| Shotcrete technology is widely used in tunnel engineering,underground engineering,road emergency repair and other projects because of its advantages of simple construction,good mobility and fast construction progress.The most important additive in shotcrete technology is accelerator,which has an important influence on the key properties of shotcrete,such as setting time,strength,rebound and so on.At present,the liquid accelerator is still in the research and development process,and its application has some problems to be solved,such as the high dosage of accelerator,the poor adaptability to different kinds of cement,and the insufficient stability of accelerator.In this paper,the research idea of the preparation of alkali free accelerator is clarified firstly,and the material and preparation method are determined.The best mix proportion and the best dosage of alkali free accelerator are determined by the orthogonal experiment method.Then the performance of accelerator is simulated and analyzed.The technical route for the development of alkali free liquid accelerator was established,the composition of the accelerator was determined,the method for the stable existence of aluminum ion in the accelerator was studied,and two key parameters for the development of the accelerator were obtained: p H value of 3 ～ 4,Al2O3/SO42-about 0.33.The preparation method and proportion of non alkali liquid accelerator were studied,and the proportion of non alkali liquid accelerator was optimized by orthogonal test design.The obtained proportion was as follows: 48.6% of quick setting component(aluminum sulfate+aluminum fluoride complex),0.8% of triethanolamine,2.3% of EDTA,1.8% of diethanolamine and 46.5% of water.The best dosage of the accelerator prepared by this mixture is 8% of the cement dosage.Under this dosage,the initial setting time is 3.2min,the final setting time is 6.5min,the compressive strength for 1d is 8.1MPa,and the compressive strength for 90 d is 56.2MPa.The regression model is used to predict the performance of the accelerator,and the regression equation with good correlation with the test results is obtained.There is a good linear relationship between the setting time,early strength and late strength of the cement paste and the content of the accelerator components and triethanolamine.The effect of accelerator on hydration of cement was simulated.The results showed that the high concentration of aluminum ions in accelerator could accelerate the formation of ettringite and reach the effect of quick setting.But ettringite affects the generation of CSH gel,which makes the early strength of cement low,and even has adverse effect on the strength and durability of later stage. |
