Research On Microstructure Characterization And Cementious Ability Of C-A-S-H Gel Modified With Polyaluminum Chloride

The vitreous industrial wastes such as blast furnace slag,fly ash,phosphorus slag,nickel and chromium slagprimarily containing silicon and aluminum have accumulated for billions of tons and been increasing more than 500 million tons year by year(mainly low grade fly ash,phosphorous slag and all kinds of metallurgical slag),which urgently demands to be solved.It is reported that these vitreous silica-alumina slag could present synergistic hydration with Portland cement to form cementitious phases.Therefore,it have been an important method for low carbon,sustainable developmentgreen building materials industry to consumelarge dosage of these vitreous silica-alumina slag.However,these slag show relatively lowreaction activity and bad cementitious ability,which reduce the strength and quality of cement and limit the larger application in building materials industry.As a result,how to improve the reaction activity and cementitious ability of these wastes becomes the key technology for expanding the application and consumption capability in cement chemistry.In this paper,a new nano-scale functional materialspolymerization aluminum slats is used as key modification agent.Also the molecular structure and cementitious ability of C-A-S-H gel the primary binding phases is investigated.Based on the assumption that polymerization aluminum slats would participate in the hydration process and alter the molecular structureof C-A-S-H gel to improve cementitious ability of cement,we compare and analyze the role of polyaluminium chloride and other aluminum salt in the hydration process of slag cement to investigate the main component of aluminum that is responded for enhancement effect and the mechanism.The main works are listed blow:1)We reveal the mechanism of the enhanced effect reduced by polyaluminium chloride and put forward that the hydroxyl aluminum ions would accelerate the hydration rate of slag and increase the amount of hydration product,thus lower the porosity of the paste.And from the point of view of molecular structure of the gel,we characterize the mechanism for modification by polyaluminium chloride.2)From the point view of mass fluxes and ion diffusion,we investigate the influence of the location of Al to the layer distance of C-A-S-H gel.Based on the mass fluxes and ion diffusion mechanism in the process of slag hydration,we proposed a method to accelerate the hydration rate of slag through increasing the gel microstructure layer plate spacing and content of gel micro-pore.3)From the perspective of molecular structure of C-A-S-H gel,the mean chain length and average polymerization degree affected by polyaluminium chloride is investigated.We analyze the location of Al in the structure of C-A-S-H and the effect on crystallite morphology and binding ability.Lower mean chain length and average polymerization degree shows that C-A-S-H gel microcrystalline tends to fine crystallize and distribute uniformity.Fine crystallization and the distribution uniformity of C-A-S-H gel showed stronger van der Waals force,thus increasing the gel gelling ability.4)From the perspective of the chemical state of Al in C-A-S-H gel,penta-coordination Al is generated from tetrahedral Al when the charge balancing site is occupied by divalent ions,Ca,Mg.Since penta-coordination Al is unstable,it will convert to stable octa-coordination site,which inevitably lead to the break of main chain of the gel.This is the reason why the paste in slag cement modified by polyaluminium chloride present lower mean chain length...