ASTM C1609
Third-Point Beam Fixture for Fiber-Reinforced Concrete
ASTM C1609 Bend Fixture – Universal Grip Data Sheet (PDF)
ASTM C1609 is the standard test method for flexural performance of fiber-reinforced concrete using a beam with third-point loading. Plain concrete snaps at first crack; fiber-reinforced concrete keeps carrying load as the fibers bridge the crack, and that post-crack behavior is what designers of slabs-on-ground, shotcrete linings and precast elements need. C1609 captures it as a full load–deflection curve under closed-loop deflection control. Universal Grip builds the third-point fixture the method describes: rolling, rotating supports and load points, an adjustable span for both standard beam sizes, and a yoke that measures net mid-span deflection independent of seating and support movement.
What ASTM C1609 Measures
From the load–deflection curve of a simply supported beam under third-point loading, the method determines the first-peak and peak loads and their corresponding stresses using the modulus-of-rupture formula, the residual loads at specified net deflections (reported as residual strengths such as f600 at L/600 and f150 at L/150), and toughness as the area under the curve up to an end-point deflection of L/150, together with the equivalent flexural strength ratio. The standard describes residual strength as an engineering stress on the gross uncracked section, not a true stress. Preferred beam sizes are 100 x 100 x 350 mm (4 x 4 x 14 in.) on a 300 mm (12 in.) span and 150 x 150 x 500 mm (6 x 6 x 20 in.) on a 450 mm (18 in.) span; results depend on specimen size and fiber alignment, so sizes should not be mixed when comparing mixes.
How the ASTM C1609 Test Works
Cast and moist-cure beams of one of the preferred sizes, then measure width and depth at the fracture section after the test for the stress calculation.
Set the support span to three times the beam depth and the loading head so the two load points sit at the third points of the span.
Fit the yoke to the beam at mid-depth over the supports and mount the displacement transducers on both sides so net deflection is averaged and twist is cancelled.
Run the test in closed-loop control of net deflection: a slow rate up to a deflection of L/900, then a faster rate up to the end point of L/150.
Record load and net deflection continuously through the first peak, the drop at cracking and the post-crack region.
Calculate first-peak and peak strengths, residual strengths at L/600 and L/150, toughness to L/150 and the equivalent flexural strength ratio.
Report with beam size, span, fiber type and dosage, since the values are size-dependent.
Specimens and Setup
Use a closed-loop, servo-controlled testing machine; the standard requires net-deflection control, and an open-loop machine cannot hold the curve through the load drop at first crack.
The yoke must measure deflection relative to the beam at the supports, not crosshead travel, so seating and support deformation are excluded.
Transducers need enough stroke to reach L/150 — 3 mm on a 450 mm span — plus margin; 0.12 in. minimum is the usual guidance.
Keep supports and load points free to rotate and roll so no longitudinal restraint builds up as the beam deflects.
Net deflection rates for the 150 mm beam are in the range of about 0.04–0.10 mm/min up to L/900 and 0.05–0.30 mm/min after; set them from the current edition's table for your beam size.
Universal Grip ASTM C1609 Fixture
Third-point loading head with rolling, rotating load points
Supports free to rotate per C1609 requirements
Yoke for net deflection measurement at mid-span, with mounts for two transducers
Adjustable span for the 300 mm and 450 mm standard beam sizes
Steel construction with corrosion-resistant finish
Load capacity 100 kN standard; higher capacities on request
Clevis pin or threaded adapters for closed-loop, deflection-controlled frames
Applications
Steel and synthetic fiber-reinforced concrete
Slabs-on-ground, shotcrete and precast design
Fiber dosage and product comparison
Specification compliance testing
Related Standards and Products
Send us your specimen dimensions, required capacity and machine connection through our contact page and we will quote an ASTM C1609 third-point beam fixture. Request a quote
ASTM C1609 FAQ
What is the difference between ASTM C1609 and ASTM C78?
C78 is a third-point flexural strength test for plain concrete that stops at rupture and reports a single modulus of rupture. C1609 uses the same loading geometry but runs under net-deflection control past first crack to L/150 and reports residual strengths and toughness, which only make sense for fiber-reinforced concrete.
Why does C1609 require closed-loop control?
At first crack the load drops suddenly. A machine controlling crosshead position or load will overshoot and the post-crack portion of the curve, which is the point of the test, is lost. Controlling on net deflection measured by the yoke keeps the test stable through the drop.
What is the yoke for?
It carries the displacement transducers on a frame attached to the beam at the supports, so the measured deflection is the beam's own bending at mid-span and not crosshead travel, seating of the beam on the rollers or deformation of the fixture.
Which beam size should I use?
150 x 150 x 500 mm on a 450 mm span is preferred when the fibers are longer than about 50 mm or when the results will be used for member design; 100 x 100 x 350 mm on a 300 mm span is acceptable for shorter fibers and reduces specimen weight. Do not compare results across sizes.