Microstructure characterization of alkali-glass particle and alkali-glass powder reacted gels with neutron scattering and imaging techniques

The major obstacles of the incorporation of recycled waste glass in concrete infrastructures are the deteriorations caused by alkali-silica reaction (ASR). Previous research found the concrete containing glass powder does not suffer from ASR. This indicates the size-effect, which is the main focus of this study, is crucial for the incorporation of waste glass in concrete. In order to gather the information for the proposed analytical models, the microstructure and morphology of the synthetic alkali-glass particle and alkali-glass powder reacted gels were characterized by using ultra small angle/small angle neutron scattering (USANS/SANS) and scanning electron microscope (SEM) techniques. The radius of gyration and the power-law constant of different gel samples were obtained by fitting the scattering intensity with a unified Guinier/power-law approach. The power-law constants were in the range from 3 to 4 for the condensed gel sample, indicating the gel particles are surface fractals with different roughness. The SEM images show that the gel particles were spherical-like with sizes around 2 to 3 μm, which is close to the characteristic size (3.4 μm) calculated from the radius of gyration. The dynamic alkali-glass particle reaction was captured with the synchrotron X-ray micro-computed tomography (X-ray micro-CT). The reacted gel particle distributions at different reaction stages were analyzed (up to 64 h). At earlier reaction stage, the majority of gel particles has a size ranged from 2 to 3 μm. At later reaction stages, more large-sized particles were observed in the reaction solution, indicating the volume change of the glass-particle reaction gel.