# What is bottom ash granulate?
**Bottom ash granulate (Dutch: BSA-granulaat, also called IBA granulate — Incinerator Bottom Ash granulate) is a recycled construction material produced by processing the residual ash from municipal waste incineration plants. After treatment — including crushing, screening, and ageing — it is used as a substitute for primary aggregates in road bases, embankments, and fill applications.**
## How it is produced
When household and commercial waste is incinerated, the non-combustible residue that collects at the bottom of the furnace is called bottom ash. This raw ash undergoes several processing steps:
1. **Metals recovery:** Ferrous and non-ferrous metals are extracted for recycling.
2. **Crushing and screening:** The ash is broken down and graded to specified particle sizes.
3. **Ageing/maturation:** Stockpiled for several weeks to allow chemical stabilization and reduce leaching potential.
4. **Quality testing:** Leaching tests verify that contaminant levels meet environmental standards.
### Key characteristics
– **Grain size:** Typically 0–32 mm or 0–40 mm grading.
– **Density:** Lower than natural gravel, approximately 1,400–1,700 kg/m3 loose.
– **Bearing capacity:** Adequate CBR values for sub-base and fill applications.
– **Environmental certification:** Must comply with soil quality regulations regarding leaching of heavy metals and salts.
## Applications
– Road sub-base and base courses
– Embankment and land-raising fill
– Pipe bedding material
– Noise barriers and earth structures
– Parking area foundations
## Related terms
– Fly ash
– Recycled aggregate
– Circular construction
– Leaching (uitloging)
– Soil quality decree
– CBR value
– Secondary raw materials
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