High- and Low-Temperature Tensile Testing of Synthetic Running Tracks

Specimen Geometry and Preparation

Dumbbell-shaped specimens are punched with cutting dies corresponding to Type 1, Type 2, or Type 3 geometries defined in GB/T 528 and ISO 37. The narrow-section thickness is measured at three points with a calibrated gauge and the median value is used for cross-sectional area calculation. Before testing, specimens are conditioned at 23 ± 2 °C and 50 ± 5 % relative humidity for a minimum of 16 hours. Specimens containing visible flaws, bubbles, or die-cutting burrs are rejected to avoid non-representative failures.

Testing Items

The standard scope of high- and low-temperature tensile testing for synthetic running tracks typically includes the following items, with the exact temperature points and acceptance limits defined by the project specification or applicable product standard:

• Tensile strength at elevated temperature, commonly evaluated at 60 °C or 70 °C to simulate summer surface conditions.
• Elongation at break at elevated temperature, confirming that the material remains sufficiently extensible under thermal softening.
• Tensile strength at low temperature, commonly evaluated at -20 °C, -25 °C, or -40 °C depending on the service climate.
• Elongation at break at low temperature, assessing embrittlement resistance and cold-weather flexibility.
• Retention rate of tensile strength, expressed as the percentage ratio of the value at the test temperature to the value at 23 °C.
• Retention rate of elongation at break, calculated on the same comparative basis.
• Baseline tensile strength and elongation at break at 23 ± 2 °C for reference comparison.
• Optional items such as tensile stress at a given elongation and tear strength under equivalent thermal conditions.

Testing Methods

Baseline Testing at Standard Conditions

Reference testing is first performed at 23 ± 2 °C using a calibrated universal testing machine. Specimens are gripped with the gauge marks aligned, and the crosshead is driven at the speed specified for the dumbbell type, most commonly 500 ± 50 mm/min. Maximum force and elongation at break are recorded, and tensile strength is calculated as the maximum force divided by the original cross-sectional area of the narrow section.

High-Temperature Tensile Testing

Specimens are placed inside the environmental chamber attached to the testing machine and conditioned at the target temperature, with a typical tolerance of ± 2 °C, until the chamber and specimen reach thermal equilibrium. A conditioning period of at least 10 minutes after temperature stabilization is generally applied for track-thickness specimens. The tensile test is then executed without removing the specimen from the chamber, so that the measured properties reflect the softened state of the material at elevated temperature.

Low-Temperature Tensile Testing

For sub-zero evaluation, the chamber is cooled to the specified low temperature using mechanical refrigeration or liquid carbon dioxide. After equilibration, each specimen is tested in sequence while the chamber temperature remains within tolerance. Care is taken to minimize heat transfer through the grips and to test promptly after loading, since localized warming of the gauge section can bias the results toward higher strength and lower stiffness.

Calculation and Retention Rate

A minimum of three specimens, and preferably five, are tested for each temperature condition, and the median values are reported as required by GB/T 528 and ISO 37. The retention rate is calculated by dividing the median tensile strength or elongation at the target temperature by the corresponding median at 23 °C and multiplying by 100. A significant decline in retention rate indicates formulation sensitivity to temperature, such as excessive plasticizer content, inadequate crosslink density, or incompatible filler loading.

Applications

High- and low-temperature tensile data for synthetic running tracks are used throughout the product life cycle, from formulation development to installation acceptance and post-construction verification. Typical application scenarios include:

• Factory quality control and batch release testing for track material producers.
• Pre-installation verification of cast-in-place system trial sections cured under site-representative conditions.
• Acceptance testing for school playgrounds, university stadiums, and public athletics facilities.
• Compliance documentation for tender submissions and material submittals in construction projects.
• Failure investigation of cracked, brittle, or softened track surfaces after extreme weather events.
• Comparative benchmarking of competing track systems during design and procurement.
• Supporting evidence for product certification and periodic quality surveillance programs.

FAQ

Why is tensile testing at extreme temperatures necessary for running tracks?

Elastomeric track materials soften and lose strength at high temperature and stiffen or embrittle at low temperature. A track that passes ambient testing may still crack during freezing winters or deform under athlete loading on hot summer afternoons. Testing at both thermal extremes demonstrates that the surface will deliver consistent performance across the full range of service conditions it will encounter.

Which temperature points are usually selected?

Common high-temperature points are 60 °C and 70 °C, reflecting peak summer surface temperatures of dark-colored tracks. Common low-temperature points are -20 °C, -25 °C, and -40 °C, selected according to the climate zone of the installation site. Project specifications or the applicable product standard define the exact requirements for each contract.

How many specimens are required for each condition?

Standards aligned with GB/T 528 and ISO 37 specify a minimum of three valid specimens, while five specimens are recommended to improve statistical confidence. The median of valid results is reported, and specimens that fail outside the narrow section are discarded and replaced unless the failure pattern itself is characteristic of the material.

Can samples be taken from an already installed track?

Yes. Core samples or cut coupons can be extracted from locations agreed with the supervising engineer, then die-cut into standard dumbbell specimens in the laboratory. Sampling locations are repaired afterward with matching material. Field-extracted samples are frequently used for acceptance disputes and post-construction quality audits.

What does a low retention rate indicate?

A substantial drop in tensile strength or elongation retention signals temperature-sensitive formulation characteristics. Common causes include excessive plasticizer that migrates at high temperature, insufficient polyurethane binder relative to rubber granule content, poor crosslink density, or high loading of incompatible fillers. Corrective action usually involves formulation adjustment and re-verification testing.

How long does the complete test cycle take?

Excluding sample curing time for cast-in-place materials, a typical program covering baseline, high-temperature, and low-temperature conditions with five specimens per condition can be completed within several working days, allowing time for conditioning, chamber stabilization, and report preparation. Accredited third-party laboratories can advise on expedited schedules when project deadlines require them.