PU (polyurethane) plastic running tracks are permanently exposed to outdoor climates, where summer surface temperatures can exceed 60°C and winter lows can fall below -30°C, making high and low temperature testing a critical part of quality control. This article explains the sample preparation, test items, standard test methods, and acceptance criteria used to verify the thermal durability and mechanical performance of PU track surfaces. It serves as a practical reference for manufacturers, contractors, testing laboratories, and facility owners seeking compliance with national and international specifications.
Technical Overview
PU plastic running track is an elastomeric sports surfacing system produced from polyurethane binders, rubber granules, and additives, applied either as a cast-in-place liquid system or as prefabricated mats. Because tracks are installed outdoors without climate protection, the material must tolerate sustained thermal stress throughout its service life, which is typically specified as 8 to 10 years or more.
High temperatures accelerate oxidation and polyurethane chain degradation, causing hardening, loss of elasticity, and reduced elongation. Low temperatures stiffen the polymer matrix and increase the risk of brittleness and cracking under foot impact or cleat loading. Repeated thermal cycling between extremes generates internal stresses that can lead to delamination, blistering, and dimensional change. High and low temperature testing reproduces these conditions in a controlled laboratory environment and quantifies their effect on the mechanical and functional properties of the track surface.
Testing is typically performed with reference to standards such as GB/T 22517.6 (technical requirements and test methods for plastic running tracks), GB 36246-2018 (safety requirements for synthetic sports surfaces in primary and secondary schools), EN 14877 (synthetic surfaces for outdoor sports areas), and the track surface specifications published by World Athletics. Base material test methods include GB/T 528 or ISO 527-type tensile testing, GB/T 531.1 or ISO 48 for Shore A hardness, EN 14808 for shock absorption, and EN 14809 for vertical deformation.
Testing Samples
Standard Laboratory Specimens
Specimens are prepared by casting the PU material into flat sheets under controlled conditions, typically 23 ± 2°C and 50 ± 5% relative humidity, followed by full curing for the period specified by the manufacturer. Dumbbell-shaped specimens are then die-cut from the cured sheets for tensile strength and elongation testing, with thickness measured at multiple points to confirm uniformity. Companion specimens are retained as unaged controls for calculating property retention rates.
Finished Product Cores
For acceptance testing of installed tracks, cylindrical cores or rectangular sections are cut from the finished surface using a hole saw or core drill. These specimens preserve the actual production formulation, layer structure, and surface texture, and they are used to verify whether the as-built track meets the thermal durability requirements.
Composite System Specimens
Specimens consisting of the PU surface layer bonded to its base layer or substrate are prepared to evaluate interlayer adhesion after thermal exposure. These samples are essential for detecting delamination caused by differential thermal expansion between the elastic surface and the underlying asphalt or concrete base.
Sufficient replicate specimens, commonly no fewer than five per condition, should be prepared so that results are statistically meaningful and anomalous values can be identified.
Testing Items
The scope of high and low temperature testing for PU running tracks typically covers the following items:
- Appearance evaluation after thermal exposure, including cracking, blistering, bubbling, delamination, surface tackiness, discoloration, and hardening.
- Tensile strength before and after high-temperature aging, expressed as a retention percentage relative to unaged control values.
- Elongation at break before and after thermal aging, which is a sensitive indicator of embrittlement in polyurethane systems.
- Shore A hardness change, used to quantify thermal hardening or softening of the surface.
- Low-temperature flexibility or brittleness, assessed by bending or impact loading at subzero temperatures to detect crack initiation.
- Shock absorption and vertical deformation measured after climatic conditioning to confirm that athlete-protection performance is retained.
- Slip resistance of the worn surface after thermal exposure, ensuring traction safety is not degraded.
- Interlayer bond or peel strength after thermal cycling to assess resistance to delamination.
- Dimensional stability, including linear shrinkage or expansion after thermal treatment.
