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The presence of ettringite in concrete affected by alkali‐silica reaction and its potential use as recycled aggregate
Author(s) -
Piersanti Matthew,
Shehata Medhat H.
Publication year - 2022
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/jmi.13093
Subject(s) - ettringite , alkali–silica reaction , aggregate (composite) , materials science , cracking , scanning electron microscope , alkali–aggregate reaction , alkali metal , composite material , cement , chemistry , organic chemistry , portland cement
Samples were collected from a 20‐year‐old concrete suffering alkali‐silica reaction for examination using scanning electron microscopy. The concrete was also exposed to cycles of freezing and thawing in service. The old concrete was processed and used as recycled concrete aggregate in new concrete tested under lab conditions. The study shows that backscattered electron imaging, energy dispersive x‐ray analysis and x‐ray mapping are helpful tools to identify the presence of alkali‐silica reaction products. X‐ray mapping was found helpful to confirm the presence of reaction products in cases where the products or the cracking are not very clear in the collected image. The study shows the presence of ettringite in the air voids of the concrete. The formed ettringite is believed to have no direct effect on the expansion due to the alkali‐silica reaction as they form in an empty space without causing swelling pressure on the concrete. The effect of the ettringite formed in the air voids on the resistance to freezing/thawing was not confirmed in this study. Recycling the old affected concrete as aggregate in new concrete was found to cause significant expansion under lab conditions.