By Chip Ray
It is sexy to be hot. It is fashionable to be warm. In today’s environment, what is it to be cold? How does “cost effective” sound?
Not very flashy? But, hey, we are talking about asphalt mixtures here, so it doesn’t have to be sexy or fashionable – it does have to be cost effective. When people throw the word “green” around like it is some kind of color, many consider cold mix asphalt as green as it gets in the world of asphalt mixtures.
From the very early origins of building roads using tar for paving streets in Baghdad in 8th century A.D. to more than 1,000 years later with the development of tar-penetration macadams, “cold-mix” applications have been used to cost effectively build roads. Although, technically, the early “cold-mix” macadams were a method of sealing out moisture by spraying tar on the layers of stone, it produced a kind of in-situ cold mix pavement.
Today, there is a wide array of materials that can be used to make cold mix asphalt, including but not limited to cationic and anionic emulsions (high float and polymer modified versions, as well), solvent-free emulsions, cutback asphalts and multi-grade asphalts. The asphalt binder type and quantity to use is dependent on the aggregate type and gradation being used for the mixture. Just about any aggregate geology can be used and gradations from single sized stone to well-graded aggregates can make up the skeleton of the mixture. However, the quality and gradation of the aggregate will have the greatest impact on the overall performance of the cold-mix asphalt since it is 95 percent of the mixture.
The aggregate and binder are typically combined mechanically using a pugmill. The main advantage of using a pugmill is that it is portable and can easily be set up at the aggregate stockpile location or one convenient to the project. A pugmill can typically be mobilized, manned and operated very economically depending on the project quantity. Other advantages include formulating the binder for immediate use on a paving project or for stockpiling purposes for later use such as winter pothole patching.
Asphalt pavements are 100 percent recyclable, and using the reclaimed asphalt pavement or RAP as part of a cold mix asphalt is another key advantage. However, the most economical use for a reclaimed asphalt pavement is to reclaim it in-place. Cold In-place Recycling (CIR) and full depth reclamation are regaining popularity for ecological reasons. Not only are natural resources being saved by using the existing pavement, but much less energy is consumed in the process as well.
According to the work presented by the Colas Group in September of 2003 “The Environmental Road for the Future, Life Cycle Analysis,” in-situ recycling presents an approximate 80 percent reduction in energy consumed per ton of laid material as compared to a virgin hot mix asphalt and an approximate 90 percent reduction when compared to a ton of concrete laid. It’s always good to be hot or sexy, but don’t forget you can also be “green” and save some “green” with cold mix asphalt.
Chip Ray is the Supply and Transportation Manager at Asphalt Materials, Inc. in Indianapolis, Indiana.