Search Results (67)

Cementitious composites are heterogeneous porous materials whose pore structure plays a critical role in resistance to chloride-ion penetration. A waterborne nano-silicate-based densifier (CF-S5) was used to examine its influence on the pore structure and resistance to the chloride ion penetration of mortar. We investigated the resistance to the chloride ion penetration of mortar with added CF-S5 admixture through the Rapid Chloride Permeability Test (RCPT). We investigated the pore structure characteristics of mortar by mercury intrusion porosimetry (MIP) coupled with fractal theory and investigated the degree of hydration of the cement paste by thermogravimetric analysis (TG). Ultimately, the degree of correlation between multifractal parameters and the chloride ion migration coefficient of mortar was examined using gray relational analysis (GRA). Results indicate that the CF-S5 admixture reduces mortar porosity and the content of harmful pores while increasing pore tortuosity, thus improving the resistance to the chloride ion penetration of mortar. Multifractal analysis indicated that the CF-S5 admixture decreased the connectivity and increased the complexity of the mortar pore structure. The CF-S5 admixture did not reduce the hydration degree of cement paste at 28 d. Additionally, the multifractal parameters show a high gray relational degree with the chloride migration coefficient; therefore, they may serve as potential indicators to reflect the resistance to the chloride ion penetration of mortar. Full article

Penetration of harmful substances, such as chloride ions, is a major contributor to durability issues in concrete structures. Low permeability is critical for long-term performance, prompting the assessment and classification of concrete based on its resistance to ionic transport. However, the transport mechanisms are complicated and influenced by a range of interdependent factors including binder type, mixture proportions, specimen age, and curing conditions. There are two widely adopted test methods used for assessing chloride ion permeability: the Rapid Chloride Permeability Test (RCPT) and the Surface Resistivity Test (SRT), a non-destructive alternative. While RCPT is well-established, its long testing time as well as its high costs and sensitivity to specimen preparation limit its practicality. The SRT offers faster, more repeatable, and easier implementation. This state-of-the-art review systematically compares RCPT and SRT results across studies, revealing a strong inverse correlation with coefficients of determination (R²) from 0.85 to 0.95, as influenced by compressive strength, testing age, water-to-cement ratio, and supplementary cementitious material (SCM) type. Results showed that RCPT often has standard deviation (SD) values exceeding 300 coulombs and coefficient of variation (COV) values up to 10%, while SRT has lower variability (SD < 3 kΩ·cm and COV ≈ 5%). The review concludes that, with appropriate calibration, the SRT can reliably classify concrete permeability, closely aligning with RCPT results. However, research gaps remain regarding the applicability of existing models to less conventional SCMs and concrete types. Future research should prioritize the development of binder-specific correlations, validation using diffusion-based methods, and exploration of alternative SCMs and curing regimens to expand SRT applicability. Full article

Little research is reported on the properties of Portland cement concrete (PCC) mixtures comprising plastic waste materials. Therefore, this novel study was initiated to evaluate the effects of plastic waste materials on different properties of PCC. Plastic boxes and containers made of polypropylene were cut, grinded, pulverized, and incorporated into PCC mixtures. Sand was partially replaced by plastic waste materials with 0%, 5%, 10%, 15%, and 20% volume ratios. Experiments were conducted using PCC cylinders and prisms to evaluate several unique properties of PCC containing plastic waste. Innovative interactions and contributions of several PCC properties including workability, air content, density, water absorption, mechanical properties, rapid chloride ion penetration, and freeze–thaw deterioration are investigated. The new experimental data indicated that the workability and density of PCC decreased with increasing plastic waste replacement levels. The maximum decreases in workability and density were 23% and 6.2% for the PCC with 20% plastic replacement, respectively. On the other hand, our research has shown that air content and water absorption of PCC increases with increasing plastic waste amount. The maximum increase in air content and water absorption were 78% and 29% for the PCC with 20% plastic waste. This study also shows that the mechanical properties of PCC (e.g., compressive and splitting strengths) after 7 and 28 days of moist curing decreased with increasing plastic waste content. Another new finding is that the rapid chloride permeability of PCC increased and the freeze–thaw durability of PCC decreased with an increase in plastic waste amount. One of the most critical discoveries of this experimental study is that plastic waste increases the durability of PCC, i.e., durability factor of PCC with 20% plastic waste was 9.3% compared to 28.5% for the control PCC without plastic waste materials. Full article

