Reduced maintenance costs of concrete structures can be ensured by efficient and comprehensive condition assessment. Ground-penetrating radar (GPR) has been widely used in the condition assessment of reinforced concrete structures and it provides completely non-destructive results in real-time. It is mainly used for locating reinforcement and determining concrete cover thickness. More recently, research has focused on the possibility of using GPR for reinforcement corrosion assessment. In this paper, an overview of the application of GPR in corrosion assessment of concrete is presented. A literature search and study selection methodology were used to identify the relevant studies. First, the laboratory studies are shown. After that, the studies for the application on real structures are presented. The results have shown that the laboratory studies have not fully illuminated the influence of the corrosion process on the GPR signal. Also, no clear relationship was reported between the results of the laboratory studies and the on-site inspection. Although the GPR has a long history in the condition assessment of structures, it needs more laboratory investigations to clarify the influence of the corrosion process on the GPR signal.

Different types of fibres are often used in concrete to prevent microcracking due to shrinkage, and polypropylene fibres are among the most often used ones. If not prevented, microcracks can lead to the development of larger cracks as drying shrinkage occurs, enabling penetration of aggressive substances from the environment and reducing durability of concrete structures. The hypothesis of the present research is that polypropylene fibres, used in concrete for controlling formation of microcracks due to shrinkage, can be replaced with recycled polymer fibres obtained from end-of-life tyres. To test the hypothesis, concrete mixtures containing polypropylene fibres and recycled tyre polymer fibres were prepared and tested. Experimental programme focused on autogenous, free, and restrained shrinkage. It was shown that PP fibres can be substituted with higher amount of recycled tyre polymer fibres obtaining concrete with similar shrinkage behaviour. The results indicate promising possibilities of using recycled tyre polymer fibres in concrete products. At the same time, such applications would contribute to solving the problem of waste tyre disposal.

In modern waste-management systems, an advantage is given to waste recycling and reuse, rather than to disposal. In the perspective of various initiatives taken worldwide in an attempt to convert waste materials into new products, the objective of this paper is to quantify contribution of unsorted recycled steel fibers from waste tires (RTSF) for use in the concrete industry. An environmentally and financially sustainable hybrid fiber–reinforced concrete (SHFRC), obtained by combining traditional components [manufactured steel fibers (M)] and unsorted RTSF is developed. This paper for the first time, demonstrates that by determining the optimal amount and ratio of fibers (M and RTSF), sustainable hybrid fiber–reinforced concrete (SHFRC) with equal or better properties compared to ordinary fiber-reinforced concrete with only M fibers can be prepared. At the same time, it is also shown that in the optimum quantity and correct ratio, synergy between RTSF and M fibers can be used even for preparation of SHFRC with deflection-hardening behavior. A crack width–deflection model for SHFRC with unsorted RTSF under four-point loading is proposed.