Search Results (1,368)

High-strength engineered cementitious composites (HS-ECCs) have garnered significant attention for their superior mechanical properties and ductility. However, their high autogenous shrinkage, caused by a low water-to-binder ratio, high cementitious content, and lack of coarse aggregate, often results in early-age cracking, limiting their broader use in civil engineering. Incorporating iron sand in HS-ECCs has enhanced their mechanical properties, reduced the carbon footprint, and moderately decreased shrinkage strain compared to traditional silica sand; however, the shrinkage strain remains substantial. This study aims to reduce the autogenous shrinkage of HS-ECCs further by incorporating united expanding admixtures (UEAs)—calcium oxide-based (CEA) and magnesium oxide-based (MEA) expansive agents—in varying amounts (3% to 10% by mass of cement). This study also examines the impact of these admixtures on the workability and mechanical properties of HS-ECCs. The results show that increasing the UEA content significantly reduces autogenous shrinkage strain, achieving a 40.66% reduction at 10% UEA, from 1007.31 με to 647.18 με. While higher UEA content decreases workability, as indicated by lower fluidity and penetration depth, the compressive strength remains largely unaffected. The tensile strength peaks at 12.38 MPa with 3% UEA but declines at higher contents, with higher UEA content effectively minimizing crack formation. The novelty of this research lies in the combined use of waste iron sand and UEA, optimizing the balance between workability, mechanical properties, and autogenous shrinkage reduction in HS-ECCs. These findings support the broader application of HS-ECCs in civil engineering projects requiring high mechanical properties and low shrinkage. Full article

In this study, the soot formation and oxidation processes in different turbulent, pre-evaporated and partially premixed diesel surrogate flames are experimentally investigated. For this purpose, a piloted jet flame surrounded by an air co-flow is used. Starting from a defined diesel surrogate mixture, different fuel blends with increasing blending ratios of poly(oxymethylene) dimethyl ether (OME) are studied. The Reynolds number, equivalence ratio, and vaporization temperature are kept constant to ensure the comparability of the different fuel mixtures. The effects of OME addition on flame structures, soot precursors, and soot are investigated, showing soot reduction when OME is added to the diesel surrogate. Using chemiluminescence images of C₂ radicals (line of sight) and subsequent Abel-inversion, flame lengths and global flame structure are analyzed. The flame structure is visualized by means of planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH). The spatial distribution of soot precursors, such as polycyclic aromatic hydrocarbons (PAHs), is simultaneously measured by PLIF using the same excitation wavelength. In particular, aromatic compounds with several benzene rings (e.g., naphthalene or pyrene), which are known to be actively involved in soot formation and growth, have been visualized. Spatially distributed soot particles are detected by using laser-induced incandescence (LII), which allows us to study the onset of soot clouds and its structures qualitatively. Evident soot formation is observed in the pure diesel surrogate flame, whereas a significant soot reduction with changing PAH and soot structures can be identified with increasing OME addition. Full article

With the growing global concerns regarding sustainable development in the building and construction industries, concentration only on the engineering properties of building materials can no longer meet the requirements. Although some studies have been implemented based on the lifecycle assessment of lightweight cement-based materials, very few attempts have been made pertaining to multi-criteria optimization, especially when fly ash cenospheres are used as lightweight aggregates and nano additives are incorporated as modifying admixtures. This investigation utilized cenospheres as fine aggregates to produce green, sustainable, lightweight cement mortar. Multi-walled carbon nanotubes at 0.05, 0.15, and 0.45% were binarily added, together with 0.2, 0.6, and 1.0% of nano silica to improve the mechanical performance. Strength tests were conducted to measure the flexural and compressive behaviors, combined with a cradle-to-gate lifecycle assessment and direct cost analysis to assess the environmental and economic viability. Integrated indexes and the TOPSIS method were adopted to systematically evaluate the mortar mixes and determine the optimal mix. The outcomes show that nano additives worked synergically to enhance the mechanical properties of the mortars. The utilization of cenospheres effectively reduced environmental impacts and improved economic feasibility. Nano additives significantly affected the sustainability and economic viability; in particular, the utilization of multi-walled carbon nanotubes increased the material costs. To minimize the impact of the price of multi-walled carbon nanotubes, it is proposed to binarily use less expensive nano silica. In the multi-parameter optimization, the mix with 0.05% multi-walled carbon nanotubes and 0.02% nano silica was recommended to be the optimal mix. Full article

