Quantifying Microscale Stress and Strain Fields in Concrete and Cementitious Composites

We will quantify the microscale stress and strain fields generated during the macroscopic compression of concrete. Currently, the macroscopic modulus and strength of concrete are predicted accurately by “mean-field” micromechanics theories and numerical models based on the postulate that each sand particle (aggregate) in the microstructure experiences the same stress state during macroscale loading and is perfectly bonded to the surrounding cement-paste matrix. Recent work by the proposers demonstrates that the aggregates instead experience significant stress variability. Our proposed experiments will exploit combined 3DXRD, scanning 3DXRD and x-ray computed tomography, with digital volume correlation, to quantify stress variability and aggregate-matrix debonding during elastic and inelastic stages of compression in-situ. Results will improve micromechanics theories and provide first-of-its-kind information on aggregate-matrix interface mechanisms previously inaccessible in-situ.

本研究将量化混凝土宏观压缩过程中产生的微观尺度应力与应变场。目前，基于"细观结构内每颗砂粒（aggregate，骨料）在宏观加载过程中承受相同应力状态，且与周围水泥浆基体完美黏结"这一假设，平均场细观力学理论（mean-field micromechanics theories）与数值模型可准确预测混凝土的宏观模量与强度。本项目申请人的前期研究表明，骨料实际承受的应力存在显著离散性。本研究拟结合三维X射线衍射（3DXRD）、扫描式三维X射线衍射（scanning 3DXRD）与X射线计算机断层扫描（X-ray computed tomography）技术，并配套数字体相关（digital volume correlation）方法，开展原位压缩实验，量化弹性与非弹性压缩阶段的应力离散性及骨料-基体脱黏现象。研究结果将改进细观力学理论，并首次提供原位条件下难以获取的骨料-基体界面力学机制相关数据。