The use of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) increased in the field of civil engineering throughout the last few decades. UHPFRC is being used considerably on a large scale in megastructure applications. High compressive and tensile strength permits reconstruction and optimization of the structural members. At the same time, its improved durability properties make it easier to extend the life of the design and can be used as thin layers, cladding, repairs, and column coverings. Although UHPC has an extremely high compressive strength, it exhibits very brittle fracture behavior compared to normal strength concrete (NSC). Since the ductility and fracture toughness of UHPC can be enhanced by adding fibers, the addition of fibers to production adds innovative features to UHPFRC structures and opens up new application areas for UHPFRC. The aim of this study is to investigate the axial behavior of square reinforced concrete (RC) columns strengthened with UHPFRC jackets. Nineteen specimens were cast (1000 mm in height and a cross-sectional area of 150 × 150 mm, whose interface treatment methods were prepared through vertical grooving (VG), horizontal grooving (HG), and without grooving (NG), with the jacket thickness (20 mm and 40 mm) and the number of strengthened sides of the column (two, three, and four sides). The results show a brittle failure for all strengthened specimens. The UHPFRC-reinforced RC columns with vertical grooving (VG) showed a higher ultimate load capacity compared to the columns with horizontal grooving (HG) and the columns without grooving (NG). The horizontal grooving (HG) gives a better result than the jacket without grooving (NG) and increases the cohesion area between the jacket and the column for two and three of the RC columns’ strengthened sides. But, in the case of strengthening the columns on four sides, the effect of confining the jacket to the column appears, and the grooving causes weakness in the body of the original column so that the jacket without grooving (NG) gives a better result than the jacket with horizontal grooving (HG).

This study aimed to evaluate the static response of prestressed reinforced concrete beams strengthened in their flexure and shear properties using different strengthening techniques, steel plates, and externally bonded woven carbon fiber fabric (WCFF). The experimental work involved testing twenty large-scale prestressed reinforced concrete beams with a length of 3000 mm, and cross-sections measuring 400 mm in height and 200 mm in breadth were cast in the factory and tested in the laboratory. Four beams without prestressing served as the reference beams; two unbonded pre-tensioned beams served as the control beams, and the remaining fourteen beams were strengthened with steel plates and externally bonded woven carbon fiber fabric (WCFF). Eight of the beams were strengthened with 4 mm thick steel plates and tested under a monotonically increasing load with manual readings recorded. The remaining six beams were strengthened with 0.5 mm thick WCFF and tested under a monotonically increasing load with manual readings recorded. The variables considered included the strengthening techniques (FRP composite sheets, steel plates), the types of strengthening (slices, U-shaped), and the flexural and shear capacities of the strengthened beams. All the implemented strengthening techniques yielded enhancements in both the flexural and shear strength outcomes of the beams compared to their respective controls. The most significant increase in load capacity, whether in terms of ultimate load or first crack load, for the prestressed concrete beams’ flexure properties occurred when strengthening with U-shaped steel plates. Additionally, the greatest reduction in deflection at the point of reaching the maximum load for the prestressed concrete beams, in terms of their flexure properties, was observed when strengthening with U-shaped steel plates. Similarly, the maximum load increase for the prestressed concrete beams, in terms of their shear properties, was achieved through strengthening with U-shaped woven carbon fiber fabric wrapping. Furthermore, a finite element model was created to simulate various experimental specimens. The finite element model’s results exhibited harmony with the experimental results, affirming the efficacy of the presented finite element model.

Bar splicing is considered an essential part of the construction process of reinforced concrete (RC) due to the ease of installation in construction, transportation constraints, and restricted length of reinforcing bars. Splices serve the primary role of joining reinforcement bars in standard RC elements such as columns, walls, beams, slabs, and joints. Bond behavior between the bars and the concrete is one of the fundamental qualities required for appropriate RC structure design and analysis, as it affects serviceability and ultimate limit states. The most common failure found in lap splice locations is debonding, which occurs at the splice region and insufficient lapped length is considered as the primary cause because of design or construction mistakes, design by outmoded code, and natural catastrophes. As a result, strengthening existing substandard splices in RC structures is critical. The purpose of this research is to analyze and summarize experimental strengthening solutions for inadequate splices. The most common methods are confining spirals, confining with internal or external steel stirrups or carbon fiber reinforced polymer (CFRP), concrete jacketing, fiber reinforced polymers (FRP), post-tensioning prestressed RC, external confining with CFRP, near surface mounted (NSM) techniques, ultra-high-performance concrete (UHPC), fiber reinforced concrete (FRC) and combinations of two methods. Each method of strengthening is evaluated based on its performance, benefits, drawbacks, application-specific elements, and variables influencing the design and scope of applicability. A comparison of the key methodologies was also carried out. The most recent studies and recommendations for improving inadequate lapped splices are provided.

Geopolymer concrete is concrete made from industrial materials, such as fly ash, GGBS, silica fume, and metakaolin, used as a cement alternative. In this study, geopolymer concrete will be based on fly ash as a binder material, alkaline activators of sodium hydroxide and sodium silicate, GPC beams of dimensions 800 mm × 250 mm × 100 mm, circular columns with diameter 350 mm and depth of 700 mm and GPC slabs of dimensions 500 mm × 500 mm × 100 mm are all cast with fly ash content of 350 kg/m³. The ratio of alkaline solution to fly ash was equal to 0.5 and was kept constant, and the Na₂SiO₃-to-NaOH ratio was 2.5 and the NaOH molarity was kept constant at 12 M. The beams reinforcement was changed to study the shear and flexural behaviour, and the slabs and columns reinforcement ratio was kept constant. The load capacity, stress–strain behaviour of the GPC and load-deflection behaviours of the members were also examined. The results showed that reinforced geopolymer members can be used as an alternative to reinforced concrete structural members, but they are more expensive than reinforced concrete. Further study is recommended to provide more practical design recommendations for incorporating geopolymer concrete into structural elements in order to accelerate the adoption of this concrete for large-scale field applications in the future.

This article focuses on the evaluation of concrete substructures of 10 road bridges in eastern Slovakia, built between 1960 and 1970, based on core sampling and compressive strength testing performed in accordance with current European procedures for in-situ strength assessment. The results confirm that the concrete was predominantly site-batched, characterized by a large aggregate size and significant strength variability. Although all tested specimens meet the design requirements valid at the time of construction, only about half of the bridges achieve the prescribed characteristic strength when assessed according to present-day European standards. Despite their age of 60–70 years, the substructures (abutments and piers) remain in very good condition. In contrast, the superstructures show extensive deterioration, dominated by reinforcement corrosion and alkali–silica reaction, which will require costly rehabilitation or replacement in the near future.

The article pertains to the gradual rehabilitation process of a load-bearing concrete structure. Emphasis is placed on pointing out the shortcomings of the constructed load-bearing structure of the building and the detected failures after its long-term use. The paper presents a proposal for the reinforcement of various parts of the load-bearing system divided into stages with regard to the inaccessibility of the premises.