The hygroscopic properties for calcium, magnesium, and sodium salts are compared in the chart. When the relative humidity exceeds 29 %, road base treated with calcium chloride will begin to absorb atmospheric moisture. When the relative humidity increases about 32 %, this uptake will occur in magnesium chloride treated road base. Roads treated with sodium chloride will not absorb atmospheric water until the relative humidity exceeds 76%.
There are many dust suppressants consisting of calcium chloride or magnesium chloride and vendors strive to highlight the merits of their company’s product in this highly competitive market. Examples of the main key scientific and economic merits are presented below.
The Royal Institute of Technology (Sweden) conducted independent, detailed research1 on a comparison between calcium chloride and magnesium chloride as dust binding agent on gravel roads and, in 1972, concluded calcium chloride is the more favorable salt.
Recently, an effort* looked at the Swedish findings as applied to applications in the United States and endorsed the original findings and added the following comment concerning retention.
“With all conditions being equal, a product that remains in the road longer more preferable.
A higher retention yields extended dust control and reduces application frequency. The fact that calcium chloride is a large heavier molecule may give it greater retention than the smaller, lighter magnesium chloride molecule.”
A field study*involving actual measurements of dust after unpaved roads were treated with various chloride salts provided data that clearly shows significantly less dust was generated from roads treated with calcium chloride at 20 to 100 days after application.
While calcium chloride is more expensive than magnesium chloride to purchase, it is more effective and results in a lower overall cost per mile. One of the nation’s largest suppliers of dust suppressants (EnviroTech Services, Inc.) reported –the following which supports a 25% savings when calcium chloride is selected.
“It takes approximately 15% to 18% more magnesium chloride at 30% concentration to hold the same amount of moisture to the road as 38% calcium chloride. Consider the costs per mile with recommended application rates per mile on 24wide road:
Magnesium chloride (30% concentration) 4,224 gallon/mile 0.30 gallon/square yard
Calcium chloride (38% concentration) 3,520 gallon/mile 0.25 gallon/square yard”
As shown below, Fossil Water® contains nearly a 1,000 times more calcium than the two other dust suppressants commonly applied to unpaved roads in Colorado, while having a comparable level of total dissolved solids, or salts.
Fossil Water® is recycled brine water that is co-produced by oil and gas wells located in western Colorado and eastern Utah. This
formation water is about 360 million years old. After removal of residual hydrocarbons, the brine water is further treated as it flows through
a series of large ponds over a period of 4 to 5 years
All Fossil Water® is chemically tested before use as a dust suppressant.
After submittal of a beneficial use plan for recycling brine water to a beneficial use, which included a detailed chemical profile of the water (about 250 analytical test) and a pilot test of Fossil Water® on a 5 mile segment of unpaved road in Montrose County, the following approval was issued by Colorado Department of Public Health and Environment’s Solid Waste and Materials Management Program.
“..the Division determined that proposed use of produced water from Pond 12 is approved as a dust suppressant for gravel roads in accordance with the Division’s beneficial use criteria as provided..”
After participation in the pilot test of Fossil Water® , the Montrose County Engineer sent a letter to the above agency stating-
To date, Montrose County is very pleased with the performance of the product and we find it to be an acceptable substitute to other commercially available magnesium chloride products.
Fossil Water® is a trademark name of Naturita Enterprises, LLC, 31527 Highway 141, Naturita, CO
*References 1. A Comparison Between Calcium Chloride and Magnesium Chloride as Dust Binding Agent on Gravel Roads. J.Reyier. Royal Institute of Technology. Sweden. 1972.
Calcium Chloride vs Magnesium Chloride – Dampness in Dust Control Applications.
Effectiveness and environmental impact of Road Dust Suppressants. T.Sanders and J.Q. Addo, Dept Civil Engineering, Colorado State University. 1993.