Ahmed Abd Al-Kader Al Sayed

This research aims to investigate the durability and behavior of Jordanian oil shale ash (OSA) as a substitute material for ordinary Portland cement (OPC) and Portland Pozzolana cement (PPC) in mortar under sulfate attack. Mortar samples with replacement ratios of 0%, 10%, 20%, and 30% of OSA were utilized in this investigation. The study is divided into two stages. In the first stage, the effect of OSA replacement on the mechanical properties and hardening time of mortar samples is examined over a curing period of 3, 7, 14, and 28 days using potable water. The second stage focuses on studying the durability of mortar samples with the aforementioned OSA replacement ratios. These mortar samples are fully immersed in a sodium sulfate solution with a concentration of 5% and subjected to wet and dry cycles for degradation at 1, 6, 12, 18, 24, 30, and 36 days. Various analyses were conducted, including compressive strength testing, SEM analysis, mass loss measurement, ultrasonic pulse velocity assessment, relative dynamic modulus of elasticity (RDME) evaluation, and visual inspection. For OPC-based mortars, compressive strength ranged from 44.00 to 49.75 MPa (0% OSA), 42.88 to 48.29 MPa (10% OSA), 44.50 to 50.88 MPa (20% OSA), and 31.00 to 36.53 MPa (30% OSA). For PPC-based mortars, compressive strength ranged from 36.00 to 42.32 MPa (0% OSA), 39.73 to 43.60 MPa (10% OSA), 44.97 to 46.06 MPa (20% OSA), and 22.35 to 28.18 MPa (30% OSA). Specimens with 0%, 10%, and 20% OSA showed continued increases in compressive strength, UPV, and RDME throughout exposure, while 30% OSA specimens showed deterioration after 24 days (OPC) and 18 days (PPC), with mass losses increasing from 0.52% to 8.4% (OPC) and 0.75% to 7.8% (PPC). The results indicate that while moderate OSA replacement (up to 20%) may be viable under sulfate exposure, 30% replacement leads to significant deterioration. However, the absence of non-sulfate controls prevents definitive separation of continued hydration from sulfate resistance. These findings provide practical guidance for the use of OSA in sulfate-prone environments.

Clay bricks are widely used in construction because they are strong, durable and fire-resistant, but their thermal insulation is still not good enough, which leads to a big loss of energy. The combined effect of alkali activation or addition of metal oxides on residual mechanical properties of clay bricks at elevated temperature has not been systematically addressed although these treatments have been studied separately. This paper presents the enhancing effects of metal oxides (Fe ₂ O ₃ , Al ₂ O ₃ and Carbon Black N550) and sodium hydroxide (NaOH) activation on residual strength of clay bricks exposed to elevated temperatures up to 800°C. Clay bricks were prepared using 82% clay, 13% fine sand, 5% fly ash and different replacement/additive dosages of Fe ₂ O ₃ (2–6 wt.%), Al ₂ O ₃ (3–7 wt.%), and Carbon Black N550 (0.25–1 wt.%) activated with 8 M NaOH. Compressive strength, bulk density, water absorption, TGA and accelerated aging tests were conducted following the international standards. The Al-7A mixture exhibited the highest compressive strength of 19.5 MPa at ambient temperature (57.3% increase over control) and retained 14.8 MPa (75.9%) after exposure to 800°C. Fe-4A and CB-0.5A achieved 16.8 MPa and 16.0 MPa at ambient with residual strengths of 11.5 MPa and 10.5 MPa at 800°C. The water absorption of Al-7A was 38.0% lower (8.8%) than that of the control (14.2%). The bulk density was increased to 1980 kg/m ³ . TGA revealed Al-7A exhibited the lowest weight loss (4.8%) and highest residual mass (95.2%). After seven accelerated aging cycles, Al-7A retained 82.1% of initial strength, outperforming Fe-4A (75.0%) and CB-0.5A (70.6%). The research demonstrates that combining alumina addition with NaOH activation offers a viable pathway for producing high-performance clay bricks with enhanced thermal stability and durability for fire-prone construction applications.

