Search

Spontaneous combustion of coal is a major problem in coal industry. In order to improve the environmental performance and effectiveness of existing inhibitors used to inhibit coal spontaneous combustion, this study utilized physical inhibitors such as chitosan (CS), acrylic acid (AA), and acrylamide (AM) and copolymerized them with the chemical inhibitor procyanidin (OPC). The resulting composite inhibitor was then in situ polymerized with modified nano-TiO2 to create an environmentally friendly gel-based composite inhibitor, referred to as TiO2/OPC/CPAAM. Scanning electron microscopy analysis revealed a significant increase in the number of laminar folds and pores within the inhibited coal samples. Additionally, thermogravimetric analysis showed that all characteristic temperature points of the inhibited coal samples were raised, with an average increase of 21.34%. Differential scanning calorimetry also indicated a reduction in the total heat release and heat release intervals of the inhibited coal samples. Gas infrared spectroscopy provided evidence that the inhibitory treatment significantly slowed the growth of CO and CO2 during the heating process of the coal samples, leading to an improvement in environmental performance. Furthermore, diffuse reflection infrared spectroscopy testing demonstrated that the inhibitory treatment resulted in the passivation of active groups' free hydroxyls and an increase in the content of stable group ether bonds. Overall, the results of this study indicate that the composite inhibitor TiO2/OPC/CPAAM offers superior inhibition effects on coal spontaneous combustion. [ABSTRACT FROM AUTHOR]

AbstractIn order to study the mechanical properties of seawater sea sand concrete and the durability damage law of seawater sea sand concrete under the action of seawater erosion, corresponding specimens were prepared and subjected to cube compressive strength, flexural strength, and dry-wet cycle tests by taking the volume dosage of glass fibers and polyvinyl alcohol fibers as variables. The test combined SEM scanning and EDS to analyze the microstructure of fiber-reinforced seawater sand concrete, and established a model based on the two-parameter Weibull probability distribution. The results show that the fiber has a significant effect on improving the mechanical properties and erosion resistance of seawater sand concrete. When the total volume content is 0.3% and the mixing ratio is 1:1, the improvement effect is the best. The maximum increase in cubic compressive strength was 24.2%; the maximum increase in flexural strength was 38.8%. After the specimens were subjected to wet and dry cycles for 360d, the maximum reduction in mass loss rate was 41.23%; the maximum reduction in strength loss rate was 27.55%. As observed from the microscopic images, the main disadvantage of SSC is that the salt crystallization and swelling matter produced by the erosion ions will weaken the bond between aggregate and mortar, resulting in defects in the interfacial transition zone (ITZ). Under the action of dry-wet cycles, the alternating dry-wet forces, the expansion pressure generated by expansive substances and the crystallization pressure generated by salt crystallization will change the microstructure, and therefore the damage of the specimen will deepen with the extension of erosion time. The microscopic images also show that the doping fibers can improve the internal integrity and compactness of the matrix, thus significantly improving the mechanical properties and durability of seawater sea sand concrete. In this test, a damage model was established based on the two-parameter Weibull distribution model, and the damage law between strength loss and dry-wet cycles was fitted, which provides a favorable basis to study the damage of seawater sea sand concrete under wet-dry cycling. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fiber concrete exhibits superior performance in various aspects compared to plain concrete and has been widely researched and applied worldwide. However, many industrially made fibers are expensive, and their cost has to be considered before use; thus, it would be economically valuable to find inexpensive fibers with excellent properties to make fiber concrete. Rural areas have many rich straw resources to be disposed of; at the same time, the rapid development of the automobile industry has introduced a large number of used tires containing steel wire with a very low reuse rate. These two low-cost materials can be processed to make fibers, making the study of mechanical properties regarding their incorporation into concrete practically significant for reducing the cost of fiber concrete. Based on this, a three-factor, three-level orthogonal test was conducted to investigate the effects of different dosages of corn straw fibers and scrap steel fibers, as well as the water–cement ratio, on the mechanical properties of concrete. The optimum level of each factor for blended straw–waste-steel-fiber concrete with different mechanical properties was obtained using the polar and ANOVA methods. It was found that the compressive strength, splitting tensile strength, flexural strength, and impact resistance of the specimens after fiber dosing were better than those of plain concrete specimens with the same water–cement ratio. The maximum improvement was 14.96% in cubic compressive strength, 42.90% in tensile strength, and 16.30% in flexural strength, while the maximum improvement in impact energy consumption at the final crack was 228.03%. Combined with SEM microanalysis, the two fibers formed a stronger whole with the C-S-H gel. When the specimen was subjected to load, the two fibers were able to withstand part of the load, thus enhancing the load-bearing capacity. Finally, the optimal mix ratio of blended straw–scrap-steel-fiber concrete was determined to be 0.8% corn straw fibers by volume, 0.6% scrap steel fibers by volume, and a 0.45 water–cement ratio by combining the weights of the levels of each factor under its four different mechanical properties through hierarchical analysis. This analysis of mechanical properties provides a reference for practical applications in future projects. [ABSTRACT FROM AUTHOR]

