Crystal penetrating sealer materials (PSMs) are commonly used on the surface of concrete to protect the surface from damage and thereby extend its service life. Such materials penetrate into existing pores or cracks and form crystals, which block potential paths through which unknown materials could enter and degrade the concrete. In this study, the constituent compounds of a PSM were divided into seven categories, labeled CAT I to CAT VII, and five discrete particle size fractions corresponding to sieve Nos. 30, 50, 100, 200, and 200 were considered. Energy dispersive spectrometry revealed that the constituent elements of the PSM were O, Ca, Si, C, Na, and Mg, and X-ray fluorescence (XRF) showed that the major chemical components of the materials were CaO, SiO2, Na2O, and MgO. In addition, XRF indicated that crystals filled the capillary pores in the microstructure of a mortar substrate at a depth of 5 mm from the mortar surface and that the main hydration products of the PSM were calcium silicate hydrate gel and CaCO3. Water permeability and rapid chloride permeability tests were applied to concrete test samples to examine the durability of the samples. The penetration depth is a critical property determining the effectiveness of concrete PSMs. In this study, we analyzed chemical composites that could be used as PSMs and determined their sealing mechanism and penetration depth. Furthermore, mercury intrusion porosimetry revealed that the PSM had the capacity to clog capillary pores of the mortar substrate, effectively sealing pores and reducing the porosity. Thermogravimetric analysis showed that the PSM layer on the concrete surface could extend up to a depth of 10 mm. Scanning electron microscopy indicated acicular crystals filling the capillary pores in the internal microstructure of the mortar substrate under a concrete surface

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