| Polycarboxylate superplasticizer (Polycarboxylate ether type superplasticizer，PCE) iswidely used nowadays in concrete industry due to its excellent performance includinglow dosage, high dispersion ability and flexible molecular structure. The two typicaltypes of PCEs are anionic polycarboxylate ether type superplasticizer (anPCE) andamphoteric polycarboxylate ether type superplasticizer (amPCE), of which themolecular structures have significant effect on early age properties of cementitiousmaterials like fluidity, early strength and hydration process. The anPCEs with varyingside-chain length or density, and amPCEs characterized by different cationic groupcontent, linkage bond or side-chain length were synthesized. The influence ofmolecular structure of superplasticizers on early age properties of cement pastes andmortars was studied by various characterization methods like fluidity, compressivestrength and calorimetric measurements.For anPCE, for a fixed quantity of adsorption group and density of side-chain, anPCEwith long side-chain shows higher adsorption amount on cement and bettercement-dispersion ability. At same weight dosage, anPCE with long side-chain canpromote the hydration of cement thus improving the early strength of cement mortar;According to the dissolution theory applied to the induction period in alite hydrationproposed by Juilland and co-workers, anPCEs adsorbed on the surface of C3S probablyenhance the energy of the formation of etch pit on the spot followed by a slowdissolution process, thus prolonging the induction period of cement hydration. At sameweight dosage, long side-chain anPCE has less influence on dissolution of C3S becauseof its less quantity compared to short side-chain anPCE due to the higher molecularweight. While at same mole dosage, the effect is reversed, anPCE with long side-chainretards the cement hydration process during acceleration period. So the anPCE mayalso effect the nucleation and growth of hydration products of C3S. For a givenquantity of adsorption group and mass ratio of adsorption groups to side-chain, anPCEwith lower side-chain density (longer side-chain at the same time) shows a higheradsorption ratio and better dispersion ability in initial age, which can also increase theearly strength by accelerating the hydration process of C3S. Then for a same quantityof adsorption group and same length of side-chain, anPCE with lower side-chaindensity leads to a higher initial fluidity of cement paste, but a reduced fluidity retention capacity. Meanwhile, the addition of lower side-chain density anPCE will retard thehydration process of both C3A and C3S phases, therefore reducing the early strength ofcement mortar.For amPCE, with the increase of cationic groups proportion, the adsorption of amPCEwas increased at the first time and then decreased. The introduction of certain amountcationic groups (10%,15%) will promote cement hydration, thus the early age strengthof cement paste is increased. Compared to amPCE with ester type linkage bond, ethertype amPCE shows higher adsorption ratio and dispersion ability. While addition ofester type amPCE ensures a higher early strength of cement paste. With the increase oflength of side chain, the adsorption of amPCE exhibites a tend of increase first andthen decrease. The amPCE with longer side-chain length is beneficial to the hydrationand early age strength development of cement paste.The studies carried out in this thesis will help to understand the effect of anPCE andamPCE on the early age properties of cement system, the structure-function of PCEmolecules and their working mechanisms on cement hydration. These researchfindings are beneficial to the molecular structure design and practical application ofPCE in the future. |
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