Abstract
The reaction between certain reactive components of aggregates (like opal and metaestable silica) and concrete pore solution is well documented. Nevertheless, in this study it has been shown that some aggregates, like granite, could develop a rapid or slow alkali-silica reaction (ASR) depending on the deleterious component involved. Mortar bars were cast with two granitic aggregates extracted from concrete cores drilled in two Spanish Dams affected by ASR, being classified as granitic rocks. The main difference between them is the reactive component: microcrystalline quartz in one case and strained and microcracked quartz in the other case. A petrographic examination was carried out in the mortar bars. Thin sections were cut and the alkalisilica gel was stained for an easier detection. Then, the thin sections were examinated with a stereomicroscope comparing the differences in the progress of the ASR for both aggregates. It can be concluded that the main mechanism of formation and storage of gel is associated to the micro-cracks instead of the subgrain boundaries.
Highlights
Stanton studied in 1940 the Parker Davis dam in California, which showed cracking and expansion
Polygonization of crystals to form microcrystalline quartz could cause the reaction. In this investigation it has been carried out a comparative study of the development of slow and rapid alkali-silica reaction in granitic aggregates
An important amount (8%) of microcrystalline quartz was found in the petrographic analysis of the Aggregate A, which explains the alkali-silica reaction (ASR) affecting the dam and its deterioration (Table 1)
Summary
Stanton studied in 1940 the Parker Davis dam in California, which showed cracking and expansion. In alcali-silica reactions (ASR) a deleterious chemical reaction takes place between certain reactive siliceous minerals in aggregates and alkali ions in the concrete pore solution. This reaction produces a gel, which imbibes water and expands when it is exposed to moisture, cracking the aggregates and the cement paste. Polygonization of crystals to form microcrystalline quartz could cause the reaction In this investigation it has been carried out a comparative study of the development of slow and rapid alkali-silica reaction in granitic aggregates. Knowing more about this kind of reaction could allow us to develop new and more accurate methods for the detection of slow-reacting aggregates
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