Research On Mechanism Of Polycarboxylate Superplasticizer On Rheological Properties Of Cement Paste

Superplasticizer has been widely used in many engineering projects in ourcountry. However, the research on working mechanism of superplasticizerstill remains incomplete. In this paper we synthesized superplasticizer productin our own lab. By adjusting dosages of different reactants, modifying themolecular structure of superplasticizer, we successfully produced productsthat had good properties, and then we analyzed the effect of superplasticizeron rheological properties of cement pastes.The molecular weight and its distribution were characterized by GPC.The number of components of polymer backbone was characterized by1H-NMR and the density of side chain of superplasticizer was found out. Byusing DSC the crystallization property of side chain of superplasticizer wastested. The results showed that the side chain was confined by backbone andbecame harder to crystallize. The conformation of superplasticizer moleculesin aqueous solution was characterized by DLS, the hydraulic radius ofsuperplasticizer molecule was found out. Meanwhile, the DLS results showedthat there might be three types of structure which was in different scales. Theeffect of concentration of SP, calcium cations and PH of solution onconformation of SP molecules was tested.The interactions between SP molecules and cement particles wereanalyzed. By TOC test the adsorption amount of SP on the surface of cementparticles was characterized. The conformation of SP molecule was found to becompacted when adsorbed. The influence of SP on hydration of cement wascharacterized by calorimetry. The discussion of the time of initial setting ofcement when different dosages of SP were added gave information of possibleretardation mechanism of SP molecules. By the test of zeta potential test inethanol/water system, surface potentials of cement particles under differenthydration degrees were obtained. The influence of SP on zeta potential on the surface of cement particles was discussed at the same time.A microstructural model of cement paste was built up. The size ofaggregated structure and distribution of cement particles in the paste beforeand after the addition of SP was observed by SEM test. The volume ratio ofdifferent types of water was obtained by fluidity test. The model was testedand analyzed by using data from the test of rheological parameters likeviscosity and yield stress. A rheological model of cement pastes was obtainedwithin different w/c ratio and dosage of SP.Retarder, air-entrained agent and defoamer were mixed with SP toanalyze the effect of these additives on rheological properties of cementpastes. A formula which could obtain high fluidity and good flow-retentionability was tested out.