Testing Methods
High-Temperature Aging Test
Specimens are placed in a forced-ventilation aging oven at a specified elevated temperature, commonly 70°C or 80°C with a tolerance of ±2°C, for durations such as 24 hours, 48 hours, or 168 hours depending on the governing specification. After exposure, specimens are conditioned at 23 ± 2°C before tensile, elongation, and hardness testing. The retention rate for each property is calculated by dividing the aged value by the unaged control value. Acceptance criteria in common specifications require retention of tensile strength and elongation at a level of at least 80 percent, with no visible cracking or structural defects.
Low-Temperature Conditioning Test
Specimens are conditioned in a cryogenic chamber at temperatures such as -20°C or -40°C for a defined holding period. Testing approaches include low-temperature bending around a mandrel, low-temperature impact for brittleness assessment, and hardness measurement in the cold state. After conditioning, specimens are inspected for surface cracking, edge splitting, and loss of flexibility, and mechanical properties may be retested after recovery to ambient temperature to evaluate permanent damage.
Thermal Cycling Test
To simulate seasonal and diurnal temperature swings, specimens are subjected to repeated cycles between a low extreme, for example -25°C, and a high extreme, for example 70°C, with defined dwell times at each plateau. After a specified number of cycles, the specimens are examined for fatigue cracking, delamination, blistering, and cumulative dimensional change, and functional properties are measured to confirm continued compliance.
Functional Property Verification
Shock absorption and vertical deformation are measured using an artificial athlete type drop device in accordance with EN 14808 and EN 14809, while slip resistance is measured with a pendulum or traction tester. These tests may be performed either at laboratory ambient conditions after climatic conditioning or inside an environmental chamber to characterize performance directly at extreme temperatures, which is valuable for projects in severe climates.
Applications
High and low temperature testing of PU running tracks is applied across the full life cycle of sports facility projects, from material development through installation acceptance and long-term quality assurance:
- Factory quality control for batch release of PU binders, prefabricated mats, and mixed systems before shipment.
- Third-party testing and certification of tracks intended for stadiums, universities, and schools under national and World Athletics requirements.
- Project acceptance testing, where cores taken from the installed surface are evaluated to confirm thermal durability of the as-built system.
- Climate-specific engineering, allowing specifiers in hot desert regions or severe cold regions to select formulations proven for local temperature extremes.
- Research and development, supporting formulation optimization of polyurethane systems for improved thermal aging resistance and low-temperature flexibility.
- Failure analysis and dispute resolution, providing objective evidence of whether premature cracking or delamination is related to material quality or installation conditions.
FAQ
Why is high and low temperature testing necessary for PU running tracks?
Tracks are exposed to outdoor temperatures that swing between extreme heat and cold over many years of service. Thermal exposure degrades the polyurethane matrix, reduces elasticity, and can cause cracking or delamination. Laboratory testing verifies that the material will retain its mechanical and protective properties throughout the intended service life.
What temperature range and duration are typically used?
Common high-temperature aging conditions are 70°C to 80°C for 24 to 168 hours, while low-temperature conditioning is typically performed at -20°C to -40°C. The exact parameters depend on the applicable standard and the climate zone of the project site.
What are the typical pass criteria?
Specifications generally require that tensile strength and elongation at break retain at least 80 percent of their original values after aging, that hardness change stays within the permitted limit, and that no cracking, blistering, or delamination is visible after exposure or thermal cycling.
Can an installed track be tested on site?
Yes. Cores can be extracted from the finished surface and tested in a laboratory, and portable equipment can be used on site for shock absorption, deformation, and slip resistance verification, subject to temperature conditioning requirements.
How does temperature testing relate to service life prediction?
Elevated-temperature aging accelerates the degradation mechanisms that occur slowly at ambient conditions. By comparing property retention after accelerated exposure with specified limits, engineers can judge whether a track system will remain serviceable for its full design life under the local climate.