Study On Synthesis And Properties Of Liquid Alkali Free Accelerator

As a kind of concrete admixture,the use of accelerator is paid more and more attention.With the development of tunnel construction in China,the dosage of accelerator is increasing year by year.At present,the accelerator used in our country still has some problems,such as high alkali content,insufficient strength in the later stage,more toxic materials and so on.With the issuance of relevant policies and stricter quality control standards,liquid alkali free accelerator will replace the previous accelerator.On the basis of a large number of theoretical analysis and practical investigation,sn-a liquid alkali free accelerator was synthesized by single component coagulation test and orthogonal test,taking the setting time and compressive strength as the main selection basis,through specific test means and adding modifier.The solid content of sn-a is 44.1%.When the content of sn-a is 6%,the setting time of cement paste is 2.6min,the final setting time is 5.3min,the 1D compressive strength is 8Mpa,the 28 d compressive strength is 62.4mpa,and the 28 d compressive strength ratio is 111%.All test data meet the first-class requirements of national standards.The properties of sn-a,such as coagulation promoting property,compressive strength,volume expansion rate,adaptability with cement and water reducing admixture,were tested.The effects of temperature,water binder ratio and adding time of accelerator on the properties of sn-a were studied.The accelerating mechanism of sn-a was preliminarily determined based on the hydration mechanism of cement and related reaction equations.SEM scanning electron microscope(SEM)was used to observe the hydration products of different ages.The study showed that the addition of SN-A accelerated the early hydration rate of cement,which was beneficial to the formation of early calcium vanadium and C-H-S gel,and consumed a lot of Ca2+,resulting in rapid setting and hardening of cement paste.Sn-a can shorten or even eliminate the induction period of C3 S,accelerate the hydration reaction,and finally show that a large number of ettringite and calcium hydroxide are wrapped by C-H-S,the cement stone is interconnected to form a whole,the cement stone structure is extremely dense,and the compressive strength is further improved,which verifies the coagulation mechanism of SN-A.