Characterization and stabilization of quarry byproducts for sustainable pavement applications

Increased emphasis in the construction industry on sustainability and recycling requires production of aggregate gradations with lower dust and smaller maximum sizes, leading to increased amounts of quarry byproducts (QB). Constituted of particles usually less than 1/4 in. in size, QB is the residue deposit from the production of required grades of aggregate often stockpiled in excess quantities. This paper provides findings of an industry survey of Illinois aggregate producers on the annual production rate, excess QB generated, and the current application areas of QB. The current uses of QB in Illinois were limited to applications with low amounts of QB, and, therefore, excessive amounts of QB may remain in the stockpiles. A detailed laboratory study conducted to characterize the engineering properties of QB materials produced in the primary, secondary, and tertiary aggregate production stages examined aggregate gradation, shape characteristics, and mineralogical analysis. Differences in shape and gradation of QB materials produced in each crushing stage were observed. Strength tests, including unconfined compressive strength (UCS) and direct shear, were conducted. Because the UCS for QB materials is very low, chemical admixtures such as portland cement and Class C fly ash were used to improve their strength properties. In general, treated QB materials were 10 to 30 times stronger than the virgin QB samples. In the case of 10% Class C fly ash-treatment, UCS values achieved were as high as 340 psi. Such significant increases observed in the strength of stabilized QB materials may indicate suitability of QB for sustainable pavement applications.