The authors at Shenzhen University greatly acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51520105012 and 51278303) and the (Key) Project of Department of Education of Guangdong Province. (No.2014KZDXM051). They also thank the Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, College of Civil Engineering at Shenzhen University for providing testing facilities and equipment.

1. Testing the Specimen and the Manufacturing Process
<ol>
	<li>Acquire a 500 mm long, 14 mm diameter plain steel bar (grade Q235) for the manufacturing of the test specimens.</li>
	<li>Polish the surface of the bar using a fine sandpaper to remove the mill scales on the surface.</li>
	<li>Cut the bar at 30 mm and 470 mm from its left end, as shown in Figure 1, using a cutting machine.</li>
	<li>Measure the weights of the three bar specimens, using a digital electronic scale.</li>
	<li>Measure the diameters of the three specimens using the five methods described in step 2, and record the results of the non-corroded bar specimens.</li>
	<li>Corrode the 440 mm bar specimen using the electrochemical method, as detailed below:
	<ol>
		<li>Cover 70 mm of each end firmly with insulation tape. Attach an electrical wire to one end of the 440 mm bar specimen.</li>
		<li>Mix an adhesive with a hardener in a 1:1 proportion to make epoxy resin. Apply the epoxy resin on the insulated 70 mm ends of the bar specimen uniformly to protect both ends from corrosion.</li>
		<li>Place the 440 mm long bar specimen into a plastic water tank that contains 3.5% NaCl as an electrolyte and a copper plate as a cathode.</li>
		<li>Connect one end of the bar specimen as a node to the positive pole and the cathode copper plate to the negative pole of a direct current (DC) power supplier, respectively, to set up an electrical circuit for the accelerated corrosion of the bar specimen.</li>
		<li>Switch on the DC power supply to apply a constant direct current of 2.5 &#956;A/cm2 onto the bar specimen for the whole period of corrosion.</li>
		<li>Switch off the current to terminate the corrosion process when the amount of corrosion of the bar specimen reaches the anticipated level of corrosion, as estimated using Faraday&#8217;s law.</li>
		<li>Place the above corroded bar specimen into a 12% HCl solution tank for 30 minutes to remove the corrosion products from its surface. Immerse the acid-cleaned bar specimen into a saturated lime water tank for neutralization and further clean using tap water.</li>
		<li>Dry the above cleaned corroded bar specimen in air. Mark its surface for the measurement.</li>
	</ol>
	</li>
	<li>Measure the morphological parameters and corrosion amount of the corroded bar specimen. 
	NOTE: Cleaning does affect the mass loss of a corroded steel bar. Different types of acid solution and the different times of immersion in the acid solution would cause different amounts of mass loss. In this test, however, no comparison was made between different cleaning techniques, For consistency, the cleaning process follows the China National Standard for test methods of long-term performance and durability of ordinary concrete30.</li>
</ol>
2. Measurement Methods and Procedures
<ol>
	<li>Mass loss method
	<ol>
		<li>Place an electronic scale on a horizontal platform and zero it.</li>
		<li>Place the polished bar specimen before corrosion horizontally onto the electronic scale and take a reading from the scale as the mass of a non-corroded steel bar m0 (g).</li>
		<li>Place the cleaned bar specimen after corrosion horizontally onto the electronic scale and take a reading from the scale as the mass of the corroded steel bar mc (g).</li>
		<li>Calculate the amount of corrosion of the bar using an equation of Qcor= (mc-m0)/m0x100%.</li>
		<li>Calculate the average area of the residual section of the corroded bar specimen using an equation Asc=As0(1-Qcor), where, As0 is the area of a non-corroded steel bar.</li>
	</ol>
	</li>
	<li>Vernier caliper method
	<ol>
		<li>Mark the surface of the bar specimen along its length in 10 mm intervals from the left end of the bar using a marker pen, as shown in Figure 1.</li>
