ASTM C78/C78M is the standard test method used to determine the flexural strength (modulus of rupture) of concrete beams using third-point loading. It is most commonly applied to pavements, slabs, bridge decks, and other concrete elements where bending performance governs design.
This test measures how concrete performs in tension under bending, which is often more representative of in‑service performance than compressive strength alone. Many CMT and geotechnical labs manage ASTM C78 results alongside other concrete tests using modern field and lab data management software built specifically for CMT workflows.
Flexural strength testing plays a growing role in:
As infrastructure projects demand faster turnaround and higher data quality, labs need ASTM‑compliant workflows that minimize manual effort and reduce risk.
ASTM C78/C78M: Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third‑Point Loading) defines the procedure for determining the modulus of rupture (MOR) of molded or sawed concrete beams.
Test objective: Determine the tensile strength of concrete in bending.
Common specimen sizes
Typical applications
Because many pavement designs are governed by flexural performance, ASTM C78 is a core quality control test for DOT and infrastructure work.
Accurate flexural strength results depend on capturing the right measurements and applying the correct calculations.
| Parameter | Description | Example Field Type in Aldoa |
|---|---|---|
| Date Sampled / Tested | Tracking specimen age | Date field |
| Age | Calculated from sampling to testing | Auto-calculated field |
| Average Depth (d) | Average cross-section depth of beam | Number field (in) |
| Average Width (b) | Average cross-section width of beam | Number field (in) |
| Span Length (L) | Support span for testing | Number field (in) |
| Maximum Load (P) | Force applied until fracture | Number field (N) |
| Distance Between Fracture | Location of fracture relative to supports | Number field (in) |
| Modulus of Rupture (MOR) | Calculated flexural strength = (P × L) ÷ (b × d²) | Calculated field |
Without modern software, these values are often handwritten, retyped, and recalculated manually, which increases the risk of error.
For third‑point loading with fracture occurring in the middle third of the span, ASTM C78 uses:
R=P×L / BxD^2
Where:
Correct unit handling is essential. For example, if P is in pounds and dimensions are in inches, R is typically given in psi. If P is in Newtons and dimensions are in millimeters, the result is in MPa.
In Aldoa, this equation is built into the digital form so technicians do not have to perform any manual calculations.
ASTM C78 and ASTM C39 are both widely used concrete strength tests, but they measure different performance characteristics. ASTM C78 evaluates flexural strength using beam specimens and third-point loading, while ASTM C39 measures compressive strength using cylindrical specimens under axial load.
Most CMT labs run both tests as part of pavement and structural concrete programs, which is why Aldoa supports compressive strength testing and flexural strength testing within the same connected platform.
A complete report typically includes:
Labs relying on paper, Excel, or legacy systems often face:
These challenges often extend beyond flexural testing, which is why many labs evaluate a purpose-built LIMS designed for construction materials testing and geotechnical labs rather than generic laboratory systems.
Aldoa provides a single, connected workflow for flexural strength testing across field and lab teams.
Example of a digital ASTM C78 flexural strength test form in Aldoa, showing specimen dimensions, applied load, and automatically calculated modulus of rupture.
Example of a client-ready ASTM C78 flexural strength report generated in Aldoa.
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This reporting approach is consistent across concrete, soils, and aggregate tests, giving teams a standardized way to deliver client-ready test reports without manual formatting.
| Benefit | Impact on the lab and project team |
|---|---|
| Faster workflows | Less time spent on manual entry and MOR calculations |
| Higher accuracy | Automated formulas and validations reduce human error |
| ASTM consistent reporting | Standardized reports support DOT and QA requirements |
| Real time visibility | Engineers and PMs see results as soon as tests are completed |
| Stronger client relationships | Faster, clearer reports improve trust and repeat work |
Infrastructure programs, DOT performance specifications, and tighter quality expectations have increased the importance of flexural strength testing. Pavement designs, fast track construction, and performance based specifications all rely on accurate flexural data.
Labs that modernize their C78 workflows gain:
Aldoa helps labs deliver that level of performance by combining field data collection, automatic calculations, and reporting in a single platform designed for end-to-end concrete testing workflows.
The ASTM C78/C78M flexural strength test is a cornerstone of concrete performance evaluation. The test itself is standardized and well understood. The friction comes from how data is captured, calculated, and reported.
With Aldoa, geotechnical and CMT firms can:
By reducing errors and saving time, Aldoa lets your team focus on delivering accurate, reliable test results rather than managing spreadsheets.
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