Moisture stability of crystalline alkali-silica reaction products formed in concrete exposed to natural environment

Abstract Crystalline ASR products were extracted from concrete exposed to natural environment and analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman microscopy, X-ray diffraction and dynamic water vapor sorption. All extracted samples display similar compositions and Raman spectra. They sorb a limited amount of water vapor between 70 and 97% relative humidity (RH), amounting to 13–25 mass-%. Three different phases are identified, with d-spacings at low diffraction angles of 13.4, 12.3 and 10.8 A. However, none of the phases show a change in d-spacing going from dry (~50% RH) to moist (~100% RH) conditions, indicating that no extra water is sorbed in the interlayer. This clearly indicates that swelling of crystalline ASR products is not responsible for stress generation and concrete cracking.