KUNSAN NATIONAL UNIVERSITY

Prof. Park Dae-Wook

Vo Viet Hai

Skid resistance is the friction developed to prevent a tire from sliding along the pavement surface.

Lower when affected by water due to the phenomenon of hydroplaning and contaminated by mud or loose detritus resulting from the day to day usage.

Important safety factor - Inadequate skid resistance will lead to higher rick of accidents.

Vehicle speed Surface texture (macro-texture) Surface condition Tire characteristics Weather Road geometry Aggregates (micro-texture)

According to BS 812

The Polished Stone Value of aggregate gives a measure of resistance to the polishing action of vehicle tires under conditions similar to those occurring on the surface of a road.

The samples are first polished by the Accelerated Polishing Machine. Then the British Pendulum tester is use to measure the PSV.

Specimens before and after polished

14 chips of sample clamped around the periphery of the 'road wheel’

2 phases of abrasion The first phase is of abrasion by a corn

emery for three hours, and then 3 hours of polishing with an emery flour

Road wheel

According to ASTM E303-93 The specimen is clamped into the holder in the

same direction it has been polished in the machine The specimen and the slider are thoroughly wetted

before each reading The mean value is reported as PSV PSV over 50 is regarded as a High Skid Resistant

Aggregate, PSV over 65 is needed for particularly high stressed sites, PSV over 70 for rick sites

Slider traverses a length of 76±0.5 mm

Micro-textureBritish Pendulum testerFeature on site measurementStatic (spot measurement) skid resistance test equipment operated by handDoes not measure the impact that macro-texture has on skid resistance as vehicle speeds increaseNot suitable for large scale investigatingCheap, portable and is suitable for site and incident investigation

According to ASTM E1911 Measure pavement surface friction as

a function of speed A disc that is made to rotate

horizontally at a specified velocity before being lowered onto a wet pavement to measure friction

The friction is measure by the resistance between the test surface and spring-loaded slider

Spring-loaded slider

Device Features (Saito et al. 1996)Measurement can be made in a very short timeThe device is designed to be compact and easy to handleCoefficient of friction is reported as a function of speed at a contact pressure similar to that of typical vehiclesThe slider can be easily replaced onsite, allowing the friction characteristics of different tire’s materials

According to ASTM E274 To take a measurement, the vehicle (or trailer) is brought to the

desired testing speed (typically 64 km/hr (40 mph)) Water is sprayed ahead of the test tire to create a wetted

pavement surface The test tire braking system is then actuated to lock the test

tire The result is reported as a Skid Number (SN).

Coefficient of friction

SN=100×µ

Skid number

Skid Number Comments

< 30 Take measures to correct

≥ 30 Acceptable for low volume roads

31 - 34 Monitor pavement frequently

≥ 35 Acceptable for heavily traveled roads

AdvantageMost commonly use in U.SReality

Typical Skid Numbers (from Jayawickrama et al., 1996)

Popular choice for the routine (proactive) monitoring of road networks

The pavement is tested wet and the vehicles are fitted with large water tanks

The test speed typically adopted is 50km/h (slip speed of 17km/h)

Expensive compared to other types of test equipment

Compact and lightweight; easy to operate and to transport

Braked wheel, fixed slip design with drag and load measured continuously

Can be towed at any of the standard testing speeds up to 130 km/h; can also be used in pushing mode

Simple on-site calibration takes only 10 minutes

Rapid and simple data acquisition and presentation

BenefitReliable - Low cost, robust and easy to maintainDurable - Excellent repeatability and reproducibilityAccurate - Readings unaffected by road curvatureVersatile - Suitable road and runwayEasy To Transport - Can be towed by a wide variety of vehiclesEfficient - 100 miles of testing with one tank of waterCorrelated Data - E274 Locked Wheel Tester, British Pendulum Tester and SCRIMData Integration - Standard and custom data integration into any pavement management system (PMS)High Resolution - One reading every 32 inches

Measurement of friction and texture Wet or dry measurements Summer and winter measuring

capability Reporting of the International Friction

Index (IFI) Reporting of the peak friction Single test wheel can be mounted to

any kind of host vehicle or trailer. Relatively expensive compared to

portable tester and the grip tester

This methodology offers several advantages over current methods used in the practice

The aggregates on the sample tray with marked grid points

The images of each sample are automatically captured for the analysis of angularity and texture

The results are showed on the computer

(Masad, 2003)Sample tray

AdvantagesAnalyze the shape of a wide range of aggregate types and sizesCombining both the coarse and fine aggregate analysis into one systemDistinct difference between angularity and texture; these properties have different effects on performance

Developed in 2004-2006 Measurement of:

◦ Macro-texture in circular path◦ Micro-texture in certain points of that path

Structure:

Rotating level

Micro camera

Adjustable mechanism

Lens + Extension ring

Converging cercal of two lasers

Built-in macro sensor

Optical precision bearer

Micro laser emitter

Translating level

According to ASTM E965 Sand gradation follow by:

Surface texture depth

Volume of sand

Diameter of sand spread

According to ASTM E2380

FeatureThis approach is chosen when the texture depth probably too low (<0.3mm)The surface is pre-wetted in 1 minuteThe time required for water drop from upper reference line to lower reference line is recordedVery short outflow time is indicative of rough surface and vice versa3 and 10 seconds are satisfactory for an asphalt pavement surface

The replacement for sand path and outflow meter

Larger quantity of valuable and less expensive

Greatly reducing the safety and traffic control problems

Report mean profiled depth (MPD)

According to ASTM E 2157 CT Meter uses a laser to

measure Record mean texture depth

(MTD) and root mean squared (RMD) for each measurement

Record date, temperature, concrete surface moisture, and concrete distress at test location

IFI is a harmonized value of Friction index to convert all skid and texture measurement to a common scale.

Developed by PIARC According to ASTM E1960 IFI consists of two parameters:

◦ F60 – the coefficient of Friction at slip speed at 60km/h (Skid)

◦ Sp - the speed constant related to the surface texture depth (Texture)

F(s) is the measurement of skid resistance made by any piece of equipment, operating with slip speed

A and B are constants, the values of which were determined for each piece of skid resistance measuring equipment

S = a slip speed

6060 ( ) exp

P

SF A B F s

S

Sp = the speed constant related to the texture depth, Tx

PS a b Tx a and b are constants relating to the texture depth measurement equipment.

SP

Design◦Choose aggregate gradation (SMA or porous)◦Reduce asphalt binder contentMaintain◦Small chip seal (with high PSV aggregate)◦Grooving◦Shot-blasting◦High velocity water retexturing◦Bush hammering◦Rotating discs◦New materials

Bauxite