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Stress-strain relationship of concrete in freeze-thaw environment

ZOU Chaoying, ZHAO Juan, LIANG Feng

《结构与土木工程前沿（英文）》 2008年第2卷第2期页码 184-188 doi: 10.1007/s11709-008-0029-3

摘要： Adopting the ASTM C666 quick freeze-thaw method, freeze-thaw tests with the number of freeze-thaw cycles being 0, 100, 150, 200, 250, and 300, were carried out on eighteen concrete prism specimens, the frost-resistant level of which, reaches D300 grade. The internal micro-structures of these specimens were observed by means of scanning electron microscopy (SEM) in order to detect damages caused by the freeze-thaw action. Afterwards these frozen-thawed specimens were tested on monotonic axial load; stress-strain testing curves after the freeze-thaw action were obtained. The testing results show that with the increasing time of freeze-thaw cycles, both the internal micro-structures and the basic mechanical parameters, including the ultimate bearing capacity, the Poisson ratio and the modulus of elasticity, degenerate in various degrees. Finally, stress-strain theoretical curvilinear equations and correlated parameters relating to the loss of relative dynamic modulus of elasticity were proposed. These results provide great reference for further research on the behavior and the calculation model of concrete structures in a freeze-thaw environment.

关键词： stress-strain theoretical freeze-thaw capacity reference eighteen concrete

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Investigation on the freeze-thaw damage to the jointed plain concrete pavement under different climate

Shuaicheng GUO, Qingli DAI, Jacob HILLER

《结构与土木工程前沿（英文）》 2018年第12卷第2期页码 227-238 doi: 10.1007/s11709-017-0426-6

摘要： Freeze-thaw damage is one of the main threats to the long time performance of the concrete pavement in the cold regions. This project aims to evaluate the influence of the freeze-thaw damages on pavement distresses under different climate conditions. Based on the Long-Term Pavement Performance (LTPP) data base, the freeze-thaw damage generated by four different kinds of climate conditions are considered in this project: wet-freeze, wet-non freeze, dry-freeze and dry-non freeze. The amount of the transverse crack and the joint spalling, along with the International Roughness Index ( ) are compared among the test sections located in these four different climate conditions. The back calculation with the Falling Weight Deflectometer (FWD) test results based on the ERES and the Estimation of Concrete Pavement Parameters (ECOPP) methods are conducted to obtain concrete slab elastic modulus and the subgrade -value. These two parameters both decrease with service time under freeze condition. Finally, MEPDG simulation is conducted to simulate the development with service year. These results showed the reasonable freeze-thaw damage development with pavement service life and under different climate conditions.

关键词： LTPP elastic modulus k-value IRI MEPDG

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Experimental investigation on freeze−thaw durability of polymer concrete

《结构与土木工程前沿（英文）》 2021年第15卷第4期页码 1038-1046 doi: 10.1007/s11709-021-0748-2

摘要： Assessing the durability of concrete is of prime importance to provide an adequate service life and reduce the repairing cost of structures. Freeze–thaw is one such test that indicates the ability of concrete to last a long time without a significant loss in its performance. In this study, the freeze–thaw resistance of polymer concrete containing different polymer contents was explored and compared to various conventional cement concretes. Concretes’ fresh and hardened properties were assessed for their workability, air content, and compressive strength. The mass loss, length change, dynamic modulus of elasticity, and residual compressive strength were determined for all types of concretes subjected to freeze–thaw cycles according to ASTM C666-procedure A. Results showed that polymer concrete (PC) specimens prepared with higher dosages of polymer contents possessed better freeze–thaw durability compared to other specimens. This high durability performance of PCs is mainly due to their impermeable microstructures, absence of water in their structure, and the high bond strength between aggregates and a polymer binder. It is also indicated that the performance of high-strength concrete containing air-entraining admixture is comparable with PC having optimum polymer content in terms of residual compressive strength, dynamic modulus of elasticity, mass loss, and length change.

