Plate 10 of 13Materials
Recycled Aggregates: Crushed Concrete, Reclaimed Asphalt and More
Old pavements and demolished buildings can become new construction material. Here is what public agencies say about how that works and where it stops.
Most people picture aggregate as something dug from a pit or blasted from a quarry. A growing share of it is instead made from material that has already been used once. This page explains what recycled aggregate is, where it comes from, what road agencies and other public bodies say it is used for, and what limits keep it from replacing natural stone, sand and gravel everywhere. If you want the basics of the natural product first, start with what aggregates are and how they are made.
What counts as recycled aggregate
Aggregate is the granular material, from fine sand to coarse crushed stone, that makes up most of a road base, an asphalt mix or a batch of concrete. Recycled aggregate is the same kind of granular material, produced by processing something that was previously part of a structure or pavement.
Two types dominate the public literature. Recycled concrete (the US Federal Highway Administration, or FHWA, uses the term reclaimed concrete material) is old concrete that has been broken up, stripped of steel and crushed to size. Reclaimed asphalt pavement, usually shortened to RAP, is old asphalt road surface that has been milled or ripped up and processed into granular form. FHWA describes RAP as usable as an aggregate substitute and as a portion of the binder, the sticky bitumen that holds an asphalt mix together.
The US Geological Survey (USGS) also lists iron and steel slag, a byproduct of metal making, among the substitutes used for crushed stone in roadbuilding. Brick, glass and ceramics can be processed too, though the public road-agency guidance concentrates on concrete and asphalt.
Where it comes from
The raw material is demolition and construction debris plus the pavements that engineers remove when a road is rebuilt. The US Environmental Protection Agency (EPA) estimated that 600 million tons of construction and demolition debris were generated in the United States in 2018, a figure that includes concrete and asphalt concrete along with steel, wood, drywall and other materials.
EPA also tracks where that debris goes next. Of the 2018 total, its table shows about 313 million tons heading to an aggregate use and about 144 million tons to landfill, with the rest going to manufactured products, fuel, compost and mulch, or soil amendment. Because that "aggregate" line covers several debris types, it is a broad indicator and not a count of crushed concrete alone.
On a large road job the source can be the road itself. FHWA notes that on large reconstruction projects, processing and recycling concrete on site is likely to reduce aggregate hauling costs.
Typical uses
FHWA's user guideline for reclaimed concrete says it can serve as coarse or fine aggregate in granular base, the compacted layer of crushed material under a pavement. The same guideline says properly processed and tested material has generally performed satisfactorily there, and it lists twenty states that used it when the document was written. For how these layers work in everyday projects, see crushed stone bases under paving and slabs.
RAP's main job is different. FHWA says the most common method combines RAP with new aggregate and new asphalt cement in a central mixing plant to produce fresh hot mix, and that substitution rates of 10 to 50 percent or more are normally used, depending on state specifications. It calls the practice standard in most jurisdictions and reports that properly specified recycled hot mix is equivalent in quality and structural performance to conventional mix in terms of rutting, raveling, weathering and fatigue cracking. Those statements come from a 1990s guideline, so current specifications may differ.
Why it is used
The reasons public bodies give are practical. Recycled material substitutes for virgin aggregate, which reduces the amount that has to be extracted. USGS says recycled asphalt and portland cement concretes are increasingly used as substitutes for virgin aggregate. It also reports that asphalt and portland cement concrete road surfaces were recycled in all 50 US states in 2025.
Diverting debris from disposal is the second reason, visible in EPA's figures above. Cost is the third. FHWA points out that crushed concrete has a lower compacted unit weight than conventional mineral aggregate, so the same weight covers a greater volume, which it calls economically attractive to contractors.
Limits: quality, contaminants and specifications
Recycled aggregate is variable because its source is variable. FHWA advises inspecting incoming RAP and rejecting contaminated loads, listing excess granular material, surface treatment and joint sealant as examples. It notes that many agencies do not allow RAP from different projects to be blended into combined stockpiles, because of that variability.
Crushed concrete has its own cautions. FHWA reports that its fine fraction absorbs more water, 4 to 8 percent for fines from air-entrained concrete compared with 2 percent or less for virgin concrete aggregate. Bearing strength drops when asphalt-coated particles make up more than about 20 to 25 percent of a granular base, according to Ontario studies it cites. FHWA also describes cases where unsuitable or improperly processed crushed concrete led to a chalky mineral deposit called tufa clogging pavement drains, and says the problem is not universal. Washing the material and leachate testing are among the measures it lists. It adds that some jurisdictions require stockpiles to sit a minimum distance from watercourses because crushed-concrete runoff is alkaline.
Finally, material has to meet the same kind of specification as natural aggregate, covering grading and quality tests. FHWA says processed crushed concrete generally satisfies standard base-course specifications, and that RAP aggregate usually can meet the standards for bituminous mixes. Sizing rules are explained in aggregate sizes, grading and choosing material. Concrete made with recycled coarse material is a more specialised subject; the ingredients of ordinary mixes are covered in concrete and mortar ingredients.
A sourced figure: how much is recycled
In its Mineral Commodity Summaries 2026, USGS reports recycled material in the crushed stone supply chain at 37 million metric tons for both 2024 and 2025 (the 2025 value is an estimate). In the same table, producers sold or used about 1,500 million metric tons of newly produced crushed stone. In its sand and gravel chapter, USGS says the percentage of total aggregate supplied by recycled materials remained very small in 2025. In other words, recycling is widespread but still a small supplement to quarried material in the United States. Other countries report different shares, and definitions vary, so figures from one country should not be applied to another.
Frequently asked questions
Is recycled aggregate the same as crushed concrete?
Crushed concrete is one kind of recycled aggregate. Reclaimed asphalt pavement is another, and byproducts such as slag are sometimes grouped nearby. Public agencies usually name the specific material because each behaves differently.
Can recycled aggregate be used under a driveway or patio?
FHWA describes granular base as the main application for crushed concrete on roads. Whether a given product suits a particular base depends on its grading, cleanliness and your local specifications, so check with the building authority or a qualified professional.
Why do some states limit reclaimed asphalt in surface layers?
FHWA's 1990s guideline reported that ten state agencies did not permit RAP in surface courses, while all permitted it in base and binder courses. Reasons include variability and the performance demands of the top layer. Practice has changed since, so current state specifications are the authority.
Does recycled aggregate cause environmental problems?
FHWA states that there do not appear to be environmental problems from crushed-concrete leachate, yet it still records the alkalinity-related stockpile distances some jurisdictions require. Handling rules differ by place and are set by local environmental regulators.
The short version
Recycled aggregate is crushed concrete, reclaimed asphalt and similar material processed back into granular form. Road agencies describe it as proven in bases and in new asphalt, with quality control needed because the feedstock varies. Rules and practice differ by country and site, and the reader's own regulator or a qualified professional has the final word.