Papers by Keyword: Retardation

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Authors: Shuang Yu, Wei Dong, Fu Min Xu, Ming Bi Fu, Yi Tan
Abstract: A conventional hot-pressing method was used to produce Al/Al-4wt%Cu functionally graded material (FGM). Heat treatment, which included solid solution treatment (T4) and aging treatment (T6), was carried out on hot-pressed (F) specimens. The creep crack growth tests were performed under constant loading of the creep-testing machines. The distribution of copper composition was investigated by line analysis via electron probe microanalysis. Fracture morphology and creep crack paths were studied by scanning electron microscopy. During heat treatment, the thickness of the graded transition layer increased due to copper composition redistribution. Creep crack growth retardation was found when crack propagated from the graded transition region to the Al-4wt%Cu layer. Greater improvement in creep crack growth resistance was achieved by the T4 and T6 states of Al/Al-4wt%Cu FGM. For T4 and T6 state specimens, the micro-cracks and crack kinking in the transition region were observed, which prevented creep crack growth.
Authors: C.S. Shin, K.C. Huang, R.Z. Li
Authors: Xiang Guo Li, Xiao Bo Yin, Bao Guo Ma, Bei Wu, Quanbin Chen, Yang Lv
Abstract: Compressive strength, setting time, hydration heat and hydration product were investigated to evaluate the effects of Zn2+ ion concentrations and the anion of zinc salts on the hydration characteristics of Portland cement paste. The results show that the hydration characteristics of zinc-doped cement pastes depend on Zn2+ ion concentrations and the anion of salts. With the incorporation of ZnCl2, the hydration heat, exothermic rate and the early-age strength of cement pastes were reduced, the arrival time of the highest temperature was delayed, and little negative influences on the compressive strength at 28 days were observed. The total hydration did not decrease incorporating ZnSO4; the hydration exothermic process was delayed. There were little negative influences on the compressive strength of the samples at 3 days and 28 days. Moreover, for the samples with the same Zn concentration, the retardation effect of ZnCl2 samples was stronger than that of ZnSO4 samples.
Authors: Cécile Rocanière, P. Dehaudt, B. Gaudreau
Authors: Mustapha Benachour, Boumedienne Zeggai, Nadjia Benachour, Mohamed Benguediab, Abdelkader Belmokhtar
Abstract: In this investigation, variable amplitude loading effect was studied on aged hardening Al-alloys in series 2000 and 7000. Generalised Willenborg model was used in order to show loading interaction effects (overload effects). Variable amplitude loading under different form of spectrum has affected highly the fatigue life and fatigue crack growth rates. Fatigue lives were increased and fatigue crack growth rates (FCGRs) were decreased in increasing of overload ratio in single overload case. In application of overload band, the fatigue lives and FCGRs were affected by band overload and R-ratio of them when level in FCGRs was increased.
Authors: Sheng Hua Lv, Rui Jun Gao, Jian Ping Duan, Xiao Liang Yan, Ming Ming Hou
Abstract: A modified polycarboxylate superplasticizer was synthesized by copolymerization of polyethylene glycol monomethyl ether methacrylate (MPEG-MA), β–Cyclodextrins grafted maleic anhydride (MAH-β-CD), methacrylic acid (MAA) and methallyl sulfonic acid (MAS). The excellent superplasticizer was obtained at the molar ratio of n(MAH-β-CD) : n(MAS) : n(MAA) : n(MPEG-MA) was 0.05:0.1:3:1 using ammonium persulfate (APS) as initiator at 90°C for 5 h. The applied results show that the product had many advantages, such as lower dosage, longer setting time, better flow-keeping ability and better compatibility with different cement. Meanwhile, the structure and relative molecular weight were characterized by FTIR and GPC respectively.
Authors: Xiao Fan Pang, Zi Ming Wang, He Qing Shen, Long Xue
Abstract: In this work, the effects of sucrose on setting time, heat of hydration and hydration products were studied, and the corresponding hydration process and regulation mechanism were discussed. With the adsorption test of sucrose on Ca (OH)2 suspensions, the “wake up” mechanism of Ca (OH)2 on sucrose-retarded cement was discussed. The results indicate that sucrose is used as retarder to increase the dormant period by adsorption to the cement surface, but there exists a critical amount of sucrose. And the XRD patterns indicate that sucrose can accelerate the reaction of C3A and the formation of AFt, but restraint the hydration of C3S. Ca (OH)2 that was used as accelerator in this paper can adsorb the sucrose up to 6.2mg sucrose/g Ca (OH)2. The combined-use of sucrose and Ca (OH)2 does not change the shape of the heat rate curves significantly. And the dormant period of sucrose-retarded cement can be decreased with the doses of Ca (OH)2 increasing, because of its high surface and preferential adsorption of sucrose.
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