Strength Improvement of Aggregate Quarry By-Products Stabilized with Cement and Metakaolin

Abstract: Strong base and subbase layers are essential pavement layers to effectively support heavy vehicular loads while maintaining the structural integrity of the entire system. Quarry by-products (QB), primarily sand-sized residual materials from quarry operations, are often underutilized, leading to their accumulation at quarries, which presents a significant challenge for aggregate producers. A sustainable approach for utilizing surplus QB materials in pavement base and subbase applications has been extensively studied at the Illinois Center for Transportation. Previous studies have shown that stabilizing QB with 3% cement can provide sufficient compressive strength and rutting resistance. Recently, the incorporation of supplementary cementitious materials (SCMs) into the cement matrix has gained attention for its potential to reduce cement content and enhance the sustainability and longevity of certain infrastructure elements. Metakaolin, or calcined clay—an SCM primarily composed of aluminum and silicon chains—is known to produce a faster and more effective pozzolanic reaction than conventional supplementary materials such as fly ash, due to its high surface area and amorphous crystal structure, thereby improving the microstructure. Thus, incorporating metakaolin along with Portland cement is expected to positively impact the strength of cement paste. This study examines the addition of metakaolin in combination with Portland cement during the stabilization process of QB materials and investigates the strength performance of the stabilized specimens after short-term curing. During sample preparation, different types of carbonate aggregate QB materials with varying chemical compositions are mixed with different combinations of cement and metakaolin contents. A comparative analysis of the stabilized QB specimens provides insight into the extent of strength improvement in the presence of metakaolin. Further, the study explores how strength improvements may vary with chemical composition and evaluates the potential for reducing cement content without compromising strength; ultimately contributing to a lower carbon footprint in pavement applications.