Premature deterioration of concrete structures in coastal areas requires a careful evaluation based on durability criteria. Electrical Resistivity (ER) serves as a valuable indicator of concrete durability, as it reflects how easily aggressive agents can penetrate its pores. This testing method offers several advantages; it is non-destructive, rapid, and more cost-effective than the chloride permeability test (RCPT). Furthermore, durable concrete typically necessitates larger quantities of cement, which contradicts the goals of sustainable concrete development. Thus, a significant challenge is to create concrete that is both durable and sustainable. This research explores the effects of pozzolanic additives, specifically Volcanic Ash (VA) and Sugarcane Bagasse Ash (SCBA), on the electrical resistivity of eco-friendly concretes exposed to the coastal conditions of the Gulf of Mexico. The electrical resistivity (ER) was measured at intervals of 3, 7, 14, 21, 28, 45, 56, 90, and 180 days across 180 cylinders, each with dimensions of 10 cm × 20 cm. The sustainability of the concrete was evaluated based on its energy efficiency. Three types of mixtures were developed using the ACI 211.1 method, maintaining a water-to-cement (w/c) ratio of 0.57 with CPC 30 R RS cement and incorporating various additions: (1) varying percentages of VA (2.5%, 5%, and 7.5%), (2) SCBA at rates of 5%, 10%, and 15%, and (3) ternary mixtures featuring VA-SCBA ratios of 1:1, 1:2, and 1:3. The findings indicated an increase in ER of up to 37% and a reduction in CO₂ emissions ranging from 4.2% to 16.8% when compared to the control mixture, highlighting its potential for application in structures situated in aggressive environments. Full article

This study investigates the potential of corn stover, an abundant agricultural byproduct, as a sustainable additive in concrete masonry units (CMUs). Preliminary trials were conducted to determine the optimal fiber length (~3 mm and ~10 mm), fiber content (0%, 1%, 3%, and 5% by volume), and alkalinization method (soaking in 0.5 M NaOH, KOH, or synthetic concrete pore solution) for corn stover fibers (CSFs). The results indicated that short fibers treated with synthetic concrete pore solution yielded the best compressive strength and workability, and were thus selected for the main study. A novel mixture was developed by replacing 10% of cement with corn stover ash (CSA) and incorporating 1% alkaline-treated CSF by volume. The resulting blocks (termed “Corncrete”) were evaluated for mechanical and durability properties, including strength, water absorption, bulk and surface electrical resistivity, rapid chloride permeability (RCPT), and fire resistance. Compared to conventional CMUs, Corncrete exhibited an 11–13% reduction in 28- and 91-day compressive strength, though the difference was statistically insignificant. Physically, Corncrete had a 4.4% lower bulk density and a 7.9% higher total water absorption compared to the control. However, its water absorption rates at early stages were 32% and 48% lower, indicating better resistance to moisture uptake shortly after exposure. Durability tests revealed a 13.7% reduction in chloride ion permeability and a 33% increase in bulk and surface electrical resistivity after 90 days. Fire performance was comparable between the two mixtures, with both displaying ~10.5% mass loss and ~5% residual strength after high-temperature exposure. These findings demonstrate that Corncrete offers balanced mechanical performance and enhanced durability, making it a viable eco-friendly option for non-structural masonry applications. Full article

