| With the all-round development of infrastructures in China, it not only accelerates the demand for concrete, but also promotes the rapid development of high-performance concrete technology. Meanwhile, high performance concrete puts forward higher requirements on the performance of superplasticizer, which has caused the traditional water reducing agent could not meet the reguests of the modern construction technology. Therefore, polycarboxylate superplasticizer of the third generation has come into being.The study is based on its sub-topics "Modern Concrete Gel Paste Microstructure Formation Mechanism" from the National973Project (2009CB623201). Focused on emergence of new technologies and new monomer raw materials, optical conditions for the preparation of ether-type polycarboxylate superplasticizer has been confirmed and performance and molecular structure of water reducer has been respectively tested and characterized. Besides, concerning the problems such as early hydration characteristics of C3A single mineral and poor adaptability between superplasticizer and cement, hydration regulation law, mechanism and control means of superplasticizer and the coordinating role of the different types of retarders and water reducer regulating C3A-CaSO4·2H2O binary system has been discussed by means of the heat of hydration, XRD, Laman, SEM etc. The main work and the conclusions are as follows:1.Researching on the influences of a single factor on the synthesis, confirming the optimal ratio of raw materials, testing the performance of superplasticizer and characterizing of molecular structure:(1)The synthetic condition of the APEG-type superplasticizer has been determined as follows:the mole proportion of the monomers APEG, MA and MAS is1:3.5:0.6, the content of initiator(APS) is4%, the temperature is80℃, and it reacts for4h.(2)The synthetic condition of the TPEG-type superplasticizer has been determined as follows:the mole proportion of the monomers TPEG and AA is 1:5, the mole ratio of L-ascorbic acid and H2O2is3:4, the mass ratio of oxidant (H2O2) is2%,3-thioglycolic acid is1%, the temperature is below50℃, and it reacts for3h.(3)The structure of the ether-type polycarboxylate superplasticizer is characterized by infrared spectroscopy and gel permeation chromatography. The results indicated that the expected functional group is introduced into structure. According to the measured data of GPC, the Mw, Wn, PDI, MCL and SCL of APEG and TPEG type superplasticizers are followed by14700and103000g/mol,7540and84500g/mol,1.95and1.22nm,2.5and1.8nm,15.3and15.3nm.2.Researching on the effect of different dosage of superplasticizer on the hydration of C3A-CaSO4-2H2O binary system and expounding the regulation mechanism:(1)The influence of superplasticizer on the regulation law of C3A-CaSO4·2H2O binary system is relevant to its content. Heat of hydration has shown that superplasticizer has delayed and weaked the hydration heat peak at low dosage, while promoting hydration heat rate and delaying effect vanished at high dosage. XRD, IR, and Laman analysis showed that superplasticizer delayed AFt generation and gypsum consumption at the early hydration and also delayed the transformation from AFt to AFm at medium-term hydration at low dosage, however, the opposite rule is concluded at high dosage, and hydration process of all samples are similar at28day. SEM studies indicated that superplasticizer significantly changed AFt crystal morphology on the whole. As far as dosage0.1%of the sample, AFt was flocculation at early stage, and then thin rod-shaped particles at later stage, in addition, detected no petal-like AFm. In terms of dosage0.3%of the sample, AFt displayed short rod-like crystals at the early, and then crystals gradually overlaped each other and growed into the dense structure of cement paste, moreover generated petal-like AFm. Concerning dosage0.5%of the sample, AFt is soft and fibrous stage at early stage, and then become aligned needle-shaped crystals latterly. Besides, appeared petal-like AFm.(2)The hydration regulation mechanism of superplasticizer: it played a dual role in the process of the hydration of C3A-CaSO4-2H2O binary system, that is delaying or promoting effect according to different dosage. When the content is low, adsorption and complexation exert the dominant role delaying the transformation time from AFt to AFm, in contrast to low content, when the content is high, dispersion plays a dominant role thus promoting change time from AFt to AFm.3.Researching on effect of superplasticizer and synergistic effect between different types of retarders and superplasticizer on hydration regulation law of different content of C3A-cement system and C3A-CaSO4·2H2O binary system:(1)As far as C3A-cement binary system, synergistic effect between different types of retarders and superplasticizer indicated different regulation law. Considering low C3A content cement, synergistic effect between PP and superplasticizer could increase the initial flow and inhibit flow-loss while synergistic effect between SJ, BS and superplasticizer have only excellent fluidity retention but not possess initial plasticizing effect. Referring to hige C3A content cement, the effect between PP and superplasticizer not only reduces the initial liquidity but also increases the loss, and the effect between SJ and superplasticizer has excellent ability to inhibit the loss, however, the effect between BS and superplasticizer owns auxiliary plasticizing effect and inhibit the loss, thus which can effectively solve adverse compatibility between superplasticizer and high C3A content cement.(2)As far as C3A-CaSO4-2H2O binary system, the regulation laws of synergistic effect between different types of retarders and superplasticizer is related to retarding components. Heat of hydration, XRD, SEM and other microscopic analysis indicates that: compared with blank samples, synergistic effect between PP and superplasticizer increases the rate of hydration heat meanwhile accelerates the generation of AFt and transformation from AFt to AFm and in the early hydration products, AFt are surrounded by a large accumulation and show the scattering of acupuncture shape and become a short rod-like structure at later stage. But the synergistic effect between SJ and superplasticizer has little effect on the heat release rate but has delayed the appearing time of the highest exothermic peak besides that, at the early hydratiob AFt has clear boundary and short cylindrical particle crystal with high crystallization then it transforms into a thin rod-like structure at the later stage. However, the synergistic effect between BS and superplasticizer greatly decrease the heat release rate even the maximum exothermic peak is about to disappear. At the same time, it also delays the formation of AFt and AFm. In addition, AFt shows amorphous gel shape at early term then gradually become fluffy fibrous shape and at later term transforms into the needle and build into a compact structure as a whole. |
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