Search Results (155)

Polypropylene (EPP) concrete offers advantages such as low density and good thermal insulation properties, but its relatively low strength limits its engineering applications. Waste steel fibers (WSFs) obtained during the sorting and processing of machining residues can be incorporated into EPP concrete (EC) to enhance its strength and toughness. Using the volume fractions of EPP and WSF as variables, specimens of EPP concrete (EC) and waste steel fiber-reinforced EPP concrete (WSFREC) were prepared and subjected to cube compressive strength tests, splitting tensile strength tests, and four-point flexural strength tests. The results indicate that EPP particles significantly improve the toughness of concrete but inevitably lead to a considerable reduction in strength. The incorporation of WSF substantially enhanced the splitting tensile strength and flexural strength of EC, with increases of at least 37.7% and 34.5%, respectively, while the improvement in cube compressive strength was relatively lower at only 23.6%. Scanning electron microscopy (SEM) observations of the interfacial transition zone (ITZ) and WSF surface morphology in WSFREC revealed that the addition of EPP particles introduces more defects in the concrete matrix. However, the inclusion of WSF promotes the formation of abundant hydration products on the fiber surface, mitigating matrix defects, improving the bond between WSF and the concrete matrix, effectively inhibiting crack propagation, and enhancing both the strength and toughness of the concrete. Full article

Epoxy resin-modified concrete (ERMC) demonstrates significant potential for enhancing the durability of concrete structures exposed to harsh environmental conditions. However, the performance of ERMC under the combined effects of salt erosion and freeze–thaw cycles remains inadequately explored. This study systematically evaluates the durability of ERMC through experimental investigations on specimens with epoxy resin-poly ash ratios of 0%, 5%, 10%, 15%, 20%, and 25%. Resistance to salt erosion was assessed using composite salt solutions with concentrations of 0%, 1.99%, 9.95%, and 19.90%, while frost resistance was tested under combined conditions using a 1.99% Na₂SO₄ solution. Key performance metrics were analyzed with microstructural observations to elucidate the underlying damage mechanisms, including the compressive strength corrosion coefficient, dynamic elastic modulus, mass loss rate, and flexural strength loss rate. The results reveal that incorporating epoxy resin enhances concrete’s resistance to salt erosion and freeze–thaw damage by inhibiting crack propagation and reducing pore development. Optimal performance was achieved with an epoxy resin content of 10–15%, which exhibited minimal surface deterioration, a denser microstructure, and superior long-term durability. These findings provide critical insights for optimizing the design of ERMC to improve the resilience of concrete structures in aggressive environments, demonstrating that ERM is a sustainable material, and offering practical implications for infrastructure exposed to extreme climatic and chemical conditions. Full article

This study investigated the effects of Trichoderma harzianum inoculation on the growth, physiological responses, and soil nutrient uptake of three turfgrass species cultivated on eco-concrete—Axonopus compressus (Sw.) Beauv., Cynodon dactylon (L.) Pers., and Zoysia sinica Hance. A 2 × 2 factorial design was used to evaluate plant growth, physiological responses, and soil metrics under cement stress, incorporating T. harzianum inoculation (inoculated vs. control) and substrate composition (eco-concrete vs. pastoral soil). Our results indicate that inoculation with Trichoderma harzianum significantly enhanced the growth potential of the three turfgrass species compared to uninoculated controls. Furthermore, under cement stress conditions in vegetated concrete, inoculation with T. harzianum significantly alleviated the inhibition of growth and development. More specifically, in the vegetated concrete habitat, inoculated plants exhibited significantly increased root length and surface area. This enhancement promoted the uptake of available nitrogen (AN), available phosphorus (AP), and available potassium (AK) from the soil. Concurrently, inoculated plants showed higher leaf epidermal cell density, stomatal width, soluble sugar content, and antioxidant enzyme activity (SOD, POD, CAT, and APX). Additionally, significant reductions were observed in root activity, relative conductivity, and malondialdehyde (MDA) and proline contents. In conclusion, T. harzianum inoculation promotes the growth of the three turfgrass species under cement stress, likely by enhancing root development, increasing osmoregulatory substance accumulation, and elevating antioxidant enzyme activities. Full article

