Study On Preparation And Properties Of A New Alkali-free Liquid Accelerator

Accelerator is an indispensable additive for shotcrete,and alkali-free liquid accelerator has gradually replaced traditional high-alkali,low-alkali powder or liquid accelerator due to its advantages of no alkali and no damage to the late strength of concrete,and has become the main research direction of accelerator.At present,the performance of alkali-free liquid accelerator abroad is good,but the cost is high.There are some other problems in the domestic development of alkali-free liquid accelerator,And the type is single.Therefore,it is of great significance to develop a new alkali-free liquid accelerator.In this paper,a high solid content accelerator base liquid A was prepared by orthogonal design,and then polycarboxylate aluminium salt dispersant B was prepared,then a new alkali-free and chlorine-free liquid accelerator AB_SNJ was prepared by mixing the base liquor A and B.When the content of AB_SNJ was 7%,the initial setting time of the slurry was 2 min 25 s,the final setting time was 7 min 45 s,the compressive strength of 1 day was 12 Mpa,and the compressive strength ratio of 28 day was 109%,which meets the requirements of the first-class products in the specifications.In this paper,the accelerating performance of AB_SNJ and its influence on mortar strength are tested.The influence of different factors on the performance of AB_SNJ is studied.The adaptability of AB_SNJ to different types of cement and different freshness degree of cement is tested.The test results show that AB_SNJ can maintain good accelerating effect in the range of 20-30℃,and the dosage of accelerator should be increased when the temperature is low;the dosage of AB_SNJ should be increased when the water cement ratio is high to achieve the target accelerating effect;In the test,AB_SNJ should be added immediately after mixing of cement and water,and the mixing time should be controlled at about 20 s after mixing with accelerator;Cement has good adaptability.The dosage of accelerator should be adjusted according to the freshness of cement in practical engineering.In this paper,the change of calcium ion concentration and bound water content in the hydration process of cement mixed with AB_SNJ was analyzed.By means of hydration heat analysis and SEM analysis,the mechanism of AB_SNJ was studied by comparing the experimental group and blank group of cement samples with different hydration ages.The results show that AB_SNJ promotes coagulation mainly by promoting the hydration of tricalcium aluminate to produce a large number of hydration products such as ettringite,shortening or even eliminating the induction period of tricalcium silicate and releasing a large amount of hydration heat.