Reference guide for bitumen mixing, compaction, and laying temperatures by grade. Includes a Celsius/Fahrenheit converter and PG grade temperature ranges.
Bitumen viscosity and adhesion depend on temperature. Too hot causes draindown and binder loss. Too cold results in poor compaction and premature failure.
Typical mixing temperature for conventional bitumen: 150–180°C (302–356°F). Warm mix additives allow 120–140°C (248–284°F).
Compaction typically 120–160°C (248–320°F). Must be completed before asphalt cools and stiffens. Cold weather shortens this window significantly.
Standard mixing, compaction, and minimum laying temperatures by penetration and PG grade.
| Bitumen Grade | Mixing Temp (°C / °F) | Compaction Temp (°C / °F) | Min Lay Temp (°C / °F) |
|---|---|---|---|
| 40/50 Pen | 160–175°C / 320–347°F | 140–160°C / 284–320°F | 135°C / 275°F |
| 60/70 Pen | 155–170°C / 311–338°F | 135–155°C / 275–311°F | 125°C / 257°F |
| 80/100 Pen | 150–165°C / 302–329°F | 130–150°C / 266–302°F | 120°C / 248°F |
| PG 64-22 | 155–170°C / 311–338°F | 135–155°C / 275–311°F | 125°C / 257°F |
| PG 76-22 | 165–180°C / 329–356°F | 145–165°C / 293–329°F | 135°C / 275°F |
| PMB (Modified) | 170–185°C / 338–365°F | 150–170°C / 302–338°F | 140°C / 284°F |
| WMA (additives) | 120–140°C / 248–284°F | 110–130°C / 230–266°F | 100°C / 212°F |
Understanding the high and low temperature performance grades for Superpave bitumen.
| PG Grade | High Temp (°C) | Low Temp (°C) | Typical Climate / Application |
|---|---|---|---|
| PG 52-34 | 52°C | -34°C | Very cold climate (northern Canada, Alaska) |
| PG 58-28 | 58°C | -28°C | Cold to moderate climate |
| PG 64-22 | 64°C | -22°C | Most common US grade — temperate climate |
| PG 70-22 | 70°C | -22°C | Hot climate or heavy traffic |
| PG 76-22 | 76°C | -22°C | Very hot / high-stress applications |
| PG 82-22 | 82°C | -22°C | Extreme heat (desert regions, slow traffic) |
The two standard temperature conversion formulas used in asphalt and bitumen work — converting between Celsius (°C) used in international specifications and Fahrenheit (°F) used in US practice.
Key temperatures to know: 150°C = 302°F — typical minimum mixing temperature; 160°C = 320°F — standard mixing for 60/70 pen; 175°C = 347°F — upper mixing limit (above this causes ageing); 120°C = 248°F — compaction minimum for dense-graded HMA; 80°C = 176°F — final rolling must be complete before this temperature to achieve target air voids.
Polymer-modified bitumen (PMB/SBS-modified) requires 10–20°C higher working temperatures than conventional pen grade bitumen. PMB mixing: 170–185°C (338–365°F). PMB compaction: 150–170°C (302–338°F). SMA mixes with PMB require compaction completed above 140°C (284°F). WMA additives reduce all temperatures by 20–30°C, enabling paving at 120°C (248°F) or lower.
Every 10°C rise above 190°C approximately doubles the rate of bitumen oxidative hardening. Over-temperature bitumen becomes stiff and brittle prematurely, shortening pavement life significantly. Under-temperature paving (below minimum lay temp) causes high air voids — for every 1% increase above target 4% air voids, pavement life decreases by approximately 10%. Monitoring plant and mat temperatures is a critical QA requirement on all contracts. See the Thickness Calculator for compaction result verification.
WMA technologies (foaming, chemical additives, zeolite) reduce production and compaction temperatures by 20–40°C compared to hot mix. Benefits include lower plant fuel consumption, reduced bitumen ageing, extended haul distances, and cold-weather paving capability. Typical WMA mixing: 120–140°C (248–284°F). If your project uses WMA, confirm temperature requirements with your plant's specific additive system.
Temperature control directly affects the quality, durability, and safety of asphalt pavement — from the plant gate to final compaction.
Plant operators monitor mixing temperature continuously as a primary quality control parameter. Most specifications require a minimum mixing temperature (e.g., 150°C for 60/70 pen) with an upper limit (typically 190°C) to prevent bitumen ageing. Temperature is logged on every plant delivery docket and cross-referenced against the mix design. Loads outside the temperature window are rejected. This reference guide helps QA officers verify that recorded docket temperatures match specification requirements for each bitumen grade in use.
Related: Material Calculator
Site supervisors check truck delivery temperatures on arrival (typically with an infrared thermometer or probe) to confirm the mix is still within compaction range before it is tipped into the paver hopper. A load arriving at 115°C on a cold day when the specification minimum is 120°C must be rejected — and this guide tells the supervisor exactly where the limit is for each grade. Cold winds and thin lifts accelerate cooling: for a 40 mm lift in 5°C ambient, the compaction window may be as short as 8–12 minutes per roller pass.
