Study On Bentonite-based Water-retaining And Thickening Mineral Admixture For Ready-mixed Mortars

Water-retaining and thickening material is an indispensable admixture for modern commercial mortar(ready-mixed mortar),which can greatly improve the workability,constructability and serviceability of the mortar.With the rapid development of buildings industrialization and the increasingly strict requirements for energy conservation and environmental protection,ready-mixed mortars have received much more attention and promotion.However,the research and development of special admixtures for domestic commercial mortars is much weaker than that of the foreign products in variety,performance and quality stability.At present,commercial special admixtures,especially the water-retaining and thickening material,still rely on foreign imports,which seriously restricted the sustainable development of commercial mortars in China.It is imperative to develop domestic high-performance water-retaining and thickening admixtures.Layer structured montmorillonite of bentonite which was riched in China has better water-absorbing,water-retaining and thickening properties.It can be used as water-retaining and thickening mineral admixtures for ready-mixed mortars.In this study,calcium-based bentonite(Ca-B),sodium-based bentonite(Na-B)and lithium-based bentonite(Li-B)were selected and used to prepare ready-mixed mortars,respectively.The effect of bentonite-based water-retaining and thickening mineral admixture on performances of ready-mixed mortar was studied.The results show that different types of bentonite have better water-retaining and thickening function for ready-mixed mortar.Performances of the mortar would be improved when Ca-B and cellulose ether were used,and cellulose ether could be partially replaced by Ca-B.Optimal water-retaining and thickening property and increased mechanical strength of as-prepared ready-mixed mortars would be obtained when Na-B,polycarboxylic acid superplasticizer and air-entraining agent were used.Smaller dosage of Li-B still showed better water-retaining and thickening property,but it will increase the 2 h consistency loss rate of the mortars.Li-B has higher compatibility with naphthalene superplasticizer.The mechanical strength of the ready-mixed mortars would be improved when Li-B and cellulose ether were used.The water-retaining and thickening properties of bentonite are related to the content and structure of montmorillonite.Higher content of montmorillonite in bentonite shows the stronger water-retaining and thickening ability in ready-mixed mortars.In addition,the composite water-retaining and thickening materials based on bentonite were obtained and applied in preparation of ready-mixed mortar.