**5.1 Internal frost damage**

The following procedure is usually used to apply the internal frost damage test:


*According to CEN/TR 15177 [*2*1] each freeze/thaw cycle includes (two hours of cooling, two hours of freezing at − 20°C, two hours of thawing, and 2 hours at + 20°C). Concrete cubes are surrounded by air in the freezing phase, while surrounded by water in thawing phase.*


**Figure 5** shows the time–temperature curve in the centre of the concrete sample, where: 1 / freeze/thaw cycle; 2 / temperature range in the reference; Y / temperature in °C; and X / time in h.

#### **5.2 Surface scaling**

In accordance with CEN/TS 12390–9 [22] (slab test) surface scaling is evaluated. The main idea the test is to determine the scaled materials amount after exposing the concrete surface to 56 freeze/thaw cycles, where the tested concrete surface should be in contact with a 3% NaCl solution. The testing procedure begins by

**Figure 5.** *The time–temperature curve in the Centre of the concrete sample [21].*

**Figure 6.** *Time–temperature curve in the freezing medium at the Centre of the test surface [22].*

cutting concrete cubes in half and using the sawn surface to come into contact with 3% NaCl solution, while the other surfaces must be isolated. For each specimen (half concrete cube), 5 mm thickness of 3% NaCl solution should be placed in contact with the sawn surface sand placed in freezer to start the freeze/thaw cycles. Each freeze/thaw cycle includes (six hours of cooling, six hours of freezing at −20°C, six hours of thawing, and six hours at +20°C). After a specified number of freeze/thaw cycles, up to 56 cycles, the scaled material is collected from the tested surface and weighed, the higher the weight, the higher the scaling.

**Figure 6** shows the time–temperature curve in the freezing medium at the centre of the test surface, where: 1 / temperature range at the centre of the test surface, whereby the time of temperature > 0°C is 7 to 9 h; Y / temperature in °C; and X / time in h.
