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General requirements for ARMs and ATs (NGA9.2)

Mix formulations are based on the constituents (including soil/aggregate, binder and water), mix proportions (including grading or pulverisation limits) and production tolerances. The mix formulation typically requires adjustment during works for variables such as water and binder addition. This is common to a wide range of construction materials and is required to accommodate differences in workability arising from variations in internal factors (e.g. variation in feedstock) and external factors (e.g. environment and temperature). These adjustments are requirements of production control to achieve the end product performance requirements of A9. Adjustments that may be considered significant and outside of this mix formulation adjustment include changing the type of binder(s) from that used in the mix design, and adjustment to binder above or below the limits established during the design testing.

There are some situations where continuity of drainage is a consideration when selecting reinstatement materials, especially backfill and sub-base. An example of this may include steep areas of road with water flowing in the foundation layers. A reinstatement cutting across this pathway, could in theory create a dam resulting in water washing materials away or creating a seepage line. SMRs have relatively low permeability owing to their physical nature. Therefore, recommendations to consider use of pea gravel in a geotextile rap are included in A9. For context, unbound mixtures (for example GSB1) are not necessarily free draining so the same consideration may be applied to their use.

SMRs have end product requirements that include strength class. They also have a performance requirement to be suitable for overlay with subsequent layers in the reinstatement. Depending on the nature and scenario where an SMR is used, it may perform well enough to be overlaid before the development of the minimum required strength class (see Table A9.1). If required, this potential may be established during the A9. approval process. This can be defined by the immediate bearing index for NFSMR which has mechanical interlock (see A10). Alternatively, this can be defined by a minimum strength class and/or period of time. Both should be linked to in situ curing of the material. It is important that the trials for this establish that overlay before full strength gain does not adversely damage the material versus its end product requirements (see Table A9.1).