| Polycarboxylate-based superplasticizer(abbr. PC) is the general term of the polymer by copolymerizing unsaturated monomer containing carboxyl and other monomer, which have a specific structure and performance. The common characteristics of this kind of PC are the main chain contain a certain number of carboxyl functional groups, the molecular structure is linear, comb-shaped or dendritic, with high water-reducing rate, excellent plasticity, and can make concrete has good physical and mechanical properties.In this dissertation, a new type of polyether-type PC(PC-1) was synthesized by free radical copolymerization, and it was comparative studied with polyester-type PC(PC-2), mainly compared the compatibility between the two types of PC and cement. The effect of soluble alkali content on fluidity of paste, zeta potential of particle surface, hydration process and the other performance of the cement added different types of PC have been investigated by changing the soluble alkali content of cement paste through adding K2CO3. The main research work includes the following aspects:(1) The synthesis of polyether-type PC: A new type of polyether-type PC was synthesized by taking allyl poly ethylene glycols, sodium allylsulfonate and acrylic acid as monomer. The effect of some factors like initiator amount, molar ratio of monomer, reaction temperature and polymerization time on dispersion property of polymerization product were studied, respectively. The optimum synthesis process parameters were obtained by the further orthogonal test is: n(AA):n(APEG):n(SAS)=18:9:13, initiator amount is 1.5%, reaction temperature is 80℃, and polymerization time is 8h.(2) The effect of soluble alkali on compatibility between PC and cement: Effect of PC-1 and PC-2 in different dosage on fluidity of cement paste were compared, and analyzed the mechanism of cement particle dispersion by these two PC. The effect of soluble alkali content on fluidity of cement paste under different types of PC was studied by adding K2CO3 to change soluble alkali content. The results show that PC-1, which saturation point is lower, has the better compatibility with cement than PC-2, it can make cement paste has high initial fluidity, and low loss of fluidity as time. When PC-1 or PC-2 dosage is below its saturation point, appropriately increase soluble alkali content has little influence on the compatibility between PC-1 and cement, but can improve the compatibility between PC-2 and cement obviously, and enhance the flow properties of paste.(3) The effect of soluble alkali on hydration reaction of the cement adding with different types of PC: The influence of interaction of soluble alkali and PC on hydration heat of cement has been researched, and the hydration products are examined with XRD and SEM analysis respectively. The results show that the hydration exothermic rate of cement was increased with PC-1 or PC-2 added, appropriate increase soluble alkali can reduce the hydration exothermic rate and heat of cement with PC-1 or PC-2. PC-1 and PC-2 both can promote the early hydration of cement, increase soluble alkali content can accelerate the hydration process of cement with PC-1 or PC-2 to a certain extent, can make the hardening cement structure tended to become more density, which is beneficial to the development of the early strength of cement stone.(4) The effect of PC and soluble alkali on cement performance: The effect of the interaction of soluble alkali and PC on setting time of cement, pore size distribution of cement stone and flexural and compressive strength of hardening cement were studied. The results show that when PC-1 dosage is low, a spot of soluble alkali have retarding effect on paste, when PC-1 dosage is high, soluble alkali can accelerate setting of paste in some extent; But for the paste added with PC-2, soluble alkali has strong accelerating effect on paste. PC-1 can make the most probable pore radius of cement stone increase, and soluble alkali can make pore volume of cement stone added with PC-1 decrease sharply, which is conducive to the development of strength of cement stone; But PC-2 has little influence on pore radius distribution of cement stone, and the improvement of soluble alkali on strength of cement stone is also not obvious. It would be beneficial to the improving of flexural and compressive strength of cement stone when the adding amount of PC-1 or PC-2 is 0.04% and the adding amount of soluble alkali is from 0.36% to 0.48%.The research of this dissertation reveals the rule of effect of soluble alkali on the compatibility between different types of PC and cement, and has broadened the application scope of PC, it also has some guiding significance to the actual project construction. |
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