Determining reactivity level of granite aggregate for concrete

Granite rubble is one of the most frequently used aggregates in concrete manufacturing. Granite rubble is considered to be a non-reactive aggregate, however, depending on the quarry, granite may have various impurities including harmful minerals containing active SiO2. The alkali – silica reaction is among the chemical reactions that have a significant effect on the durability of concrete. During the alkali – silica reaction certain forms of silica present in concrete aggregates react with high alkali content leading to formation of hygroscopic gel that expands in humid environment and slowly, although strongly enough degrades concrete structures. Concrete rubble of 3 different fractions was used for the test: 2/8 (Mix D); 11/16 (Mix E); 5/11 (Mix G). The tests revealed that granite rubble used for the tests contained few reactive rocks containing amorphous silica because after 14 days the expansion did not exceed 0.1 % ((D Mix expanded by 0.059 %, E Mix expanded by 0.066 %, G Mix expanded by 0.079 %) according to RILEM AAR-2 test method. After 56 days of testing none of the test specimens demonstrated significant micro-cracking and scaling specific to alkali corrosion; only gel deposits on the surface were observed