To study the flexural performance of damaged reinforced concrete beams reinforced with carbon fiber nets (CFNs), seven beams were designed for a flexural test. The physical parameters, such as damage phenomena, characteristic load, deflection variation, concrete strain, reinforcement strain, and CFRP mesh strain, were analyzed using different forms of U-hoops and the preload amplitude as variables. The results show that the magnitude of the preload and the different U-hoop forms affect the ultimate load capacity, crack distribution, and deflection of the beams. Compared with the unreinforced beams, the yield load, ultimate load, and cracking load of the reinforced beams were significantly increased; CFNs reinforcement could significantly improve the flexural load-carrying capacity of the beams. Under the same preload amplitude, the X-shaped diagonal U-hoop has better diagonal crack suppression capability than the vertical U-hoop. Under secondary stress conditions, CFNs reinforcement inhibits the appearance and development of cracks and increases the flexural load capacity, which can effectively alleviate the stiffness degradation caused by the preload. The simulation of the test results using the ANSYS (v2023 R1) 2016 platform produced good agreement, with an error of about 10%, which verifies the feasibility of using the finite element method to simulate the test beam. Full article

Asphalt concrete has a unique low-temperature fracture mechanism due to the complex interaction between macro- and micro-cracks. This study investigated the toughening effect of micro-cracks on the crack propagation behavior of asphalt concrete at low temperatures. The Taylor model was applied to establish a modulus damage model of asphalt concrete. In combination with the discrete element method (DEM), a 2D microstructure damage model of asphalt concrete with heterogeneity (aggregate, mortar, and voids) and multi-level (aggregate gradation) characteristics was constructed. A virtual semi-circular bending (SCB) test was performed to reveal the toughening effect of the micro-cracks in terms of macroscopic and microscopic parameters, such as the modulus damage variable, dynamic parameters associated with the main crack propagation, and stress field distribution, laying a foundation for predicting the propagation behavior and path of macroscopic cracks in asphalt concrete. The results showed that (1) the proposed modulus damage model based on the Taylor model produced results that were in good agreement with the numerical simulation (virtual SCB test) results. With an increase in the micro-crack density, the influence of the main cracks on the modulus damage of asphalt concrete gradually reduced, indicating that the micro-cracks exhibited a toughening effect on the main crack propagation; (2) At the meso-scale, the toughening effect of the micro-cracks extended the duration of the crack propagation stage and macro-crack formation stage; that is, the toughening effect of the micro-cracks had a shielding effect on the main crack propagation; (3) The toughening effect could inhibit the shear stress field, contributing to preventing the deterioration in the modulus of asphalt concrete. Full article

To address the challenge of balancing static and dynamic strength in the engineering application of foam concrete, this study proposes a strategy to improve the static and dynamic mechanical properties of foam concrete by synergistically adding rubber particles and polypropylene fibers, and systematically analyzes the effects of rubber content, rubber particle size, and fiber content on the material’s compressive strength, flexural strength, and impact toughness. The results show that rubber enhances the dynamic strength of foam concrete through high elastic deformation, with a maximum increase of up to 200%. However, due to the obstruction of hydration reaction, the increase in rubber content reduces the compressive and flexural strength of foam concrete. Meanwhile, the influence of rubber particle size on static strength follows a parabolic trend, with the optimal overall performance achieved at a particle size of 20-mesh, resulting in an approximately 50% enhancement in compressive strength. The addition of fibers to form a three-dimensional mesh structure connecting the cement matrix and rubber particles to inhibit the expansion of cracks can effectively alleviate the deterioration of the static strength of foam concrete caused by rubber particles. The optimal fiber content is 0.2%. In addition, the fiber can also improve the dynamic strength of foam concrete. In addition, the mechanism behind the synergistic improvement of static and dynamic strength by rubber and fiber was summarized. Finally, the optimized proportion and the prediction formulas of static and dynamic strength are established for the above three strength indexes, and the accuracy of the prediction formulas can reach more than 90%. Full article

In this study, the temperature change and its control measures caused by hydration heat in the construction process of bridge mass concrete cap in severe cold area are discussed. The finite element analysis method was used to simulate the temperature field of the mass pile cap concrete of the No. 13 pier of the swivel bridge in Dehui City under different construction conditions. The effects of different pouring methods, cooling water pipe layout, and its parameters on temperature control were investigated. The research shows that layered pouring combined with multi-layer cooling water pipe arrangement can effectively reduce the core temperature of concrete, thereby reducing the temperature gradient and stress concentration. Among them, the four-layer metal cooling water pipe scheme can significantly reduce the temperature peak, improve the temperature field distribution, and reduce the risk of cracks. In this study, a ‘layered pouring and four-layer metal cooling water pipe collaborative temperature control system’ was proposed for the first time. Combined with the environmental characteristics of severe cold regions, the core temperature of concrete was reduced from 63.55 °C without control to 40.70 °C, and the temperature decreased by 22.85 °C (about 36%). At the same time, the temperature gradient and temperature stress are significantly reduced, which inhibits the stress concentration caused by the temperature gradient and effectively controls the risk of crack formation. In addition, this study explores the influence of cooling water pipe diameter, material and water flow rate on the internal temperature of concrete, and proposes an optimized construction strategy that provides a scientific basis and engineering reference for the construction of mass concrete caps under cold climate conditions. Full article

