# Carbon Fiber Traces in Cracked Surfaces of Mortar Prisms
## 4 Fiber Traces on the Cracked Surfaces
The CF 2.0-2 is mostly covered with cemented fiber clusters and fiber-laden mortars, as shown by the dark spots, and divided into seven regions specified by the solid curved lines in Figure 11b: hump (hollow), high hump (deep hollow), hollow (hump), deep hollow (high hump), hump (hollow), hollow (hump) and deep hollow (high hump) for the left (right) image. These seven hump-hollow pairs induce seven dividedness II. There are 12 other traces in the CF 2.0-2: 2 uprootedness, 1 of types I and II, 5 avulsions, 3 of type I and 2 of type II, 4 separations, 2 of types II and III, and one overlay. The nearly vertically aligned cemented fiber cluster in the right image is situated at the bottom of the deep hollow. Its matching area in the left image on the top of the high hump shows no fiber vestige, except a small fiber chunk extended horizontally near the top of the area. Hence, the cemented fiber cluster is avulsion I. The small fiber chunk represents the overlay trace because the cemented fiber cluster in the right image is the same one that induces the avulsion I. The fiber chunk is aligned nearly vertically with the fiber cluster. There are also fiber clusters in the top and bottom of the nearly vertically aligned cemented fiber cluster. In the matching areas at the top and bottom of the left image, only vestiges and cemented fiber bunches are shown. This reveals avulsion II in the top and separation III in the bottom. The smaller cemented fiber bunch is found in the right side of the nearly vertically aligned cemented fiber bunch on the slope side of the high hump. The matching area in the left image shows no fiber vestige. It reveals avulsion I. In the bottom of the smaller cemented fiber cluster, another small fiber cluster in a groove is observed. Its matching area in the left image also shows a fiber cluster. It is a separation III trace. The partly cemented dark areas in the center and top right of the left side image represent fiber clusters. Their matching areas in the right image are a fiber-laden mortar and a cemented fiber cluster. Hence, they reveal avulsion I and separation II traces, respectively. The dark spots are all fiber clusters except the dark area in the top left of the left side image and the long dark line in the top right of the right side image. These are mostly not fibers but broken areas during the breaking of the prism sample into two parts due to the crack. Figure 11: Fiber traces on the cracked surfaces of CF 2.0. (**a**) CF 2.0-1, (**b**) CF 2.0-2. In Table 1, the total numbers of each trace and regions in each prism sample are summarized. It looks as though the numbers of each trace for the two samples of each fiber percentage are too different, but they are actually very similar to each other. Since avulsion, separation and overlay can be considered as one because of the involvement of fiber clusters, if they are summed together, the number of each trace for two samples becomes nearly the same as shown in Table 2, except for the uprootedness. Since the inhomogeneity of the prism is a major factor in reducing the flexural strength and is mainly related to fiber clusters and fiber-laden mortar, the summed number of the three traces and the number of dividedness informs us that the two samples of each fiber contents, except CF 0.5, have almost the same characteristics. Table 1 shows the following:  
1. The overlay and separation type I are rare: No type I separation is shown in the sampled areas specified in Figure 7, but type II prevails. 2. The number of regions between the same fiber percentage prism samples is not too different from each other; they have almost the same number of regions. 3. The uprootedness is decreasing from 10 (CF 0.5) to 9 (CF 1.0), 6 (CF 1.5) and 3 (CF 2.0) as the percentage increases. These numbers indicate that the fiber percentage increase from 0.5 to 1.0 reduces the number of uprootedness just a little. However, when