Expansive mineral growth and concrete deterioration: a microstructural and microanalytical study

In order to evaluate the role of newly-formed minerals in premature deterioration of highway concrete, a three-phase study was undertaken. In the first phase, petrographic and SEM/EDAX analyses were performed to determine chemical and mineralogical changes in the aggregate and cement paste of samples taken from Iowa highways that showed premature deterioration. In the second phase, experimental simulations of environmental changes in highway concrete after applying different deicer chemicals were conducted to evaluate the role of deicers in premature deterioration. In the third phase, experiments were done to evaluate whether crystallization inhibitors can reduce damage and the growth of secondary minerals in concrete and to help understand the mechanism of deterioration by secondary mineral growth in concrete;In the first phase of study, it was evidenced that two major expansive minerals, ettringite and brucite, were responsible for premature deterioration. Severe expansion cracking of cement paste was often associated with ettringite locations, and strongly suggests that secondary ettringite was a major cause. Brucite forms in cement paste of concretes containing reactive dolomite aggregate via dedolomitization reactions. No cracking was observed to be spatially associated with brucite, but expansion stresses associated with its growth at innumerable microlocations might be relieved by cracking at weaker locations in the concrete;Deicer salts cause characteristic concrete deterioration by altering dedolomitization rims at the coarse-aggregate paste interface, altering cement paste and/or forming new secondary minerals. Magnesium in deicer solutions caused the most severe paste deterioration by forming non-cementitious magnesium silicate hydrate and brucite. Chloride in deicer solutions promotes decalcification of paste. CMA and Mg-acetate produced the most deleterious effects on concrete, with Ca-acetate being much less aggressive. In order to use CMA as an alternative deicer and to prevent premature deterioration, it is recommended that it possess a high Ca/Mg ratio;Three types of commercially inhibitor chemicals, polyphosphonate, polyacrylate, and phosphate ester, were effective in reducing the formation of ettringite and also in reducing concrete expansion due to ettringite. Phosphonate inhibitors are the most effective among those inhibitors. These inhibitors are not effective in preventing formation of brucite and MSH from CMA and magnesium acetate solution

Marker of Difference: Historical Construction of Stigmatization toward Zainichi Koreans

Abstract This paper explores the historical construction of stigmatization toward Zainichi Koreans in Japan, as well as the consequences of such stigmatization. Zainichi Koreans are a minority group of ethnic Koreans living in Japan as special permanent residents, a unique identity formed as a result of the history of Japanese war imperialism and post-war nationalism. Zainichi Koreans have been residing in Japan for many generations now, and are no different from Japanese except for their ethnicity, or lack of Japanese blood. The homogeneity of Japan that boasts of pure Japanese blood is constantly conflicted by the long-term presence of Zainichi Koreans, which not only is one of many other ethnic minority groups that has been eroding that highly-sought-after homogeneity but is also a remnant of Japan’s history as aggressive colonizers. This conflict results in the stigmatization of the Zainichi Koreans, which is defined as a historically constructed process through which a person or group of people are seen as threatening the status quo of the society. This stigmatization can be explained by the system justification theory as well as the status characteristic theory, and is present in two aspects, namely structural, as well as intergroup stigmatization. Both posing unique sets of challenges and negative consequences to the Zainichi Koreans

Effect of evaporation through nanoporous medium on diffusiophoresis

Diffusiophoresis near a nanoporous medium is the phenomenon that particles were spontaneously moved from low concentration region to high concentration region. However, unidirectional particle motion impeded further application of this phenomenon and lack of studies about the external convective flow effect such as evaporation through a nanoporous medium were reported. In this work, we investigated the evaporation effect through a nanoporous medium on spontaneous particle exclusion zone induced by diffusiophoresis. Consequently, particles motion was divided into three regimes: diffusiophoresis regime, transition regime, and evaporation regime depending on the evaporation effect. The experiment in which the time of initiating evaporation effect was controlled by adjusting the region of PDMS on a nanoporous medium showed that evaporation plays a critical role in studying the spontaneous particle exclusion zone. This rigorous analysis would provide a useful strategy for optimizing a spontaneous particle preconcentration/detection platform.This work is supported by the Basic Research Laboratory Project (NRF2018R1A4A1022513) and Mid-Career Project (NRF-2020R1A2C3006162) by the Ministry of Science and ICT

Dynamic analysis of the extended space charge layer using chronopotentiometric measurements

