Microstructural Changes Due to Alkali-Silica Reaction during Standard Mortar Test.

Area of Science:

• Materials Science
• Civil Engineering
• Geochemistry

Background:

• Alkali-silica reaction (ASR) is a deleterious process in concrete, particularly with siliceous aggregates.
• Understanding ASR's microstructural development is crucial for predicting material durability.

Purpose of the Study:

• To analyze the microstructural evolution of mortar bars with silica glass aggregate undergoing ASR.
• To characterize crack formation and ASR gel development under ASTM C1260 conditions.

Main Methods:

• Scanning electron microscopy (SEM) for microstructural analysis.
• Qualitative X-ray microanalysis to identify ASR gel.
• Mortar bar expansion testing following ASTM C1260.

Main Results:

• Significant cracking observed in aggregate, hydrated paste, and at the paste-aggregate interface.
• Expansion reached approximately 2% by 53 days, with failure by 63 days.
• Two distinct zones identified: an inner ASR-affected region and a more damaged outer zone.

Conclusions:

• Microstructural cracking is a key factor in ASR development and material degradation.
• ASR can initiate even before exposure to the alkaline solution.
• The study provides insights into the progression of ASR damage in mortar bars.