ZHANG Bojie¹，YU Li¹，ZHANG Dongsheng²，ZHANG Wenbo¹，YANG Qiuning¹

( 1. School of Civil and Hydraulic Engineering， Ningxia University， Yinchuan 750021， China；2. Department of Civil Engineering， KU Leuven， Bruges 8200， Belgium )

Abstract

Objective With the global emphasis on environmental protection and resource conservation， improving the utilization rate of industrial waste and reducing the exploitation of natural resources have become research hotspots. Fly ash and coal gangue are the major wastes from thermal power generation and coal mining processes. Their large-scale accumulation not only occupies valuable land resources， but also pollutes the environment. Therefore， this study aims to explore the enhancement mechanism of high-content fly ash on the performance of cement-stabilized coal gangue base. It provides a new way for the effective utilization of industrial waste while reducing the exploitation of natural gravel， thereby achieving the dual goals of environmental protection and resource conservation.

Method In this study， high-quality coal gangue was selected as the aggregate to replace traditional natural gravel. Appropriate amounts of cement were selected as the bonding material， and different proportions of fly ash （4%，8%，12%，16%） were mixed. Through accurate calculations and optimized design， the composition of the mixture with different proportions was determined. To evaluate the mechanical properties of the mixture， unconfined compressive strength tests， splitting tests， and compressive rebound modulus tests were carried out. These tests comprehensively reflected the key mechanical indicators of the mixture such as compressive strength， splitting strength， and elastic modulus. To evaluate the durability of the mixture， water stability tests and freeze-thaw tests were carried out. The water stability tests simulated the performance changes of the mixture under water immersion， while the freeze-thaw test simulated the performance changes after freeze-thaw cycles in cold areas. The study also discussed the strength formation mechanisms of mixture with different fly ash content.

Result When fly ash was added to the cement at a content of 4% and 8%， a pozzolanic reaction occurred between the cement and fly ash， producing new hydration products. These newly generated hydration products were very fine and could effectively penetrate into the internal pores of the binding materials， serving to fill and reinforce them. This filling not only enhanced the compactness of the mixture， but also significantly improved its overall strength， providing a more stable foundation for construction. As the fly ash content further increased to 12%， the properties of the mixture changed significantly. Under external loads，the mixture showed excellent deformation resistance， with the deformation amount reaching its minimum. This indicated that at a specific fly ash content， the stability of the mixture was significantly improved， enabling it to withstand greater external pressure and changes. When the fly ash content increased to 16%， the micro-aggregate effect of fly ash began to show its unique advantages. This effect ensured that the fly ash particles were more evenly distributed in the mixture， enhancing their cohesion and thereby greatly improving the mechanical properties of the mixture. Experimental data showed that at this content level， the unconfined compressive strength and splitting strength of the mixture were significantly improved after 28 days of curing.

Conclusion This study showed that with the increase of fly ash content， the unconfined compressive strength and splitting strength of the cement-stabilized coal gangue base mixture gradually increased， while the compressive rebound modulus first increased and then decreased. This indicated that an appropriate amount of fly ash can improve the mechanical properties of the mixture， but an excessive content may lead to a decline in its performance. In addition， although the incorporation of fly ash slightly reduced the water stability and frost resistance of the mixture， it still met the overall engineering requirements. By analyzing the hydration reactions and microstructural changes of the mixture， it was found that the addition of fly ash promoted the hydration reaction of the cement， generating more hydration products. These hydration products filled the gaps between aggregates and improved the compactness and strength of the mixture. Moreover， the addition of fly ash also improved the pore structure of the mixture and reduced the number of large and interconnected pores. Therefore， the application of high-content fly ash in cement-stabilized coal gangue base has broad prospects. It not only increases the utilization rate of industrial waste and reduces the exploitation of natural resources， but also provides high-performance building materials for road engineering and other fields.

Keywords：coal gangue； fly ash； mechanical property； durability

DOI：10.13732/j.issn.1008-5548.2024.04.004