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This study explores and enhances the resistance of an ultra-high-performance concrete (UHPC) to explosive spalling under elevated temperatures. This study investigates the impact of lightweight aggregates (LWAs) on the mechanical and microstructural properties of the UHPC. Various UHPC specimens were created by replacing silica sand with LWAs in percentages ranging from 0% to 30%. The evaluation of these specimens involved assessing their compressive and flexural strengths, density, mass loss, shrinkage, porosity, and microstructural characteristics using scanning electron microscopy (SEM). This study provides valuable insights by analyzing the influence of lightweight aggregates on the strength, durability, and microstructure of UHPC. The results reveal that incorporating LWAs in the UHPC improved its flowability while decreasing its density, as the percentage of LWAs increased from 5% to 30%. Including 30% LWA resulted in a mass loss of 4.8% at 300 °C, which reduced the compressive and flexural strengths across all curing durations. However, the UHPC samples subjected to higher temperatures displayed higher strength than those exposed to ambient conditions. The microstructure analysis demonstrated that the UHPC specimens with 30% LWA exhibited increased density due to continuous hydration from the water in the lightweight aggregate. The pore size distribution graph indicated that incorporating more of the LWA increased porosity, although the returns diminished beyond a certain point. Overall, these findings offer valuable insights into the influence of lightweight aggregates on the physical and strength characteristics of UHPC. This research holds significant implications for developing high-performance, lightweight concrete materials.

The objective of this study was to investigate the effectiveness of different confinement materials in strengthening geopolymer concrete (GP) columns subjected to axial compression loading. This research encompassed both experimental and numerical analyses. The experimental phase involved testing seven circular GP columns, while the numerical phase involved developing 3D finite element (FE) models using ABAQUS software. The primary focus of this study was to assess the impact of using outer and inner steel tubes, as well as an outer polyvinyl chloride (PVC) tube and a carbon-fiber-reinforced polymer (CFRP) sheet. To validate the FE models, the experimental results were utilized for comparison. The findings of this study revealed that the outer steel tube provided superior confinement effects on the GP column’s concrete core compared to the PVC tube and CFRP sheet. The axial capacities of the columns confined with steel, PVC, and CFRP materials were observed to increase by 254.7%, 43.2%, and 186%, respectively, in comparison to the control specimens. Furthermore, the utilization of all confinement materials significantly enhanced the absorbed energy and ductility of the columns. The FE models demonstrated a reasonably close match to the experimental results in terms of load–displacement curves and deformation patterns. This correspondence between the numerical predictions and experimental data confirmed the reliability of the FE models and their suitability for generating further predictions. In summary, this study contributes to the field by exploring the efficacy of various confinement materials in strengthening GP columns. The results highlight the superior performance of the outer steel tube and demonstrate the positive influence of PVC and CFRP materials on enhancing the structural behavior of the columns. The validation of the FE models further supports their reliability and their potential for future predictions in similar scenarios.

Ultra-high-performance concrete (UHPC) is a form of cementitious composite that has been the most innovative product in concrete technology over the last three decades. Ultra-high-performance concrete has been broadly employed for the design of numerous forms of construction owing to its excellent mechanical characteristics and durability, and studies on its behavior have grown fast in the last decades. While the utilization of ultra-high-performance concrete in bridge engineering (BE) is limited owing to its high costs, little is recognized about the utilization of UHPC in various BE elements. As a result of these issues, a comprehensive review of the current UHPC development trends should be conducted to determine its present state and perspective. This study presents a review of the state-of-the-art UHPC applications in BE. This review also discusses the current status, limitations, challenges, and areas for the further investigation of UHPC in BE. The aim of this research to help various construction stakeholders understand the distinctive characteristics, benefits, and barriers to the broad utilization of ultra-high-performance concrete applications. The understanding of UHPC will aid in increasing its entire market share in both the national and worldwide building sectors.

Globally, several million tons of various wastes are produced each year, and these quantities are projected to rise. Environmental issues arise from the landfilling or burning of many of these wastes. These wastes can gradually be used as replacement construction materials to reduce their harmful impacts on the environment. In this context, geopolymer foam concrete (GFC) could be used to incorporate these wastes in high volumes owing to its low strength requirement. GFC is a material developed by combing of foam concrete with geopolymer technologies. It helps reduce the consumption of natural resources, carbon dioxide, and energy used in buildings. GFCs have also emerged as one of the most intriguing composites in recent years thanks to their extraordinary benefits, low cost, and eco-friendly synthesis techniques. Recent developments in this area have led to the production of GFC, which combines performance advantages and operational energy savings with cradle-to-gate emissions reductions acquired using a geopolymer binder. This review discusses the sustainability of GFC with different wastes and major parameters affecting its stability, performance, and microstructure to provide a better understanding of the characteristics of GFC and its large-scale advantages. Limitations, challenges, and potential GFC futures for the various uses are outlined and extensively addressed. This review also presents the extraordinary potential of geopolymer foams in high-value applications as a PC-based foam alternative, which could encourage their broad technological utilization. Graphical abstracts

