Microcrack and Porosity Development in Sealed Cement Mortars Measured with Micro-Computed Tomography

For the first time, this paper explores the role of hydration kinetics on microcrack development in cement mortars using the μ-CT technique with a resolution of 2.2 µm. Three binders were tested: fine-grained ordinary Portland cement (OPC) with Blaine fineness of 391 m²/kg, coarse-grained OPC made from the same clinker with Blaine fineness of 273 m²/kg, and H-cement as a representative of the alkali-activated binder. It was found that most microcracks have a width in the range of 5-10 µm, increasing their occurrence with the progress of sealed hydration. While H-cement and coarse-grained OPC showed a comparable number of microcracks, fine-grained OPC exhibited more than twice the number of microcracks. In this sense, high hydration kinetics induce more microcracks, promoting later coalescence into visible cracks and disintegration of concrete at the end. Therefore, durable concrete with minimum microcracks should be derived from slow hydration kinetics or alkali-activation processes.