Sallal Rashid Abid

The article aims to evaluate the post-high temperature exposure residual response of self-compacting concrete (SCC) in the presence of continuous internal voids. The influence of high temperatures on the mechanical behavior, especially compressive strength, have been reported in literature, while its interaction with the influence of void content, geometry, and distribution has not been rigorously characterized. This study presents an experimental program that investigates the absolute compressive strength response of SCC containing voids of varying dimensions across multiple mix grades (M30, M40, and M50) subjected to progressive heating levels of 100, 200, 300, 400, and 600 °C. In addition to solid reference specimens, three groups of specimens incorporated distinct void geometries VD1, VD2, and VD3 with dimensions of 50 × 50 × 150 mm, 75 × 75 × 150 mm, and 100 × 100 × 150 mm were selected to represent three levels of void ratios and to evaluate their impact on the absolute response of the specimens. The test results showed that for solid SCC specimens, compressive strength exhibited a temperature-dependent evolution, increasing with thermal exposure up to 300 °C, where the M50 grade attained 78.72 MPa, approximately 17.23% higher than its ambient value. Beyond this threshold, strength declined markedly, with reductions of 20–40% observed at 600 °C across all mix grades (M30-M50), reflecting thermally induced microstructural degradation. The presence of voids exerted a pronounced effect on absolute performance at elevated temperatures: at 600 °C, M50 specimens exhibited absolute strengths of 38.07 MPa (VD1), 18.41 MPa (VD2), and 10.84 MPa (VD3), representing an overall loss exceeding 80% relative to the room-temperature solid specimen.

The current paper presents an innovative form of the cold‐formed U‐shape steel encasing concrete composite beam (CUCB). The suggested CUCB consists of a cold‐formed U‐shaped steel encasing plain concrete beam which are connected to each other using continuous transversal threaded stud bolts. The experimental program consisted of eight beam specimens tested in the four‐point bending set‐up. One of them was a normal reinforced concrete beam and considered as a reference specimen while the remaining specimens were CUCB specimens without ordinary flexural and shear reinforcement. Four parameters were studied in this paper: (i) the thickness of the U‐shaped steel, (ii) the spacing between the stud bolts, (iii) the arrangement of the bolts, and (iv) the number of the bolt's rows. Results indicated an overall improvement in the load‐carrying capacity and stiffness of most CUCB specimens in comparison with the reference specimen. It was found that the using of three rows of bolts can significantly improve the ductility and toughness of the CUCB specimen in comparison with two rows of bolts. On the contrary, an increase in the bolt spacing entails a decrease in the CUCB specimens' toughness.

The fire resistance of construction materials is an essential part of safety requirements in the construction industry. In this work, experimental investigations were conducted to understand the thermal behaviour, spalling, transfer characteristics, strength, and microstructures of self-cured high-strength plain (HSGC) and steel-fibre-reinforced geopolymer concrete (S–HSGC) under severe fire scenarios with peak temperatures of 275, 560, and 825 °C; the peak was maintained for a period of 120 min after reaching it. Forty-eight standard cylindrical specimens for each mixture were prepared to test and analyse their time–heat response, gradients, visual appearance, spalling, density change, water absorption, and compressive strength before and after fire exposure. Additionally, Scanning Electron Microscopy (SEM) along with Energy Dispersive X-ray Analysis (EDX) were utilised to analyse the internal structures and phase transformations. The thermal analysis showed that no cases of explosive spalling were recorded during sample exposure to various fires, while the used hook-end steel fibres had an influence on the considered test variables. The sample cores almost reached the target heat, and the thermal saturation degree at the peak ranged from 55 to 97%. The experimental findings also revealed slight surface cracking after exposure to 560 °C fires, while the surface cracking was more obvious for specimens exposed to 825 °C. Moreover, the residual compressive strength of the S–HSGC at various fires was noticeably 10.20% higher than that of the HSGC. Also, state-of-the-art research data were used to discuss the prediction model’s performance. The SEM and EDX results showed that the self-cured geopolymerization process was effective and successful in producing gels, in addition to the significant phase transformations in microstructures at different fires. This study presented sophisticated data on the behaviour of HSGC and S–HSGC exposed to fires up to 825 °C.