Study on dimensional stability of ultra-high performance concrete (UHPC)

Ultra-high performance concrete (UHPC), a new cement-based material, has character of superior mechanical properties and excellent durability. Especially, it possesses compressive strength higher than 150 MPa, which is approximately 3 times as that of conventional concrete. UHPC is nearly impermeable to carbon dioxide, chlorides and sulphates. The superior durability leads to long service life with significantly reduced maintenance. This thesis focuses on the dimensional stability of UHPC, which is one of the most significant factors of the material. Unlike in normal concretes which are mixed at a regular water/cement ratio (w/c = 0.32-0.5), UHPC usually consists of extremely low w/c (0.140.24). At the conditions of ultra-low w/c and high dose of superplasticizer, the hydration process of cement particles is different, resulting in the occurrence of high early age shrinkage. High autogenous shrinkage correlated with high binder content makes UHPC highly vulnerable to shrinkage cracking, which requires urgent resolution for its engineering application. On the other hand, at the conditions of ultra-low w/c, abundant amounts of un-hydrated cementitious materials in the matrix may affect the long-term performance of UHPC. The ongoing hydration of cement particles in UHPC has a retrieving effect on physicochemical properties of UHPC, also known as “autogenous/self-healing” products, which plays an important role in determining the microstructure of finally obtained UHPC. This project is proposed to conduct fundamental research on the dimensional stability (early age shrinkage and long-term stability) of cement with partial replacement of ultra-fine fly ash (UFA) under the UHPC condition, especially long-term stability of UHPC in different exposure conditions (the seawater, tap water or outdoors). Results show that the addition of 30% UFA significantly improved the early-age as well as later-age compressive strengths of ordinary and high-volume fly ash concretes. The effectiveness of UFA in the blended system lies in producing high packing density and in accelerating the pozzolanic activity to produce more C–S–H gel by consuming calcium hydroxide (CH) in HVFA concretes. In the case of UHPC specimens exposed to seawater, the CH was efficiently even after 1080 days. TGA/DTG results indicated that the CH was consumed, which was accompanied by the formation of CaCO3 (calcite), due to the 2 carbonation effect at outdoor conditions. Whereas for the water and seawater immersion conditions, the CH was transformed into other reaction products including Mg(OH)2 and ettringite. Fiber addition improved the performance of fly ash based UHPC, because of the formation of a denser microstructure, as evidenced by the dramatic decrease in the diffusion coefficient and porosity. XRD and SEM analyses imply that the UHPC sample exposed to outdoor and seawater condition underwent less deterioration compared to fly ash (FA) containing UHPCs, more calcite was formed than the calcite formed in water condition. The surface layer of the sample immersed in seawater had some brucite and calcite formation as well as Friedel’s salt and sulfoaluminates. However, under the outdoor condition, the surface pH dropped due to the penetration of CO2 into the binder neutralizing the pore solution. As time passed, either large or small sized pores were formed in the seawater because of the expanding effect induced by ettringite, whereas for outdoor environments, the formation of calcites tended to promote the development of medium-sized pores

Effects of dietary copper intake on blood lipids in women of childbearing age and the potential role of gut microbiota

