Polishing in Pavement: Types, Causes, Safety & Prevention
Everything you need to know about polishing in pavement: what it is, why it happens, its types, whether polished road surfaces are safe, testing methods like Polished Stone Value (PSV), advantages, disadvantages, and how engineers prevent it.
2. Why Does Pavement Polishing Happen?
Why does this happen at all? Every time a tyre rolls, brakes, or turns over an aggregate particle, a small amount of mechanical wear occurs. Over millions of load cycles, this constant rubbing erodes the sharp micro-asperities on the stone surface. Several factors drive the rate and severity of polishing:
Traffic Volume & Speed
Higher traffic volumes and speeds increase the number and force of tyre-aggregate contacts, accelerating wear at a given site.
Aggregate Mineralogy
Soft, calcareous stones (like some limestones) polish faster than hard, siliceous stones (like granite or quartzite gritstone).
Braking & Turning Stress
Approaches to junctions, roundabouts, and sharp curves see far higher polishing rates due to combined braking and lateral tyre scrub.
Climate & Weathering
Freeze-thaw cycles, rainfall, and chemical weathering can soften certain aggregates, making them more susceptible to polishing.
Mix Design & Binder Film
A thick bitumen film initially coats chippings; once worn through, the exposed stone begins its own polishing cycle.
Contact Pressure
Heavy commercial vehicles and studded or worn tyres apply higher unit pressure, wearing down aggregate texture more quickly.
3. Types of Polishing in Pavement
Engineers generally classify types of pavement polishing by the mechanism and location of wear. Understanding the type helps target the right maintenance solution.
a) Traffic-Induced Polishing
The most common type, caused by the cumulative abrasive action of normal rolling traffic over time, uniformly smoothing exposed aggregate across a travel lane.
b) Braking-Zone Polishing
Concentrated polishing at approaches to signals, stop signs, pedestrian crossings, and roundabouts, where repeated braking forces accelerate wear far faster than free-flowing sections.
c) Cornering / Lateral Scrub Polishing
Occurs on curves and roundabout circulatory carriageways where lateral tyre scrub, rather than straight-line rolling, wears the aggregate.
d) Mortar / Binder-Film Polishing
Early-life polishing of the thin mortar or bitumen film that initially coats new chippings, exposing the underlying stone texture beneath.
e) Chemical / Weathering Polishing
Gradual softening and smoothing caused by rainfall, freeze-thaw cycling, and chemical attack (e.g., from de-icing salts) rather than direct tyre contact alone.
f) Aggregate-Specific Polishing
Classified by stone type: calcareous aggregates (limestone) typically polish faster than siliceous aggregates (granite, gritstone, quartzite), which resist polishing due to differential hardness between mineral grains.
4. How Polishing Affects Pavement Performance
Pavement texture is generally described at two scales, and polishing primarily attacks one of them:
| Texture Scale | What It Controls | Effect of Polishing |
|---|---|---|
| Microtexture (aggregate surface, < 0.5 mm) | Low-speed skid resistance, initial tyre grip | Directly reduced — this is what “polishing” wears away |
| Macrotexture (between particles, 0.5–50 mm) | High-speed skid resistance, water drainage, spray reduction | Reduced more slowly, mainly by binder loss and surface ravelling |
As microtexture is lost, the coefficient of friction between tyre rubber and stone drops, particularly in wet conditions where a thin water film cannot be broken through by a smooth aggregate surface. This is the core engineering concern behind monitoring polishing.
5. Is Polished Pavement Safe? (Safety Concerns)
A frequently asked question is: is polishing in pavement safe? The honest engineering answer is that a heavily polished surface is not safe without corrective treatment. As microtexture disappears, skid resistance drops, and the risk of skidding increases sharply in wet weather, at higher speeds, and under braking.
Safety risk: Polished pavements are strongly associated with increased wet-weather crash rates, longer stopping distances, and reduced cornering stability, which is why highway authorities set minimum PSV requirements for high-risk sites.
Because of this, road authorities classify certain locations, such as approaches to traffic signals, pedestrian crossings, roundabouts, and steep gradients, as high-risk sites that require aggregates with a higher minimum Polished Stone Value than a typical straight, low-speed rural road.
6. How Pavement Polishing Is Measured (PSV & Other Tests)
How do engineers actually quantify polishing resistance before an aggregate is even used? The industry relies on standardized laboratory and field tests:
Polished Stone Value (PSV) Test
The Polished Stone Value test artificially polishes aggregate samples in an accelerated polishing machine, then measures the resulting friction using a portable pendulum tester. A higher PSV number indicates greater resistance to polishing, meaning the stone retains skid-resistant texture for longer under traffic.
British Pendulum Tester (Skid Resistance)
Used both in the lab and directly on in-service pavements, this swinging pendulum measures the frictional resistance of a wet surface, producing a Pendulum Test Value (PTV) that correlates with real-world skid risk.
