Researchers have developed an efficient water jigging method that recovers concrete aggregates from construction and demolition waste (CDW) with 99 % purity and an 80 % recovery rate, offering a scalable solution for sustainable recycling.
Study: Contaminants Removal from Construction and Demolition Waste (CDW) with Water Jigs. Image Credit: bogubogu/Shutterstock.com
Background
CDW remains one of the largest contributors to landfill waste worldwide, made up of materials like concrete, bricks, metals, ceramics, and polymers. As the construction industry seeks more sustainable practices, recycling CDW, particularly into usable concrete aggregates, offers a way to ease the demand on natural resources and reduce environmental strain.
However, impurities such as bricks and gypsum compromise the quality of recycled aggregates, leading to low strength, high porosity, and poor chemical stability. These issues limit their structural applications and often make recycling less viable. Traditional sorting techniques - manual or mechanical - typically fall short in separating materials with high precision and are rarely cost-effective at scale.
To address this, the study discussed here evaluated water jigging, a gravity-based separation technique that uses pulsed water flows to sort particles by density and shape. The researchers tested this method at a lab scale to determine its effectiveness in isolating clean concrete from mixed waste and to assess its performance across varying contamination levels.
Methodology and Approach
To replicate real-world waste conditions, the team prepared CDW mixtures by crushing concrete, bricks, and gypsum into coarse aggregates ranging from 5 to 20 mm. These mixtures were created with three levels of contamination - 10 %, 20 %, and 30 % by weight - to test the jigging method under different scenarios.
The water jigging system was set to operate at 35 pulses per minute with a 14 cm stroke length and a 3-minute retention time. These parameters were crucial in enabling separation based on particle characteristics like density and shape.
Once processed, the materials were divided into three distinct layers: light, middling, and dense. Each layer was oven-dried and visually inspected to determine its composition. Further analysis included standard tests for density, water absorption, particle shape, grain size distribution, and bulk density. This comprehensive characterization enabled a clear understanding of the separation efficiency and recovery rate across the different sample conditions.
Results and Discussion
The physical differences among the materials proved to be key drivers in the success of the jigging process. Concrete exhibited the highest density (approximately 2.04 g/cm3), low water absorption (~5 %), and nearly spherical particles. In contrast, bricks were less dense (~1.77 g/cm3), more porous, and had flatter, lamellar shapes. Gypsum had the lowest density (~1.11 g/cm3) and absorbed significantly more water (~47 %).
In all three contamination scenarios, single-stage jigging reliably produced concrete aggregates with 99 % purity in the dense fraction. Even at 30 % impurity, the recovery rate remained at 80 %, underscoring the method’s robustness. The middling fraction contained partially separated particles, suggesting that additional separation stages could push the recovery rate even higher.
Notably, the recycled aggregates in the dense layer not only met the standard criteria for reuse but also showed improved physical properties compared to the original waste - higher density and lower water absorption. These enhancements indicate that water jigging not only separates but also upgrades the quality of recovered aggregates, making them suitable for structural reuse.
Conclusion
The strength of this method lies in its straightforward, physics-based approach. By using density and shape to separate materials, water jigging avoids the complexity of chemical processing or sensor-based systems, making it practical for integration into existing recycling operations.
The middling fraction, which still contains partially liberated aggregates, indicates that a multi-stage setup could improve overall recovery without significantly increasing system complexity. This presents a clear path for technical refinement.
Moving forward, the focus shifts to scaling the process beyond the lab. Pilot-scale trials, performance benchmarking, and integration with other CDW processing steps will be critical for validating the method under real operating conditions. The process also raises broader questions around how to standardize quality control for recycled aggregates in structural applications.
With these next steps, water jigging could become a reliable component in construction waste management - offering a consistent way to recover usable material and reduce landfill volumes without adding unnecessary operational burden.
Journal Reference
Barkat, H., Teixeira, A. B.,et al. (2025). Contaminants Removal from Construction and Demolition Waste (CDW) with Water Jigs. Minerals, (9), 981. DOI:10.3390/MIN15090981. https://www.mdpi.com/2075-163X/15/9/981
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