Search Results (701)

Using recycled asphalt pavement (RAP) as a natural aggregate (NA) replacement supports environmental preservation but requires performance evaluation. This study investigated the mechanical properties of concrete containing RAP and the potential of silica fume (SF) and superplasticizer (SP) to enhance these properties. Thirty-five concrete mixtures were prepared with a 0%, 25%, 50%, 75%, or 100% replacement of natural coarse aggregate by crushed coarse RAP. SF (0–21%) and SP (0–2.1% per 100 kg of cement) were added separately as admixtures. Tests on compressive, splitting, and flexural strength showed that RAP generally reduced compressive and splitting tensile strength but increased flexural strength at low RAP content. SF and SP partially restored strength losses, with higher RAP content benefiting more from these admixtures. Optimal compressive strength gains ranged from 8% to 58%, with splitting and flexural tensile strength improvements of 40% and 28%, respectively. The ideal SF and SP contents were 5–7% and 0.8–1.5%, respectively. These findings demonstrate that 100% RAP concrete, combined with appropriate admixtures, can meet performance requirements, offering a sustainable solution for structural applications and promoting resource conservation. Full article

The main objective of this study is to reduce CO₂ emissions resulting from rapidly increasing cement production and utilization rates worldwide. For this purpose, the effects of NS (nano-silica) and SF (silica fume) materials, which are the post-production wastes of industrial products, the substitute material obtained by grinding SG (silica gel) wastes used for packaging purposes in the preservation of industrial electronic products and many other areas, and MLS (micritic limestone) obtained by grinding limestone, a natural resource, on mortars after cement substitutions were evaluated. MLS and SG contents were sieved through a 0.063 mm sieve and substituted into the mixtures, while specific surface area values for SF and NS were obtained as 23 m²/g and 150 m²/g. Each of these materials was used in mortars by substituting between 0% and 10% cement by weight. The samples were subjected to consistency determination and then evaluated for setting time. Subsequently, flexural tests were carried out on 40 mm × 40 mm × 160 mm specimens placed in molds, and compressive tests were carried out on prism fragments broken after flexural tests. The experimental results showed that substitution of SG substitutes with cement at 3–10 wt% was highly effective against SF, NS and MLS in terms of strength and workability properties. Full article

Conventional cement production is a major source of carbon dioxide emissions, which creates a significant environmental challenge. This research addresses the problem of how to reduce the carbon footprint of cement paste production using agricultural and industrial waste by-products, namely wheat straw ash (WSA) and silica fume (SF). Currently, accurate models that can predict the mechanical properties of cement pastes incorporating these waste materials are lacking. To fill this gap, our study proposes a model based on response surface methodology and Box-Behnken design, designed to predict the strength of cement pastes with partial substitutions of WSA and SF. Through mechanical and characterization tests, the model demonstrated high accuracy in predicting the strength of the pastes, validated with three mixes, which showed maximum errors of less than 6% at different ages (7, 28, and 56 days). Response surface analysis revealed that replacing cement with 0–20% WSA and more than 5% SF can effectively reduce the carbon footprint by maximizing waste incorporation. This model allows for the calculation of optimal cement substitution levels based on the required strength, thus promoting sustainability in the construction industry through the use of local waste/resources. Full article

The splitting tensile strength of concrete is crucial for structural integrity, as tensile stresses from load and environmental changes often lead to cracking. This study investigates the effectiveness of advanced ensemble machine-learning models, including LightGBM, GBRT, XGBoost, and AdaBoost, in accurately predicting the splitting tensile strength of silica fume-enhanced concrete. Using a robust database split into training (80%) and testing (20%) sets, we assessed model performance through R², RMSE, and MAE metrics. Results demonstrate that GBRT and XGBoost achieved superior predictive accuracy, with R² scores reaching 0.999 in training and high precision in testing (XGBoost: R² = 0.965, RMSE = 0.337; GBRT: R² = 0.955, RMSE = 0.381), surpassing both LightGBM and AdaBoost. This study highlights GBRT and XGBoost as reliable, efficient alternatives to traditional testing methods, offering substantial time and cost savings. Additionally, SHapley Additive exPlanations (SHAP) analysis was conducted to identify key input features and to elucidate their influence on splitting tensile strength, providing valuable insights into the predictive behavior of silica fume-enhanced concrete. The SHAP analysis reveals that the water-to-binder ratio and curing duration are the most critical factors influencing the splitting tensile strength of silica fume concrete. Full article

