冻融环境下纳米增强水泥基注浆材料物性演化微观机理

Grouting is a commonly adopted method to enhance the resistance to frost damage of the underground structures sustaining the freeze-thaw geological environment. It is difficult, however, for the traditional grouting materials to meet the requirement of cold weather conditions for high frost resistance. The carbon nanotubes (CNTs)/graphene oxide (GO) enhanced cement provide a new idea for developing cement-based grouts with the enhanced performance in strength and frost resistance, whereas more research is needed to know the influencing laws of freeze-thaw conditions on its material parameters. Therefore, in this project, the macroscopic physical and mechanical properties of the CNTs/GO enhanced cement-based grouts under the freeze-thaw conditions will be studied firstly. Then the effects of temperature variations on the characteristics of micro-fracture, nanoscale Young’s modulus and pore structures of the grouts will be furtherly investigated by utilization of Nano-characterization techniques of atomic force microscope (AFM), backscattered electron imaging (BSE), focused ion beam - scanning electron microscopy (FIB-SEM), et al., comprehensively. The micro damage model that can evaluate and forecast the changes of strength performance of grouts caused by freeze-thaw conditions will be established. After that, the molecular dynamics simulation model simulating the cement-based grouts containing CNTs/GO will be established, according to which the micromechanical mechanism of CNTs/GO influencing the fracture and strength performance of grouts will be revealed. This research aims to clarify the micro mechanism of the material parameters changing of the nanoscale reinforced cement-based grouts caused by freeze-thaw environment. The results can work as the theoretical basis for the designing of grouting projects conducted in cold regions with high altitude or high latitude.

注浆是提高冻融环境下的地下建筑结构抗冻胀破坏能力的常用技术手段，传统注浆材料难以满足严寒气候条件对其高抗冻性的要求。碳纳米管（CNTs）/氧化石墨烯（GO）等纳米增强水泥为研制高强抗冻水泥基注浆材料提供了新的科学依据，但目前尚不明确冻融对其基本物性的影响规律和机理。有鉴于此，本项目拟对CNTs/GO增强水泥基注浆材料在冻融环境下的宏观物理力学性质进行系统研究；然后结合原子力显微镜、背散射电子成像、聚焦离子束-扫描电镜等纳米表征技术，探究冻融对材料微观断裂、纳观杨氏模量和孔隙结构等特征的影响，建立可以评价和预测冻融导致材料强度变化的微观损伤模型；建立模拟含CNTs/GO的水泥基注浆材料分子动力学模型，揭示冻融环境下CNTs/GO影响材料变形破坏及强度特性的微观力学机理。研究旨在阐明冻融环境导致纳米增强水泥基注浆材料物性变化的微观机理，为高海拔、高纬度寒区内注浆加固工程的设计提供理论依据。

近年来，碳纳米管（CNTs）、氧化石墨烯（GO）等纳米材料在制备高性能复合水泥材料领域的应用日益广泛，为研制高强抗冻水泥基材料提供了新的科学依据。课题通过室内试验，明确了冻融循环作用对CNTs和GO增强水泥材料物理力学性能的影响规律；综合运用Peak force QNM技术和分子动力学模拟方法，探究了GO增强水泥的微观力学特性及其在微观拉伸作用下的力学行为，模拟了离子在含GO的纳米孔隙内的扩散特征；从宏观和微观尺度对水泥材料与非水反应高聚物接触面的力学行为进行了试验和模拟研究。结果表明，在水泥内加入0.02~0.04 wt.%的CNTs后，其抗压和抗拉强度提升了15.5~26.6%和36.2~125.2%，加入0.02~0.04 wt.%GO后，其抗压和抗拉强度提升了19.1~28.1%和76.2~159.5%；冻融循环后，CNTs/GO增强水泥的强度均降低了，且冻融次数越多，强度降低的越明显，但含CNTs或GO的水泥强度比普通水泥强度高；硬化后的水泥内低密度水化产物和高密度水化产物的微观杨氏模量分别介于18.21~20.63 GPa 和 26.99~27.14 GPa之间，随着GO含量的增加而增加；水泥内加入GO后，其微观裂隙、低密度水化产物及未水化颗粒的量最大降低幅度分别为18%、12.6%和39%；在冻胀力作用下，水泥会发生破坏，生成新的微裂隙；微观尺度上，GO在水泥的开裂过程中起到桥接作用，因此能有效提升其峰后的微观拉伸应力；对于含GO的微观孔隙，GO的吸附作用能有效阻碍离子的运输迁移，钙离子的扩散系数最大降幅为降77.9%，与微观孔隙内所分布的GO的比表面积正相关；微观尺度上高聚物与水泥材料之间有卡扣锁固作用，且高聚物密度越大，其与水泥材料贴合的愈紧密，接触面的剪切强度和粘聚力就越大（粘聚力范围为0.42~1.44 MPa）；水泥-高聚物接触面在剪切作用下的破坏区域的厚度为9~10 mm；随着接触面上水分子层厚度由0增大至20 Å，其微观剪切强度先增大后减小，在水分子厚度为10 Å时达到最大值，约为0.8 GPa；基于统计强度理论和损伤力学所建立的水泥-高聚物接触面剪切损伤模型能较好的反映其剪应力-应变曲线特征。研究内容阐明了GO影响水泥基材料物理力学性能的微观机理。.