In the present paper, results of alkali reactivity tests for selected silica aggregates, both rapid and slow alkali reactive, with the use of ASTM procedures, have been presented.
The aim of the present paper has been to estimate alkali reactivity of selected silica aggregates with the application of a variety of standard testing methods.
The present paper includes test results and alkali reactivity assessment of the selected silica aggregates, both rapid and slow alkali reactive.
Also micro-crystalline or imperfectly crystallised quartz (stressed quartz) may be the reason for alkali reactivity in similar slow alkali-reactive aggregates .
In like manner, Jensen  claims that alkali reactivity of slow-expansive rocks may be estimated through a microstructure analysis and well known field observations, rather than basing on a list of rocks derived from the traditional classification.
Applied methods of aggregate alkali reactivity testing
Results of the alkali reactivity tests for quartzite and granite aggregates, hornstone and quartz sand with opal have been shown in Figs 1-4.
However, the bars with the remaining three aggregate types: quartzite, hornstone and granite have not shown expansion which would testify to aggregate alkali reactivity (Fig 2) during the test of up to 180 days.
In contrast, the results of the accelerated expansion test of the mortar bars with the aggregates tested (mortar bars stored in NaOH solution at 80[degrees]C) have shown, in all cases, expansion exceeding 0,1% after 16 testing days (Fig 3), which remains in compliance with the reactive/ non-reactive criterion; all aggregates tested have demonstrated alkali reactivity.
While analysing the test results obtained, and taking the views quoted in [15-17] into account, one can claim that the chemical method and the long-term method of the mortar bar testing may underestimate alkali reactivity of a slow reactive aggregate.
Standard Test Method for Potential Alkali Reactivity of Aggregates (Chemical Method).