Search Results (67)

Since people spend most of their time in indoor environments, they are continuously exposed to various contaminants that threaten human health. The air quality in these settings is therefore a crucial factor in maintaining health safety. In order to reduce the concentration of indoor air pollutants and improve air quality, photocatalytic oxidation has drawn the attention of researchers. This study aims to provide a comprehensive view of the nanomaterials used in the photocatalytic oxidation of the most common pollutants in indoor environments. The effects of various parameters like humidity, airflow, deposition time, and light intensity were also evaluated, as they can significantly influence photocatalytic reactions. The most common nanomaterials used in photocatalysis are TiO₂-based and, in this study, they were classified and examined based on their morphology. TiO₂ doping with metals and non-metals has demonstrated an enhancement of its adsorption properties and photocatalytic efficiency for the removal of several pollutants. The role of carbon-based nanomaterials in photocatalysis was also evaluated due to their adsorption capabilities towards various pollutants. In addition, other less common photocatalysts such as ZnO, MnO₂, WO₃, CeO₂, and CdS also exhibited high photocatalytic activity for pollutant degradation. Applications of these photocatalysts in air purifiers, paints, and building materials e.g., concrete, glass, and wallpapers, lead to efficient reduction of pollutants in indoor settings. Full article

The collapse of surface goaf beneath highways can result in instability and damage to roadbeds. However, filling the goaf areas with foam concrete can significantly enhance the stability of the roadbeds while considerably reducing the costs of filling materials. This study analyzes the effects on destructive characteristics, mechanical properties, stress–strain curve features, and relevant metrics, while also observing the microstructure of basalt fiber-calcined gangue-silty clay foam concrete (BF-CCG-SCFC). The results indicate that the water–binder ratio significantly influences the cubic compressive strength, split tensile strength, and fluidity of BF-CCG-SCFC. Silty clay reduces the cubic compressive strength, split tensile strength, and fluidity of BF-CCG-SCFC. Conversely, an appropriate amount of calcined gangue and basalt fiber significantly increases the cubic compressive strength and split tensile strength, while decreasing fluidity. To satisfy the strength and fluidity requirements of the filler material in hollow areas, the optimal water–binder ratio for BF-CCG-SCFC is 0.55, the ideal mixing ratio of calcined gangue to silty clay is 2:2, and the basalt fiber content should be 1%. The study examines the influence of varying water–binder ratios, the combined proportions of calcined gangue and silty clay, and different basalt fiber contents on the elastic modulus, peak stress, and peak strain of BF-CCG-SCFC. Additionally, the water–binder ratio influences the matrix strength through the non-hydration reactions of doped particles, while gangue and clay induce a “gradient hydration effect” during the hydration process. The incorporation of basalt fibers enhances the mechanical interlocking between the fibers and the matrix. Full article

Chloride binding technology can effectively reduce the content of free chloride ions in seawater (used for cementitious materials), thereby extending the service life of seawater concrete structures. Currently, affordable and highly dispersed nanomaterials that can enhance the chloride binding capability of seawater cement are finite. This paper presents the first experimental study on N-doped graphene quantum dots (NGQDs), an innovative carbon nanomaterial with low price and high dispersibility, to strengthen the mechanical and chloride binding capabilities of seawater cement. Concretely, NGQDs are prepared through the hydrothermal process. The morphology and structure of NGQDs are measured by TEM, AFM, FTIR, and XPS. And the strengths and chloride binding performance of different specimens are analyzed by compressive/flexural strength tests and chloride adsorption equilibrium tests. The phase compositions of various specimens are analyzed by XRD, TGA/DTG, and SEM. The consequences indicate that the unique structure of the prepared NGQDs endows them with excellent water solubility and dispersibility. Notably, the introduction of NGQDs enhances the mechanical performance of seawater cement and 0.05 wt.% NGQDs have the greatest improvement effect. The compressive and flexural strengths of seawater cement containing 0.05 wt.% NGQDs increase by 8.21% and 25.77% after 28 d curing, respectively. Additionally, the seawater cement containing 0.2 wt.% NGQDs have the best chloride binding capability and are 41.08% higher than the blank group. More importantly, the chloride binding mechanism is that NGQDs accelerate seawater cement hydration, resulting in an increased formation of hydrated calcium silicate (C–S–H) and Friedel’s salt (Fs), thereby strengthening the physisorption and chemical combination of chloride. This study highlights an inexpensive and highly dispersible nanomaterial to heighten the stability of seawater concrete structures, opening up a new path for the better utilization of seawater resources. Full article

