Concrete Micromechanics Validated with In-Situ Stress and Strain Measurements

This research will examine the mechanical response of concrete at micrometer to centimeter length scales to validate theories and computational models used to predict its behavior and failure. Concrete is the world’s most-common building material and extensive research efforts are on-going to improve its resiliency and environmental friendliness. Concrete is composed of particles and inclusions with varying properties and dimensions ranging from nanometers to centimeters that interact during mechanical loading.

The results of these interactions are captured by theories and computational models in the field of micromechanics. While micromechanics-based theories accurately predict many mechanical properties of concrete, the assumptions underlying these theories have not been validated at small length scales. Furthermore, determining the resolution needed for accurate computational modeling of concrete is still challenging.

This research project will employ new, advanced x-ray measurements to assess the response of concrete from micrometers to centimeters, to test the hypotheses underlying micromechanics theories, and to provide the research community with high-fidelity data for validating models. The results of this research are expected to improve predictions of concrete’s mechanical response and promote understanding of its properties.

The research results will also be used to teach advanced concepts in a graduate engineering course and to provide research opportunities to under-represented high school students interested in STEM careers.

This research consists of making in-situ x-ray tomography and diffraction measurements of stress and strain at micron to centimeter length scales during mechanical loading of concrete specimens at laboratory and synchrotron facilities. These measurements will be used to validate and extend micromechanics theories, such as Eshelby’s inclusion and Mori-Tanaka’s theories, and their underlying assumptions across length scales.

For instance, the measurements will be used to examine whether average inclusion stresses used as intermediate variables in deriving homogenized material properties are accurate and to what degree individual inclusion stresses deviate from the average. The measurements will also be used to examine the accuracy of mesoscale modeling with varying levels of microstructural refinement, addressing open problems related to the length scales that must be captured in such models.

The outcomes of the project will be a fundamental understanding of stress and strain variability across length scales in concrete, guidance for mesoscale modeling, and high-fidelity datasets for calibration and validation of theories and models used throughout the research community.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.