This study presents the results of using innovative and sustainable recycled fibers in different asphalt mixtures. Laboratory design and performance evaluation were focused on the cracking and rutting resistance of asphalt mixtures reinforced with recycled fibers. Two mixtures were designed for this research: 1. A dense-graded hot-mix asphalt (HMA) mixture containing 15% reclaimed asphalt pavement (RAP) and a PG 64-22 asphalt binder. 2. A cold-recycled mixture (CRM) incorporating silica fume and Portland cement as a mineral filler and CSS-1H asphalt emulsion. The recycled fibers used in this study included PET, LDPE, and carbon and rubber fibers. A balanced mix design (BMD) approach based on cracking and rutting performance parameters was used to design the control mixtures. The IDEAL-CT (ASTM D8225) was conducted to assess the cracking resistance, and the IDEAL-RT (ASTM D8360) was applied for rutting resistance. For the HMA mixture, results showed that the addition of PET, carbon, and rubber fibers enhanced cracking resistance and influenced the rutting resistance; ANOVA analyses revealed statistically significant differences in both CT index and RT index between the control mixture and the fiber-reinforced mixtures. In the case of the cold-recycled mixtures, the addition of LDPE, PET, and rubber improved cracking resistance; however, a decrease in rutting resistance was also observed among the evaluated CRM samples. Full article

Fly ash–cement composite backfill slurry, prepared by partially replacing cement with fly ash, has been demonstrated to effectively reduce the mine backfill costs and carbon emissions associated with cement production. However, the use of fly ash often results in insufficient early and medium-term strength of the backfill material. To address the demand for high medium-term strength in backfill materials under continuous mining and backfilling conditions, this study developed a silica fume–fly ash–cement composite backfill slurry. The effects of varying silica fume contents on the slurry’s flowability, uniaxial compressive strength, microstructure, and pore characteristics were systematically investigated. The results showed that increasing the silica fume content significantly reduced the slurry’s flowability. However, at a silica fume content of 5%, the slurry achieved optimal medium-term strength, with a 14-day uniaxial compressive strength of 3.98 MPa, representing a 25% improvement compared to the control group. A microstructural analysis revealed that a moderate silica fume content promoted the formation of calcium silicate hydrate gel, filled micropores, and optimized the pore structure, thereby enhancing the overall strength and durability of the material. Conversely, an excessive silica fume content above 5% led to a marked decrease in both flowability and strength. Based on a comprehensive evaluation of silica fume’s effects on the flowability, strength, and microstructure, the optimal silica fume content was determined to be 5%. This study provides a theoretical basis and practical guidance for improving the efficiency of continuous mining and backfilling operations, and for designing high-performance backfill materials suitable for continuous mining and filling conditions. Full article

By volume, cement concrete is one of the most widely used construction materials in the world. This requires a significant amount of Portland cement, and the cement industry, in turn, causes a significant amount of CO₂ emissions. Therefore, the development of concrete with a reduced cement content is becoming an urgent problem for countries with a significant level of production and consumption of concrete. Therefore, the purpose of this article is to critically investigate the possibility of using inert granite dust in combination with highly active silica fume in reactive powder concrete. The main physical and mechanical properties, such as the compressive strength at different curing ages and the water absorption, were studied using mathematical planning of experiments. The consistency and microstructure of the reactive powder concrete modified with granite dust in combination with silica fume were also analyzed. Mathematical models of the main properties of this concrete are presented and analyzed, and the graphical dependencies of the influence of composition factors are constructed. A more significant factor that affects the compressive strength at all curing ages is the silica fume content, increases in which to 50 kg/m³ lead to a 25–40% increase in strength at 1 day of age, depending on the granite dust content. In turn, an increase in the amount of granite dust from 0 kg/m³ to 100 kg/m³ in the absence of silica is followed by an increase in strength of 8–10%. After 3 days of curing, the effect of granite dust becomes more significant. Increases in the 28-day strength of 25%, 46% and 56% were obtained at a content of 50 kg/m³ of silica fume and 0 kg/m³, 100 kg/m³ and 200 kg/m³ of granite dust in concrete, respectively. It is shown that the effect of inert granite dust is more significant in combination with silica fume at its maximum content in the range of variation. The pozzolanic reaction between highly active silica and Ca(OH)₂ stimulates the formation of hydrate phases in the space between the grains and causes the microstructure of the cement matrix to compact. In this case, the granite dust particles act as crystallization centers. Full article

