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MIT Researchers Target ASR Gels

Thursday, June 6, 2019

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According to the staff at the Massachusetts Institute of Technology-hosted Concrete Sustainability Hub (CSHub), new research shows that alkali-silica reaction is a substantial cause of premature concrete deterioration.

This effect can often be caused by the increase of viscosity when ASR gel imbibes calcium with age, while an affiliated expansion creates a concrete failure. Another possibility is that the ASR gel’s rate of flow is slower than the rate at which the microstructure forms, which in turn builds stress that can’t be relieved.

In their current research brief, “Simulating the Formation of ASR Gels,” researchers test their hypotheses on the matter.

Testing

By using atomistic methods to overcome various time-scale issues, researchers simulated formations at an atomic scale, helping to determine structural and mechanical properties of the ASR gels.

Courtesy of MIT CSHub

The configuration of a pure silicate gel after the gelation in a wet environment. The structure of these chains is a complex 3D skeleton that includes branching and silicate rings, according to MIT.


“Modeled gels respond to chemical changes, such as water content, and relative composition of alkali and calcium. More importantly, [the method] demonstrates that drying the gel strongly affects its structure. This drying effect has not been considered in past research and provides an opportunity to reconsider [previously] proposed mechanisms … Additionally, we observed a reduction in the volume of gel as it calcifies, which offers further insight into reasons for concrete failure.”

The same method is often used in studying an alkali-Ca exchange during calcification or the effects of pH when changing alkali concentrations. For the research brief, the team coupled parallel tempering to quicken the dynamics with a grand canonical Monte Carlo method to account for wet areas inside the pores during gel formation.

Results

In using the method mentioned above, researchers were able to efficiently simulate the formation of gels and its impact on water to silicon ratios. Now, researchers plan to compare the elasticity with the compiled experimental data.

“Better control of ASR requires knowledge of gel’s molecular structure; a simulation approach at the atomic level is an efficient way of examining gel structure; and, progress in simulation techniques could help characterize gels, advancing the industry’s approach to ASR,”said authors and MIT research scientists Romain Dupuis and Rolland Pellenq.

The team’s work continues with CSHub sponsor oversight, the Ready Mixed Concrete Research & Education Foundation and Portland Cement Association.

   

Tagged categories: alkali-silica reaction (ASR); Asia Pacific; Colleges and Universities; concrete; Corrosion; Deterioration; EMEA (Europe, Middle East and Africa); Gel; Latin America; North America; Program/Project Management; Research; Silicone; Sustainability; Z-Continents

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