Abstract
In order to address issues such as large rebound rate, high dust concentration, and low compressive strength of shotcrete when adding liquid accelerator during wet spraying, the factors influencing the efficiency of liquid accelerator were experimentally analyzed. The single-admixture, combination, and orthogonal tests were conducted on the five fundamental raw materials required to develop the new liquid accelerator. The WT-1 type liquid accelerator, which had better adaptability to different kinds of cement, was developed with the mass concentration ratio of 55% aluminum sulfate octadecahydrate, 4% sodium fluoride, 2.5% triethanolamine, 0.5% polyacrylamide, 5% bentonite, and 33% water. Experimental investigation showed that the initial setting time of the reference cement with 6% mass content of this liquid accelerator was 2 minutes and 15 seconds, and the final setting time was 7 minutes and 5 seconds. The compressive strength after 1 day of curing was 13.6 MPa and the strength ratio after 28 days of curing was 94.8%, which met the first grade product requirements of the China National Standard. Compared with the conventional type liquid accelerator, the proposed type WT-1 accelerator is capable of effectively reducing the rebound rate and dust concentration while significantly increasing the compressive strength of the shotcrete.
Highlights
As one of the key techniques to ensure the safety of an underground coal mine roof, anchor and spray support is widely employed in sinking and drifting engineering
The research on the development of low alkaline liquid accelerator began in the early 1990s, when the Nitto Chemical Industry Co
Burge synthetised a type of alkali-free liquid accelerator containing an aluminium salt, corrosion inhibitor, and complexing agent which produced concrete with compressive strengths at 1 day, 3 days, and 28 days of 19 MPa, 32 MPa, and 48 MPa, respectively, but the setting time of concrete was longer [9]
Summary
As one of the key techniques to ensure the safety of an underground coal mine roof, anchor and spray support is widely employed in sinking and drifting engineering. Han et al developed a type JL-1 low alkaline liquid accelerator using sulphur aluminate and neutral sodium salt as coagulant and optimised the product using polymer [17] This accelerator effectively reduced the rebound rate and the strength loss at 28 days was minimal. Due to the rigorous environmental conditions in underground coal mines, problems with the development of shotcrete persist These include low durability, low long-term strength, large rebound rates and dust concentration, poor adaptability for various types of cement, and corrosive damage. These problems significantly affect the health of the workers and the quality of the projects and hinder the promotion of wet shotcreting in mines. It is of particular interest to develop a liquid shotcrete accelerator that is highly efficient, economical, and environmentally friendly
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