ASR Potential of Volcanic Aggregates Using the Gel-Pat Test and the Phosphoric Acid Method

In previous research, volcanic rocks from the Azores Islands (Portugal), Brazil, Canada, Canary Islands (Spain), Hawaiian Islands (USA), Iceland, Japan, Mozambique, New Zealand, Norway, and Turkey were studied to assess their potential reactivity to alkalis. The analyzed samples correspond to basalt, andesite and rhyolite. Several tests were performed, namely, petrographic characterization by optical microscopy and scanning electron microscopy, bulk rock chemical analysis, accelerated mortar-bar test and concrete prism test. In volcanic rocks, the possible reactive forms of silica are not only of minute size, and hard to identify, but are also usually present in very low content, and often below the detection limits used in chemical bulk rock analysis. This study reports the results obtained in additional tests to characterize the aforementioned aggregates: 1) the phosphoric acid method, by dissolution of silicates of the rock reduced to powder, preserving the free silica forms of the sample; and 2) the gel-pat test, applied on lengthwise slabs of concrete prisms prepared with the selected aggregates, to obtain the possible presence of reactive components, in particular volcanic glass and free silica polymorphs. The results from the two tests are presented and the possible correlations with the results from the petrographic characterization and from the expansion tests are discussed.