Last winter our company was asked by the city street department to supply concrete for temporarily patching some large sections of failed pavement during breaks in the cold weather. When the weather warmed up, the city permanently repaired the patches with hot-mix asphalt. We'd like to show that a concrete patch can be placed in cold weather, without having to be replaced later. Where can we find information about mixes for fast-setting patching mixes?
You could try two different approaches. One would require you to use fast-track concrete, which is a high-cement-content concrete made with accelerating and water-reducing admixtures that would produce the rapid strength gain required. To aid in curing, workers would probably need to cover the repairs with insulating blankets after placement to ensure that the heat of hydration is retained. It might also be wise to add 3 pounds of synthetic fibers per cubic yard of patching mix, similar to the procedure used for ultra-thin whitetopping, so, if the patch fails, small chunks of concrete won't be dislodged. The other possibility is use of proprietary patching mixes or admixtures made specifically for repair applications. Some are portland cement-based and rely on chemical admixtures to provide high early strength (see
Concrete Journal, November 1996, page 742). Others are based on different cement chemistries such as magnesium ammonium phosphate. These materials have a short pot life and generally have to be mixed at the jobsite. For large applications, volumetric mixers would work best. For information about fast-track mixes, contact the American Concrete Pavement Association, 5420 Old Orchard Rd., Skokie, IL 60077 (847-966-2272, fax: 847.966.9970).