In order to improve early-age strength, steam curing is mostly used for railway prefabricated components, which consumes a lot of energy and affects the durability of concrete. Synthetic calcium silicate hydrate (C-S-H) has an excellent early-age strength effect, which can improve the early-age strength of concrete and help to reduce the energy consumption of steam curing, but C-S-H will increase the shrinkage of concrete and affect the durability of concrete. In this work, C-S-H/SRPCA was synthesized using a shrinkage-reducing polycarboxylate superplasticizer (SRPCA) in order to increase the early-age strength and decrease the shrinkage of concrete. The effects of 0.5%, 4.0%, and 8.0% C-S-H/SRPCA on the shrinkage and strength of concrete were studied. Meanwhile, the internal mechanism was also explored through cement hydration, the physical aggregation morphology of hydration products, pore structure and classification, and the chemical properties of pore solution. The results suggest that C-S-H/SRPCA can shorten the setting time and accelerate cement hydration. Specifically, when the dosage of C-S-H/SRPCA is 4.0%, the initial setting time of concrete is shortened by 2.5 h and the final setting time is shortened by 6.2 h compared with the control group. As a result, the 1-day compressive strength is effectively increased by 29.5%, and the plastic shrinkage is reduced. In the stage of plastic shrinkage, the plastic shrinkage time of the concrete with 4.0% C-S-H/SRPCA is 4.1 h, which is 6.1 h shorter than that of the control group. In addition, C-S-H/SRPCA decreases the porosity. When the dosage is 4.0%, the porosity of the hardened cement paste at 28 days is reduced by 15% compared with the control group. It lessens the content of the capillary pores at 10–50 nm. At 24 h, the content of 10–50 nm capillary pores in the paste with 4.0% C-S-H/SRPCA is 40% lower than that of the control group. It also reduces the surface tension of the pore solution. The surface tension of the simulated pore solution with 4.0% C-S-H/SRPCA is 34 mN/m, which is 53% of that of the control group, and it inhibits the volatilization of the pore solution. At 28 days, the evaporation rate of the pore solution in the paste with 4.0% C-S-H/SRPCA is 40% lower than that of the control group. Thus, the drying shrinkage of concrete is inhibited. Given the above, at the optimum content of 4.0%, C-S-H/SRPCA improves the 1-day compressive strength of concrete by 29.5%, reduces the 28-day total shrinkage by 21.7%, and restrains the development of microcracks. Full article

Corrosion inhibitors play a crucial role in the corrosion protection of rebars in reinforced concrete structures under harsh service conditions. However, conventional corrosion inhibitors often suffer from low efficiency and environmental concerns. This study investigates a low-cost and environmentally friendly lotus leaf extract (LLE) as a corrosion inhibitor and examines its effects on carbon steel rebar corrosion under various conditions. The structure and composition of LLE were characterized using SEM, FTIR, and LC-MS. The effects of LLE on rebar corrosion behavior under different environmental conditions were investigated using electrochemical tests, Mott–Schottky analysis, and XPS. The main findings indicate that LLE is rich in polar chemical bonds and functional groups, which facilitate adsorption and film formation on the rebar surface. In a 3.5% NaCl solution, rebar corrosion is primarily influenced by the solution pH, and low concentrations of LLE exhibit effective corrosion inhibition. In a simulated concrete pore solution, higher concentrations of LLE promote the formation of a passivation film in a chloride-alkaline environment. Studies on pre-passivated rebar indicate that LLE effectively protects the passivation film, with the optimal LLE concentration for passivation film protection and adsorption film quality being 0.5 wt%. This study contributes to the application and development of novel LLE-based corrosion inhibition technology for carbon steel rebar. Full article

