| Polycarboxylate-type water-reducing agent (PC) acting as a new general water-reducing agent had many merits, such as low dosage, strong dispersing ability, good ability for keeping slump, good regulation and control of molecular structure, and no formaldehyde in production. PC has become the development direction and the hot research area of high performance water-reducing agent for concrete. However, due to the complicated molecular structure of PC, the relationship between its molecular structure and application properties was not clear, and the conformation of PC adsorbed on cement particles was in debate. Hence, the research of PC was beneficial for improving its application properties, mastering fully the rule of application properties and promoting the development of concrete with high efficiency.Firstly, the dissertation studied systematically the synthetic technology of PC and the effect of monomers on its dispersing properties. On that basis, the dissertation designed and synthetized four series PC, including (1) PC with different side chains containing short side chains, long and short side chains, long side chains; (2) PC with different sulfonic group having an increasing trend of sulfonic group content; (3) PC with different carboxylic group having an increasing trend of carboxylic group content; (4) PC with different molecular weights having an increasing trend of molecular weight. After that, the dissertation measured the molecular weights and structures of PC using the GPC, IR, NMR, respectively. Secondly, the dissertation studied the microstructure of PC in solution, analysed the application properties of it in cement systems and researched the effect of it on the rheological properties of cement pastes. At last, the dissertation studied the relationship between the molecular structure and the dispersing properties of PC by the method of the theoretical calculation.The dissertation studied the microstructure of PC with different side chains and PC with different molecular weights by fluorescent spectroscopy, AFM, TEM, DLS. Result showed that PC presented as aggregates with hyprebranched strcture. In addition, in neutral solution, PC with different side chains had different degree of aggregation. The order was: PC with long side chains>PC with long and short side chains>PC with short side chains. Their root-mean-square roughness measured by self-assembly film on quartz glass presented a decreasing trend, and the values was 0.568nm, 0.300nm, 0.440nm, respectively. The degree of aggregation of PC with larger molecular weight was higher than that of PC with smaller molecular weight, and their root-mean-square roughness was 0.521nm、0.630nm, respectively. When the solution was strong basic, the order of aggregation degree of PC with different side chains was: PC with short side chains>PC with long side chains>PC with long and short side chains. But the PC with different molecular weights had the same degree of aggregation.The results of TEM and DLS indicated that, in neutral solution, PC aggregates presented in different sizes with a non-uniform size distribution. For PC with different side chains, the aggregate size was in the following order: PC with long side chains>PC with long and short side chains>PC with short side chains, and their Z-Average diameters were 96.8nm, 76.9nm, 36.5nm, respectively. For PC with different molecular weights, aggregate size increases with molecular weight. Z-Average diameter of the aggregates obtained from PC with large molecular weight was 272.0 nm, while that of the aggregates obtained from PC with low molecular weight was 48.2 nm.The dissertation studied systematically the application performance of four series PC in cement system, including the fluidity of cement pastes, the losing rate of fluidity, the setting time and the reducing-water rate. The results indicated that, for PC with different side chains, PC with long and short side chains presented a better dispersing properties than PC with short side chains, and PC with long side chains was in between. PC with long side chains lead to a larger losing rate of fluidity than PC with short side chains, and PC with long and short side chains was in between. PC with short side chains lead to a longer setting time for pastes than PC with long side chains, PC with long and short side chains was in between, and the final setting time were 205min, 177min, 154min, respectively. PC with short side chains lead to a higher bleeding rate for mortar than PC with long side chains, PC with long and short side chains was in between, and the bleeding rate were 1.01%, 0.81%, 0.65%, respectively.For PC with different sulfonic groups and PC with different carboxylic groups, with the increasing of sulfonic groups and carboxylic groups content, their dispersing ability all presented an increasing trend at first and then a decreasing trend, PC with ratio of carboxylic groups to side chains being 3.6:1 presented the best dispersing property. The losing rate of fluidity produced by them existed an increasing trend. The setting time of paste produced by them were prolonged in different degree, the increasing of sulfonic groups lead to an unobvious increase and increasing of carboxylic groups lead to an obvious increase for setting time. The bleeding rate produced by them had an obvious increase.For PC with different molecular weights, with the increasing of molecular weight, their dispersing ability presented an increasing trend at first and then a decreasing trend, PC with the weight-average molecular weight being 62100 presented a good dispersing property. The losing rate of fluidity produced by them existed an increasing trend. The setting time of paste produced by them were prolonged with a slight degree. The bleeding rate produced by them had a slight increase.The dissertation fitted the rheological curves of paste using five classical rheological model, and found that the Herschel-Bulkley model was the optimal model. After that, the dissertation studied the effect of four series PC on the rheological property of pastes. The results found that PC with long and short side chains had the better ability for reducing the apparent viscosity of paste than PC with short side chains, and PC with long side chains fell in between. With the increasing of sulfonic groups content and carboxylic groups content of PC, the apparent viscosity produced by them presented an increasing trend at first and then a decreasing trend. When the dosage or the water/cement ratio changed, PC with medium molecular weight all lead to the lowest apparent viscosity. In the large dosage or high water/cement ratio, PC with large molecular weight lead to a lower apparent viscosity than PC with low molecular weight, however, in the low dosage or low water/cement ratio, PC with large molecular weight lead to a larger apparent viscosity than PC with low molecular weight, which provided an important guidance for the practical application of PC.The dissertation calculated the total potential energy of repulsion force using the interaction energy formula of electrostatic exclusion and potential energy formula of steric hindrance. The results found that the total potential energy of repulsion force produced by PC with short side chains was low, and range of its action also was short. The total potential energy of repulsion force produced by PC with long and short side chains was larger than that by PC with long side chains in the range of less than 10～13nm, by considering the paste experiment, it was thought that range of interaction among cement particles may occur in this range. With the increasing of sulfonic groups content and carboxylic groups content of PC, the total potential energy of repulsion force produced by them presented an increasing trend at first and then a decreasing trend. The total potential energy of repulsion force produced by PC with medium molecular weight was larger than that produced by PC with low molecular weight or by PC with large molecular weight. It was concluded that the varying rule of the total potential energy of repulsion force produced by four series PC was consistent with that of their dispersing ability in paste, and the calculated results explained the relationship between molecular structures of PC and their dispersing property in theory. |
