Investigation of mechanical properties, chemical composition and microstructure for composite cementitious materials containing waste powder recycled from asphalt mixing plants

In recent years, there has been a significant increase in the production of waste powder recycled from asphalt mixing plants (hereafter named WP-AMP). However, the current treatment methods, such as landfill or open stacking, result in severe environmental pollution and resource waste. To address this issue, a synergistic activation method involving component adjustment, hightemperature reconstruction, and mechanical grinding was proposed. The composite cementitious materials containing the WP-AMP under various treatment conditions and dosages were prepared. Standard tests were conducted to determine water requirement of normal consistency, setting time, and soundness of these materials. Additionally, flexural and compressive tests were performed on mortar specimens made from the composite cementitious materials at different ages (3 d, 7 d, and 28 d). Furthermore, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) tests were used to analyze the hydration products. A hydration mechanism model for composite cementitious materials containing WPAMP was also established. The results indicate that the optimal activation effect for WP-AMP is achieved through synergistic activation at a calcination temperature of 1150 degrees C. The recommended WP-AMP dosage is 30 % by the weight of cement. At this dosage, the flexural strength of mortar specimens at 3 d and 28 d reaches 4.08 MPa and 10.88 MPa, respectively, while the compressive strength at the same ages reaches 19.25 MPa and 45.20 MPa, meeting the requirements of P & sdot;O 42.5 cement. The intensity of spectrum peaks for hydration products gradually weakens with the increase in waste powder dosage. Particularly, the decrease of Ca(OH)2 and C-SH gel content in hydration products leads to a decline in the mechanical strength of the mortar specimens, as confirmed by the microstructure of hydration products with varying waste powder dosages. The formation of mechanical strength in the composite cementitious material primarily relies on the hydration of cement and some WP-AMP, as well as the morphological filling effect of un-hydrated WP-AMP. This study demonstrates the significant potential of WP-AMP as an auxiliary cementitious material in composite cement.