Recently, fiber has been incorporated into concrete mixtures, where its distribution in the concrete matrix helps to improve and enhance the mechanical properties of fiber-reinforced concrete (FRC). The aim of this study is to investigate the influence of steel and synthetic fiber parameters, along with different coarse aggregate maximum sizes (CAMZs) on FRC performance. Additionally, in past research, the empirical relationships among the compressive, tensile, and flexural strengths of plain concrete and FRC were assessed, and correlations between these mechanical properties of FRC were examined. For each CAMZ, four fiber dosages for each fiber type were considered. The results demonstrate the mechanical properties of FRC enhanced as the fiber length increased from 13 mm to 60 mm, the CAMZ increased from 9.5 mm to 37.5 mm, and the ratio of the fiber length to the CAMZ was in the range of 0.35–5.68. All mixtures have been intended to exhibit similar compressive strengths; however, the synthetic/steel fiber advanced the brittleness ratio of specimens with G10, G19, and G38 to approximately 36.8%, 40.7%, and 47.4% greater than the contral specimens, respectively. In addition, from the regression analysis investigation, there are strong correlations from the regression analysis of the mechanical property results of FRC.

The bond strength at the interface zone between two concrete sections plays a critical role in enhancing long-term durability, ensuring that both materials perform homogenously. Ensuring compatibility at the interfaces between repair and concrete materials is one of the most challenging aspects of constructing composite systems. Despite various studies, a comprehensive understanding of the engineered cementitious composite (ECC) bonding mechanism at the repair interface is still limited. The objective of this research is to identify the interfacial properties between lightweight concrete (LWC) and engineered cementitious composite (ECC) with varying fiber dosages of polyvinyl alcohol (PVA) and glass fibers under different surface roughness conditions. The study tested LWC-ECC specimens in direct shear using slant shear and bi-surface shear tests, recording the maximum shear stress at failure. Two grades of LWC—normal-strength lightweight concrete (NSLW) and high-strength lightweight concrete (HSLW)—were used as substrates, while the ECC overlays contained varying fiber dosages: 2% PVA, 1.5% PVA with 0.5% glass, 1.0% PVA with 1.0% glass, and 0.5% PVA with 1.5% glass. The surface conditions considered included grooved and as-cast substrates. The results indicated that the highest bond strength was achieved by specimens with 1.5% PVA and 0.5% glass fiber, with a maximum shear strength of 24.05 MPa for grooved HSLW substrates. Interface roughness had minimal impact on shear strength for NSLW substrates but significantly affected HSLW substrates, with bond strengths varying from 13.81 MPa to 24.05 MPa for grooved surfaces. This study demonstrates the critical role of fiber dosage and surface roughness in enhancing the bond performance of composite materials.

The objective of this research is to investigate the bond performance of high-strength lightweight concrete (HLWC) substrate and lightweight engineered cementitious composites (LECC) used as overlay repair materials with varying amounts (0%, 30%, 70%, and 90%) of fly ash cenosphere (FAC) as a replacement of sand with different surface roughness conditions (as-cast surface and grooved surface). In the preparation of the LECC mixtures, a novel combination of polyvinyl alcohol (PVA) and glass fibers (GF) was used. Mechanical properties such as compressive strength, flexural strength, and density of the HLWC and LECC were tested. Additionally, the bond strength at the interface between the HLWC substrate and the LECC was evaluated by conducting both the slant shear test and the direct shear test (bi-surface) at the age of 28 days. Results indicated that replacing the sand with 70% FAC reduced the density of the LECC by about 35% and improved the specific strength ratio by about 8.6% relative to the mixture with 0% FAC. Results also showed that for both tests (slant shear and bi-surface shear), maximum bond strength was recorded for the grooved surface. For the grooved surface under the slant shear test, replacing the sand with 30% and 70% FAC provided a bond strength of 21.85 MPa and 18.35 MPa, respectively. For bi-surface shear, replacing the sand with 30% and 70% FAC showed a bond strength of 13.85 MPa and 10.3 MPa, respectively. This research reported on the production of a repair material with comparable strength, a high specific strength ratio, and an outstanding strength-to-weight reduction ratio, making it the perfect option for repair applications where durability and load-bearing capability are essential.

Lightweight concrete (LWC) is a long-standing development in the area of construction materials. LWC has become increasingly important for sustainable construction due to its reduced susceptibility to cracking. However, when exposed to extreme temperatures during fires, LWC can lose its compressive strength and ductility. This study investigates the performance of lightweight expanded clay aggregate (LECA) concrete T-beams exposed to elevated temperatures. The research also focuses on the use of an engineered cementitious composite with a basalt fiber-reinforced polymer grid (ECCBFG) as a rehabilitation method for fire-damaged T-beams. Key variables considered include the concrete cover thickness (20 and 30 mm), fire exposure duration (30 and 60 min), and thickness of the ECCBFG layer. Thermocouples were installed at various points within the beams to monitor the heat gradient across the cross-section. Fourteen concrete beam specimens were tested, including control beams, fire-damaged beams, and beams strengthened with the ECCBFG layer. Key performance parameters, such as the energy absorption, cracking load, ductility index, maximum load capacity, and corresponding displacement, were analyzed. The experimental results showed that the strengthened beams outperformed the fire-damaged beams, closely matching the performance of undamaged reference beams in most aspects, except energy absorption. The findings suggest that further research is needed to optimize certain performance indicators and address challenges in strengthening fire-damaged beams.

Each year, a significant quantity of date palm waste is produced, placing strain on the ecosystem and necessitating an urgent disposal solution. This research is distinctive as it utilizes easily available waste materials from industrial and agricultural sources in Iraq. This experiment used Iron filing waste (IF) as a complete substitute for silica sand and date seed ash (DSA) at replacement ratios of 25%, 50%, 75%, and 100% of fly ash, compared to a reference standard ECC. This study investigates the fresh and mechanical properties (compressive strength, flexural tensile strength, and compressive strain behavior) of environmentally friendly concrete (ECC) using waste materials from the surrounding region. The results indicated that IF and DSA were acceptable choices for ECC composite base materials. ECC fluidity and bleeding prevention were improved by replacing silica sand with waste iron filing (IF). Fly ash and date seed ash (DSA) substitution ratios of 25%, 50%, 75%, or 100% reduced ECC mixed workability efficiency within the permit. Flexural strength initially increased with a 50% date seed ash (DSA) replacement ratio but eventually decreased. All ECC combinations had compressive properties more strain rate-sensitive than the reference mixture. Instead of fly ash, 50% date seed ash (DSA) enhanced strain capacity by 17% and preserved load-bearing capacity.

This research studied the effect of high temperature and silica fume as a replacement material in concrete. Compressive strength, tensile strength and flexural