Flinders University researchers have a solution to combat alkali-silica reaction in concrete.

The formula, using ground granulated blast furnace slag (GGBS) and fly ash as binders, mitigates alkali-silica reaction (ASR) effects, maintaining mechanical properties and durability.

Dr Aliakbar Gholampour, an expert in sustainable construction materials at Flinders University, explained: “The results of this study point to the significant potential of combining fly ash and GGBS at an optimum ratio to mitigate the ASR effect on recycled aggregate concrete containing crushed glass sand.

“The developed technology can be used in different applications where natural sand or gravel are currently being used, such as road construction, landscaping and infrastructure projects.”

The research revealed that a blend of 20% GGBS and 30% fly ash proved to be optimal, exhibiting comparable strengths and water absorption rates to concrete made with natural sand.

Higher GGBS content led to diminished strengths and elevated water absorption levels.

“By integrating these recycled materials into construction and manufacturing practices, industries can contribute to a more sustainable built environment and circular economy,” said Dr Gholampour.

Research also found that:

- The full replacement of natural sand with glass sand leads to a significant ASR expansion of mortar bars. Replacing 30% of cement with fly ash leads to an 88% decrease in the expansion rate of the bar. The GGBS is less effective in reducing this expansion, with only a 3%, 9%, and 12% decrease in the expansion by adding 20%, 40%, and 70% GGBS to the concrete containing 30% fly ash, respectively.

- Replacing natural sand with glass sand causes a 37% and 20% decrease in compressive and flexural strengths of concrete, respectively. However, incorporating 30% fly ash leads to an 18% and 10% increase in the strengths of the ASR-affected RCA concrete with glass sand, respectively. It is notable that combining 20% GGBS with 30% fly ash develops similar strengths to RCA concrete with natural sand.

- ASR-affected RCA concrete with glass sand exhibits a 67% higher water absorption than concrete made with natural sand. Combining 30% fly ash with 20% GGBS causes similar water absorption to concrete with natural sand. However, further increase in GGBS content leads to an increase in water absorption.

- Incorporating 20% GGBS leads to a significant increase in the chloride attack resistance of ASR-affected RCA concrete that contains glass sand. An increase in the GGBS content from 20% to 70% causes a 27% increase in the chloride ion penetration of the concrete.

"Concrete containing recycled concrete coarse aggregate and crushed glass sand: Mitigating the effect of alkali-silica reaction,” by Aliakbar Gholampour, Armin Memarzadeh, Mahdi Nematzadeh, Mohammad Valizadeh Kiamahalleh, Tuan D. Ngo

Full Article - https://onlinelibrary.wiley.com/doi/10.1002/suco.202301029