Every year, demolition crews across the Atlanta metro area tear out millions of square feet of concrete — driveways, slabs, foundations, sidewalks, bridge decks, parking structures. For most of the twentieth century, all of that material went to a landfill. Today, a well-developed regional recycling infrastructure means that same concrete can be processed, graded, and returned to service as a valuable construction material — often within miles of where it was demolished.
Understanding how the process works, from the moment a sledgehammer hits a slab to the moment a grader spreads finished base course, helps owners, contractors, and project managers make better decisions about demolition, material procurement, and sustainability compliance. Here's a step-by-step look at the full concrete recycling cycle.
Step 1: Pre-Demolition Assessment and Sorting
The recycling process begins before demolition starts. A pre-demolition assessment identifies what types of concrete are present on site, what contaminants may be mixed in, and whether on-site processing or haul-out to a recycling facility makes more sense economically and logistically.
Quality recycled aggregate starts with clean source material. The primary contaminants to identify and remove before crushing are:
- Rebar and embedded steel: Reinforcing steel must be separated from concrete. Some steel is removed mechanically during crushing; magnetic separators pull remaining fragments from the crushed product. Isolated rebar removed pre-demolition is typically sold for steel scrap separately.
- Asphalt: Pavement projects often involve both concrete and asphalt layers. These should be stockpiled and processed separately, since mixed material produces an inferior product and limits end-use options.
- Soils and organics: Concrete with significant soil contamination or biological material mixed in requires additional screening to meet specification.
- Hazardous materials: Lead paint, asbestos-containing joint fillers, and chemical contamination from industrial sites require separate handling. Concrete from sites with known contamination history requires testing before it can enter the recycling stream.
Good sorting at the front end dramatically improves the quality and value of the finished aggregate. Experienced demolition contractors and recycling processors work together to establish a sorting protocol before the first piece of concrete is broken.
Step 2: Demolition and Breaking
Demolition of concrete structures typically involves hydraulic breakers (hoe rams), excavator-mounted pulverizers, or wrecking balls for larger structures. The goal is to break concrete into manageable pieces — generally under 24 to 36 inches — that can be loaded into a crusher.
For slab-on-grade demolition, a hydraulic breaker on an excavator is the most common tool. It breaks the slab into irregular chunks, which are then grabbed and moved to a stockpile or directly into the crusher's feed hopper.
Structural concrete — beams, columns, walls — is often processed differently. Pre-cutting or saw-cutting sections before demolition can produce cleaner breaks and reduce the amount of entangled rebar. Demolition sequencing matters: bringing a structure down in sections produces better material and safer working conditions than a single-pass collapse.
Step 3: Primary Crushing
The first stage of processing is primary crushing, which reduces large concrete chunks to a workable size — typically minus-3-inch or minus-4-inch material. The two most common primary crusher types used for concrete recycling are:
Jaw crushers: A jaw crusher uses opposing plates — one fixed, one moving — to compress and break material as it passes through the narrowing gap. Jaw crushers are robust, handle large feed sizes well, and are the standard choice for primary crushing. They produce a somewhat angular, flaky product that can require secondary crushing to achieve well-graded aggregate.
Impact crushers: Impact crushers use high-speed rotating hammers or blow bars to shatter material against a breaker plate. They're more efficient at reducing cement paste from aggregate surfaces — which improves the quality of the finished RCA — and tend to produce a more cubical particle shape. However, impact crushers wear faster when processing hard material or when rebar contamination is high.
For large demolition projects in Georgia, mobile jaw crushers are frequently deployed on-site, allowing primary crushing to happen at the point of demolition rather than requiring transport of bulky demolished material to a fixed facility. This reduces truck movements, fuel costs, and tipping fees, while producing a material that can often be reused directly on the same project.
Step 4: Rebar and Metal Separation
After primary crushing, the material passes through magnetic separation equipment — typically an overband magnet or magnetic drum positioned in the conveyor line. This pulls ferrous metals (steel rebar, wire mesh, embedded anchors) out of the material stream. Magnetic separation is highly effective at removing most rebar fragments, though very fine wire can pass through.
Collected steel is stockpiled separately and sold as scrap metal, generating a small revenue stream that partially offsets processing costs. For reinforced structural concrete, the steel content can be substantial — sometimes hundreds of tons per project.
Non-ferrous metals (copper, aluminum) are less common in concrete but can be recovered through air classification or eddy-current separation in more sophisticated processing facilities.
Step 5: Secondary Crushing and Screening
After primary crushing and metal separation, the material typically goes through secondary crushing and screening to achieve the specified gradation. A cone crusher or secondary jaw crusher reduces the material to the target maximum particle size, and vibrating screens separate the product into size fractions.
Common finished gradations for Recycled Concrete Aggregate (RCA) in Georgia include:
- GDOT #57 (3/4-inch nominal): Clean, open-graded coarse aggregate used in drainage applications, pipe bedding, and drainage blankets under slabs.
