DETERMINATION AND EVALUATION OF ALTERNATE METHODS FOR MANAGING AND CONTROLLING HIGHWAY-RELATED DUST

The mechanisms of dust suppression can be considered as two processes: increasing particle size of the surface fines by agglomeration and inhibiting degradation of the coarse material. Agglomeration may occur by capillary tension in the pore water, surfactants that increase bonding between clay particles, and cements that bind the mineral matter together. Hygroscopic dust suppressants such as calcium chloride have short durations of effectiveness because capillary tension is the primary agglomeration mechanism. Somewhat more permanent methods of agglomeration result from chemicals that cement smaller particles into a mat or larger particles. The cements include lignosulfanates, resins and asphalt products. The duration of the cements depends on their solubility and the climate. The only dust palliative that decreases aggregate degradation is shredded shingles that act as cushions between aggregate particles. It is likely that synthetic polymers also provide some protection against coarse aggregate attrition. Calcium chloride and lignosulfanates are widely used in Iowa. Both palliatives have a useful duration of about 6 months. Bentonite appears to be effective for up to two years and works well with surface materials having low fines and plasticity and works well with limestone aggregate. Selection of appropriate dust suppressants should be based on characterization of the road surface material. Novel dust control agents that need research for potential application in Iowa include: acidulated soybean oil (soapstock), soybean oil, ground up asphalt shingles, and foamed asphalt.