Research On Physical And Chemical Characteristics Of Steel Slag And Performances Of Steel Slag Based Asphalt Concrete

Steel slag should be subjected to some proper treatement to improve its volume stability before it can be used.This is because it contains some active components,which can cause volume expansion by reacting with water.Weathering treatment is a common and effective way for this aim.Some physical and chemical charactersitics of steel slag will get modified during weathering treatment process.Although many research focus on the steel slag asphalt concrete have been conducted,the physical and chemical characteristics of weathered steel slag and performances of weathered steel slag?WSS?asphalt concrete were not well revealed.The following research work were carried out based on the above background:Firstly,the weathering mechanism of steel slag was determined based on the changes of mineral phases,and modern testing equipments such as SEM,EPMA etc.were adopted to investigate the physical and chemical characteristics of weathered slag.Secondly,the deterioration mechanism of slag aggregate was revealed based on the results of physical and chemical characteristics,and the preparation of slag aggregate with high quality was discussed.Finally,the main performances of WSS asphalt concrete were evaluated,and failure mechanisms of WSS asphalt concrete under different moisture damage conditions were investigated,and some approaches to improve the moisture damage resistance were also proposed.The following items can be concluded:?1?The essence of weathering is that both free lime?f-CaO?and silicate minerals?C₂S,C₃S?participate in the carbonation reaction,and the CaCO₃ products fill some surface pores of steel slag.The CaCO₃ product layer solidifys on the surface of steel slag due to the gelatinization of silicate minerals.The outermost particles of product layer generate some new gaps due to loose packing.The gelatinization of silicate minerals also results in the solidification of impurity layer on the surface of traditional steel slag aggregate and poor stability of steel slag aggregate's particles gradation.The preparation of high-quality slag aggregate can be realized by equipping vibrating screen before and after each crush equipment and high-pressure water clean technique.?2?WSS asphalt concrete possesses good volume stability,fatigue durability,low-temperature carrying capacity and high-temperature stability.While its moisture resistance depends on what types of moisture damage condition is used.For hot water damage,product layer bonds tightly with the fully weathered steel slag,which can easily resistant the hot water damage,and the stripping away of asphalt film becomes the main failure mode.CaCO₃ products coarsen the surface of steel slag,and product layer partly interlocks with asphalt binder.Therefore the stripping percent of asphalt film is very small.As a result,WSS asphalt concrete shows good stability at hot water damage.For freeze-thaw cycle damage,the volume expansion of water infiltrating into product layer causes the fracture of product layer.Therefore the fracture of product layer is the main failure mode,which results in bad freeze-thaw damage resistance of WSS asphalt concrete.?3?The freeze-thaw damage resistance of WSS asphalt concrete can be improved by modifying weathered slag with silicone resin or modifying asphalt mastics with high-alkaline inorganic fillers.Silicone resin seals the product layer by filling the retained pores and newly generated gaps on the surface of weathered slag.Therefore water can not infiltrate into the product layer.Three types of inorganic fillers namely cement,CHS powder?grinding slag aggeragte which contains some honeycomb particles?and Flue Gas Desulfurization?FGD?residues can all enhance the interaction between asphalt mastic and product layer,which can minimize the probability of water infiltrating into the product layer by breaking through the asphalt film.