| As one of the three cementing materials, gypsum has become one of the future development of environmental protection and new energy-saving materials in the future,because of its light weight, thermal insulation, sound absorption, environmental protection,fire resistance, dimensional stability and other excellent properties. However, due to its insufficient water resistance, greatly limiting the wide application of gypsum in various fields.In order to solve the problem of the poor water resistance of gypsum, this paper analyzed the reasons of its insufficient water resistance, comprehensively analyzing the present situation of research on gypsum and various means and ways to its modification at home and abroad. Through mixing and coating silica sol, this paper done some modification research of gypsum from the mechanical properties, water resistance, curing time and volume stability of the gypsum based cementitious composites,Experimental study indicated that the mechanical strength of gypsum get enhanced overall after mixing with the silica sol. When the content of the silica sol was 6%, comparing to the blank gypsum, the dry flexural and compressive strength for 7d of gypsum were increased by 25% and 39.76% respectively, and the water saturated flexural and compressive strength were increased by 28.16% and 61.33% separately. Adding silica sol has a little effect on the volume stability of gypsum, whose percentage change in length was controlled within the range of 0.5%. The best dosage of silica sol is 6%.The modification method of coating and mixing of silica sol in gypsum effectively improved the dry and wet strength of gypsum cementitious materials. When at the best content of the sol of 6%, the dry flexural and compressive strength for 7d of the specimens mixed and coated with the silica sol were increased by 41.55% and 49.59% respectively than blank gypsum, and that were increased by 13.24% and 7% respectively than that single mixing with silica sol. The water-saturated flexural and compressive strength of modified specimen were increased by 151.9% and 297.4% than the blank gypsum, and that were increased by 96.5% and 148.1% than that single mixing with silica sol. Mixing and coating with silica sol showed the positive superposition effect, which better improved all aspects ofperformance for gypsum.For the gypsum based composite mortar, when the gum-sand ratio is 2.5, the dry flexural and compressive strength for 7d were improved by 15.34% and 26.45% separately than blank gypsum, and 7d full water flexural strength was reduced by 17.09%, the compressive strength increased by 45.63%.The dry flexural and compressive strength for 7d were decreased by7.7% and 9.5% than that single mixing with silica sol, and the water saturated flexural strength for 7d were decreased by 35.71% and the compressive strength were increased by9.72%. Water absorption of the gypsum based composite mortar was decreased by 31.17%than blank gypsum, and that was decreased by 14.84% than that single mixing with silica sol.The final and setting time of gypsum adding with sand reduced at the beginning, and then increased, and finally leveled off, which decreased sharply when the gum-sand ratio is 1.5,decreasing by 26.61% and 46.99%. It has a little effect on the volume stability of gypsum mixing with sand, whose percentage change in length was controlled within the range of 0.5%.The best gum-sand ratio is 2.5.Microscopic tests showed that the incorporation of the silica sol can positively affect growth and development of crystal, making gypsum crystals closely arranged. Main crystal structure is long strip and plate, and the surface of crystals were covered with a small amount of calcium silicate gel.On the whole, the properties of gypsum based cementitious composites had been improved to a certain extent through adding the silica sol, which can provide a reference for performance improvement and expansion of gypsum application. |
PDF Full Text Request