## 2 Laboratory Study
### Scaling under Freezing and Thawing According to SS 13 72 44  
The Swedish Standard SS 13 72 44 (2005) is used to determine the resistance to scaling of a horizontal concrete surface exposed to freezing and thawing cycles with or without the presence of de-icing chemicals. Concrete cubes \(150\times 150\times 150\) mm are cured in water \(20\pm 2\)\({}^{\circ}\)C until the 7 th day of age, after which they are placed in a climate chamber at \(20\pm 2\)\({}^{\circ}\)C and \(65\%\pm 5\%\) R.H. At \(21\pm 2\) days of age, a 50 mm slab is sawn of the cube. The specimen is then returned to the climate chamber for 7 days, during which a rubber sheet is glued in all surfaces of the specimen except the sawn surface as test surface. At 28 days of age, the specimen is re-saturated by pouring tap water onto the test surface. After \(72\pm 2\) h, the tap water is removed and the freezing medium (saline solution with 3% NaCl) is applied at a depth of 3 mm. The specimen is thermally insulated with 20 mm of polystyrene, and covered with a tight plastic foil to prevent evaporation. The test set-up is shown in Figure 6. The specimen is then placed in the freezer and the test begins, at the 31 st day of age. Figure 4: Test setup of the Rapid Chloride Migration test. (**a**) Schematic representation [10]; (**b**) Execution of the tests. Figure 5: Test specimens for the Rapid Chloride Migration test after being sprayed with silver nitrate solution. In the freezer, the specimens are subjected to repeated freezing and thawing. The temperature in the freezing medium cycles from -20 \({}^{\circ}\)C to 20 \({}^{\circ}\)C over a period of 24 h, with the temperature exceeding 0 \({}^{\circ}\)C for at least 7 h, but not more than 9 h in each cycle. After 7, 14, 28, 42, 56, 70, 84, 98 and 112 cycles, the scaled-off material is collected and weighted. The results are expressed as accumulated mass of scaled material per area of test surface as function of freeze/thaw cycles. At every 7 th cycle, the scaled material is collected and weighted, and the mass loss per area, m\({}_{n}\) (kg/m\({}^{2}\)), is determined and registered, according to Equation (2),  
\[m_{n}=\frac{M_{n}}{A} \tag{2}\]  
where \(m_{n}\) is the accumulated mass of scaled material (kg) after n cycles and \(A\) is the area of the test surface (m\({}^{2}\)). Figure 7 shows the tests preparation phase, while Figure 8 presents the weighting of the scaled material. Figure 6: Freeze/thaw test set-up. A: Thermo element; B: Protection against evaporation; C: Freezing medium; D: Test specimen; E: Rubber cloth; F: Thermal insulation. [9]. Figure 7: Preparation of salt-frost scaling tests. **Left**: Application of the rubber cloth and silicone sealant on the test specimens; **Right**: Salt-frost scaling test specimens placed in the climate chamber. The first resistance of a concrete quality is evaluated according to the following criteria (Table 2):  
The number of specimens per test, the age at which they were tested and the geometry of the specimen are described in Table 3.  
GGBS concrete presents a slower rate of hydration than Portland cement concrete, which may lead to a lower degree of hydration at the age of 28 days. A lower degree of hydration usually results in a more porous concrete, with lower compressive and tensile strengths. Given that the freeze/thaw test starts at 31 days of age, the salt-frost resistance of concrete with GGBS may be adversely affected by its lower hydration degree, when compared with Portland cement concrete. In order to evaluate the effect of a more prolonged hydration of the concrete specimens with GGBS before being exposed to the freeze/thaw cycles, 3 specimens from each of the mixes with 50% of GGBS replacement and different air content (Mix 3 and Mix 5) were subjected to prolonged pre-treatment. From each cube of these mixes, two slabs (instead of one) were cut and tested. One slab was pre-conditioned according to the standard procedure described in SS 13 72 44. The other slab was kept in the climate chamber for