Recycled aggregate concrete (RAC), which is made by replacing all natural coarse and fine aggregates with recycled aggregate, plays a significant role in improving the recycling rate of construction materials, reducing carbon emissions from construction, and alleviating ecological degradation issues. However, due to its low strength and significant shrinkage and deformation problems, RAC has limited application. The effort of fiber type, fiber admixture, and fiber hybridization on autogenous shrinkage were studied to improve the structural safety of building materials and broaden the application of RAC. Test results indicate that the shrinkage of RAC decreases with an increase in fiber admixture, and steel fiber-reinforced RAC is more resistant to shrinkage deformation than polypropylene fiber-reinforced RAC. The shrinkage deformation of the hybrid fiber group is smaller than that of the single fiber group, and the inhibition of shrinkage deformation is most effective when the volume fraction of steel fiber is 0.5% and the polypropylene fiber content is 1.5 kg/m³. At 120 days, the PF15SF05 mixture showed a 65.3% reduction in shrinkage compared with ordinary RAC. By merging the shrinkage deformation characteristics of fiber-reinforced RAC and introducing the fiber influence coefficient, three theoretical calculation models for autogenous shrinkage applicable to single and hybrid fiber-reinforced RAC were established based on the experimental data. Full article

The inherent porous structure of concrete enables the penetration of water and Cl⁻ ions through its pores, which eventually leads to rebar corrosion within the concrete. Consequently, the densification and impermeability of concrete protective layers play a critical role in the durability of reinforced concrete structures. This study proposes a composite anti-corrosion treatment for mortar protective layers by integrating nano-ion capillary crystalline with silane hydrophobic processing. Targeting existing mortar samples, a series of experiments were conducted, utilizing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimetry-thermogravimetry (DSC-TG), X-ray computed tomography (X-CT), contact angle measurements, permeability tests, and electrochemical tests. These experiments systematically evaluated the effects of composite anti-corrosion treatment on the microstructure of hydration products, pore characteristics, surface hydrophobicity, impermeability, and the overall corrosion resistance of mortar-rebar samples in a Cl⁻-contained environment. The results reveal that nano-ion capillary crystalline materials react with free calcium ions in the mortar to produce secondary hydration products, effectively filling micro-pores, densifying the pore structure and inhibiting the invasion of Cl⁻ ions. The combination of capillary crystalline and silane hydrophobic processing synergistically enhances surface hydrophobicity and impermeability, preventing the ingress of corrosive agents, such as Cl⁻ ions, and significantly improving the anti-corrosion performance of mortar in a Cl⁻-contained environment. Full article

The service of reinforced concrete structures (RCSs) in harsh coastal environments is often threatened by chloride corrosion. The penetration of chloride ions through concrete pores into the steel/concrete interface will cause the depassivation and corrosion of steel rebars, which will lead to the deterioration and failure of RCSs durability. It is important to repair and protect the corrosion damage of existing concrete structures and ensure their high durability, and the high performance of repairing and protecting materials is crucial. In this paper, a novel cement-based protective coating material with low porosity, high impermeability and chloride-corrosion resistance was designed and prepared by introducing polypropylene fiber and high-performance cement into commercial cement-based protective materials through the double modification strategy of fiber-toughening and substrate-enhancing, in order to provide a reliable corrosion protection solution for the high durability and long life of RCSs under chloride erosion environment. Based on this, the microstructure and pore structure of the double-modified coating material was systematically analyzed by SEM, XRD, X-CT and other characterization methods. The impermeability and chloride corrosion resistance of this material were scientifically evaluated, and the protection mechanism was systematically discussed. The results show that the impermeability of the double-modified coating material is about 2.8 times higher than that of the untreated mortar. At the same time, the corrosion current density was significantly reduced to 8.60 × 10⁻⁷ A·cm⁻², which was about 86% lower than that of the untreated sample (6.11 × 10⁻⁶ A·cm⁻²). The new cement-based coating material optimized by double-modification effectively inhibits the formation and propagation of microcracks in the protective coating through the bridging effect of fibers. At the same time, the regulation of cement hydration products and the densification of pore structure are realized by adjusting the composition of cement matrix. Based on the above two aspects of microstructure improvement, the chloride-corrosion protection performance of the novel cement-based protective coating material has been greatly improved. Full article

