Preparation And Performance Study Of A New Alkali-free And Chloride-free Liquid Accelerator

Shotcrete technology is a very good technique for solving problems of the repairing ofslope, support of rocks, repairing and reinforcement of tunnel, plugging, rapid repairing andreinforcement of roads, One of the important steps during shotcrete construction is theselection of accelerator, The accelerator in powder form had been widely used, but problemssuch as a high alkaline content, heavy dust and a great loss of materials during constructionhave limited its application. Most liquid accelerator contained alkali, chlorine, affect thedurability performance of concrete. In order to improve the performance of the accelerator, aliquid state, low-alkaline or alkaline-free accelerator is greatly desired.A new alkali-free and chloride-free liquid accelerator was synthesized in laboratory andits performances such as setting time and compressive strength were systematically evaluated.Meanwhile, the microscopical mechanism was also analyzed by using XRD and SEM. Theresults indicated that:Ⅰ. The composed of a new alkali-free and chloride-free liquid accelerator:(1) Use chemical reagent compose accelerator. Add the various components and rawmaterials step by step according to the synthetic process, got a stable product. It can met therequirements of the standard of JC477-2005. Due to the high price of chemical reagent, Souse the industrial raw material to synthesis and research;(2) Use industrial raw material compose accelerator. Add the various components andraw materials step by step according to the synthetic process, got the product. Anewly-prepared accelerator was a kind of colorless and transparent liquid, it was a alkali-free,chlorine-free, non-toxic, orderless, acidity. The density of the new accelerator was1.2to1.4g/cm3(depends on the concentration). The product can be stored for a long time (sixmonths) without sedimentation or segregation;Ⅱ. The performance of the accelerator synthesized with industrial raw material. When4%~6%accelerator was added, the setting time,1d compressive strength and28d compressivestrength ratio of cement samples met the requirements of the standard of JC477-2005; Whenthe addition ratio of the accelerator was4%,28d compressive strength ratio reached100.2%;When4.5%accelerator was used, the28d compressive strength ratio reached99.7%; When the addition ratio of the accelerator was5%and5.5%, the loss of28d compressive strengthwas5.8%and7.1%. Considering the factors of accelerating effect, economy etc, the optimaldosage of this accelerator was4%to5%;Ⅲ. The adaptation between the accelerator and the different mineral admixtures:(1) When the replacement ratio of slag was in the range of20%~50%, the setting time,1d compressive strength and28d compressive strength ratio of cement met the requirementsof the standard of JC477-2005; When20%~40%of cement was replaced by slag, the1dcompressive strength of sample without the accelerator was higher than the one withaccelerator; however, when the replacement ratio was50%and60%, the opposite effect wasobserved; At a replacement ratio of30%, the biggest28d compressive strength ratio was seen,so a slag-replacement ratio of30%was determined as having the best compatibility with theaccelerator;(2) With the addition of fly ash, the setting time will be elongated, but the setting time,1d compressive strength and28d compressive strength ratio of cement still met therequirements of the standard of JC477-2005; An addition of20%~40%fly ash was found tobe well-adapted with the accelerator;Ⅳ. The adaptation between the accelerator and the different cement. When4.5%or5%accelerator was added, the setting time,1d compressive strength and28d compressivestrength ratio of P·O42.5cement and P·C32.5cement meets the requirements of the standardof JC477-2005; With the increase of addition of the accelerator, the setting time will beshorten; With the addition of the accelerator, the1d compressive strength increased and28dcompressive strength ratio was larger than100%was increased; The accelerator had a goodcompatibility with P·O42.5and P·C32.5cement, but its compatibility with SAC was poor;Ⅴ. The adaptation between the accelerator and different water reducing agent. The newalkali-free and chloride-free liquid accelerator had a bad compatibility with calciumlignosulfonate water-reducing admixture, but its compatibility with naphthalene andpolycarboxylate water-reducing admixture was good.