- FCRs are cement-bound materials that have been prepared off-site or can be mixed on-site, generally as prescribed mixes, at an approved mixing plant and under appropriate quality control procedures. They are flowable and do not require compaction when placed. FCRs do not necessarily incorporate a coarse aggregate.
- FCRs must not encase cables or be used within 300 mm of a gas pipe.
- All aggregate used in FCRs must pass a 6.3 mm sieve and comply with the MP and FP grading limits given in BS EN 12620. Larger size aggregate may be used provided it can be shown to be practicable.
- The composition of recycled aggregate including recycled concrete aggregate must be classified by hand sorting coarse aggregate particles in accordance with BS EN 933-11. The test must be carried out by a suitably trained laboratory technician competent in classifying the constituent classes in accordance with the test method. The content of other materials (Class X) must not exceed 1% by mass or by volume, whichever is the greater.
- FCR permissible constituents must exclude potash and incinerator bottom ash aggregate (IBAA).
- Layer thickness and compressive strength at 7 days requirements must be in accordance with Table A2.1.
Table A2.1 FCRs minimum layer thickness and compressive strength requirements
Footways, Footpaths and Cycle tracks
Combined Binder Course & Sub-base
Base NP NP NP
--- Base & Sub-base NP
--- Sub-base or below 150 mm
NP = Not permitted
Minimum asphalt overlay thickness as per A3 to A7.
FCR is not permitted as CBGM base replacement.
- FCR for backfilling excavations and trenches under carriageway must have the following compressive strengths:
- A minimum cube compressive strength of 4 N/mm2 at 7 days.
- A maximum cube compressive strength of 10 N/mm2 at 7 days.
- The compressive strength must be determined by testing foamed concrete cubes made in accordance with BS EN 12390-1, except that the FCR must be placed in the mould without any tamping or vibration other than gently rocking the mould on a firm base. Test cubes must be cured in accordance with BS EN 12390-2 and tested for compressive strength in accordance with BS EN 12390-3.
- The compressive strength of FCR must be determined in accordance with the principles of BS EN 12390-3, and the following:
- Test specimens may be prepared at the time of placement by casting within a test mould or recovered from site by extracting cores from the reinstatement.
- Specimen shape and dimensions must be in accordance with BS EN 12390-1 with the addition that specimens may also be manufactured with an aspect ratio of 1. Flowable moulds may be manufactured from cellular foam (preferably polystyrene) and include a cellular foam lid. The samples must not be compacted except for minimal tamping to allow the mould to be filled without leaving excessive areas of voids.
- The top and bottom surfaces of core test specimens may be grouted to ensure flat, parallel loading surfaces.
- Following preparation or recovery, the test samples must be stored upright at either 20°C or 40°C, depending on the nature of the material (in accordance with the manufacturer’s instructions), and tested in compression at 7 days after placement of the material on site.
- FCRs must be produced to prescribed mix formulations by an approved mixing plant in accordance with approved manufacturing processes under quality control procedures.
- The wet density of FCRs must be checked before placement. Depending on the manufacturer’s instructions, the quality of the foaming agent added on site must be checked before being incorporated in the mix. Any on-site addition of a foaming agent must be in accordance with the approved mix design.
- In excavations containing water, the minimum density for foamed concrete is 1050 kg/m3.
- The sub-base and base must not be reinstated over FCR until it has attained sufficient strength to allow compaction of the material.
- FCRs must not be tamped or compacted unless otherwise specified by the manufacturer.
- To avoid FCRs flowing into damaged drains or ducts in or adjacent to the excavation, plastic sheeting or other protective measures must be used during pouring and curing.
- FCRs must be cured for the period specified by the manufacturer. During this period, the reinstatements must be protected.