关键词： durability test freeze-thaw resistance polymer concrete residual compressive strength ASTM C666-15

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Influence of construction-induced damage on the degradation of freeze–thawed lightweight cellular concrete

《结构与土木工程前沿（英文）》 2021年第15卷第3期页码 781-792 doi: 10.1007/s11709-021-0733-9

摘要： During the construction of lightweight cellular concrete (LCC), material damage frequently occurs, causing the degradation and deterioration of the mechanical performance, durability, and subgrade quality of LCC. The construction-induced damage can be more significant than those from the service environment of LCC, such as freeze–thaw (F–T) action in cold regions. However, the effect of construction-induced damage on LCC during F–T cycles is often ignored and the deterioration mechanisms are not yet clarified. In this study, we investigated the factors causing damage during construction using a sample preparation method established to simulate the damage in the laboratory setting. We conducted F–T cycle tests and microstructural characterization to study the effect of microstructural damage on the overall strength of LCC with different water contents under F–T actions. We established the relationship between the pore-area ratio and F–T cycle times, pore-area ratio, and strength, as well as the F–T cycle times and strength under different damage forms. The damage evolution is provided with the rationality of the damage equation, verified by comparing the measured and predicted damage variables. This study would serve as a guide for the construction and performance of LCC in cold regions.

关键词： lightweight cellular concrete construction-induced damage freeze-thaw action microstructure degradation mechanism

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emissions evaluation of the dynamic splitting tensile properties of steel fiber reinforced concrete under freeze–thaw

《结构与土木工程前沿（英文）》页码 1341-1356 doi: 10.1007/s11709-023-0988-4

摘要： This study empirically investigated the influence of freeze–thaw cycling on the dynamic splitting tensile properties of steel fiber reinforced concrete (SFRC). Brazilian disc splitting tests were conducted using four loading rates (0.002, 0.02, 0.2, and 2 mm/s) on specimens with four steel fiber contents (0%, 0.6%, 1.2%, and 1.8%) subjected to 0 and 50 freeze–thaw cycles. The dynamic splitting tensile damage characteristics were evaluated using acoustic emission (AE) parameter analysis and Fourier transform spectral analysis. The results quantified using the freeze–thaw damage factor defined in this paper indicate that the degree of damage to SFRC caused by freeze–thaw cycling was aggravated with increasing loading rate but mitigated by increasing fiber content. The percentage of low-frequency AE signals produced by the SFRC specimens during loading decreased with increasing loading rate, whereas that of high-frequency AE signals increased. Freeze–thaw action had little effect on the crack types observed during the early and middle stages of the loading process; however, the primary crack type observed during the later stage of loading changed from shear to tensile after the SFRC specimens were subjected to freeze–thaw cycling. Notably, the results of this study indicate that the freeze–thaw damage to SFRC reduces AE signal activity at low frequencies.

关键词： steel fiber reinforced concrete freeze–thaw cycling Brazilian disc splitting test acoustic emission technique dynamic splitting tensile acoustic emission properties

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Influence of freeze–thaw damage gradient on stress–strain relationship of stressed concrete

《结构与土木工程前沿（英文）》页码 1326-1340 doi: 10.1007/s11709-023-0014-x

摘要： Influence of freeze–thaw damage gradient on stress–strain relationship of stressed concrete

关键词： strain relationship concrete

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Biosorption of Cr(III) from aqueous solution by freeze-dried activated sludge: Equilibrium, kinetic and

