The use of near-surface mounted (NSM) Glass fiber reinforced polymer (GFRP) bars is one of the most popular and effective techniques for strengthening reinforced concrete (RC) beams. This paper presents an experimental research program to study the flexural strengthening of RC beams comparing two areas of bottom tensile reinforcing steel and three development lengths of NSM GFRP bars. The beam test results indicated that the beam flexural strength increased up to 110% and 58% for the cases of low and high tensile reinforcing steel ratios, respectively. The effect of the tensile reinforcing steel area on the critical value of the development length of NSM GFRP bars was also investigated. It was found that decreasing the axial stiffness ratio, reduced the strengthening efficiency and the critical development length of the NSM GFRP bars. Finally, a 3D Finite Element (FE) model using ANSYS was constructed and was validated using the experimental results. Good agreement was seen between experimental and FE model results.

Experimental and numerical programs were invoked to investigate the effect of concrete cover and area of main steel reinforcement on the flexural behavior of strengthened RC beams by near-surface mounted glass fiber reinforced polymeric (NSM GFRP) bars of different lengths. Nine beams divided into three main groups were tested under four-point bending. The three beams of the first group were strengthened by different lengths of GFRP bars and having a concrete cover of 50 mm, while the three beams in the second group were strengthened in a similar manner as those of the first group but the concrete cover was 30 mm. The main steel reinforcement in the first and second groups was 2Ø10. The three beams of the third group were similar to those of the first and second group but the main steel reinforcement was 2Ø16. The 3-D FE commercial ANSYS program was used for the numerical work. The experimental results showed that decreasing the concrete cover increased the flexural capacity of the strengthened RC beams but this improvement disappeared by decreasing the NSM GFRP bar length. The RC beams flexural strength increased with increasing area of main steel reinforcement. The numerical results showed an agreement with the experimental results.

This work presents experimental and numerical research to evaluate the compression confinement techniques of HSC beams reinforced with different ratios of high-strength steel reinforcement. Twelve specimens of high-strength reinforced concrete beams with two different compression confinement techniques were tested experimentally. The first method is used carbon fiber reinforced polymers sheets (CFRPs) around the compression zone, CF, and the steel fibers reinforced concrete is used in the compression zone by 1% of volume fraction, SF, in the second case. A 3-D finite element analysis was done; using the ANSYS program to simulate and idealize all experimental specimens. The numerical and experimental results of the RC beams were validated and compared in this work. The results showed that there is a good idealization using 3-D finite element models with the experimental specimens. Also, it was found that using the suggested techniques can increase the strength ratio and increase the ductility index depending on the tensile reinforcement ratios. Moreover, the energy absorption and the mode of failure were enhanced.

This work presents the mechanical and durability evaluation of high-performance concrete, HPC, mixes, used for tunnels, after exposed to different temperatures. Nine HPC mixes were investigated. The first group has W/C ratios; 0.25, 0.31 and 0.37. Second group has silica fume addition by about 5.0%, 10%, and 15% of cement weight. In the second one, the polypropylene fibers were added to concrete by the ratios of 0.211% from the concrete volume. The mechanical properties were measured at room temperature and after subjected to 400°C and 800°C for curing periods of 28 and 56 days. The durability was evaluated by water penetration depth at room temperature (RT). SEM micrographs results were, also, investigated. The results indicate that at temperature of 400°C, the compressive strength of the concrete increased. With further increases in temperature over 400°C to 800°C, they decreased. At 400°C, the highest compressive strength improvement is achieved by about 18.2% after 56 days curing in the case of 10% SF, while with addition of PP=0.211 fibers, Fc has a significant increase after curing for 56 days by about 32.1%. Moreover, at 800°C, the highest tensile strength improvement achieves by about 87.5% after curing for 56 days in the case of SF=10%. The lowest porous penetration depth of water was found for mix containing W/(C+SF) = 0.37, SF=10%, and PP=0.211%.

The present study examined the mechanical performance of sustainable concrete with silica fume (SF), fly ash (FA), cooled cast iron (CCI), and crushed quartz powder (CQ) used as partial cement replacements at three water-to-binder ratios (0.36, 0.41, and 0.46). Fifteen concrete mixtures were cast and tested for compressive, splitting tensile, and flexural strengths at 7, 28, and 90 days. Results indicated that the lowest water–binder ratio of 0.36 produced the highest strengths, consistent with values of 78 MPa compressive strength at 28 days and 87.8 MPa at 90 days, which were better than those obtained from mixes having the other two ratios by up to 34% in early ages and by up to 33% in later ages. The partial replacement of SF by FA lowered the early-age strength, but very significant long-term gains were recorded; replacing three-quarters of SF with FA increased the 90-day compressive strength by 5.9%, 30.4%, and 30.1% for groups 0.36, 0.41, and 0.46, respectively, compared to their corresponding mixes with SF only. Incorporating CQ led to reductions in strength at 28 days of 9.3–13.4%; however, reductions at 90 days remained modest, 8.1–13.6%, indicating improved long-term pozzolanic contributions. It is noted that tensile-to-compressive strength ratios for all mixtures ranged from 9.8 to 12.2%, and flexural-to-compressive ratios ranged from 13.6 to 14.7%, which are better than the ACI318 predictive correlations for concretes using industrial by-products. The results confirm that optimized SCM blending higher fly-ash proportions at lower water–binder ratios enhances long-term mechanical performance while enabling significant cement reduction, supporting more environmentally sustainable high-strength concrete.

N Libya, the accumulation of construction waste has increased due to the war, which damaged structural buildings, as well as demolition, construction, and rehabilitation. Estimates indicate that the amount of post-conflict waste is approximately 82 million tons, which could be recycled or further processed for use in building construction and other economic sectors. At the same time, there is a continuous depletion of natural resources (fine and coarse aggregates) in the production of concrete, posing a challenge to the environment and the sustainability of natural resources. This study explored the use of construction waste recycling to create eco-friendly concrete by replacing 10% and 20% of the fine aggregate by weight with brick, marble powder, and ceramic waste. Cubic specimens of 150 × 150 × 150 mm and cylindrical specimens of 150 × 300 mm were cast to determine compressive and splitting tensile strengths, respectively. Eighty-four cubes and twenty-one cylinders were prepared and tested at ages 7, 28, and 56 days. The results indicated that the marble powder concrete mixture with 10% replacement had the lowest workability. Furthermore, at 56 days, the compressive strength of the ceramic waste concrete mixture increased by 25.41% when replacing 20% of the fine aggregate, while the highest tensile strength for the sustainable marble powder waste concrete mixture was recorded at 39.89% using the optimum 10% replacement at 28 days.