In this paper, the damage constitutive model of reactive powder concrete (RPC) in uniaxial tension is investigated. The relationship between the uniaxial tensile strength of RPC and the steel fiber admixture was analyzed by preparing RPC specimens with different steel fiber volume admixtures for uniaxial tensile tests, and the stress–strain curves were recorded. The test results show that the uniaxial tensile strength of RPC is significantly enhanced with an increase in steel fiber doping, especially after the doping amount is greater than 2%, showing a linear increase. Based on the classical damage mechanics and Weibull distribution, the damage evolution equation and the constitutive model of RPC uniaxial tension were established. The validation shows that the model can effectively describe the damage process of RPC in uniaxial tension, which provides a theoretical basis for the application of RPC in engineering practice. Full article

To explore the mechanical properties and fracture modes of basalt fiber-reinforced concrete, single-doped and hybrid-doped basalt fiber-reinforced concrete was prepared, and uniaxial failure tests under different basalt fiber-reinforced concrete contents were carried out. At the same time, the smooth kernel function in the traditional SPH method was improved, and the basalt fiber random generation algorithm was embedded in the SPH program to realize the simulation of the progressive failure of basalt fiber-reinforced concrete. The results show that under the circumstance with no basalt fiber, the specimen final failure mode is damage on the upper and lower surface, as well as the side edge, while the interior of the specimen center is basically intact, indicating that there is an obvious stress concentration phenomenon on the upper and lower surface when the specimen is compressed. Under the circumstance with basalt fiber, longitudinal cracks begin to appear inside the specimen. With the increase in the content, the crack location gradually develops from the edge to the middle, and the crack number gradually increases. This indicates that appropriately increasing the fiber content in concrete may improve the stress state of concrete, change the eccentric compression to axial compression, and indirectly increase the compressive strength of concrete. The numerical simulation results are consistent with the test results, verifying the rationality of the numerical simulation algorithm. For the concrete model without the basalt fiber, shear cracks are generated around the model. For the concrete model with basalt fiber, in addition to shear cracks, the tensile cracks generated at the basalt fiber inside the model eventually lead to the splitting failure of the model. The strength of concrete samples with basalt content of 0.1%, 0.2%, and 0.3% is increased by 1.69%, 5.10%, and 4.31%, respectively, compared to the concrete sample without basalt fiber. It can be seen that with the increase in the content of single-doped basalt fiber, the concrete strength is improved to a certain extent, but the improvement degree is not high; For hybrid-doped basalt fiber-reinforced concrete, the strength of concrete samples with basalt content of 0.1%, 0.2%, and 0.3% is increased by 14.51%, 15.02%, and 30.31%, respectively, compared to the concrete sample without basalt fiber. Therefore, compared with the single-doped basalt fiber process, hybrid doping is easier to improve the strength of concrete. Full article

In order to rationalize the consumption of graphite tailing sand and reduce its pollution of the environment—with sodium silicate being a commonly used activator for improving the strength of concrete composites—in this study, the joint effects of sodium silicate (SS) and graphite tail sand (GT) on the strength and frost resistance of graphite tail sand high-performance mortar (GT-HPM) were investigated. Experiments were conducted to evaluate the bulk density, water absorption, compressive strength, speed of sound, and working performance status of GT-HPM before and after freezing and thawing at different SS dosages and different GT substitution rates. The microstructural properties of GT-HPM were also analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM/EDS). The results showed that 4% SS doping improved the performance of GT-HPM more obviously. Moreover, with an increase in the GT substitution rate, the mechanical properties and frost resistance of GT-HPM increased firstly and then decreased, and the best performance of GT-HPM was obtained when the GT substitution rate was 20%. At 6% SS doping, the performance of GT-HPM gradually decreased with the increase in the graphite tailing sand substitution rate. FT-IR testing showed that there was no significant change with the type of hydration products used, and the Si–O–T absorption peak and average bond length of GT-4 were the largest. SS and GT promoted the generation of hydration products. Microstructural analysis showed that 4% SS promoted the hydration reaction; in addition, an appropriate amount of GT improved the pore structure of HPM, increased the strength and frost resistance, and provided fundamental insights for the subsequent comprehensive utilization of graphite tailing sand. Full article

