Sun Jishu 1a，1b， Xie Shaokang 1a，1b， Zhang Min 2 ， Li Hui 1a ， Liu Lanbin 1a
1a. School of Civil and Transportation Engineering，1b. Civil Engineering Technology Research Center of Hebei Province，Hebei University of Technology， Tianjin 300401， China；2. Tianjin Expressway Group Limited， Tianjin 300384， China
Abstract
Objective This study addresses the issue that recycled aggregates from construction waste are prone to particle crushing under compaction during road construction， which leads to gradation deterioration and a decline in mechanical properties. The study investigates the crushing characteristics and evolution of mixtures incorporating recycled aggregates of different particle sizes and volume fractions， and explores the relationship between changes in recycled aggregate gradation and crushing performance， thereby providing a theoretical basis for the rational application of recycled aggregates in road bases.
Methods Recycled concrete aggregates and recycled brick aggregates from construction waste were used as the research object. Using the equal volume replacement method， recycled aggregates with particle sizes of 9.5-19 mm， 19.1-26.5 mm， and a mixture of 9.5-19 mm and 19.1-26.5 mm were used to replace natural aggregates at volume fractions of 20%， 40%， 60%， 80%， and 100%. A total of 15 groups of compaction tests were designed. Sieve analysis was conducted to obtain the gradation changes of aggregates before and after the compaction tests. The relative crushing rate and crushing index were employed to quantitatively evaluate the crushing degree of aggregates. Based on a particle size-mass correlation model， the fractal dimension and its growth rate of aggregates before and after the compaction tests were calculated. The correlation between fractal dimension growth rate， relative crushing rate， and crushing index was then analyzed. For test groups where the aggregate gradation after the compaction tests did not meet the specification requirements， fractal dimension back-calculation and gradation optimization were performed. The effectiveness of the gradation optimization was verified through 7-day unconfined compressive strength tests.
Results and Discussion When recycled aggregates with a particle size of 9.5-19 mm replaced natural aggregates， the relative crushing rate， crushing index， and fractal dimension growth rate all continuously increased with the increasing volume fraction of recycled aggregates. When recycled aggregates with a particle size of 19.1-26.5 mm replaced natural aggregates， the relative crushing rate， crushing index， and fractal dimension growth rate all showed a trend of first decreasing and then increasing， reaching their minimum values at a recycled aggregate volume fraction of 60%， indicating the optimal crushing resistance of the system. When a mixture of recycled aggregates with particle sizes of 9.5-19 mm and 19.1-26.5 mm was used to replace natural aggregates， the relative crushing rate， crushing index， and fractal dimension growth rate showed little change when the volume fraction did not exceed 80%. However， when the volume fraction reached 100%， these values increased sharply. Correlation analysis between fractal dimension growth rate， relative crushing rate， and crushing index indicated that when natural aggregates were replaced by recycled aggregates of a single particle size， the fractal dimension growth rate had a significant positive linear correlation with both the relative crushing rate and the crushing index， respectively. For test groups where the aggregate gradation after compaction tests did not meet the specification requirements， fractal dimension back-calculation and gradation optimization were performed using the aggregate particle size-mass correlation model. After optimization， the aggregate gradations all met the specification requirements. The 7-day unconfined compressive strength tests showed that the compressive strength of the samples was significantly improved after gradation optimization.
Conclusion The multi-index collaborative evaluation system of fractal dimension， relative crushing rate， and crushing index， when natural aggregates are replaced by recycled aggregates of a single particle size， consistently and effectively characterizes the crushing behavior of recycled aggregates from three different dimensions—geometric morphology evolution， particle size distribution， and particle crushing degree. This demonstrates the rationality and effectiveness of the system. The aggregate particle size-mass correlation model based on fractal geometry theory can accurately describe the gradation evolution patterns of recycled aggregates and can be used to guide the gradation optimization of recycled aggregates， showing good engineering applicability.
Keywords： recycled aggregate； particle crushing； fractal dimension； gradation control； unconfined compressive strength
Get Citation: Sun Jishu， Xie Shaokang， Zhang Min， et al. Study on crushing performance of recycled aggregates under collaborative control of fractal dimension and particle size distribution［J］. China Powder Science and Technology， 2026， 32（4）： 1-11.
Received: 2025-10-26, Revised: 2026-03-12, Online: 2026-05-19.
Funding：The research was supported by the National Natural Science Foundation of China (Grant No. 52378231).
DOI：10.13732/j.issn.1008-5548.2026.04.013
CLC No.：U414
Type Code: A
Serial No.：1008-5548（2026）04-0001-11
