3.4.1 SEM text
In order to clarify the pore size distribution of the prepared specimens in different groups, SEM test is carried out for statistical analysis. Bubble holes are uniformly selected from the test surface of the specimens for measurement and Figures 8~10 show the pore size distribution results.
Figure 8(a) is the SEM image of foam concrete in Group O, and Figure 8(b) shows the corresponding pore size distribution. As displayed in Figure 8(b), most of the bubble holes in group O have a pore size of 0-400 µm, accounting for 86.85%, and there are no holes larger than 800 µm. The maximum and minimum pore diameters are 66 µm and 796 µm respectively, and the average is 260 µm. The SEM images of the specimens after doping with 0.6 wt.% carbon fiber and the corresponding pore size distribution are shown in Figure 9. The pore size of the C2 group is also concentrated within 400 µm as that of the O group, accounting for 83.78%. However, the percentage of pore size within 200 µm is 43.69%, which is greater than that of group O (38.50%). Therefore, the small pore proportion of the foam concrete can be increased by adding carbon fiber. The minimum pore diameter is 52 µm, which is 14 µm lower than that of group O. This is because during incorporating the foam and the slurry, the carbon fibers evenly dispersed in the slurry effectively split the bubble holes, thus decreasing the size of the bubbles and making the distribution uniform. Furthermore, the random distribution of carbon fibers in the cement slurry can provide support to the slurry, so that the foam mixed into it can remain stable during the hardening of the cement slurry.
Figure 10(a) is the SEM image of foam concrete in group C2S1, and Figure 10(b) shows the corresponding pore size distribution. As exhibited in Figure 10(b), the proportion of pores ranging from 0 to 400 µm is 77.83%, which is 5.95% lower than that of group C2. In group C2, most small bubble holes have the size of 0-200 µm, while those in group C2S1 are between 200 and 400 µm. It indicates that adding 2wt.% graphite can make the pore size distribution of carbon fiber specimens shift to the right. The reason may be that with the addition of graphite and carbon fiber, the slurry becomes too thick due to their dual effects on fluidity, making foams easily broken when mixed with foam. This extends the time required for the cement slurry to mix evenly with the foam.