When using seawater and sea sand as mixes, the mechanical properties and durability of concrete are adversely affected because the raw materials themselves contain harmful ions. Fly ash is the tailings formed in the process of industrial production, the use of which does not require the burning of clinker, reducing CO2 emissions. Moreover, it belongs to a new type of cementitious materials with low emissions and high environmental protection. Fly ash enhances the properties of concrete and reduces the effect of harmful ions on concrete. Based on the above considerations, the corresponding specimens were prepared and subjected to cubic compressive strength, flexural strength, and seawater freezing and thawing resistance tests by using fly ash admixture as the main variable. A combination of macro-analysis and micro-analysis was used to investigate the effect of fly ash on the performance of seawater sea sand concrete. The results showed that fly ash significantly enhanced the mechanical properties and resistance to seawater freezing and thawing of seawater sea sand concrete. The best improvement in compressive strength and resistance to seawater freezing and thawing was achieved at a substitution rate of 20%. The maximum increase in compressive strength was 13.22%. The maximum reduction in mass loss rate was 57.26% and the strength loss rate was 43.14% after the specimens were subjected to seawater freezing and thawing 75 times. The maximum enhancement in flexural strength was 17.06% for a substitution rate of 10%. Through microanalysis, it can be seen that the incorporation of coal ash can enhance the compactness of concrete through the microaggregate effect as well as the volcanic ash reaction to promote the secondary hydration reaction, so as to strengthen the seawater freeze–thaw resistance of seawater sea sand concrete. Finally, the damage prediction model established using the mean GM (1, 1) model of gray system theory meets the requirements of the first level of prediction accuracy and can accurately predict the damage of seawater sea sand concrete under seawater freezing and thawing. [ABSTRACT FROM AUTHOR]

The use of seawater and sea sand as replacements for fresh water and river sand in the preparation of seawater and sea sand concrete can effectively address issues such as high transportation costs, extended construction periods, and resource wastage. Nevertheless, in northern coastal areas, the problem of concrete durability in the complex and changing marine environment is more prominent. Research on the durability of seawater sea sand concrete is beneficial to the widening of its application range. To investigate the impact of glass fiber (GF) and polyvinyl alcohol fiber (PVA) with different blending methods on the seawater freeze–thaw resistance of seawater sea sand concrete (SSC), corresponding specimens were prepared, and seawater freeze–thaw cycling tests were conducted. By adopting the slow-freezing method and combining macro-structure and micro-morphology, the damage mechanism and the deterioration law of fiber-reinforced SSC under seawater freezing and thawing were investigated. The results indicate that, macroscopically, the incorporation of GF and PVA can effectively mitigate the damage to the matrix and reduce the effects of external erosive substances on the rate of strength loss, the rate of mass loss, and the relative dynamic elastic modulus. After 75 cycles, the SSC with a total volume doping of 0.3% and a blending ratio of 1:1 showed a 41.23% and 27.55% reduction in mass loss and strength loss, respectively, and a 29.9% improvement in relative dynamic elastic modulus compared with the basic group. Microscopic analysis reveals that the combined effect of freezing and expansion forces, the expansive substances generated by seawater intrusion into the interior of the matrix, and salt crystallization all weaken the bond between aggregate and mortar, leading to accelerated deterioration of the concrete. The incorporation of fibers enables the matrix to become denser and improves its crack-resistant properties, resulting in a better durability than that of the basic group. The damage prediction model established by the NSGM(1,N) model of gray system theory exhibits high accuracy and is suitable for long-term prediction, accurately predicting the damage of seawater sea sand concrete under seawater freeze–thaw coupling. [ABSTRACT FROM AUTHOR]

As a countermeasure to the problem of brittleness of seawater sea sand concrete (SSC), volumetric admixture of glass fiber (GF) and polyvinyl alcohol (PVA) fiber was used as variable, the corresponding specimens were prepared, and the cube compressive strength, splitting tensile strength, axial compressive strength, and elastic modulus were tested. The microstructure of fiber reinforced seawater sea sand concrete was analyzed by scanning electron microscope (SEM) scanning and energy dispersive spectroscopy (EDS) dot scanning, and a model was established based on the grey system theory. The research results show that the fiber can effectively reduce the formation of cracks, leading to a ductile failure of the specimen. In general, the mechanical properties of mixed fiber were improved better than that of single fiber, and the hybrid ratio 2:1 brings a improvement of 24. 2% and 38. 8% for the compressive strength and splitting tensile strength, respectively. The hybrid ratio of 1:1 increases the axial compressive strength and elastic modulus by 34. 5% and 15. 5%. It was observed by SEM and EDS that fiber incorporation could densify the matrix, while the main disadvantage of SSC was that the salt crystallization generated by corrosive ions and swelling substances weakened the bond between aggregate and mortar, resulting in defects of interfacial transition zone (ITZ) . The established NSGM(1, 3) model has a high accuracy, the accuracy reaches class II and conforms to the long-term prediction, which provides a favorable basis for the study of the strength evolution of fiber reinforced seawater sea sand concrete. [ABSTRACT FROM AUTHOR]

What Is Already Known on This Topic?: The global efforts to address the hepatitis C virus (HCV) are progressing, but there are still significant gaps in the diagnosis and treatment of HCV, leading to an increasing number of deaths related to HCV., What Is Added by This Report?: An extensive investigation was conducted to assess HCV RNA diagnosis, treatment uptake, and associated factors among individuals infected with HCV within Jiangsu Province. The study encompassed a large geographical area and utilized a substantial sample size., What Are the Implications for Public Health Practice?: Implementing focused interventions to improve the timely diagnosis of HCV RNA and increase the uptake of HCV treatment could effectively reduce the future burden of HCV-related health problems, deaths, and healthcare expenses. This is essential for achieving the global target of eliminating hepatitis C., Competing Interests: No conflicts of interest., (Copyright and License information: Editorial Office of CCDCW, Chinese Center for Disease Control and Prevention 2024.)