Study On Preparation And Properties Of High Toughness Low Shrinkage High Crack Resistance Bonding Mortar

With the advancement and development of prefabricated building systems,prefabricated wallboard supporting mortar has been widely promoted and applied,but the existing mortar has a series of problems such as easy cracking,large shrinkage and low bonding performance.This article aims at the requirements of non-shrinkage,high crack resistance and high toughness of mortars for assembled components.This paper studies the effect of water-binder ratio,poly-ash ratio,fly ash,solid curing agent and fiber on the performance of the bonding mortar.The results show that increasing the ash ratio and fly ash content can effectively reduce the shrinkage of the mortar and improve the crack resistance.Decreasing the water-binder ratio and increasing the poly-ash ratio can improve the mortar’s bonding performance,but will reduce the mortar consistency.Appropriate amount of solid curing agent and sulfoaluminate expansion agent can effectively compensate shrinkage.Incorporation of fibers can increase the tensile strength of the bonded mortar,limit shrinkage and improve crack resistance.In this paper,the effects of polyacrylate emulsion（PAE）and ethylene-vinyl acetate copolymer emulsion（VAE）on the properties of the bonding mortar are compared,and the effects of blending PAE and VAE at different ratios on the properties of the bonding mortar are studied.The results show that the PAE modification effect is better than VAE in terms of workability,flexural strength,compressive strength and tensile strength at the same dosage,but it is weaker than VAE in terms of the bonding performance,shrinkage and crack resistance.When the ratio of the two is 1:1 blending,it has a synergistic effect on the performance of the bonding mortar,effectively making up for the deficiencies caused by the single mixing of the two.In this paper,silane coupling agent was used to modify nano-SiO₂.The effects of nano-SiO₂ and modified nano-SiO₂ on the workability,mechanical properties and shrinkage of VAE modified mortar were compared.The results show that the incorporation of nano-SiO₂ and modified nano-SiO₂ can improve the hardness,impact resistance,acid and alkali resistance of VAE coatings.Incorporation of nano-SiO₂reduces the fluidity and drying shrinkage of the mortar,and improves the bending resistance,compressive strength and bonding strength.Modified nano-SiO₂ can reduce the negative effect of nano-SiO₂ on the fluidity of mortar.At the same time,modified nano-SiO₂can further improve the bonding strength and tensile strength of modified VAE cement mortar,and reduce drying shrinkage and self-shrinkage.The final prepared bonding mortar has a consistency of 62mm,water retention rate greater than 99%,initial setting time 180min,final setting time 260min,7d bond strength 1.04MPa,28d tensile strength 4.7MPa,28d auto-shrinkage rate 12×10^-6,28d drying shrinkage rate310×10^-6,cracking index is less than 1.