Calcium Chloride (CaCl2) has been well established in the construction industry as an accelerator in the production of portland cement and as a dust palliative for controlling dust and soil erosion on unsurfaced roadways. More recently, the results of a series of field tests in Texas and Louisiana have shown that the addition of CaCl2 into mixtures containing fine, high-surface area particulates such as fly ash, cements and clays not only controlled traffic-induced dust erosion (see Figure 1), but also resulted in a significant improvement in early strength and ridability of the unsurfaced road (see Figure 2). This benefit is brought about due to increase in surface tension of the particles created by the CaCl2 which subsequently enhances compaction efficiency. This phenomenon is referred to as “surface-activated stabilization” and has also been incorporated into the fabrication of construction units for the home building industry (see Figure 3).
While the use of CaCl2 improves the setting time and the strength of Class C (high lime) fly ash, its inclusion has also allowed the use of Class F (low lime) fly ash in road construction by accelerating the setting time and increasing the early and long-term strength of the roadway. Other structural roadway benefits derived from the use of the CaCl2/fly ash treatment include:
decrease in plasticity index of clays and soils with high moisture contents;
decrease in porosity;
long-term stability and durability;
resistance to sulfate attack;
lower heat of hydration; and
reduced cost.
In road construction when cement is used, CaCl2 has shown to reduce the amount of cement requirement in favor of the lesser expensive fly ash. It also improves the setting time, which allows for speedy completion of the construction work, hence substantial savings in equipment utilization, labor, and material costs. The latter is currently being achieved where up to 60 percent of portland cement (a greenhouse gas producer) is being replaced by coal ash and further enhanced with the addition of CaCl2. According to the National Technical Information Service of Springfield, Virginia:
“If 50 percent of the portland cement used in Texas, alone, were replaced with coal ash, greenhouse gas emissions (CO2) would be reduced by 6 million tons annually