Freshwater resources are scarce in coastal areas, and using seawater as mixing water can alleviate the scarcity of freshwater resources. However, the presence of chloride ions in seawater affects the generation of hydration products and the durability of concrete structures. In order to investigate the effect of hydrated calcium silicate (C-S-H) gel and calcium hydroxide (CH) generation in seawater-mixed cement pastes under 50 °C curing, their microscopic morphology was investigated using differential scanning calorimetry analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The relationship between the amount of C-S-H gel and CH production and the amount of chloride ion dosing, fly ash dosing, and the age of curing were investigated. The degree of influence between hydration products and influencing factors was analyzed using the grey correlation analysis. It was shown that 50 °C curing promoted the hydration reaction and generated more hydration products compared with ASTM standard. The content of C-S-H gel and CH increased with chloride dosage. The content of C-S-H gel increased by 13.5% under 50 °C curing compared with the control group at a chloride dosage of 1.3%. Fly ash is rich in active SiO₂ and AI₂O₃, and other components, which can react with Ca(OH)₂ generated by cement hydration and then generate C-S-H gel. With the increase of fly ash, the content of C-S-H gel also increases, but the CH content decreases. When 25% of fly ash was doped under 50 °C curing, the C-S-H gel content increased by 5.02% compared to the control group. The CH content decreased by 31.8% compared to the control group. With the growth of the maintenance age, the hydration reaction continues, the generation of C-S-H gel and CH will continue to increase, and their microstructures will become denser. C-S-H gel and CH content increased the most by raising the curing temperature at 7 days of curing, increasing by 10.11% and 22.62%, respectively. C-S-H gel and CH content had the highest gray relation with fly ash dosing. Chloride dosage and age of maintenance had the highest correlation with CH content at room temperature maintenance of 0.788 and 0.753, respectively. Full article

Phase change materials can be converted between solid, liquid, and gaseous states, absorbing or releasing a large amount of heat. PCM is incorporated into concrete to adjust the temperature difference between inside and outside of concrete, which can reduce cracking. In this paper, the finite element analysis method is used to establish the model of an ordinary concrete structure, doped with phase change materials, on the basis of mechanical properties and a temperature regulation test performed by calculating the adiabatic temperature rise of concrete with different contents of composite phase change material, comparing the experimental and simulation results of the ordinary concrete structures with phase change materials, and analyzing the change in temperature field of the concrete structure with the content of self-prepared composite phase change materials. It is found that the addition of self-prepared composite phase change materials reduces the temperature peak of the concrete structure in the stage of hydration heat and delays the time taken to reach the temperature peak. Then, the temperature field of the phase change mass concrete structure is established, and the influence law of composite phase change material admixture on the temperature field of mass concrete is summarized through the time–temperature curves of different admixture amounts and positions so as to predict the possibility of cracks in mass concrete. Full article

Ultra High-Performance Concrete (UHPC) is a cement-based composite material with great strength and durability. Fibers can effectively increase the ductility, strength, and fracture energy of UHPC. This work describes the impacts of individual or hybrid doping of basalt fiber (BF) and steel fiber (SF) on the mechanical properties and microstructure of UHPC. We found that under individual doping, the effect of BF on fluidity was stronger than that of SF. Moreover, the compressive, flexural, and splitting tensile strength of UHPC first increased and then decreased with increasing BF dosage. The optimal dosage of BF was 1%. At a low content of fiber, UHPC reinforced by BF demonstrated greater flexural strength than that reinforced by SF. SF significantly improved the toughness of UHPC. However, a high SF dosage did not increase the strength of UHPC and reduced the splitting tensile strength. Secondly, under hybrid doping, BF was partially substituted for SF to improve the mechanical properties of hybrid fiber UHPC. Consequently, when the BF replacement rate increased, the compressive strength of UHPC gradually decreased; on the other hand, there was an initial increase in the fracture energy, splitting tensile strength, and flexural strength. The ideal mixture was 0.5% BF + 1.5% SF. The fluidity of UHPC with 1.5% BF + 0.5% SF became the lowest with a constant total volume of 2%. The microstructure of hydration products in the hybrid fiber UHPC became denser, whereas the interface of the fiber matrix improved. Full article

