Enamel coated steel reinforcement for improved durability and life-cycle performance of concrete structures: microstructure, corrosion, and deterioration

This study is aimed (a) to statistically characterize the corrosion-induced deterioration process of reinforced concrete structures (concrete cracking, steel mass loss, and rebar-concrete bond degradation), and (b) to develop and apply three types of enamel-coated steel bars for improved corrosion resistance of the structures. Commercially available pure enamel, mixed enamel with 50% calcium silicate, and double enamel with an inner layer of pure enamel and an outer layer of mixed enamel were considered as various steel coatings. Electrochemical tests were respectively conducted on steel plates, smooth bars embedded in concrete, and deformed bars with/without concrete cover in 3.5 wt.% NaCl or saturated Ca(OH)₂ solution. The effects of enamel microstructure, coating thickness variation, potential damage, mortar protection, and corrosion environment on corrosion resistance of the steel members were investigated. Extensive test results indicated that corrosion-induced concrete cracking can be divided into four stages that gradually become less correlated with corrosion process over time. The coefficient of variation of crack width increases with the increasing level of corrosion. Corrosion changed the cross section area instead of mechanical properties of steel bars. The bond-slip behavior between the corroded bars and concrete depends on the corrosion level and distribution of corrosion pits. Although it can improve the chemical bond with concrete and steel, the mixed enamel coating is the least corrosion resistant. The double enamel coating provides the most consistent corrosion performance and is thus recommended to coat reinforcing steel bars for concrete structures applied in corrosive environments. Corrosion pits in enamel-coated bars are limited around damage locations --Abstract, page iii

Corrosion resistance of enamel coating modified by calcium silicate and sand particle for steel reinforcement in concrete

Porcelain enamel has stable chemical property in harsh environments such as high temperature, acid and alkaline, and it can also chemically react with substrate reinforcing steel resulting in improved adherence strength. In this study, the corrosion resistances of enamel coating modified by calcium silicate and sand particles, which are designed for improved bond strength with surrounding concrete, were investigated in 3.5 wt% NaCl solution. It consists of two papers that describe the results of the study. The first paper investigates the corrosion behavior of enamel coating modified by calcium silicate applied to reinforcing steel bar in 3.5 wt% NaCl solution by OCP, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The coatings include a pure enamel, a mixed enamel that consists of 50% pure enamel and 50% calcium silicate by weight, and a double enamel that has an inner pure enamel layer and an outer mixed enamel layer. Electrochemical tests demonstrates that both pure and double enamel coatings can significantly improve corrosion resistance, while the mixed enamel coating offers very little protection due to connected channels. The second paper is focused on the electrochemical characteristics of enamel coating modified by sand particle applied to reinforcing steel bar in 3.5 wt% NaCl solution by EIS. Six percentages by weight are considered including 5%, 10%, 20%, 30%, 50%, and 70%. Results reveal that addition of sand particle does not affect its corrosion resistance significantly. Most of the sand particles can wet very well with enamel body, while some have a weak zone which is induced during the cooling stage due to different coefficient of thermal expansion. Therefore, quality control of sand particle is the key factor to improve its corrosion resistance. --Abstract, page iv

Coaxial Cable Sensors and Sensing Instrument for Crack Detection in Bridge Structures -- Phase I: Field Qualification/Validation Planning

The objectives of this study are to pre-test analyze a decommissioned RC bridge that is selected in consultation with New York State Department of Transportation (NYSDOT), and design and plan the field tests of the bridge for the performance qualification and validation of distributed crack sensors and a fast Electrical Time Domain Reflectometry (ETDR) instrument to their full potential. The scope of work includes: (a) Selection of a decommissioned bridge, (b) Pre-test analysis of the select bridge structure to evaluate its progressive damage and determine the locations for sensor deployment, (c) Design and planning of field tests of the select bridge, (d) Field instrumentation with coaxial cable and fiber optical sensors for performance comparison, and (d) Summary of the findings of this study. Once fully validated and demonstrated in field conditions, distributed crack sensors and sensing instruments are expected to play a significant role in routine inspections and bridge ratings and in the rapid assessment of structural conditions for post-event evaluations and responses, improving the safety and security of transportation infrastructure at the height of a crisis. These roles are due primarily to their unique ability of permanently recording the widest crack a RC member experienced during a recent event. Such an attribute ensures the availability of damage data even if a fast ETDR system experiences malfunction during the event, greatly improving the reliability of bridge inspections