BackgroundCopper (Cu) is a vital trace element involved in numerous physiological processes, including glycolysis and lipid metabolism. Imbalances in Cu homeostasis can contribute to various diseases. However, current research on the impact of Cu on lipid metabolism has yielded inconsistent findings. Moreover, studies investigating the effects of dietary Cu intake on blood lipids among women of childbearing age are rare. Understanding of this relationship could enhance lipid management, given that most women obtain Cu through their diet. Additionally, the gut microbiota may play a role in this process. This study aims to investigate the effects of dietary Cu intake on blood lipids in women of childbearing age and to analyze the role of gut microbiota in this process.MethodsThis study utilized data from the National Health and Nutrition Examination Survey (NHANES) to conduct a preliminary analysis of the correlation between dietary Cu levels and blood lipid indicators in women of childbearing age. Subsequently, an on-site research was conducted to further investigate this relationship, followed by animal experiments to verify the effect of different Cu doses on blood lipid levels. Multiple linear regression models, ANOVA, XGBOOST were employed to analyze the impact of Cu on blood lipids and the role of intestinal microbiota in this process.ResultsIn the population study, the NHANES results were consistent with on-site findings. The TG, and TC levels in women with childbearing were increased with higher dietary Cu intake. Animal experiments have shown that as Cu intake increases, TC levels increase. Furthermore, when the Cu intake reached 8 mg/day (the recommended dietary Cu intake limit of China, RDI), the TG levels in the research animals decrease, alongside a reduction in the abundance of Weissella cibaria (probiotics related to lipid metabolism), and the levels of LPS and IL-6 increase.ConclusionThe blood lipid levels of women of childbearing age increase with higher dietary Cu intake. RDI of 8 mg/day for women of childbearing age in China may need to be appropriately reduced. Regulating the gut microbiota, especially by increasing the abundance of Weissella cibaria may be an effective intervention for blood lipids

Behaviour of steel-reinforced concrete columns under combined torsion based on ABAQUS FEA

A computational model for studying the mechanical performance of steel-concrete columns under combined torsion is established via ABAQUS. The model is validated by experimental results. Through numerical simulations, the influence of the axial load ratio, torsion-bending ratio, concrete strength, steel ratio, longitudinal reinforcement ratio, stirrup ratio, and shear-span ratio on the torsional behaviour of steel-concrete columns is comprehensively investigated. The initial torsion stiffness and ultimate torsion strength of the column increase with increasing concrete strength and decreasing shear-span ratio. The parameters in descending order of influence on the ultimate torsion strength are steel ratio, torsion-bending ratio, tirrup ratio, longitudinal reinforcement ratio, and axial load ratio. Furthermore, the seven parameters in descending order of influence on the ductility coefficient are the steel ratio, shear-span ratio, concrete strength, axial load ratio, stirrup ratio, torsion-bending ratio and longitudinal reinforcement ratio

Laser-induced breakdown spectroscopy for analysis of soil elements

peer reviewedA laser—induced breakdown spectroscopy(LIBS)set—up has been established，and a series of experiments have been carried out with soil samples．The calibration curves of the lines intensities versus the mass fraction of the elements were acquired by the experiment．Eighteen elements including Mg，Ca and Na were found in the sample of the soil around the South—Central University for Nationalities by qualitative analysis．Only three elements，Fe，Mg and Ca，were found in the rock at Zhuyufeng peak．These results indicate that the physical composition of soil sample impact on the precision of LIBS

Behaviour of steel-reinforced concrete columns under combined torsion based on ABAQUS FEA

A computational model for studying the mechanical performance of steel-concrete columns under combined torsion is established via ABAQUS. The model is validated by experimental results. Through numerical simulations, the influence of the axial load ratio, torsion-bending ratio, concrete strength, steel ratio, longitudinal reinforcement ratio, stirrup ratio, and shear-span ratio on the torsional behaviour of steel-concrete columns is comprehensively investigated. The initial torsion stiffness and ultimate torsion strength of the column increase with increasing concrete strength and decreasing shear-span ratio. The parameters in descending order of influence on the ultimate torsion strength are steel ratio, torsion-bending ratio, stirrup ratio, longitudinal reinforcement ratio, and axial load ratio. Furthermore, the seven parameters in descending order of influence on the ductility coefficient are the steel ratio, shear-span ratio, concrete strength, axial load ratio, stirrup ratio, torsion-bending ratio and longitudinal reinforcement ratio.Accepted Author ManuscriptMaterials and Environmen

Detection of Heavy Metal Elements in Fume by Laser-Induced Breakdown Spectroscopy

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Autogenous shrinkage of high performance concrete: a review

