ASSESSMENT TECHNIQUES FOR ALKALI-SILICA REACTION DIAGNOSIS IN MASS CONCRETE STRUCTURE

This paper reported the results of several techniques used to diagnose Alkali-Silica Reaction (ASR) distress in concrete. Two screening tests looked for the appearance of the fluoresced gel of uranyl acetate treated samples and the changed color areas of the chemical staining treated samples. The results agreed well with the expansion of the cored samples in warm water and in NaOH solution and also supported the previously measured expansion in the field. The petrographic analysis found many microcracks with ASR gel filling in cement paste, interface zone (ITZ) between aggregates and paste, and internal cracks in aggregates. Microstructural analysis revealed the characteristics of slow reactive aggregates and two forms of products; amorphous gel with shrinkage cracks in cement paste cracks and in the ITZ, and cryptocrystalline reaction products consisting of plate-formed crystals, rosettes and globular found mostly in internal cracks of aggregates and air voids. The SEM/EDS analysis differentiate reactive from non-reactive aggregates. Ettringite crystals were also observed lining the air voids and some cracks but there was no evidence linking it to the cause of continued expansion. Fine grain black quartzite within the aggregates and sericite were identified as the cause of ASR The combination of different techniques effectively identified ASR as the primary cause of deterioration and the continued expansion of the investigated structure.