ISO 12236
Static Puncture (CBR) Test for Geosynthetics

Downloads: ISO 12236 CBR Puncture Fixture for Geosynthetics – Universal Grip Data Sheet (PDF)

Written by Chris Thomas, Universal Grip Company · Reviewed by Frank Bertini · Updated October 31, 2026

ISO 12236 is the international static puncture test for geosynthetics, better known as the CBR test. A specimen is clamped between two steel rings with a 150 mm opening, and a flat-ended 50 mm diameter plunger is pushed through its centre at constant speed while force and displacement are recorded. The maximum force, called the push-through force, is one of the headline numbers on every geotextile data sheet, because it tells a designer how well the product survives sharp aggregate, construction traffic and stones pressed into it under load. Manufacturers run it for CE-marking declarations and factory production control, labs run it for conformity testing, and specifiers use it to rank separation, filtration and protection geotextiles. The test looks simple, but small things change the answer: specimens slipping in the rings, the wrong plunger edge radius, testing the wrong face, or starting displacement from the wrong point. This guide covers the current edition, specimens, conditioning, speed, the Universal Grip CBR puncture fixture, machine choice, the procedure, a worked calculation, common errors and how ISO 12236 compares with ASTM D6241.

ISO 12236 at a glance

• Current edition: ISO 12236:2026 (third edition, published May 2026), adopted in Europe as EN ISO 12236:2026. It replaced ISO 12236:2006.

• Scope: most geosynthetic products, tested normally as dry, conditioned specimens; not applicable to products with apertures greater than 10 mm.

• Clamping: two steel rings with an internal diameter of 150 mm; the clamping system must prevent slippage and must not cut the specimen.

• Plunger: stainless steel, flat-ended, 50 mm diameter, with a small radius on the leading edge (2.5 mm in the 2006 edition).

• Speed: constant displacement rate of 50 mm/min.

• Specimens: five per sample, taken at random per ISO 9862; each face tested separately if the faces differ.

• Conditioning: (20 ± 2) °C and (65 ± 5) % RH per ISO 554.

• Results: push-through force F_p (kN), push-through displacement h_p (mm) and the force-displacement curve.

• Related standards: ASTM D6241, ASTM D4833, ISO 10319, ISO 13433 and ISO 9862.

What ISO 12236 measures and who uses it

The CBR name comes from the California Bearing Ratio soil test, whose 50 mm piston gave the plunger its size. Instead of measuring how a soil resists penetration, ISO 12236 measures how much force it takes to push that plunger through a geotextile or other geosynthetic held in a 150 mm ring. Because the specimen is restrained all round, the product is stretched biaxially, much as it is when an aggregate particle is pushed into it on site. That makes the CBR result a useful indicator of installation survivability and a standard property in European product standards for geotextiles used in roads, railways, drainage, erosion control, tunnels and landfills.

Typical users are geotextile and geocomposite manufacturers, notified bodies and third-party labs, highway and rail authorities checking deliveries, and landfill engineers specifying protection layers above geomembranes. The test is a quality and index test; site survivability also depends on aggregate size, installation method and dynamic damage, which other standards address.

• Push-through force F_p: the maximum plunger force recorded in each test, in kN.

• Push-through displacement h_p: the plunger travel at maximum force, in mm, measured from a small preload (20 N in the 2006 edition).

• Force-displacement curve: shows the stiffness of the product and whether failure is sudden (typical of wovens) or progressive (typical of nonwovens).

ISO 12236 test specimens

Size and shape

Each specimen must be large enough to cover the full clamping area of the rings with no wrinkles or folds; the 150 mm internal diameter is the free test area. Circular specimens cut to suit the outer diameter of the clamping rings are the most practical, and a ribbon-steel cutting die on an arbor press makes them quickly and repeatably. Check the figure in the current edition for the clamping geometry, which was revised in the 2026 edition.

Number of specimens and sampling

Test five specimens taken at random from the laboratory sample in accordance with ISO 9862, avoiding roll edges and damaged areas. If the two faces of the product differ physically or because of the manufacturing process, test each face separately, which means a separate set for each face and a note in the report of which face met the plunger.

Preparation

• Mark the face and the machine direction on each specimen before cutting.

• Cut cleanly; nicks at the edge do not affect the free area, but folds or creases can cause local slippage.

• Record mass per unit area and thickness where the specification asks for them (ISO 9864 and ISO 9863-1); CBR force scales strongly with mass per unit area for nonwovens.

• For geocomposites, decide and record which component faces the plunger.

