Behavior of high water-cement ratio concrete under biaxial compression after freeze-thaw cycles

The high water-cement ratio concrete specimens under biaxial compression that completed in a triaxial testing machine were experimentally studied. Strength and deformations of plain concrete specimens in two loading direction under biaxial compression with stress ratio of a=0, 0.25, 0.5, 0.75, 1.0 were obtained after 0, 25, 50 cycles of freeze-thaw. Influences of freeze-thaw cycles and stress ratio on the peak stress and deformation of this point were analyzed according to the experimental results, Based on the test data, the failure criterion expressed in terms of principal stress after different cycles of freeze-thaw, and the failure criterion with consideration of the influence of freeze-thaw cycle and stress ratio were proposed respectively.     

不同亲水性能的纤维对混凝土抗冻耐久性的影响

为了研究不同亲水性能的纤维对混凝土抗冻性能的影响规律,本文选择了3种不同回潮率的纤维,采用快冻法对纤维混凝土的抗冻耐久性进行了试验研究;分析了不同纤维混凝土的冻融损伤规律,以及回潮率对其冻融损伤的影响。利用SEM对冻融前后纤维-水泥石基体进行了观测,进一步探讨了纤维亲水性对混凝土抗冻性能的影响机理。结果表明,亲水性良好的纤维能够与水泥石更好的共同作用,有效抑制混凝土内部初期微缺陷及冻融过程中微缺陷的生长;而疏水性纤维难以与水泥石难以形成有效的共同作用体系,对于冻融循环过程中微缺陷的生长抑制能力较弱,其纤维-水泥石之间的薄弱带甚至可能会加速混凝土的冻融损伤;且随着冻融循环次数的增加,纤维的亲水性对混凝土的抗冻性能影响愈加明显。     

皖南红层软岩崩解特性试验分析

采用皖南地区3种红层软岩开展了室内"饱水-干燥"循环(湿-干循环)条件下的崩解试验.研究了不同湿-干循环次数下岩石的崩解现象和特征;分析崩解物的颗粒粒径分布随湿-干循环次数的变化规律;对浸泡岩样的水溶液离子浓度进行测试,同时对经历不同湿-干循环次数的岩样开展扫描电镜(SEM)试验;探讨软岩的崩解机理,比较分析不同岩石崩...     

一类有密度制约的捕食者——食饵种群数学模型的研究

通过调整捕捞系数和研究种群作用系数,使得策略最优.运用动力系统理论对2种群捕食—食饵系统的捕获与优化进行了定性的分析,证明了该系统不存在极限环的充分条件,并讨论了其生态意义.     

LW10B-252型断路器动作计数器故障分析及处理

针对某变电站LW10B-252型断路器动作计数器故障问题,提出在该计数器回路接线良好条件下,采用其回路的空气开关模拟断路器动作的试验方法查找故障计数器.分析了试验中出现的计数器故障原因,给出将计数器回路接入辅助开关常开触点、调整辅助开关结构和寻求性能优良的计数器3种方案,有效解决计数器损坏问题,提高电力系统的安全稳定性.     

冻融循环对再生保温混凝土性能影响的试验研究

再生保温混凝土是将建筑材料的再生利用和结构自保温相结合而提出的一种新型绿色建材,为了研究冻融循环对其性能的影响,在再生保温混凝土优化配合比的基础上,设计了5种不同比例再生粗骨料的配合比进行0、15、30、50次冻融循环,并测定相应的抗压强度和导热系数。试验结果表明,再生保温混凝土经过冻融循环后强度有所降低,运用回归分析法确定了不同再生粗骨料取代率的混凝土在不同冻融循环次数后对其抗压性能的定量影响规律,从而为再生保温混凝土在冻融环境下的工作机理研究提供依据。     

可溶性大豆多糖对春卷皮冻融循环过程中品质变化的影响

为解决春卷皮冻藏失水引起的品质下降、春卷皮油炸后含油量高等加工实践问题，研究冻融循环（0、4、8、12 次和24 次）条件下不同添加量（0%、0.3%、0.6%和0.9%）可溶性大豆多糖（soluble soybean polysaccharide，SSPS）对春卷皮加工性能和食用品质的影响。结果表明，SSPS能显著提高春卷皮的含水量（P＜0.05），减少冻融过程中的水分损失，提高春卷皮的质构特性和抗冻融性能。SSPS维持了冻融过程中春卷皮微观结构的完整性和紧密性，显著降低了油炸春卷皮的含油量（P＜0.05），提高了春卷皮油炸后的脆性和色泽。感官评价结果显示，SSPS提高了春卷的综合评分，SSPS可以作为一种有效的品质改良剂用于高品质春卷皮的生产加工。     

Cathodic protection of buried steel structures: Processes occurring at the steel/soil interface during wet/dry cycles

The behavior of steel coupons buried in soil under cathodic protection (CP) was studied during wet/dry cycles using electrochemical impedance spectroscopy and voltammetry. The coupons were left at open circuit potential for 7 days before applying CP for 51 days at potentials of −0.8 and −1.0 V versus Cu/CuSO₄ on coupons 1 and 2, respectively. Wet/dry cycling was achieved by first saturating the soil with an electrolyte inside a sealed electrochemical cell and by allowing the soil to dry by opening the top lid of the cell for various periods in the experiment. Surface analysis was performed after the experiments by X-ray diffraction and Raman spectroscopy. The soil electrolyte resistance R_s depended mainly on the variations of soil moisture for coupon 1 but was strongly affected by the effects induced by CP for coupon 2. Residual corrosion rates of 17–18 and 7–10 µm/year for coupons 1 and 2, respectively, were estimated via voltammetry. The kinetic parameters vary with the polarization level so that the data obtained with a coupon polarized at a given potential cannot be used to predict the residual corrosion rate of a coupon polarized at another potential.     

Investigation of Zr-doped ceria for solar thermochemical valorization of CO2

This study belongs to the estimation of the CO₂ conversion ability of Ce_1−xZr _xO₂ (CZ) materials performing multiple thermogravimetric CO₂ splitting (CDS) cycles. By varying the molar concentrations of Zr in the range of 0.05 to 0.5, the CZ materials were prepared by using co-precipitation method. By employing various analytical methods, the physical properties such as phase and elemental composition, crystallite size, and particle morphology of the as-synthesized CZ materials were recognized. The systematic estimation of the reactivity of each CZ material was performed by conducting multiple cycles in a thermogravimetric analyzer (TGA). Obtained findings indicated that Ce_0.7Zr_0.3O₂ (CZ30) and Ce_0.85Zr_0.15O₂ (CZ15) were proficient towards producing maximum amounts of O₂ () and CO ( n_CO ) than other CZ materials. It was further understood that, to achieve higher and n_CO as compared with CeO₂, the molar concentration of the Zr should be in the range of 15% to 35%.