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Locally Made Concrete Demonstrates Promise, Benefits

Thursday, October 19, 2017

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Researchers based out of the Massachusetts Institute of Technology have begun investigating a new way to formulate concrete that involves the hierarchy arrangements of a natural building block method, which could make concrete stronger and more sustainable.

The study, led by Oral Buyukozturk, professor of civil and environmental engineering at MIT, investigated a key component of concrete, down at the atom level, which contributes to the substance’s overall strength and durability.

Research Simulations

To assist with the study, researchers developed a computer simulation of the behavior of individual atoms that form molecular building blocks within a hardening material. What the simulations revealed was that these structures demonstrated a “frictional” resistance under sliding deformation.

Images: Massachusetts Institute of Technology

According to the university, the team is currently examining ways in which cohesive and frictional forces of groups of atoms are improved by adding in elements such as volcanic ash or refinery slag. The simulation may also help advise designers in choosing local additives for future projects, which can result in the engineering of stronger concrete.

From there, the team developed a cohesive-frictional force field that incorporated these interactions within larger scale particles.

The purpose behind this? To better understand the way strength develops in concrete.

According to the university, the team is currently examining ways in which cohesive and frictional forces of groups of atoms are improved by adding in elements such as volcanic ash or refinery slag. The simulation may also help advise designers in choosing local additives for future projects, which can result in the engineering of stronger concrete.

“The conditions of the world are changing,” Buyukozturk said. “There are increased environmental demands, including from earthquakes and floods, and stresses on infrastructure. We need to come up with materials that are sustainable, with much longer design life and better durability. That is a big challenge.”

Research Simulation

In the study, researchers simulated mixtures containing Portland cement. What was simulated was the mechanical response of calcium-silicate-hydrate, which is the main phase that forms when Portland cement reacts with water. The researchers modeled the movements of the atoms in a C-S-H building block. Cohesive forces influenced particles to stick together.

This was expanded to a larger size, which was dubbed “mesoscale” in the study. Upon further investigation, MIT noted, researchers discovered that the degree to which the frictional properties resisted the movement and separation of colloids at the mesoscale was the strongest factor in determining the strength of concrete at the centimeter scale.

“The material science of cement strength is still in its infancy regarding molecular-level descriptions and an ability to perform quantitative predictions,” said Sidney Yip, professor emeritus in MIT’s Department of Nuclear Engineering, who is also working on the study.

“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.”

Local Inspiration

In looking to use local elements in concrete materials, Buyukozturk admits that he was inspired by the Romans, who, through using nearby materials in the creation of their concrete, built buildings that have lasted over 2,000 years.

In response to the decay of the U.S.’s concrete-based infrastructure, much of which has not been designed to accommodate modern-day stressors, researchers based out of the Massachusetts Institute of Technology have started to investigate a new way of formulating concrete—using the hierarchy arrangements of a natural building block method that could make concrete both stronger and more sustainable.

“They probably did this through intuition,” Buyukozturk said. “Ours is an effort to hopefully implement that kind of philosophy of using materials that are locally available, by understanding the underlying scientific principles within those materials.”

Moving Forward

Currently, researchers are working on incorporating more additives to investigate their effect. Preliminary studies indicate that there is a chemical dependence of the friction value. In the future, the influence of additives on the chemical composition of these colloidal phases will be investigated, and the information may assist with the creation of a database that would be geared toward the optimization of concrete materials.

“We know relatively little of what happens when additives are used in concrete,” Steven Palkovic, a graduate student working on the study, said.

“We would not expect volcanic ash from Saudi Arabia to give the same performance as volcanic ash from Hawaii. So we need this greater understanding of the material, that starts at the atomistic scale and accounts for the chemistry of the material. That can give us greater control and understanding of how we can use additives to create a better material.”

The results of the study were published in the Journal of the Mechanics and Physics of Solids. Research was partially funded by the Kuwait Foundation for the Advancement of Sciences.

   

Tagged categories: Cement; Colleges and Universities; concrete; Research and development

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