Slag and Macadam Stabilized with Cement and Fly Ash

The materials used for slag and macadam stabilized with cement and fly ash mixture are as follows:

Cement: P·O 42.5 R Ordinary Portland Cement obtained from Ningxia Horse Racing Cement Co., Ltd., Yinchuan, China;

Fly ash: grade III fly ash produced by Thermal Power Plant in Xixia District, Yinchuan, China;

Slag: slag produced by Thermal Power Plant in Xixia District, Yinchuan, China;

Macadam: macadam from Helan Mountain, Yinchuan, China;

Water: tap water.

The main mineral and chemical compositions of the slag and fly ash were detected by X-ray diffraction (XRD) and X-ray fluorescence (XRF). The XRD test results of the slag and fly ash are shown in Figure 2, and the XRF test results of slag, fly ash, and cement are shown in Table 1. The tests were conducted to evaluate the crushing value, apparent density, packing density, and water absorption rate of 0–4.75 mm slag and graded macadam with four grades of particle size, as shown in Table 2. The performance indicators of the cement are shown in Table 3.
Table 1 shows that the main components of the fly ash and slag are SiO₂, Al₂O₃, and Fe₂O₃ with small amounts of alkaline oxides such as CaO and K₂O. The mass fraction of SiO₂ and Al₂O₃ in the fly ash is relatively large, accounting for ~78% of the total mass, and the loss-on-ignition is less than 10%, which meets the standard for pavement base filling materials. The mass fraction of SiO₂ and Al₂O₃ in the slag is ~70%, and the alkaline oxide accounts for ~14% of the total. Therefore, the slag has high activity and is weakly alkaline. The slag is composed mainly of glass matrix and nCaO·SiO₂. Under the action of water, these alkaline oxides react with SiO₂, Al₂O₃, and Fe₂O₃ to show hydraulic gelling properties [19 (link),20 (link),21 (link),22 ]. Slag and fly ash are suitable as pavement base materials when considering the chemical reaction process and the specimen strength formation mechanism. The slag has a crushing value of 38.4%, which is 19.5% greater than the average crushing value of macadam. Additionally, the water absorption of slag is much higher than that of macadam, which is determined by the porous and uncompacted structure of slag. Table 2 shows that the water absorption and crushing value of macadam are smaller than those of slag, indicating that the compactness of crushed stone is higher than that of slag and has better road performance.