The repair and reinforcement of concrete structure has become an important engineering field.In order to investigate the shear strength curve and crack evolution law of new and old concrete bonded and locked under the notch,the mechanical parameters of new and old concrete were extracted,providing a method to establish a refined concrete model.Combined with the numerical simulation method,the shear peak stress and failure mode of new and old concrete composite under the notch with different normal angles of 0°,16°,30°,41°,49°and notche under different positions of 3.5 cm,5.5 cm,7.5 cm,9.5 cm,11.5 cm the old concrete from the loading surface were further studied.The results show that the shear stress-shear deformation curve of new and old concrete composite under the triangular sawtooth notch is composed of five parts:elastic stage,the first elastic-plastic stage,the second elastic-plastic stage,brittle fracture stage and residual strength stage.The microcracks are mainly shear failure in the new and old concrete binding surface,and mainly pull failure in the saw-tooth.The change of notch position and the change of triangular notch angle will affect the peak stress.With the notch position far away from the force surface,the shear strength of the new and old concrete binding surface will decrease.The shear strength of the test block un-der the independent and continuous sawtooth notch increases with the increase of the normal angle of the notch,and when the normal angle is drom 40 degrees to 50 degrees,there is a significant increase.The micro-cracks are more dispersed,the independent cracks increase,and the macro-cracks have a tendency to develop into the concrete.
3D printing technology is one of the most likely construction technologies to be used when building extraterrestrial bases in the future. The Mars 1 Base project in Gansu Province, China simulates the Martian landscape and uses concrete 3D printing technology to construct houses, creating a unique cultural tourism industry project. In June 2022, the 3D printing construction of five Martian hotel buildings began. The 3D-printed hotel is egg-shaped, with a total height of 9 m and a floor area of 46 square meters, divided into two floors with triangular windows and a skylight on the top. After the concrete components are 3D printed in the factory, they are transported to the project site for assembly and construction. This article introduces the structural design, 3D printing process and overall installation and construction of the Mars house. The five 3D-printed Martian houses and hotels were built in the Gobi Desert and took three months to complete. Based on digital printing and concrete 3D printing construction, the entire printing, installation, and construction process was safe, fast, and accurate, with a complete structural design and installation process. This project is currently the world's largest egg-shaped 3D printed structure, and its construction process provides experience for more 3D printing designs and is of positive significance for exploring the addition of intelligent building technology.
In order to study the bonding performance of fiber reinforced concrete,the tensile stress,bonding strength,equivalent bonding strength,average bonding strength,and local bonding stress are used as indicators to analyze the bonding performance.The electronic universal testing machine is used to study the bonding performance of fiber reinforced concrete with different fiber mixing types,different fiber mixing ratios,and different loading rates.The test shows that adding end-hook steel fiber into concrete can improve the bonding performance of fiber reinforced concrete,and the optimal total fiber content is 2%.The bonding performance of fiber reinforced concrete with hybrid steel fiber is better than that of fiber reinforced concrete with end hook steel fiber alone.The best mixing ratio is 1%for end hook steel fiber and 1%for straight steel fiber,which has significant inhibition effect on crack formation and propagation of fiber reinforced concrete.When the concrete grade is the same,the greater the loading rate,the greater the value of each viscosity index,that is,the better the bonding performance.When the loading rate is the same,increasing the strength grade of concrete can improve the bonding performance of fiber reinforced concrete and reduce the sensitivity of end-hook steel fiber to the loading rate.
采用纳米SiO2、纳米TiO2 和纳米CaCO3 分别替代部分水泥,研究了 3种不同类型的纳米颗粒对水泥基材料流变性能、早期水化过程、早期强度和微观特性的影响.通过压汞孔隙度测定法(MIP)、热重分析仪(TG)、X射线衍射法(XRD)和扫描电子显微镜(SEM)观察纳米材料对水泥基材料早期微观结构及形貌的影响.探讨了 3种纳米颗粒在改善水泥混凝土材料早期强度方面的差异.结果表明,纳米材料的填充效应、火山灰活性、成核效应,纳米尺寸效应及分散性等对水泥混凝土材料的早期力学性能有显著影响.
坝区高温低湿、大风等极端天气会使分层浇筑混凝土层间结合性能发生劣化.通过测定极端天气环境(如:高温低湿、大风)下混凝土的层面状态(含水量、贯入阻力)和层间劈裂抗拉强度,对3种施工措施(如表面不处理、覆盖保温被和界面凹槽)进行了研究.结果表明:碾压混凝土坝在极端环境下浇筑存在施工风险.在高温低湿条件下覆盖保温被并不能有效避免层间结合质量的下降,界面凹槽可以小幅度地提高坯层间结合强度;在大风条件下坯层表面覆盖保温被及采用界面凹槽处理是比较可行的措施,可以保证坯层间结合质量满足要求.在大风条件下覆盖保温被,一方面防止了水分的散失,另一方面延缓了混凝土的凝结速率,使得层间劈拉强度得到保证.
