Experimental study of the effect of the thermal conductivity of EAF slag aggregates used in asphaltic concrete of wearing courses on the durability of road pavements

Abstract

Electric Arc Furnace (EAF) steel slag is the basic material used to obtain good quality aggregates in different layers of road pavements. Many scientific papers have reported on the high frictional and abrasion resistance of this material. EAF slag aggregates are hard, dense, chemically stable and have good adhesion with bitumen, all characteristics related with its high alkaline character. These properties are important in hot mix asphalt for wearing courses where high wear is present and optimal skid resistance is required. In some EAF slags, calcium and specially magnesium oxides are not completely combined, and upon contact with moisture convert into the corresponding hydroxides that could lead to volume changes. Only EAF slags with less than 3,5% expansion are used in Europe as aggregates for asphalt concrete or hot mix asphalt. In this paper, we present the experimental results of a study evaluating the consequences of the lower thermal conductivity of the EAF slag aggregates used in Catalonia (Spain). These aggregates have the necessary mechanical and chemical properties, as well as a very low expansion (0,5 to 1,5%). The EAF slag aggregates have a lower thermal conductivity (0,85-1,20 W/mK) than natural aggregates, such as granite that are used in wearing courses (1,60-1,80 W/mK). This property of the EAF slag aggregates can represent up to 30% less conductivity in asphalt concrete or hot mix asphalt. The different levels of depth in the wearing course with slag aggregates will be at lower temperature. This is especially important during the spring, summer and early fall months in the interior territories of the Mediterranean Coast, when due to the high temperatures the modulus of the mix in the wearing course is lower. The layer containing EAF slag is stiffer and the pavement has a better ability to resist the tendency to develop ruts and deformations.