Pore blocking characteristics of corrosion products formed on Aluminum coating produced by arc thermal metal spray process in 3.5wt.% NaCl solution

Lee, H.S.,Singh, J.K.,Park, J.H. Butterworth Scientific ; Elsevier Science Ltd 2016 Construction and Building Materials Vol.113 No.-

Arc thermal metal spray coating is very efficient process to protect the steel from corrosion in industrial, humid and saline/coastal environments. This paper incorporates the experimental results for the performance of Aluminum coating deposited on mild steel substrate by arc thermal metal spray. Different electrochemical techniques, FE-SEM, Raman spectroscopy and XRD were used to assess the performance of deposited coating. Electrochemical studies revealed the enhanced corrosion resistance properties of coating in 3.5wt.% NaCl solution. The formation of α-Al(OH)<SUB>3</SUB> on coating substrate during exposure periods block the pores of coating and impede the penetration of corrosive species to react with substrate.

Crack propagation speed in ultra high performance concrete (UHPC)

Pyo, S.,Alkaysi, M.,El-Tawil, S. Butterworth Scientific ; Elsevier Science Ltd 2016 Construction and Building Materials Vol.114 No.-

This paper investigates crack speed in ultra-high performance concrete (UHPC) using pre-notched three-point bending specimens. The experimental parameters are fiber volume fraction and rate of loading. A hydraulic servo-controlled testing machine is used to apply lower notch tip strain rates, in the range of 0.025-1.01/s, while a newly developed impact testing system is used to achieve higher notch tip strain rates, ranging from 6.8 to 41.11/s. A high-speed camera is used to record images of the UHPC specimens during testing. Notch tip strain and crack speed are computed from the images, which show that crack speed increases asymptotically as the crack initiation strain rate increases. Crack speeds of up to 514m/s were achieved at the lower notch tip strain rates and up to 1454m/s for the higher notch tip strain rates. The achieved relationships are incorporated into a recently proposed crack-velocity dependent dynamic fracture model. The model is validated using published experimental data and used to show that, like conventional concrete, the strain rate sensitivity of UHPC is strongly associated with the characteristics of dynamic crack growth.

Ultra-fast bull's eye-like self-healing using CNT heater

Kim, Heejin,Yarin, Alexander L.,Lee, Min Wook Butterworth Scientific Ltd. etc. 2019 Polymer Vol.180 No.-

<P><B>Abstract</B></P> <P>In the present work, carbon nanotubes (CNTs) are dispersed in the polydimethylsiloxane (PDMS) matrix and used as an embedded heating source. The electrically conductive CNT layer provides the Joule heating of the released healing materials into cracks. This accelerates the release and polymerization (self-healing) rates. It is demonstrated that with this modification the healing process, which originally required at least 24 h, is shortened to only 10 min. In addition, it is proved that this approach works very well even in the low-temperature environment, where otherwise, the healing efficiency is low because of the high viscosity of the healing agents and reduced rate of the polymerization reaction. The bull's eye-like geometry proposed in this work can be replicated to protect large areas.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The healing time is reduced remarkably from 24 h to 10 min with an improved toughness. </LI> <LI> This approach works very well even in the ice water bath (T~1 °C). </LI> <LI> The bull's eye-like unit geometry is replicable to protect large areas. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Review of magnetostrictive patch transducers and applications in ultrasonic nondestructive testing of waveguides

Kim, Y.Y.,Kwon, Y.E. Butterworth Scientific Ltd., etc.] 2015 Ultrasonics Vol.62 No.-

A magnetostrictive patch transducer (MPT) is a transducer that exploits the magnetostrictive phenomena representing interactions between mechanical and magnetic fields in ferromagnetic materials. Since MPT technology was mainly developed and applied for nondestructive ultrasonic testing in waveguides such as pipes and plates, this paper will accordingly review advances of this technology in such a context. An MPT consists of a magnetic circuit composed of permanent magnets and coils, and a thin magnetostrictive patch that works as a sensing and actuating element which is bonded onto or coupled with a test waveguide. The configurations of the circuit and magnetostrictive patch therefore critically affect the performance of an MPT as well as the excited and measured wave modes in a waveguide. In this paper, a variety of state-of-the-art MPT configurations and their applications will be reviewed along with the working principle of this transducer type. The use of MPTs in wave experiments involving phononic crystals and elastic metamaterials is also briefly introduced.