Due to its unique geotechnical properties, loess presents itself as a cost-effective and energy-efficient material for engineering construction, aiding in cost reduction and environmental sustainability. However, to meet engineering specifications, loess often requires enhancement. Evaluating its permeability properties holds significant importance for employing improved loess for construction materials in landfills and artificial water bodies. This study investigates the influence of dry densities, grain size characteristics, grain size distribution, and admixture contents and types on the permeability of improved loess, focusing on the Malan and Lishi loess. The falling head permeability test was conducted to analyze how each factor affects the permeability of the improved loess. The findings indicate that the permeability coefficient decreases with increased dry density and admixture content. Conversely, it demonstrates a linear increase with the average grain size (d₅₀), restricted grain size (d₆₀), and the product of the coefficient of uniformity and coefficient of curvature (C_u × C_c). The primary influencing factor is the type of admixture, followed by C_c and d₆₀. Furthermore, this study developed a predictive model for permeability using a support vector machine (SVM), surpassing the predictive accuracy of linear regression and neural network models. The model provides a robust prediction for the permeability of superior loess material. Full article

To reduce land use and avoid further pollution, incineration for power generation has become the main method for municipal solid waste treatment. This research focused on the potential for transforming Municipal Solid Waste Incineration Bottom Ash (MSWIBA) into a finely ground powder. The impact of the powder’s fineness and the amount of water used on its effectiveness was analyzed using a method called grey theory. MSWIBA was used as a partial substitute for cement in making MSWIBA foam concrete and lightweight wall panels. By modifying the fineness and water utilization of the recycled micro-powder, its maximum activity index can be increased to 90.1. This study determined the influence of factors including apparent dry density, water–cement ratio, foaming agent dilution ratio, and admixture dosage on the strength of the recycled foam concrete, and established the optimal mix ratio. This study employed a combination of physical experiments and numerical simulations to elucidate the impact of panel material, core layer thickness, and layer sequence on sound insulation performance. The simulation results were in close agreement with the experimental findings. Full article

The walleye pollock, Gadus chalcogrammus (Pallas, 1814), is one of the most commercially and ecologically valuable species in the Northwestern Pacific. However, combined pressures of overfishing and environmental changes have led to a substantial decline in its production in Japan and Russia since the 1990s, and a collapse in Korea since the 2000s. The objective of this study was to comprehensively examine its genetic diversity and population structure with an extensive sampling effort of 16 populations across the Northwestern Pacific including South Korea, Japan, and Russia. A multiplex PCR assay composed of seven microsatellite markers revealed a moderate level of observed heterozygosity (Ho = 0.369–0.599), which is lower than that reported in previous studies of this species. All loci were highly polymorphic, with the mean PIC ranging from 0.608 to 0.793. The structure of the 16 populations was characterized by heterozygote deficiency, a modest effective allele number (Ne = 4.551–7.969), low genetic differentiation (F_ST = 0.000–0.054), a weak population structure, a genetic admixture, and no significant correlation between the genetic and geographic distance. These characteristics are typical of pelagic marine species with large population sizes due to a consistent gene flow among populations when there are no physical boundaries in the open ocean. The seasonal and country-specific genetic structure indicated that G. chalcogrammus populations in the Northwestern Pacific region should be managed as a single management unit. The findings from this study provide critical information for future genetic monitoring, conservation management, and the development of strategies aimed at restoring the populations of this species. Full article

