**3. Types of freeze/thaw deteriorations**

The cement paste combines several types of voids which directly affect its properties. The typical scales of both the voids and the solid phases in the hydrated cement paste are shown in **Figure 2**. While the hydration reaction progresses, the spaces that are initially filled with water, are replaced by the hydration product this residual space is called capillary pore [8]. According to **Table 1**, capillary pores are divided into three groups: small, medium, and large capillary pores.

Since the pores which are smaller than 10 μm in diameter have less influence on permeability, capillary pores are defined as medium and large capillaries, with diameters from 10 nm to 10 μm. The pores in this range would mostly affect the permeability and diffusivity of the cement paste. The hydrated product occupies more volume than the cement particles, and with the development of the hydration reaction, in the gel form continues to expand into the capillary system. Physical deterioration and damage-inducing processes causing cracking and other effects in concrete structures can arise from various causes including freeze/thaw effects. Concrete structures are periodically exposed to the deteriorating effect of freezing/thawing damage and that comes in two types [7, 11, 12]: internal frost damage and surface scaling. The former is caused by the freezing water inside the

### *Concrete Performance in Cold Regions: Understanding Concrete's Resistance… DOI: http://dx.doi.org/10.5772/intechopen.99968*

**Figure 2.**

*Typical dimensions of different phases in the hardened cement paste [7].*


### **Table 1.**

*Classification of pores in hydrated cement paste [9, 10].*

concrete body, as a result of internal frost damage; weight change and compressive strength loss can occur. When the concrete surface comes into contact with weak saline solutions, surface scaling occurs and causes small flakes or chips of concrete on the surface.

The two types of freezing/thawing damages are visualized in **Figure 3**. The adoption of air-entraining admixtures is one of the best solutions for enhancing the freeze/ thaw resistance of concrete [11]; the addition of a specific amount of appropriately sized air voids allows for the accommodation of any increase in water volume in case of freezing. As shown in **Figure 4**, air-entraining agent enhances the concrete's resistance to freeze/thaw cycles, as sample A (with air-entraining) experience less deterioration after 300 freeze/thaw cycles than sample B (without air-entraining) [14].

However, the result of such treatment is not always satisfactory, and the debate is ongoing. Thus, standards have recommended limitations regarding air void parameters, such as the spacing factor between voids and minimum air content of the fresh mixture [15, 16]. The recommended level of air-entraining is about 5%, which already causes a reduction in mechanical properties. It is necessary to compensate for this loss by technological steps to retain the required class of concrete.

**Figure 3.**

*The two main types of internal frost damage [13].*

#### **Figure 4.**

*Specimens A and B after 300 freeze/thaw cycles, where B without air-entraining agent but A with an appropriate air-entraining agent (0.2) [14].*
