Cold-mix is a mixture of asphalt emulsion and mineral aggregate blended together and used in paving courses primarily for rural and secondary roads.
There are two types of cold-mix blends, open graded and dense graded. Open graded mixes consist of a single size aggregate containing little or no mineral filler that has relatively large void spaces in the compacted pavement. Open graded mixes are simple to produce and are the least sophisticated.
Open graded mixes can be produced with only one aggregate size uniformly mixed with asphalt emulsion through a pug mill or mix paver requiring a minimum amount of stockpile space.
The mix can be made from clean graded crushed stone of any type. A lab mix design should be done to determine compatibility of the emulsion and aggregate. Open graded mixes should not be used where there is a long haul from the mix sight to the paver. Once the mix is placed it should be lightly sanded or “chinked” to avoid tracking. Sanding or chinking also helps stabilize the mix and get traffic on it quicker.
Dense graded mixes contain aggregate that is uniformly graded and produced with two or more aggregate sizes with the object of obtaining an asphalt mix with a controlled void content and high stability. Dense graded mixes will stand up to heavy traffic quicker than open graded mixes and in most cases do not need to be sanded or “chinked”.
All cold mixes should be topped with a surface treatment of some type. A single course chip seal, slurry seal, or micro- surfacing are excellent top courses for cold mix. Late season work can be temporarily coated with a fog or sand seal for the winter and then sealed the following season with a permanent top course.