Sources of Recycled Construction Aggregates
Construction and demolition waste represents a significant portion of the material sent to landfills every year. In many countries, concrete, bricks, blocks and other material from demolished buildings and structures account for over 30% of landfill volumes. Recycling this material to produce recycled construction aggregates is an effective way to reduce waste while providing a sustainable source of aggregate for new building projects.
Concrete: Decommissioned concrete structures such as roads, bridges and building foundations provide a Recycled Construction Aggregates significant source of crushed concrete that can be used to produce recycled aggregate. Concrete consists largely of aggregate bound together in a cement matrix making it well suited for recycling.
– Bricks and blocks: Demolished masonry structures like walls provide crushed brick and concrete blocks suitable for aggregate recycling. The bricks must be crushed and screened to produce consistent sized aggregate.
– Asphalt: Milled and crushed asphalt pavement removed during roadworks can be recycled as aggregate for new roads or in other construction applications. Asphalt consists of aggregate bound with bitumen binder.
– Glass: Recycled glass from construction and demolition debris, or from bottle recycling programs, can be crushed and added to aggregate blends in some applications. The glass must be processed to consistent aggregate size.
– Roofing materials: Shingles, tiles and other roofing waste generated during reroofing projects or demolition are a potential resource. The materials need to be segregated and any non-mineral components like tar paper or nails removed.
Processing Recycled Construction Aggregates
The material collected from demolition sites undergoes processing to produce the recycled aggregates. The steps involved in processing include:
– Sorting: The incoming waste stream is manually or mechanically sorted to separate valuable materials from contaminants like wood, plastics, metals which are removed.
– Size reduction: Oversized concrete rubble and other material is reduced in size using a crushing machine to produce crushed aggregate in consistent sizes and shapes.
– Screening: The crushed material passes over screens to separate aggregates by size into coarse and fine fractions meeting specifications. Any too small or large pieces are recirculated.
– Quality testing: Samples of the final recycled aggregates are tested to ensure they meet specifications for properties like strength, durability and contamination levels. Additional processing may be required if standards are not met.
Using Recycled Construction Aggregates in New Projects
Once processed, the recycled aggregates can be used as a substitute for virgin aggregates in various construction applications, helping to reduce the environmental impacts of resource extraction. Some common uses of recycled aggregates include:
– Road Bases and Sub-bases: Recycled aggregates perform well in road building below the level requiring high strength aggregates when used as structural fill or drainage layers in road construction.
– Concrete Production: Recycled aggregate is widely used in the production of lower strength non-structural concrete for applications like pavements or parking lots where high quality is not required. It replaces a portion of virgin natural aggregates.
– Asphalt Production: Recycled asphalt pavement is commonly incorporated into the production of new asphalt for road surfacing, replacing a portion of virgin aggregates.
– Drainage layers and backfill: Recycled aggregates function well as free draining granular fill material for foundation drainage layers and for compacted structural backfill.
– Landscaping: Crushed recycled concrete aggregate is used as decorative aggregate for walkways or in landscaping beds where it contributes to sustainability.
Benefits of Recycled Construction Aggregates
Increasing the use of recycled aggregates produces multiple environmental and economic benefits compared to continued reliance on virgin natural aggregates:
– Waste reduction: It diverts large volumes of construction and demolition waste from overburdened landfills, helping communities meet waste diversion targets.
– Resource conservation: Using recycled aggregates conserves non-renewable natural aggregate resources and reduces demands for sand, gravel and rock extraction.
– Lower transportation impacts: Recycled aggregates can often be sourced locally, reducing transportation distances and associated greenhouse gas emissions versus importing virgin materials.
– Cost savings: The processing of recycled aggregates into consistent sizes and quality often results in a product as good or better than virgin materials at a lower material and transportation cost.
– Green building points: Using recycled aggregates can contribute points toward green building certifications like LEED recognizing the environmental advantages over virgin materials.
As awareness of sustainability issues increases, recycled aggregates are poised to play a growing role in reducing waste and conserving resources through greater use in construction projects worldwide. With proper processing, they provide a durable, cost-effective solution for new buildings.
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