Micropillar Compression Test Technique Helps to Measure Strength of Concrete
Phillip Keane posted on November 23, 2017 |
Researchers manufacture microscale test pieces to isolate strength-giving compounds in concrete.

A team of researchers at North Carolina State University has developed a new technique for measuring the compressive strength of concretes. The new method uses a small sample called a micropillar to determine micro-scale mechanical strength characteristics and will aid future researchers when analyzing the failure properties of materials containing cement.

“The information collected using this technique can be used to better understand the behavior of concrete when it fails, as well as providing key data for ‘constitutive’ models that are used for designing and determining the safety of large-scale civil engineering structures,” said Rahnuma Shahrin, lead author of the paper published in the Journal of Nanomechanics and Micromechanics.

First, the cement aggregate is analyzed using energy-dispersive spectroscopy spot analysis in order to identify calcium-silicate-hydrate (C-S-H) locations. C-S-His the key ingredient that gives concrete its strength, but until now, researchers have not been able to isolate the locations of this compound due to the small. That has now changed, and once these locations were identified in the spot analysis, they were formed into pillars by use of focused ion-beam milling. The pillars measured at a mere 2 μm wide by 4 μm high. After manufacture of the specimens, compression testing of the specimens was performed using nanoindentation equipment.The researchers have identified two primary deformation mechanisms at the point of failure. These failure modes were identified as axial splitting and plastic collapse of the micropillar.

Scanning electron microscope image of a micropillar. (Image courtesy of North Carolina State University.)
Scanning electron microscope image of a micropillar. (Image courtesy of  North Carolina State University.)

“There are lots of ways to make cement, and it can be made with different constituents in different ratios,” continued Shahrin. “We’ve shown that the micropillar technique can be used to give us precise measures of C-S-H compressive strength in these different types of mixtures. This information can be used to help us understand how various processes, and the constituents added during cement production, can affect the cement’s strength. It’s basically a tool that can be used to develop better, stronger cement.”

And stronger cement means that less cement can be used for the same jobs as before. And less cement means less CO2.

“The research outcomes will lead to significant impacts in the study of failure of materials containing cement,” said Shahrin. “The production, transportation and use of concrete accounts for between 5 and 9 percent of total carbon dioxide emissions worldwide. The knowledge from this study can be applied toward development of stronger, more sustainable materials for civil infrastructure, reducing consumption of natural resources and production of CO2."

That is excellent news for the planet, as CO2 produced from cement manufacturing accounts for 4.5 percent of global anthropogenic CO2 emissions. And given the fact that China used more cement between 2011 and 2013 than the United States did in the entire 20th century, it’s fair to say that our love affair with concrete is going to get a lot more intense in the future.

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