Initial Study and Verification of a Distributed Fiber Optic Corrosion Monitoring System for Transportation Structures

For this study, a novel optical fiber sensing system was developed and tested for the monitoring of corrosion in transportation systems. The optical fiber sensing system consists of a reference long period fiber gratings (LPFG) sensor for corrosive environmental monitoring and a LPFG sensor coated with a thin film of nano iron and silica particles for steel corrosion monitoring. The environmental effects (such as pH and temperature) are compensated by the use of the reference LPFG sensor. The sensor design, simulation, and experimental validation were performed in this study to investigate the feasibility of the proposed sensing system for corrosion and environment monitoring. The detailed investigations of the proposed sensing system showed that within the detection limitation of the thin coated layer, the proposed sensor could monitor both the initial and stable corrosion rate consistently. Compared to the traditional electrochemical method, the proposed optical fiber sensing system has a converter coefficient of 1 nm/day=3.746×10-3 A/cm2. Therefore, the proposed nano iron/silica particles dispersed polyurethane coated optical fiber sensor can monitor the critical corrosion information of the host members in real time and remotely. With multiple LPFGs in a single fiber, it is possible to provide a costeffective, distributed monitoring solution for corrosion monitoring of large scale transportation structures

An Embeddable Strain Sensor with 30 Nano-Strain Resolution based on Optical Interferometry

A cost-effective, robust and embeddable optical interferometric strain sensor with nanoscale strain resolution is presented in this paper. The sensor consists of an optical fiber, a quartz rod with one end coated with a thin gold layer, and two metal shells employed to transfer the strain and orient and protect the optical fiber and the quartz rod. The optical fiber endface, combining with the gold-coated surface, forms an extrinsic Fabry—Perot interferometer. The sensor was firstly calibrated, and the result showed that our prototype sensor could provide a measurement resolution of 30 nano-strain (nε) and a sensitivity of 10.01 µε/ µm over a range of 1000 µε. After calibration of the sensor, the shrinkage strain of a cubic brick of mortar in real time during the drying process was monitored. The strain sensor was compared with a commercial linear variable displacement transducer, and the comparison results in four weeks demonstrated that our sensor had much higher measurement resolution and gained more detailed and useful information. Due to the advantages of the extremely simple, robust and cost-effective configuration, it is believed that the sensor is significantly beneficial to practical applications, especially for structural health monitoring

Corrosion Resistance of a Sand Particle-Modified Enamel Coating Applied to Smooth Steel Bars

The protective performance of a sand particle-modified enamel coating on reinforcing steel bars was evaluated in 3.5 wt% NaCl solution by electrochemical impedance spectroscopy (EIS). Seven percentages of sand particles by weight were investigated: 0%, 5%, 10%, 20%, 30%, 50% and 70%. The phase composition of the enamel coating and sand particles were determined with the X-ray diffraction (XRD) technique. The surface and cross-sectional morphologies of the sand particle-modified enamel coating were characterized using scanning electron microscopy (SEM). XRD tests revealed three phases of sand particles: SiO2, CaCO3 and MgCO3. SEM images demonstrated that the enamel coating wetted well with the sand particles. However, a weak enamel coating zone was formed around the sand particles due to concentrated air bubbles, leading to micro-cracks as hydrogen gas pressure builds up and exceeds the tensile strength of the weak zone. As a result, the addition of sand particles into the enamel coating reduced both the coating and corrosion resistances

Coated Steel Rebar for Enhanced Concrete-Steel Bond Strength and Corrosion Resistance

This report summarizes the findings and recommendations on the use of enamel coating in reinforced concrete structures both for bond strength and corrosion resistance of steel rebar. Extensive laboratory tests were conducted to characterize the properties of one- and two-layer enamel coatings. Pseudostatic tests were performed with pullout, beam and column specimens to characterize mechanical properties and develop design equations for the development length of steel rebar in lap splice and anchorage areas. The splice length equation was validated with the testing of large-scale columns under cyclic loading. For corrosion properties, ponding, salt spray, accelerated corrosion, potentiodynamic and electrochemical impedance spectroscopy (EIS) tests were conducted to evaluate the corrosion resistance and performance of enamel-coated steel and rebar. Experimental procedures and observations from various laboratory tests are documented in detail. The corrosion performances of enamel and epoxy coatings were compared. It is concluded that a one-layer enamel coating doped with 50% calcium silicate has improved bond strengths with steel and concrete but its corrosion resistance is low due to porosity in the coating, allowing chloride ions to pass through. Based on limited laboratory tests, a two-layer enamel coating with an inner layer of pure enamel and an outer layer of enamel and calcium silicate mixture has been shown to be practical and effective for both corrosion resistance and bond strength. A coating factor of 0.85 is recommended to use with the current development length equations as specified in ACI318-08. The large-scale column tests indicated that the column-footing lap splice with enamel-coated dowel bars had higher load and energy dissipation capacities compared to uncoated dowel bars. When damaged unintentionally, chemically reactive enamel coatings limit corrosion to a very small area whereas epoxy coatings allow corrosion expansion in a wide area underneath the coating

