Research For The Effect Of Admixture And Curing System On Drying Shrinkage Of Wet-Mixed Plastering Mortar

Wet-mixed mortar has the advantages of high production efficiency,stable quality,energy conservation and environmental protection,etc.,with the promotion of green buildings in China,wet-mix mortar develops rapidly,but the problems such as hollowing,cracking,dropping and other engineering quality of wet-mix plastering mortar happen occasionally.The inconsistency of shrinkage between plastering mortar and wall is the main cause of quality problems in plastering works,the shrinkage rate of plastering mortar is larger than that of ordinary building walls,and the inconsistency of shrinkage will produce shrinkage stress,when the shear stress caused by shrinkage stress is greater than the sum of tensile strength of mortar at a weak point and the bonding strength between mortar and wall at this point,then the hollowing,cracking and dropping will appear,therefore,reducing drying shrinkage of wet-mixed plastering mortar is of great significance to effectively reduce plastering engineering quality problems,improve engineering quality and promote the healthy development of ready-mixed mortar.Adding admixture is an important technical way to reduce drying shrinkage of mortar,meanwhile,the temperature and humidity environment have a remarkable effect on drying shrinkage of mortar.In order to research the influence of temperature and humidity environment and admixture on drying shrinkage of wet-mixed plastering mortar systematically,based on presenting a self-made new method for measuring shrinkage of mortar,the effect of temperature and humidity on drying shrinkage of wet-mixed plastering mortar was researched by changing curing conditions in this paper,then was the researching of the effects degree of SAP,SRA and air entraining admixtures with different mixing amount on the drying shrinkage of wet mixed mortar.The paper also systematically research the construction performance,mechanical properties,rheological properties and the distribution of micro-pore structure of mortar,to provide theoretical support for the application and popularization of wet-mixed plastering mortar,reducing the occurrence of hollowing,cracking and dropping in plastering engineering and the research and development of new plastering mortar.Through the in-depth and systematic research in this paper,the effects of temperature and humidity conditions and admixture on drying shrinkage of wet-mixed plastering mortar are as follows:?1?When the humidity is 90%and the temperature is in the range of 20?⁴0?,the drying shrinkage,water loss per unit volume and strength of wet-mixed plastering mortar increase with the increase of temperature;The drying shrinkage water loss per unit volume of wet-mix plastering mortar increase,and the strength value decreases obviously with the decrease of humidity when the temperature is 40?and the humidity is in the range of30%⁹0%,however,when the humidity is reduced to 30%,the drying shrinkage of M5mortar increases continuously,while that of M10-M20 mortar decreases;?2?When the mortar is maintained at room temperature after curing in standard curing conditions for 63 days,the drying shrinkage of mortar increases obviously with the increase of strength;?3?The type of water exchange has a great influence on drying shrinkage of wet-mixed plastering mortar.,the larger the space of water exchange is,the larger the shrinkage of mortar.is during curing;?4?The optimum mixing amount of SRA in wet-mixed plastering mortar is 2.5%of cement quality.,at this time,the drying shrinkage of mortar in 63 days is 45×10^-5,which is19.6%lower than that blank group is,and the strength value in 56 days decreased by 28.1%,and the water loss rate of mortar can be significantly reduced,meanwhile,the water loss rate of mortar decreases obviously;?5?Drying shrinkage,strength and compression-folding ratio of wet-mixed plastering mortar decrease with the increase of air content;?6?The optimum mixing amount of powder SAP in wet-mixed plastering mortar ranges from 0.2%to 0.4%of cement quality,at this time,the average drying shrinkage of mortar in 90 days decreases by25.5%and the average strength in 56 days decreases by 12.9%,but the drying shrinkage increases when the mixing amount exceeds this range;?7?When keeping the water cement ratio of mortar remains constant,the strength increases gradually with the increase of the mixing amount of additional pre-absorbent SAP,and the drying shrinkage increases firstly and then decreases gradually.,which reaches the maximum at 90 days and exceeds that of blank group to 59×10^-55 with the mixing amount of SAP at 0.4%;?8?When keeping the consistency of mortar constant,the optimum mixing amount of pre-absorbent SAP is 0.6%of the cement quality,at this time,the drying shrinkage of mortar in 35 days decreases by 17.3%to 43×10^-55 compared with blank group,and the strength in 56 days increases by 6.6%.