Abstract
Alkali release from aggregates can constitute a source of alkalis in concrete exposed to wet environments for long periods of time. Feldspars are one of the minerals that can release alkalis to the concrete with time. The formation of reaction products in the interface with the paste due to the alkali release from sodium and potassium feldspars has been observed in a concrete with granite aggregates. This has been observed after more than 25 years of exposure. It is necessary to evaluate the amount of alkalis releasable to define the formulation of concrete before manufacturing. Different test methods have been used to evaluate the potential alkali release from the granite extracted from the same quarry as that used in the dam. The test solutions have different composition and concentration, and different temperatures were used. Finally, the results of potential extraction are evaluated to determine the most realistic with respect to the field behavior.
Highlights
Different aggregates may give rise to the leaching of alkalis to the concrete
The ions leached at the end of each test are analyzed, determining the concentration by inductive plasma spectroscopy (ICP), using Varian 725-ES equipment
In the case of the solutions only with calcium, the extraction can be attributed to the Na-Ca or K-Ca ionic exchange; the behavior observed in the solution with the three ions (D6) indicates that the potential migration of alkalis to the concrete is feasible
Summary
Different aggregates may give rise to the leaching of alkalis to the concrete. According to [1,2,3,4,5,6] the leaching of alkalis from feldspars has been confirmed. According to [4,6,8], there is only indirect evidence of the leaching of alkalis from the aggregates in the concrete to bring about an increase in the aggregate-alkali reaction in real concretes. According to [9,10] there is direct evidence of damage caused by AAR in concrete, due to the leaching of alkalis from feldspars, associated with the presence of dawsonite and nepheline. [6] indicates that the sodium and potassium feldspars present in the alaskite may give rise to expansion and the formation of aggregate-alkali reaction products, concluding that feldspars may give rise to an increase in expansion in the concrete, especially when cements are used with a low content of alkalis, due to the incorporation of alkalis at the porous phase. [11] observes that aggregates with potassium feldspars contribute to the formation of aggregate-silicate reaction products
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