🏗️ Tensile splitting strength of concrete

Construction PN-EN 12390-6

Overview

The standard PN-EN 12390-6 specifies a method of determining the tensile splitting strength of specimens of hardened concrete. The reference specimens are cast cylinders; cores of at least 75 mm diameter conforming to PN-EN 12504-1 may be tested by the same method, and the use of cubic and prismatic specimens is set out in Annex A. The main change of the 2023 edition (PN-EN 12390-6:2024-04) was the inclusion of the testing of cored specimens; in cases of dispute the reference method is cast cylinders of 150 mm diameter and 300 mm length.

The interlaboratory programme cited in the introduction showed that splitting between ordinary flat platens of the machine gives the same results as special curved platens (retained as an option), that the material of the packing strips affects the strength measured (hence the standardisation on hardboard, which gives the smallest deviations) and that cubes give results about 10 % higher than cast cylinders, while 150 mm cubes give lower results than 100 mm cubes.

In Polish practice 150 mm cubes are still common: the Institute of Building Materials and Concrete Technology (IMBiTB) runs proficiency tests of splitting on 3 specimens of 150×150×150 mm according to Annex A, and the WWiORB technical specifications of GDDKiA for concrete pavements require the test on cast cubes of 150 mm side with a mean of three specimens of at least 3.0 MPa (traffic categories KR1–KR4) or 3.5 MPa (KR5–KR7). It is good practice to determine the density before the test as a check on the compaction.

Method principle

A cylindrical specimen is subjected to a compressive force applied in a narrow strip along its length. The resulting perpendicular tensile force causes the specimen to fail in tension. The load is transmitted through strips of hardboard (EN 316) of a density ≥ 900 kg/m³, a width of (15 ± 1) mm and a thickness of (4 ± 1) mm, longer than the line of contact; the strips are used once only. The load is increased at a constant rate of stress of 0.04–0.06 MPa/s (the rate of loading required R = s·π·L·d/2) until the specimen can carry no greater load. The strength fct = 2F/(π·L·d), where F is the maximum load [N], L the length of the line of contact [mm] and d the cross-sectional dimension [mm]; the result is given to 0.05 MPa.

Applications

• Testing of pavement concrete (the WWiORB technical specifications of GDDKiA: 150 mm cubes, ≥ 3.0 MPa or ≥ 3.5 MPa)
• Assessment of the tensile strength of concrete in structures on cores of Ø ≥ 75 mm
• Quality control of concrete in precasting and in conformity testing
• Proficiency testing of laboratories (Annex A, 150 mm cubes)
• Estimation of the tensile strength for the design of pavements

Key parameters

Standard

Standard number

PN-EN 12390-6:2024-04

Title (PL)

Badania betonu — Część 6: Wytrzymałość na rozciąganie przy rozłupywaniu próbek do badań

Title (EN)

Testing hardened concrete — Part 6: Tensile splitting strength of test specimens

Step-by-step procedure

1. Specimens

   Cylinders conforming to PN-EN 12390-1 and PN-EN 12390-2; cores conforming to PN-EN 12504-1, of a diameter of ≥ 75 mm, without reinforcement. Examine the specimens and record any irregularities. Reject specimens outside the tolerances or correct them by grinding (irregularities) and cutting/grinding (angles).

2. Marking of the plane of loading

   If no centring jig is used, draw two opposite lines in one axial plane, joined at both ends of the specimen, marking the plane of loading.

3. Preparation

   Wipe excess moisture from specimens kept in water. Wipe the bearing surfaces of the jig, the strips, the loading pieces and the platens; remove any loose grains from the surface of the specimen where it makes contact with the strips.

4. Setting up

   Place the specimen centrally in the machine (optionally in the jig) and lay the strips and any loading pieces along the upper and lower lines of the plane of loading. Ensure that the platens are parallel during loading; keep the specimen central at the first application of load with the jig or with temporary supports.

5. Loading

   After the preload (≤ about 20 % of the failure load), increase the load without shock, continuously, at a constant rate of stress of 0.04–0.06 MPa/s (±10 %) until the specimen can carry no greater load. On manual machines correct any fall of the rate before failure; on automatic ones check the constancy of the rate from time to time.

6. Recording and examination

   Record the maximum load. Examine the split specimens and the appearance of the concrete; record any unusual features.

7. Calculation

   fct = 2F/(π·L·d) in MPa, to 0.05 MPa. Where the dimensions depart from those of the standard, the calculation may be based on the actual dimensions. State the type of specimen in the test report: a cast cylinder, a cube, a prism or a core.

Required equipment and apparatus

Health and safety (OHS)

• The splitting occurs suddenly — the guard of the machine and safety goggles, the hands outside the loading zone
• Lay the strips and the loading pieces at zero load; do not adjust the setting under load
• Cutting and grinding of concrete wet or with dust extraction

Frequently asked questions