In this paper, we experimentally verified the length (LESC) and the concentration (cESC) of the extended space charge (ESC) layer in front of the electrical double layer (EDL) using the chronopotentiometric measurement and the equivalent circuit model analysis. From the experimentation, the coupled-response of the EDL and the ESC layer was discriminated from the contribution of electro-osmotic flow (EOF). In addition, we derived the potential differences across the ESC (VESC) layer using the circuit model of the ICP layer under rigorous consideration of ESC and EDL. As a result, we obtained that VESC was linearly proportional to the square of the applied current (iapplied). Hence, LESC and cESC were quantitatively provided, where LESC is linear to the iapplied and cESC is constant regardless of iapplied. Thus, this experimentation could not only clarify an essential ICP theory but also guide in ESC-based applications.This work is supported by the Basic Research Laboratory Project (NRF2018R1A4A1022513) and Mid-Career Project (NRF-2020R1A2C3006162) by the Ministry of Science and ICT. I. Cho was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (NRF-2020R1F1A1072960)

Exploring the kinetics of switchable polymer surfaces with dynamic tensiometry

Switchable polymer multilayer coatings consisting of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) were prepared via Layer-by-Layer (LbL) assembly and post-functionalized with poly(ethylene glycol methyl ether) (PEG). This resulted in a soft polar coating that reversibly and repeatedly rearranges from hydrophobic to hydrophilic (or vice versa) when contacted with water (or air). Goniometry is used to quantify the forward surface rearrangement in the form of transient measurements of the water contact angle. By examining the time evolution of the water contact angle at various temperatures, the apparent activation energy for the forward surface rearrangement (E[subscript a,f]) can be determined. Further insight can be gained into the kinetics of this surface reconstruction process by utilizing dynamic tensiometry to measure the evolution in the contact angle of a liquid meniscus at several rates and temperatures as it advances or recedes over the multilayer films. A simple first-order thermally-activated rate process is shown to describe the forward and reverse surface reconstruction and enables the shape of the measured tensiometric force curves during repeated immersion and emersion to be predicted quantitatively. Using this model we show that the character of this switchable surface coating can appear to be hydrophobic or hydrophilic depending on a single dimensionless parameter which incorporates the characteristic time-scale for temperature-dependent surface rearrangement, the speed of immersion and the capillary length of the liquid meniscus.Air Force Research Laboratory (Wright-Patterson Air Force Base, Ohio). Propulsion DirectorateUnited States. Air Force Office of Scientific ResearchUnited States. Army Research Office (Contract W911NF-07-D-0004)National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-0819762

Effects of Various Deicing Chemicals on Pavement Concrete Deterioration

The deleterious effects of deicers on concrete pavements and bridges have concerned concrete researchers for several decades. The present study experimentally investigates the effects of different deicers on concrete deterioration. Laboratory simulations of environmental conditions (wet/dry and freeze/thaw cycling) were conducted on highway concrete samples with various deicer chemicals (NaCl, CaClv MgC12, calcium magnesium acetate (CMA) of 5 different Ca/Mg ratios, Ca-acetate, and Mg-acetate). Each deicer produced characteristic effects on the concrete samples by physically and chemically altering the dolomite coarse aggregate, the dolomite coarse aggregate-paste interface, and cement paste. Chloride solutions commonly promoted decalcification of paste and altered ettringite to chloroaluminate. Magnesium-bearing deicer solutions ( e.g., CMA, Mg-acetate and MgC12) caused severe paste deterioration by forming brucite and noncementitious magnesium silicate hydrate. For acetate solutions, the effects caused by Ca-acetate on concrete deterioration was much less severe than those caused by Mg-bearing acetates. For the experimental conditions utilized herein, NaCl solution was the least deleterious to the cement paste and aggregate