Virgin coconut oil (VCO) is an edible vegetable oil that is eco-friendly, biodegradable, and sustainable, with high thermal and chemical stability as a phase change material (PCM). In this work, VCO filled with fumed silica A200 nanoparticles was tested as a cutting fluid in drilling processes. Silica concentrations ranging from 1 to 4 vol% were analyzed. Thermal properties were evaluated by differential scanning calorimetry (DSC) and thermal conductivity measurements at different temperatures and concentrations. Thermal conductivity showed an enhancement with the addition of silica powder and reduced with increasing temperature. Based on thermal and flow properties, VCO-3A200 was found to be the optimal concentration. The thermal images of this nanofluid taken after 60 s of drilling exhibited a reduction of 12 °C with respect to the dry process. The friction coefficient versus shear rate was also measured. With 8% VCO, a reduction in the friction coefficient of 8% compared to the dry test was achieved. The addition of 3 vol% of silica to the base oil reduced the friction coefficient by 16% compared to the dry test. The use of fumed silica dispersed in VCO has proven to be a sustainable, recyclable, and environmentally friendly refrigerant and lubricant cutting fluid. Full article

Supplementary cementitious materials (SCMs), such as fly ash, slag, and silica fume, predominantly derived from industrial waste, are widely utilized in concrete due to their proven ability to enhance both its mechanical and durability properties. Moreover, these SCMs play a crucial role in mitigating the carbon footprint of concrete by reducing its cement content, which is responsible for approximately 8% of global CO₂ emissions. However, the sustainability and long-term availability of conventional SCMs are increasingly under scrutiny, particularly in light of the impending shutdown of coal-fired power plants, which threatens the future supply of fly ash. As a result, the concrete industry faces an urgent need to identify alternative SCMs to maintain and advance eco-friendly practices. This article stands out from previous reviews by employing a bibliometric analysis to comprehensively explore the use of commonly utilized agricultural ashes (rice husk, palm oil, and sugarcane bagasse), prevalent in tropical and subtropical regions as SCMs. Additionally, it provides valuable insights into the potential of cold-weather crops (e.g., barley, canola, and oat) that demonstrate promising pozzolanic reactivity. The study critically evaluates and compares the physical and chemical characteristics of agricultural ashes from both hot and cold climates, assessing their influence on the fresh, mechanical, and durability properties of concrete. It also addresses the challenges and limitations associated with their use. Furthermore, in line with the United Nations and Environmental Protection Agency (EPA) sustainability goals, the review evaluates the environmental benefits of using agricultural ashes, emphasizing waste reduction, resource conservation, and energy savings. This comprehensive review paper should deepen the understanding of agricultural ashes as sustainable SCMs, providing a strategic direction for the construction industry to adopt low-carbon concrete solutions across various climates while promoting advancements in production methods, performance standards, and emerging technologies such as hybrid materials and 3D printing. Full article

The formulation of binary, ternary, and quaternary supplementary cementitious materials (SCMs) on an optimized silica fume amount using fly ash, ultrafine (MQ), and limestone powders (LS) is the most sustainable approach to recycling these types of solid wastes for durable concrete. The optimum replacement level of 10% silica fume was blended with different replacement levels of 5, 8, 10, and 15% MQ to formulate different ternary mixes to evaluate the filling effect of MQ. Different ternary mixes containing 10% silica fume and 5, 10, and 15% LS were also produced to examine the effectiveness of both ternary mixtures with either MQ or LS. The quaternary mixtures with 10% silica fume optimized with 20% fly ash and 10% MQ or 10% LS were evaluated for compressive strength, chloride permeability, and porosity. The MQ showed the best filling effect compared to LS. The hot curing conditions significantly enhanced the performance of ternary and quaternary mixtures. Two effects of fillers were observed: the diluting effect brought on by replacement levels and the enhanced filling effect. At early curing, the strength loss resulting from the high replacement level was around 39%; however, this drop could be minimized to approximately 7% under hot curing conditions. It has been demonstrated that the binary, ternary, and quaternary systems offer the best solution to the environmental and durability issues caused by cement. The economic analysis highlights that optimized HPC mixtures with SCMs and fillers, particularly the quaternary mix, achieve superior cost-efficiency and mechanical performance, demonstrating their potential for sustainable and high-performance engineering applications. Full article

Microfluidic devices offer promising solutions for automating various biological and chemical procedures. Epoxy resin, known for its excellent mechanical properties, chemical resistance, and thermal stability, is widely used in high-performance microfluidic devices. However, the poor printability of epoxy has limited its application in 3D printing technologies for fabricating epoxy-based microfluidic devices. In this study, fumed silica is introduced into epoxy resin to formulate a yield-stress fluid suspension as a support bath for embedded 3D printing (e-3DP). The study demonstrates that increasing the fumed silica concentration from 3.0% to 9.0% (w/v) enhances the yield stress from 9.46 Pa to 56.41 Pa, the compressive modulus from 19.79 MPa to 36.34 MPa, and the fracture strength from 148.16 MPa to 168.78 MPa, while reducing the thixotropic time from 6.58 s to 1.32 s, albeit with a 61.3% decrease in the transparency ratio. The 6.0% (w/v) fumed silica–epoxy suspension is selected based on a balance between yield stress, transparency, and mechanical performance, enabling high-fidelity filament formation. Two representative microfluidic devices are successfully fabricated, demonstrating the feasibility of a fumed silica–epoxy suspension for the customizable e-3DP of epoxy-based microfluidic devices. Full article

