Tearing strength testing of fiber fabrics for curing applications is a critical quality-control procedure that measures a fabric's resistance to tear propagation after an initial cut or damage, ensuring that concrete curing covers, geotextile mats, and related textile materials withstand the mechanical stresses of jobsite handling. This article explains the testing principles, specimen preparation, internationally recognized test methods such as ISO 13937, GB/T 3917, ASTM D1424, ASTM D2261, and ASTM D5587, as well as typical applications and frequently asked questions. Whether you are a manufacturer, contractor, or quality engineer, understanding these procedures helps you specify, verify, and optimize curing fabrics for reliable construction performance.
Technical Overview
Fiber fabrics used for curing—such as nonwoven polypropylene mats, woven polypropylene sheets, jute or cotton burlap, and coated composite curing covers—are placed over freshly finished concrete to retain moisture, regulate temperature, and prevent plastic shrinkage cracking. During installation, fastening, repeated wetting, and removal, these fabrics are dragged over rough surfaces, snagged on reinforcement or formwork edges, and stressed around pins and weights. A fabric with inadequate tear resistance will propagate small cuts into large ruptures, compromising moisture retention and reducing reusability.
Tearing strength (also called tear force or tear resistance) is defined as the force required to propagate a tear that has been initiated by a precut slit or notch in the specimen. Unlike tensile breaking strength, which measures the force to rupture an intact strip, tearing strength reflects the localized yarn or fiber sliding and breaking behavior at the tip of a growing tear. The principal international and national standards for this property include the ISO 13937 series, the GB/T 3917 series, ISO 9073-4 for nonwovens, ASTM D1424, ASTM D2261, ASTM D5587, ASTM D4533 for geotextiles, GB/T 13763, and JIS L 1096. Testing is commonly performed by accredited third-party laboratories as part of factory quality control, incoming material inspection, and project compliance verification.
Testing Samples
Woven Curing Fabrics
Woven materials such as burlap, cotton sheeting, and woven slit-film polypropylene are sampled in both the warp (lengthwise) and weft (crosswise) directions, because tear behavior differs significantly with yarn structure, twist, and weave geometry. Specimens are cut no closer than one tenth of the fabric width (and normally at least 100 mm) from the selvedge, and areas with visible creases, folds, or damage are excluded.
Nonwoven Curing Fabrics and Geotextile-Based Curing Mats
Spunbond, needle-punched, and thermally bonded nonwovens—widely used as moisture-retaining curing mats—are sampled in both the machine direction (MD) and cross-machine direction (CD). Fiber orientation produced by the web-forming process typically produces directional tear values, so both directions must be reported. The trapezoid method described in ISO 9073-4 and ASTM D4533 is particularly suitable for these materials.
Coated and Composite Curing Covers
Laminated burlap-polyethylene covers, reflective curing sheets, and multilayer composites are tested with all layers intact as a finished assembly. Because coating layers can bridge yarns and alter tear propagation, specimens must be cut cleanly without delaminating the edges, and the direction of the principal structural layer governs the reported orientation.
Conditioning Requirements
All specimens are conditioned in a standard atmosphere in accordance with ISO 139 or GB/T 6529 (typically 20 ± 2 °C and 65 ± 4 % relative humidity) for a minimum of 24 hours, or as specified by the governing product standard. Since curing fabrics are used in the wet state, some specifications additionally require testing specimens in the wet condition after a defined soaking period, with conditioning details clearly stated in the test report.
Testing Items
Typical measured and reported parameters include:
- Warp-direction tearing strength and weft-direction tearing strength for woven curing fabrics, expressed in newtons (N).
- Machine-direction and cross-machine-direction tearing strength for nonwoven and geotextile-based curing mats.
- Maximum single-peak tear force and the mean or median of multiple tear peaks within the propagation zone, depending on the method.
- Tear strength retention after wetting, which reflects performance under saturated jobsite conditions, particularly for hydrophilic natural fibers such as cotton and jute.
- Tear strength retention after artificial weathering or ultraviolet exposure, using apparatus consistent with recognized weathering standards, to assess outdoor durability.
- Statistical reporting of individual values, mean, coefficient of variation, and the number of specimens tested for each direction.
Testing Methods
Elmendorf Pendulum Method
The ballistic pendulum method per ISO 13937-1 / GB/T 3917.1 or ASTM D1424 uses a falling pendulum to tear a slit specimen held between fixed and moving clamps. Specimens are typically 100 mm × 75 mm with a 20 mm precut slit, producing a tear propagation length of approximately 43 mm. The pendulum capacity is selected so the measured value falls between about 20 % and 80 % of the scale range. This method is fast, economical, and well suited to routine production control of lightweight and medium-weight curing fabrics.
Trouser (Pant-Leg) Method
The trouser test per ISO 13937-2 / GB/T 3917.2 uses a rectangular specimen (commonly 200 mm × 50 mm) with a central longitudinal cut that creates two legs. Each leg is gripped in a constant-rate-of-extension (CRE) tensile machine with a gauge length of about 100 mm and an extension rate of 100 mm/min. Tear force is evaluated from the peaks recorded during steady tear propagation. The method is applicable to most woven and nonwoven curing fabrics and provides a full force-extension trace for analysis.