Conditioning

Specimens are conditioned in the ISO 554 standard atmosphere of (20 ± 2) °C and (65 ± 5) % relative humidity. In the 2006 text, specimens are considered conditioned when the change in mass between weighings at least 2 h apart is no more than 0.25 % of the specimen mass. Conditioning may be omitted only when it has been shown that results for that product type (same structure and polymer) are not affected by atmosphere outside these limits, and that must be stated in the report. National adoptions sometimes use a different temperature; always report the atmosphere actually used. The test is normally run dry, so an environmental chamber is not usually needed.

Test speed and machine requirements

• Speed: constant plunger displacement rate of 50 mm/min (the 2006 edition sets ± 5 mm/min; clause 8 was updated in 2026, so confirm against the current text).

• Machine accuracy: force-measuring system verified to ISO 7500-1, class 1 or class 0 in the 2006 edition.

• Recording: continuous force and displacement, so the push-through force, its displacement and the full curve can be reported.

• Plunger: stainless steel, 50 mm diameter with the specified edge radius; check for nicks that would cut rather than stretch the specimen.

• Clamping system: 150 mm internal diameter rings that prevent slippage and cutting; the 2006 edition also limits the distance from the inner ring diameter to the start of the gripping zone to 7 mm.

• Travel: enough for push-through plus clearance; nonwovens can deflect a long way before the plunger breaks through, so allow generous stroke below the specimen.

Speed control matters more than it seems. Polypropylene and polyethylene geotextiles are rate-sensitive, so a machine that overshoots the set speed, or accelerates unevenly at the start, will shift the push-through force. Use closed-loop speed control, let the plunger reach constant speed before it meets the specimen, and keep the data rate high enough to capture the peak on stiff wovens that fail suddenly. If your lab also runs ASTM D4833 at a much higher speed, double-check the method selected before each batch.

The Universal Grip ISO 12236 CBR puncture fixture

Universal Grip builds a static puncture (CBR) fixture for geosynthetics to ISO 12236. The specimen is clamped between two ring plates on a pillar-supported cylinder, and a flat-ended cylindrical plunger on the crosshead is pushed through its centre, recording puncture force and plunger displacement until the plunger pushes fully through the specimen. It sits in our puncture fixtures range.

• Clamping rings to ISO 12236 geometry with a 150 mm opening and gripping faces.

• 50 mm flat-ended plunger with a defined edge radius and a ground finish.

• Knob-tightened clamp ring for quick, even specimen clamping.

• Pillar-supported base gives clearance for plunger push-through.

• Load capacity: 20 kN standard; higher capacities on request.

• Construction: stainless steel and anodized aluminium.

• Machine connection: clevis pin or threaded adapter to suit your frame; compatible with electromechanical and servo-hydraulic universal testing machines.

• Also suits ASTM D6241, which uses the same plunger and ring size.

• Part reference: UGC-ISO12236-PF.

When you ask for a quote, tell us the product type and expected puncture force, the clamping face style you need and your machine connection. Face style matters: smooth or slick products, such as some geomembranes and coated composites, are the ones most likely to pull in from the rings. Specifications are typical and are confirmed at the time of quote.

Choosing a testing machine for ISO 12236

CBR forces are moderate. Lightweight nonwoven separators often push through at around 1 to 3 kN, heavier protection geotextiles can exceed 10 kN, and robust wovens and composites sit in between or above. Pick a machine whose verified load-cell range covers your strongest product with margin, and which has stroke for the push-through displacement.

Mark-10 motorized testers

For QC labs testing light and medium-weight geotextiles, a Mark-10 F1505 (1,500 lbF, about 6.7 kN) or F755 (750 lbF, about 3.3 kN) runs 50 mm/min comfortably within its 10 to 600 mm/min range, with 813 mm of travel, ±0.2 % speed accuracy and 5,000 Hz sampling. Be honest about the limits: heavy protection geotextiles exceed 6.7 kN, the frame and load cell must be verified to ISO 7500-1 over the range you use, and the fixture fit should be confirmed when quoting. Smaller Mark-10 models are too light for most CBR work.

Galdabini universal testing machines

A Galdabini universal testing machine is the better choice for accredited labs and mixed geosynthetic programmes, because the same frame can also run ISO 10319 wide-width tensile tests.

• 10 kN benchtop: most nonwoven and woven geotextiles.

• 25 kN benchtop: covers the full 20 kN standard rating of the fixture, including heavy protection geotextiles.

• 50 kN or 100 kN benchtop: when the same machine also runs ISO 10319 on woven geotextiles and geogrids.

Grips, extensometers and accessories

No grips or extensometers are needed for the puncture test itself. Displacement is plunger travel measured by the machine, starting at the small preload, so an extensometer adds nothing. Labs that run both standards add wide-width vise grips for ISO 10319 on the same frame. Useful extras are a ribbon-steel cutting die for round specimens, an arbor press or die press, adapters for your frame, and software that reports F_p, h_p, mean and coefficient of variation automatically. For the smaller-probe pin puncture test, see ASTM D4833.

