Determination of Evaporation Loss of Bitumen: Principles, Standards, and Testing Procedures

The evaporation loss test is a fundamental laboratory procedure for evaluating the thermal stability and short-term aging resistance of bitumen (asphalt binder) used in road paving, roofing, and waterproofing applications. By heating a bitumen sample at 163 °C for five hours and measuring the resulting mass change, engineers can quantify the loss of volatile components, predict in-service hardening, and verify compliance with recognized standards such as ASTM D6, GB/T 11964, and JTG E20 T 0608. This article provides a detailed technical review of the test principle, applicable sample types, testing items, procedures, calculations, and practical applications of bitumen evaporation loss determination.

Technical Overview

Evaporation loss determination, also known as the loss-on-heating test, measures the change in mass of a bituminous binder after it is held at an elevated temperature under controlled oven conditions. In the standard procedure, a measured quantity of bitumen is placed in a shallow metal dish and heated in a ventilated oven maintained at 163 °C ± 1 °C for 5 hours. The difference between the initial and final mass of the sample, expressed as a percentage, represents the evaporation loss of the binder.

This test simulates the short-term thermal aging that bitumen undergoes during hot-mix production, transportation, and paving operations. During these processes, the binder is exposed to temperatures in the range of 150 °C to 180 °C, during which light volatile fractions evaporate and mild oxidation begins. A binder with excessive evaporation loss will harden prematurely, becoming more brittle and more susceptible to cracking, raveling, and moisture damage in service.

The test is standardized internationally by several recognized bodies. ASTM D6 (Standard Test Method for Loss on Heating of Oil and Asphaltic Compounds) is the widely referenced international method. In China, GB/T 11964 governs the determination of evaporation loss of petroleum asphalt, while JTG E20 (T 0608) specifies the corresponding procedure for highway engineering bitumen. Related dynamic aging methods, such as ASTM D1754 (Thin-Film Oven Test) and ASTM D2872 (Rolling Thin-Film Oven Test), and the EN 12607 series of European standards, are frequently used alongside the static evaporation method to provide a more complete picture of binder aging behavior.

The evaporation loss value is typically reported together with the penetration of the residue, which allows engineers to assess both mass change and consistency change. Accredited third-party laboratories routinely perform this test as part of binder acceptance, quality control, and research programs.

Testing Samples

Penetration-Grade Paving Bitumen

Unmodified road bitumens graded by penetration are the most common materials tested. These binders are sampled directly from refinery storage tanks, transport tankers, asphalt mixing plants, or delivery drums. The test verifies that the binder meets specification limits for mass loss and retained penetration before it is used in pavement construction.

Polymer-Modified and Specialty Binders

Styrene-butadiene-styrene (SBS) modified bitumen, crumb-rubber modified bitumen, and other specialty binders may also be evaluated. Because modified binders tend to be more viscous and may exhibit different volatile characteristics, careful sample handling and homogenization before testing are essential. Some specifications for modified binders instead reference thin-film or rolling thin-film aging methods, so the applicable standard should always be confirmed.

Industrial, Roofing, and Waterproofing Bitumen

Oxidized (blown) bitumens used in roofing felts, waterproofing membranes, pipe coatings, and joint sealants are tested to assess their thermal stability during high-temperature processing and application. Excessive volatile loss in these products can cause shrinkage, embrittlement, and loss of adhesion.

Asphaltic Compounds and Heavy Petroleum Products

ASTM D6 is formally applicable to oils and asphaltic compounds generally, including heavy fuel oils, fluxing oils, and cutback binder components. For such materials, the test provides an indication of volatility and the tendency to thicken when heated.

Testing Items

A typical evaporation loss determination program includes the following measured and derived parameters:

• Mass loss on heating (evaporation loss), expressed as a percentage of the original sample mass
• Penetration of the residue after heating, measured at 25 °C with a 100 g load and a 5-second dwell time
• Retained penetration (penetration ratio), calculated as the penetration of the aged residue divided by the penetration of the original bitumen, expressed as a percentage
• Change in softening point before and after heating, where required by the product specification
• Change in ductility or other consistency indicators, where supplementary characterization is needed
• Visual observations of the residue, such as skin formation, foaming, or non-uniform hardening

Testing Methods

Test Principle

A known mass of bitumen is exposed to a controlled temperature of 163 °C in a shallow dish for a fixed period of five hours. Volatile components evaporate, and minor oxidation may occur. The resulting change in mass, together with the consistency of the residue, characterizes the short-term aging susceptibility of the binder. The relatively thick static film (approximately 20 mm for a 50 g sample in a 55 mm diameter dish) makes this test less severe than thin-film methods, in which the film thickness is only a few millimeters.

Apparatus and Materials

• A forced-ventilation oven capable of maintaining 163 °C ± 1 °C, equipped with a shelf positioned at the center of the oven and a thermometer or calibrated temperature sensor with its sensing element at shelf level
• Flat-bottomed cylindrical metal dishes, typically about 55 mm in internal diameter, clean and dry
• An analytical balance with a resolution of 0.001 g or better
• A desiccator for cooling samples in a dry atmosphere without absorbing moisture
• A thermometer capable of reading the oven temperature within the required tolerance
• Personal protective equipment, including heat-resistant gloves and eye protection

Sample Preparation

The bitumen sample is gently heated with occasional stirring until sufficiently fluid to pour, taking care to avoid local overheating, entrapped air bubbles, and loss of volatile matter. The temperature during melting should be kept as low as practicable and should not exceed the minimum required for pouring. Approximately 50 g of the homogenized sample is poured into each prepared dish, and the dishes are allowed to cool to room temperature before the initial weighing.

