Mechanical Activation of Portland Cement Improves Resistance to Acid Attack: Insights from 4D X-Ray Computed Tomography

Concrete structures exposed to biological attack undergo degradation caused by organic acids produced by microorganisms. To improve the resistance of cementitious materials, this study applied mechanical activation of Portland cement using a vortex layer device. Porosity and compressive strength of control and mechanically activated hardened cement paste (HCP) specimens were evaluated after 0, 14, and 28 days of exposure to a model acidic environment (pH 3, a mixture of carboxylic acids). Spatiotemporal heterogeneity of degradation in control and activated HCP was assessed for the first time by 4D X-ray computed tomography, which tracked individual pores across the same time points and revealed degradation patterns inaccessible to bulk measurements. Mechanical activation was found to increase the initial compressive strength by 33% (59.3 MPa vs. 44.5 MPa). After 28 days, the activated specimens retained 75% of their initial strength, compared with 62% for the control ones. Despite higher initial porosity (1.5% vs. 1%), the mechanically activated specimens exhibited lower volumetric loss (27% vs. 56%) and maintained spatial stability of the pore framework. These findings support the potential of this approach for structures operating under microbiological corrosion conditions.