Bitumen Skid Resistance
Last updated: 2026-09-30
Bitumen Skid Resistance
Bitumen skid resistance describes the friction performance of a bituminous pavement surface, typically measured as a British Pendulum Test (BPT) value or Sideway-force Coefficient Routine Investigation Machine (SCRIM) coefficient. A well-designed asphalt surface should deliver a Pennant pendulum test value of at least 45–55 BPN on wet roads, which corresponds to a SCRIM sideway-force coefficient (SFC) of about 0.45–0.55. Below 0.35 SFC, accident risk rises sharply, which is why most European and Gulf highway authorities specify a minimum of 0.40–0.45 SFC at the time of handover.
What Is Bitumen Skid Resistance and Why Does It Matter?
Skid resistance is the friction generated between a vehicle tyre and the road surface when the tyre is locked or sliding, especially in wet conditions. It depends on two surface properties:
- Microtexture – the fine-scale roughness of aggregate particles (typically 0.001–0.5 mm). This breaks the water film and provides dry and wet friction at high speed.
- Macrotexture – the coarse-scale roughness from the mix design (typically 0.5–2 mm). This drains water and prevents hydroplaning.
The bitumen binder itself is not the friction provider — aggregate and surface texture are. However, the bitumen grade, polymer modification, and ageing behaviour determine how well the aggregate stays in place and how long the texture lasts. Oxidised bitumen that hardens and embrittles over 10–15 years can polish under traffic, reducing skid resistance by 0.05–0.15 SFC on high-volume roads.
| Factor | Effect on Skid Resistance | Typical Range / Value |
|---|---|---|
| Aggregate Polished Stone Value (PSV) | Higher PSV = better long-term friction | PSV 55–68 for high-friction surfaces |
| Binder type | Polymer-modified (PMB) retains texture longer | PMB 40/55–60/70 vs. pen 60/70 |
| Macrotexture depth | Deeper texture drains water faster | 0.6–1.2 mm sand patch mean |
| Traffic polishing | Reduces BPN over time | 10–20 BPN loss in 5 years |
| Wet vs. dry | Wet friction is 30–50% lower | Dry BPN 70+ / Wet BPN 45+ |
| Temperature | Hot binder softens, can bleed | >60°C risk of binder film |
Bitumen Grades and Their Skid Resistance Performance
Not all bitumen behaves the same under traffic and weather. The table below compares common export grades used in the Middle East, Africa, and South Asia.
| Bitumen Grade | Penetration (0.1 mm) | Softening Point (°C) | Skid Resistance Suitability | Best Use |
|---|---|---|---|---|
| Penetration 60/70 | 60–70 | 49–56 | Standard, requires high-PSV aggregate | Wearing courses, moderate traffic |
| Penetration 40/50 | 40–50 | 52–60 | Better for hot climates | High-temperature roads |
| Penetration 80/100 | 80–100 | 45–52 | Good workability, lower rutting resistance | Base and binder courses |
| PMB 40/55 | 40–55 | 55–65 | Excellent texture retention | High-friction wearing courses |
| PMB 60/70 | 55–65 | 60–70 | Best for wet, high-speed roads | Motorways, airports |
| Cutback / Emulsion | Varies | Varies | Temporary or surface dressing | Maintenance, chip seals |
Rule of thumb: For skid-critical roads (motorways, wet climates, steep gradients), specify PMB 40/55 or PMB 60/70 with aggregate PSV ≥ 60. Standard pen 60/70 will pass minimum SFC at handover but can drop below 0.40 SFC within 3–5 years under heavy traffic.
| Binder Type | Approx. FOB Price (USD/MT, 2025) | Relative Cost | Expected Skid Life |
|---|---|---|---|
| Pen 60/70 | $480–$560 | Baseline | 3–5 years |
| Pen 40/50 | $500–$580 | +4% | 4–6 years |
| PMB 40/55 | $620–$740 | +25–35% | 7–10 years |
| PMB 60/70 | $640–$760 | +30–40% | 8–12 years |
Payback logic: A 30% premium on binder cost adds roughly $1.50–$2.50 per square metre to a 50 mm wearing course. Preventing one wet-weather skid accident (average cost $50,000–$200,000 in liability and repair) pays back the premium across 20,000–80,000 m² of pavement. For a typical 10 km, 7 m wide motorway, that is a fraction of one lane-km.
How Bitumen Skid Resistance Is Measured and Specified
Different countries use different devices, but the underlying physics is the same. Below is a comparison of the main test methods.
| Test Method | Measure | Wet/Dry | Typical Minimum Spec | Standard |
|---|---|---|---|---|
| British Pendulum Test | BPN (0–100) | Wet | 45–55 BPN | BS EN 13036-4 |
| SCRIM | SFC (0–1) | Wet | 0.40–0.45 SFC | BS 7941-1 |
| GripTester | GN (0–1) | Wet | 0.45–0.55 GN | ASTM E1960 |
| Dynamic Friction Tester | DF20 / DF60 | Wet | 0.45+ at 60 km/h | ASTM E1911 |
| Sand Patch Method | Mean texture depth (mm) | Dry | 0.6–1.2 mm | ASTM E965 |
When ordering bitumen for skid-critical projects, confirm these points in the technical datasheet:
- Penetration at 25°C – match to climate (60/70 for temperate, 40/50 for hot).
- Softening point – above 55°C for PMB, above 49°C for pen grades.
- Elastic recovery – ≥ 75% for PMB (EN 13398), indicating polymer network.