ISO 12236 test procedure step by step

• 1. Prepare: cut five specimens per face, mark face and direction, and condition them.

• 2. Set up: mount the fixture base on the lower platen or adapter and the plunger on the crosshead or load cell; check that the plunger is centred on the ring opening and perpendicular to the specimen.

• 3. Clamp: lay the specimen flat on the lower ring, place the upper ring and tighten the clamp knobs evenly so the specimen is held without wrinkles or pre-tension; a guide block helps centre it.

• 4. Zero: bring the plunger close to the specimen and zero force.

• 5. Test: advance the plunger at 50 mm/min onto and through the specimen, starting the displacement record at the preload.

• 6. Observe: watch for slippage at the rings, a tear starting at the clamp, or the specimen pulling inward; note any irregular failure.

• 7. Remove and repeat for the remaining specimens and the other face if required.

• 8. Calculate and report F_p, h_p and their statistics, with the curves.

ISO 12236 calculations

For each specimen, read the maximum force F_p and the displacement h_p at that force from the curve. For the set, calculate the mean and the coefficient of variation; see clause 9 of the current edition for the exact statistics and rounding required.

• Mean push-through force: F_p,mean = (F_p1 + F_p2 + … + F_p5) / 5, in kN.

• Standard deviation: s = √[ Σ (F_pi − F_p,mean)² / (n − 1) ].

• Coefficient of variation: CV = s / F_p,mean × 100 %.

• Mean push-through displacement: the average of h_p for the five specimens, in mm.

Worked example

• Five specimens of a nonwoven geotextile give F_p = 2.84, 2.96, 2.71, 3.05 and 2.89 kN.

• Sum = 14.45 kN, so F_p,mean = 14.45 / 5 = 2.89 kN (2,890 N).

• Deviations from the mean: −0.05, +0.07, −0.18, +0.16 and 0.00 kN; squared deviations sum to 0.0654 kN².

• s = √(0.0654 / 4) = √0.01635 = 0.128 kN.

• CV = 0.128 / 2.89 × 100 = 4.4 %.

• Push-through displacements of 48.2, 50.1, 46.9, 51.4 and 49.4 mm give a mean h_p of 246.0 / 5 = 49.2 mm.

• Report: push-through force 2.89 kN (CV 4.4 %), push-through displacement 49.2 mm.

Typical results and the test report

Results depend mostly on polymer, structure and mass per unit area. Nonwovens show a long, rounded curve with large push-through displacements, while wovens are stiffer and fail more suddenly at shorter displacements. Compare results only with values obtained by the same standard and face orientation.

• Reference to ISO 12236:2026 and any deviations.

• Product identification and which face met the plunger.

• Conditioning atmosphere, or a statement that conditioning was omitted and why.

• Each F_p and h_p, the means and coefficient of variation.

• Force-displacement curves.

• Any specimens showing slippage or irregular failure.

• Machine and fixture used.

Reading the force-displacement curve

The curve says more than the single peak value. A nonwoven typically shows a low initial slope while fibres straighten and reorient, a long, steadily rising section as the specimen stretches into a cone around the plunger, then a rounded peak and a gradual drop as fibres pull apart. A woven geotextile rises more steeply, reaches its peak at a much shorter displacement and drops sharply as yarns break. Geocomposites may show two peaks as each component fails in turn; report the maximum as F_p and note the shape. A sawtooth pattern before the peak, or a peak followed by a slow plateau with no clear break, usually points to slippage in the rings rather than material behaviour, and those specimens should be examined before they are included in the mean.

How CBR results are used in specifications

In Europe, the product standards for geotextiles in civil engineering applications list static puncture to EN ISO 12236 among the properties manufacturers declare, so the CBR value appears on declarations of performance next to wide-width tensile strength to ISO 10319. Specifiers then set minimum values for a given application, sometimes combined with the cone drop result into a robustness classification. In North America, the equivalent property is usually specified through ASTM D6241. Because declared values are often stated as a mean minus a tolerance, labs should report the coefficient of variation and keep raw curves, so a borderline result can be investigated rather than simply retested.

Fixture care and verification

• Inspect the plunger edge regularly; nicks or burrs cut specimens and lower the push-through force.

• Clean the ring gripping faces so fibres and coating residue do not reduce grip.

• Check that the plunger travels centrally and square to the ring before each series, especially after changing adapters.

• Keep the force-measuring system within its ISO 7500-1 verification interval, and verify across the range you actually use for light products.

• Record the fixture identification on each test report for traceability.

