High and low temperature testing is a critical evaluation process used to verify the thermal durability, mechanical stability, and safety of synthetic (plastic) running tracks exposed to extreme climatic conditions. By subjecting track specimens to accelerated thermal aging and sub-zero conditioning in accordance with GB, EN, ISO, and ASTM standards, accredited third-party laboratories can determine whether the material retains its tensile strength, elasticity, hardness, and shock absorption performance over its service life. This article provides a comprehensive technical overview of sample requirements, test items, methodologies, acceptance criteria, and practical applications of high and low temperature testing for athletic track surfaces.
Technical Overview
Synthetic running tracks—typically manufactured from cast-in-place polyurethane systems, prefabricated rubber sheets, or EPDM granule-based composites—are permanently exposed to outdoor environments where surface temperatures can range from approximately -40°C in severe winter climates to above 60°C under intense summer solar radiation. Repeated thermal cycling accelerates polymer chain scission, crosslink degradation, plasticizer migration, and hardener imbalance, which manifest as surface hardening, cracking, blistering, delamination, and loss of shock-absorbing capability.
High and low temperature testing (also referred to as thermal aging resistance and cold-resistance testing) evaluates how track materials behave after controlled exposure to elevated and sub-ambient temperatures. The tests quantify the retention rates of key mechanical properties—such as tensile strength, elongation at break, and Shore A hardness—and verify that functional characteristics like force reduction and slip resistance remain within specification after thermal conditioning.
The principal governing references include GB/T 14833-2020 (Synthetic Materials Running Tracks for Sports), GB 36246-2018 (Synthetic Surfaces for Sports Areas in Primary and Secondary Schools), EN 14877 (Surfaces for Outdoor Sports Areas), GB/T 3512 and ISO 188 (vulcanized rubber thermal aging in air), ISO 37 and GB/T 528 (tensile properties), ISO 48 (hardness), and ASTM D573 (rubber deterioration in an air oven). Products intended for certification under World Athletics (formerly IAAF) track certification programs must also demonstrate performance retention after accelerated aging.
Testing Samples
Cast-in-Place Polyurethane Track Specimens
Samples are prepared from the mixed polyurethane system poured into leveled molds at the nominal installed thickness (commonly 9 to 13 mm). Dumbbell-shaped specimens are die-cut according to ISO 37 Type 1 or Type 2 geometry after full cure (typically 7 to 14 days at standard laboratory conditions of 23°C ± 2°C and 50% ± 5% relative humidity).
Prefabricated Track Sheet Specimens
For factory-manufactured rolls, specimens are taken from at least three positions along the length and width of the roll to account for production variability. Samples must be free from visible defects and conditioned for a minimum of 24 hours before testing.
Field-Cored Samples from Installed Tracks
When evaluating existing installations, cylindrical cores or cut sections are extracted from the track surface, photographed for documentation, and transported to the laboratory under conditions that prevent deformation or contamination. Site samples are primarily used for verification testing and dispute resolution.
Sample Quantity and Dimensions
- Tensile specimens: minimum of five dumbbells per condition per standard practice
- Hardness specimens: flat pieces at least 6 mm thick, assembled layers permitted
- Low-temperature bend specimens: strips of 100 mm × 10 mm × track thickness
- Force reduction specimens: 150 mm × 150 mm sections or full-thickness cored discs
Testing Items
The high and low temperature evaluation program typically encompasses the following measurable parameters:
- Tensile strength before and after thermal aging (MPa), expressed as retention percentage
- Elongation at break before and after aging (%), expressed as retention percentage
- Shore A hardness change after high-temperature exposure (Δ Shore A)
- Low-temperature flexibility and bend performance at -25°C or -40°C
- Low-temperature retraction or brittleness assessment
- Force reduction (shock absorption) retention after aging, per EN 14809 test methodology
- Vertical deformation retention after thermal conditioning
- Surface appearance evaluation: cracking, blistering, tackiness, discoloration, and delamination
- Mass change and dimensional stability after oven exposure
- Thickness change and compression recovery behavior
For products supplied to the primary and secondary school market under GB 36246-2018, the thermal aging test is accompanied by mandatory chemical safety testing, as environmental compliance and mechanical durability are assessed together in a full conformity evaluation.