SCRIM & Network Skid Surveys
The Sideway-force Coefficient Routine Investigation Machine (SCRIM) is a vehicle-mounted system that continuously measures skid resistance across an entire road network, helping authorities prioritize resurfacing where polishing has progressed furthest.
Aggregate Abrasion Value (AAV)
A complementary test measuring resistance to abrasive wear (rather than polishing specifically), often specified alongside PSV for a fuller picture of aggregate durability.
7. How to Prevent or Reduce Pavement Polishing
Here is how to reduce or manage polishing at the design, construction, and maintenance stages:
- Specify high-PSV aggregates at high-risk sites such as junctions, roundabouts, and curves, where polishing risk and consequence are both greatest.
- Blend aggregates of different mineralogy in the surface mix to combine durability with cost-efficiency.
- Apply surface dressing or a thin surface course renewal once skid resistance surveys flag a section approaching its investigatory level.
- Use High-Friction Surfacing (HFS), a resin-bound, calcined-bauxite system, at extreme-risk locations like approaches to pedestrian crossings and sharp bends.
- Monitor network-wide with regular SCRIM or pendulum surveys to catch declining sections before they become unsafe.
- Retexture existing worn concrete or asphalt surfaces using grooving, shot-blasting, or planing where full resurfacing is not yet economically justified.
8. Advantages of Understanding & Managing Pavement Polishing
Improved Road Safety
Maintaining adequate skid resistance directly reduces wet-weather crash frequency.
Longer Surface Life
Selecting the right PSV aggregate upfront delays the need for early resurfacing.
Lower Lifecycle Cost
Preventive treatment at flagged sites is cheaper than reactive full-depth reconstruction.
Data-Driven Maintenance
PSV and SCRIM data let authorities prioritize limited maintenance budgets objectively.
Reduced Liability
Documented skid-resistance management lowers legal exposure after wet-weather incidents.
9. Disadvantages of Polished Pavement
Reduced Skid Resistance
The core problem: loss of microtexture lowers tyre-road friction, especially when wet.
Longer Stopping Distances
Vehicles need more distance to stop safely on a polished, low-friction surface.
Higher Crash Risk
Curves, junctions, and crossings with polished surfaces see elevated skidding-related crash rates.
Costly Remedial Work
Severely polished sections may require full resurfacing or high-friction surfacing, both of which carry a real cost.
Aesthetic & Noise Changes
Polished, worn surfaces can also affect ride comfort and tyre noise characteristics.
10. Uses & Applications of Polishing / PSV Data
Understanding and testing for pavement polishing is applied across many parts of civil and highway engineering:
- Highway surface course specification — setting minimum PSV values by site category.
- Airport runway and taxiway design — where high-speed braking makes skid resistance critical.
- Urban intersection and roundabout design — high-risk braking and turning zones.
- Network asset management — prioritizing resurfacing budgets using skid survey data.
- Forensic crash investigation — assessing whether pavement condition contributed to a wet-weather collision.
- Quarry and aggregate supply certification — classifying stone sources by their PSV rating for approved supplier lists.
11. Related Keywords & Glossary
Key terms closely related to polishing in pavement that are useful for further research:
12. Frequently Asked Questions (FAQ)
It is the gradual smoothing and rounding of aggregate particles on a road surface caused by repeated tyre contact, which reduces microtexture and lowers skid resistance over time.
It happens because repeated wheel loads and tyre abrasion wear down the sharp micro-asperities of aggregate particles, especially in softer stone, and it progresses faster at braking and turning zones.
Traffic-induced polishing, braking-zone polishing, cornering/lateral scrub polishing, mortar or binder-film polishing, chemical/weathering polishing, and aggregate-specific polishing based on stone mineralogy.
No, a heavily polished surface is not considered safe without treatment, because reduced skid resistance increases stopping distance and crash risk, especially on wet roads.
Mainly through the Polished Stone Value (PSV) test, the British Pendulum Tester for on-site skid resistance, and SCRIM surveys for network-level monitoring.
By specifying high-PSV aggregates at high-risk sites, applying surface dressing or high-friction surfacing, blending aggregates, and using regular skid-resistance surveys to schedule timely maintenance.
Improved safety, longer surface life, lower lifecycle maintenance cost, objective data-driven prioritization, and reduced liability exposure.
Reduced skid resistance, longer stopping distances, higher crash risk in wet weather, costly remedial resurfacing, and changes in ride and noise characteristics.
In highway surface course specification, airport runway design, urban intersections and roundabouts, network asset management, forensic crash investigation, and aggregate supplier certification.
Microtexture is the fine roughness on individual aggregate particles that governs low-speed skid resistance and is lost through polishing; macrotexture is the larger-scale texture between particles that governs high-speed skid resistance and drainage.