Using Local Materials
Roads are absolutely necessary for economies to succeed. Yet in these perilous economic times, funds are not available to build them to luxury standards. However there is technology available that allows the construction of very usable roads using materials already in-place.
Asphalt Emulsion Stabilized Bases. With soils with a plasticity index of 6 or less asphalt emulsions could be considered for base stabilization. This technology has been around for decades. I published a paper in the 1965 Proc. Asphalt Paving Technology on asphalt emulsion stabilized bases which included a mix design. We had found that one inch of stabilized base could replace about 1 ¼” of crushed aggregate base. For roads with low truck traffic a chip seal might be used as a wearing surface. A word of caution, the same care must be taken for compaction as with soils, and in calculating the maximum density; the liquid would be the sum of the emulsion and added water. There are some sophisticated emulsion formulations in which the emulsion “sets” and kicks out water, however they are not available everywhere.
Another caution. Just because an emulsion is labeled “slow set” does not mean it will necessarily mix with all in-place soils. We once were working with a particular slow set emulsion that was working quite well. On this project we first treated the soil with lime then stabilized it with a slow set emulsion. To save money, the contractor switched to another slow set emulsion, which didn’t work. In emulsion stabilization the mixed soil should be brown. In this case it came out the same color as it was before mixing, indicating that then emulsion was coagulating and balling up rather than coating.
Emulsion Based Macadams. When I was in Panama many years ago I witnessed the construction of a macadam using CRS-2 asphalt emulsion. The emulsion was manufactured by a company for whom I was doing consulting on asphalt emulsion manufacturing. A typical macadam construction technique was used. First a layer of large stone was place followed by a layer of asphalt emulsion. Following that were consecutive layers of aggregate and emulsion with each aggregate size ½ the size of the proceeding one. The last layer was sand. Since CRS-2 emulsions break as soon as it contacts the aggregate, it appeared to work in the tropics.
Lime Stabilization. For soils too plastic for using asphalt emulsions, lime stabilization might be the selection.
Cold In-Place Recycling. Cold in-place recycling is being used in the United States especially in place of hauling new aggregate base. For low truck traffic the wearing surface could be a single or double chip seal. For heavier traffic, however, hot mix should be used.
This short piece was to suggest that there may be lower cost options for constructing roads in rural areas. For any question contact me at firstname.lastname@example.org in English or Spanish. (I have also had a couple of years of Russian but that was a lifetime ago, but I can read the Cyrillic alphabet. Although my knowledge of Russian has retreated to the far reaches of my brain, we do have a large Russian population here so we can accept Russian inquiries.)
Robert L. Dunning. www.petroleumsciences.com