The effect of three-stage ionization on the structure formation of a concrete mixture during shotcrete

Abstract

The article deals with the problem of reducing rebound and dust formation, as well as increasing the strength of shotcrete. It is known that with “dry” shotcrete, the rebound is especially significant, since the mixture does not have time to acquire sufficient adhesive properties when mixing different phases. As a result, there is an irreparable loss of a significant part of the applied material. The formation of crystal centers that ensure the strength of concrete also occurs slower than with “wet” shotcrete, since the contact of the binder with water in the nozzle of the shotcrete machine is too short. This leads to a decrease in strength characteristics, slowing down the setting of shotcrete. To solve this problem, a method was developed for applying a concrete mixture to enclosing structures using a previously patented experimental nozzle and electrostatic treatment. This method, for a long time, has been successfully used for painting various surfaces, and its modernization will allow the introduction of electrostatics in shotcrete. A systematic ionization of the binder and then the finished mixture is proposed, as a result of which the shotcrete will be attracted to the shotcrete structure along the power lines. To obtain empirical data and confirm theoretical calculations, laboratory tests were carried out, during which the samples of both the initial shotcrete and those exposed to electrostatics were formed. During the application of the mixture, the magnitude of the rebound was recorded at various distances of the nozzle with the nozzle fixed on it from the shotcrete surface. Samples of the resulting concrete were examined on universal testing machines in order to determine the specific heat release, as well as the compressive and bending strength. The experiments showed that electrostatic treatment allows to speed up the time of the initial setting of the cement dough due to faster hydration of the mixture. An improvement in the strength of shotcrete and a significant reduction in rebound were recorded.