# Influence of Polypropylene Fiber on Tensile Property of a Cement-Polymer Based Thin Spray-On Liner
## 4 Test Results and Discussions
### SEM Analysis and Discussion  
A scanning electron micrograph of the fracture surface corresponding to a 28-day curing TF-A specimen is shown in Figure 13. Porosities of different diameters occurred on this surface and may have resulted from the following factors: the remaining tiny bubbles, which were probably generated during mixing of the slurry containing the TSL powder and water. The slurry exhibited high viscosity and easily lost fluidity. Therefore, the elimination of bubbles via vacuuming and vibrating was difficult. A cement-polymer based TSL powder was considered, and the loss of water from the specimens during curing may have also contributed to the occurrence of the aforementioned porosities. Porosities is potentially detrimental to the integrity therefore the tensile performance of the TSL. As shown in  
Figure 11: Comparison of elongation at break. Figure 12: Comparison of tensile toughness at different curing. Figure 4, slurries with fiber exhibited a higher viscosity than that of plain TSL. Thus, fiber addition is potentially detrimental to the tensile performances from the perspective of improved viscosity. Fibers in the TSL matrix were lying in random orientation. As shown in Figure 9, rare (only three that were recognized) fibers were broken exactly at the fracture surface of the specimen (see circled regions in Figure 13). Tens of the fibers in the SEM picture seemed to be pulled out from the substrate and this can also be observed in Figure 8c. This phenomenon may owe to the huge difference of the elasticity and plasticity between the PP fibers and the TSL matrix. However, fibers played a role of bridging the matrix at the fracture surface before they were broken or pulled out from the matrix. Thus, fibers lying parallel with the loading direction were beneficial to the tensile strength of the specimen. The pulled out fibers indicated the poor adhesion between the fiber and the matrix. Strong adhesion will absolutely improve the tensile strength owing to the higher stiffness of fibers than that of the TSL matrix. [PERSON] [28] carried out some experiments on the influence of silicone oil on load-reducing fiber-reinforced polymer cement mortar. They observed from SEM that the fibers were pulled out while maintaining its shape as the adhesion between the fiber and matrix was degraded due to the silicone oil. They argued that the reduction in adhesion between the fiber and the matrix had an impact (reduction) on the strength characteristics. However, additional investigation on the influence of adhesion between fibers and matrix on tensile strength of fiber-reinforced materials is needed. On the other hand, there were an amount of fibers that lay fully or partly in the fracture surface. The evidence was the straight openings of different length that can be seen notably at the fracture face, which were marked with red lines (with the length of each other nearby) in Figure 13. Failure process of plain TSL is illustrated in Figure 14. Tiny cracks began to occur when the specimen was loaded Figure 14a. With the growing of load, more cracks were generated and the cracks propagated Figure 14b. The propagated cracks connected with the adjacent ones and finally made the rupture of the specimen Figure 14c. Concerning to the fiber contained specimens, fibers lying perpendicular with the loading direction undoubtedly aggravated the propagation of the cracks and therefore the rupture of the specimens. Hence, specimens with fibers exhibited a quite smaller elongation at rupture than that of plain TSL, and fiber incorporation is detrimental to the deformability of the TSL. Such perpendicular  
Figure 13: Scanning electron micrograph of a fracture surface. fibers were detrimental to the tensile strength, however, this reduction might be overcome by the benefit of the parallel ones in this test. Since the tensile toughness depends on both the stress and deformability, the influence of fibers on tensile toughness were indeterminate for the influence of fiber on the tensile strength and elongation is not coincident.