Abstract:
Wet shotcrete support is widely used in mines as an efficient means of support. However, in the process of pumping concrete using pipes, the problem of pipe blockage is often encountered, which has a serious impact on the safety and efficiency of the construction. The use of air-entraining agents can significantly enhance the fluidity of concrete and reduce the possibility of pipe blockage. In order to investigate the influence of the addition of air-entraining agent on the working performance and pumping effect of shotcrete, a 27 m long shotcrete conveying pipeline was laid based on the wet shotcrete pumping test platform, in which a strain collector was arranged, to investigate the changes in the pumping resistance of the air-entraining wet shotcrete and the changes in the working characteristics of the air-entraining concrete before and after the pumping, and analyze the pressure drop of the pipe conveyance during the pumping process. The results show that when the addition amount (mass fraction) of air-entraining agent is increased from 0.025% to 0.050%, the pipeline pumping resistance of air-entraining wet-sprayed concrete at each measurement point shows a decreasing trend, with a decrease of 8.64% to 18.81%, this is because the air-entraining agent can enhance the fluidity of concrete and reduce the pumping resistance of concrete pipeline transportation; the average unit pressure drop was 18.5 kPa for every 1 m increase in the pumping length of concrete with 0.050% air-entraining agent; the average unit pressure drop was 20.7 kPa for every 1 m increase in the pumping length of concrete with 0.025% air-entraining agen. In addition, the number of pumping cycles had a significant effect on the workability and rheological parameters of the concrete, the air content of the concrete before and after pumping increased by 15.7% and 64.0%, and the relative yield stress increased by 25.1% and 28% for the concrete with 2 pumping cycles and 4 pumping cycles, respectively.