Study On The Liquid Alkali-free Accelerator

The Liquid Alkali-free Accelerator(LAA) for sprayed concrete is a concrete additive, it can significantly shorten the setting and hardening time of concrete. Compared with the traditional alkaline powdery accelerators LAA have many advantages such as low-alkalinity、low powder dust concentration in the air when constructing and can fully disperse in mixture,so it can reduce the eroding damage when the workers during the working process、improve the sprayed concrete strength and avoid the wide quality fluctuations of sprayed concrete.As such that the liquid alkalifree accelerator substitute for traditional accelerator has become a period echo,and is the inevitable trend of modern materials industry also.In this paper, the development history of accelerating additive and its research and application actualities were introduced in detail, summed up the shortage of additive, then the necessity to development and research of the liquid alkali-free accelerating additive was pointed out, and the paper has do a lot of exploration and theoretical analysis also, that the main research results show as follows:(1)We have prepared the HZ liquid alkali-free accelerator successfully.This accelerating additive at normal temperature is a transparent solution, the value of PH is about 4, the alkali content less than 3.0%. At the W/C ratio of 0.4, 7.0% addition of HZ was added, the experiment showed that the cement paste could reach the initial set and final set in 2′06〞and 5′01〞respectively,1d、3d and 28d flexural strength and compressive strength of cement mortar were 3.7MPa、6.9MPa、8.3MPa and 14.7MPa、37.5 MPa、48.3MPa respectively. Its early-time strength is increased widely, 28d compressjve strength ratio is 91.7%. All of the guidelines can meeting the requirements of grade A in national standards, its a good accelerating additive and has an excellent prospective in application.(2)A quantity of experiment tests on the comprehensive performances of HZ liquid alkali-free accelerator was carried out in this paper.The test results show that: the adaptability of this accelerating additive with most of cement was satisfactory, just in the setting time with a few factories producd cements were not good as what we expected, but can be adjusted by increasing the addition of the rapid-set accelerators appropriately to meet the requirements; Although its adaptability with superplasticlzer was very good,but in the composite using we must through the tests to adjusting and ensuring the addition and W/C ratio of the accelerating additive; The mixtures which added this accelerating additive still have good rapid-set accelerator effect when in the 0℃~30℃environment; But if added the accelerating additive after watering and stirring 15minutes, the accelerator effect would be significantly diminished, and the setting time nearly could not meet the requirements of the accelerating additive standards. So in the specific project construction, once after watering and stirring we should add the accelerating additive to spraying as soon as possible so as not to affect the accelerator effect. In short that the comprehensive performances of the HZ liquid alkali-free accelerator are very good, and can be widely used in the projects of different regions and different temperature cabins, have an excellent prospective in popularization.(3)In this paper, we have done a lot researchs and analysis on the hydration process of cement and mechanism of the main contents in cement clinker, and the cement experiment that has added HZ accelerating additive was explored by the means of SEM, we think this accelerating additive is primarily through accelerating the hydration of C3A and shortering or disappearing the induction period of C3S to achieve the accelerator effect.