Silica fume (SF) has been widely used in engineering; however, its densification during transportation reduces its original pozzolanic activity. This paper investigates the effects of wet grinding and chemical activation on the mechanical properties and hydration products of silica fume in cement-based materials, revealing the mechanism by which wet grinding improves these properties. The results indicate that wet grinding effectively reduces the particle size of silica fume. Under optimal excitation conditions (250 r/min, 20 min), the median particle size is reduced to 12.1 μm, 2.27 times smaller than before excitation. The 28-day compressive strength of the silica fume cement paste reaches 60.8 MPa, 23.7% higher than that of the reference group. This approach effectively mitigates nano-agglomeration, enhances the pozzolanic activity of silica fume, and promotes AFt and C-S-H gel formation. The findings demonstrate that wet grinding activation can further enhance the utilization rate of silica fume. Full article

Inorganic sand cores involving sodium silicate binder and microsilica have environmental advantages during the casting process of aluminum alloy. Nevertheless, the bending strength of sodium silicate-bonded sand (SSBS) needs to be further improved. In this research, the effect of hydrophobic fumed silica on the bending strength of sand cores was studied. The experimental results revealed that hydrophobic fumed silica with the addition of 0.050 wt.% can be adopted as an optimal modifier to enhance the bending strength of SSBS. According to scanning electron microscope and spectroscopy techniques, dense bonding bridges and a complex Si–O–Si network containing specific silicon molecules with a silicon atom bonded to three other silicon atoms contribute to the excellent bending strength, with a 53.1% increase in cold strength (24 h) compared to a commercial sample of a modified sand core. Meanwhile, the newly formed Si–O–Al chemical bond plays a crucial role in increasing the bending strength of sand cores. Full article

SBS-modified asphalt produces a large number of hazardous fumes in the preparation process, which severely endangers health and causes environmental pollution. This paper details the design of a fume generation and collection device for asphalt and proposed a comprehensive method for analyzing fume composition. Two deodorants were incorporated into SBS-modified asphalt to mitigate the hazards of the original hazardous emissions. Then, ultraviolet–visible spectrophotometry, gas chromatography–mass spectrometry, and Fourier-transform infrared spectroscopy were combined to analyze the main component differences between asphalt fumes before and after adding deodorant, and to specify the mechanism of action of deodorants on hazardous fumes and SBS-modified asphalt. Finally, the road performance, including the physical and rheological properties of SBS-modified asphalt blended with deodorant, was evaluated. The results indicated that both deodorizers were effective in reducing the emission of hazardous substances in the fumes of SBS-modified asphalt, and no new hazardous substances were generated. Under hot mixing conditions, the addition of 0.3% of deodorant A (high boiling point ester) was effective in reducing the emission of volatile organic compounds (VOCs) by up to 41.7%, while the reduction in benzene congeners reached at least 50%. On the other hand, 1% of deodorant B (silica–magnesium compounds) reduced the emissions of VOCs and benzene congeners by 36% and 20–42%, respectively, under the same conditions. Furthermore, the addition of deodorant did not affect the original road performance, and even improved the rheological properties to a certain extent, which was conducive to the application of deodorant in pavement engineering. Full article

The development of sustainable infrastructure is essential to address the challenges of climate change and reduce CO₂ emissions. The use of alternative materials, such as agro-industrial ashes and silica fume, emerges as a promising option to enhance the durability of concrete and diminish its environmental impact. These materials can partially replace conventional cement, contributing to the construction of more sustainable infrastructure without compromising performance, even under adverse environmental conditions. In this study, we present an analysis of the use of sugarcane bagasse ash (SBA) and silica fume (SF) as a 15% cement replacement. The behavior of these materials was investigated under coastal conditions, analyzing climatic variables and degrading gases such as CO₂, CH₄, and N₂O. Electrochemical techniques were employed to measure corrosion rate and potential, in addition to conducting carbonation and compressive strength tests. The mixtures with a 15% addition of SBA and SF showed improvements compared to conventional mixes. SBA reduced the corrosion rate by 25% and increased compressive strength by 12% after 150 days, while SF enhanced carbonation resistance by 20% and compressive strength by 25%. The incorporation of SBA and SF provides significant durability in coastal environments, contributing to the sustainability of infrastructure exposed to adverse weather conditions. Full article