Lithium slag (LS), a by-product of lithium extraction processes, poses a significant disposal challenge during the rapid development of new energy technologies. In this study, LS was used to replace partially washed sand in the process of mortar production to compensate for the content of stone powder in sand. Five mortar mixes containing varying proportions of LS were prepared, and the macroscopic performance was evaluated. A comprehensive microscopic analysis, including microstructure observations, hydration product identification, and pore structure analysis, was conducted. The impact of LS on the chloride ion permeability of mortar was also investigated in this study. The results indicate that an increase in LS content gradually reduces the workability of the mortar, with a 39.29% decrease in fluidity when 40% of the sand is replaced with LS. Moreover, the compressive and flexural strengths of the mortar initially increase and then decrease with higher LS content. Microscopic tests reveal that 20% LS substitution significantly optimizes the pore structure of the mortar, resulting in a lower chloride ion permeability coefficient. Consequently, 20% LS substitution is recommended as the optimal dosage for use as fine aggregate in mortar. Full article

Considering the harsh marine environment characterized by dry–wet cycles, freeze–thaw action, chloride penetration, and sulfate attack, four optimized ultra-high-performance concrete (UHPC) mix designs were developed. Durability was assessed via electric flux, dry–wet cycles, and rapid freeze–thaw tests to evaluate the effects of curing methods, aggregate types, and mineral admixtures on key durability indicators, including chloride ion permeability, compressive strength loss, and mass loss. Scanning electron microscopy (SEM) examined microstructural changes under various conditions. Results showed that curing method significantly affected chloride ion permeability and sulfate resistance. High-temperature curing (70 ± 2 °C) reduced 28-day chloride ion electric flux by about 50%, and the compressive strength loss rate of specimens subjected to sulfate attack decreased by 2.7% to 45.7% compared to standard curing. Aggregate type had minimal impact on corrosion resistance, while mineral admixtures improved durability more effectively. Frost resistance was excellent, with mass loss below 0.87% after 500 freeze–thaw cycles. SEM analysis revealed that high-temperature curing decreased free cement particles, and mineral admixtures refined pore structure, enhancing matrix compactness. Among all mixtures, Mix Proportion 4 demonstrated the best overall durability. This study offers valuable insights for UHPC design in aggressive marine conditions. Full article

The concrete industry increasingly seeks sustainable alternatives to conventional materials to reduce the environmental impact while maintaining structural performance. This study evaluates the use of locally sourced rhyolite as a coarse aggregate combined with recycled supplementary cementitious materials (SCMs) to address the sustainability and durability. Due to its high silica content, rhyolite is prone to the alkali–silica reaction (ASR), which may affect concrete durability. Concrete mixtures incorporating rhyolite with silica fume (SF), Class F fly ash (FA), and slag cement (SC) were tested for compressive strength, porosity, density, absorption, mortar bar expansion, electrical resistivity, and rapid chloride permeability. All rhyolite-based mixtures—regardless of SCM incorporation—achieved higher 90-day compressive strengths than the conventional control mixture, with 10% SF reaching the highest value. Additionally, each recycled SCM effectively reduced ASR-induced expansion, with 20% FA showing the most significant reduction and superior durability, including the greatest decrease in chloride permeability and the highest electrical resistivity, indicating enhanced corrosion resistance. These results confirm that rhyolite aggregates, when combined with SCMs, can improve durability and reduce ASR. Therefore, rhyolite shows potential for use in structural concrete under standard exposure conditions. This strategy supports circular economy goals by incorporating regional and recycled materials to develop concrete with improved durability characteristics. Full article

Recent studies have shown the viability of low-grade calcined clays as a partial substitute for cement in construction applications. However, there is limited information about the performance of low-grade calcined clay in withstanding chloride-rich environments. This paper investigates the durability performance of mortar prepared by partially substituting cement with low-grade calcined clay. Naturally occurring clay having a kaolinite content of 17% was calcined at 900 °C, blended and used to prepare composite cement samples containing up to 40% by weight low-grade calcined clay. Durability studies were conducted using the rapid chloride penetration test (RCPT), freeze and thaw, sorptivity, permeable porosity, ultrasonic pulse velocity (UPV), and autogenous shrinkage. The incorporation of calcined clay resulted in significant improvements in durability properties, including reductions in sorptivity, permeable porosity, and chloride ion penetration. Additionally, enhanced freeze–thaw resistance was observed, indicating the ability of calcined clays to mitigate deterioration under harsh environmental conditions. These improvements in durability translate to extended service life and reduced maintenance requirements for concrete structures. Full article