Dietary factors may be implicated in the formation of kidney stones and should be closely monitored. To achieve this aim, patients are routinely assessed by means of generic dietary recall, a tool widely used by authors in a range of extensive patient populations to record food intake; the findings obtained, however, may be skewed due to dietary variations and underestimation of the effect of food additives. Fifty Frequent Kidney Stone Formers (FKSFs, mean age: 54.3 ± 13.9 years) with normal kidney function, absence of comorbidities, and reliable compliance were selected from a total of 68 patients’ resident in Sardinia, an Italian island where genetic admixtures have been relatively rare for generations. The study, conducted from 1 January 2020 to 31 December 2023, was aimed at assessing nutritional values based on the meticulous recording of food quantities, quality, and potential modifications related to food preparation. Patients were selected during an initial clinical check-up and all efforts made to ensure they were capable of reliably recording all food and drinks consumed. A seven-day food diary was provided in which food and drink intake and their impact on 24 h urine output was recorded. The following parameters were measured in both foods and urine output: citrates, oxalates, calcium, phosphorous, uric acid, proteins and nitrogen compounds, magnesium, sulfates, potassium, carbohydrates, free fatty acids. Study outcomes established the presence of hypocitraturia, hyperoxaluria, hypercalciuria, and moderately high levels of nitrogen compounds. Univariate analysis followed by multivariate analysis for further confirmation were performed and the following observations made. Citrate intake correlated with citraturia but did not promote oxaluria; calcium intake promoted onset of sulfaturia, azoturia, and ammoniuria, whilst magnesium correlated with magnesiuria but not with oxaluria, calciuria, phosphaturia, and azoturia; sulfate intake elicited onset of azoturia but not kaliuresis; potassium intake promoted oxaluria and protein intake resulted in onset of ammoniuria and azoturia. (A) The chemical composition of urine based on dietary intake is hard to predict without taking into account the presence of dietary and urinary interferents; (B) the geographic isolation of patients studied underlines the importance of epigenetics in maintaining a traditional dietary heritage. (C) Moreover, the widespread use of food additives should consistently be taken into account to ensure a correct diagnosis of FKSF and set up a valid treatment plan. Full article

This study validates the attributes of the mineral carbonation process employing circulating fluidized bed combustion (CFBC) ash, which is generated from thermal power plants, as a medium for carbon storage. Furthermore, an examination was conducted on the properties of construction materials produced through the recycling of carbonated circulating fluidized bed combustion (CFBC) ash. The carbonation characteristics of circulating fluidized bed combustion (CFBC) ash were investigated by analyzing the impact of CO₂ flow rate and solid content. Experiments were conducted to investigate the use of it as a concrete admixture by replacing cement at varying percentages ranging from 0% to 20% by weight. The stability and setting time were subsequently measured. To produce foam concrete, specimens were fabricated by substituting 0 to 30 wt% of the cement. Characteristics of the unhardened slurry, such as density, flow, and settlement depth, were measured, while characteristics after hardening, including density, compressive strength, and thermal conductivity, were also assessed. The findings of our research study validated that the carbonation rate of CFBC ash in the slurry exhibited distinct characteristics compared to the reaction in the solid–gas system. Manufactured carbonated circulating fluidized bed combustion (CFBC) ash, when used as a recycled concrete mixture, improved the initial strength of cement mortar by 5 to 12% based on the 7-day strength. In addition, it replaced 25 wt% of cement in the production of foam concrete, showing a density of 0.58 g/cm³, and the 28-day strength was 2.1 MPa, meeting the density standard of 0.6 grade foam concrete. 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

The development of super high-rise building projects has become crucial for mitigating land shortages in rapidly growing urban areas. Super high-rise steel structures, particularly RC core wall-steel frame systems, have become the preferred choice due to their superior performance, high prefabrication level, and construction efficiency. Despite their benefits, super high-rise buildings face challenges related to higher energy consumption and carbon emissions. Consequently, it is important to analyze the carbon emissions of these buildings throughout their lifecycle and propose low-carbon construction strategies. A carbon emission analysis focused on super high-rise buildings with RC core wall-steel frame structures is conducted in this study. A carbon emission analysis model is constructed based on BIM-enabled LCA through a real-world case study. The emission factor method is combined with the BIM model to calculate carbon emission. Furthermore, carbon emissions across various construction strategies are compared, with a particular focus on the manufacturing processes of the main materials. The results indicate that incorporating admixtures in concrete, along with adopting the electric arc furnace (EAF) method and utilizing recycled scrap steel in steel manufacturing, significantly reduces the carbon emissions of the buildings. Lastly, effective low-carbon approaches for these buildings are proposed. Full article