Alkali-activated recycled aggregate concrete (AARAC) offers a sustainable alternative to traditional concrete but suffers from complex, non-linear mechanical behavior that challenges conventional prediction methods. This study develops and compares five machine learning models, linear regression (LR), M5P, Random Forest (RF), K-Nearest Neighbors (KNN) and XGBoost, for predicting the compressive strength (Cs), flexural strength (Fs), splitting tensile strength (Ss), pull-out bond strength (PT), and water absorption (Wa%) of AARAC. A dataset of 360 experimental samples, incorporating natural aggregate, recycled concrete aggregate (RCA), cement block aggregate (CBA), water-to-cement ratio (W/C), alkaline treatment status, and slump, was used. Models were evaluated via train/test split (80/20) and 10-fold cross-validation using R², MAE, RMSE, and MAPE. Random Forest achieved the highest test R² (0.8736) and lowest test MAPE (1.418%) and XGBoost (R² = 0.8605, MAPE = 1.557%). KNN and M5P performed moderately, while LR was the weakest (R² = 0.6958, MAPE = 2.147%). All tree-based models exhibited overfitting, with training R² up to 0.98. Scatter plot analysis revealed systematic underprediction by RF for Cs (constant offset of ~2 MPa) and increasing bias for PT, Ss, and Wa% at higher values. XGBoost gave perfect predictions for PT and Wa% but underpredicted Cs and Fs. K-fold cross-validation confirmed XGBoost as the most robust (mean R² = 0.9844). Correlation analysis showed W/C strongly increases Wa% (r = 0.80) and decreases PT (r = −0.73); RCA negatively affects mechanical properties, while CBA and alkaline treatment improve them. The study concludes that ensemble tree models, particularly Random Forest, are superior for AARAC prediction, but systematic bias requires post hoc calibration.

A series of concrete mixtures was prepared by substituting cement with zeolite at replacement levels of 0, 25, 50, 75 and 100 wt%. The study examined the mechanical properties, corrosion behavior of embedded steel reinforcement, and various nuclear radiation attenuation parameters for five concrete mixes. Corrosion performance was assessed through multiple electrochemical methods and optical microscopy. Furthermore, three neutron energy levels and nine gamma-ray energy lines (ranging from 121.78 to 1407.92 keV) were employed to determine the macroscopic neutron cross-sections (Σ, cm⁻¹) and the mass attenuation coefficients (σ, cm²/g) for gamma rays within the concrete speci-mens. The findings indicated that both the mechanical strength of the concrete and the corrosion resistance of the embedded steel improved with the addition of zeolite up to 50 wt.%. For the mass attenuation coefficients corresponding to most of the investigated gamma-ray energies, the optimal zeolite content was found to be 50 wt.%.

This study aims to enhance the mechanical and thermal performance of lightweight expanded clay aggregate (LECA) concrete through geopolymerization using iron oxide (Fe₂O₃) and polyethylene glycol 400 (PEG400), combined with surface treatment of LECA aggregates. An experimental program was conducted to evaluate workability, density, water absorption, compressive strength, splitting tensile strength, and bulk electrical resistivity (BER). Various mixtures with different proportions of Fe₂O₃ and PEG400 were prepared with and without aggregate surface treatment. The findings indicate that surface treatment significantly improves the interfacial transition zone, resulting in enhanced overall performance. The optimal mix (treated LECA with 3% PEG400 and 20% Fe₂O₃) achieved a compressive strength of 45 MPa and a splitting tensile strength of 4.0 MPa, representing increases of over 70% compared to the control mix. Additionally, water absorption decreased by 35.6%, while BER increased by 127%, reflecting improved durability and reduced permeability. Workability was also enhanced, with up to a 100% increase in slump without compromising strength. The novelty of this study lies in the synergistic integration of treated LECA, PEG400, and iron oxide within a geopolymer matrix to produce a high-performance, durable, and thermally efficient lightweight concrete. This approach offers a sustainable solution for advanced construction applications.

In recent years, near-surface-mounted (NSM) FRP has become a strong alternative to the externally bonded (EB) technique. Compared to the EB approach, the NSM tech-nology is less susceptible to external damage sources and improves the bond between the FRP reinforcement and the surrounding concrete. However, one of the most com-mon reasons why RC beams reinforced with NSM technology fail is debonding via concrete cover separation (CCS), which begins and ends at low strain levels in the NSM reinforcement. Scientists therefore put a lot of effort into figuring out how to de-lay or prevent this kind of failure. In this investigation, two different bar configura-tions with straight and bent ends were used. The purpose of the bent end is to delay or prevent the CCS failure. A numerical analysis utilizing non-linear finite element mod-eling (FEM) was performed in ANSYS® to confirm the experimental results. Overall, there was good agreement between the numerical results and the corresponding ex-perimental data at each loading level.

This research intends to investigate and analyze the usage of Jordanian oil shale ash (OSA) as a replacement material for ordinary Portland cement and pozzolanic cement in mortar. To start, oil shale was collected from the Wadi Al-Shallala location, crushed, sieved and burned at 800 °C for 24 h. OSA partially replaced the ordinary Portland and pozzolanic cements with ratios of 10%, 20%, and 30%. This research looked into the effect of cement substitution on the standard consistency and hardening time for cement paste. The water contents as well as beginning and final hardening times increased due to the higher replacement ratios of the cements. Also, pozzolanic activity index (PAI) along with scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) testing and mechanical properties (compressive and flexural strengths) of mortar with both types of cement substitution were evaluated. The compressive strength and flexural strength were checked following 3, 7, 14, 28, 56 and 90 days of curing, while (SEM) was conducted just at 28 days old with a 20% replacement ratio in mortar specimens. Results show that 20% OSA substitution for ordinary Portland cement or Pozzolanic cement raises compressive strength and flexural strength, plus provides better morphology. Thus, oil shale is seen as a natural pozzolanic material that increases efficiency in cement mixtures.

