Microstructure of Potsdam sandstone and applicability of accelerated tests for alkali-silica reactivity

To evaluate the effect of the microstructure of aggregate on the applicability of accelerated tests of alkali-silica reactivity for rocks, the expansion behavior of Potsdam sandstone was studied using the concrete prism test and several accelerated tests: accelerated mortar bar test, Chinese autoclave method and Chinese accelerated mortar bar test. The microstructure of the mortar bars was also studied after the expansion tests. The results show that the alkali reactivity of Potsdam sandstone is not properly identified with any of these accelerated tests because the aggregate, used in the tests has too many of fine particles, and therefore it does not reflect the special microstructure characteristics of the sandstone. The results also show that, in addition to the type and amount of reactive constituent in the rock, the microstructure of the rock has a significant influence on the location where the alkali-aggregate product forms and on the expansion behavior of the rock. In order for accelerated tests to accurately predict the alkali-expansivity of Potsdam sandstone as well as other multi-mineral and heterogeneous rocks, it is critical to use aggregate particles suitable to maintain the microstructure characteristics of the rocks.