		<li>Move the Vernier scale of the caliper to its original position. Make the two jaws touch each other and line up the two zero lines of the Vernier and main scales. Then push its zero button to zero the Vernier scale.</li>
		<li>Place the Vernier caliper across the diameter of the bar specimen. Move the Vernier scale to make its two jaws touch the bar surface gently. Measure the diameter of the bar specimen at the marked section and at the given angle.</li>
		<li>Repeat step 2.2.3 four times to measure the bar diameters at the marked section and at angles of 0&#176;, 45&#176;, 90&#176; and 135&#176;, respectively, as shown in Figure 2.</li>
		<li>Average the above four measured diameters and take it as the representative diameter Di (mm) of the bar specimen at the marked section.</li>
		<li>Calculate the cross-sectional area of the bar specimen at the marked section using an equation Ai=pDi2/4 (mm2).</li>
		<li>Repeat steps 2.2.3 to 2.2.6 for all the marked sections of the bar specimen to measure the distribution of its cross sections along its length after corrosion.</li>
	</ol>
	</li>
	<li>Drainage method
	<ol>
		<li>Set up the electromechanical universal testing (EUT) machine, as shown in Figure 3.</li>
		<li>Place a glass container under the head of the EUT machine and pour tap water into the container until the water level reaches the outlet.</li>
		<li>Place a 200 mL beaker on the platform of an electronic scale right below the outlet of the glass container.</li>
		<li>Clamp one end of the bar specimen using the head of the EUT machine vertically.</li>
		<li>Switch on the EUT machine to move its head down slowly until the other end of the bar specimen just touches the top surface of the water in the container.</li>
		<li>Take the initial reading of the electronic scale as Mi.</li>
		<li>Run the EUT machine to move the bar specimen down into the water in the container at a rate of 1.0 mm/min.</li>
		<li>Take the final reading of the electronic scale as Mi+1 for the mass of the water that has been discharged from the container due to the 10 mm displacement of the bar specimen into the water in the container.</li>
		<li>Assume the cross-section of the 10 mm displaced bar specimen is uniform, calculate the cross-sectional area of the h=10 mm displaced bar using the equation of Ai= (Mi+1 - Mi)/(&#961;h), where (Mi+1 - Mi ) is the measured mass of the water discharged from the container for the 10 mm displaced bar specimen. &#961;=1,000 kg/m3 is the density of water.</li>
		<li>Repeat steps 2.3.6 to 2.3.9 for each 10 mm long displaced bar specimen until displacing the whole length of the bar into the water to measure the distribution of bar cross sections along its length.</li>
	</ol>
	</li>
	<li>3D scanning method
	<ol>
		<li>Spray white developer on the surface of the bar specimen and dry it in air. Place it horizontally onto the platform of a 3D scanner, as shown in Figure 4.</li>
		<li>Calibrate the position of the bar specimen on the platform of the 3D scanner by randomly making white small dots on label paper for the 3D reconstruction of the bar specimen.</li>
		<li>After launching the 3D scanner and the corresponding data extraction software, scan the bar specimen along its length and collect the corresponding scanned data via the 3D scanner. Use manufacturer&#8217;s instructions.</li>
		<li>Develop the spatial model of the bar specimen using the software and collect the relevant date files.</li>
		<li>Place the developed spatial model data of the bar specimen and two self-compiled MATLAB programs in the same folder of a computer.</li>
		<li>Run the first MATLAB program on the developed spatial model data of the bar specimen to generate the relevant MAT file. Save the obtained MAT file in the same folder.</li>
		<li>Run the second MATLAB program on the above obtained MAT file to generate the relevant morphological data of the bar specimen, including sectional area, moment of inertia, polar moment of inertia, eccentric distance etc.</li>
	</ol>
	</li>
	<li>XCT method 
	NOTE: After the four measurements on the 440 mm long bar specimen, the fifth measurement was done on the 30 mm long bar specimens using the XCT method due to its bar length limitation.
