Abstract
A full understanding of the workability and unconfined compressive strength (UCS) of the cemented high-porosity (CHPB) material, made of surface sand, widely distributed in the western mining area, foam, and cementing materials, is important for applying in ecologically fragile mining areas of western China. In this article, the influence of solid content, density grade, sand/binder ratio, and silica fume dosage in binder on workability and strength development of CHPB samples in different curing ages is studied. Test results show that the fresh CHPB mix has good workability, due to the existence of a large number of bubbles. With the increase of density grade, the UCS of the CHPB sample increases exponentially. Workability of fresh CHPB samples significantly decreases with increasing solid content due to the reduction of interparticle distance. For a given mix proportion, the optimal solid content of CHPB samples is 83.7%. The variation of the sand/binder ratio from 3 to 4.5 results in a slight increase of workability and a significant increase of the UCS. Silica fume demonstrates improvement on workability and strength behavior, and the optimal dosage in the binder should not exceed 10%.
Highlights
Underground mining leads to a series of mining damage and environmental problems, such as the destruction of aquifer resources, surface subsidence damage to ground buildings, and surface vegetation death caused by ecological environmental damage [1, 2], which will become more prominent, with the development of coal resources gradually shifting its focus to arid and semiarid areas in western China [3]
Cemented paste backfill (CPB) and cemented tailings backfill (CTB) are widely used in underground metal mining [10]; fly ash, blast furnace slag, silica fume, pozzolanic ash, and alkali-activated materials were used as binder instead of ordinary Portland cement to reduce the cost of CPB mix [11,12,13,14]
It can be noticed that when the solid content is less than 83.7%, the strength gain of cemented high-porosity backfill (CHPB) samples increases with increasing solid content. is can be attributed to the content of calcium silicate hydrate (C-S-H) gel and total porosity within CHPB increasing and decreasing, respectively, with higher solid content and resulting in denser structure and higher strength [28]
Summary
Underground mining leads to a series of mining damage and environmental problems, such as the destruction of aquifer resources, surface subsidence damage to ground buildings, and surface vegetation death caused by ecological environmental damage [1, 2], which will become more prominent, with the development of coal resources gradually shifting its focus to arid and semiarid areas in western China [3]. The main raw materials of cement paste materials, such as coal gangue, tailings, and other solid wastes, are still far less than the mining space, so it is difficult to meet the needs of filling in large-volume goaf, especially in the urgent need of green mining in mining areas of western China. E author uses the surface sand of the mining area as the main raw material, mixes it with cementitious material into slurry, and adds foam to form the cemented high-porosity backfill (CHPB) material, which has the advantages of light weight and low cost [18]. E effects of the raw material ratio and foam expansion rate on curing time and compressive strength of CHPB were studied [24], and the UCS prediction model for foam-cemented paste backfill was proposed. E objectives of this study are to experimentally investigate the impacts of a number of parameters such as solid content, density grade, sand/binder ratio, and silica fume dosage on workability and strength properties of the CHPB matrix
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