Technologies Of Mining Wet-mix Shotcrete With Lower Pipage Resistance And Less Dust Based On Rheology

Wet-mix shotcrete technology has many advantages such as lower dust,less rebound and so on when compared with dry-mix or semi-wet shotcrete.Due to the materials used for wet-mix shotcrete belongs to dense particle flow,large pipage resistance,even blockage may occur in pipes.Especially for the application of shotcrete in complex underground environment,the requirements of mining wet-mix shotcrete on pumpability,shootability and spraying dust are rigid.In this paper,several methods like theoretical analysis,experiment and numerical simulation were used to study the technologies of reducing pipage resistance and spraying dust of wet-mix shotcrete.Firstly,the special requirements of mining wet-mix shotcrete on constitution and workability were analyzed.The particle tracing technology was used to analyze the flow law of concrete materials in pipes.Combination with mechanical analysis,the formation of lubrication layer in pipes and the mechanism of reducing pipage resistance was studied.The importance of lubrication layer on pipage resistance was identified.The reason why wet-mix shotcrete produces less spraying dust was analyzed with the dust suppression technology of original wet mix,the opinion of second capturing spraying dust was proposed based optimizing adding air structure.The experiment platform of pipage and spray of wet-mix shotcrete was built.These tests like rheological properties,slump,air content were conducted for those concrete samples taken before pump,after pump(before spray)or after spray.The influence law of different mixture content and wet-mix shotcrete behavior on rheological properties and workability was studied,respectively.This influence of mixture on properties of fresh concrete was generated by both of"ball effect" and "free paste effect".The wet-mix shotcrete behavior has the serious effect on the concrete with air entraining agent.The largest influence range was at the yield shear stress;compared with plastic viscosity,the yield shear stress had the better relationship with pumpability and shootability of fresh concrete.The predicting range for pumpability present polygon based on two parameters of yield shear stress and plastic viscosity.The lower the rheological parameters is,the bigger the probability of pump is.The quantitative prediction models of pump and shoot were obtained with multiple linear regression analysis.The switch air entraining agent used for reducing pipe resistance was developed with main foam material of soapberry and other materials such as sudsbooster,foam stabilizer and switch agent.Foam materials A includes 1.5%soapberry,0.5%dodecyl trimethyl ammonium chloride and 0.3%polyacrylamide;switch agent B includes 0.5%laurylsodiumsulfate and 0.7%siliconeoil.The application of switch air entraining agent guaranteed the shootability of fresh concrete,also reduced the pipage resistance and shotcreting dust.With the working principle of concrete pump with double plugs,the blockage reasons was analyzed at priming and middle stage of pump process.The calculation method used for pre-pumping cement paste was proposed.The pre-pumping cement paste volume was consisted of lubricating inner pipe wall and buffering the larger particle gather.With simulation and experimental verification,the optimal adding air location,10m apart from nozzle,was determined to secondly capture the dry dust produced by nonuniform mixing.Finally,field application was conducted.