	<ol>
		<li>Cut a 30 mm bar specimen from both ends of a 500 mm long steel bar and from the 440 mm long corroded steel bar, as shown in Figure 1. Use them as the non-corroded and corroded bar specimens, respectively.</li>
		<li>Place the bar specimens onto the rotatable platform of the XCT instrument, as shown in Figure 5. Close the door of the XCT instrument. The bar specimen is sandwiched between the radioactive source and the signal receiver of the XCT instrument.</li>
		<li>Run the XCT operation software installed on a computer to set up shooting parameters. Adjust the bar specimen to the shooting position.</li>
		<li>Set up the pixel size and magnification factor in the &#8220;image control&#8221; table of the XCT instrument operation software.</li>
		<li>Run the XCT instrument by clicking the Start button to scan the bar specimen. Collect the scanned data of bar specimen.</li>
		<li>Run the software package on the above scanned data to produce the geometric parameters of the bar specimen accordingly.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Cavaco, E. S., Bastos, A., Santos, F. A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+corrosion+on+the+behaviour+of+precast+concrete+floor+systems.">Effects of corrosion on the behaviour of precast concrete floor systems.</a> Construction &amp; Building Materials. 145, (2017).</li><li>Cavaco, E. S., Neves, L. A. C., Casas, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+robustness+to+corrosion+in+the+life+cycle+assessment+of+an+existing+reinforced+concrete+bridge.">On the robustness to corrosion in the life cycle assessment of an existing reinforced concrete bridge.</a> Structure and Infrastructure Engineering. 14 (2), 137-150 (2017).</li><li>Muthulingam, S., Rao, B. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-uniform+corrosion+states+of+rebar+in+concrete+under+chloride+environment.">Non-uniform corrosion states of rebar in concrete under chloride environment.</a> Corrosion Science. 93, 267-282 (2015).</li><li>Apostolopoulos, C. A., Papadakis, V. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Consequences+of+steel+corrosion+on+the+ductility+properties+of+reinforcement+bar.">Consequences of steel corrosion on the ductility properties of reinforcement bar.</a> Construction &amp; Building Materials. 22 (12), 2316-2324 (2008).</li><li>Fernandez, I., Bair&#225;n, J. M., Mar&#237;, A. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Corrosion+effects+on+the+mechanical+properties+of+reinforcing+steel+bars.+Fatigue+and+&#963;+-+&#949;+behavior.">Corrosion effects on the mechanical properties of reinforcing steel bars. Fatigue and &#963; - &#949; behavior.</a> Construction &amp; Building Materials. 101, 772-783 (2015).</li><li>Papadopoulos, M. P., Apostolopoulos, C. A., Zervaki, A. D., Haidemenopoulos, G. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Corrosion+of+exposed+rebars,+associated+mechanical+degradation+and+correlation+with+accelerated+corrosion+tests.">Corrosion of exposed rebars, associated mechanical degradation and correlation with accelerated corrosion tests.</a> Construction &amp; Building Materials. 25 (8), 3367-3374 (2011).</li><li>Castro, H., Rodriguez, C., Belzunce, F. J., Canteli, A. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+properties+and+corrosion+behaviour+of+stainless+steel+reinforcing+bars.">Mechanical properties and corrosion behaviour of stainless steel reinforcing bars.</a> Journal of Materials Processing Technology. 143 (1), 134-137 (2003).</li><li>Almusallam, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+degree+of+corrosion+on+the+properties+of+reinforcing+steel+bars.">Effect of degree of corrosion on the properties of reinforcing steel bars.</a> Construction &amp; Building Materials. 15 (8), 361-368 (2001).</li><li>Papadopoulos, M. P., Apostolopoulos, C. A., Alexopoulos, N. D., Pantelakis, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+salt+spray+corrosion+exposure+on+the+mechanical+performance+of+different+technical+class+reinforcing+steel+bars.">Effect of salt spray corrosion exposure on the mechanical performance of different technical class reinforcing steel bars.</a> Materials &amp; Design. 28 (8), 2318-2328 (2007).</li><li>Zhang, W., Song, X., Gu, X., Li, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tensile+and+fatigue+behavior+of+corroded+rebars.">Tensile and fatigue behavior of corroded rebars.</a> Construction &amp; Building Materials. 34 (5), 409-417 (2012).</li><li>Clark, L. A., Chan, A. H. C., Du, Y. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Residual+capacity+of+corroded+reinforcing+bars.">Residual capacity of corroded reinforcing bars.</a> Magazine of Concrete Research. 57 (3), 135-147 (2005).</li><li>Chan, A. H. C., Clark, L. A., Du, Y. