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Liu J.,Jiangsu Research Institute of Building Science | Liu J.,Jiangsu Bote New Material Ltd. | Yang Y.,Jiangsu Research Institute of Building Science | Zhou D.,Jiangsu Research Institute of Building Science | Ran Q.,State Key Laboratory of High Performance Civil Engineering Materials
American Concrete Institute, ACI Special Publication | Year: 2015

Slump loss of fresh concrete was a common issue in engineering construction, especially under high temperature and long distance transportation conditions. Therefore, slow-release polycarboxylate superplasticizers (PCEs) have been widely used to reduce the slump loss in various engineering projects. In this study, three kinds of PCEs with different proportions of hydroxyl ester groups (HEG) were synthesized and characterized by 1H-NMR and Gel Permeation Chromatography (GPC). The effects of the HEG content on dispersion retention, adsorption kinetics and zeta potential of fresh cement suspensions were systematically investigated to figure out the mechanism. For PCEs with the same molar ratio of carboxyl group and reactive polyether, the dispersion retention ability of PCEs is improved with the increasing of HEG ratio. HEG in PCEs can be slowly converted to carboxyl groups in the alkaline environment of cement suspension, which could enhance the adsorption of PCE molecules onto the surface of cement particles. Despite major of the initially adsorbed-PCE molecules might have been embedded in hydration products, free PCE molecules with released carboxyl groups in the solution can continuously adsorb onto the surface of cement particles and play a role in dispersion. This explains why slow-release PCEs have a dispersion retention effect on cement particles within a certain time. Source

Lv J.,State Key Laboratory of High Performance Civil Engineering Materials | Lv J.,Jiangsu Subote New Materials Co. | Liu J.Z.,Jiangsu Subote New Materials Co.
Applied Mechanics and Materials | Year: 2014

In order to investigate the bond strength between deformed steel fiber and concrete, various deformed steel fibers, like hooked end fiber, spiral type fiber, bundle fiber, hooked fiber and so on, are produced. Straight type fiber and deformed fiber were embedded in mortar to do the bond strength experiment. A comparison with each other was carried out. It has been found that the change of the fiber cross section increases the bond strength between steel fiber and concrete matrix, growth range outweighs 100%. When modified both ends of anchorages, the bond strength raises 400% in contrast with straight type steel fiber. Besides, the deformed fiber, which went through two modified methods, enhances the bond strength over 700% in comparison with straight type fiber. © (2014) Trans Tech Publications, Switzerland. Source

Ran Q.,State Key Laboratory of High Performance Civil Engineering Materials | Ran Q.,Jiangsu Research Institute of Building Science | Wang X.,Jiangsu Sobute New Materials Co. | Shu X.,Jiangsu Sobute New Materials Co. | And 3 more authors.
Journal of Dispersion Science and Technology | Year: 2016

Different AA-OEGMA copolymers with random and block distributions were synthesized using free radical polymerization and reversible addition-fragmentation chain transfer polymerization, respectively. Studies on the dispersion ability, adsorption isotherm, adsorption conformation, and zeta potential revealed that the random and block architecture behaved differently. Sequence structure of polycarboxylate polymers (PCPs) had a significant influence on its performance. Both monomer ratio and sequence structure had influences on the dispersion of cement paste. Compared with random PCPs, PCPs with block distribution adsorbed faster on cement particle surfaces because of the higher density of exposed carboxylic groups. For random PCPs, the adsorption was a thermodynamic spontaneous process and driven by entropy, while it was driven by Gibbs free energy for block PCPs. Besides, the hydrodynamic radius of random PCPs in solution was larger than the block PCPs. However, the adsorbed layer thickness of random PCPs was close to that of block PCPs. Furthermore, the zeta potential illustrated that the PCPs with block distribution may adopt a more extended conformation compared with random PCPs. All these findings found from the differences between random PCPs and block PCPs will help the researchers to explore high-performance PCPs. © 2016, Copyright © Taylor & Francis Group, LLC. Source

Song Z.,Hohai University | Jiang L.,Hohai University | Li W.,State Key Laboratory of High Performance Civil Engineering Materials | Xiong C.,Hohai University | Chu H.,Hohai University
Construction and Building Materials | Year: 2016

Fatigue damage is one of the most important factors impacting the chloride diffusion coefficient in concrete. In this paper, the electrical impedance spectra (EIS) method is used to analyze the damage level of the fatigue concrete. An electrical equivalent circuit is established to extract the electrochemical parameters from the impedance spectra. It is shown that the fitting results of the equivalent circuit match well with the experimental spectra. By analyzing the physical meanings of the parameters, the reciprocal of the overall resistance (1/RCDP + 1/RCCP) is finally adopted as an indicator of the fatigue damage level. Chloride diffusion coefficients of concrete undergoing fatigue damage were determined by a modified RCM method. It is found that the chloride diffusion coefficients decrease linearly with the overall resistances. The reduction in DRCM is found to be rapid for the high w/c ratio (w/c 0.5) concrete and gradual for the low w/c ratio (w/c 0.36) concrete. It is also found that DRCM increases nonlinearly with the indicator IDF. The increasing rates get smaller when IDF grows, and DRCM has a maximum value when IDF trends to infinity. © 2016 Elsevier Ltd. All rights reserved. Source

Shi L.,Jiangsu Research Institute of Building Science | Liu J.,State Key Laboratory of High Performance Civil Engineering Materials
Procedia Engineering | Year: 2012

Polymer coating is progressively being used in fields of concrete curing and concrete surface strengthening. However, only very few researches have been reported to investigate the effect of polymer coating on the properties of surface layer concrete. The effects of polymer coating on shrinkage, mechanical property, carbonation, capillary absorption and chloride ion diffusion of surface layer concrete were studied in the present investigation. The experimental results showed that polymer coating could obviously reduce the mortar shrinkage of the concrete surface, and the thicker the polymer coating, the greater shrinkage reducing ratio at early ages. It has been found that the polymer coating enhanced the mortar early age strength of the concrete surface. Meanwhile, the carbonation resistance of surface layer concrete, as well as the mortar infiltration resistance on the surface of concrete was improved by polymer coating. The results also demonstrated that the capillary absorption ratio of mortar in the surface layer of concrete cured under the polymer coating condition could be reduced by 87% and 78%, respectively compared with dry and standard curing conditions. In the same way, polymer coating had an improvement effect on chloride ion diffusion resistance of surface layer concrete. © 2011 Published by Elsevier Ltd. Source

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