Water reducer and water-repellent admixture are very important in improving the workability and durability of cement-based materials. However, the synergistic effect of the two types of admixtures has not been well investigated. In this study, polycarboxylate ether-based superplasticizer (PCE) and octyltriethoxysilane (OTS) were adopted as water reducer and water-repellent admixture, respectively. Their synergistic effect on the fluidity, compressive strength, and water absorption rate of cement-based materials was investigated. Particularly, the pore structure and hydration state of cement paste were analyzed using ¹H Low-Field Nuclear Magnetic Resonance (¹H LF NMR). The result showed that the fluidity of cement paste containing different dosages of PCE was reduced by 5–10 mm by incorporating 1% OTS, and the compressive strength at the early age of 3 d of mortar containing high PCE dosage of 0.25% decreased up to 15% by using 1% OTS. In contrast, the compressive strength of mortar containing 0.20% PCE was slightly enhanced by the addition of 1% OTS. ¹H LF NMR analysis revealed that the combination of PCE and OTS would increase the pore size and total pore volume of cement paste, and more bleeding water would be generated at high PCE dosage. The intensity-weighted T₂ values of the main peak (T2¯) implied that both PCE and OTS produced a retardation effect on cement hydration. However, the water absorption rate decreased by 46.6% despite the increase in pore size and total pore volume. The conflict phenomenon powerfully revealed that the internal hydrophobic treatment by OTS has been successfully achieved. Overall, the combination of 0.20% PCE and 1% OTS exerted a positive synergistic effect in improving the compressive strength and water-repelling ability of cement-based materials, which is meaningful for improving their durability and service life. Full article

The use of silico-manganese slag as a substitute for cement in the preparation of concrete will not only reduce pollution in the atmosphere and on land due to solid waste but also reduce the cost of concrete. To explore this possibility, silico-manganese slag concrete was prepared by using silico-manganese slag as an auxiliary cementitious material instead of ordinary silicate cement. The mechanical properties of the silico-manganese slag concrete were investigated by means of slump and cubic compressive strength tests. The rates of mass loss and strength loss of silico-manganese slag concrete were tested after 25, 50, and 75 cycles. The effect of the silica–manganese slag admixture on the microfine structure and properties of concrete was also investigated using scanning electron microscopy (SEM). Finally, the damage to the silica–manganese slag concrete after numerous salt freezing cycles was predicted using the Weibull model. The maximum enhancement of slump and compressive strength by silica–manganese slag was 17.64% and 11.85%, respectively. The minimum loss of compressive strength after 75 cycles was 9.954%, which was 34.96% lower than that of the basic group. An analysis of the data showed that the optimal substitution rate of silica–manganese slag is 10%. It was observed by means of electron microscope scanning that the matrix structure was denser and had less connected pores and that the most complete hydration reaction occurred with a 10% replacement of silica–manganese slag, where an increase in the number of bladed tobermorite and flocculated C-S-H gels was observed to form a three-dimensional reticulated skeleton structure. We decided to use strength damage as a variable, and the two-parameter Weibull theory was chosen to model the damage. The final comparison of the fitted data with the measured data revealed that the model has a good fitting effect, with a fitting parameter above 0.916. This model can be applied in real-world projects and provides a favorable basis for the study of damage to silica–manganese slag concrete under the action of salt freezing. Full article