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+corrosion+on+ductility+of+reinforcing+bars.">Effect of corrosion on ductility of reinforcing bars.</a> Magazine of Concrete Research. 57 (7), 407-419 (2005).</li><li>Zhu, W., Fran&#231;ois, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Corrosion+of+the+reinforcement+and+its+influence+on+the+residual+structural+performance+of+a+26-year-old+corroded+RC+beam.">Corrosion of the reinforcement and its influence on the residual structural performance of a 26-year-old corroded RC beam.</a> Construction &amp; Building Materials. 51 (2), 461-472 (2014).</li><li>Fran&#231;ois, R., Khan, I., Dang, V. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impact+of+corrosion+on+mechanical+properties+of+steel+embedded+in+27-year-old+corroded+reinforced+concrete+beams.">Impact of corrosion on mechanical properties of steel embedded in 27-year-old corroded reinforced concrete beams.</a> Materials &amp; Structures. 46 (6), 899-910 (2013).</li><li>Torres-Acosta, A. A., Castro-Borges, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Corrosion-Induced+Cracking+of+Concrete+Elements+Exposed+to+a+Natural+Marine+Environment+for+Five+Years.">Corrosion-Induced Cracking of Concrete Elements Exposed to a Natural Marine Environment for Five Years.</a> Corrosion. 69 (11), 1122-1131 (2013).</li><li>Li, D., Wei, R., Du, Y., Guan, X., Zhou, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+methods+of+geometrical+parameters+and+amount+of+corrosion+of+steel+bar.">Measurement methods of geometrical parameters and amount of corrosion of steel bar.</a> Construction &amp; Building Materials. 154, 921-927 (2017).</li><li>Kashani, M. M., Crewe, A. J., Alexander, N. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+a+3D+optical+measurement+technique+for+stochastic+corrosion+pattern+analysis+of+reinforcing+bars+subjected+to+accelerated+corrosion.">Use of a 3D optical measurement technique for stochastic corrosion pattern analysis of reinforcing bars subjected to accelerated corrosion.</a> Corrosion Science. 73 (13), 208-221 (2013).</li><li>Tang, F., Lin, Z., Chen, G., Yi, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+corrosion+pit+measurement+and+statistical+mechanical+degradation+analysis+of+deformed+steel+bars+subjected+to+accelerated+corrosion.">Three-dimensional corrosion pit measurement and statistical mechanical degradation analysis of deformed steel bars subjected to accelerated corrosion.</a> Construction &amp; Building Materials. 70 (2), 104-117 (2014).</li><li>Zhang, W., Zhou, B., Gu, X., Dai, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Probability+Distribution+Model+for+Cross-Sectional+Area+of+Corroded+Reinforcing+Steel+Bars.">Probability Distribution Model for Cross-Sectional Area of Corroded Reinforcing Steel Bars.</a> Journal of Materials in Civil Engineering. 26 (5), 822-832 (2013).</li><li>Wang, X. G., Zhang, W. P., Gu, X. L., Dai, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+residual+cross-sectional+areas+of+corroded+bars+in+reinforced+concrete+structures+using+easy-to-measure+variables.">Determination of residual cross-sectional areas of corroded bars in reinforced concrete structures using easy-to-measure variables.</a> Construction &amp; Building Materials. 38, 846-853 (2013).</li><li>Stewart, M. G., Al-Harthy, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pitting+corrosion+and+structural+reliability+of+corroding+RC+structures:+Experimental+data+and+probabilistic+analysis.">Pitting corrosion and structural reliability of corroding RC structures: Experimental data and probabilistic analysis.</a> Reliability Engineering &amp; System Safety. 93 (3), 373-382 (2008).</li><li>Darmawan, M. S., Stewart, M. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+Spatially+Variable+Pitting+Corrosion+on+Structural+Reliability+of+Prestressed+Concrete+Bridge+Girders.">Effect of Spatially Variable Pitting Corrosion on Structural Reliability of Prestressed Concrete Bridge Girders.</a> Australian Journal of Structural Engineering. 6 (2), 147-158 (2015).</li><li>Stewart, M. G., Mullard, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatial+time-dependent+reliability+analysis+of+corrosion+damage+and+the+timing+of+first+repair+for+RC+structures.">Spatial time-dependent reliability analysis of corrosion damage and the timing of first repair for RC structures.</a> Engineering Structures. 29 (7), 1457-1464 (2007).</li><li>Kashani, M. M., Lowes, L. N., Crewe, A. J., Alexander, N. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Finite+element+investigation+of+the+influence+of+corrosion+pattern+on+inelastic+buckling+and+cyclic+response+of+corroded+reinforcing+bars.">Finite element investigation of the influence of corrosion pattern on inelastic buckling and cyclic response of corroded reinforcing bars.</a> Engineering Structures. 