具有超强护筋能力的碳纳米管/水泥基机敏材料的构建及机理研究

Steel reinforced concrete is one of the most widely used civil engineering materials, and its degradation will decrease the service life of construction and lead to a serious economic implication. CNTs/cement composite, having high mechanical properties and an excellent piezoresistivity property, may be used for developing a self-sensing structural material for health monitoring.. However, there are several related problems standing in the way of realizing the ultimate potential of CNTs in civil engineering: poor dispersion, poor interfacial adhesion to cement matrix and impacting the corrosion resistance of reinforced concrete. . CNTs exhibit great Vander Waals forces and very high aspect ratio, which makes them extremely difficult to be uniformly dispersed in cement-based material. To overcome this drawback, the common approach is to apply a sonication process with a surfactant agent. Due to the surfactant often acts as an air entraining agent in cement composites, the extra adding of surfactant agent increases the porosity and pore size greatly and, eventually, degrades the mechanical properties as well as the penetration resistance of cement-based material. Additionally, CNTs may fail in bridging macro-cracks due to their poor interfacial adhesion to cement matrix as well as their small size. The propagation of macro-cracks may significantly decrease the mechanical property and durability of cement-based material. Thus, achieving better dispersion of CNTs and promoting strong interfacial interaction are critical factors to develop high performance CNTs/cement composites. Besides the aforementioned factors, as CNTs having high electron conduction capacity, the addition of CNTs may increase the conductivity of cement-based material, which may accelerate the corrosion rate of steel rebar in concrete. . It is well known that chemical force is more powerful than van der Waal's, which will be used to disperse CNTs and enhance the interfacial behavior of CNTs/cement matrix in this project. Additionally, this project will ‘link’ CNTs together into a longer chain by using polymer and form a three-dimensional network within cement matrix. The unique polymer network may enhance the fracture toughness, durability properties and the stable of piezoresistivity behavior of cement-based material. Furthermore, this project will construct a “capacitance effect” by coating CNTs with polymer film to enhance the piezoresistivity behavior of CNTs/cement composite. In addition, the “capacitance effect” may inhibit both the anodic and cathodic processes of steel rebar corrosion, which is expected to enhance the corrosion resistance of reinforced concrete greatly. The degradation of steel reinforced concrete containing CNTs during the corrosion process will be monitored by using its self-sensing behavior. The mechanisms for explaining their behaviors will be proposed in our project.

钢筋混凝土结构是目前最为常用的一种结构形式，其安全性至关重要，一旦失事，将会造成巨大的经济损失和人员伤亡。碳纳米管(CNTs)/水泥基材料具有优良的力学性能和压~阻效应，有望在提高钢筋混凝土的性能和实现其健康监测中发挥重要作用，研究意义重大。.但是，CNTs/水泥基机敏材料的应用尚存在“瓶颈”问题：导电性高、增加钢筋电化学腐蚀风险、压~阻效应稳定性差、宏观抗裂能力弱。.本项目将研究：1）利用化学作用力改善界面性能并驱散CNTs；2）优化微纳观结构，构筑三维互穿网络，提高复合材料的宏观控裂能力、耐久性和压~阻效应稳定性；3）构筑巨量微细电容器，显著提高复合材料的护筋性能和压~阻效应；4）采用快速实验方法结合数值分析，获得复合材料的力学性能和耐腐蚀性能，并利用其自身机敏特性进行实时监测；5）系统分析宏微观性能，获得构筑具有显著压阻效应及超强护筋能力的CNTs/水泥基材料的科学方法和机理理论。

水泥基材料中加入适量的碳纳米管（CNTs）后具有优良的力学性能、耐久性能和压~阻效应，有望在提高钢筋混凝土的力学性能、耐腐蚀性能和实现其健康监测中发挥重要作用。但是，CNTs/水泥基机敏材料在钢筋混凝土中的应用存在“瓶颈”问题：1）CNTs/水泥基机敏材料具有较高的导电性，将增加钢筋电化学腐蚀风险；2）环境湿度显著影响CNTs/水泥基材料的机敏性能，压~阻效应的稳定性差、可重复性差；3）界面作用力弱、微纳米尺寸的CNTs的宏观抗裂能力和应力传递能力较弱。. 本项目解决了上述“瓶颈”问题，首先利用化学作用力在水泥混凝土中构筑CNTs/聚合物三维互穿网络，减少混凝土中的孔隙率，优化孔结构，提高混凝土的力学性能和耐久性。同时降低混凝土的亲水性，减少环境湿度对混凝土导电性的影响，提高压~阻效应的稳定性和可重复性。其次，利用化学作用力分散碳纳米管并改善界面性能，并利用互穿网络实现CNTs的长纤维效应和微细环箍效应，提高混凝土的控裂能力和极限承载能力。另外，本项目还利用电容器效应提高CNTs/水泥基材料的压~阻效应并显著增加钢筋混凝土的耐腐蚀性能。通过采用SEM、FTIR、XRD、MIP等常用的微观分析方法对其微观结构进行了系统分析，利用分形理论建立了微观结构与宏观性能的相互关系。. 通过对掺入不同聚合物、不同碳纳米管的水泥基材料（包括砂浆和混凝土）的抗压强度、抗折强度、强度发展、断裂性能、机敏性能、抗冻性能、干缩性能、吸水率、耐化学腐蚀性能和护筋性能的系统分析(共计1600多个试样)，最终，我们获得了一种高性能水泥基机敏材料，其力学性能、耐久性能显著提高，氯离子腐蚀时间延长了60%，吸水率、干缩性显著降低。. 由于具有优良的物理力学性能和耐久性，同时还具有极低的吸水率和干缩性，该材料可以用于超严酷环境建筑中。通过努力，目前已经在楼房养殖排粪沟的得到了初试，使用面积超过5000平方米，用户评价优良。