Lightweight fill materials

Lightweight filling materials in road construction denote materials with design unit weights that may be utilised favourably in bearing capacity considerations (settlements, stability).
The main applications for such materials may be:
· Reduction of load on subsoil both on new roads or roads subjected to settlement damage
· Reduction of horizontal pressure on retaining walls and bridge abutments.
· Reduction of differential settlements in transition zones near fixed structures (bridges etc.) where settlements are undesirable
· Repair of slide areas
· Compensated foundations (no additional load on subsoil)
· Reduction of area required (vertical walls)

Lightweight filling materials commonly used so far has been bark, sawdust, cellular concrete waste, lightweight clay aggregate (Leca/LWA) and blocks of Expanded Polystyrene (EPS). In general Leca (design unit density r = 600 kg/m3) and EPS (design unit density r = 50 kg/m3) have until recently been the sharpest competitors on the road market.

In Norway some 20 000 tons of car tyres are discarded annually. Of these approximately 80 % are recycled – mainly through utilizing the combustion energy but also to some extent on construction sites. The remaining part is exported. In Norway it is the responsibility of the producer to collect discarded car tyres. The cost is covered by a fee paid by the user when buying the tire.

RagnSells AS is the supplier of used tire products in Norway and the company is responsible for collecting and processing (shredding) the tyres. Shredded tyres are produced in various sizes, typically 100 – 300 mm. This product has a low unit weight and may easily be compacted.

Basis for documentation: CEN«Workshop agreement CWA 14243 and «TA 1853/2002» also «Disponering av rene, naturlige masser og gjenvunnet materiale» (”Use of natural aggregates and recycled material”) published by the Norwegian Pollution Control Authority (SFT).

Applications: Lightweight filling material for road embankments and noise barriers.
Use of shredded tyres in road structures requires evaluation of environmental risks and approval by SFT.

Foam glass is a glass product based on recycling of granular glass aggregate. The material is foamed in a process where toxic metals and other possible pollutants are removed. The finished product has low unit density, favourable thermal insulation properties and high compressive strength.

Hasopor AS located at Meråker in Trøndelag is presently the only supplier in Norway.

Basis for documentation: A proposal for a new European standard specification (CUAP) is presently being evaluated for approval. This is likely to result in an ETA (European Technical Approval).

Applications: Handbook 018 Road Construction (revision 2003) describes foamglass as a frost insulating material and a lightweight filling material.

Contact: manager of WP5 Lightweight fill materials roald.aaboe@vegvesen.no