Tensile strain causing cracks

First - Uniform tensile load applied to the anchorage zone reduces the load carrying capacity of the anchorage unit and causes a reduction in the maximum tensile strain at cracking. 

In Figure 2 we can observe the variations of tensile strain versus number of cycle for failure. As it can be seen, waste tire reinforeement ean decrease the tensile strain in contrast to non- reinforced sample. In certain bitumen percent, the tensile strain in reinforced sample is less than the tensile strain in non- reinforced specimen. It can be seen that the number of cycle for failure in reinforced sample is more than non - reinforeed sample. Therefore, the reduction in fatigue cracks in reinforced specimen is expected. In samples with 5 and 6 percents of bitumen, the number of cycles for failure is increased signifieantly. It should be noted that with 5 percent of bitumen the application of waste rubber ean cause a better cohesion between aggregates and bitumen. While using 4% bitumen the difference between tensile strain in reinforced specimen and non- reinforced sample is poor. This is because of percent reduction in the bitumen quantity. However, for 5 percent bitumen this difference is noticeable. Although the bitumen percent used is not optimum, therefore, the waste rubber reinforcement, lead to the decrease in tensile strain in contrast to non - reinforced sample. The result has shown in Figure 2. 

Repetitive tensile strain applied during the pavement s service life will initiate the first crack at the underside surface of the bottom asphalt layer (or hydraulically bound layer), which will propagate to the surface causing surface cracking. Similarly, repetitive compressive strain at the surface of the subgrade will cause subgrade deformation, which will eventually spread to the surface of the pavement, resulting in surface or structural deformation. 

Cracks could also initiate from the top asphalt layer and propagate down to the lower asphalt layers. These cracks are non-load related and caused by repeated tensile strains... 

The formation of passive film is most important, because SCC takes place commonly in alloys that are covered by a highly protective film, such as aluminum or steel alloys. Under a tensile strain, the slip plane breaks the protective film as shown in Fig. 4.45a, a small part of the film undergoes dissolution as shown in (b) and later repassivation takes place as in (c). As pointed out earlier, if repassivation occurs too rapidly, corrosion attack would be too small and the crack would propagate slowly. On the other hand, if repassivation occurs very slowly, excessive metal dissolution occurs on the crack tip and sides. This widens and blunts the crack tip, and the crack grovvTh is arrested. The greatest damage is caused by moderate repassivation rates. 

Volume effects of the reactions should also be taken into accotmt (not only in gas corrosion of refractories). The reactions of oxidation of nitride-bonded silicon carbide side lining are positive. The positive volume effect of the reaction may play a positive role, diminishing the open porosity (Table 1.11). However, on the other hand, it may cause tensile strains, which may result in either spalling or cracking of the refractory (Fig. 1.26). 

---