Over the past few months we have had many client enquiries relating to clarification on SMR materials. This is mainly driven by the fact that such materials can be used as a combined Binder/Sub-Base replacement in footway reinstatements as specified within current Specification for Reinstatement of Openings in the Highway (SROH) Appendice – A9.3.1.d).

However where problems arise is where this option is selected it is paramount that it is applied as a combined Binder/Sub-Base layer (footways only) and performs as a bound material from which a sample may be extracted.

From a laboratory viewpoint, regardless of what the material is or may be designated, it cannot determine any unbound material as SMR if it is not demonstrating properties of a bound construction. The more likely issue remains around overall bound layer depth compliance excluding Sub-Base (A2.5). Clients may also apply core sample extraction to determine crush strength where materials will have to reach performance specification requirements as stated in SROH Table A9.1 to determine it is a SMR and performing as such.

Where SMRs are found to be utilised as a combined Binder/Sub-Base construction within a footway it would be expected that a sample could be retrieved at 150mm layer thickness from the reinstatement (ie. Binder course at 50mm + Sub-Base at 100mm = 150mm) as SMR material cannot be used as a footway Binder course replacement only. It is also recognised that certain HBM materials may fragment through coring process which will still allow for removal of such fragments for layer depth measurement as per SHW 700 series. However it should also be noted that fragmentation is not determined as an unbound material and will be recorded as such. Unclassified unbound materials will be determined where no adherence or binding is encountered and is manifesting as loose material from sample extracted as the laboratory can only report on actual findings.

This applies to foamed concrete reinstatements,  flowable structural materials for reinstatement (FSMRs,) non-flowable structural materials for reinstatement (NFSMRs), and hydraulically bound materials (HBMs) as per SROH A9.2.a).

The definition of SMR materials as quoted directly from the SROH A9.1.2.a) – “This generic group is intended to include proprietary or alternative bound reinstatement materials that include a cementitious, chemical or hydraulic binder or are inherently self-cementing”.

 Core sample extracted from SMR material

Such materials may be subject to cube testing from materials at time of manufacture or batching, however it should also be noted that testing prescribed within the SROH document determines such FCR’s and FSMRs may have test specimens prepared at time of placement (during application), or recovered after placement by the extraction of core samples (A9.3.3.1.a) to ensure material complies with SROH Table A9.1 for compressive strength. This also applies to NFSMRs as prescribed within SROH A9.3.4.1a.

Advice on HBM materials can be found by clicking on the image below:

Definitions from Oxford Learners Dictionary –

Binder: a substance that makes things stick or mix together in a solid form.

Hydraulic: hardening in presence of water