Activation and Application of Wet Shotcrete Concrete with Coal Gasification Slag Aggregate

Abstract

By analyzing the shortcomings of the existing dry shotcrete process in the coal mines and the shortage of natural sand and gravel resources, it is proposed to use coal gasification slag to replace all natural sand and gravel in the preparation of wet shotcrete. Coal gasification slag has alkali-activated cementitious activity, and its strength as an aggregate in cement mortars still shows significant growth after 28d of age. First of all, the gasified slag aggregate cement mortar was mixed with calcium carbide residue to further stimulate its activity, and the effect law of different amounts of calciumcarbide residue on mortar strength was studied. The results showed that the mortar strength increased continuously with the increase of calcium carbide residue admixture, and the mortar strength increased slowly after the admixture reached 8%. With 8% admixture, the flexural strength at 90d age increased by 58.9%, and compressive strength increased by 13.6% compared with 28d age. MIP, XRD and SEM microscopic analyses showed that the incorporation of CCR promoted the alkali-activated cementation reaction of the gasified slag aggregate, eliminated the oriented aggregation of calcium hydroxide at the cement-aggregate interface, improved the interfacial bonding, and significantly reduced the percentage of harmful pores (50-200 nm) and more harmful pores (>200 nm) in the mortar, which explained the microscopic mechanism of the significant increase in mortar strength. Then the mining wet shotcrete was prepared with coal gasification slag as aggregate and calcium carbide residue as cementing material, and the 28d compressive strength reached 34.8MPa, which significantly improved the concrete strength and ensured the stability of the coal mine roadway support.