Performance Evaluation of Steel Slag and Mill Scale Utilization as Partial Aggregate Replacement in Hot Mix Asphalt

Abstract

Roads are valuable assets of a country and with the increase in road traffic and the emergence of trade through CPEC routes; the need for proper roads has significantly increased in Pakistan. Roads serve a very important role in the functioning of a country. In Pakistan, the majority of the roads are built using asphalt concrete. The technique of using waste/ alternative materials was though introduced earlier in the twentieth century, it’s use has significantly increased in the last couple of decades. Waste products are produced in steel making processes which can be utilized in road pavement as aggregate. The past two decades have seen an increase in the production of waste products in the steel industry, considerably. The steel industry’s goal of zero-waste is becoming achievable because of ground-breaking technology developments and collaborations with other industries. This prevents the coverage of areas due to landfills, helps preserve natural resources, and reduces the emission of CO2 in the environment. The depletion of natural resources and energy use in the production phase is reduced by substituting natural resources with waste products. If steel slag and mill scale is disposed of in a landfill, then it has hazardous effects on the environment and it engages valuable land which can otherwise be used for important purposes. Therefore the analysis is done on the use of Induction Furnace steel slag as coarse aggregate and mill scale as fine aggregate in hot mix asphalt. The materials that were used in this research comprised of aggregate from Margalla quarry, Induction Furnace steel slag and mill scale from Pak Iron steel mill Islamabad, plus binder from Parco (Pak Arab refinery limited) having a penetration grade of 60/70. Different percentages i.e. 5%, 10%, and 15% of IF slag whereas 3%, 6%, and 9% of mill scale by weight of total aggregate, were replaced. Performance tests were carried out, i.e. resilient modulus and moisture susceptibility of asphalt samples were investigated. Moisture damage was measured using the Universal Testing Machine (UTM) by performing the Indirect Tensile Strength (ITS) test. The addition of IF steel slag gave promising results as far as Indirect tensile strength, tensile strength ratio, and resilient modulus are concerned. Mixes with 15% steel slag gave better indirect tensile strength and resilient modulus results than the rest of the mixes, whereas TSR values for steel slag are almost similar xiii and comparable to that of the conventional mix, with a very minute decrease. For mixes with mill scale, ITS (dry) increased at 6% from that of 3% and then decreased at 9%. Whereas ITS(wet) slightly decreased with an increase in the percentage of mill scale from 3 % to 6%, therefore this resulted in a minor decrease in TSR values comparatively, whereas a significant decrease in TSR occurs at 9% mill scale because of a decrease in ITS(wet) values but, still the value is quite above than the minimum requirement. This depicted that mixes with 9% mill scale are more moisture susceptible and sensitive in comparison to mixes with 3%, 6% mill scale, steel slag, and conventional mixes. Whereas in resilient modulus tests steel slag showed better performance but replacing mill scale with conventional aggregate resulted in a gradual decrease in resilient modulus although 6 % showed optimum result for resilient modulus. Mixes with 9% mill scale gave comparatively the least value for resilient modulus. Low percentages replacement was carried out in this research study for the IF steel slag and mill scale. IF steel slag showed quite promising results and mill scale results were satisfactory as for as these two performance testing parameters were concerned. But small percentages of mill scale up to 6% showed good results. This seems that these materials can show some interesting behavior in other performance tests and for practical applications, trial sections can be beneficial as they will show on-ground results of using these materials, within the indigenous environmental factors and situations of Pakistan. Key words: Steel slag, resilient modulus, hot mix asphalt, tensile strength ratio, indirect tensile strength.