An industrial floor resting on the ground fails in bending: racks, forklifts and trucks bend it, and its underside cracks in tension. That is why these floors are specified by their modulus of rupture (MR), the flexural strength of the concrete, and are controlled by testing beams, not only compression cylinders. In the construction oversight of Bodegas Centurión, in Barranquilla, DDES tracked 55 beams between September 2024 and April 2025.
What a beam test measures
The beam is a concrete prism supported at its ends and loaded at the third points of its span until it breaks (ASTM C78 test). The result, in MPa, is directly the flexural tensile strength of the concrete: the same value used to design the thickness of a pavement or an industrial floor.
The cylinder, on the other hand, measures compression (f′c). The two strengths are related, but not exactly. The NSR-10 estimates the modulus of rupture as fr = 0.62 λ √f′c (equation C.9-10), a formula meant for computing cracking and deflections of beams, not for accepting a floor: with it, a 28 MPa concrete would have an fr of about 3.3 MPa. To guarantee 4.2 MPa, the safe way is to measure it.
What was specified at Centurión
- Interior floors of the warehouse and the administrative area: MR 3.9 MPa (the first pours, with accelerated concrete, MR 4.2 MPa).
- Truck yards, ramps, side road and drinking-water tank slab: MR 4.2 MPa.
- Structure (foundations, columns, mezzanine slabs and stairs): f′c 28 MPa concrete, controlled with cylinders.
The results
| Specified MR | Beams with a 28-day result | 28-day average |
|---|---|---|
| 3.9 MPa | 15 | 4.68 MPa (120%) |
| 4.2 MPa | 39 | 4.94 MPa (118%) |
On average, the beams reached 118% of the specified modulus. Three samples fell short at 28 days (93%, 95% and 97%), but no average of three consecutive results dropped below 103%, and the sample that was also tested at 56 days reached 127%.
What else is checked on a floor
Strength is only part of it. At Centurión, the record also notes the slump of every truck: between 15 and 24 cm, typical of a fluid floor concrete. As general practice, a floor also calls for control of the slab thickness, the granular base, the contraction joints and the curing: a strong floor with late-cut joints or poor curing cracks all the same.
See the full project at Bodegas Centurión and how structural concrete is accepted in concrete cylinder tests.
Sources: concrete control record of the DDES oversight at Bodegas Centurión; NSR-10, equation C.9-10; ASTM C78.
Frequently asked questions
Why is an industrial floor tested with beams?
Because a floor on the ground fails in bending and is designed with the modulus of rupture of the concrete. The beam test (ASTM C78) measures that strength directly; the cylinder measures compression, which is only approximately related to bending.
What modulus of rupture is used for a warehouse floor?
The floor design sets it according to its loads. At Bodegas Centurión, 3.9 MPa was specified for interior floors and 4.2 MPa for truck yards, ramps and roads.
