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Specifications for the Reinstatement of Openings in Highways 2nd edition July 2002 (England only) SR0Hv2 600-1000kg/m Single Drum Vibrating Roller Trials HAUC(UK) (UK) SR0H Website note- July 2004



Background

The Department for Transport (DfT) letter of August 2002 reinserted the 600-1000kg/m single drum vibrating rollers as acceptable items of compaction plant against the Method Specification for narrow trenches (less than 250mm wide). For 40mm layer thicknesses, this meant the original 10 passes of the roller, as specified under the June 1992 SROH.

Since then, the two main Roller manufacturers (Benfords and Bomag) have undertaken trials (approved by the SROH Working Party), with a view to demonstrating the effectiveness of single-drum vibrating rollers.

Independent Trials were scoped by TRL, who also monitored the trials and prepared the Final Report. The main Contractor for the tendered work was Scott Wilson Pavement Engineering. The trials were undertaken in the Autumn of 2003.

Hot Rolled Asphalts (HRAs), Stone Mastic Asphalts (SMAs) and 10mm Close Grained (CGSCs) carriageway materials were tested, along with 6mm Dense (DSC) footway material.


Trial Findings

All materials met the Voids criteria set out in the SROHv2, as amended by DfT letter of August 2002, but with a differing number of passes. HRAs and SMAs met the criteria within 8 passes. CGSCs just met the Voids criteria at 10 passes and 6mm DSC only marginally better at the same 10 passes.

It was encouraging to note that there was no noticeable difference in compaction between the two rollers. However, the Working Party believes there is still insufficient confidence to permit a reduction to the desired maximum of 8 passes, an agreed objective of the SROH Working Party, set down as part of its review of the June 1992 SROH.

A number of physical issues were identified during the trials, which the Working Party considers could have influenced the results. The key issue revolved around the amount of mounded loose material (surcharge) placed prior to rolling, which proved inadequate at times, causing the rollers to ‘span’ the trench, thus reducing compactive effort on later compaction passes.


Working Party Recommendations to HAUC(UK)

The SROH Working Party presented its recommendations to HAUC(UK), at the April 2004 Quarterly meeting:

Recommendation 1: that the Amendment made under DfT August 2002 letter should continue, and for the remaining life of the SROHv2, that 600-1000kg/m single drum vibrating rollers be still classed as acceptable items of compaction equipment, against the Method Specification for narrow trenches (less than 250mm wide). [Please note that for all trenches and patch excavations where Core testing is possible, that the SROHv2 end-Product compliance (i.e. meeting the Voids Criteria) effectively leaves the choice of compaction equipment to the Undertaker.]

Recommendation 2: that HAUC(UK) calls for further trials to be undertaken, with a view to fulfilling the original Working Party objective in achieving a reduction to 8 passes. In particular, like for like trials to examine the effect of increased surcharge materials for the CGSCs and DSCs should be considered a priority.


HAUC(UK) Decisions

HAUC(UK) agreed with Recommendation 1, which, as stated, confirms the suitability of Single Drum Rollers as acceptable items of compaction plant against the Method Specification for narrow trenches (less than 250mm wide), during the lifetime of the SROHv2.

HAUC(UK) provided broad support for Recommendation 2 – further trials. However, the mechanism and timing of these trials will be considered over the course of the next HAUC(UK) Meetings.
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