# Research on the Pavement Performance of Slag/Fly Ash-Based Geopolymer-Stabilized Macadam
## 1 Introduction  
Cement and lime have been widely used in infrastructure as conventional binding materials for earth and rocks. However, their production consumes a lot of mineral resources, resulting in environmental pollution and excessive emissions of CO\({}_{2}\). At the same time, the secondary development and reuse of large quantities of industrial waste can provide a lot of raw materials for infrastructure construction. Geopolymer is an important type of nonmetallic cementitious material prepared by natural Si-Al materials or industrial wastes such as slag, fly ash, and/or steel slag [1; 2; 3]. Compared with traditional Portland cement, geopolymer exhibit excellent characteristics, including early strength, high strength, low CO\({}_{2}\) emissions, excellent corrosion resistance, and durability [4; 5; 3]. Therefore, many researchers use geopolymers to prepare mortar and concrete and strive to improve their properties. [PERSON] et al. [6] used low-calcium fly ash as raw material to prepare geomeric, and by adding CaO and Ca(OH)\({}_{2}\) to the raw material system, the 28 d mechanical strength of the product increased from 11.8 MPa to 29.2 MPa. [PERSON] et al. [7] carried out indoor experiments and found that with increased activator concentration and maintenance temperature, the compressive strength of low-calcium fly-ash-based geopolymer mortar was increased. [PERSON] et al. [8] studied the influence of activator concentration on the characteristics of fly-ash/slag-based geopolymer concrete. It was found that the developmentof compressive strength was earlier in geopolymer concrete than in ordinary Portland cement, and that it formed satisfactory bond with aggregates. Furthermore, with increased curing time, zeolite phase products played the leading role, resulting in minor drying shrinkage. [PERSON] et al. [9] studied the main factors that influenced the compressive strength of metakaolin-based geopolymer, which supports that the Si/Al (mole ratio) is the most important parameter, followed by Al/Na (mole ratio). The water cement ratio has less influence in the compressive strength of metakaolin-based geopolymer, differing from ordinary Portland cement. [PERSON] et al. [10] studied the change of fluidity and mechanical strength of geopolymers prepared with various water cement ratios. Results showed that the fluidity of geopolymers improved, but the mechanical strength decreased as the water cement ratio increased. Geopolymers are expected to be suitable for serving as a potential cementitious material for stable aggregate base of pavements. According to the Detailed Rules for Highway Base Course Construction Techniques (JTG/T F20-2015), it is required that the stabilized macadam base course shall meet the requirements such as adequate strength, water stability, small shrinkage and deformation and strong resistance to scouring. Therefore, in addition to mechanical properties of geopolymers, many scholars also studied the aggregate adhesion and volume shrinkage of geopolymers. In geopolymer concrete, there is a transition area between slurry and aggregates [11; 12; 13; 14], which controls the strength, resistance to chemical corrosion, permeability and other macro performance of geopolymer concrete [15; 16]. [PERSON] et al. [14] found that both wet curing and early-stage temperature rise curing can improve the transition area to obtain stronger adhesion. [PERSON] et al. [15] found that the increased NaOH concentration in alkali-activator through high solubility of aluminosilicate raw material, and that as a result, the micro structure of the transition area of interface was improved with reduced thickness. [PERSON] and [PERSON] [16] found that when steel slag coarse aggregates were used, the Ca and Mg in aggregates participated in chemical reaction of geopolymers, which brought denser transition areas of interface and stronger adhesion. [PERSON] et al. [17] found that the use of soluble silicate in alkali-activator could effectively improve the adhesion of interface.