Assessment of slag incorporation in cold recycled mixtures emulsified asphalt: Mechanical performance and environmental impact

Recycled Asphalt Pavement (RAP) has been used for several decades. RAP material varies and can include limestone, granite, gravel, and sometimes recycled materials like slag. In Taiwan, RAP is mostly used in base courses as Cold Recycled Mixtures Emulsified Asphalt (CRME). However, the use of slag in base courses is prohibited in Taiwan due to its potential for leaching and expansion properties. Unfortunately, RAP containing slag may occasionally be inadvertently introduced into CRME. This research proposes incorporating slag as aggregate in CRME, analyzing its mechanical properties and environmental effects to simulate the potential consequences when slag is unintentionally introduced into CRME. Three types of slag—Basic Oxygen Furnace slag (BOFs), Electric Arc Furnace slag (EAFs), and Incinerator Bottom Ash (IBA)—were added to the mixture at a percentage of 15 %, reflecting the possible inclusion of slag in CRME. Emulsified asphalt was used as a binder. The optimum contents of emulsified asphalt, cement, and water were determined before performance testing. Laboratory tests included indirect tensile strength (ITS), tensile strength ratio (TSR), and static creep tests. The environmental impact was assessed using the Toxicity Characteristic Leaching Procedure (TCLP) and volume expansion tests. The results of the mechanical tests showed that BOFs and EAFs mixtures provided higher strength, improved resistance to moisture damage, and better resistance to permanent deformation. In the TCLP test, all materials exhibited concentrations of specified heavy metals below the standard limits. The results of the expansion stability test showed that all materials expanded by less than 0.5 % at seven days, which meets the required limit. The study concludes that a 15 % addition of slag for cold recycled mixtures positively impacts mechanical properties and the absence of environmental impacts and volume expansion stability issues. Despite the above, pavement engineers should prioritize further studies on the long-term effects of slag addition on the environment and mechanical performance. ● The study supports the sustainable reuse of industrial slag in Cold Recycled Mixtures Emulsified Asphalt (CRME). ● In this study, Basic Oxygen Furnace slag (BOFs) and Electric Arc Furnace slag (EAFs) are conditionally used for CRME. ● Incorporating 15 % BOFs and EAFs into CRME significantly improved mechanical properties and resistance to moisture.