Reinforced concrete (RC) walls are mainly used in RC structures to resist gravity and lateral forces. These structural elements may need to be upgraded to withstand additional forces and extend their life cycle. Therefore, it is crucial to provide effective strengthening techniques using low-cost sustainable materials under optimal conditions to rehabilitate RC walls. This study presents an experimental and numerical investigation of reinforced normal concrete (NC) walls strengthened with near-surface mounted (NSM) steel bars, confined with or without an externally bonded reinforced (EBR) galvanized steel sheets (GSSs). A total of six RC walls were constructed, loaded, and tested to failure. The examined parameters included the type of strengthening technique, materials used, and the position and configuration of the strengthening. Both EBR and NSM techniques were applied using GSSs and steel bars, respectively. The configurations were introduced in vertical and horizontal positions to resist gravity and lateral forces, respectively. The experiments revealed that these parameters significantly influenced the crack control, energy absorption, mode of collapse, and ultimate load capacity. Nonlinear three-dimensional finite element models were developed and verified against experimental results, achieving a validation accuracy of 95% on average. This was followed by a parametric study investigating the effect of confinement with or without vertical reinforcements. Both experimental and numerical results confirmed that the strengthening could increase the ultimate load capacity from 20% to 38%.

Punching shear failure poses a critical risk in flat slab–column structures, potentially leading to catastrophic collapses. Retrofitting methods typically involve flexural or shear strengthening. Recent studies, however, reveal that combining indirect flexural strengthening with direct shear strengthening augments the punching shear performance. This research employed ultra-high-performance engineered cementitious composites (UHP-ECC) and ultra-high-performance steel-fiber-reinforced concrete (UHP-SFRC) as a bonded layer on the slab’s compression zone confining column as indirect flexural strengthening and galvanized threaded steel bolts as direct shear strengthening through slab thickness to augment the punching shear capacity. Six square flat slabs with central circular columns were constructed and then experimented to collapse to verify the effect of this proposed strengthening technique. The effects of various mesh and concrete types are investigated. Results showed that combining the UHP-ECC or UHP-SFRC bonded layer in the compression side with bonded galvanized threaded steel bolts significantly enhanced the punching shear strength of the slabs. The experimental findings demonstrated a remarkable increase of 62% and 111% over the unstrengthened slab for the UHP-ECC and UHP-SFRC strengthened slabs with single-layer mesh, respectively. Further enhancements were observed by adding a second steel reinforcement mesh to the UHP-bonded layer. A numerical model was developed using the finite-element (FEM) method to predict the structural behavior of tested slabs. Numerical results revealed that the FEM predicts well the performance of the slab–column connection, aligning well with experimental findings.

Eco-friendly sustainable construction materials with low carbon dioxide emissions and low energy consumption which utilize agricultural and industrial waste are widely recommended. Utilizing high-volume fly ash waste (FA) as a cement replacement will contribute to a reduction in the environmental problems related to cement production and landfill disposal. It is well known that the inclusion of high amounts of FA (up to 50%) as a cement replacement leads to low strength performance, especially at a concrete’s early age (below 7 days). In this study, a cement mortar with high-volume FA (60%) was developed with strength enhancement. With nanotechnology and nanomaterial benefits, nanoparticles from bottle glass waste (BGWNP) were produced and used to replace 2, 4, 6, 8, and 10% of cement–FA binder. The results showed that the compressive strength significantly improved with the inclusion of the BGWNP in a high-volume FA matrix and the strength trend increased from 21.3 to 328 MPa with increasing nanoparticle content from 0 to 6%. However, the results indicated that the inclusion of nanoparticles up to 6% led to a slight reduction in strength value. Similar trends were observed for other engineering and microstructure properties and the matrix containing 6% of BGWNP achieved the highest performance compared to that of the control sample. It is concluded that, with the utilization of BGWNP, there is an ability to produce high-volume FA-based cement with acceptable engineering properties as well as achieve sustainability goals by reducing pollution, recycling waste, and resolving landfill issues.

