Testing alkali-reactivity of selected concrete aggregates

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 tests have covered the determination of the aggregate silica content dissolved in a solution of sodium hydroxide; scale of the expansion of mortar and concrete bars with the silica aggregate and high-alkali cement; as well as scale of the expansion of the mortar bars stored in a sodium hydroxide solution at 80°C. Exemplary photographs of the microstructure of alkali reaction products for the selected silica aggregates have also been presented. Summing up the results of standard methods of the aggregate testing, considering their alkali sensitivity, the method which tests the deformation of the concrete bars including the aggregate at issue and increased alkali content cement seems to be the most conclusive. However, the test duration up to 180 days is too short, particularly for defining the slow-reactive aggregates reactivity, such as, for example, granites or quartzites. A major diagnostic symptom which confirms the occurrence of the alkali-aggregate reaction is the presence of the reaction products (alkali silicate gel) in the concrete.