Chloride induced mechanical degradation of ultra-high performance fiber-reinforced concrete:Insights from corrosion evolution paths

Chloride-induced corrosion of ultra-high-performance fiber-reinforced concrete (UHPFRC) inevitably affects structural durability. However, the process of multi-fiber corrosion and mechanical deterioration still lacks sufficient understanding. This work aims to reveal the fiber corrosion degradation mechanism from a microscopic to macroscopic view, applying multiple analytical analyses of atomic absorption spectrometry, SEM-EDS, nano-indentation, polarization, and macroscopic mechanical testing. Results show that the flexural strength of specimens decreases significantly with the increase of corrosion degree, and a clear reduction of up to 47% is found at a high corrosion degree. Elastic modulus and nano-hardness of corroded samples vary in a wide range of 30–189 GPa and 0.16–6.41 GPa. With the increase in fiber content, two distinctive corrosion mechanisms are proposed. The corrosion path deteriorates from fiber edge to inner by the invasion of erosive solution through the matrix at low contents (<2 vol%). Considering impurities, greater interfacial defects and macro-cell potential differences at high contents (≥2 vol%), another corrosion path originates from the fiber inner outward to the matrix. Fiber corrosion damages the fiber’s structural integrity and induces matrix deterioration, the micromechanics of the matrix along the fiber edge 20 μm decreases at least 10% more than the concrete matrix. This work firstly sheds light on the mechanical deterioration of UHPFRC from the perspective of fiber corrosion paths considering different initiation scenarios

Corrosion-induced deterioration and fracture mechanisms in ultra-high-performance fiber-reinforced concretet

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is an excellent material for harsh environments, but corrosion will change its internal microstructure and complicate the fracture evolution, bringing great difficulties in evaluating the long-term service life. Limited attention has been paid to the fracture mechanism of the UHPFRC upon corrosion. In the present study, integrating acoustic emission (AE) and digital image correlation (DIC) techniques are used to assess the micro/macrocracking characteristics of the specimens upon various corrosion degrees. Results show that the 56-day corroded UHPFRC with 2 vol% presents a remarkable decrease rate of 32%, 29% and 30% in the flexural stiffness, flexural strength and compressive strength. During the loading process, compaction of the original defects induced by fiber corrosion is concentrated in the elastic stage, the newborn cracks triggered by loading mainly occur in the strain-hardening stage, and the expansion of cracks mainly lies in the strain-softening stage. Corroded UHPFRC specimens with higher corrosion damage have a greater maximum strain value at the crack. In addition, the failure mode changes from shear crack failure to a brittle failure of tensile crack as corrosion damage increases. The macroscopic destruction of the corroded UHPFRC is a manifestation of internal microdamage evolution in fiber corrosion and matrix deterioration.</p

Corrosion risk and corrosion-induced deterioration of ultra-high performance fiber-reinforced concrete containing initial micro-defects

Micro-defects in UHPFRC, inevitably generated from the manufacturing to engineering service stage, impact its durability under extreme service environments. However, relevant understanding is still insufficient. This work assesses the corrosion risk and corrosion-induced deterioration in UHPFRC containing initial micro-defects, simulated by a combination of mechanical pre-loading and thermal treatment. Analytical analyses include electrochemical tests (OCP, Tafel, EIS), SEM, MIP, compressive strength measurements, etc. Results show that initial defect degree and steel fiber contents have significant effects on the corrosion resistance and mechanical performance of UHPFRC. Micro-cracks and pores are the major channels to deepen fiber corrosion risk, degrading mechanical performance up to 52%-56% in the most severely damaged UHPFRC. The porosity is increased by the corrosion/increased defects and fiber contents up to a growth rate of 35%, 56% and 78%, respectively, as corrosion triggers the occurrence of new defects (e.g., fiber splitting, newborn micro-cracks, pores). The present results provide a reference for predicting the corrosion potential of the defective UHPFRC.</p

Effects of cage vs. net-floor mixed rearing system on goose spleen histomorphology and gene expression profiles

Due to the demands for both environmental protection and modernization of the goose industry in China, the traditional goose waterside rearing systems have been gradually transitioning to the modern intensive dryland rearing ones, such as the net-floor mixed rearing system (MRS) and cage rearing system (CRS). However, the goose immune responses to different dryland rearing systems remain poorly understood. This study aimed to investigate and compare the age-dependent effects of MRS and CRS on the splenic histomorphological characteristics and immune-related genes expression profiles among three economically important goose breeds, including Sichuan White goose (SW), Gang goose (GE), and Landes goose (LD). Morphological analysis revealed that the splenic weight and organ index of SW were higher under CRS than under MRS (p &lt; 0.05). Histological observations showed that for SW and LD, the splenic corpuscle diameter and area as well as trabecular artery diameter were larger under MRS than under CRS at 30 or 43 weeks of age (p &lt; 0.05), while the splenic red pulp area of GE was larger under CRS than under MRS at 43 weeks of age (p &lt; 0.05). Besides, at 43 weeks of age, higher mRNA expression levels of NGF, SPI1, and VEGFA in spleens of SW were observed under MRS than under CRS (p &lt; 0.05), while higher levels of HSPA2 and NGF in spleens of LD were observed under MRS than under CRS (p &lt; 0.05). For GE, there were higher mRNA expression levels of MYD88 in spleens under CRS at 30 weeks of age (p &lt; 0.05). Moreover, our correlation analysis showed that there appeared to be more pronounced positive associations between the splenic histological parameters and expression levels of several key immune-related genes under MRS than under CRS. Therefore, it is speculated that the geese reared under MRS might exhibit enhanced immune functions than those under CRS, particularly for SW and LD. Although these phenotypic differences are assumed to be associated with the age-dependent differential expression profiles of HSPA2, MYD88, NGF, SPI1, and VEGFA in the goose spleen, the underlying regulatory mechanisms await further investigations