Common errors in ISO 12236 testing

• Slippage in the rings: the specimen draws inward, inflating displacement and lowering force; use suitable gripping faces and even clamping.

• Cutting at the clamp edge: sharp ring edges cut the specimen before the plunger breaks it.

• Worn plunger edge: a damaged or wrong edge radius cuts instead of stretching, lowering F_p.

• Wrong speed: running at the 300 mm/min used for ASTM D4833 pin puncture instead of 50 mm/min.

• Off-centre plunger: loads one side of the ring first and lowers the result.

• Wrong displacement zero: starting from first contact by eye instead of the preload changes h_p.

• Testing only one face of a product with different faces.

• Wrinkled or pre-tensioned specimens: either changes the curve shape and stiffness.

• Undersized load cell or insufficient stroke for heavy nonwovens.

ISO 12236 vs ASTM D6241 and related standards

• ASTM D6241: the North American CBR equivalent, also with a 50 mm probe, a 150 mm ring opening and 50 mm/min; results are reported in newtons. North American specifications such as AASHTO M 288 now use it for geotextile puncture.

• ASTM D4833: pin puncture with an 8 mm probe in a 45 mm ring at 300 mm/min; a different test whose results cannot be converted to CBR.

• ISO 13433: dynamic perforation (cone drop) test, often specified alongside CBR for robustness.

• ISO 10319: wide-width tensile test, the other main mechanical property on geotextile data sheets.

• ISO 13934-1: strip tensile test for general textile fabrics, not used for geosynthetic declarations.

• ISO 9862, ISO 9863-1, ISO 9864 and ISO 10318-1: sampling, thickness, mass per unit area and terminology.

Equipment summary for ISO 12236

• Fixture: ISO 12236 CBR puncture fixture, 20 kN standard, higher on request; also suits ASTM D6241.

• Machine: Galdabini 10 kN or 25 kN benchtop, or a Mark-10 F1505 for lighter products.

• Specimen prep: cutting dies, arbor press and die press.

• Same-frame tensile testing: wide-width vise grips for ISO 10319.

• Related pages: puncture testing, compression testing, textiles and the full ISO standards library.

ISO 12236 FAQ

What is ISO 12236?

ISO 12236 is the international static puncture test for geosynthetics, called the CBR test. A 50 mm flat-ended plunger is pushed through a specimen clamped in 150 mm rings, and the push-through force and displacement are reported.

What is the current edition of ISO 12236?

ISO 12236:2026, the third edition, published in May 2026. It replaced ISO 12236:2006 and is adopted in Europe as EN ISO 12236:2026.

What changed in ISO 12236:2026?

The foreword lists a revised Figure 4, updated clause 8 (procedure) and clause 10 (test report), and consistent units. Check the new procedure and report clauses before updating your method.

Why is it called the CBR test?

The plunger size comes from the California Bearing Ratio soil test, which uses a piston of about 50 mm. The geosynthetic test borrowed the plunger, not the soil calculation.

What speed is used for ISO 12236?

A constant plunger displacement rate of 50 mm/min. The 2006 edition gave a tolerance of ± 5 mm/min; confirm the tolerance in the 2026 text.

How many specimens does ISO 12236 require?

Five specimens, taken at random per ISO 9862. If the two faces of the product differ, each face is tested separately.

What results does ISO 12236 report?

The push-through force F_p in kN, the push-through displacement h_p in mm, the force-displacement curves, and the mean and coefficient of variation.

Is ISO 12236 the same as ASTM D6241?

They use the same plunger diameter, ring opening and nominal speed, and our fixture suits both, but they are separate standards with their own details and reporting units, so specify the one your contract names.

What is the difference between CBR puncture and pin puncture?

CBR (ISO 12236, ASTM D6241) uses a 50 mm plunger in a 150 mm ring and stretches the product biaxially. Pin puncture (ASTM D4833) uses an 8 mm probe and measures resistance to a sharp point; the results are not interchangeable.

Can ISO 12236 be used on geomembranes?

The scope covers most geosynthetic products except those with apertures greater than 10 mm, and CBR is widely used on barriers and protection layers. Slick surfaces need suitable clamping faces to avoid slippage.

Can I run ISO 12236 on a Mark-10 tester?

Yes for lighter products: the F1505 (about 6.7 kN) and F755 (about 3.3 kN) cover 50 mm/min with 813 mm travel. Heavier geotextiles need a 10 kN or 25 kN universal testing machine.

What capacity is the Universal Grip CBR fixture?

The standard fixture is rated 20 kN, with higher capacities on request. It has 150 mm clamping rings and a 50 mm flat-ended plunger, with clevis or threaded adapters.

Need a fixture, grips or a complete test system for ISO 12236? Contact Universal Grip with your material, specimen size and machine connection and we will quote the right setup.