- GDOT #467 (1.5-inch nominal): Larger open-graded aggregate for drainage layers and base applications where drainage is critical.
- Graded aggregate base (GAB) — 1.5-inch minus well-graded: The standard road base and parking lot subbase specification. Contains both coarse and fine fractions for maximum compaction and load-bearing capacity. This is the highest-volume product from most concrete recyclers.
- Crushed concrete fill (minus 4-inch): Used for general structural fill, building pad preparation, and utility trench backfill where gradation specification is less restrictive.
Oversized material rejected by screens loops back into the secondary crusher. Fines (material passing a No. 4 or No. 200 sieve) are either blended into GAB products at controlled proportions or stockpiled separately for use in applications where fine material is acceptable.
Step 6: Quality Control Testing
Responsible recyclers test their product systematically. For RCA supplied to road base and structural applications, standard tests include:
Sieve analysis (ASTM C136): Confirms the material meets the target gradation — the distribution of particle sizes from coarse to fine. Gradation is the most critical property for compaction and load-bearing performance. A well-graded aggregate with a balanced distribution of particle sizes compacts tighter and achieves higher density than a gap-graded or uniformly graded material.
Los Angeles Abrasion (ASTM C131): Measures resistance to mechanical degradation under loading. RCA typically has higher abrasion loss than virgin granite because the residual cement paste is softer than the original aggregate. For most base-course applications, the abrasion values are within acceptable limits, but this test is important to document for structural applications.
Proctor compaction (ASTM D698 / D1557): Determines the optimum moisture content and maximum dry density for compaction. RCA's higher absorption rate means it behaves differently than virgin aggregate under compaction, and the geotechnical engineer specifying the base course should account for this in the design.
Sulfate soundness (ASTM C88): Tests resistance to deterioration from sulfate attack. Elevated sulfate content in some RCA — particularly from concrete that contained calcium sulfoaluminate cement or was exposed to sulfate-rich soils — can cause expansion and degradation. This test is particularly important for RCA from sites where soil chemistry is unknown.
Reputable processors provide test certificates with each major shipment. Project owners and specifying engineers should request these certificates and verify that the material meets the project specification before accepting delivery.
Step 7: End-Use Applications
Processed and tested RCA has a well-established range of applications in Georgia construction:
Road Base and Subbase
Graded aggregate base (GAB) from recycled concrete is approved for use in road base and subbase applications under Georgia DOT specifications. It performs well as a load-distributing layer beneath asphalt or concrete pavement, providing the stable, well-drained platform that pavement requires. Many DeKalb, Gwinnett, Fulton, and Cobb County road projects have used RCA base course successfully.
Parking Lot Subbase
Commercial parking lots are a natural fit for RCA subbase. The material is typically placed at 6 to 12 inches of compacted depth, depending on traffic loading and the CBR value of the native subgrade. RCA's self-cementing tendency — caused by residual unhydrated cement in the paste — can actually produce a base that stiffens over time, improving pavement support.
Building Pad Preparation
Structural fill beneath building slabs can use RCA where the geotechnical report approves fill material. Proper compaction to the specified density is critical, and RCA is typically compacted in lifts of 6 to 8 inches, verified by nuclear density gauge testing. Vapor retarder placement above the RCA fill is standard practice to manage moisture migration.
Drainage Applications
Clean, washed RCA graded to a coarse, open gradation (GDOT #57 or similar) performs well in drainage applications — pipe bedding and haunch material, drainage blankets under slabs, and French drain systems. Its hydraulic conductivity is comparable to natural crushed stone at equivalent gradations.
Utility Trench Backfill
RCA crushed-concrete fill is widely used for backfilling utility trenches after pipe installation. It compacts well, provides stable support for the pipe zone, and allows some drainage in the trench — beneficial for managing groundwater in wet conditions.
Environmental Benefits of the Full Cycle
Stepping back to see the full life cycle, concrete recycling creates a closed loop that eliminates two separate environmental burdens: landfill disposal of demolished concrete and quarry extraction of virgin aggregate. Each ton of concrete recycled and reused displaces approximately one ton of quarried material and eliminates one ton of landfill disposal — a double environmental benefit per ton processed.
At the scale of a major demolition project — say, a 50,000-square-foot commercial slab averaging 4 inches thick and weighing roughly 250 tons per 1,000 square feet — recycling rather than landfilling prevents over 12,000 tons of concrete from entering the landfill, eliminates the quarrying of an equivalent volume of virgin aggregate, and reduces the truck movements associated with both hauling waste out and material in.
For projects pursuing sustainability documentation — LEED, Georgia DCA green building programs, or federal sustainability requirements — the concrete recycling chain provides documented, quantifiable environmental performance that supports project certification.
At Rare Earth Ltd, we work with Georgia project owners and general contractors to source, supply, and place recycled aggregate for commercial and government construction projects. Whether you need certified GAB for a parking lot, drainage aggregate for a site utility project, or help documenting materials sustainability for LEED, contact us to discuss your needs.