Preparation And Application Of Bentonite-based Viscosity-modifying Admixtures

The working performance of freshly mixed mortar is closely related to its workability and will affect its mechanical properties and durability.Viscosity-modifying admixture is an important additive to improve the working performance of mortar.At present,this type of additive is mainly cellulose and its derivative polymers,but it also entrains air easiness,retards the cement,and is difficult to obtain homogeneous due to its small amount—disadvantages of mixing evenly with other materials.Some clay materials have been used as viscosity-modifying admixture in cement-based materials,which can not only overcome the shortcoming of the above polymer viscosity-modifying admixture,but also improve the working performance of fresh mixes.Based on the advantages of bentonite resources in China and its water absorption,swelling and suspension stability characteristics,three bentonites were selected in this study.Bentonite-based Viscosity-modifying Admixture.(BVMA for short),was prepared by shearing and dispersing in aqueous solution and entirely standing foraging,focusing on its effects on the rheological and mechanical properties of different cementitious material systems.For cement mortar,the yield stress of 3% lithium-based BVMA samples at 15 min,30min,45 min,and 60 min increased by 219.8%,171.1%,236.6%,and 151.1%,respectively,compared to the blank sample.When the lithium-based BVMA content is 1%,the structure rebuilding rate of the cement slurry is 1.36 times that of the reference sample.When the lithium-based and sodium-based BVMA content is less than 1% and 2%,there is no significant effect on the fluidity and mechanical properties of the cement mortar,and then it decreases with the increase of the content.The low content of lithium-based BVMA increases the yield stress of the fresh cement paste and speeds up the structure rebuilding rate of cement slurry.For gypsum mortar,the incorporation of lithium-based and sodium-based BVMA causes the gypsum slurry to undergo a change from shear-thinning to shear-thickening.Calcium-based BVMA has little effect on the rheological properties of the gypsum slurry.Lithium-based BVMA has the most significant increase in the yield stress and thixotropy of architectural gypsum slurry.The plastic viscosity of gypsum slurry decreases with the increase of lithium-based and sodium-based BVMA.The addition of calcium-based BVMA does not significantly change the plastic viscosity of the slurry.The fluidity of gypsum slurry decreases with the increase of BVMA content,and the water retention rate increases with the increase of BVMA content.Lithium-based BVMA reduces the flexural and compressive strength of gypsum slurry.For lime-based mortar,the fluidity of the lime-based mortar gradually decreases with the increase of the BVMA content.When the lithium-based BVMA content is 3%,the flexural strength and compressive strength of the lime-based mortar are improved.The results show that lithium-based bentonite and sodium-based bentonite are suitable as viscosity-modifying admixtures,which incorporating cement,gypsum,and lime as primary cementitious materials,respectively.