Availability of computacional power calls for the responsible use of mechanical models that faithtfully represent material behavior even in complex cases, as is concrete undergoing Alkali-Silica Reaction (ASR) expasion. In this paper, a series of tests aimed towards obtaining meaningful data for mechanical characterization of an existing, old-aged, ASR-affected dam concrete are presented. These tests, consisting mainly in long-term measurement of free and confined expansions of core-drilled specimens extracted from different locations in the dam, are designed to provide data for a material model. A specific methodology is developed and applied, including procedures for test design, mechanical loading and data acquisition in harsh environmental non-laboratory conditions. Conclusions about the possibility of ASR-expansion mitigation through confinement are drawn from experimental data.