Human Hepatocytes with Drug Metabolic Function Induced from Fibroblasts by Lineage Reprogramming

SummaryObtaining fully functional cell types is a major challenge for drug discovery and regenerative medicine. Currently, a fundamental solution to this key problem is still lacking. Here, we show that functional human induced hepatocytes (hiHeps) can be generated from fibroblasts by overexpressing the hepatic fate conversion factors HNF1A, HNF4A, and HNF6 along with the maturation factors ATF5, PROX1, and CEBPA. hiHeps express a spectrum of phase I and II drug-metabolizing enzymes and phase III drug transporters. Importantly, the metabolic activities of CYP3A4, CYP1A2, CYP2B6, CYP2C9, and CYP2C19 are comparable between hiHeps and freshly isolated primary human hepatocytes. Transplanted hiHeps repopulate up to 30% of the livers of Tet-uPA/Rag2−/−/γc−/− mice and secrete more than 300 μg/ml human ALBUMIN in vivo. Our data demonstrate that human hepatocytes with drug metabolic function can be generated by lineage reprogramming, thus providing a cell resource for pharmaceutical applications

Adsorption Behavior of Polymer Chain with Different Topology Structure at the Polymer-Nanoparticle Interface

The effect of the polymer chain topology structure on the adsorption behavior in the polymer-nanoparticle (NP) interface is investigated by employing coarse-grained molecular dynamics simulations in various polymer-NP interaction and chain stiffness. At a weak polymer-NP interaction, ring chain with a closed topology structure has a slight priority to occupy the interfacial region than linear chain. At a strong polymer-NP interaction, the &ldquo;middle&rdquo; adsorption mechanism dominates the polymer local packing in the interface. As the increase of chain stiffness, an interesting transition from ring to linear chain preferential adsorption behavior occurs. The semiflexible linear chain squeezes ring chain out of the interfacial region by forming a helical structure and wrapping tightly the surface of NP. In particular, this selective adsorption behavior becomes more dramatic for the case of rigid-like chain, in which 3D tangent conformation of linear chain is absolutely prior to the 2D plane orbital structure of ring chain. The local packing and competitive adsorption behavior of bidisperse matrix in polymer-NP interface can be explained based on the adsorption mechanism of monodisperse (pure ring or linear) case. These investigations may provide some insights into polymer-NP interfacial adsorption behavior and guide the design of high-performance nanocomposites

On the instrumental variable estimation with many weak and invalid instruments

We discuss the fundamental issue of identification in linear instrumental variable (IV) models with unknown IV validity. We revisit the popular majority and plurality rules and show that no identification condition can be "if and only if" in general. With the assumption of the "sparsest rule", which is equivalent to the plurality rule but becomes operational in computation algorithms, we investigate and prove the advantages of non-convex penalized approaches over other IV estimators based on two-step selections, in terms of selection consistency and accommodation for individually weak IVs. Furthermore, we propose a surrogate sparsest penalty that aligns with the identification condition and provides oracle sparse structure simultaneously. Desirable theoretical properties are derived for the proposed estimator with weaker IV strength conditions compared to the previous literature. Finite sample properties are demonstrated using simulations and the selection and estimation method is applied to an empirical study concerning the effect of trade on economic growth

Stabilizing undulated lamellae by diblock copolymers confined in alternately adsorbed thin films

The self-assembly behavior of AB diblock copolymer confined in staggering alternately adsorbed thin films is studied using the self-consistent field theory (SCFT) and dissipative particle dynamics (DPD), focusing on the emergence and stability of the undulated lamella (UL) phase. Phase diagrams for the volume fraction of blocks, period of the adsorbed pattern and thickness of the confinement are constructed. Our results indicate that the UL phase can be stable in the case with a large period of adsorbed pattern, and is more favorable in the asymmetrical diblock copolymer with volume fraction around f = 0.40, which becomes cylindrical phases (C) with too small f and transforms into tilted lamellae (TL) on the contrary. Furthermore, the number of layers in the UL phases can be regulated by adjusting the period of the adsorbed pattern and the confinement degree of the thin film. In addition, the formation of the UL is verified by DPD simulations. The study demonstrates that the specially confined diblock copolymers provide an efficient route to regulate the stability of the complex UL phases