Research On Dehydrated Paste Actived Slag Cementitious Materials With Keggin-Al₁₃

The rapid consumption of natural resources and the treatment of waste concrete in the product of cement and concrete are two major problems to be solved in the global construction industry.Therefore,it is of great significance to study the preparation of recycled cementitious materials by using colloidal components in waste concrete.In this paper,a regenerated cementitious material with good mechanical properties was prepared by using slag power and the dehydrated paste from calcinning waste cement paste at 800oC.The work performance,mechanical properties and dry shrinkage performance of the cementitious material was studied with the corporation of polyaluminun through porosity test,hydration level test of slag and micro-test include XRD,SEM,TG-DSC and NMR.The main work and research results of this paper are as follows:Taking dehydrated paste as solid alkali activator with means of volcanic ash reaction principle,a composite cementitious material with good mechanical properties was prepared.The technologies of XRD,SEM and TG-DSC combined test of the hydration degree of slag were utilized to study the hydration process and the hydration product of cementitious materials.The results showed that the cementitious material prepared by the dehydrated paste and the slag ratio with ratio 1:1 got the best mechanical property,and the hydration products of cementitious materials are AFm,Ca?OH?₂,CaCO₃,C-S-H gels.The change in structure and composition of the C-S-H gels with polyaluminum chloride were studied by ²⁹SiNMR and EDS-SEM.The mechanism of polyaluminum chloride in the hydration process of dehydrated paste-slag materials was studied in detail.The results show that the polyaluminium chloride accelerates the destruction of slag vitreous,and the Al from the polyaluminium chloride entered the structure of C-S-H gels.The mean chain length of the C-S-H gels increased,and the hydration products formed a channel for the ion transport in the pores.With the hydration degree of slag increasing,the amount of hydration products improved and condensed slurry structure.Finally,the cement stone macro-mechanical property was enhanced.The feasibility of using commonly used slag vitreous activator NaOH,Na₂CO₃,Na₂SO₄ and polyaluminium chloride to stimulate the vitreous of the slag was studied.The experimental results showed that the combination of polyaluminium and common activator of slag may not good due to the fact that Al in the polyaluminum chloride and OH-combined to form Al gels,which adversely affected the strength of the cementitious material.The effects of polyaluminium sulfate and polyaluminum-ferric Silicates on the mechanical properties and dry shrinkage properties of dehydrated paste activated slag powder cementitious materials were studied.The results showed that the polyaluminium sulfate could enhance the compressive strength of the cementitious material,polyaluminum-ferric Silicates has no obvious effect on the mechanical properties of cementitious materials.The addition of appropriate polyaluminium sulfate could improve the dry shrinkage performance of cement stone.Addition of polyaluminum chloride is disadvantageous to the drying shrinkage of cement stone.