Experimental Study On The Mix Design Of Surface Dry-mixed Mortar And The Bonding Strength With Wall Materials

In the popularization and application of the new wall materials, the metope plasterer layer often crazes and falls off in the large area. One of important reasons is that the traditional confecting way of mortar is still used and new wall materials and mortar don't match. Dry-mixed mortar has many obvious advantages such as high and stable quality, low environmental pollution and huge market potential. However this kind of product in domestic is applied in a relatively short time and a limited range. The amount of usage of surface mortar is huge and it is the significant constituent part of dry-mixed mortar. Therefore, it is necessary to research systemically on the performance of the surface dry-mixed mortar and to provide technical reference for application.This paper studies the impact of the bentonite, cellulose ether, re-dispersible latex powder, fibers, reducing agent and fly ash on the surface dry-mixed mortar performance. The results of the study indicate that bentonite improves on mortar water-retaining property indistinctively and makes the compressive strength declined greatly. Cellulose ether can greatly improve water retention, but have adverse effect on compressive strength and bond strength. Latex powder can increase the bonding strength obviously. A reasonable amount of fiber can make shrinkage reduced. Water reducer can reduce the water-cement ratio of the mortar and make the tensile bond strength and compressive strength increased to varying degrees. Fly ash can make the compressive strength and tensile bonding strength declined and have a smaller reduction on the the mortar with polymer than the mortar without polymer.Through the above tests, the proportion of surface dry-mixed mortar modified by polymer is determined. The water-retaining property rises up to 99.8% and bonding strength is up to 1.43 MPa after testing, both of which can satisfy the requirements of surface dry-mixed mortar in JG/T 230-2007. After the microstructure analysis it is realized that cement hydration products and polymer membranes form the interpenetrating network structure because of the mix of polymer. Such weaknesses as the interface between the aggregate and cement pastes are strengthened and it helps improve bond properties of the mortar.Aiming at the poorer cohesion between wall materials and mortar during popularization and application of new wall materials and the phenomenon of the plasterer layer falling off easily and leakage, the bond properties between the surface dry-mixed mortar and wall materials are studied. It is found that the bonding strength between the same mortar and different wall materials has a big difference. It can greatly improve the bonding strength by adding cellulose ether into ordinary surface mortar, but it is still less than the bonding strength of polymer surface mortar.With water content of block increased, bond strength of the mortar modified by cellulose ether increases, but bond strength of the polymer surface mortar increases firstly, and then decreases. In addition good water-retaining property is very favorable to the development of bond strength.Through the study of the performance of surface dry-mixed mortar in different curing conditions, it is found that in relatively dry curing condition, the 28d compressive strength of the mortar with needful cellulose ether can exceed the mortar without cellulose ether. In the event of certain admixture the optimal curing condition corresponding to the mortar is different. In addition, under low-humidity curing conditions, some cellulose ether is conducive to the development of bond strength.