Testing Methods
High-Temperature Accelerated Aging
Specimens are suspended in a forced-ventilation air oven at 80°C ± 2°C for 168 hours (7 days), following the procedures of GB/T 3512, ISO 188 (method A), or ASTM D573. After removal, samples are conditioned at 23°C ± 2°C for 16 to 24 hours before tensile, hardness, and visual assessments are performed. Some specifications permit 70°C × 168 h or 70°C × 96 h alternatives where the material formulation is thermoset-stable; the selected condition must be stated in the test report.
Low-Temperature Conditioning
Samples are placed in a climatic chamber at -25°C ± 3°C (or -40°C ± 3°C for severe-climate projects) for a defined period, typically 24 hours for flexibility testing or up to 168 hours for property-retention assessment. Bend tests are conducted by wrapping specimens around a mandrel of specified diameter at the test temperature, immediately examining for cracks and fracture. Hardness and tensile measurements are taken after recovery conditioning at laboratory temperature unless the specification requires low-temperature measurement in situ.
Thermal Cycling (Alternate Temperature Exposure)
For climatic durability assessment, specimens undergo repeated cycles—for example, 2 hours at 70°C followed by 2 hours at -20°C, repeated for 10 to 50 cycles—inside a two-chamber or programmable cycling chamber. This method reveals fatigue-related failures at bonded interfaces, seams, and granule-matrix boundaries that single-condition aging may not expose.
Post-Aging Mechanical and Functional Testing
Aged and unaged (control) specimens are tested in parallel using the same methods: tensile testing per ISO 37 / GB/T 528 at a crosshead speed of 500 mm/min for thermoplastic elastomers or 200 to 500 mm/min as specified; hardness per ISO 48 / GB/T 531; force reduction per EN 14809 using an artificial athlete apparatus; and vertical deformation per EN 14808 or GB/T 22517.6. Retention is calculated as the ratio of the aged value to the unaged value, expressed as a percentage.
Typical Acceptance Criteria
- Tensile strength retention after 80°C × 168 h: not less than 80% (per most project specifications and GB/T 14833 guidance)
- Elongation at break retention after thermal aging: not less than 80%
- No cracking, fracture, or delamination after low-temperature bend at -25°C
- Force reduction change after aging: within the range stated in the product standard or certification protocol
- No surface blistering, abnormal tackiness, or hardening exceeding the specified Shore A tolerance
Applications
High and low temperature test reports serve multiple purposes across the track construction and certification supply chain:
- Factory quality control for polyurethane binder, prefabricated sheet, and EPDM granule manufacturers verifying formulation stability before mass production
- New construction acceptance testing for school playgrounds, university stadiums, and professional athletics facilities
- Product certification support for domestic standards conformity and international athletics certification schemes
- Comparative material selection during tender evaluation, allowing project owners to rank candidate systems by aging resistance
- Failure and dispute analysis when installed tracks exhibit premature cracking in cold regions or softening and odor release in hot climates
- Service-life estimation and maintenance scheduling for tracks in extreme-climate regions such as high-altitude plateaus, northern winters, and intense equatorial solar exposure
FAQ
What temperature conditions are most commonly specified for track thermal testing?
The most widely applied conditions are 80°C ± 2°C for 168 hours for high-temperature aging and -25°C ± 3°C for low-temperature flexibility, with -40°C conditioning specified for projects in severely cold regions. Thermal cycling protocols between 70°C and -20°C are increasingly requested for durability demonstration.
How are retention rates calculated and reported?
Retention is the aged specimen result divided by the unaged control result multiplied by 100%. For example, if tensile strength is 2.5 MPa before aging and 2.2 MPa after aging, the retention is 88%, which passes an 80% threshold. Test reports must clearly state both values, the aging conditions, and the calculation basis.
Can testing be performed on samples taken from an already installed track?
Yes. Accredited third-party laboratories routinely test cored or cut samples from installed surfaces for acceptance and dispute purposes, provided sampling locations, quantities, and documentation follow the project specification and relevant standard sampling rules.
How long does a complete high and low temperature evaluation take?
Allowing for specimen preparation, curing or conditioning, the aging exposure itself (typically 7 days), recovery conditioning, and mechanical testing, a complete program generally requires 2 to 4 weeks. Thermal cycling programs with 50 cycles may extend the timeline further.
Why does a track pass room-temperature testing but fail after thermal aging?
Room-temperature results alone do not reveal progressive polymer degradation. Inadequate MDI-TDI balance, excess free TDI, poor moisture control during installation, insufficient crosslink density, or low-quality fillers and recycled content can all produce acceptable initial properties that deteriorate sharply after heat exposure. Thermal aging testing is therefore the decisive indicator of long-term field durability.