Background/objectives: Schistosomiasis is a parasitic disease that represents a serious public health problem. An alternative for the control of snails, intermediate hosts of schistosomiasis, is the use of molluskicides. Niclosamide, recommended by the WHO, has limitations, such as environmental toxicity, which has driven the search for safer and biodegradable alternatives, especially of plant origin. In this context, this study investigated the biological activity of Cymbopogon winterianus essential oil on embryos, juveniles, and adults of Biomphalaria glabrata and cercariae of Schistosoma mansoni. Methods: Essential oils (EOs) were extracted from fresh leaves via the Clevenger system and characterized via gas chromatography (GC/MS and GC/FID), revealing geraniol (25.0%), citronellal (29.2%), citronellol (10.5%) and elemol (9.6%) as the main components. Results: The results revealed lethal concentrations 90 (LC₉₀) for young and adult snails of 60.72 mg/L, 74.21 mg/L and 115.35 mg/L, respectively. In the histological analysis, no changes were observed in the tissues of the mollusks exposed to the lethal concentration 25 (LC₂₅). However, the lethal concentrations 50 (LC₅₀) and 75 (LC₇₅) caused crystalline concretions in proximity to the renal saccular portion. At a concentration of 60 mg/L, the oil resulted in 100% lethality in embryos and cercaricidal activity greater than 90% in 3 h. Acute toxicity tests in mice via the intraperitoneal or oral route did not reveal toxic effects, with hematological and biochemical parameters within the reference values. Furthermore, the oil did not inhibit acetylcholinesterase (AChE), indicating low toxicity to fish, and caused a slight reduction in human butyrylcholinesterase (hBChE) activity without affecting human AChE, which suggests low toxicity to mammalian tissues. In terms of environmental impact, the oil was not toxic to algae until the 75th day, with mortality observed thereafter. Conclusions: These results indicate that essential oils have great potential as biodegradable and safe alternatives for controlling mollusks and interrupting the schistosomiasis cycle. Full article

Research on the effects of magnetic fields on water and aqueous solutions has produced various findings, such as the suppression of scale formation in pipes and boilers, inhibition of metal corrosion, enhancement of concrete strength, and changes in properties like viscosity and electrical conductivity. However, the challenges in quantifying these effects, the issues with reproducibility affected by trace elements in the water used in the experiments, and the involvement of complex parameters and mechanisms have led to ongoing debates, with some questioning the very existence of magnetic field effects. The “memory effect”, where the impact of magnetic exposure persists for a certain period, further complicates explanations of these phenomena. To fully elucidate and enable practical applications of these effects, further research is essential. In this study, we aimed to investigate the magnetic field effects on water, including memory effects, where the quantification and elucidation potentially lead to various applications, including environmentally friendly solutions on scale suppression and life science issues. The results revealed that the vaterite phase precipitation ratio significantly increased in magnetically treated water, reaching up to 51%, from 26% without the treatment, which is high reproducibility; furthermore, a reduction in mean particle size was observed when using magnetically treated water, suggesting that it may help prevent scaling. Furthermore, when solutions of calcium carbonate, calcium chloride, and sodium bicarbonate were individually subjected to magnetic treatment, the most notable increase in the vaterite phase precipitation ratio was observed when calcium chloride and sodium bicarbonate solutions were magnetically treated separately and then reacted to precipitate calcium carbonate. Full article

In coastal areas, the presence of concrete cracks provides pathways for hazardous ions to ingress from the exterior into the interior of concrete, while the migration of the ions further accelerates concrete deterioration and causes durability problems. The incorporation of graphene oxide (GO) into concrete can inhibit crack initiation and development starting at the nanoscale, improving the concrete microstructure, thereby affecting concrete’s resistance to hazardous ion transport and the resulting deterioration. In this study, a multi-scale transport model for cementitious materials with a GO admixture was established to predict the resistance to hazardous ions. Based on the determination of hydration types and hydration kinetics, microstructure modeling was conducted at three scales, the sub-microscale, microscale, and mesoscale, upon which transport property simulations were performed. At the microscale, the effects of both the cement paste matrix and the interfacial transition zone (ITZ) were considered. Through the simulation, it was found that the addition of GO reduced the duration of the induction period and increased the rate of hydration development after the induction period. Moreover, the incorporation of GO could reduce the porosity of cementitious materials at all simulation scales at both early and later ages. At the microscale, it improved the pore structure of the cement matrix and ITZ by reducing large pores and increasing small pores. At all three simulation scales, GO could increase the diffusion tortuosity in hydration products, suppress ion transport, and improve the resistance to hazardous ions of cementitious materials. Full article