The Research Of New Type Of Alkali-Free Liquid Accelerator Based On Complexation Effect

As an indispensable key material in shotcrete,alkali-free liquid accelerator plays an important role in the rapid setting and hardening of shotcrete.However,dosage of alkali-free liquid accelerator in practical application is so high,and problems such as poor stability,low early strength still exist.In this paper,aiming at the problems encountered in the study of alkali-free liquid accelerator in the study,and based on that,a new type of alkali-free liquid accelerator has been developed,combined cement with C3S and C3A hydration,coagulation mechanism of alkali-free liquid accelerator,lay the foundation for the study to next generation of alkali-free liquid accelerator.The following conclusions are obtained through the study:1.The complexation mechanism of alcohol amine complex with aluminum ion and the effect of pH value on the stability of accelerator solution were studied.The effect of coordination agent on the solubility of aluminum sulfate was studied by means of XPS and electrical conductivity,and the mechanism of coordination of different coordination agents on the coordination of aluminum ions and the difficulty of forming different coordination bonds were analyzed.The results show that the coordination reaction between alcohol amine and aluminum ion is the first to form the coordination bond between the alcohol amine central nitrogen atom and the aluminum ion,but when its consumption is finished,the hydroxyl group at the distal end of the alcohol amine structure can also react with the aluminum ion to further increase the solubility of the aluminum ion.In addition,the DLS and the macro stability test are used.The effect of different pH values on the stability of the accelerator solution was investigated.The results showed that when the pH value was below 3,the stability of the non alkali liquid accelerator was good,and it was not stratified at 28 days at 20±2?.2.The influence of main components of coagulant on the setting time and strength of cement was studied.As the main condensing component,aluminum sulfate can obviously shorten the initial and final setting time of cement,and with the increase of the content of that,the coagulation effect is more and more significant.the setting time of the cement is shortened with the increase of the content of the ametholamine.When the dosage of ametholamine is 0.2%to 0.25%,the setting time of cement is the shortest,and the stabilizer has a certain retarding effect on the hydration of cement;aluminum sulfate has an positive effect on the early strength and the retention of the late strength of cement mortar;while the content of alcohol amine is less than 0.1%,it can improve the strength of the mortar for 1 day.The strength and strength of mortar decreased significantly at the same time and the strength of 28 days increased.Stabilizers also reduce the 1-day strength of mortar,but have no obvious side effects on late strength.The 1-day intensities of the three element system of aluminum sulfate and amine stabilizers were obviously improved by Glauber's powder and nano silica,and the early strength of three isopropanolamine,as a common early strength agent,had no obvious improvement on the early strength of the alkali free liquid accelerator in Al-olamine sulphate system.3.According to the related research basis,a new type of initial liquid free liquid accelerator CG was designed and evaluated.The accelerator was composed of aluminum sulfate?A?,alcohol amine?B?,stabilizer?C?,early strength agent?D?and thickening component?E?as the main component.The initial formulation was as follows:mass percentage of A?56%?,B?8.5%?,C?2%?,D?2%?and E?0.05%?,respectively.Based on the setting time and strength data and the stability study,it is shown that the initial setting time of cement can be shortened to 3'38",the end setting time is 8'49",the compressive strength of the 1 day is 9.2MPa,and the retention rate of28 days strength is 98%.It is not crystallized and precipitated for 28 days.4.The hydration mechanism of aluminum sulfate type alkali free liquid accelerator for cement and single ore has been studied.The alkali-free liquid accelerator will accelerate the early hydration of cement,accelerate the formation of ettringite and the consumption of Ca²⁺in the slurry,resulting in rapid solidification and hardening of the slurry.Aluminum sulfate can accelerate the hydration of C₃S to ettringite,shorten the hydration induction period,and make the slurry rapidly coagulate and harden.Under the presence of no gypsum,aluminum sulfate makes C₃A hydrated mainly a sheet of C₄AH₁₃,which is attached to the surface of the C₃A crystal,delaying the transport of ions and water,thus inhibiting the early hydration of C₃A,and the existence of aluminum sulfate can obviously improve the hydration degree of C₃A for 28 days and the amount of C₃A that did not react with water decreased significantly.