In the context of reinforced concrete (RC) arch bridges, while the incorporation of full sections of steel fibers can enhance the bridge’s toughness, cracking resilience, and bearing capacity, achieving an optimal balance between structural performance and economic viability in this manner remains challenging. This article introduces a novel computational approach—the distributed steel fiber concrete (LSFRC) arch—which considers the spatial distribution of damage in RC arches. The static performance of SFRC elements and LSFRC beams was compared and analyzed using the concrete plastic damage model (CDP) in ABAQUS software. This study validated the rationality of the model and investigated the impact of varying steel fiber volume ratios and steel fiber layer heights on the damage evolution of LSFRC arches. The results of this study demonstrate that the cracking load and bearing capacity of an RC arch can be effectively enhanced through the addition of steel fibers to a local area under static loading. Furthermore, the deflection and damage to the arch waist and arch roof can be significantly reduced. Furthermore, the incorporation of steel fibers at an increased volume rate and at a greater height within the doped section can effectively slow the rate of damage evolution within the section. This results in the inhibition of crack extensions and in an improvement in the ductility and reliability of the damage stage. The LSFRC arches offer superior economic and practical advantages over their full cross-section doped steel fiber (FRC) counterparts. This study offers novel insights and methodological guidance for the design and implementation of concrete arch bridges. Full article

Precast ultra-high-performance concrete (UHPC) has emerged as indispensable in the engineering sector due to its cost-effectiveness and superior performance. Currently, precast UHPC grapples with challenges pertaining to slow setting times and insufficient early strength, largely attributed to its high water-reducing agent content. Effective utilization of early strength agents to augment UHPC’s early strength is pivotal in addressing this issue. This study investigates the efficacy of two distinct concrete early strength agents, namely calcium formate (Ca(HCO₂)₂) and aluminum sulfate (Al₂(SO₄)₃). A UHPC system with a water/cement ratio of 0.17 was used; both single and compound doping experiments were conducted using varied dosages of the aforementioned early strength agents. Our results show that both early strength agents significantly reduce setting time and enhance early strength at appropriate dosages. Specifically, the addition of 0.3% Ca(HCO₂)₂ led to a 33.07% decrease in setting time for UHPC. Moreover, the incorporation of 0.3% Ca(HCO₂)₂ and 0.5% Al₂(SO₄)₃ resulted in a strength of 81.9 MPa at 1.5 days, representing a remarkable increase of 118.4%. It is noteworthy that excessive use of Ca(HCO₂)₂ inhibits the hydration process, whereas an abundance of Al₂(SO₄)₃ diminishes the early strength effect. Simultaneously, this article provides recommendations regarding the dosage of two distinct early strength agents, offering a novel solution for expediting the production of prefabricated UHPC with a low water/cement ratio and high water-reducing agent content. Full article

In the production of cement, raw materials can be partially substituted by regenerable waste provided from glasses, construction and demolition waste in order to reduce the environmental problem and burden of landfills. In this study, limestone–silicate composites were synthesized using starting materials such as glass waste and lime, brick, autoclaved aerated concrete (ACC), mortar or plaster waste. The structure and mechanical properties of the nano-composite materials have been studied. The mean CaCO₃ crystallite sizes are higher for composites containing ACC and brick than for doping with lime, mortar and plaster. Cement-based materials are formed by replacing 2.5% of the Portland cement with limestone–silicate composites. The results indicate new possibilities for introducing 2.5%of composites in cement paste because they promote the formation of the C-S-H network, which provides strength and long stability for the cement paste. The influence of varied types of mix composites in the expired cement on the initial cracking strain and stress, tensile strength and compressive strength were investigated. The compressive strength values of composite-expired cement specimens are situated between 11.8 and 15.7 MPa, respectively, which reflect an increase from 22.9 up to 63.54% over the compressive strength of expired cement matrix. Full article

This study assesses the influence of extra-short extra-fine steel fibers on the performance of self-compacting concrete (SCC) modified with fly ash. Replacing standard steel fibers with volume fractions ranging from 0%, 1.5%, 3%, 5% and 6%, the study optimizes the mix design for enhanced workability and mechanical properties. The findings reveal that, although the addition of steel fibers had a negative effect on the flowability, the cohesion is significantly improved, providing a basis for a significant improvement in the mechanical properties. The optimal fiber content is identified at 5%, achieving the highest compressive strength of 71.7 MPa, split tensile strength of 8.2 MPa, and flexural strength of 12.8 MPa at 28 d. However, further increases in fiber content beyond 5% lead to a deceleration in compressive and splitting tensile strength improvement and a 27.5% drop in flexural strength at 28 d. The study also emphasizes the good dispersion within the concrete, which helps to enhance its ductility and crack resistance, to some extent. Full article