Qian YAO, Hua ZHANG, Jun WU, Liming SHAO, Pinjing HE,

《环境科学与工程前沿（英文）》 2010年第4卷第3期页码 286-294 doi: 10.1007/s11783-010-0025-4

摘要： Batch biosorption experiments were conducted to remove Cr(III) from aqueous solutions using activated sludge from a sewage treatment plant. An investigation was conducted on the effects of the initial pH, contact time, temperature, and initial Cr(III) concentration in the biosorption process. The results revealed that the activated sludge exhibited the highest Cr(III) uptake capacity (120 mg·g) at 45°C, initial pH of 4, and initial Cr(III) concentration of 100 mg·L. The biosorption results obtained at various temperatures showed that the biosorption pattern accurately followed the Langmuir model. The calculated thermodynamic parameters, Δ (−0.8– −4.58 kJ·mol), Δ (15.6–44.4 kJ·mol), and Δ (0.06–0.15 kJ·mol·K) clearly indicated that the biosorption process was feasible, spontaneous, endothermic, and physical. The pseudo first-order and second-order kinetic models were adopted to describe the experimental data, which revealed that the Cr(III) biosorption process conformed to the second-order rate expression and the biosorption rate constants decreased with increasing Cr(III) concentration. The analysis of the values of biosorption activation energy ( = −7 kJ·mol) and the intra-particle diffusion model demonstrated that Cr(III) biosorption was film-diffusion-controlled.

关键词： activated sludge biosorption chromium film diffusion kinetics thermodynamics

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Intracellular trehalose improves the survival of human red blood cells by freeze-drying

HE Hui, LIU Baolin, HUA Zezhao, LI Chuan, WU Zhengzheng

《能源前沿（英文）》 2007年第1卷第1期页码 120-124 doi: 10.1007/s11708-007-0014-x

摘要： Freeze-drying of human red blood cells has a potential important application for blood transfusion. The aim of this study was to investigate the effects of intracellular trehalose on the survival of red blood cells after freeze-drying and rehydration. Fresh red blood cells were incubated in trehalose solutions of various concentrations at 37vH for 7 h following freeze-drying. Polyvinylpyrrolidone, Trehalose, sodium citrate, and human serum albumin were used as extracellular protective agents for the freeze-drying of red blood cells. The results indicated that the intracellular trehalose concentration was increased with increasing concentration of extracellular trehalose solution, and the maximum concentration of intracellular trehalose reached 35 mmol/L. The viability of freeze-dried red blood cells increased with the increment of intracellular trehalose concentration.

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具有聚集诱导发光活性的抗冻水凝胶用于低温环境下多级信息的加密和解密 Article

睢晓洁, 汪晓东, 蔡诚诚, 马君怡, 杨静, 张雷

《工程（英文）》 2023年第23卷第4期页码 82-89 doi: 10.1016/j.eng.2022.03.021

摘要：

抗冻水凝胶可以在零下温度环境中调节内部水分子的冻结行为，从而保持其优异特性（如智能响应性和液体运输）以及拓展其在寒冷条件下的应用。本文开发了一系列具有聚集诱导发光（AIE）活性的抗冻水凝胶，可实现在零下温度的信息加密和解密。通过改变水凝胶内的甜菜碱含量，该水凝胶可呈现出不同的冻结温度（T_f）。当温度高于/低于T_f时，编码于水凝胶内的AIE荧光分子不发射/发射荧光，从而可以实现信息的加密和解密。此外，通过调控水凝胶的冻结程序或者在水凝胶内原位引入具有光热效应的硫化铜纳米颗粒并结合特定的照射条件，可以实现信息的多级加密和解密，从而增强信息的安全性。最后，由于解密的信息图案对温度波动具有不可逆性，因此该具有AIE活性的抗冻水凝胶可作为无需外界供能的防伪标签，用于实时和可视化监测冷冻运输（−80 ℃）过程中生物样本（如间充质干细胞和红细胞）的活性。

关键词：抗冻水凝胶聚集诱导发光加密解密防伪

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Fabrication of cellulose aerogel from wheat straw with strong absorptive capacity