Hydrodynamic fluorescence emission behavior of molecular rotor-based vinyl polymers used as viscosity sensors

Jin, Young-Jae,Park, Hyosang,Ohk, Young-Jin,Kwak, Giseop Butterworth Scientific Ltd. etc. 2017 Polymer Vol.132 No.-

<P><B>Abstract</B></P> <P>A molecular rotor compound containing an allyl group (aMR) was synthesized and copolymerized with the vinyl monomers methyl methacrylate (MMA), styrene (St), and 2-hydroxyethyl methacrylate (HEMA). The absorption and fluorescence (FL) emission maxima of the solution of aMR in THF were observed at 445 and 485 nm, respectively. The FL quantum yield (FLQY) of aMR in THF was quite low (0.21%). However, it was found that the FL intensity significantly increased as the viscosity of the fluid increased. This change was expressed using the Förster-Hoffmann equation, log <I>I</I> = <I>C</I> + <I>x</I> log <I>η</I>, where <I>I</I> and <I>η</I> are the FL intensity of the probe and the viscosity of the fluid, respectively. The value of <I>x</I> was determined to be 0.66 and 0.53 for the methanol/ethylene glycol mixtures and alcohols, respectively. The absorption and FL emission spectra of the aMR-incorporated vinyl polymers were almost similar to those of aMR. The FLQYs of P(MMA-<I>co</I>-aMR), P(St-<I>co</I>-aMR), P(HEMA-<I>co</I>-MMA-<I>co</I>-aMR) films were 4.9, 4.3, and 5.1%, respectively. These FLQYs are ∼10 times of the values obtained with their solutions. As soon as the polymer film came into contact with the fluids, its FL emission started to decrease and reached an equilibrium state after a few minutes. It was found that the equilibrium FL emission became weaker as the viscosity of fluid decreased. The FL intensity ratio was also expressed using the modified Förster-Hoffmann equation. The <I>x</I> values of P(MMA-<I>co</I>-aMR) for alcohols and methanol/ethylene glycol mixtures, P(St-<I>co</I>-aMR) for hydrocarbons, and P(HEMA-<I>co</I>-MMA-<I>co</I>-aMR) for the methanol/ethylene glycol mixtures were 0.26, 0.24, 0.29, and 0.53 respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A fluorescent molecular rotor was incorporated into various vinyl polymers by copolymerization method. </LI> <LI> The polymer films had much greater fluorescence (FL) quantum yields relative to the solutions. </LI> <LI> When the films were exposed to fluids, the FL emission became weaker as the viscosity of fluid decreased. </LI> <LI> The FL intensity ratios were expressed as a modified Förster -Hoffmann equation and showed high viscosity sensing abilities. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Mechanical properties and setting characteristics of geopolymer mortar using styrene-butadiene (SB) latex

Lee, N.K.,Kim, E.M.,Lee, H.K. Butterworth Scientific ; Elsevier Science Ltd 2016 Construction and Building Materials Vol.113 No.-

The present study assesses the mechanical properties and setting characteristics of geopolymer mortar using styrene-butadiene (SB) latex. Fly ash/slag based geopolymer mortar incorporating SB latex was fabricated, and their setting time, early-age compressive strength and flexural strength were measured in an effort to determine the optimum alkali modulus (SiO<SUB>2</SUB>/Na<SUB>2</SUB>O) of alkali-activator and slag contents in geopolymer. The fastest setting time was achieved by the geopolymer mortar with the slag content of 30% and alkali modulus of 2.27 as exhibiting the initial and final setting time of 9min and 70min, respectively. The flexural strength was improved by 50% when the addition of SB latex increased from 0% to 10% due the enhanced bonding interactions of the geopolymer matrix. Based on the derived mix proportions, the bonding strength and thermal conductivity of the rapid setting geopolymer mortar were examined. The geopolymer mortar incorporating 10% SB latex showed the highest bonding strength of 1.93MPa when using epoxy resin at the interface and the thermal conductivity of 0.506W/(m.K).

