超低温环境下超高性能混凝土力学行为及其温脆效应

Ultra-high-performance concrete (UHPC) is a new type concrete material for the future demand, and cryogenic temperature is one of the extreme service conditions of UHPC. Therefore, it is of great scientific significance of exploring the mechanical behavior and the effect of temperature embrittlement on practical applications of UHPC in cryogenic conditions. Firstly, the mechanical performance test and online monitoring methods and instruments for cryogenic UHPC are designed. The development of mechanical properties, the thermal properties and the mechanism of water phase transition of UHPC at cryogenic temperature are investigated. Consequently, the mechanical behavior model for cryogenic UHPC is established. Secondly, the evolution of microstructure within UHPC under the conditions of cryogenic temperature and its cryogenic freeze-thaw cycles is to be discovered using testing methods such as cryogenic SEM and thermoporometry. The bond properties of the interface and its corresponding strengthening or weakening mechanism are ascertained. Thirdly, the performance evolution of cryogenic C-S-H gel is tested by nanoindentor and atom force microscope. The acoustic emission device is designed to track the process of temperature embrittlement transition of steel fiber and C-S-H gel. The theory of molecular dynamic will be used to simulate the mechanical properties of C-S-H gel and its structure damage at cryogenic temperature. Therefore, the mechanism of temperature embrittlement effect of UHPC at cryogenic temperature can be proposed. The research achievements above will provide scientific guidance for solving scientific problems and key techniques of practical applications of UHPC under the extreme cryogenic conditions.

超高性能混凝土（UHPC）是面向未来需求的一种新型混凝土材料，而超低温是其最极端服役环境条件之一，探索超低温下UHPC力学行为及其温脆效应具有重要的科学意义。首先设计超低温下UHPC力学性能测试与在线监测方法装置，研究超低温下UHPC力学性能发展规律、热工性能与水相变机制，建立超低温下UHPC力学行为模型；采用低温扫描电镜、热孔计法等方法揭示超低温及其冻融循环作用下UHPC微观结构演变规律，探明超低温下UHPC界面粘结特性及其增强或弱化机制；采用纳米压痕与原子力显微镜测定超低温下C-S-H凝胶低温性能演变规律，设计出超低温下声发射在线检测仪追踪超低温下钢纤维及C-S-H凝胶温度脆化过程，并运用分子动力学理论模拟超低温对C-S-H凝胶力学性能及其结构的损伤规律，从而阐明超低温下UHPC温脆效应形成机理。研究成果可为解决UHPC在超低温特种环境下应用的关键科学问题与技术问题提供科学指导。

超高性能混凝土（UHPC）因其优异的综合性能使得其在极端温度环境中的应用成为可能。为此，本项目利用自主开发的极端温度环境下混凝土力学性能测试设备，研究了UHPC在超低温下的力学行为演变规律及纤维-UHPC基体界面劣化机制，探讨了超低温下UHPC的温脆效应并提出了相应的评价公式，揭示了在温变过程中混凝土的温度场分布规律，同时利用声发射测试监测了混凝土在不同温度下的开裂形式及裂缝形成与扩展。此外，在微观层次研究了超低温及其冻融循环作用下UHPC微观结构演变特征，探明了超低温下C-S-H凝胶低温性能演变规律以及温脆过程，探讨了超低温对C-S-H凝胶力学性能及其结构的损伤成因。研究成果可为解决UHPC在超低温及其它温变环境下应用的关键科学问题与技术问题提供科学指导。