.

Typical Applications

Surface recycling prepares the roadway for a new surface by converting the old surface to an intermediate course without grinding the asphalt; the process costs significantly less than milling the old surface and placing an intermediate course of virgin hot mix asphalt. Remixing takes it a step further, converting the old surface into a wearing course. Both are popular maintenance treatments for roads that are far from asphalt plants. Repaving, the HIR technique that recycles the old pavement and lays virgin asphalt atop it in one operation, is popular in commercial and residential areas because it blocks driveways for minutes, not hours or days. It has been used successfully on interstate highways.

Tricks of the Trade

Contractor experience and expertise is critical in HIR, from gauging additives for remixing to the equipment itself. Keys to success include using modern indirect radiant or infrared heating units, and bringing the pavement temperatures up gradually using multiple pre-heaters operating at lower temperatures. This produces a high quality recycled mix, no vapors, and an excellent bond between the hot recycled pavement and the heated pavement beneath it.

What it Costs

Hot in-place recycling costs vary widely according to which process is employed and the condition of the old pavement, but it usually costs 10-20% less than a mill-and-fill of the same depth.