Critical evaluation of accelerated test methods for detecting the alkali-reactivity of aggregates

Abstract

Three recently proposed, accelerated test methods (the infrared (IR) spectroscopy technique, the mortar bar expansion tests in a 1 N NaOH bath at 80°C or in a saturated NaCl bath at 50°C) were used to evaluate the potential alkali-reactivity of opal,fused silica, Nymolle sand and Torre Lago sand. Macrocrystalline quartz was used as a reference aggregate, and classical ASTM test methods were adopted as reference tests. It was found that the NaOH bath test method is the most suitable for evaluating the alkali-reactivity of the aggregates tested. The NaCl bath test method and the infrared spectroscopy technique overestimate the reactivity of Nymolle sand, while the ASTM C 227 mortar bar test is not suitable for the evaluation of the two types of sand. For the IR technique, merely a little modification of the criteria established for slowly reactive aggregates is necessary to make this method completely satisfactory. The mineralogical composition of the cement significantly affects the expansion level of mortar bars in both NaOH and NaCl bath tests.