Applying ordinary repair mortars onto the surface of degraded concrete elements has been a common approach in restoration operations. Since the properties of cement-based composites depend on nano-structural features, proper addition of nanoparticles can enhance performance. In the present study, the physico-mechanical performance of concrete and mortar mixtures incorporating magnesium nanoparticles was investigated. The workability and flowability of the mixtures, along with compressive, tensile, and flexural strengths of specimens were evaluated. A total of 284 cylindrical, cubic, and prismatic beam specimens having different dosages of magnesium nanoparticles as partial replacement for cement were assessed to quantify the effects of adding magnesium nanoparticles. Furthermore, analysis of the compatibility between the repair mortar and the existing concrete substrate was examined using four-point bending tests on repaired beam elements to characterize the different modes of failure. Two approaches of substrate surface preparation featuring smooth and rough interfaces were adopted, and the effect of interface texture on the mechanical properties of the repaired beam specimens was evaluated. The results show that specimens incorporating magnesium nanoparticles achieved 37%, 37%, and 63% higher compressive, tensile, and flexural strengths, respectively, compared with that of the reference specimens. Moreover, the set of concrete beams with rough interface showed compatible failure modes, while those with smooth contact interface had incompatible modes of failure.

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