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 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

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

Advance on risk assessment methods of multiple chemicals combined exposure and its enlightenment to the construction of relevant systems in China

People in the real world are exposed to multiple chemicals via multiple routes and co-exposure to multiple agents may induce joint effects, which draws extensive attention from the international community. Regulations of many countries oblige risk assessors to conduct cumulative risk assessments based on their own guidelines, findings of which provide the basis for scientific decision-making. By analyzing the method and frameworks of international risk assessment models of multiple chemicals, this paper explores the establishment of a risk assessment framework of multiple chemicals combined exposure to in food in China

A laser-engraved wearable sensor for sensitive detection of uric acid and tyrosine in sweat

Wearable sweat sensors have the potential to provide continuous measurements of useful biomarkers. However, current sensors cannot accurately detect low analyte concentrations, lack multimodal sensing or are difficult to fabricate at large scale. We report an entirely laser-engraved sensor for simultaneous sweat sampling, chemical sensing and vital-sign monitoring. We demonstrate continuous detection of temperature, respiration rate and low concentrations of uric acid and tyrosine, analytes associated with diseases such as gout and metabolic disorders. We test the performance of the device in both physically trained and untrained subjects under exercise and after a protein-rich diet. We also evaluate its utility for gout monitoring in patients and healthy controls through a purine-rich meal challenge. Levels of uric acid in sweat were higher in patients with gout than in healthy individuals, and a similar trend was observed in serum

Application of Chitin/Chitosan and Their Derivatives in the Papermaking Industry

Chitin/chitosan and their derivatives have become of great interest as functional materials in many fields within the papermaking industry. They have been employed in papermaking wet-end, paper surface coating, papermaking wastewater treatment, and other sections of the papermaking industry due to their structure and chemical properties. The purpose of this paper is to briefly discuss the application of chitin/chitosan and their derivatives in the papermaking industry. The development of their application in the papermaking area will be reviewed and summarized

RISK21: risk analyzing tool on dietary exposure of phthalic acid esters

Objective To analyze the risks of dietary exposure of diethylhexyl phthalate (DEHP), dibutyl phthalate (DBP), diisononyl phthalate (DINP), butylbenzyl phthalate (BBP), diisobutyl phthalate (DIBP), dimethyl phthalate (DMP) and diethyl phthalate (DEP) to 2-6 years children in China using RISK21, so as to provide risk management strategy for phthalic acid esters (PAEs). Methods RISK PLOT module was used to analyze and rank risks, with toxicity as Y-axis and exposure as X-axis and margin of exposure (MOE) and uncertainty factor as parameters. Matrix calculation was conducted, risks level and rank of 7 kinds of PAEs to 2-6 years children were illustrated by visualized graphs. TTC PLOT module was used to analyze risks of DMP, DEP and DIBP, which were lacking of toxicity data. Results RISK PLOT showed that the risks of 7 kinds of PAEs for general population located in the green area, which demonstrated that they had low risk to 2-6 years children, and the risks of high food consumption population ranked in descending order were DBP, DIBP, DEHP, DMP, DEP, DINP and BBP. TTC PLOT showed that the risks of DMP, DEP and DIBP were lower than the corresponding threshold of toxicological concern (TTC) that demonstrated low risks. Conclusion RISK21 framework and tools could be a very useful tool for risk assessment and further risk management, and low risks of dietary exposure of 7 kinds of PAEs to 2-6 years children in China by RISK21 analyzing

Excellent Photoelectro-Catalytic Performance of In₂S₃/NiFe-LDH Prepared by a Two-Step Method

In this work, we synthesize hierarchical In2S3/NiFe-layered double hydroxide (In2S3/NiFe-LDH) nanoarrays on an F-doped SnO2 glass substrate via a two-step method, which the In2S3 electrode film was firstly prepared using chemical bath deposition on F-doped SnO2 glass substrate, and then the layered NiFe-LDH was deposited on In2S3 electrode film by hydrothermal synthesis. The two-component photoanode In2S3/NiFe-LDH exhibits significantly enhanced photoelectrochemical properties compared with the In2S3 single-component; due to that, the NiFe-LDH nanosheets depositing on the surface of In2S3 nanocrystal can reduce the accumulation of photogenic holes, facilitate the separation of photogenerated charge carriers, and enhance the light response and absorption. After being decorated with the NiFe-LDH nanosheets, the In2S3/NiFe-LDH photoanode displays a lower onset potential of 0.06 V and an enhanced photocurrent density as high as 0.30 mA·cm−2 at the potential of 1.0 V (vs. RHE). Furthermore, it also displays a 90% degradation rate of xylose oxidizing into xylose acid in 3 h under UV light. This work provides a promising approach for designing new heterojunctions applied to biomass degradation