P di ti f P t S f Skid RPrediction of Pavement Surface Skid RPrediction of Pavement Surface Skid REffect of Smaller Chip SEffect of Smaller Chip Sp

Birendra KumarBirendra KumarDr Douglas WilsonDr Douglas Wilson

Introduction ResultsIntroductionResearch has demonstrated that the road based transport

ResultsResearch has demonstrated that the road based transport

h i h kid i f d fThe DFT (μ) friction results

crash rate increases as the skid resistance of road surface(μ)

surface sample (initial skid rdecreases. This research compares the equilibrium skid

surface sample (initial skid raccelerated polishing in hourdecreases. This research compares the equilibrium skid

resistance level of various natural and artificial surfacingaccelerated polishing in hourdiff l (resistance level of various natural and artificial surfacing

i l di i h hi i ddifferent aggregate samples (

aggregates including varying the aggregate chip size under artificial electric arc furnace)laboratory based accelerated polishing and in response to

artificial electric arc furnace)of the materials (greywackey p g p

changes in environmental conditions Previous research hasof the materials (greywacke

ith t diff t hi ichanges in environmental conditions. Previous research hash th t t kid i t f hi l f i t

with two different chip sizesshown that wet skid resistance of chipseal surfaces is not value at which the DFT (μ) lonly a function of the polishing resistance of the aggregate,

(μ)sample is shown graphicallyy p g gg g ,

but also of its size shape and spacingsample is shown graphically E ilib i Skid R i tbut also of its size, shape and spacing. Equilibrium Skid Resistance

Experimental MethodologyExperimental MethodologyA l b i d i d h U i i fA laboratory experiment was designed at the University ofAuckland (UoA) to simulate the in-field skid resistance( )performance of surfacing aggregates The experiment Initial Skid Resistanceperformance of surfacing aggregates. The experiment

i d l t d l b t li hi f i ti t tirequired accelerated laboratory polishing, friction testingwith a Dynamic Friction Tester (DFT) and surfacingy ( ) gsamples to be constructed that were compatible with eachsamples to be constructed that were compatible with eachother The testing process and methodological steps areother. The testing process and methodological steps areshown in Figure 1.

Figure 2: Friction (μFigure 2: Friction (μ

Step 1: Preparing an Step 3: Friction Testing a Step 1: Preparing an t l t t t

p gprepared Sample DFT (μ) Figures 3 and 4 respectivelyaggregate sample to test p p p (μ) Figures 3 and 4 respectively

greywacke and a South Aucgreywacke and a South Auckid i iskid resistance improvemen

chip size from a Grade 4 tochip size from a Grade 4 todemonstrate the effect on mdemonstrate the effect on mth dditi f i tthe addition of various contreached (oedometer clay, le( y,powder) with accelerated pStep 2: Polishing with The Dynamic Friction Testerpowder) with accelerated p

h dp gAccelerated Polishing Machine

The Dynamic Friction Tester and Rubber sliders

reached. g and Rubber slidersFigure 1: Testing MethodologyFigure 1: Testing Methodology

R i t d thResistance and theResistance and the izeize

THE UNIVERSITY OF AUCKLAND FACULTY OF ENGINEERING DEPARTMENT OF CIVIL ANDDEPARTMENT OF CIVIL AND

ENVIRONMENTAL ENGINEERING

from a newly prepared y p presistance) throughresistance) through rs for three geologicallyrs for three geologically ( k b l d(greywacke, basalt and an ) are shown in Figure 2. Two) are shown in Figure 2. Two and basalt) were then tested and basalt) were then tested (G d 4 G d 6) Th (Grade 4 vs. Grade 6). The

levelled off for each aggregate gg gand described as the polishedand described as the polished (ESR) l le (ESR) level.

Fi 3 Chi Si ff f G kFigure 3: Chip Size effects for Greywacke aggregate

Polished Equilibrium SkidPolished Equilibrium Skid Resistance (ESR) levelResistance (ESR) level

Figure 4: Chip Size effects for Basalt aggregateμ) vs Polishing Time

g p gg g

Research Conclusionsμ) vs Polishing Time

Research Conclusions1) Th tifi i l El t i A F t (G d 4)1) The artificial Electric Arc Furnace aggregate (Grade 4)y for a South Auckland

performed the best of the three geological materials andy for a South Auckland ckland Basalt demonstrate the p g g

contaminants had very little effectckland Basalt demonstrate the

f d i h contaminants had very little effect2) The Grade 4 gre acke and basalt aggregates performed

nt of reducing the aggregate 2) The Grade 4 greywacke and basalt aggregates performedo Grade 6. The figures also

very similarly at ESR level although the basalt had a mucho Grade 6. The figures also measured skid resistance with y y g

higher initial skid resistancemeasured skid resistance with t i t ft ESR h b higher initial skid resistance

3) Both the greywacke and basalt aggregate demonstrated ataminants after ESR has been

3) Both the greywacke and basalt aggregate demonstrated ai ifi i h ll G d 6

eighton buzzard sand , emery significant improvement when a smaller Grade 6

g , ypolishing after ESR has been

aggregate chip was used in comparison to a Grade 6 chippolishing after ESR has been

agg ega e c p was used co pa so o a G ade 6 c p(24% and 35% improvement respectively)(24% and 35% improvement respectively).