The rapid growth of Natural Fiber Laminate (NFL) innovation is a direct response to environmental challenges, positioning these materials as superior alternatives to synthetic fiber composites. This paper delved into the outcomes of an extensive experimental study investigating the influence of sisal fiber (SLF), banana fiber (BF), and glass fiber (GF) on the mechanical and microstructural characteristics of concrete. The water absorption curves were established for sisal fiber concrete (SLFC), banana fiber concrete (BFC), and glass fiber concrete (GFC). Furthermore, Scanning Electron Microscope (SEM) observations were conducted to perform microanalysis and failure analysis of the tested specimens. The results revealed significant improvements in the concrete containing fibers compared to its counterpart in fiber-free concrete. For mixtures with a water-to-binder (W/B) ratio of 0.3, the most optimal mix (GF-30-135) showed improvements in compressive strength, flexural strength, and splitting tensile strengths by 4.13%, 8.93%, and 10.10%, respectively. On the other hand, for W/B of 0.4, mix GF-30-135 showed improvements of 5.05%, 8.55%, and 11.60%, respectively. Furthermore, as the fiber content increased, microscopic analyses revealed a weakening of the bond between the fibers and the rest of the matrix, contributing to the deterioration of the mechanical properties.

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.

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.