🏗️ Freeze-thaw resistance of concrete — the ordinary method (the F grades)

Construction PN-B-06265

Overview

PN-EN 206 defines neither a method of testing freeze-thaw resistance nor criteria for assessing it — in Poland that is the purpose of the national supplement PN-B-06265, which gives a method of testing freeze-thaw resistance and criteria of assessment defining the grades and categories of freeze-thaw resistance. The so-called ordinary method verifies the freeze-thaw resistance grade F designed for the concrete; the grade corresponds to the index N equal to the number of years of service of the structure expected (up to 25 years — F25, 26–50 — F50, 51–75 — F75, 76–100 — F100, 101–150 — F150, 151–200 — F200, more than 200 — F300). The method takes into account both the internal damage of the concrete, characterised by the strength of the specimen, and the external damage assessed visually and through the loss of mass. The present description is based solely on the literature (a data sheet of Heidelberg Materials, the WWiORB technical specifications of GDDKiA) — the text of the standard was not available; before implementation the current edition PN-B-06265:2022-08 with Az1:2025-08 is to be consulted.

The freeze-thaw resistance grade is attained if, after the required number of freeze-thaw cycles, the specimens show no cracks, the total mass of the losses (damaged corners and edges, spalling) does not exceed 5 % of the mass of the specimens before the test, and the fall of the compressive strength relative to the specimens not frozen does not exceed 20 %. Besides the ordinary method, PN-B-06265 provides for a surface method (56 cycles with a 3 mm layer of deionised water or of 3 % NaCl solution on the surface of the specimen, the assessment of the mass of the scaled material), used together with PKN-CEN/TS 12390-9 for pavements of cement concrete.

In pavements of cement concrete the WWiORB technical specifications of GDDKiA require, for the traffic categories KR4–KR7, the testing of the resistance of the concrete to the action of frost in accordance with PN-B-06265 after 150 cycles (freeze-thaw resistance F150): a loss of mass of the specimen of not more than 5 %, a fall of the compressive strength of not more than 20 %.

Method principle

The freeze-thaw cycles consist in freezing the whole specimen in air and thawing it in water in turn; a complete cycle lasts at least 6 h. From one batch of concrete 12 cubic or cylindrical specimens are tested (as for the compressive strength test, or regular specimens cut from a structure or a product; the minimum side or diameter is 100 mm), kept at a temperature of 18 ± 2 °C at a relative humidity of more than 90 %. Six specimens stay in water throughout the test as reference specimens; six are subjected to the cycles. The result: the mean loss of mass ΔG = (G1 − G2)/G1 · 100 % (G1 — the mean mass of the saturated specimens before the first freezing, G2 — after the last thawing) and the mean fall of strength ΔR = (R1 − R2)/R1 · 100 % (R1 — the mean strength of the reference specimens, R2 — of the specimens tested after the last thawing, both in the water-saturated state).

Applications

• Verification of the freeze-thaw resistance grade designed for a concrete (F25–F300) in the exposure classes XF
• Pavements of cement concrete for the traffic categories KR4–KR7 (the WWiORB technical specifications of GDDKiA: F150, a loss of mass of ≤ 5 %, a fall of strength of ≤ 20 %)
• Structural concrete in road engineering structures (testing of the resistance to the action of frost according to the specifications)
• Assessment of the freeze-thaw resistance of concrete cut from a structure or a product (regular specimens of ≥ 100 mm)

Key parameters

Standard

Standard number

PN-B-06265:2022-08

Title (PL)

Beton — Wymagania, właściwości użytkowe, produkcja i zgodność — Krajowe uzupełnienie PN-EN 206+A2:2021-08

Title (EN)

Concrete — Specification, performance, production and conformity — National supplement to PN-EN 206+A2:2021-08 (working translation)

Step-by-step procedure

1. Specimens

   Prepare 12 specimens from one batch of concrete (cubes or cylinders as for compression, a size of ≥ 100 mm; regular specimens cut from a structure or a product are permitted). Keep them at 18 ± 2 °C at a relative humidity of more than 90 %.

2. Saturation

   Saturate all the specimens with water for at least 7 days.

   ⏱ Time: ≥ 7 days

3. Division into sets

   Leave six specimens in water at a temperature of 18 ± 2 °C throughout the test (the reference specimens). Wipe the water from the other six and weigh them to 0.2 %.

4. Freezing part of the cycle

   Freeze the specimens under test in air at a temperature of −18 ± 2 °C for at least 4 h.

   ⏱ Time: ≥ 4 h • 🌡 Temperature: −18 ± 2 °C

5. Thawing part of the cycle

   Thaw them in water at a temperature of +18 ± 2 °C for 2–4 h; a complete cycle lasts at least 6 h. Repeat the cycles up to the number following from the F grade (for example 150 cycles for F150).

   ⏱ Time: 2–4 h • 🌡 Temperature: +18 ± 2 °C

6. Assessment after the last cycle

   After the last cycle weigh the specimens, examine them for cracks and for losses of corners, edges and spalling, and then test the compressive strength of the tested and of the reference specimens in the water-saturated state.

7. Calculation and assessment

   ΔG = (G1 − G2)/G1 · 100 %, ΔR = (R1 − R2)/R1 · 100 %. The F grade is attained when there are no cracks, ΔG ≤ 5 % and ΔR ≤ 20 %.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The freezing chamber at −18 °C — insulated (cold-protective) gloves when taking the specimens out; the specimens are wet and slippery
• Specimens of 100–150 mm are heavy and after the cycles may have loose corners — handle them carefully and do not damage them before weighing
• Strength testing in the machine — the guard, goggles, the hands outside the loading zone

Frequently asked questions