Characterization, Evaluation, And Repair of Full-Scale Alkali-Silica Reaction Affected Structural Concrete
Author(s)
Kumar, Devin
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Abstract
Alkali–silica reaction (ASR), a chemical reaction occurring in concrete between reactive siliceous minerals in some aggregates and alkalis in the concrete pore solution, can produce an expansive gel that, in the presence of sufficient moisture,
leads to expansion and cracking. This not only decreases mechanical properties but also increases permeability and, as a result, increases potential for degradation
by other aggressive agents. Traditional methods to mitigate or repair damage of affected concrete include surface coatings and external confinement, but a re-assessment of new repair technologies and materials may offer greater benefit. Additionally, it is known that earlier detection of ASR-affected concrete can increase the long-term success of repair. Therefore, it is necessary to explore new
characterization and evaluation techniques that can aid in detection.
In this research, ASR-affected laboratory-cast and field-exposed ASR-affected concrete are examined and repaired. Laboratory-cast samples are repaired with silane and nanosilica-based coatings, and others are confined with fiber-reinforced
ultra-high performance concrete (UHPC). In the field, cracked concrete traffic (i.e., Jersey) barriers are repaired with flexible caulk and silane and slurry surface treatments. The efficacy of each is monitored through measurements of expansion and crack growth. Additionally, new techniques involving ultrasound-based nondestructive evaluation (NDE) and spatially resolved micro x-ray fluorescence (µXRF) are used to detect and characterize laboratory and field ASR-affected
concrete.
Although the monitoring of repaired samples remains ongoing, initial
measurements of internal expansions of the UHPC-confined columns indicate effective restraint in expansion, compared with chemical-based surface treatments.
Further, internal ASR-induced damage occurring in the laboratory-cast large-scale samples were detected by a novel non-collinear ultrasonic wave mixing technique, where accumulated damage can be quantified through nonlinear parameters measured at varying depths; this new non-destructive evaluation (NDE) approach
shows potential for early detection of ASR-affected concrete in the field. Finally, cored concrete from structures in the field showing indications of ASR were examined by µXRF, which is one of the first application of this method for identification of ASR damage in concrete. Scans of smaller regions of interest (i.e.,1 cm2) were compared with quantitative measurements made through the established petrographic Damage Rating Index (DRI). The small-region scans were then followed by a more intensive, larger 36 cm2
region to understand the influence in scan and elemental map settings in observing ASR-distress features,
serving as a stepping stone for incorporation of µXRF as an analytical technique for ASR identification. From these findings, recommendations for repair of ASR affected concrete are made, based upon the extent of damage, type, and criticality
of structure.
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Date
2024-12-09
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Text
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Dissertation (PhD)