Study On The Preparation And Performance Of New Type Alkali-free And Chlorine-free Liquid Accelerator

Accelerator is an additive that can make concrete solidify in a short time and produce the admixture with a certain intensity.With the continous construction and development of underground projects,the demand of the accelerator is increasing day by day.Alkali-free liquid accelerator can effectively avoid the alkali aggregate reaction and thus reduce the loss of late-stage strength of concrete,and also protect health and safety of operation workers.In this paper a novel energy-saving method-grinding at room temperature was employed to prepare poly(aluminum sulfate)PAS accelerator with higher A1 content.And it can be kept stable for a long time by the combination of the compound.Poly(aluminium sulfate silicate)setting accelerator was prepared by using reaction of MgSiF6 with PAS accelerator in order to further improve the coagulation effect and stability.The specific research contents are as follows:(1)The preparation of poly(aluminum sulfate)PAS accelerator.It was found that poly(aluminum sulfate)PAS accelerator prepared by the two methods(the room temperature-grinding method and traditional heating-mixing method)in the optimal conditions has the similar initial setting and final setting time,and the 1 d compressive strength and the 28 d compressive strength ratio are also very close.Ferron complexing colorimetric method was used to detect the distributions of A1 type in the products by the two methods respectively.Results show that the PAS prepared by room temperature-grinding method has a higher content of Alb,indicating the advantages of energy conservation and environmental protection.(2)Complexation of PAS accelerator.A series of hydroxyl carboxylic acids such as glycolic acid,lactic acid,malic acid,tartaric acid and citric acid were selected to complex with the PAS accelerator prepared by room temperature-grinding method.The impact of hydroxyl and carboxyl on coagulation function and stability of accelerator was investigated by measuring the initial and final setting time and observing the initial time of PAS crystallization precipitation.Especially glycolic acid and malic acid have the least negative effect on coagulant,while the best stability improvement.Further complexation with triethanolamine and phosphorus acid by using glycolic acid and malic acid can make the as-prepared PAS accelerator keep stable for 150 d with the least loss of coagulant function.(3)Preparation of poly(aluminium sulfate silicate)setting accelerator.An alkali-free and chlorine-free accelerator liquid accelerator-poly(aluminum silicate sulfate)(PASS)was prepared by hydrolysis and polymerization of magnesium silicofluoride within self-made polyaluminium sulfate matrix,coupling with"hydrolysis-polymerization-concentration" three-in-one technology.The stability of the as-prepared accelerator was effectively improved due to the introduction of the silicon in product without adding any other stabilizers.Furthermore,both Mg and F element can play a certain amount of coagulation function in the process of early hydration of cement.(4)Possible mechanism of poly(aluminium sulfate silicate)setting accelerator.The compositions and microstructures of cement at different hydration stages were analyzed by using XRD and scanning electron microscopy(SEM)techniques.The possible coagulation mechanism of liquid accelerator PASS was proposed as follows:a skeleton of ettringite(AFt)was formed and the thickness of calcium silicon layers covering the surface of calcium silicate(C3S)was decreased by increasing the osmotic pressure.And calcium silicate(C-S-H)was generated and filled between the skeletons of the ettringite by progressive hydrolysis of the C3S in cement slurry,thus eventually achieving the effect of coagulation in a short time by the above series of reactions.