Wing Rip Method
The wing method per ISO 13937-3 / GB/T 3917.3 uses a wing-shaped specimen in which the two legs are set at an angle to the tear line, concentrating stress at the tear tip. It is mounted in a CRE machine with a 100 mm gauge length and a 100 mm/min rate. The wing configuration reduces jaw slip and produces a more stable tear path in fabrics where the trouser test tends to deviate into a tensile-type failure.
Trapezoid Method
The trapezoid method per ASTM D5587, ISO 9073-4, ASTM D4533, and GB/T 13763 is the preferred procedure for nonwoven curing fabrics and geotextile-related products. A rectangular specimen (commonly about 150 mm × 75 mm) is marked with nonparallel lines defining a trapezoid, and a short starter slit (about 15 mm) is cut on the short side. The marked edges are aligned in the clamps of a CRE or constant-rate-of-traverse machine, typically operated at 300 mm/min, so the tear propagates across the width. Its reproducibility and robustness make it the reference method in many geosynthetic and nonwoven specifications.
Tongue (Single Rip) Method
The tongue procedures per ASTM D2261 and the double-tear tongue approach in ISO 13937-4 / GB/T 3917.4 use specimens with a longitudinal cut forming a tongue that is gripped while the remainder of the fabric is held in the second clamp. A maximum force criterion is applied, making the method suitable for coated and composite curing covers where the tearing behavior is less uniform.
Common Procedural Requirements
Regardless of the method, testing should observe the following: verify calibration of load cells or pendulum capacity before use; cut specimens with sharp dies or blades to ensure clean, consistent slits; test at least five valid specimens per direction (with additional specimens when specified); reject specimens that tear across the slit, slip in the jaws, or fail outside the designated tear zone; and report the method, conditioning, orientation, individual values, and statistics. If disputes arise, ISO and ASTM standards generally designate the CRE-based reference method for decision.
Applications
- Factory quality control during production of nonwoven and woven curing fabrics, ensuring each batch meets declared tear-force levels.
- Incoming inspection of curing covers for highway pavements, bridge decks, airport runways, canal linings, and mass concrete placements.
- Verification of compliance with project specifications that supplement moisture-retention requirements for curing sheet materials with mechanical durability indices.
- Comparative material evaluation, such as polypropylene versus polyester versus natural jute, or needle-punched versus thermally bonded structures.
- Durability assessment after wet-dry cycling, freeze-thaw exposure, and artificial UV weathering to justify repeated reuse of curing mats.
- Research and development of coated, laminated, and treated curing fabrics where binder level, coating weight, and calendering affect tear propagation.
- Independent verification and certification support through accredited third-party laboratories for tenders, audits, and dispute resolution.
FAQ
Which tearing strength method is most suitable for curing fabrics?
For nonwoven and geotextile-based curing mats, the trapezoid method (ASTM D5587, ISO 9073-4, ASTM D4533, GB/T 13763) is generally preferred due to its reproducibility. For lightweight woven fabrics, the Elmendorf pendulum method (ISO 13937-1, GB/T 3917.1, ASTM D1424) is widely used for rapid routine control. The trouser, wing, and tongue CRE methods are selected when a full force-extension record or coated-composite behavior is required. The chosen method must always be stated because results from different methods are not directly comparable.
How many specimens should be tested?
As a minimum, five valid specimens are tested for each fabric direction. Standards for geotextiles and certain project specifications may require ten or more specimens per direction to improve statistical confidence. Invalid results caused by jaw slip or off-line tearing are replaced with additional specimens.
Why do warp and weft tear values differ?
Tear propagation depends on yarn density, twist, crimp, and the mobility of yarns at the tear tip. In woven curing fabrics, the direction with fewer, more mobile yarns typically shows higher tear force because yarns bundle at the tear tip and share the load, whereas tightly woven directions fail more yarn-by-yarn. Nonwovens show MD/CD differences driven by fiber orientation during web formation.
How is tearing strength different from tensile breaking strength?
Tensile breaking strength measures the maximum force an intact strip can carry in tension, involving all yarns across the width. Tearing strength measures the force needed to continue an existing cut, involving only a few yarns or fibers at the tear tip at any moment. A fabric can have high tensile strength yet low tear strength, so both properties are usually specified together.
What units are used and what values are acceptable?
Results are reported in newtons (N), or millinewtons for very lightweight fabrics in the pendulum method. Acceptance values depend on the product class and project specification; lightweight nonwoven curing fabrics may be specified at relatively modest tear forces, while heavy geotextile-based mats and reusable composite covers require substantially higher values. Acceptance criteria should be taken directly from the governing specification or agreed contractual documents.
Does the wet state affect the results?
Yes. Curing fabrics operate in a saturated condition, and hygroscopic fibers such as cotton, viscose, and jute can lose a significant portion of their tear resistance when wet, while synthetics such as polypropylene and polyester are largely unaffected. When wet performance is relevant, specifications should explicitly require wet-condition testing with a defined soaking procedure.
Can retained tear strength after weathering be evaluated?
Yes. Specimens are first exposed to artificial weathering or ultraviolet light using apparatus consistent with recognized weathering standards, then conditioned and tested by the same tear method. The percentage retention of tear force compared with unexposed controls provides a practical durability index for outdoor curing applications.