Autogenous shrinkage is a major concern in early age cracking of high performance concrete (HPC). Low water-to-binder ratio and incorporation of supplementary cementitious materials (SCMs) can remarkably affect the pore structure, relative humidity, self-stress, degree of hydration, and interface structure; hence, increase the shrinkage in the matrix. In this paper, the mechanism of autogenous shrinkage of HPC and influential factors in its development are discussed. In general, autogenous shrinkage is more pronounced in HPC, albeit, using low heat cement, fly ash, shrinkage reducing agents, lightweight aggregates, and fibers can effectively reduce it. The effects of SCMs on autogenous shrinkage, relationship between different types of shrinkage and autogenous shrinkage as well as the effect of internal curing on autogenous shrinkage need to be further studied

MULTISCALE MODELING FOR HIGH-PERFORMANCE CONCRETE: A REVIEW

High-performance concrete (HPC) has a complex mechanical performance due to its multiscale and multiphase com- posite structure. In this review, the various methods of multiscale modeling from different disciplines are summarized and discussed. The conjoint use of multiscale modeling and other methods such as image reconstruction technology for HPC is introduced. The failure mode modeling of HPC using multiscale methods is discussed. Lastly, the multiscale extended finite-element method (XFEM) for high-performance fiber-reinforced concrete (HPFRC) is elaborated. The benefits and perspectives of developing multiscale modeling techniques for HPC are presented

Topic Modelling for Object-Based Unsupervised Classification of VHR Panchromatic Satellite Images Based on Multiscale Image Segmentation

Image segmentation is a key prerequisite for object-based classification. However, it is often difficult, or even impossible, to determine a unique optimal segmentation scale due to the fact that various geo-objects, and even an identical geo-object, present at multiple scales in very high resolution (VHR) satellite images. To address this problem, this paper presents a novel unsupervised object-based classification for VHR panchromatic satellite images using multiple segmentations via the latent Dirichlet allocation (LDA) model. Firstly, multiple segmentation maps of the original satellite image are produced by means of a common multiscale segmentation technique. Then, the LDA model is utilized to learn the grayscale histogram distribution for each geo-object and the mixture distribution of geo-objects within each segment. Thirdly, the histogram distribution of each segment is compared with that of each geo-object using the Kullback-Leibler (KL) divergence measure, which is weighted with a constraint specified by the mixture distribution of geo-objects. Each segment is allocated a geo-object category label with the minimum KL divergence. Finally, the final classification map is achieved by integrating the multiple classification results at different scales. Extensive experimental evaluations are designed to compare the performance of our method with those of some state-of-the-art methods for three different types of images. The experimental results over three different types of VHR panchromatic satellite images demonstrate the proposed method is able to achieve scale-adaptive classification results, and improve the ability to differentiate the geo-objects with spectral overlap, such as water and grass, and water and shadow, in terms of both spatial consistency and semantic consistency

Application of Different Indices for Soil Heavy Metal Pollution Risk Assessment Comparison and Uncertainty: A Case Study of a Copper Mine Tailing Site

The concentrations of Cu, Zn, As, Pb, Cr, and Cd in soil were analyzed in a mining area in the Inner Mongolia Autonomous Region, China. The average metal concentrations in the soil samples were 204.07 mg/kg, 88.15 mg/kg, 14.47 mg/kg 88.52 mg/kg, 56.45 mg/kg, and 0.235 mg/kg, respectively. Based on the evaluation standards, background values of the soil heavy metals, multiple soil pollution assessment indices, such as the single factor index (Pi), the geological accumulation index (Igeo), the Nemerow index (Pn), the ecological risk index (ER), and the health risk index (HI) were applied to evaluate the soil environmental risks in the study area. It was found that in different soil layer depths (0–10 cm, 10–30 cm, and 30–50 cm), the evaluation result of each index showed that there were significant spatial differences in soil pollution levels, and the focus of different indices differed greatly from each other. The Pi put 18.14% of the area at high risk of soil contamination levels, due to the fact that this index highlights the Cu pollution factor more than other indices and relatively amplifies hazards in some high-risk areas. While the Pn indicated that 61.36% of the study area was at a safe level of soil contamination, it can underestimate the regional soil heavy metal pollution risk. In order to scientifically carry out soil-pollution-risk prevention and control, it is necessary to comprehensively compare and analyze the information disclosed by different indices