X-ray microtomography (microCT) of the progression of sulfate attack of cement paste

High-resolution X-ray computed tomography (i.e., microCT or microtomography) was used to study the sulfate attack of cylinders of Type I cement paste cast with water–cement (w/c) ratios of 0.45, 0.50 and 0.60. Damage levels in samples exposed to a Na 2SO 4 solution with 10,000 ppm sulfate ion concentration were qualitatively rated from 0 ( no damage) to 4 ( extreme damage) based upon visual examination of the samples' exteriors and microtomography of the samples' interiors. The greater the w/c ratio, the more rapid the onset of sulfate damage. The corners of the cylinders appeared to be particularly susceptible to spalling, and damage may have continued into the cement paste by formation of subsurface cracks.