High-performance concrete (HPC) is commonly used in the main structures of bridges. HPC is widely applied in the main structures of bridges, yet some skepticism remains with integrating fly ash and mineral powder as admixtures into prestressed HPC bridges. To address this, this study conducted scaled-model experiments to analyze the flexural fatigue behavior of prestressed HPC bridges with double-mineral fine powder admixtures (PB-DA). This study derives the similarity criteria for a simply supported beam bridge under a concentrated load based on similarity theory. Subsequently, in following these criteria, a 30 m long actual bridge is scaled down to a 6 m PB-DA at a 1:5 scale. For this scaled PB-DA, the concentrated load is reduced to 1/25 of the actual bridge, while the strain remains the same as in the actual bridge. The double-mineral fine powder admixture (D-A) was produced and used to fabricate PB-DA by mixing fly ash and mineral powder. Five PB-DAs were constructed, with C50 and C80 concrete strength grades, and admixture ranges from 10% to 32%. Sinusoidal half-wave constant stress amplitude loading at 5 Hz frequency was applied, with 2 million fatigue loading cycles. After fatigue loading, a continuously increasing static load was applied until the PB-DA failed. The experimental results show that the upper part of the PB-DA is compressed, and the lower part is in tension. The PB-DA strain distribution from top to bottom generally conforms to the plane section assumption. During 2 million fatigue loading cycles, 200,000 cycles mark the beam strain and stiffness evolution boundary. Below 200,000 cycles, the PB-DA strain rapidly increases, and flexural stiffness quickly decreases. Beyond 200,000 cycles, the rate of increase in strain and the rate of decrease in flexural stiffness significantly slow down. After fatigue loading, the PB-DA displacement increases exponentially under a continuously increasing static load. The crack distribution is uniform across all PB-DA, with the cracks being sparsest at a 30% admixture. A comprehensive analysis shows that all PB-DAs demonstrate good flexural fatigue behavior. Notably, when D-A content reaches 30%, strain increases, but reductions in flexural stiffness and damage in PB-DA significantly decrease. This paper’s conclusions provide a reference for applying D-A at PB-DA. Full article

This paper presents the results of a study of the mineralogical and chemical composition of zinc and lead metallurgical slags. These slags contain numerous elements, including toxic metals, which form conglomerates or multiphase intergrowths. The phase composition of slags is one of the main factors that determine their behaviour in weathering environments, that is, their ability to release metals when exposed to atmospheric factors. In this paper, the release of elements from slags and their mobility in a hypergenic environment is determined based on the results of leachability tests and on geochemical modelling, thus assessing the environmental impact of landfilled slags. The elements released from slags in the largest quantities are zinc and lead. Zn is leached out over a long period of time. It was found that after 12 years, the concentration of Zn in the eluate exceeds by 40 times the permissible value of 200 mg/kg for hazardous waste. The degree of leaching of lead from slags as a function of time (after 12 years), despite its significant solubility in water, is much lower than the degree of leaching of zinc. The most mobile phase components of slags in the studied hypergenic environment are the lead phases (anglesite and galena) and, to a lesser extent, the zinc phases (sphalerite and willemite). Anglesite and galena in almost the entire Eh-pH range, along with admixtures of elements, decompose into ionic forms: PbCl₄²⁻, Pb²⁺, and PbOH⁺. Sphalerite in the soil and water environment (oxidizing and acidic conditions) will decompose into the mobile ionic form Zn²⁺. Willemite, which is resistant to weathering, will undergo similar decomposition. It can therefore be assumed that the carriers of toxic metals are primarily lead sulphides and sulphates, zinc sulphides, and, less frequently, zinc, lead, and iron oxides. Full article

Clays are components in the fine portion of aggregates, less than 75 microns in size (micro-fines), which are usually washed away when producing coarse or fine (manufactured sand) aggregates in quarries. When marginal sources of aggregates are being used, the content of this washed portion can be quite high, and there is an incentive to keep as much of it in the aggregate, including the clays. The present paper presents a comprehensive treatment of the role of clays in terms of the characterization of their composition and quantification of their effects on the rheological and mechanical properties of cementitious systems, as well as the means to mitigate deleterious influences. It is shown that the strategy for neutralizing the effect of micro-fines containing clays on increased water demand in concrete can be quantified in terms of the combination of their content in concrete and their nature as characterized by the methylene blue value (MBV); this is a more rational approach to considering their influence than their content in specific aggregates as specified in standards. The effect of low and medium MBV aggregates on the water requirement can be neutralized by lignosulfonates when their content in the concrete is below a threshold value of about 150 kg/m³; polycarboxylates (PC) are required at higher contents; for high MBV aggregates, a combination of PC and clay mitigating admixture (CMA) is required. It is also demonstrated that with proper treatment, such micro-fines can be turned into useful fillers, enhancing the strength of concrete and thus also serving as a means for reducing cement content. Full article