Influence of equivalent reactive quartz content on expansion due to alkali silica reaction

Application of Image Analysis to Identify Quartz Grains in Heavy Aggregates Susceptible to ASR in Radiation Shielding Concrete

“…A very small content of highly reactive quartz (0.08%) and reactive quartz (2.67%) in hematite aggregate caused the occurrence of ASR. These are smaller values than in studies done by Alaejos and Lanza [ 32 ], but they tested quartzites, quartzarenites, and limestones with chert rocks, and they stated that their results correspond to the tested aggregates and that other different rock types should be tested to confirm these results.…”

“…It is known that the grain size reduction of quartz enhances reactivity by increasing the surface area of quartz grain boundaries available for reaction [ 28 ]. Earlier studies done by Alaejos and Lanza [ 32 ] showed that when the content of quartz crystals between 10 and 60 μm is taken into account, not only highly reactive quartz <10 μm, the expansion due to ASR is larger. At the same time, quartz crystal size greater than 60 μm (doubtful quartz: 60–130 μm) has no effect on expansion, so it can be considered innocuous.…”

“…The threshold applied to rocks with micro and cryptocrystalline quartz texture is also different in each country [ 31 ]. So, the classes of the quartz size were established according to the Norwegian Criteria, as shown in the research of Alaejos and Lanza [ 32 ]. The reactive forms of quartz have been classified depending on the crystal size as innocuous quartz: >130 μm; doubtful quartz: 60–130 μm; reactive quartz: 10–60 μm and highly reactive quartz: <10 μm.…”

Influence of granitic aggregates from northeast Brazil on the alkali-aggregate reaction

“…However, the petrographic analyses indicated that the differences could be explained by the different textural properties. In sample C, the presence of subgrains of microcrystalline quartz smaller than 20 µm (Figure 6), which have been described as being reactive to highly reactive 13 , resulting from the process of recrystallization of larger grains, could explain the fast dissolution of silica and greater expansion in the mortar bars. The smaller size of the quartz subgrains in sample C implies that this material had a greater surface area and an increased number of grain boundaries, compared to samples A and B, favoring faster reaction at the solid-liquid interface, in agreement with the kinetics of a heterogeneous chemical reaction.…”

“…The deformation of quartz, with the development of subgrains and the presence of cryptocrystalline and microcrystalline material, provides important features for evaluation during petrographic analysis 12,13 . Wigum 14 , in a study of deformed granitic rocks, found that with the formation of subgrains of quartz, the total grain boundary area and size of grains were the variables that had the greatest influence on the expansion process.…”