Adsorption And Rheology Regulation Mechanism Of Superplasticizers On Different Cementitious Materials

The thesis relied on one of the national “973” program (Grant No.2009CB623201)subject: the formation mechanism of modern concrete cementitious slurrymicrostructure, aimed at differences in physicochemical properties of cementitiousmaterials including cement, fly ash Ⅰ, fly ash Ⅱ, superfine slag powder and silicafume, and diversity of molecular structure of superplasticizers. The thesis establishedrelationship between physicochemical properties of cementitious materials, amountadsorbed of superplasticizers, rheological properties of slurry, simultaneouslyproposed regulation methods of optimizing adsorption process of superplasticizersand rheology property of slurry by superplasticizers molecular structure design, andestablished adsorption and rheology model of superplasticizers, laid the foundation ofmolecular structure design and performance optimization of superplasticizers, basedon systematical research on influence of factors to amount adsorbed ofsuperplasticizers and rheology behaviors of slurry, these factors contained differentdosage of superplasticizers, adsorption time, temperature, particle size, pH value.Research results were as follows:1. Research on adsorption between cementitious materials and superplasticizers(1) The amount of superplasticizers adsorbed by cementitous materials increasedwith the increase of superplasticizers dosage.(2) The order of polycarboxylatesuperplasticizers saturated adsorption amount by cementitious materials from large tosmall was that: silica fume, cement, superfine slag powder, fly ashⅠ, fly ashⅡ. Theorder of naphthalene superplasticizers saturated adsorption amount by cementitiousmaterials from large to small was that: superfine slag powder, cement, fly ashⅠ, flyashⅡ, silica fume.(3) The amount of superplasticizers adsorbed by cement at5minutes increased with the increase of temperature, while increased with the decreaseof particle size. Particularly, the amount of superplasticizers adsorbed by superfineslag powder increased with the increase of pH value.(4) Adsorption process ofcementitious materials to superplasticizers could be adjusted via simultaneously usingKH-5and KH-B1, to achieve the requirments of dispersibility and dispersionstability. 2. Rheology research of slurry added superplasticizers and cementitousmaterials(1) The saturated dosage of KH-5was0.115%, and the saturated dosage of PNSwas0.65%.“over-fluidization” phenomena occurred when slump retention typeKH-B1polycarboxylate superplasticizers were added. The saturated dosage ofKH-B1was0.125%when reference time of rheology property was set at1hour. Theinitial fluidity, fluidity after1hour and2hours of slurry simultaneously added KH-5and KH-B1were between KH-5alone and KH-B1alone.(2) The rheology propertyof slurry added superplasticizers and cementitous materials was related tophysicochemical properties and dosage of cementitious materials, Adsorptionbetween cementitous materials and superplasticizers, and so on.(3) The rheologyproperty of cement paste could basically fit Bingham model, viscosity and yield stressdecreased with the increase of the dosage of superplasticizers. The cement pasteadded mineral admixtures at the dosage of10%could basically fit Bingham model.(4)Fluidity of cement paste increased with the increase of superplasticizers adsorbed bycement, while viscosity and yield stress decreased.3. Research on water-reducing mechanism and adsorption model ofsuperplasticizers(1) Naphthalene superplasticizers improved the dispersion by electrostatic effect.Converse of adsorption conformation of PNS in cement hydration process was one ofthe main reason why cement paste added PNS had a large fluidity loss by time.(2)KH-5and KH-B1improved the dispersion mainly by the steric effect.(3) The ester ofKH-B1hydrolyzed at a high alkaline environment created by the hydration of cement,then formed to the molecule which had a lager carboxyl density than KH-5, enlargethus increased the fluidity of cement paste.“over-fluidization” phenomena occurredwhen slump retention type KH-B1polycarboxylate superplasticizers were added.