The alkali-silica reaction (ASR) is a chemical reaction between the alkaline pore solution in concrete and its aggregates, mainly those rich in silicates. The ASR products can lead to a significant amount of cracking upon swelling due to pore solution uptake. The aggregate swelling leads first to aggregate cracking, then to crack propagation through the mortar matrix. We present an overview of how X-ray tomography and respective 3D image analysis allow investigating the ASR damage temporal evolution.