In an attempt to reutilize marble waste, a new approach is presented in the current study to promote its use in the field of shielding against ionizing radiation. In this study, we aimed to develop a novel and sustainable/eco-friendly lead-free radiation shielding material by improving artificial marble (AM) produced from marble waste combined with polyester by reinforcing it with bismuth oxide (Bi₂O₃) nanoparticles. Six samples of AM samples doped with different concentrations ($0\%$,$5\%$,$10\%$,$15\%$, $20\%$, and $25\%$) of Bi₂O₃ nanoparticles were prepared. The linear attenuation coefficient ($LAC$) values were measured experimentally through the narrow beam method at different energies $(0.0595 \mathrm{M}\mathrm{e}\mathrm{V}$, $0.6617 \mathrm{M}\mathrm{e}\mathrm{V}$, $1.1730 \mathrm{M}\mathrm{e}\mathrm{V}$, and $1.330 \mathrm{M}\mathrm{e}\mathrm{V}$) for all samples with various concentrations of Bi₂O₃. Radiological shielding parameters such as half value layer ($HVL$), tenth-value layer ($TVL$), and radiation shielding efficiency ($RSE$) were estimated and compared for all the different samples. The results prove that increasing the concentration of Bi₂O₃ leads to the enhancement of the radiation shielding properties of the AM as a shielding material. It was observed that as the energy increases, the efficiency of the samples falls. High energy dependence was found when calculating the $HVL$ and $TVL$ values of the samples, which increased with increases in the energy of the incident photons. A comparison between the sample with the most efficient gamma radiation attenuation capability (AM-$25\%$), concrete, and lead was conducted, and a discussion regarding their radiation shielding properties is presented herein. The results show that the AM-$25\%$ sample is superior to the ordinary concrete over all the studied energy ranges, as evidenced by its significantly lower $HVLs$. On the contrary, lead is superior to the AM-$25\%$ sample over all the studied energy ranges owing to its unbeatable density as a shielding material. Overall, this new type of artificial marble has the potential to be used as a radiation shielding material at low- to medium-gamma energy regions, specifically in medical imaging and radiation therapy. Full article

An indoor accelerated freezing and thawing test of polypropylene fibre-reinforced concrete in chloride and sulphate environments was conducted using the “fast-freezing method” with the objective of investigating the damage law of the post-freezing mechanical properties of hydraulic concrete structures and studying the effects of different mixing amounts of polypropylene fibres on the mechanical properties of concrete. Furthermore, in order to reduce the cost of concrete tests and shorten the time required for conducting concrete tests, a backpropagation neural network based on a Beetle Antenna Search algorithm (BAS-BPNN) was established to simulate and predict the mechanical properties of polypropylene fibre-reinforced concrete. The accuracy of the model was verified. The results indicate that the order of improvement in the macro-physical properties of concrete due to fibre doping is as follows: PPF1.2 exhibited the greatest improvement in macro-physical properties of concrete, followed by PPF0.9, PPF1.5, PPF0.6, and PC. When the freezing and thawing medium and the number of cycles are identical, all four assessment indexes (R2, RMSE, SI, MAPE) demonstrate that the four groups of polypropylene fibre concrete exhibit superior performance to the control group of ordinary concrete. This indicates that polypropylene fibre can enhance the mechanical properties and freezing resistance of the concrete matrix, delay the process of freezing and thawing damage to the matrix, and extend the lifespan of the matrix, yet cannot prevent the ultimate failure of the matrix. The application of intelligent algorithms to optimise the parameters of an artificial neural network model can enhance its capacity to generalise and predict the mechanical properties of concrete. In terms of the coefficient of determination (R2), the Beetle Antenna Search algorithm (0.9782) outperforms the Particle Swarm Optimization (PSO; 0.9676), the Genetic Algorithm (GA; 0.9645), and the backpropagation neural network (BPNN; 0.9460). The improved backpropagation neural network based on the Beetle Antenna Search algorithm not only avoids the trap of local optimality but also improves the model accuracy while further accelerating the convergence speed. This approach can address the complexity, non-linearity, and modelling difficulties encountered during the freezing process of concrete. Moreover, it offers relatively accurate prediction outcomes at a reduced cost in comparison to traditional experimental methodologies. Full article