## 3 Results
### Concrete Shrinkage Influence on the CSFRC Behavior  
Concrete shrinkage evidently influences CSFRC behavior and hence this influence, which is in fact the influence of carbon fiber reinforcement on concrete shrinkage, will be briefly explained. For this purpose, the similarities with classical reinforced concrete structures are considered [41; 42; 43].  
Concrete without reinforcement is shortened due to shrinkage--\(\epsilon_{sh}\) (Figure 7a)--without causing any stress in concrete members. Since these shrinkage strains do not cause any stress in concrete members, they are not strictly a strain in the classical sense and do not combine with strains resulting from other influences (e.g., external load) causing internal stress in concrete members and, hence, their degradation. For CSFRC, the fibers suppress the development of concrete shrinkage, and the CSFRC elements are shortened as much as the fibers allow. This shortening presents an achieved concrete shrinkage strain, \(\epsilon_{sh,a}\), while, by comparing it to concrete shrinkage strain viewed in Figure 7a, one part of concrete shrinkage strain remains suppressed, and this strain is called the prevented concrete shrinkage strain, \(\epsilon_{sh,p}\) (Figure 7b). The achieved concrete strain, \(\epsilon_{sh,a}\), is a compressive strain, and it causes the appearance of compressive forces in carbon fibers, which are transferred to concrete as tensile forces, \(\overset{\rightarrow}{T}\) (Figure 7b). These tensile forces, \(\overset{\rightarrow}{T}\), cause tensile stresses in concrete members and consequent tensile strain equal to the prevented concrete shrinkage strain, \(\epsilon_{sh,p}\). Hence, the prevented concrete shrinkage strain, \(\epsilon_{sh,p}\), presents strain having the same character as strains from other influences, e.g., from external load, and contributes to the total concrete strain (Figure 7c). The higher the prevented concrete shrinkage strain, \(\epsilon_{sh,p}\), the lower the contribution of the strains from other sources, e.g., external load, to the total concrete strain (Figure 7c).  
Similarly to the autogenous shrinkage strain of unreinforced concrete, \(\epsilon_{sh}\), the prevented concrete shrinkage strain of CSFRC, \(\epsilon_{sh,p}\), also increases over time. This fact can be used to explain the behavior of the specimens tested in the \"life periods\" 2 and 3 (Figure 6c-h). For example, the shrinkage strain of the unreinforced concrete at the ages of 21, 28, 35, 49, and  
Figure 7: Concrete shrinkage development in unreinforced concrete element (**a**) and a CSFRC element (**b**); total strain in a CSFRC element (**c**).  
70 days is 76%, 81%, 85%, 88%, and 95%, respectively, of the concrete shrinkage at the age of 91 days [40]. This increase in shrinkage strain in the unreinforced concrete, \(\varepsilon_{sh}\) (Figure 7a), is followed by an increase in the prevented shrinkage strain in the CSFRC, \(\varepsilon_{sh,p}\) (Figure 7b), and its contribution to the total concrete strain will thereby increase over time while, on the other hand, the contribution of the strain caused by external load will decrease (Figure 7c). This explains why the average ultimate strain is lower at the ages of 70 and 91 days than at the ages of 21, 28, and 35 days and how concrete shrinkage decreases the average ultimate CSFRC strain.  
If this prevented shrinkage strain, \(\varepsilon_{sh,p}\), is sufficiently large, then it can cause the appearance of micro-cracks in the hardened CSFRC (\"life periods\" 2 and 3) before its loading. These micro-cracks caused by \(\varepsilon_{sh,p}\) will dissipate one part of energy introduced in CSFRC by the external load before the appearance of micro-cracks caused by the external load. This fact contributes to the increase in tensile strength (Figure 2) and stress that results in appearance of the first micro-crack (caused by external load--Figure 3) in \"life periods\" 2 and 3.