Influence Of Polypropylene Fiber And Silica Fume On Permeability And Crack Resistance Of Tunnel Lining Concrete

Tunnel engineering is now widely used in mountain area with the constant expansion of traffic infrastructure and the rapid national economic development. Various kind of engineering problems also come out at the same time. Especially the problems such as tunnel lining seepage and cracking now are becoming common phenomenon in tunnels. Thus, carring out research on how to increase the abilities of waterproof, anti-seepage and anti-crack resistance of tunnel lining from the point of concrete material property itself, is of great significance to improve the performance and durability of tunnel lining structures, and surely will promote its popularization and application of tunnel engineering.This paper adopts a methodology by adding polypropylene fiber (PPF) and silica fume into the common concrete to improve the abilities of anti-seepage and crack resistance of tunnel lining concrete. Systematic indoor experimental and theortical studies are employed to investigate its effectiveness and rationality. The performance of concrete with PPF and silica fume, including mechanical properties, impermeability and early crack resistance, are fully discussed in detail. The influencial mechanism are interpreted from viewpoint of pore structure and fractal characteristic by using SEM photos, fractal theory and mercury intrusion porosimetry. The major conclusions are summarized below:(1)There is an interaction between PPF and silica fume on concrete strength. Silica fume increases concrete strength progressively, while increases brittleness of concrete. PPF is of little influence on concrete strength, much weaker than silica fume. Excessive content of PPF decreases concrete strength. But PPF can restrain the crack propagation, and increase residual stress.(2)Experiments on the impermeability of concrete show that the impermeability of concrete increases by silica fume but decreases by PPF. Experiments on preload impermeability of concrete further explain silica fume increases brittleness of concrete. Besides, there is a good correlation between the impermeability and compressive strength of concrete, therefore increasing the compressive strength is beneficial to concrete impermeability.(3)PPF can restrain the early crack of concrete, and control the deterioration of preload impermeability of concrete. Wide, long and concentrated cracks on plain concrete gradually develop to thin, short and diffuse cracks on PPF concrete with silica fume. PPF can significantly improve concrete early crack resistance performance while silica fume not.(4)Scanning electron microscope (SEM) graphs show the random three-dimension distribution state of PPF, and PPF are closely bonded with concrete matrix, beneficial to common deformation.(5)The decrease of the box-counting dimension from fractal theory illustrates the compactness and impermeability of concrete with silica fume increases gradually. Mercury intrusion porosimetry (MIP) tests furtherly show the average pore diameters and critical pore diameters of concrete with silica fume decrease, and the pore distribution is improved.The experiment results are beneficial to recognize the properties of PPF tunnel lining concrete with silica fume, and may serve as a theoretical basis and reference for tunnel projects.