Self-healing concrete provides an eco-efficient approach for restoring cracks through autonomous repair, reducing maintenance demands and enhancing long-term durability. This study evaluates concrete incorporating Bacillus subtilis bacteria and sisal fibers to examine their individual and combined effects on mechanical performance and microstructural development. Bacterial cells at a concentration of 2 × 10⁸ CFU/mL were introduced with calcium lactate as a nutrient source at varying dosages, while sisal fibers were added at a volume fraction of 0.9%. Concrete mixes containing 0%, 2.5%, and 5% bacterial content were tested under fresh-water curing. Compressive, splitting tensile, and flexural strengths were assessed at multiple ages, accompanied by SEM and EDS analyses to investigate healing products and microstructural alterations. Bacteria-enhanced mixes demonstrated improved long-term compressive behavior, with B5/5/1 reaching 50.1 MPa at 56 days, while higher bacterial content slightly reduced early-age strength but benefited later performance. Incorporating sisal fibers consistently improved mechanical resistance, notably in combination with bacteria. The SB5/5/1 mix achieved 55.2 MPa at 56 days, representing a 30% gain over the control. Tensile strength was particularly influenced by fibers, with SB10/5/1 recording 6.3 MPa at 56 days (≈70% increase). Flexural strength results similarly highlighted the superior behavior of hybrid systems, where SB10/5/1 attained 9.2 MPa (+67%), reflecting enhanced self-healing efficiency even under challenging curing conditions.

Concrete structures in marine environments face significant degradation due to reinforcement corrosion caused by chloride ingress and sulfate attack. Poor construction quality, inadequate standards, and suboptimal design can further accelerate deterioration. Non-destructive testing (NDT) has proven valuable for durability assessment, yet its application remains limited due to the complex microstructural characteristics of concrete. This study establishes a comprehensive procedure for evaluating precast concrete degradation in marine environments using multiple characterization techniques. Two precast concrete elements with different cement types, CEM II A-L 42.5R and CEM I 42.5 R/SR, were analyzed through compressive strength tests, open porosity measurements, mercury intrusion porosimetry (MIP), ultrasonic wave transmission, and scanning electron microscopy (SEM). The results indicate that CEM I 42.5 R/SR exhibits superior compressive strength and lower porosity, making it more durable and suitable for load-bearing applications. Higher ultrasonic pulse velocity (UPV) further confirms its resilience. In contrast, CEM II A-L 42.5R shows lower mechanical performance and greater susceptibility to marine-induced degradation. Over time, pore size distribution shifts, potentially compromising mechanical integrity. SEM analysis reveals gypsum and brucite formation in degraded regions, demonstrating microstructural changes due to seawater exposure. A strong negative correlation between porosity and UPV underscores the detrimental effect of increased porosity on material density and structural stability. This study highlights the effectiveness of UPV and porosity analysis as reliable NDT techniques for assessing concrete deterioration. The strong correlation between UPV and porosity trends suggests that UPV serves as an early indicator of durability loss, enabling timely maintenance interventions. These findings provide valuable insights into material selection for enhanced structural performance in marine environments and emphasize the role of NDT in long-term structural health monitoring.

The construction sector in the Kingdom of Saudi Arabia has shown notable growth and progress as seen by the transformation of outdated neighborhoods into modern smart infrastructure that aligns with the 2030 vision of the nation. As a result of this development trend, which is led by the Jeddah region, many older buildings are being demolished, and a significant amount of concrete is being produced. Utilizing recycled aggregates from construction and demolition waste has been recognized as an effective approach to addressing the current environmental problems that our world faces. An appropriate process of treatment techniques must be incorporated into the production of recycled aggregate in order to enhance its properties and optimize its use. The purpose of this study is to determine the potential benefits of an alkaline Ca(OH)₂ activated by fly ash Class F (FA_F) for various concrete mixes composed using recycled concrete aggregate (RCA). Seven mixes were developed to determine the effects of several factors on the properties of recycled concrete aggregate (RCA), including the type of recycled aggregate, the activator used, and the impact of the filler material. The study assessed how different forms of recycled aggregate affected physical characteristics. The compressive strength, flexural strength, indirect tensile strength, and pull-out strength of the concrete mixes was measured. The aggregate water absorption of Jeddah concrete aggregate (JRCA) and variable concrete aggregate (VRCA) was evaluated. Activated JRCA water absorption drops to 1.7% while inactivated JRCA water absorption was 3.95%. The AIV values of JRCA rise to 18.4 while the AIV for NA is 13. The same trend complies with the findings, which demonstrated that the strength performance and other characteristics of the various concrete mixes under study were significantly impacted by the type of recycled aggregate utilized and the mix design. Among these, Jeddah recycled concrete aggregate (JRCA) showed promising results that could lead to a wider use of (JRCA) in civil engineering applications.