P25 Specification forHigh Skid-Resistant Surfacings

Joanna Towler, NZ Transport AgencyMark Owen, NZ Transport Agency

Simon Fletcher, Fletcher Corporation Ltd3rd International Surface Friction Conference, Safer Road Surfaces – Saving Lives, Gold Coast, Australia,

16 May 2011

Perceptions of High Skid Surfacings

Durable binder and aggregate-based surfacings that provide high skid resistance

That HSRS is not value for money$40 to $60/m2

C.S. $2 - $8/m2; A.C. $11 to $32/m2

There are quality issues HSRS delaminates in a short period of timeSubstrate fails earlyLack of skilled workforce

Whole of Life Costs

In locations where:Natural aggregate polishes within 2 yearsGeometric improvements expensive or impracticalHigh wet-road crash rate

The whole of life costs may show that a HSRS is value for money

Case Study: SH2 Petone Overbridge

SH2 Petone Overbridge

15 – 20 Crashes/yearSpeed environmentIn 1997 calcined bauxite at $50/m2

Post installation: 0.5 Crashes/year

21 year history of injury accidents at SH2 Petone Overbridge

Resurfacing – Open Graded Porous Asphalt (OGPA)

Calcined Bauxite laid 1997

Cost of resurfacing = $40,000Annual crash savings = $1.9 millionFirst year rate of return = 48 (B/C ≈ 400) At the time, the cost of applying calcined bauxite amounted to just two weeks’ crash savings.

P25 Specification

P25 Specification for High Skid-Resistant Surfaces (HSRS)

P25 Summary of Performance Criteria

The HSRS is required to achieve, for the defects liability period:

the specified level of skid resistance (microtexture and macrotexture)the specified levels of material retention and adhesion to the substrate

The substrate shall be strong enough to resist failure planes through the substrate

P25 Performance Criteria

Skid Resistance 0.65 ESC Over 95% of 10 m sections

0.6 ESC Over 100% of 10 m sections

Texture 0.9 mm MPD

P25 Performance Criteria

Binder & Aggregate Retention/Loss

< 0.25 linear m In any 10 m section (both wheelpaths)

< 0.15% In any 10 m section

< 0.1% In any whole site

P25 Performance Criteria

Visual Appearancebinder and aggregate retention/losscrackingjoint cracking

Binder overspill/underspill

Edges, Ridges and joins

P25 Performance Criteria

Loose Aggregate < 150 g/m2 In first 2 months of life

< 50 g/m2 From 2 months to end of Defects Liability Period

Specification Notes

Apply to a completely bone-dry substrateWithin the atmospheric moisture dew point toleranceOn ‘as clean as possible’ substrateApply resin binder to correct minimum thicknessAvoiding laying on multi-layered chip seal (which has poor structural integrity).Strictly following all elements within the manufacturer’s Method Statement

P25 – Next Steps

Currently out for industry sign-offIssue on NZTA website in next 6 weeksNext year we will do P33 Coloured SurfacingE-mail joanna.towler@nzta.govt.nz if you wish to review the current draftOr visit us at the NZTA stand