- Storage stability – ≤ 2.5°C difference after 3 days at 180°C.
- Flash point – ≥ 230°C for safety in transit and handling.
- Ageing (RTFOT) – retention of properties after thin-film oven test.
Bold point: Buyers who skip elastic recovery testing often receive "PMB" that is only marginally modified and will polish as fast as standard bitumen.
Design and Maintenance Strategies to Improve Skid Resistance
Skid resistance is a whole-life property. The table below links strategy to expected performance gain.
| Strategy | Action | Expected SFC Gain / Retention |
|---|---|---|
| High-PSV aggregate | Use PSV 60–68 in wearing course | +0.05–0.10 SFC at 5 years |
| Polymer-modified binder | PMB 40/55 or 60/70 | +0.05–0.08 SFC, slower decline |
| Surface dressing | 10–14 mm chippings, PMB emulsion | Restores 0.50+ SFC immediately |
| Micro-surfacing | Cold mix with PMB | +0.05–0.10 SFC, 4–6 year life |
| Grooving / texturing | Diamond grinding | +0.10–0.15 SFC on concrete |
| Anti-polishing aggregate | Calcined bauxite, slag | PSV 65–75, 10+ year retention |
| Drainage improvement | Permeable asphalt (PA) | Reduces hydroplaning, +0.05 SFC |
| Timely resurfacing | At 0.40 SFC threshold | Prevents drop below 0.35 SFC |
- Design the mix with a target air void content of 4–7% for dense asphalt; permeability increases macrotexture.
- Compact properly – under-compaction reduces texture depth by 0.2–0.4 mm.
- Avoid binder-rich mixes – excess bitumen fills texture and lowers SFC by up to 0.10.
- Monitor annually – schedule SCRIM surveys every 12 months on high-speed roads.
- Intervene early – resurface or surface-dress when SFC falls below 0.45, before it reaches the 0.35 accident-risk threshold.
Costs, Quantities and Lead Times for Skid-Resistant Bitumen Supply
Export buyers need concrete numbers. The table below gives indicative figures for a 20 MT trial order and a 500 MT project order from a Gulf or Asian refinery.
| Item | 20 MT Trial | 500 MT Project |
|---|---|---|
| Binder type | PMB 40/55 | PMB 40/55 |
| Unit price (FOB) | $700/MT | $660/MT |
| Binder cost | $14,000 | $330,000 |
| Aggregate (PSV 65) | $3,000 | $60,000 |
| Total material | $17,000 | $390,000 |
| Production lead time | 10–14 days | 25–35 days |
| Shipping (bulk) | 7–14 days | 14–21 days |
| Drums vs. bulk | Drums +$40/MT | Bulk preferred |
| Payment terms | 30% TT advance | LC at sight |
Note: Prices shift with crude oil benchmarks. In 2025, bitumen FOB prices moved ±8–12% within a single quarter. Always confirm with a live quote before budgeting.
For a 3.65 m lane, 50 mm compacted wearing course, at 2.4 t/m³:
- Volume = 3.65 × 1000 × 0.05 = 182.5 m³
- Mass = 182.5 × 2.4 = 438 MT per lane-km
- Binder at 5.5% = 24 MT of bitumen per lane-km
For a 10 km two-lane road, that is 480 MT of binder and roughly 8,760 MT of asphalt. Ordering in bulk saves $30–$60/MT versus drums, which on 480 MT is $14,400–$28,800 — enough to fund the polymer upgrade entirely.
FAQ: Bitumen Skid Resistance
Q1: What is a good skid resistance value for bitumen roads?
A good wet skid resistance is 0.45–0.55 SFC (SCRIM) or 45–55 BPN (pendulum). Values below 0.35 SFC are considered hazardous and trigger investigation or resurfacing. Most specifications set a minimum of 0.40–0.45 SFC at handover.
Q2: Does bitumen grade affect skid resistance?
Yes, indirectly. The binder does not provide friction, but polymer-modified bitumen (PMB 40/55 or 60/70) holds aggregate in place and slows texture loss, keeping SFC 0.05–0.10 higher after 5 years than standard pen 60/70. Standard grades can still meet specs with high-PSV aggregate, but decline faster.
Q3: How often should skid resistance be tested?
On high-speed or high-volume roads, test every 12 months with SCRIM or GripTester. On lower-volume roads, every 24 months is acceptable. New surfaces should be tested at handover and again at 6 months to confirm the initial polish has stabilised.
Q4: What causes low skid resistance in bitumen pavements?
The main causes are aggregate polishing (low PSV stone), binder bleeding (excess bitumen filling texture), under-compaction (shallow macrotexture), and ageing (brittle binder loss). Traffic polishing alone can cut BPN by 10–20 points over 5 years on a low-PSV surface.
Q5: Can I improve skid resistance without full resurfacing?
Yes. Surface dressing with 10–14 mm high-PSV chippings and PMB emulsion restores SFC to 0.50+ immediately for a fraction of full reconstruction cost. Micro-surfacing and grooving are also effective, adding 0.05–0.15 SFC with 4–10 year service life depending on traffic.
Close the Loop on Your Bitumen Budget with 6Tar
Skid resistance starts with the right binder at the right price. Before you commit to a PMB upgrade, run your quantities, grades and shipping terms through the 6Tar cost calculator — it gives you live FOB and CIF estimates, compares drum vs. bulk pricing, and shows the true cost per lane-km. Try 6Tar today and lock in your skid-safe specification without overpaying.