MaTestLab > ASTM Methods > ASTM C78 Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)
Last updated 12th June 2025
ASTM C78 Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)
ASTM C78 offers a commonly accepted technique to ascertain the model of the concrete disintegration, therefore representing its tensile strength in bending. A conventional testing approach for flexural strength of concrete (employing simple beams with third-point loading). Where resistance to flexural stress and cracking is paramount, this approach is especially vital for assessing the concrete used in pavements, beams, slabs, and other structural components. By putting the load on the third digit with a simply supported beam, this test offers a trustworthy estimate of concrete's ability to resist bending failure, therefore becoming an essential tool in structural design validation and quality control.
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ASTM C78 Introduction
The ASTM C78 test method describes the standardized method of testing the concrete beam under the third-point loading configuration, giving consistent and reliable results. For applications like pavement, slabs, and beams, flexural strength is an important measure for ascertaining the structural integrity and performance of concrete. Where tensile stress considerations become key, this testing procedure is most suitable for determining the bending-load capacity of concrete.
ASTM C78 Test Method Procedure
Support Setup
Place the concrete beam on two rounded support rollers spaced at a standard span (typically 18 in. or 457 mm).
Loading Arrangement
Position two loading rollers symmetrically at the third point of the span length.
Loading Process
Apply load continuously and without shock at a constant rate until failure occurs.
Failure Observation
Ensure the specimen fails in flexure between the loading points, avoiding shear failure or failure outside the third-point region.
Calculation
Determine flexural strength (modulus of rupture) using the maximum applied load, span length, and specimen dimensions via the formula: R = (PL)
ASTM C78 Equipment and Sample Preparation
Specimen Details
Prismatic concrete beams, typically 6 in. × 6 in. × 20 in. (150 mm × 150 mm × 500 mm)
Specimen Preparation
Cast in standard molds, moist cured for 28 days or as specified
Specimen Dimensions
Span length: 18 in. (457 mm) typically; beam must have 2:1 span-to-depth ratio minimum
ASTM C78 Results and Interpretation
The blow is described in Sai or MPA and reflects the flexural strength of the concrete. High values indicate better resistance to cracking under bending stress. Variations in results may arise from inconsistent treatment, surface flaws, or improper alignment during tests. The result is used to evaluate the durability of solid structures under quality control, pavement design, and flexural loading
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ASTM C78 Related Test Methods
The compressive strength of concrete cylinders is usually determined by ASTM C39, which gives a clear indication regarding the general load-bearing capability of the material. The splitting tensile test provided in ASTM C496 is a testing method that can be used for cylindrical specimens when tensile strength is determined indirectly.
ASTM C78 Applications and Industry Use
Design and quality inspection of concrete pavements, slabs on grade, beams, and structural components frequently use this testing technique. It is especially pertinent in precast concrete components, industrial flooring, airport runways, and highway building, everywhere flexural performance is a major design factor.
ASTM C78 Materials Commonly Tested
Normal-weight and lightweight concrete beams, including those containing supplementary cementitious materials (SCMs), fibers, or admixtures, are applied. This is also suitable for structural lightweight aggregates or mixed aggregate systems.
ASTM C78 Common Challenges and Troubleshooting
Invalid results can arise from misaligned loading points, incorrect curing, and dimensional inaccuracies. It is necessary to make sure the beam fails inside the middle third span. Surface fissures or gaps can serve as early failure sites, therefore lowering strength values. Accuracy depends on machine calibration and correct roller placement.
ASTM C78 Safety and Best Practices
Testing necessitates extreme loads and possible sudden failure of samples. Safety shields and PPE, including goggles, gloves, and steel-toed boots. Make certain all equipment is well calibrated and kept up to avoid errors or accidents.
ASTM C78 Importance
For concrete elements under bending stresses, flexural strength is critical. This method offers a repeatable, industry-standard technique to assess this feature, helping engineers guarantee the structural durability and life span of concrete constructions.
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Please contact us for a detailed quote for your astm c78 testing needs. Cost incurred to carry out different astm c78 testing methodology depends on the type of raw material; number of samples, coupons, or specimens; test conditions, turn around time etc. Costs of some ASTM testing methods start from $100 and the final value depends upon the factors listed above. Please contact us for the best and latest prices.
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The required number of samples or specimens should comply with the procedure given in the astm c78 standard. However, the MaTestLab operations team can assist you for your special requirements once you share your testing details with us.
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The turnaround time for astm c78 test methodology depends upon the test procedure mentioned in the standard test document. However, we at MaTestLab understand your research requirements and hence try to get your test completed within the least possible time.
Where can I get the astm c78 tested?
You can share your astm c78 testing requirements with MaTestLab. MaTestLab has a vast network of material testing laboratories, spread across the USA and Canada. We support your all material testing needs ranging from specific astm c78 test to various testing techniques.
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