Related: Thickness Calculator
Pavement engineers specifying bitumen grades for different climatic zones use temperature properties to select the appropriate PG grade. In hot desert climates, a PG 76-22 or PG 82-22 prevents rutting at high pavement surface temperatures (often 60–70°C in summer). In cold northern climates, a PG 52-34 or PG 58-34 maintains flexibility at -28 to -34°C to prevent low-temperature cracking. The PG grading system was specifically developed to match binder performance to the temperature extremes experienced at a project location.
Related: Metric Calculator
Choose your bitumen grade from the dropdown — pen grade (40/60, 60/70, 80/100, 160/220), performance grade (PG 64-22, PG 76-22, etc.), or viscosity grade (VG-30, VG-40). Each grade has specific recommended mixing, compaction, and discharge temperatures that vary by specification. The correct temperature is critical for workability and bond quality.
Enter a temperature in Celsius or Fahrenheit to convert between the two scales. International projects often require converting between metric (°C) and imperial (°F) temperature specifications. Mix design temperatures from European standards (EN 13108) use Celsius; US AASHTO specifications commonly reference Fahrenheit for mixing and compaction temperatures.
Review the reference table for your selected bitumen grade to confirm correct plant temperature (typically 150–180°C for standard grades), mixing temperature, compaction window, and minimum laying temperature. Bitumen laid below minimum temperature will be under-compacted; bitumen overheated at the plant suffers hardening and reduced performance life.
Standard dense-graded HMA using 60/70 pen bitumen should be laid at 130–155°C and compacted to completion before it cools below 80–85°C. Most specifications require the final rolling to be completed before the mix reaches 80°C. Higher-viscosity polymer-modified binders (PMB) require higher working temperatures — typically 155–175°C lay temperature and final compaction above 100°C. WMA additives lower these temperatures by 20–30°C.
Standard 60/70 pen bitumen is stored at 140–160°C in heated tanks at the asphalt plant. PMB (polymer-modified bitumen) is stored at 160–185°C. The bitumen must remain fluid enough to pump and spray uniformly through the mixing plant. Storage temperatures are a balance between maintaining fluidity and avoiding oxidative hardening from excessive heat. Bitumen should not be heated above 200°C as this causes rapid degradation of the binder properties.
Most road authority specifications restrict asphalt paving when ambient temperature is below 5–10°C and falling, or when the surface is wet or frost-affected. Thin overlays (under 25 mm) require higher minimum temperatures than thick layers because they cool faster relative to their heat content. Some specifications also restrict paving when wind speed exceeds a threshold as high winds dramatically accelerate cooling. Warm Mix Asphalt (WMA) technologies extend the paving season into cooler conditions.
The high temperature number in a PG grade (e.g., PG 64-22) is the maximum pavement temperature in °C at which the binder is designed to remain sufficiently stiff to resist rutting. A PG 64-22 binder is specified when the pavement surface temperature will not exceed 64°C in the hottest week of the design period. In very hot climates where summer pavement temperatures reach 70–76°C, you would specify PG 70-22 or PG 76-22 to prevent rutting. Pavement temperature is significantly higher than air temperature — a typical relationship is T_pavement ≈ T_air + 20°C on a summer day in full sun.
Insert a probe thermometer into the centre of the truck load (not on top, which cools faster) within 5 minutes of arrival. For standard 60/70 pen HMA, the minimum acceptable delivery temperature is typically 130–140°C — check your specification. A load arriving below spec minimum temperature should be rejected and returned to the plant. If in doubt, also check haul time: most specifications limit haul time to 90–120 minutes maximum from discharge at the plant. For remote sites with long haul distances, insulated truck bodies help maintain temperature.
Cold weather dramatically shortens the compaction window. At 5°C ambient temperature, a 50 mm asphalt lift may cool from 150°C to 80°C (the minimum compaction temperature) in as little as 8–10 minutes. Below 80°C, the asphalt becomes too stiff to compact further, locking in whatever air void content has been achieved. If target density (typically 97% maximum theoretical density) has not been reached before the mat cools, the layer will have excessive air voids, leading to premature oxidation, moisture damage, and early structural failure. Strategies include using PMB for extended compaction window, higher mix delivery temperature, and multiple rollers working in echelon to maximise compaction speed.
Penetration grade (pen grade) bitumen (e.g., 40/50, 60/70, 80/100) is classified by the depth in tenths of a millimetre that a standard needle penetrates the bitumen at 25°C under a 100g load for 5 seconds. Softer grades have higher pen values. Performance Grade (PG) bitumen, developed under the US SHRP research programme, is classified by high and low temperature performance limits (e.g., PG 64-22) measured using rheological testing (DSR, BBR). PG grades are more directly related to actual field performance than pen grades. Most international specifications now specify PG grades; pen grades remain in use in some regions (UK, parts of Asia, Africa) and often appear on bitumen supplier documentation alongside PG equivalents.