Jian LI,Caichao WAN,Yun LU,Qingfeng SUN

《农业科学与工程前沿（英文）》 2014年第1卷第1期页码 46-52 doi: 10.15302/J-FASE-2014004

摘要： An effectively mild solvent solution containing NaOH/PEG was employed to dissolve the cellulose extracted from the wheat straw. With further combined regeneration process and freeze-drying, the cellulose aerogel was successfully obtained. Scanning electron microscope, X-ray diffraction technique, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller were used to characterize this cellulose aerogel of low density (about 40 mg·cm ) and three-dimensional network with large specific surface area (about 101 m ·g ). Additionally, with a hydrophobic modification by trimethylchlorosilane, the cellulose aerogel showed a strong absorptive capacity for oil and dye solutions.

关键词： cellulose aerogel absorptive capacity waste wheat straw freeze-drying

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Comparison study on strategies to prepare nanocrystalline Li

Qiang XIAO, Xiaodan TANG, Yefeng LIU, Yijun ZHONG, Weidong ZHU

《化学科学与工程前沿（英文）》 2013年第7卷第3期页码 297-302 doi: 10.1007/s11705-013-1346-1

摘要： A comparison study has been conducted on the strategies for synthesizing nanocrystalline Li ZrO and K-doped Li ZrO absorbents for CO capture at high temperatures, including solid-state and liquid-phase methods, citrate route, and starch-assisted sol-gel method combined with freeze-drying technique. The absorption properties, including uptake rate and absorption capacity, of synthesized absorbents were investigated by thermogravimetric analysis (TGA) at different CO partial pressures. The nanosized Li ZrO crystals synthesized by the citrate route exhibit a faster uptake and a higher, nearly stoichiometric absorption capacity than those synthesized by the solid-state and liquid-phase methods. The doping of K into Li ZrO can significantly improve the uptake rate of CO , especially at low CO partial pressures. For the synthesis of K-doped Li ZrO , the citrate route has poor reproducibility and scalability, whereas the starch-assisted sol-gel method combined with freeze-drying technique is reproducible and easily scaled up, and the thus synthesized absorbents possess excellent CO capture properties.

关键词： CO₂ capture Li₂ZrO₃ K-doped Li₂ZrO₃ citrate starch freeze-drying technique

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冷冻-萃取/真空干燥法制备坚固和耐疲劳的聚酰亚胺纤维气凝胶及其增强阻燃性复合材料 Article

姚恺清, 宋崇虎, 方红, 王峰, 陈炼, 蒋少华, 查国君, 侯豪情

《工程（英文）》 2023年第21卷第2期页码 152-161 doi: 10.1016/j.eng.2021.08.024

摘要：

在现代新材料的快速发展中，用节能、省时、低成本和简便的新型方法制备具有优良机械性能和热学性能的轻质、低密度和高孔隙率气凝胶十分必要。在本工作中，我们使用短切电纺聚酰亚胺（PI）纤维作为支撑骨架，通过开发出一种无需特殊干燥方法的真空干燥（VD）与冷冻-萃取相结合的方法，制备出高性能PI 纤维气凝胶（PIFAs）。所得PIFAs 具有低密度（≤52.8 mg⋅cm⁻³）和高孔隙率（>96%）。该PIFA在至少20 000 次的循环压缩过程中展现出高度的耐疲劳性及低能量损失系数。密度为39.1 mg⋅cm⁻³的PIFA具有40.4 mW⋅m⁻¹⋅K⁻¹的热导率。通过进一步使用聚硅氮烷对PIFAs复合改性后，其具备更强的耐火性和氮气氛围中的高残留率（>70%）。这些优异的性能使PIFAs 及其复合材料成为可应用于建筑工业、航空和航天工业轻质材料、隔热和防火层以及高温反应催化剂载体的可选材料。此外，本工作中提出的冷冻-萃取/VD法因其节能、省时和节约成本而可被拓展用于制备其他材料。

关键词：聚酰亚胺气凝胶冷冻萃取真空干燥机械性能隔热性能防火性能