Manufacturing Artificial Aggregates from Overburden Coal Mine Waste and Their Properties for Pavement Applications

Owing to a severe shortage of natural aggregates in terms of quantity and quality, alternative aggregate resources must be utilized in civil engineering construction to meet significant increase in aggregate demand. This study focuses on manufacturing artificial aggregates for pavement applications using two waste materials- mine overburden waste from the coal mining industry and fly ash from thermal power plants. Liquid alkali activator, a mixture of sodium silicate and sodium hydroxide, is used as a binder. The centrifugal forces generated due to a rotating disc pelletizer enables mixing the said components resulting in formation of spherical-shaped pellets. The nucleated pellets are oven cured at 70°C for 7 days. Based on extensive laboratory test trials, the optimal features to produce competent aggregates in terms of angle and revolution speed of the disc pelletizer, dosage of the liquid alkali activator and the concentration of the NaOH are proposed. Finally, the manufactured aggregates are tested for properties relevant to flexible pavement applications. The aggregate impact and Los Angeles abrasion values are found to be 17% and 21.6%, indicating satisfactory resistance to impact and abrasion of aggregate particles under traffic loads. The basic material properties of these aggregates are found to conform to the Indian Roads Congress (IRC) and American Association of State Highway and Transportation Officials (AASHTO) standards for base and subbase layers. Moreover, base/subbase layers prepared with artificial aggregates and mine waste showed high California bearing ratio (CBR) of 54.3% and 80.5% for 2.5 mm and 5.0 mm penetration of the plunger, respectively, indicating high load-bearing capacity of pavement layers.