Test Procedure

• Clean, dry, and weigh each empty dish to the nearest 1 mg and record the mass.
• Pour approximately 50 g of the prepared sample into each dish and allow it to cool at room temperature for the specified period.
• Weigh the dish plus sample to the nearest 1 mg and record the initial mass.
• Preheat the oven to 163 °C ± 1 °C with the shelf in position and the thermometer at shelf level.
• Place the dishes on the shelf so that they do not touch each other and are uniformly exposed to the circulating air.
• Maintain the oven at 163 °C ± 1 °C for 5 hours, timing from the moment the samples are placed in the oven (or from the recovery of temperature, as specified by the governing standard), with a permissible timing deviation of no more than ±5 minutes.
• Remove the dishes, cool them to room temperature in a desiccator, and weigh them again to the nearest 1 mg.
• Where required, immediately transfer the residue to a penetration vessel and determine the penetration of the aged bitumen.

Calculation and Expression of Results

The evaporation loss is calculated using the following relationship: evaporation loss (%) = (m1 − m2) / m1 × 100, where m1 is the mass of the sample before heating and m2 is the mass of the sample after heating. A positive result indicates a mass loss due primarily to evaporation of light components. If the sample gains mass, the result is reported as a negative loss or as a mass gain, which may occur when oxidative uptake exceeds volatile loss, particularly in highly oxidized binders. The retained penetration is calculated as the penetration of the residue divided by the penetration of the original binder, multiplied by 100. Both the evaporation loss and the penetration ratio are reported to the precision specified in the governing standard.

Precision and Quality Control

Duplicate determinations should be performed whenever possible. Results of duplicate tests must agree within the repeatability limits stated in the applicable standard; if they do not, the test should be repeated. Critical quality control points include oven temperature calibration and uniformity, accurate timing, consistent sample mass and dish geometry, prevention of moisture pickup during cooling, and careful handling to avoid sample spillage or skin loss. laboratories should participate in interlaboratory proficiency programs and maintain traceable calibration records for ovens, balances, and penetration equipment.

Safety Precautions

Hot bitumen can cause severe burns and releases hydrocarbon fumes when heated. Testing should be conducted in a well-ventilated area or under a fume hood, with appropriate heat-resistant gloves, long sleeves, and eye protection worn at all times. Sample dishes remain extremely hot after removal from the oven and must be handled with suitable tools and placed on heat-resistant surfaces during cooling.

Applications

Evaporation loss determination is applied throughout the bitumen supply chain and across multiple industries:

• Road construction quality control and acceptance testing of paving-grade bitumen at refineries, mixing plants, and construction sites
• Verification of compliance with national and project specifications that limit mass loss, typically to a maximum of about 0.5% to 1.0%, and that require minimum retained penetration values often in the range of 50% to 65% depending on grade
• Evaluation of the aging resistance of new binders, modified binders, warm-mix asphalt additives, and anti-aging agents in research and development programs
• Production control of roofing and waterproofing bitumens, where thermal stability affects product durability and dimensional stability
• Forensic and condition surveys investigating premature pavement hardening, bleeding, or cracking attributable to binder volatility
• Comparative benchmarking between the static evaporation method and dynamic aging methods such as the Thin-Film Oven Test and Rolling Thin-Film Oven Test

By quantifying how much binder mass and consistency change under thermal stress, the test helps engineers select durable binders, optimize mix design, and extend the service life of asphalt pavements and waterproofing systems.

FAQ

What is the purpose of the bitumen evaporation loss test?

The test measures how much mass a bitumen sample loses when heated at 163 °C for five hours, simulating the thermal exposure the binder experiences during hot-mix production and paving. The result indicates the content of volatile fractions and the susceptibility of the binder to short-term hardening.

Which standards govern the test?

The primary standards are ASTM D6 for loss on heating of oil and asphaltic compounds, GB/T 11964 for the determination of evaporation loss of petroleum asphalt, and JTG E20 (T 0608) for highway engineering bitumen in China. Related aging tests include ASTM D1754, ASTM D2872, and the EN 12607 series.

Why are 163 °C and 5 hours used?

A temperature of 163 °C closely represents typical hot-mix plant mixing temperatures, and a five-hour exposure provides a standardized, reproducible thermal load long enough to drive off volatile components while remaining practical for routine laboratory testing.

What sample size and dish are used?

The standard configuration uses approximately 50 g of bitumen in a flat-bottomed metal dish about 55 mm in internal diameter, producing a sample layer roughly 20 mm deep. Masses are determined to the nearest 1 mg using an analytical balance.

How does the test differ from the Thin-Film Oven Test and Rolling Thin-Film Oven Test?

The evaporation loss test heats a thick, static film, whereas the TFOT spreads the binder into a 3.2 mm film and the RTFOT rotates glass cylinders to create continuously renewing thin films with forced airflow. The dynamic methods are more severe and correlate more closely with plant aging, but the static evaporation test remains widely used for its simplicity and long specification history.

Why is penetration measured on the residue after heating?

Penetration of the residue reveals how much the binder has hardened, independent of mass change. Two binders may show the same mass loss but very different hardening behavior, so the retained penetration provides essential complementary information about aging susceptibility.

What does a negative evaporation loss mean?

A negative result indicates that the sample gained mass during heating. This can occur when oxygen uptake through oxidation exceeds the mass of evaporated volatiles, most commonly with heavily oxidized or air-blown bitumens. The result should be reported as a mass gain in accordance with the governing standard.

What are typical acceptance criteria?

Most paving specifications limit mass loss to a maximum of approximately 0.5% to 1.0% and require retained penetration values of at least about 50% to 65%, with the exact limits depending on the binder grade and the applicable national or project specification. Always confirm the governing specification for the specific binder being tested.