**8.2 Fly ash**

Fly ash is one of the most popular mineral additives that used in the concrete industry, it helps in improving the consistency of fresh concrete and reducing the hydration heat. The use of fly ash has been investigated extensively in the literature and it is found that it is beneficial for the durability of concrete, and it enhances the permeability properties. Replacement cement by over 40% of fly ash causes a serious reduction in the service life. Fly ash has a low carbon content and very variable properties, thus its effect on freeze/thaw resistance is not clear. Despite of the complexity of defining the influence of fly ash on freeze/thaw resistance, it is favorable due to its positive effect on the long-term durability of concrete [47, 48, 55].

### **8.3 Blast furnace slag**

Blast furnace slag is a by-product formed during pig iron production. The incorporation of ground blast furnace slag into concrete is very beneficial because of its positive effect on the durability properties [56]. Blast furnace slag has a positive effect on many engineering properties, such as bleeding, consistency of the fresh mixture, the heat of hydration and permeability. The relatively high bulk density of a cement matrix modified by slag frequently leads to a decrease in the frost resistance, however, the results of experimental studies are inconsistent [57]. This could be partly a result of the different experimental procedures and also because of the use of modifying agents such as plasticizers, which significantly affect the character of the porous system.

#### **8.4 Silica fume**

Using silica fume as a substitution of cement usually does not exceed 5–10%. Therefore, its effect on the frost resistance seems to be marginal, provided the air content is maintained on a level, that is high enough. Besides, the long-term tests indicate, that a negative effect occurs only when the amount of silica fume exceeds 10% [13], **Figure 13**.

### **8.5 Metakaolin**

Metakaolin has been generally used as a filler or supplementary cementitious material in concrete, and it was proved to be able to enhance its performance.

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

**Figure 13.** *Result of exposure tests on the long-term behavior of air-entrained concrete containing fly ash, blast furnace slag and silica fume [13].*

The introduction of metakaolin into concrete as a supplementary cementitious material can improve its freeze/thaw resistance significantly. Where metakaolin decreases the total porosity and improves the pore structure of concrete which is directly related to the mechanical properties [58]. It was found that the freeze/thaw resistance corresponds to the content of insoluble hydrates in the cement paste. However, the used binder system also significantly affects the character of the concrete capillary system. In general, modern concrete mixtures with reduced water to cement ratio exhibit increased frost resistance; nevertheless, this approach tends to increase the autogenous shrinkage, which could cause propagation of surface cracks during hardening in the case of a poor curing regime, resulting in the reduction of the durability and especially the frost resistance [51, 55].