Utilization of excavated soil in coal ash-based controlled low strength material (CLSM)

Kim, Y.s.,Do, T.M.,Kim, H.k.,Kang, G. Butterworth Scientific ; Elsevier Science Ltd 2016 Construction and Building Materials Vol.124 No.-

Coal ash generated from the combustion process of thermal power plants and excavated soil from construction sites in Jeolla Province (South Korea) have significant environmental and economic impacts. The aim of this study is to evaluate the feasibility of controlled low strength material (CLSM) production using wastes (e.g., ponded ash, fly ash, and excavated soil) and cementless binder as full replacement of Portland cement in CLSM mixtures by assessing its engineering properties. First, control mixtures were produced with Portland cement or cementless binder, Class F fly ash, ponded ash, and water. Then, for other mixtures, excavated soil substituted for ponded ash in amounts of 10, 20, 30, and 40% by weight. The bleeding, flowability, and initial setting time of fresh CLSM mixtures were measured; afterward, they were hardened and tested for compressive strength, water absorption, and corrosivity. It was found that the engineering properties of CLSM with excavated soil, possibly up to 30%, satisfied the specifications of ACI 229R. In particular, it was found that an increase in excavated soil content as replacement could lead to an improvement in the stability (bleeding rate) of the proposed CLSM mixtures. Finally, it is worth noting that cementless binder could be feasibly used to completely replace Portland cement in CLSM production.

Can credit spreads help predict a yield curve?

Abdymomunov, A.,Kang, K.H.,Kim, K.J. Butterworth Scientific Limited 2016 JOURNAL OF INTERNATIONAL MONEY AND FINANCE - Vol.64 No.-

In this paper we investigate whether information in credit spreads helps improve the forecasts of government bond yields. To do this, we propose and estimate a joint dynamic Nelson-Siegel (DNS) model of the U.S. Treasury yield curve and the credit spread curve. The model accounts for the possibility of regime changes in yield curve dynamics and incorporates a zero lower bound constraint on yields. We show that our joint model produces more accurate out-of-sample density forecasts of bond yields than does the yield-only DNS model. In addition, we demonstrate that incorporating regime changes and a zero lower bound constraint is essential for forecast improvements.

A study on frictional behavior of PMMA against FDTS coated silicon as a function of load, velocity and temperature

Saha, B.,Toh, W.Q.,Liu, E.,Tor, S.B.,Lee, J. Butterworth Scientific ; Elsevier Science Ltd 2016 Tribology international Vol.102 No.-

Rapid developments of soft polymeric materials have inspired for a better understanding of their tribological characteristics. The tribological behavior of polymethylmethacrylate (PMMA) against 1H,1H,2H,2H-perfluorodecyltrichlorosilane [CF<SUB>3</SUB>(CF<SUB>2</SUB>)<SUB>7</SUB>(CH<SUB>2</SUB>)<SUB>2</SUB>SiCl<SUB>3</SUB>] (FDTS) coated silicon (Si) substrate (F-Si) as a function of the applied-temperature, load and sliding velocity was studied and reported in this paper. It was observed that friction coefficient vs. applied-temperature curves follow the viscoelastic behavior of PMMA, which indicates that molecular relaxation of PMMA is the dominating factor of its tribological properties at temperature below its glass transition temperature (T<SUB>g</SUB>). Furthermore, consistent shifts of friction coefficient vs. temperature curves toward low temperatures with increase in load in addition to sliding velocity further signified, the importance of friction induced-temperature on the tribological properties of PMMA.

Durability of sustainable sulfur concrete with fly ash and recycled aggregate against chemical and weathering environments

Shin, M.,Kim, K.,Gwon, S.W.,Cha, S. Butterworth Scientific ; Elsevier Science Ltd 2014 Construction and Building Materials Vol.69 No.-

Fossil fuel consumption is rapidly increasing all over the world, and so is the amount of sulfur yielded as a byproduct of petroleum refining processes. A huge cost of waste disposal will be demanded if no counterplan is prepared for constantly growing sulfur production. As an innovative solution, using sulfur for the role of a binder in concrete has been recently pursued to replace entire cement and water. This study investigates the mechanical and durability properties of sulfur concrete made with fly ash and recycled aggregate; effects of the sustainable materials are explored as an effort to maximize the sustainability of sulfur concrete. Based on the results of preliminary tests, three types of mix proportions are designed for further investigation. The key test variables are the partial replacement of modified sulfur by fly ash and the type of coarse aggregate (natural or recycled). In all concrete mixtures, neither cement nor water is included. The durability properties of sulfur concrete in severe chemical and weathering environments are explored, including chemical resistance, freezing-thawing resistance, and coefficient of thermal expansion. Essential mechanical properties such as compressive and tensile strengths and elastic modulus are also examined.