PCC Pavement Deterioration and Expansive Mineral Growth

In order to evaluate the importance of newly-formed minerals in the premature deterioration of Iowa highway concrete, a two-phase study was undertaken. In the first phase, we performed petrographic and SEM/EDAX analyses to determine chemical and mineralogical changes in the aggregate and cement paste of samples taken from Iowa concrete highways that showed premature deterioration. In the second phase, we experimentally simulated environmental changes occurring in highway concrete after different deicer chemicals were applied in order to evaluate the role of deicers in premature deterioration. In highways exhibiting premature concrete deterioration, ettringite, 3CaO. Al2O3 . 3CaSO4 .32H2O, completely fills many small voids and lines the walls of larger voids. Microscopic ettringite is also commonly disseminated throughout the paste of many samples. Severe cracking of cement paste is usually associated with ettringite locations, and strongly suggests that ettringite contributed to deterioration. Pyrite, FeS2, is present in coarse/fine aggregates in several concretes. Sulfate ions released by its oxidation contribute to ettringite formation. In poorly performing concretes containing reactive dolomite aggregate, brucite, Mg(OH)2, resulting from partial dedolomitization of the aggregate, was most common. No cracking was observed to be spatially associated with brucite, but most brucite crystals are microscopic in size and widely disseminated in the cement paste of less durable concretes. Expansion stresses associated with its growth at many microlocations may be relieved by cracking at weaker sites in the concrete. In the experimental phase of the study we found that each deicer salt can cause characteristic concrete deterioration by altering dedolomitization rims at the coarse-aggregate paste interface, by altering cement paste, and/or by forming new expansive minerals in the paste. Magnesium in deicer solutions produces the most severe paste deterioration by forming noncementitious magnesium silicate hydrate and brucite. Chloride in deicer solutions promotes decalcification of paste and alters ettringite to chloroaluminate. Acetate seems to accentuate Mg-induced deterioration. Magnesium chloride, calcium magnesium acetate (Ca3Mg7Ac), and magnesium acetate were the most deleterious

Effect of the Phosphorus Gettering on Si Heterojunction Solar Cells

To improve the efficiency of crystalline silicon solar cells, should be collected the excess carrier as much as possible. Therefore, minimizing the recombination both at the bulk and surface regions is important. Impurities make recombination sites and they are the major reason for recombination. Phosphorus (P) gettering was introduced to reduce metal impurities in the bulk region of Si wafers and then to improve the efficiency of Si heterojunction solar cells fabricated on the wafers. Resistivity of wafers was measured by a four-point probe method. Fill factor of solar cells was measured by a solar simulator. Saturation current and ideality factor were calculated from a dark current density-voltage graph. External quantum efficiency was analyzed to assess the effect of P gettering on the performance of solar cells. Minority bulk lifetime measured by microwave photoconductance decay increases from 368.3 to 660.8 mu s. Open-circuit voltage and short-circuit current density increase from 577 to 598 mV and 27.8 to 29.8mA/cm(2), respectively. The efficiency of solar cells increases from 11.9 to 13.4%. P gettering will be feasible to improve the efficiency of Si heterojunction solar cells fabricated on P-doped Si wafers.open1

A Closer Look at Small-Scale Magnetic Flux Ropes in the Solar Wind at 1 AU: Results from Improved Automated Detection

Small-scale interplanetary magnetic flux ropes (SMFRs) are similar to ICMEs in magnetic structure, but are smaller and do not exhibit ICME plasma signatures. We present a computationally efficient and GPU-powered version of the single-spacecraft automated SMFR detection algorithm based on the Grad-Shafranov (GS) technique. Our algorithm is capable of processing higher resolution data, eliminates selection bias caused by a fixed \avg{B} threshold, has improved detection criteria demonstrated to have better results on an MHD simulation, and recovers full 2.5D cross sections using GS reconstruction. We used it to detect 512,152 SMFRs from 27 years (1996 to 2022) of 3-second cadence \emph{Wind} measurements. Our novel findings are: (1) the radial density of SMFRs at 1 au (${\sim}1$ per \si{10^6\kilo\meter}) and filling factor (${\sim}$35\%) are independent of solar activity, distance to the heliospheric current sheet (HCS), and solar wind plasma type, although the minority of SMFRs with diameters greater than ${\sim}$0.01 au have a strong solar activity dependence; (2) SMFR diameters follow a log-normal distribution that peaks below the resolved range ($\gtrsim 10^4$ km), although the filling factor is dominated by SMFRs between $10^5$ to $10^6$ km; (3) most SMFRs at 1 au have strong field-aligned flows like those from PSP measurements; (4) in terms of diameter $d$, SMFR poloidal flux $\propto d^{1.2}$, axial flux $\propto d^{2.0}$, average twist number $\propto d^{-0.8}$, current density $\propto d^{-0.8}$, and helicity $\propto d^{3.2}$. Implications for the origin of SMFRs and switchbacks are briefly discussed. The new algorithm and SMFR dataset are made freely available