MIT researchers have discovered the beginnings of a new approach to producing concrete that is inspired by the hierarchical arrangements of simple building blocks in natural materials. The findings could lead to new ways to make concrete stronger and to use more sustainable, local materials as additives, to offset concrete’s greenhouse gas emissions.
In the new study, Oral Buyukozturk, a professor of civil and environmental engineering, and his colleagues analyzed a key property in concrete, at the level of individual atoms, that contributes to its overall strength and durability. The group developed a computer model to simulate the behavior of individual atoms which arrange to form molecular building blocks within a hardening material.
These simulations revealed that an interface within the molecular structure exhibited a “frictional” resistance under sliding deformation. The team then developed a cohesive-frictional force field, or model, that incorporates these atom-to-atom interactions within larger-scale particles, each containing thousands of atoms. The researchers say that accurately describing the forces within these assemblies is critical to understanding the way strength develops in concrete materials.
The team is now examining ways in which the cohesive and frictional forces of groups of atoms, or colloids in cement, are improved by mixing in certain additives such as volcanic ash, refinery slag, and other materials. The team’s computer model may help designers choose local additives based on the molecular interactions of the resulting mixtures. Through careful design at the microscopic level, he says, designers and engineers can ultimately build stronger, more environmentally sustainable structures.
Designers often use the properties of cement at the centimeter scale to predict the strength of a final, much larger-scale structure. The researchers thus implemented the results of their atoms-to-colloids simulations within computer models of the hardened microstructure, to allow for comparison with actual, centimeter-sized laboratory experiments. Buyukozturk found the team’s predictions matched with experimental outcomes better than predictions made with simulations that neglect frictional interactions.
“The material science of cement strength is still in its infancy regarding molecular-level descriptions and an ability to perform quantitative predictions,” Yip says. “The issue of frictional force, addressed in our work, pertains to the mechanical behavior of cement that varies over time. This rate sensitivity is an aspect of the scientific challenges at the mesoscale, which is the research frontier where microscale concepts and models developed in several physical science disciplines are linked to macroscale properties for technological applications.”