轻集料高强混凝土中拱壳的形成机制及其对力学和介质传输性能的影响

In the high strength concrete using prewetted lightweight aggregate, the hydration of interfacial transition zone is more sufficient than that of the matrix due to internal curing of water released from lightweight aggregate, and interfacial transition zone structure cladding lightweight aggregate with better performance is formed. If the prewetted lightweight aggregate is spherical, the interface zone structure is formed in arch shell style. Shell shape (spherical degree, thickness, scale), distribution and microstructure are important affecting factors for mechanical and medium permeation properties of lightweight aggregate high strength concrete. Starting from mesomicroscopic and microscopic scale, this project studies the optimization of arch shell morphology and microstructure, and improve mechanical and medium permeation properties of lightweight aggregate high strength concrete; Arch shell formation and acting mechanism are studied in the lightweight high strength concrete structure by modern analysis technique of SEM、AFM、NMR etc, computer modeling and numerical analysis, the formation of desired arch shell depends on the characteristics of light aggregate, water-binder ratio, composition of cementitious materials and particle size distribution. The effect of arch shell is ascertained on mechanical properties and medium permeation performance, and a form model and the related macroscopic properties correlation model of arch shell structure will be established for the lightweight aggregate high strength concrete. Based on the studied results, the structure damage and property degradation mechanism will be explored of the lightweight aggregate high strength concrete with the arch shell structure under load and chemical action, and the design and preparation method will be proposed of lightweight aggregate high strength concrete used as-studied lightweight aggregate. The study aims at providing the preparation fundamental of high strength and high performance concrete using spherical lightweight aggregate with high absorption and medium or low strength.

在预湿轻集料高强混凝土中，轻集料的释水内养护作用使其界面区浆体水化相对基体更为充分，形成性能优于基体的界面区，若预湿轻集料为球形，则形成拱壳状界面区。拱壳的形态（球型度、厚度、尺度）、分布和微结构是影响轻集料高强混凝土力学和介质传输性能的重要因素。本课题拟从细观和微观尺度出发，优化拱壳的形态和微结构，改善轻集料高强混凝土的力学和介质传输性能；以SEM、AFM、NMR等现代测试技术为手段，研究轻集料颗粒特性、水胶比、胶凝材料组成与颗粒级配对拱壳形态和微结构的影响，探明拱壳对轻集料高强混凝土力学和介质传输性能的影响机理；采用数值分析和计算机模拟技术，建立拱壳的形成模型及其与轻集料高强混凝土宏观性能相关性模型。在此基础上，探明荷载和侵蚀介质作用下具有拱壳状界面区轻集料高强混凝土的损伤劣化机理，提出具有拱壳状界面区轻集料高强混凝土的设计与制备方法，为轻集料高强混凝土的设计和原材料选择提供依据。

在预湿轻集料高强混凝土中，轻集料的释水内养护作用使其界面区浆体水化相对基体更为充分，形成性能优于基体的界面区，若预湿轻集料为球形，则形成拱壳状界面区。拱壳的形态、分布和微结构是影响轻集料高强混凝土力学和介质传输性能的重要因素。为了探明拱壳状界面区的形成与作用机理，本课题从细观和微观尺度出发，优化拱壳的形态和微结构，改善轻集料高强混凝土的力学和介质传输性能。课题以NMR、SEM、XRD等现代测试技术为手段，研究了轻集料颗粒特性、水胶比、胶凝材料组成与颗粒级配对拱壳形态和微结构的影响。在较低水灰比（0.3）时，拱壳状界面区的水化程度、C-S-H凝胶聚合度和显微硬度均高于水泥石基体，且随轻集料吸水率增大，拱壳状石界面区的水化程度、C-S-H凝胶聚合度和显微硬度增大；探明了拱壳对轻集料高强混凝土力学和介质传输性能的影响机理，建立了侵蚀介质的传输模型，发现SO42-、Na+和水分子随机分布于界面区凝胶孔中。而拱壳状界面区特殊的界面区形态能够均匀分散压应力，并能有效阻止Cl-、SO42-、CO32-等有害离子在毛细孔中的迁移，进而提高了轻集料混凝土的力学性能和耐久性能；利用相对动弹性模量定义轻集料高强混凝土的损伤度，建立了损伤度和浸泡时间的损伤演化方程：Erd=f(t)=A+Bt+Ct2，诠释了荷载和侵蚀介质作用下具有拱壳状界面区轻集料高强混凝土的损伤劣化机理；最后，课题提出了具有拱壳状界面区轻集料高强混凝土的设计与制备方法，为轻集料高强混凝土的设计和原材料选择提供了依据。本课题研究对于丰富和完善轻集料混凝土界面理论和高强混凝土设计制备理论，提高轻集料高强混凝土综合性能具有重要意义。