1. Introduction
Most of the earth’s surface in modern cities is covered by impervious pavement structure, which has led to many urban problems, such as floods, groundwater decline, and urban heat island effects [
1,
2,
3]. The recent torrential rains, rising temperatures, and depletion of water resources around the world are good examples [
4,
5,
6,
7]. All these problems have triggered people’s thinking about modern urban diseases. The pervious concrete pavement structure has been widely studied and applied as a feasible solution [
8]. Due to the porous structure of pervious concrete, it can realize the function of water permeability and ventilation [
9,
10]. It has a very positive effect on solving urban water logging, replenishing groundwater, mitigating surface temperature and realizing urban ecosystem circulation [
11,
12,
13,
14]. Compared with traditional concrete, pervious concrete generally contains no or little sand, and the gradation of coarse aggregate is generally single. Its strength is generally not very high, and can only be used for pavement structures with low-medium traffic loads or non-traffic loads, such as parking lots, sidewalks, parks, etc. [
8,
15,
16,
17].
At present, research on pervious concrete mainly focuses on mix design, strength characterization, permeability property, and internal pore structure [
18,
19,
20,
21,
22]. There are relatively few studies on the fatigue performance of pervious concrete. This is mainly because the fatigue test itself is time-consuming and costly, and there are many other factors affecting the fatigue test, factors from the material itself (gradation, porosity, raw material properties, etc.), factors from the fatigue test conditions (fatigue test mode, stress level, load frequency, load type, etc.) [
8,
17]. As an aspect of the durability of pavement materials, fatigue is a major factor causing structural damage and has an important impact on the structure life [
23]. A lot of research has been carried out on the fatigue problem of traditional concrete. The research on the fatigue performance of pervious concrete was limited, and it needs comprehensive and in-depth research.
Chandrappa and Biligiri [
24] studied the effect of stress level and loading frequency on the flexural-fatigue characteristic of pervious concrete and established the laboratory fatigue model. The results indicated that the stress level and stiffness were significant in affecting the fatigue life, and the loading frequency has little impact on fatigue life. The three-parameter Weibull distribution was suitable for the fatigue life fitting of pervious concrete. Zhou et al. [
25] studied the flexural fatigue behavior of polymer-modified single-sized aggregate pervious concrete under different stress levels (0.65, 0.70, 0.75, 0.80, and 0.85) and stress ratios (0.08, 0.2, and 0.5) with two-parameter Weibull distribution. The results indicated that the fatigue life decreased with the increase of stress level and stress ratio. When the stress level and stress ratio were the same, the fatigue life increased with the decreasing aggregate sizes. Chandrappa and Biligiri [
26] also studied the effect of the pore size and porosity on the fatigue of pervious concrete and established the stiffness reduction model for pervious concrete. It concluded that the porosity at the fractural face was more influential than the volumetric porosity on the fatigue and stiffness reduction. The large pore size has more significant effect on the fatigue life than the small pore size. Pindado et al. [
27] conducted compressive-fatigue experiments on polymer-modified porous concrete with cylinder specimens. The addition of polymer significantly improved the fatigue behavior at the high stress level, but the improvement decreased when the stress level was relatively low. Chen et al. [
28] studied the flexural-fatigue of continuous gradation pervious concrete with different stress ratios. The fatigue equations under different stress levels and equivalent stress levels were established. Based on the established fatigue equations, the load fatigue stress coefficient and tensile strength structural coefficient were obtained.
Fatigue is a complex problem for concrete materials. Compared to conventional concrete, the porous structure of pervious concrete makes its fatigue behavior different from that of conventional concrete. In order to improve fatigue properties, some modifiers, such as polymers and fiber, have been added. In our previous research, it was found that the ground tire rubber, as an elastic material, significantly improved the flexural strain and deformability of pervious concrete. However, it reduced the strength of pervious concrete, especially at the high dosage [
29]. Silica fume, as an excellent supplementary cementitious material, was a by-product of iron alloys in the smelting of ferrosilicon and industrial silicon and usually used to improve the mechanical properties of pervious concrete [
30]. The addition of ground tire rubber and silica fume into pervious concrete can not only achieve waste utilization and reduce cement consumption, but also reduce environmental pollution and obtain economical ways to utilize them. If the ground tire rubber and silica fume are incorporated into pervious concrete at the same time, will the fatigue performance of the pervious concrete be improved with sacrificing the strength? So, in this paper, in order to verify the effect of ground tire rubber and silica fume on the performance of pervious concrete, especially on the flexural fatigue of pervious concrete under different stress levels, the ground tire rubber and silica fume were added into pervious concrete. The static flexural strength tests and flexural-fatigue tests were conducted. The Weibull distribution was adopted to analyze the fatigue data and the fatigue equations were established for pervious concrete. The research outline (shown in
Figure 1) of the study are as follows:
Mix design and pervious concrete beams production for two mixes with same aggregate size, porosity, and water-to-binder ratio
Conducting the static flexural tests and determination of the static flexural strength and flexural strain of two kinds of pervious concrete beams
Selection of the stress level, loading frequency and stress ratio for flexural-fatigue tests
Conducting the flexural-fatigue tests of two kinds of pervious concrete under different stress levels
Analysis of the effect of stress level and modifier on the fatigue property of pervious concrete
Fitting of fatigue-life distribution based on the Weibull distribution and conducting good-of-fit test
Establishment of the fatigue-life equation