# Laboratory Evaluation of Eco-Friendly Pervious Concrete Pavement Material Containing Silica Fume
## 1 Introduction  
In recent years, urban floods have occurred frequently and caused huge casualties and property loss, due to the imperfect urban stormwater management system and large-area impervious pavement [1; 2; 3; 4; 5; 6; 7]. In order to solve this problem, sustainable pavement material--pervious concrete--has been developed. Pervious concrete was first used in the 1970s in the United States [8]. However, it has not been widely used in the world. At the beginning of the 21 st century, pervious concrete regained the attention of researchers and engineers due to the emergence of various urban problems, such as urban floods, urban heat island effects, groundwater decline, etc. [9; 10; 11; 12]. Compared with traditional concrete, pervious concrete, as a porous material with high porosity, has great advantages [13; 14; 15; 16]. First, it is an excellent and effective material in solving urban stormwater. It can allow stormwater permeating into underground, reduce surface water runoff, and improve the slip resistance of roads [13]. On the other hand, water infiltrated from pervious concrete can quickly recharge groundwater and improve urban ecological environments [14]. In addition, its high porosity is able to accumulate more heat, regulate city temperature and humidity, and alleviate heat islandeffect [15]. What's more, the high porosity of pervious concrete can absorb the noise generated by vehicles and create a safe and comfortable driving environment [16]. All these make pervious concrete sustainable and environmentally friendly material. However, some shortcomings still restrict its wide applications [17; 18; 19]. The main disadvantages of pervious concrete are its low strength and poor durability, especially for freeze-thaw resistance in seasonal frozen areas [19]. It therefore becomes the focus of current research how to improve strength and durability of pervious concrete without sacrifice of permeability. Silica fume is the by-product waste of industrial silicon production with high content of SiO\({}_{2}\), and has always been an excellent supplementary cementitious material [20]. Due to their small particle size and large specific surface area, silica fumes can fill in the pores between the cement particles and increase the density and strength of the cement binder. Generally, the SiO\({}_{2}\) in silica fumes is up to 90%, it can react with the cement hydration product (Ca(OH)\({}_{2}\)), and form a pozzolanic C-S-H gel, which improves the property of traditional C-S-H gel and strengths the bonding between the hardened cement binder and the aggregate. On the other hand, the micro-aggregate effect of silica fumes can optimize the microscopic pore structure of the cement paste, and thus increase the strength of the concrete [21; 22]. Based on the superior performance, silica fumes have been widely used in traditional cement concrete as a modifier. The positive effects of silica fume on cement concrete properties have been reported by many researchers. [PERSON]. [23] studied the improvement of silica fumes on cement concrete durability. The results indicated that the addition of silica fumes increased the sulfate resistance of cement concrete. [PERSON] et al. [24] investigated the effect of silica fumes on fresh and aged mechanical properties. In this study, the durability of coral aggregate concrete, the compressive strength, splitting tensile strength, chloride penetration, and micro-hardness of the interfacial transition zone were measured. Compared with the control group, silica fumes significantly improved compressive strength, splitting tensile strength, chloride penetration, and micro-hardness of the interfacial transition zone of coral aggregate concrete. [PERSON] et al. [25] conducted experiments on silica fume-modified engineered cementitious composites; the ductility and compressive strength were tested. The results showed that the addition of silica fumes increased the compressive strength, but decreased the ductility of engineered cementitious composites. [PERSON] et al.