The reinforced concrete (RC) water retaining tank walls with horizontal construction joints are prone to experiencing seepage under high hydrostatic pressure, which can affect the structural integrity and functionality. To evaluate the impermeability of construction joints with different improvement measures, the permeability test of concrete with and without horizontal construction joints was conducted. The test results show that the addition of Polypropylene fibers (PP fiber) and Cementitious Capillary Crystalline Waterproofing materials (CCCW) can improve the self-waterproofing ability of concrete. The impermeability at the construction joint is much lower than that of single-casting concrete. Moreover, applying CCCW to the water-facing surface of the construction joint can significantly enhance its impermeability. Then, two 1:2 scaled RC tank wall specimens were manufactured, with one wall of conventional concrete and the other wall of modified concrete. The impermeability tests of the typical single-casting and double-layer casting parts of the two wall specimens were carried out respectively. The experimental results show the RC tank wall with construction joint is prone to generate initial defects and seepage, making it difficult to achieve the design watertight requirements. The use of modified concrete materials and surface treatment in the relevant part can effectively improve the impermeability performance of the construction joint. Finally, the BP neural network was used to establish a prediction model between the impermeability of concrete and its material parameters and construction technology.
Recycled concrete with manufactured sand (RCM) is a type of recycled concrete that uses manufactured sand as fine aggregate, and there have been limited reports on the investigation of its high temperature performance in the construction industry. This study, starting from two curing regimes, explored the high temperature performance of RCM with water-to-cementitious ratios of 0.32, 0.4, and 0.48. Various physical properties of the samples in each group were tested, including surface morphology changes, mass loss rate, microstructure and composition alterations, as well as fundamental mechanical properties like compressive strength and elastic moduli. The experimental results indicate that RCM specimens exhibit slightly higher compressive strength after 7 d of high-temperature water curing compared to the 30 d standard curing. Furthermore, following high temperature tests ranging from 200 °C to 800 °C, the strength reduction in the specimens is not significantly pronounced when compared to those subjected to standard curing. Utilizing the measured stress-strain curves and existing constitutive models for high temperature behavior of recycled concrete, this study analyzes the influencing factors affecting the performance of RCM under high temperature conditions. The findings provide theoretical support for the practical engineering application of RCM.
热激励去极化电流(TSDC)测量技术可以提供存在于材料体系中的缺陷类型信息,例如空间电荷、偶极子、陷阱电荷等.通过TSDC谱分析,可研究偶极子和可动离子的性质,以及激活能、弛豫时间、荷电粒子浓度等微观参数,进而更好地理解与缺陷有关的物理本质.本文介绍了当前TSDC技术在无机材料中的应用现状,整理归纳出TSDC技术在线性介质、非线性介质、陶瓷-聚合物复合材料中的研究结果与最新进展,从本质上揭示无机材料中缺陷与性能之间的内在关联.有望拓展TSDC技术在无机材料中的应用,为无机材料微观机制研究提供新思路.
在质子交换膜燃料电池(PEMFC)运行过程中,产生的自由基会攻击质子交换膜,使其开裂或形成孔洞,导致电池失效.常见的改性方法是在质子交换膜(PEM)中添加自由基清除剂材料.基于此,本文合成了Sn掺杂CeO2自由基清除剂,通过提高Ce3+浓度来增强其在PEMFC中自由基清除性能,避免PEM厚度迅速减薄,从而提高质子PEMFC的耐久性.密度泛函理论计算和试验结果表明,Sn掺杂会引起CeO2产生晶格畸变,降低氧空位形成能,促进CeO2中Ce3+的形成.同时,Sn2+的加入可将CeO2-Sn样品中的Ce4+还原为Ce3+,提升Ce3+的浓度,从而提高PEM的耐久性.单电池测试结果表明,经70 h的开路电压衰减测试,CeO2-Sn-5％改性后的质子交换膜组装的单电池电压衰减率最低(18％),且功率保留率(56％)比其他样品更高,表明该样品具有更优异的耐久性.
In order to overcome the disadvantage of poor mechanical properties of composite cementitious material system with large dosage,the response surface method was adopted to optimize the hybrid fiber composite cementitious material system,and the prediction model was established by taking the dosage of steel fiber,polypropylene fiber and desulphurization gypsum as the variable factors,and 28 d flexural strength and compressive strength of cement mortar as the evaluation indexes.Besides,the test of cement mortar and concrete was carried out to verify the predictive model.The results show that when the volume dosage of steel fiber is 0.4% ,the volume dosage of polypropylene fiber is 0.116% and the mass dosage of desulphurization gypsum is 8% ,the working and mechanical properties of composite materials reach the optimum,the predicted values of the 28 d flexural and compressive strength can be up to 7.0 and 37.4 MPa.The relative errors of flexural and compressive strength between the predicted values and the experimental values are only 2.86% and 1.32% and the standard deviation of the test values of flexural strength and compressive strength is 0.148 8 and 1.345 9,proving that the response surface method has high prediction precision,accuracy and scientificity.The optimisation effect of the composite cementitious material system is proved through this study,which provides a new solution idea and test basis for the multi-objective optimisation problem of composite materials.
