Mechanical Performance and Recyclability of Cement-Stabilized Materials with Different Gradation of Recycled Brick-Concrete Aggregates

Abstract

This study investigated the optimization of gradation and performance of cement-stabilized materials incorporating recycled brick-concrete aggregates (RBCA) with various replacement ratios of recycled brick aggregate (RBA). A gradation structure, referred to as the refined-dense (RED) gradation, was developed using discrete element method simulations and a multi-step blending strategy to minimize packing porosity. In addition, two conventional gradation types, namely skeleton-dense (SKD) and suspension-dense (SUD), were included for comparison. The optimized RED gradation reduced the porosity to 3.15%, indicating enhanced aggregate packing and structural compactness. Mechanical performance was evaluated through unconfined compressive strength and splitting tensile strength tests. At 30% RBA replacement ratio, the RED gradation reached 3.69 MPa in 28-day UCS, which was 3.6% and 27.2% higher than the SKD and SUD gradations, respectively. In tensile tests, the RED gradation consistently delivered superior performance, achieving a 28-day tensile strength of 0.88 MPa at 0% replacement, which was 15.8% and 20.5% higher than SKD and SUD. Recyclability was confirmed by acceptable crushing value and flakiness index of second-generation recycled aggregates from RED specimens across all RBA replacement levels. Even at a 30% RBA replacement ratio, the second-generation recycled aggregates still met the Class II specifications for subbases of secondary and lower-grade highways. At RBA replacement levels up to 16%, the second-generation recycled aggregates met Class II standards for subbases of expressways and primary highways. When the replacement ratio increased to 24%, they still satisfied Class I standards applicable to subbases of secondary and lower-grade highways.

Keywords

cement-stabilized materials / recycled brick-concrete aggregates / discrete element method / mechanical performance / recyclability

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