The Research On Performance Of Special Cementitious Material For Dry Mixed Mortar

The end of the twentieth century, dry-mixed mortar was introduced in our country’s construction market as a newly building. This mortar has more accurate proportion, more proper additives, it has excellent workability and better quality assurance after experimental demonstration, it can also use a large number of fly ash, gypsum, slag and other industrial waste and relieve environmental pressure, save material stacking sites for the construction site, improve construction efficiency etc. Minimum strength grade of our common Portland cement is32.5MPa, and dry mixed mortar (such as grade of plastering mortar strength is M5, M10, M15and M20) Strength is relatively low. At present there is no special mortar cement in our market, general Portland cement (i.e. pure cement mortar) formulated mortar directly in the construction, which led to the waste of cement and mortar quality problems occurred frequently, Dry mixed mortar enterprises use common Portland cement mixing of mortar, and mixed with large amount of fly ash by modulating the intensity grade. How to play the cementitious role of fly ash in dry mixed mortar, further reduce the cement content of dry mixed mortar to reduce the cost and improve the quality of mortar, which is in need of the problem of solving by mortar enterprises.The original fly ash and ground fly ash of Zhengzhou power plant, Luoyang low calcium fly ash, desulfurization gypsum in Zhengzhou power plant as main raw materials were taken in this paper. The study method of fixed variables was used, the cementitious material of " low cement content with a large volume of fly ash and flue gas desulfurization gypsum " was studied systematically in this paper. The results showed that:Zhengzhou power plant fly ash performance indicators are not up to class Ⅲ ash index, but after ground treatment, which achieves class Ⅱ ash index. Ground ash can completely replace the grade Ⅱ Luoyang low calcium fly ash in dry mixed plastering mortar, and the performances of producing mortar are better; The compressive strengths of the mortar produced by " low cement content with a large volume of fly ash and flue gas desulfurization gypsum " increase with the cement content increase, and there is an optimal value of compressive strengths with the increase of the gas desulfurization gypsum content. For example, when the cement content is of20%and30%and flue gas desulfurization gypsum is of30%in " low cement mixed with large amount of ground fly ash and flue gas desulfurization gypsum ", the compressive strengths of producing mortars are19.3MPa and24.6MPa, this value reaches our country masonry cement strength grade of12.5and22.5; The volume shrinkage of the mortar produced by " low cement content with a ground of fly ash and flue gas desulfurization gypsum" increase with cement content increase and reduce with flue gas desulfurization gypsum content increase, and the volume shrinkage of the mortar with pulverized fly ash is smaller than that of the mortar with original fly ash.The scanning electron microscope (SEM) and Ⅹ ray diffraction (XRD) analysis were used in this paper, the results showed that compared with original fly ash, the ground fly-ash has faster speed of hydration hardening and more compact microstructure and higher strength of hardened paste because of the surface of mechanical activation and cement and gypsum double excitation.