On-site recycling turns broken concrete, brick, asphalt, and stone from demolition into useful aggregate for new construction. Instead of hauling rubble to a landfill and bringing in fresh gravel, a mobile crusher and screening unit can process material directly at the job site. This saves fuel, reduces truck traffic, lowers disposal costs, and keeps valuable mineral material in use.
The main idea is simple: break large pieces into smaller pieces, sort them by size, and remove unwanted contaminants.
Key Facts
- Mass recovery = usable aggregate mass / input rubble mass
- If 120 t of rubble produces 96 t of aggregate, recovery = 96 / 120 = 0.80 or 80%
- Crusher reduction ratio = feed size / product size
- A 600 mm concrete chunk crushed to 75 mm has reduction ratio = 600 / 75 = 8
- Screening separates particles by size using mesh openings, such as 40 mm, 20 mm, and 10 mm decks
- Recycling saves hauling energy because fuel use is reduced when fewer truck trips are needed
Vocabulary
- Mobile crusher
- A tracked or wheeled machine that breaks large pieces of rubble into smaller aggregate at the construction site.
- Screening machine
- A machine that sorts crushed material into size ranges by passing it over vibrating mesh screens.
- Aggregate
- Granular material such as gravel, crushed concrete, or crushed stone used in roads, foundations, and concrete mixes.
- Contaminant
- An unwanted material such as wood, plastic, soil, or metal that must be removed from recycled aggregate.
- Reduction ratio
- The ratio of the original feed particle size to the final crushed particle size.
Common Mistakes to Avoid
- Treating all rubble as reusable aggregate, which is wrong because wood, plaster, soil, plastics, and hazardous materials can weaken the product or make it unsafe.
- Ignoring particle size distribution, which is wrong because base layers and concrete mixes need a controlled range of sizes to compact and perform properly.
- Assuming crushing alone finishes the recycling process, which is wrong because screening, metal removal, and quality checks are also needed.
- Forgetting moisture and dust control, which is wrong because dry crushing can create airborne dust while very wet material can clog screens and reduce efficiency.
Practice Questions
- 1 A mobile crusher processes 150 tonnes of demolition rubble in one day and produces 112.5 tonnes of usable aggregate. What is the mass recovery percentage?
- 2 A crusher takes in concrete pieces with an average size of 480 mm and produces material with an average size of 60 mm. What is the reduction ratio?
- 3 A site has the choice to haul rubble 25 km to a landfill or recycle it on-site using a mobile crusher and screen. Explain two environmental benefits and one engineering quality check needed before the recycled aggregate is reused.