The vast amounts of construction waste generated during urban renewal and infrastructure projects need no longer be treated merely as solid waste destined for landfills. Through standardized, integrated processing technologies—encompassing sorting, crushing, shaping, and screening—this waste can be transformed into recycled aggregates capable of replacing natural sand and gravel. Producing high-quality recycled aggregates with stable performance that meet engineering standards requires more than simple crushing; it demands targeted process design and specialized equipment combinations to overcome inherent flaws such as poor particle shape, high impurity content, and excessive water absorption. The ultimate goal is to yield qualified products suitable for diverse applications, including road base layers, recycled concrete, and prefabricated building materials.

Production Process for High-Quality Recycled Aggregates:

 

1. Pre-treatment and Impurity Separation

 

Upon arrival, construction waste is often contaminated with various debris, such as rebar scraps, plastics, wood chips, and woven bags. Direct crushing would not only accelerate equipment wear but also result in finished aggregates with excessive impurity levels. This stage begins with a high-intensity magnetic separator to completely remove metal components like rebar and iron wire—metals that can subsequently be recycled. Next, an air separation system removes lightweight debris such as plastics and foam, while manual sorting removes difficult-to-separate items like large pieces of wood and fabric. This process achieves a material purity of over 95%, ensuring the fundamental quality of the recycled aggregates right from the source.

 

2. Multi-stage Crushing and Granulation

 

Once impurities are removed, the material enters a specialized multi-stage crushing process. Primary crushing is performed by a jaw crusher; utilizing the reciprocating squeezing action of the movable jaw plate, it reduces large chunks of concrete and masonry—some exceeding 1 meter in size—into medium-sized fragments under 300mm. This stage also liberates residual rebar fragments, preventing jams or blockages in subsequent processing steps. The initially crushed material is fed into an impact crusher or a vertical shaft crusher for secondary crushing. Impact crushers efficiently strip away old, loose mortar from the aggregate surface, while vertical shaft crushers utilize "rock-on-rock" impact to produce well-shaped, cubical particles. This process allows for precise control of the final particle size within the 0–40 mm range, meeting specific granularity requirements for various applications.

 

3. Screening, Washing, and Dust Removal

 

The mixed material resulting from multi-stage crushing undergoes precise classification by particle size using multi-deck high-frequency vibrating screens. This strictly separates recycled coarse aggregate (>4.75 mm) from recycled fine aggregate (≤4.75 mm) and allows for the further subdivision of customized fractions—such as 5–10 mm and 10–20 mm—preventing size mixing that could compromise the workability of the resulting concrete. For high-quality production lines, a bucket-wheel sand washer may be added to thoroughly remove silt and mortar fragments from the aggregate surfaces. Some advanced processes incorporate low-temperature heat treatment to moderately embrittle the old mortar layer before stripping it off, thereby further reducing the aggregate's water absorption rate. The entire process is equipped with an enclosed dust removal system to ensure compliance with environmental protection standards.

 

4. Quality Inspection and Storage

 

Finished recycled aggregates must undergo standardized batch testing before being placed in storage. Key testing parameters include the crushing value (reflecting compressive strength), water absorption (indicating porosity), and the content of chloride ions and sulfates (affecting durability), as well as the proportions of organic matter and lightweight impurities; auxiliary parameters such as particle gradation and the content of flaky or elongated particles are also verified. Once all indicators meet relevant national and local standards for recycled aggregates, the materials are classified by grade and conveyed to the corresponding storage silos. A secondary sampling inspection is conducted prior to dispatch to ensure that every batch delivered to the construction site meets performance specifications and is ready for direct use in applications such as recycled concrete production and road base construction. Transforming construction waste into high-quality recycled aggregates is a key pathway for achieving the circular utilization of solid construction waste. Through the synergistic operation of specialized equipment systems, discarded building materials—which would otherwise be destined for landfills—are converted into high-value green building materials. This process reduces the demand for natural sand and gravel extraction while significantly lowering land use and carbon emissions associated with waste disposal, thereby providing a sustainable material solution for urban green infrastructure.