This licentiate thesis is part of a Ph.D. project entitled “CDU:T43 Different methods for dust control and evaluating dust control on Nordic gravel roads”. The Ph.D. project is financially supported by the Swedish Road Administration (SRA) through the Centre ofResearch and Education in Operation and Maintenance of the Infrastructure (CDU)within the Swedish Network of Excellence – Road Technology (RT). Much of the research described in this thesis has been carried out in collaboration with SRA Construction and Maintenance, which also contributed financially.One of the most significant problems associated with gravel roads is traffic-generateddust which facilitates the deterioration of the road surface and acts as a major source of particulate matter in the air, thus affecting traffic safety, public economics, and environmental quality.This work describes different programs for evaluating the effectiveness of different dust suppressants and the results obtained from completion of these experiments. Inchapter one, a general introduction into this project and its objective will be offered. The next chapter gives insight into the basic concepts of gravel roads. In the third chapter the existing literature concerning dust control of gravel roads is briefly retold. The fourth chapter gives an account of the research methodology. A field evaluation of different dust suppressants will be described in the fifth chapter. Chapter six describes methods for analysing dust suppressant residual concentration of samples taken from the different test road sections included in the above mentioned field evaluation. The objective is to investigate the longevity of these dust suppressants. Results from the analyses of the horizontal diffusion of gravel road generated dust are presented in chapter eight. The ninth chapter offers a description and evaluation of the objective method used for quantitative dust emission measurements by means of a visual method. In chapter tendust emissions are correlated to other general deformation processes on the gravel road.Chapter eleven defines laboratory trials concerning the leaching of dust suppressants from gravel wearing course material when subjected to water. Concentrations of dust suppressant as well as size distribution of gravel material were factors examined in this context. In chapter twelve, laboratory examinations of the drying rate for different combinations of aggregate gradations and chloride compounds will be presented. The thirteenth chapter gives a description of a developed laboratory equipment for evaluatingdust suppressant effectiveness, while chapter fourteen offers a conclusive summary. / QC 20101115

Approximately 75 percent (300 000 km) of the total Swedish road network and 20 percent(20 000 km) of the national road network consists of gravel roads. One of the most significantproblems associated with gravel roads is traffic-generated dust emission, which contributes tothe deterioration of the road surface and acts as a major source of particulate matter releasedinto the atmosphere, thereby involving public economics, road safety, human health, andenvironmental quality. In order to bind the fine granular material, which is prone to rise into theair, dust suppressants are applied on roads on a yearly basis. Methods for evaluating the efficiency of dust suppressants will facilitate in the selection of themost appropriate product and its optimal application rate. For example, methods forsupervision of residual dust suppressant concentration are valuable tools for estimatinglongevity and optimal application rates, and, consequently, effectiveness of different products. Application of the proper dust suppressant to a gravel road ensures road safety and ridingcomfort as well as creating a cleaner and healthier environment for residents in buildingsadjacent to the road. It also reduces the need and cost for vehicle repair, road maintenanceactivities, and aggregate supplementation. Both field-based and laboratory research were performed to evaluate the efficiency of varioussuppressants and the influence such factors as product concentration, leaching, and fine materialcontent have on the efficiency of different products. Within the field-based research, a newlydeveloped mobile methodology was used to measure dust emission on numerous test sectionstreated with various dust suppressants. In general, all dust suppressants tested, except apolysaccharide (sugar) and products, which form a brittle surface crust, i.e. lignosulphonate andbitumen emulsion, showed acceptable dust reduction. Test sections treated with a magnesium- or calcium chloride solution were the most effectivelydust suppressed. The application of solutions instead of a solid salts achieves a more uniformproduct distribution and, therefore, probably a more efficient performance. By applying acalcium- or magnesium chloride solution instead of traditionally used solids, the cost for annualdust control, as well as the environmental impact from the release of these chemicals in theenvironment, can be reduced by 50 percent. A significant problem when using dust suppressants is their tendency to leach during rainfalldue to their soluble properties. Residual chloride could be detected in the gravel wearing courseover a longer period of time than lignosulphonate and, therefore, showed more effective longtermperformance. Optimal percentages of fine material for minimal lignosulphonate andchloride leaching were found to be 15 percent by weight and 10-16 percent by weight,respectively. Ions of calcium chloride seemed to initiate flocculation of clay particles, therebypreventing them from leaching. Still, the fine material in gravel wearing courses has to be replenished regularly as indicated by studies of the longevity of fine material. Loss up to80 percent was found after two years. Toxicity tests show that dust suppressant application for dust control purposes, at traditionallyused application rates, does not constitute a threat to sensitive aquatic life. Tests on subsoilwater samples indicated elevated chloride levels, which possibly could cause corrosion to pipes,but not high enough to flavour drinking water. / QC20100616