Despite extensive research on fiber-reinforced lightweight concrete, the synergistic effects of combining different types of fibers, such as polymer and basalt fibers, on the mechanical properties and durability of lightweight concrete have not been fully investigated. This study aims to fill this scientific gap by examining the combined use of polymer and basalt fibers to enhance the performance of lightweight concrete (LWC). Lightweight concrete is widely used to reduce the weight of structures and improve seismic performance. However, its brittle nature and lower mechanical properties compared to normal-weight concrete (NWC) limit its application in high-stress environments. This study seeks to overcome these limitations by optimizing the use of polymer and basalt fibers to improve the mechanical properties and durability of lightweight concrete. In this research, 320 cylindrical samples were prepared, and the results show that adding 1% polymer fibers significantly improved the compressive and tensile strengths of lightweight concrete by 24.4% and 66.13%, respectively, at 28 days. Additionally, the combination of polymer and basalt fibers showed a positive synergistic effect, leading to improved mechanical properties and durability of the concrete, including a 45.38% reduction in final water absorption and a 43.15% reduction in chloride ion penetration at 90 days. This study provides new insights into the synergistic effects of polymer and basalt fibers in lightweight concrete and proposes a practical solution for improving its mechanical properties and durability. The findings of this research contribute to the development of lightweight concrete structures with greater reliability and flexibility. Full article

This study investigates groundwater flow patterns in a landslide area above the settlement of Koroška Bela in NW Slovenia using a series of tracer tests with sodium chloride (NaCl) and fluorescein (uranine). The tracer experiments, using a combination of pumping tests and continuous groundwater observations, reveal two distinct groundwater flow horizons within the landslide body: a prevailing shallower flow within highly permeable gravel layers and a slower deep flow in the weathered low-permeability clastic layers. Uranine injections suggest longer retentions, indicating complex hydrogeological conditions. Groundwater is recharged by the infiltration of precipitation and subsurface inflow from the upper-lying carbonate rocks. In the upper landslide, highly permeable gravel layers accelerate flow, especially during heavy rainfall, while downstream interactions between permeable gravel and less permeable clastic materials create local aquifers and springs. These groundwater dynamics significantly influence landslide stability, as rapid infiltration during intense precipitation events can lead to transient increases in pore water pressure, reducing shear strength and potentially triggering slope movement. Meanwhile, slow deep flows contribute to prolonged saturation of critical failure surfaces, which may weaken the landslide structure over time. The study emphasizes the region’s geological heterogeneity and landslide stability, providing valuable insights into the groundwater dynamics of this challenging environment. By integrating hydrogeological assessments with engineering measures, the study provides supportive information for mitigating landslide risks and improving groundwater management strategies. Full article

The large-scale application of aromatic polyamide (PA) thin-film composite (TFC) membranes for reverse osmosis has provided an effective way to address worldwide water scarcity. However, the water permeability and salt rejection capabilities of the PA membrane remain limited. In this work, cyclic micropores based on crown ether were introduced into the PA layer using a layer-by-layer interfacial polymerization (LbL-IP) method. After interfacial polymerization between m-phenylenediamine (MPD) and trimesoyl chloride (TMC), the di(aminobenzo)-18-crown-6 (DAB18C6) solution in methanol was poured on the membrane to react with the residual TMC. The cyclic micropores of DAB18C6 provided the membrane with rapid water transport channels and improved ion rejection due to its hydrophilicity and size sieving effect. The membranes were characterized by FTIR, XPS, SEM, and AFM. Compared to unmodified membranes, the water contact angle decreased from 54.1° to 31.6° indicating better hydrophilicity. Moreover, the crown ether-modified membrane exhibited both higher permeability and enhanced rejection performance. The permeability of the crown ether-modified membrane was more than ten times higher than unmodified membranes with a rejection above 95% for Na₂SO₄, MgSO₄, MgCl_2, and NaCl solution. These results highlight the potential of this straightforward surface grafting strategy and the modified membranes for advanced water treatment technologies, particularly in addressing seawater desalination challenges. Full article