Social Determinants of Community Health Services Utilization among the Users in China: A 4-Year Cross-Sectional Study

Background To identify social factors determining the frequency of community health service (CHS) utilization among CHS users in China. Methods Nationwide cross-sectional surveys were conducted in 2008, 2009, 2010, and 2011. A total of 86,116 CHS visitors selected from 35 cities were interviewed. Descriptive analysis and multinomial logistic regression analysis were employed to analyze characteristics of CHS users, frequency of CHS utilization, and the socio-demographic and socio-economic factors influencing frequency of CHS utilization. Results Female and senior CHS clients were more likely to make 3–5 and ≥6 CHS visits (as opposed to 1–2 visits) than male and young clients, respectively. CHS clients with higher education were less frequent users than individuals with primary education or less in 2008 and 2009; in later surveys, CHS clients with higher education were the more frequent users. The association between frequent CHS visits and family income has changed significantly between 2008 and 2011. In 2011, income status did not have a discernible effect on the likelihood of making ≥6 CHS visits, and it only had a slight effect on making 3–5 CHS visits. Conclusion CHS may play an important role in providing primary health care to meet the demands of vulnerable populations in China. Over time, individuals with higher education are increasingly likely to make frequent CHS visits than individuals with primary school education or below. The gap in frequency of CHS utilization among different economic income groups decreased from 2008 to 2011

A reporting tool for practice guidelines in healthcare: the RIGHT Statement

The quality of reporting of practice guidelines is often poor and there is no widely accepted guidance or standards for the reporting of practice guidelines in healthcare. An international working group (the RIGHT working group) was therefore established to address this gap. The group followed an existing framework for developing health research reporting guidelines and the EQUATOR (Enhancing the QUAlity and Transparency Of health Research) Network approach. We developed a checklist and an explanation and elaboration document. The RIGHT checklist includes 22 items that we consider essential for good reporting of practice guidelines. These items encompass basic information (items 1-4), background (items 5-9), evidence (items 10-12), recommendations (items 13-15), review and quality assurance (items 16-17), funding and declaration and management of interests (items 18-19), and other information (items 20-22). The RIGHT checklist can assist developers when reporting their guidelines, support journal editors and peer reviewers when considering guideline reports, and help healthcare practitioners understand and implement a guideline

REPORTING ITEMS FOR PRACTICE GUIDELINES IN HEALTHCARE: DOCUMENT RIGHT

Kvaliteta objavljenih kliničkih smjernica često je niska te ne postoje široko prihvaćene upute ili standardi za takav oblik publikacije u zdravstvenoj skrbi. Međunarodna radna skupina RIGHT (Reporting Items for practice Guidelines in HealThcare) uspostavljena je radi rješavanja tog problema. Grupa je pratila postojeći radni okvir za razvoj smjernica ­namijenjenih prikazu rezultata zdravstvenih istraživanja i pristupu mreži EQUATOR (Enhancing the QUAlity and Transparency Of health Research). Sastavljen je popis za provjeru i dokument s objašnjenjima i argumentima. Popis za provjeru RIGHT sastoji se od 22 elementa koje smatramo nužnima za dobro sastavljene kliničke smjernice: osnovni podaci (ele­menti 1 do 4), povjesnica (elementi 5 do 9), dokazi (elementi 10 do 12), preporuke (elementi 13 do 15), vrjednovanje i kontrola kvalitete (elementi 16 i 17), financiranje, izjava o upravljanju i upravljanje sukobom interesa (elementi 18 i 19) i ostale informacije (elementi 20 do 22). Popis za provjeru RIGHT može pomoći autorima u razvoju smjernica, urednicima časopisa i stručnim recenzentima pri njihovu razmatranju za objavu, a zdravstvenim djelatnicima u razumijevanju i primjeni smjernica