Non-destructive testing (NDT) and semi-destructive testing (SDT) have recently been more frequently used for the evaluation and condition assessment of concrete floors in various types of buildings. The subject of the article is to briefly introduce the reader to the problem of adhesion between overlays and substrates in concrete floors and to illustrate the current state of knowledge on the subject. The aim of this paper was to briefly describe the recently used non-destructive and semi-destructive testing methods and the parameters useful for characterizing the adhesion between overlays and substrates in concrete floors, as well as the methods useful to characterize the functional properties of the overlays. A recent literature survey, related to the adhesion between the overlays and substrates in concrete floors, is thus shown. Special emphasis was placed on the critical review of the current research results. Based on the analysis of the literature review, research gaps have been presented in order to highlight future research directions.

In civil engineering, overlays should have appropriate strength and functional parameters. In order to obtain these parameters to the desired level, additional actions are applied in the form of dispersed reinforcement, surface hardening and impregnation. There is a lack of detailed results of studies on the impact of amorphous SiO 2 nanospheres contained in the cement mortar of the overlay in concrete floors on its bonding with the concrete substrate, as well as on its functional parameters. Considering the above, the article presents the results of research regarding the impact of amorphous SiO 2 nanospheres. It was also shown that the most favourable results (understood as lower abrasion resistance, higher subsurface tensile strength and a higher overlay hardness), when compared to the reference mortar, are achieved with the use of amorphous SiO 2 nanospheres in an amount of 0.5% in relation to the cement mass. This is confirmed by studies carried out using scanning electron microscopy, which confirmed that these improvements are due to the fact that the mortar with the addition of amorphous SiO 2 nanospheres in an amount of 0.5% of the cement mass is characterized by a lower ratio of pores within the range from 0.83 to 7.50 μm.

This article focuses on the development of nanoalumina-based cement mortars for overlay applications in concrete floors. It focuses on the effect of applying aluminum oxide (Al2O3) nanopowder to the cement mortar used to make the overlay, on the adhesion of this overlay to concrete substrate and on its functional properties. It was claimed that the addition of 0.5% of Al2O3 nanopowder has a positive effect on the adhesion of the cement mortar used to make the overlay to the substrate made of concrete. The prior studies performed using scanning electron microscopy (SEM) confirmed that the reason for the improvement in adhesion is the fact that cement mortar used to make the overlay with the addition of 0.5% of Al2O3 nanopowder is less porous than the reference mortar within the interphase. The article concurs that the most favorable results, in terms of lower abrasion resistance and higher subsurface tensile strength of the cement mortar used to make the overlay, are mainly brought about by adding 0.5% of Al2O3 nanopowder.