The naturally occurring wastes contain a large number of active groups. In this study, shrimp shell wastes were modified chemically to form chitosan. When mixing concrete with a natural polymer the result revealed a synergistic impact on the characteristics and functionality of the concrete structure. The formed chitosan was characterized by Fourier-Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Five concrete mixes were designed to achieve the study objective. For certain concrete mixes, admixtures such as a natural polymer (chitosan), and chemical (superplasticizer) were added with 0.05% by weight of the cement content. Those admixtures were added to study their behavior on the characteristics of the concrete mixes, and then compare test results with control concrete mixes. Also, the purpose of the experiment was expanded to study the impact of adding the admixtures to fibrous concrete, as this fibrous concrete faces interlocking due to steel fiber's presence in the fresh concrete mixture. The results indicated that concrete-embedded chitosan exhibited significant enhancement in the mechanical properties. Further, the surface shape of concrete was characterized by the presence of chitosan crystallites which spread and filled the spaces in the chitosan structure. Also, it’s noted that chitosan can delay the rate of cement hydration to a small value, which may help in hot weathering concrete.

The opened beams always confused the designers due to the guidelines missing. In this research, six hybrid beams reinforced with mixed steel and basalt fiber-reinforced polymer (BFRP) bars and having constant cross-sections of 150 mm × 300 mm and a clear span of 1800 mm were cast and tested under a four-point loading setup. Generally, five beams had symmetrical rectangular openings with dimensions of 150 mm × 250 mm located at a distance of 250 mm (equivalent to the beam effective depth) from the beam support, while an additional solid beam served as a control. The studied parameters included the effect of using internal reinforcement (steel or BFRP bars) provided adjacent to the opening sides or by incorporating an external BFRP sheet around the opening corners. Also, double enhancement with internal steel reinforcement bars together with external strengthening BFRP sheet was investigated. The relevant results showed that the opened beam without enhancement lost 75% of the maximum load compared with the solid beam. Placing internal steel or BFRP bars around the openings increased the maximum load by 62% and 60%, respectively, compared to the non-enhanced opened beams. Using an external BFRP sheet to strengthen the opening corners of the beam enhanced the maximum load by 76% compared with the non-enhanced opened beam. Consequently, by combining both the internal steel reinforcement and external BFRP sheet around the openings, the maximum load increased by 137% compared with the non-enhanced opened beam. Ultimately, a numerical analysis of the three-dimensional finite element model was performed to confirm the experimental findings, and the relevant results showed compatibility correlations with the experimental ones. Also, the effect of various parameters such as BFRP reinforcement ratio and number of BFRP sheet layers around the openings was investigated by adapting the validated numerical model.

It is well known that through the structural design, the safety and economic considerations of the project represent major factors, which must be always in mind. From this point of view, the concept and idea of “Stratified Concrete” were developed. Stratified Concrete consists of two or more types of concrete; in particular, composite materials consisting of High Strength Concrete (HSC) and Normal Strength Concrete (NSC). This study showed the flexural behavior for stratified sections (HSC-NSC) by taking a short time lap (1 h) between the two mixes to get a good bond between them. An experimental program was conducted to investigate the flexural behavior of NSC (25 MPa), HSC (60 MPa), and three HSC-NSC with the effect of changing the thickness of the HSC layer of slabs (20, 40, 75 mm) that had subjected to double static loads. As well, these slabs’ experimental results were numerically verified. The most important achievement is the success of the idea of casting different strengths of concrete layers using a short time interval to improve the bending behavior of the slabs, and reach the superior thickness of the HSC layer, which represents almost a quarter of the slab thickness.

Hybrid reinforced concrete structures are efficient systems that include steel and fiber-reinforced polymer (FRP) reinforcement advantages, which are called fiber steel reinforced concrete (FSRC). On the other hand, passing service pipes through creating holes in reinforced concrete (RC) beams completely changes their structural behavior. Besides, RC beams with holes require rigorous nonlinear finite element (NLFE) analysis which is not typically done by design engineers. The behavior of simply-supported FSRC beams (hybrid reinforced with basalt FRP (BFRP) and steel bars) having two end holes under the effect of four-point bending loading tests was investigated. Also, NLFE models were developed, verified, and implemented in an extensive parametric study. The studied parameters related to (1) hole shapes: circular, square, and rectangular shapes; (2) height/or diameter: ho=0.2h, 0.3h, 0.4h, and 0.5h; and length: Lo=0.3h, 0.5h, 0.7h, and 1.0h. Compared to a similar beam without holes, the holes produce reductions of up to 53%, 44%, 85%, 64%, and 58% in the beam’s cracking load, ultimate strength, absorbed energy, post-cracking stiffness, and post-yield stiffness, respectively (the lowest in cases of circular holes). It was noted that hybrid reinforcement significantly affects the behavior of beams with holes. In order to obtain the benefit of this behavior, it is recommended to drill the beam with a hole size diameter of up to 0.4h and up to a hole size length of 0.3h for square holes. On the contrary, the effect of hybrid reinforcement gains less significant enhancement in the case of the rectangular holes.

Undoubtedly, the interest in using Geopolymer Concrete (GPC) recently speared. Hence, it's essential to study the behavior of GPC. In the current research, the mechanical properties of GPC were studied to investigate the performance at the time interval of 28 days to 90 days. The study extended to include water absorption, water permeability, and sulfate attack tests. The experimental work program was conducted to cover the effect of the curing method (steamer with 60°C or warm air) in addition to the curing period (seven days or three days). Also, the bond strength was investigated between steel reinforcement bars and concrete. Furthermore, the GPC ingredients were captured internally using a scanning electron microscope (SEM) to analyze their integrity. The results showed that the recorded slump value of the GPC mixture was more than the conventional concrete (CC) mixture by 130%, afterward the GPC mixture became stickier, and hardening happened. The GPC mixtures achieved significant enhancement, and the strength was highly developed after 28 days more than CC, especially for GPC cured in a steamer at 60°C for seven days, which reached the limits of high-strength Geopolymer Concrete (HSGPC) after 90 days.