Self-healing concrete is an advanced, sustainable technique that has the potential to reduce maintenance costs by automatically repairing cracks. Some Bacillus species produce a urease enzyme to precipitate calcite during biomineralization, which can act as a binding filling material. This study investigated the effects of bacteria type, content and concentration, and nutrient content on the properties of self-healing concrete, especially at the age of 90 days. Bacillus Sphaericus and Bacillus Megaterium were introduced into the concrete at two concentrations, 2 × 10⁸ and 2 × 10⁹ (CFU/ml), and different percentages of bacteria were selected using calcium lactate as a nutrient material. Tests were performed for compressive strength, SEM, EDS, water permeability, rapid chloride permeability, and TGA/DTG. The results show significant development in compressive strength and microstructure characterization of concrete, especially with Bacillus Megaterium using a 2.5% bacterial proportion with a concentration of 2 × 10⁹ CFU/ml and 1% of calcium lactate.

Flexural behavior of up-graded steel I-beams, IPE 160, with bonded/welded steel plates and bonded carbon fiber reinforced polymer (CFRP) plates/sheets were evaluated in this work. Different types of end anchorage (belted CFRP sheet, steel clamped, and end welded) were applied to enhance the efficiency of the bonded element. The present experimental results showed that, plate end anchorage increased markedly the efficiency of bonded steel and CFRP plates. CFRP sheet showed higher resistance to debond than CFRP plate. Two separate CFRP strips bonded below the lower flange of the I-beam is the best method for bonded CFRP plate to I-beams. Bonded/welded hybrid joint technique for attachment of the steel plate in tension side is the most efficient technique. All strengthened beams and control beam failed due to distortional buckling after the yield occurrence.

Construction deficiencies can cause serious problems that significantly decrease the design strength of concrete structures, such as the unreinforced drilled openings. With the absence of sufficient reinforcement, the stress concentrations generated around the opening corners produce cracks in the beams. The size and location of the opening significantly affect the behavior of the beam under static and dynamic load. In this work, an experimental and numerical program was performed to investigate the behavior of drilled reinforced concrete beams with and without strengthening using CFRP sheets. Energy absorption and SDOF analyses were performed to preliminary assess the behavior of the beams under the dynamic load, such as blast. One control beam without any openings, six beams with tension-zone openings, and six beams with shear-zone openings were tested. It was found that the samples with tension-zone openings were slightly affected by the opening, where the reduction in the ultimate strength was approximately 7 to 14%. The beams were able to recover up to 46% of the lost strength by CFRP strengthening. On the other hand, the shear-zone opening significantly decreased the strength and energy absorption and increased the blast response. It can be concluded that it is not recommended to drill any opening at the shear zone as strength loss can reach 57% even with the strengthening, especially for blast resisting structure; in addition, the strength recovered from approximately 11.95 to 32.46% only. The finite element model was able to predict the strength of the beams. The results were closer in the case of tension-zone opening than those in the case of the shear-zone opening. Shear cracks were observed at the corners of the openings even if the opening exists at the tension zone. A reduction in the density of cracks can be observed after the strengthening, where the FRP sheet decreases the stress in the concrete.

This research aims to illustrate and express the impact of analytical techniques such as TOPSIS- and FTOPSIS-based Taguchi models on obtaining the optimum design of fiber-reinforced concrete (FRC).Three levels of silica fume content, fly ash content, water-to-cementitious (W/C) ratio, and superplasticizer content were examined in the present work. However, the steel fiber content (1%) and the maximum aggregate size of 14 mm were kept constant for all mixes. Once the experimental results were obtained following Taguchi’s method, it was used as input data to the TOPSIS and FTOPSIS models. The optimum set of mixture factor levels was determined by identifying the two modules. The optimal FRC mix proportions obtained from the TOPSIS- and FTOPSIS-based Taguchi model were 5% silica fume content, 0% fly ash content, 0.27 W/C ratio, and 0.5% superplasticizer. Multi-response optimization approaches are essential to optimize the concrete mix proportions to achieve the required strengths, workability, and production cost. ANOVA was used to analyze the experimental results to find the contribution of each independent variable to the compressive strength and splitting tensile strength of FRC. ANOVA showed that the most predominant factor that affects the FRC mix proportions was the W/C ratio, followed by the fly ash, silica fume, and superplasticizer contents, respectively, in descending order.