CHAMPAIGN, Ill. — A new test developed at the University of Illinois Urbana-Champaign can predict the performance of a new type of cementitious construction material in five minutes — a significant improvement over the current industry standard method, which takes seven or more days to complete. This development is poised to advance the use of next-generation resources called supplementary cementitious materials — or SCMs — by speeding up the quality-check process before leaving the production floor.
Due to declining coal production, traditional SCMs like coal-based fly ashes are in short supply. One promising alternative is newer SCMs like calcined clays, which can partially replace ordinary Portland cement and result in durable, low-cost concrete that produces less carbon dioxide during production.
The study, led by civil and environmental engineering professor Nishant Garg , uses a low-cost analysis called colorimetry and camera technology for real-time quality control of calcined clays in industrial settings. Calcined clays are SCMs that contain aluminum- and silicon-containing minerals that become chemically reactive when heated to 600 to 900 degrees Celsius.
The study findings are published in the journal Cement and Concrete Research, and Garg's team is enthusiastic to connect with other research teams and industry partners working in this area.
After heat treatment, the aluminum and silicon in calcined clays become very chemically reactive, which allows them to contribute to the reactions that lead to long-term strengthening in mortar and concrete. The level of reactivity can be measured, and researchers can use this to predict the product's final strength and quality.
"There are testing methodologies currently in place for measuring the chemical reactivity of the aluminum and silicon in calcined clays, but they require expensive testing equipment and consume a lot of laboratory time," said Garg, who also is affiliated with the Institute for Sustainability, Energy and Environment . "Our new test can be run on the fly by the people working in the plant for real-time quality control. Our technique introduces an analyzer that can be used on the production line every five minutes, allowing workers to collect a small sample from their conveyor belt and quickly determine if the quality is consistent."
In the lab, Garg's team developed a way to measure calcined clay's reactivity very rapidly. To do it, the researchers first expose the clay to a heated, aggressive alkaline solution for five minutes, which dissolves the clays, freeing the aluminum and silicon ions for measurement. "We spent quite a bit of time optimizing the alkalinity and temperature of our solution so that it can be done in minutes rather than hours or days like the conventional tests currently available," Garg said.
Once the solution was ready, the researchers measured the concentration of aluminum and silicon ions dissolved in the solution and then combined those values into a single dissolution index. "And this is where our new approach becomes exciting," Garg said. "We found that instead of sending these solutions off to a lab to be analyzed using expensive analytical equipment, we could simply add a coloring agent to the solution that reacts with the ions to produce distinct colors depending on the concentrations of aluminum and silicon. We can then quantify the color using a low-cost colorimeter, which is a device that measures how much light a solution absorbs at a specific wavelength."
The team ran many experiments to calibrate the colors corresponding to the clay solution's aluminum and silicon concentrations. With increasing concentrations of aluminum and silicon, the solutions show stronger pink and blue colors, respectively, the study reports.
"Both colors are in the visible light spectrum, so we can photograph the colored solutions using a low-cost, say $30, camera, and assign the corresponding RGB values from the images to previously established calibration curves to determine the precise amount of aluminum and silicon in the solution based on color," Garg said. "We ran statistical analysis and found that using this camera image analysis method is comparable with the results obtained using a quantitative analytical device called a UV-VIS spectrophotometer. On 47 diverse clay samples, our five-minute test strongly correlates with the seven-day industry standard test, thus enhancing speed, reducing cost and still maintaining accuracy. "
These results show that camera-based colorimetry can be used as an alternative to the absorbance at certain wavelengths for quantitative analysis, the study reports.
"This study is exciting for our team here at Illinois and the cement and concrete industry in general because of the opportunity it will present to reduce the testing time while screening for new materials and ensure consistent quality during production at a low cost," Garg said.
Partnerships will be key to refining and implementing this technology because there are a few more hurdles to clear, Garg said.
So far, the team said the method works only for calcined clays but there are many other types of supplementary cementitious materials being considered for use in future sustainable cement and concrete mixes. Newer materials called natural pozzolans, reclaimed ashes, as well as older materials like coal fly ashes and blast furnace slags could be potential targets.
"We call on industrial producers to share samples and help us verify if our ultra-rapid test can be honed and extended to these systems so that we can predict the performance of any material in a few minutes," Garg said. "We also call on original equipment manufacturers to help us automate the test into a commercial device."
The U.S. Department of Energy and the National Science Foundation partially supported this study. Garg and his coauthors have a pending patent application for this technology, filed through The University of Illinois Urbana-Champaign Office of Technology Management.
