Research On The Performance Regulation And Mechanism Of Plant Polyphenols On Alkali-Activated Slag Materials

Alkali-activated slag（AAS）is a kind of cementitious material that utilizes slag as the main binding material.It features rapid setting,early strength development,good acid and alkali resistance,as well as characteristics such as absence of clinker and environmental friendliness.It is considered the most promising low-carbon alternative material to cement and has become a hot research topic in the field of building materials.However,AAS tends to set quickly,shrink significantly,and crack easily,which not only increases the difficulty of its use but also leads to deterioration in durability,seriously affecting its development and application.Despite attempts to regulate the relevant properties of AAS using cement-based admixtures such as polycarboxylate superplasticizers,expanders,and shrinkage reducers,both theory and practice indicate that there are issues with the effectiveness and compatibility of admixtures developed based on cement in AAS systems.Therefore,effectively controlling the material properties of AAS and selecting admixtures that are compatible with and effective for AAS become key challenges in the design and performance control of AAS materials.To address this issue,inspired by the strong adsorption capacity of dopamine molecules from marine mussels in complex environments,and based on research on plant polyphenols in cement-based systems,this study utilizes natural plant polyphenols with similar hydroxyl group molecular structures,including tannic acid,gallic acid,xylitol,and waste tea polyphenols,as performance modifiers for AAS.The study utilizes the ion chelation,particle adsorption,and functional dispersion properties of plant polyphenols to regulate the workability and autogenous shrinkage behavior of AAS.Through analysis from the perspectives of pore solution changes,AAS hydration characteristics,and microstructural changes,the study analyzes and reveals the role characteristics and mechanisms of plant polyphenols in regulating the performance of AAS.The main research findings are as follows:（1）Pore solution analysis results indicate that plant polyphenols can affect the hydration process and properties of pore solutions and nearby slag through particle adsorption,Ca²⁺chelation,electrostatic repulsion,and spatial hindrance effects.The particle adsorption effect of plant polyphenols inhibits the early hydration of slag and prolongs the induction period of hydration.Based on this,the setting time and fluidity of AAS are significantly improved and enhanced,especially the yield stress and plastic viscosity of AAS paste show a decreasing trend with increasing tannic acid content.（2）Analysis of AAS hydration mechanisms indicates that different types of polyphenols have different effects on the hydration characteristics of AAS,which are closely related to their molecular weight and structure.As AAS hydration progresses,plant polyphenols form numerous polyphenol-Ca complexes through hydroxyl group chelation,providing more hydration product growth nuclei during the hydration acceleration period,promoting local oversaturation of Ca²⁺,and dissolution of hydration products.In addition,polyphenols can also produce good dispersion effects by adsorbing onto the hydrated micro-particle system,thereby accelerating the AAS hydration process.The higher the molecular weight of polyphenols,the more significant the acceleration of AAS hydration and the more hydration products formed.（3）Based on the ion chelation effect of plant polyphenols on AAS hydration promotion,the compactness of AAS mortar pore structure is improved,accompanied by a decrease in capillary pore volume,which significantly suppresses excessive autogenous shrinkage of AAS caused by capillary self-drying.The higher the content of plant polyphenols,the smaller the autogenous shrinkage.On one hand,polyphenols can promote cement hydration through ion chelation,greatly reduce porosity,and achieve efficient shrinkage reduction.On the other hand,polyphenols significantly alter the multi-scale mechanical properties of AAS,promote the formation of a high elastic modulus phase,and enhance the ability to resist shrinkage deformation.Moreover,polyphenols delay the early hydration of AAS,reduce its chemical shrinkage,maintain internal humidity at a higher level,and greatly alleviate the self-drying problem of AAS.（4）Polyphenols with different molecular weights have different effects on the compressive strength of AAS.This is related to the hydration promotion and hydration retarding effects of plant polyphenols.At the same mass,polyphenols with larger molecules such as tannic acid and waste tea polyphenols have fewer molecules,which simultaneously dilutes the hydration retarding effect produced by particle adsorption and the hydration promotion effect produced by ion chelation.The hydration promotion effect outweighs the hydration retarding effect on the macroscopic behavior of AAS,thereby strengthening the macroscopic performance of AAS.Conversely,polyphenols with lower molecular weights exhibit stronger hydration retarding effects,affecting the development of AAS macroscopic properties.Therefore,it is necessary to optimize the molecular weight and corresponding content of plant polyphenols to achieve efficient control of AAS performance.（5）Compared with commercial admixtures,using plant polyphenols as performance modifiers for AAS is not only economical and efficient but also environmentally friendly.The research results show that compared with traditional commercial admixtures,the use of four types of plant polyphenols can significantly reduce the carbon emissions of AAS and improve its economic and ecological benefits.Using waste tea leaves as a source of waste tea polyphenols eliminates the extraction and purification steps of plant polyphenols,resulting in lower carbon emissions and raw material costs for AAS.When the concentration of waste tea polyphenols is 10%,both the ecological and cost benefits of AAS can be increased by 50.9%.This is conducive to promoting the resource utilization of tea waste and provides a more environmentally friendly waste-based source of plant polyphenols for AAS green performance modifiers.The research results reveal the impact of different polyphenols on AAS performance and establish a method for regulating AAS performance based on plant polyphenols.This method boasts economic,efficient,and environmentally friendly advantages,not only providing theoretical foundations and technical support for the development and application of AAS but also serving as a reference for the development of other low-carbon cementitious materials.Figure 67 Table 19 Reference 273...