The Influencing Mechanism Of Gypsum And Alkali Sulfate On The Compatibility Of Cement With Superplasticizers

Superplasticizers have become an important component of highperformance concrete and other advanced cementicious composite materials.Along with its extensive application, the compatibility of cement withsuperplasticizers is becoming an intensive research topic. Incompatibility leadsto some problems of cement paste, such as bad performance of superplasticizers,cement paste bleeding, rapid flow loss, abnormal setting, low strength ofconcrete, etc., which not only restricts the development and application of newsuperplasticizers, but also reduces other properties of advanced cementiciouscomposite materials. However, few existing study focus on the compatibility ofcement with superplasticizers and its mechanisms, which fail to direct theapplication of superplasticizers or improve compatibility.The compatibility of cement with superplasticizers is chosen as theresearch topic in this thesis. The performance, adsorption, electrochemistryproperties of superplasticizers and the microstructure of cement paste withsuperplasticizers are studied. Combined with the mechanism of superplasticizerfunctions, cementicious chemistry theory, microstructure of hydration productsand surface chemistry theory in cement paste, the influence of gypsum andalkali sulfate content on the evaluation indicators of compatibility of cementwith superplasticizers is clarified. The mechanisms of bad performance ofsuperplasticizers, cement paste rapid flow loss and abnormal setting arediscussed.Bleeding is commonly considered as a special incompatibility problem. Inthis research, free solution amount of cement paste is measured and themicrostructure of cement paste is observed through microscope. Combined withthe change of cement paste flowability, the model of different kinds of solutionin cement paste is raised, and the mechanism of bleeding is clarified. Finally,the free solution amount is considered as an indicator of compatibility. Theinfluence of gypsum and alkali sulfate content on bleeding is investigated through the measurements of free solution. The methods of improving bleedingproblem are raised from the mechanism level.The influence of superplasticizers on hydration products is one of the hottopics of the superplasticizer research, which always present obviousdifferences and divergences. However, it is very important to clarify itsmechanism in the research of compatibility. Combined with the results by XRD,SEM and ESEM, TEM methods with its high-accuracy EDX were used toinvestigate the influencing mechanism of superplasticizers on cement hydrationproducts and its secondary effects on the compatibility. The crystallization andmorphology of cement hydration products are not severely influenced bysuperplasticizers. These conclusions provide an important theoretical basis forcompatibility research.The main contribution of this thesis is as follows: the influencingmechanism of gypsum and alkali sulfate on compatibility is investigated. Themechanism of bleeding is clarified through the model of cement paste solution.The theory of superplasticizer performance and the theory of cement pastehydration with superplasticizers added are complemented and optimized. Theeffects of superplasticizers on cement hydration products are studied. Animportant theoretical basis for the compatibility research is discussed, which isable to direct the production and application of superplasticizers and improvecompatibility of cement with superplasticizers.