Title:
New Test Method for Alkali-Silica Reaction (ASR) and the Role of Additional Calcium Ions in the Reaction Process
Author(s):
Frank S. Ong, Michael Myers, Mark Bury, Trevor Larch, Charles Nmai, Paul Seiler, Lesley S. C. Ko
Publication:
Symposium Paper
Volume:
355
Issue:
Appears on pages(s):
41-52
Keywords:
Alkali-Silica Reaction (ASR); Expansion; Test Method; Calcium Ions; ASTM C1260, ASTM C1567
DOI:
10.14359/51736011
Date:
7/1/2022
Abstract:
Alkali silica reactivity (ASR) is a reaction of OH- in pore solution with reactive silica aggregate to form an absorptive, deleterious gel and the expansion of mortar or concrete bar specimens is used as a measure of the magnitude of the reaction. Several test methods have been developed to measure ASR expansion and, currently, the ASTM C1567, ASTM C1260, and ASTM C1293 standards are the most widely used test methods. In both ASTM C1567 and ASTM C1260 test methods, mortar bars are immersed in 1N NaOH solution at 80 oC. During the immersion process, two phenomena can occur (1) leaching out of ionic species and (2) NaOH penetrating the mortar bars. The results of these two events might underestimate the ASR mitigating effect of soluble salts, such as Ca(NO2)2. A new ASR expansion test method has been developed and proposed to address these two issues and the details of the new test method will be presented in this paper. In addition, the role of calcium ions (Ca2+) in ASR has been investigated and debated for many years. Using the new test method, the effects of Ca2+ additions on ASR expansion have been investigated. The studies show that if the Ca2+ addition is relatively lower than the alkali content in the system, ASR expansion is increased. However, if the Ca2+ addition is relatively higher than the alkali content in the system, ASR expansion is reduced. If the Ca2+ addition is high enough, the ASR expansion is inhibited. Potential ASR mitigating options based on these findings are presented.
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