In many offshore structures, structural components are often subjected to compressive forces and seawater corrosion. Therefore, understanding their resistance to chloride ion-induced corrosion under compression is crucial. This study investigates the effects of macro polypropylene fibers and macro steel fibers on the chloride permeability and damage of concrete under uniaxial compression. Ultrasonic testing is performed before and after the uniaxial compression test to assess the damage to concrete specimens at different stress levels. Simultaneously, the Rapid Chloride Migration test is conducted on the specimens subjected to various compressive stress levels. The results reveal that the chloride permeability of concrete is influenced by the stress level after uniaxial compression. Additionally, a threshold phenomenon is observed in the chloride permeability: after reaching the threshold stress level, the chloride diffusion coefficient increases significantly. Compared with plain concrete, incorporating macro fibers raises the threshold stress level for chloride ion penetration. Furthermore, this threshold stress level increases with higher fiber content. The variation in ultrasonic velocity with stress level is also found to be an effective indicator for evaluating the chloride permeability of concrete under uniaxial compression. Moreover, a prediction model for the chloride permeability of FRC (fiber reinforced concrete) is proposed based on the results. Full article

The increasing global emphasis on sustainable construction practices has spurred significant international research into developing durable and eco-friendly concrete materials. This study investigates the potential of metakaolin and glass powder as supplementary aluminosilicate materials in slag- based geopolymer mortars, aiming to enhance their mechanical properties and durability. To further improve the performance, polypropylene fibers were incorporated at various dosages. Therefore, 13 mixtures of geopolymer mortar based on blast furnace slag have been developed. The control mix does not contain fibers or slag replacement materials, whereas in the other formulations, glass powder and metakaolin have been employed as substitutes for slag at weight percentages (relative to the weight of slag) of 5% and 10%, separately and in combination. Additionally, the fiber-containing samples are divided into two groups based on the volume percentage of polypropylene fibers, comprising 0.2% and 0.4%. The results of the investigation show that the use of glass powder, particularly at a replacement percentage of 10%, leads to an improvement in the 28-day compressive strength. Furthermore, the mixes containing glass powder demonstrated higher flexural strength compared to those containing metakaolin, irrespective of the volume percentage of fibers. The best performance in the rapid chloride permeability test is associated with the mix containing a combination of glass powder and metakaolin at a replacement percentage of 10%. Satisfactory results have been obtained when using fibers at volume percentages of 0.2% and 0.4%. Additionally, this study utilized a fuzzy inference system to predict compressive strength. The results indicate that, by considering uncertainties, the compressive strength of the mortar can be predicted with an error of less than 1% without the need for complex mathematical calculations. Full article

Properties of high early-strength concretes (HESCs) containing Type V, Type III, and rapid hardening calcium sulfoaluminate (CSA) cements were investigated at curing ages of opening time, 24 h, and 28 days. Investigated properties included the fresh (workability, setting time, air content, unit weight, and released heat of hydration), mechanical (compressive and flexural strengths), transport (absorption, volume of permeable voids, water penetration, rapid chloride permeability, and accelerated corrosion resistance), dimensional stability (drying shrinkage), and durability (de-icing salt and abrasion resistance) properties. Test results revealed that the HESC containing Rapid-Set cement achieved the shortest opening time to attain the required minimum strength, followed by Type III and Type V cement HESCs. For the most part, Type V cement HESC produced the best transport and de-icing salt resistance, whereas Rapid-Set cement HESC displayed the best dimensional stability and wear resistance. Full article