# Study on Seepage Effect of Roadway Based on Polyformaldehyde(POM) Fiber Concrete
## 3 Results and Analysis
### Analysis of Percolation Mechanism of Polyformaldehyde Fiber Concrete  
#### 3.3.1 Interaction Between Fiber Surface and Concrete  
The interior of concrete contains a large number of pores, cracks, and tiny microcracks. A micromorphology diagram of polyformaldehyde fiber and concrete is shown in Figure 7. Polyformaldehyde fiber dispersed uniformly in concrete can form a good bonding effect with it, which enhances the elastic modulus of the concrete. Compared with ordinary concrete, the tensile strength of polyformaldehyde fiber concrete is enhanced, and the pores, cracks, and micro-cracks generated in the initial hardening of the concrete are inhibited. The addition of polyformaldehyde fiber significantly improves the compactness of concrete, effectively blocks the formation of many cracks and pores in the concrete, reduces the porosity of the concrete, and increases the density of the concrete. The mixture of the fiber and concrete makes the polyformaldehyde fiber and concrete form a dense whole and improves the cohesion within the concrete. When subjected to external stress, concrete can transfer stress through fiber, thereby inhibiting the formation and development of the concrete's cracks, avoiding stress concentration, and improving the stability of the concrete. As shown in Figure 8, a three-dimensional network structure can be formed when the polyformaldehyde fibers fill the pores or cracks of concrete, and under the three-dimensional network structure, the polyformaldehyde fibers can effectively inhibit the development of pores or cracks.  
Figure 6: Water seepage height of different fiber mixing specimens.  
Figure 8: Polyformaldehyde fiber’s reticular structure (scale: 50 \(\upmu\)m).  
Figure 7: Polyformaldehyde fiber in concrete (Scale: 1 mm).  
3.2 Analysis of Influence Mechanism of Percolation of Polyformaldehyde Fiber Concrete with Different Lengths and Dosages  
Polyformaldehydefiber is uniformly dispersed in concrete and can form a good bonding effect with it, enhancing the elastic modulus of the concrete, and the polyformaldehydefiber enhances the tensile strength of the concrete, inhibits the cracks generated and expanded in the initial hardening of the concrete, significantly improves the compactness of the concrete, and effectively blocks the formation of numerous cracks and pores inside the concrete [22; 23; 49; 50]. In addition, the internal porosity of the concrete is reduced, and the difficulty of water migration in the concrete is increased, which effectively improves the impermeability of the polyformaldehydefiber concrete [51]. However, with the increase in the length of the polyformaldehydefiber, its dispersion uniformity in the concrete gradually becomes worse, and it becomes more prone to an aggregation phenomenon, which will not only form additional voids, as shown in Figure 9, but also likely cause these voids to be connected to each other, which will reduce the impermeability of the concrete. Therefore, the selection of an appropriate fiber length can ensure that the concrete has excellent impermeability [52].  
With the further increase in the content of polyformaldehyde fiber, the seepage height inside the concrete also increases obviously, which indicates that its impermeability also decreases with the increase in the content. This is mainly due to the fact that a large number of polyformaldehyde fibers are incorporated into the concrete to form entanglement, clumping, etc., which affects the combination of polyformaldehyde fibers and concrete, resulting in the reduction of the concrete's fluidity and the formation of new cracks and voids in the concrete, thus weakening the permeability of the concrete [53]. Therefore, reasonable control of the content of polyformaldehyde fiber can maintain or improve the impermeability of concrete.