Excessive use of natural resources and environmental concerns are key issues motivating the recycling of waste materials in the construction industry to minimize landfill problems. Free cement binders such alkali-activated binders have emerged as a prospective alternative to ordinary Portland cement, wherein diverse industrial, agriculture, and by-product waste materials have been converted as valuable spin-offs. Annually, tens of millions tons of red brick wastes are generated, which leads to several environmental problems. Thus, waste red brick powder (WRBP) was used as binder or a fine aggregate (silica sand) substitute to prepare some new types of alkali-activated mortars (AAMs). These mortars contained ground blast furnace slag (GGBFS) and metakaolin (MK) with various levels of WRBP (0, 15, 30, and 45%) as a substitute for silica sand. The prepared AAMs were cured at 300 °C, 600 °C, and ambient temperature. All the specimens were tested to determine the effects of various WRBP contents on the workability, strengths, and microstructures of the designed AAMs. The workability of the fresh AAMs was considerably dropped due to the incorporation of WRBP as binary binder or fine aggregate replacement. In addition, AAM containing 15% of WRBP as GGBFS and MK replacement displayed a significant improvement (by 30.7%) in the strength performance. However, the increasing content of WRBP to 30% and 45% significantly led to a decrease in compressive strength from 49.9 MPa to 44.7 and 34.2 MPa, respectively. Overall, the mortars’ strength was increased with the increase in WRBP contents from 0 to 45% as sand substitute. Conversely, the mortars strength was reduced with the increase in curing temperatures. The microstructure analyses of the studied mortars revealed an appreciable enhancement of the geopolymerization process, gels formulation, and surface morphology, leading to an improvement in their compressive and flexural strength characteristics. It was asserted that high-performance mortars with customized engineering properties can be designed via the inclusion of WRBP into alkali-activated MK-GGBFS mixes.

Reinforced concrete (RC) deep beams often necessitate openings in their web to facilitate building utilities. These openings compromise the shear resistance of the beams and, therefore, should be strengthened in their critical shear zone. This study proposes externally bonded high-performance concrete (HPC) mortars layers strengthened with steel wire mesh to strengthen the shear capacity of high-strength RC deep beams with openings within their shear span. To facilitate this, an experimental program consisting of testing ten high-strength RC deep beams was carried out. The test parameters include the effects of opening, types of HPC mortars, namely, engineered cementitious composites (ECC) and ultra-high-performance fiber-reinforced concrete (UHFRC) mortars, the configuration of the opening (circular, square), and the size of the openings. Two strengthened beams were fabricated without openings, while the remaining incorporated various opening configurations. The results demonstrated the shear performance of the beams increases using the proposed strengthening technique. The increases in ultimate load capacity ranged from 5 to 68%, elastic stiffness improved between 8 and 97%, and energy absorption capacity enhanced from 7 to 127%. Increasing the opening size reduces the strength, stiffness, and energy absorption capacity of the beam. Furthermore, beams with circular openings exhibited better performance than their square counterparts. The specific design and strengthening strategies employed effectively improve their load-bearing capacity concerning the opening size ratio. Application of the HPC mortars with higher compressive and tensile strength further results in the improvement of their shear performance. In addition, a finite element model (FEM) was developed to simulate the performance of tested beams and compare the accuracy of the FEM against the test results. It was found that the adaptation of the Concrete Damage Plasticity (CDP) model with the parameters adopted in this study can accurately predict the behavior of the tested beams. An average error of only 4% was obtained for the experiment-to-predicted load for cracking and ultimate load. Furthermore, based on the parametric study performed on beams with circular openings strengthened with ECC layers, it is proposed that for practical design purposes the thickness of the ECC layer to the thickness of the beam ( t ECCC / t beam ) ratio should not exceed 0.32.

Recycled construction cementitious materials (RCCM) and red mud (RM) could be considered a type of discarded material with potential cementitious properties. Generally, landfilling and stacking are utilized to dispose of this type of solid waste, which can be detrimental to the environment and sustainability of the construction sector. Accordingly, a productive process for making eco-efficient alkali-activated slag-based samples with the inclusion of RCCM and red mud is studied in this paper. Dehydrated cement powder (DCP) is attained through the high-temperature treatment of RCCM, and red mud can be obtained from the alumina industry. Subsequently, DCP and RM are utilized as a partial substitute for granulated blast furnace slag (GBFS) in alkali-activated mixtures. Two different batches were designed; the first batch had only DCP at a dosage of 15%, 30%, 45%, and 60% as a partial substitute for GBFS, and the second batch had both DCP and RM at 15%, 30%, 45%, and 60% as a partial substitute for GBFS. Different strength and durability characteristics were assessed. The findings show that when both dehydrated cement powder and red mud are utilized in high quantities, the strength and durability of the specimens were enhanced, with compressive strength improving by 42.2% at 28 days. Such improvement was obtained when 7.5% each of DCP and RM were added. The results revealed that DCP and RM have a negative effect on workability, whilst they had a positive impact on the drying shrinkage as well as the mechanical strength. X-ray diffraction and micro-structural analysis showed that when the amount of DCP and RM is increased, a smaller number of reactive products forms, and the microstructure was denser than in the case of the samples made with DCP alone. It was also confirmed that when DCP and RM are used at optimized dosages, they can be a potential sustainable binder substitute; thus, valorizing wastes and inhibiting their negative environmental footprint.