75, 113-125 (2014).</li><li>Apostolopoulos, C. A., Demis, S., Papadakis, V. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chloride-induced+corrosion+of+steel+reinforcement+-+Mechanical+performance+and+pit+depth+analysis.">Chloride-induced corrosion of steel reinforcement - Mechanical performance and pit depth analysis.</a> Construction and Building Materials. 38, 139-146 (2013).</li><li>Imperatore, S., Rinaldi, Z., Drago, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Degradation+relationships+for+the+mechanical+properties+of+corroded+steel+rebars.">Degradation relationships for the mechanical properties of corroded steel rebars.</a> Construction and Building Materials. , 219-230 (2017).</li><li>Kashani, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Size+effect+on+inelastic+buckling+behaviour+of+accelerated+pitted+1+corroded+bars+in+porous+media.">Size effect on inelastic buckling behaviour of accelerated pitted 1 corroded bars in porous media.</a> Journal of Materials in Civil Engineering. 29 (7), (2017).</li><li>Meda, A., Mostosi, S., Rinaldi, Z., Riva, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+evaluation+of+the+corrosion+influence+on+the+cyclic+behaviour+of+RC+columns.">Experimental evaluation of the corrosion influence on the cyclic behaviour of RC columns.</a> Engineering Structures. 76, 112-123 (2014).</li><li>Kashani, M. M., Crewe, A. J., Alexander, N. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+capacity+assessment+of+corroded+RC+bridge+piers.">Structural capacity assessment of corroded RC bridge piers.</a> Proceedings of the Institution of Civil Engineers - Bridge Engineering. 170 (1), 28-41 (2017).</li><li>National Standard of the People's Republic of China. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Standard for test methods of long-term performance and durability of ordinary concrete, Ministry of Housing and Urban-Rural Development of the People's Republic of China, GB/T 50082-2009. , (2009).</li></ol>

The authors have nothing to disclose.

Figure 6A and 6B show that the measured diameters of the non-corroded bar specimen do not vary significantly along its length. The maximum difference between the measured diameters along the bar length is only about 0.11 mm with a maximum deviation of 0.7%. This indicates that the geometry of a non-corroded bar can be well evaluated using a Vernier caliper. However, the measured diameters at different angles of the same cross-section differ consistently and considerably from...

Corrosion of a steel bar is one of the principal reasons for deterioration of a concrete structure and is caused by concrete carbonation and/or chloride intrusion. In concrete carbonation, corrosion tends to be generalized; while in chloride intrusion, it becomes more localized1,2. No matter what the causes are, corrosion cracks the concrete cover from radial expansion of corrosion products, deteriorates the bond between a steel bar and its surrounding concrete, penetrates the bar surfaces, and decreases the bar cross-sectional area considerably3,4.
Due to the non-homogeneity of structural concrete and variations in the service environment, corrosion of a steel bar occurs randomly over its surface and along its length with great uncertainty. Contrary to the generalized uniform corrosion caused by concrete carbonation, the pitting corrosion caused by chloride intrusion causes attack penetration. Furthermore, it causes the residual section of a corroded bar to vary considerably among the bar surface and length. As a result, the bar strength and bar ductility decrease. Extensive research has been performed to study the effects of corrosion on mechanical properties of a steel bar5,6,7,8,9,10,11,12,13,14,15. However, less attention has been given to the measurement methods of morphological parameters and corrosion characteristics of steel bars.
Some researchers have used mass loss to evaluate the amount of corrosion of a steel bar5,10,11,14. However, this method can only be used to determine the average value of the residual sections and cannot measure the distribution of the sections along its length. Zhu and Franco have improved this method by cutting a single steel bar into a series of short segments and weighing each segment to determine variations of the areas of the residual sections along its length13,14. However, this method causes extra loss of the steel material during the cutting and cannot touch the minimum residual section of the corroded bar exactly, which dominates its bearing capacity. A Vernier caliper is also used to measure the geometric parameters of a steel bar14,15. However, the residual section of a corroded bar is very irregular, and there is always a significant deviation between the measured and actual sectional dimensions of a corroded bar. Based on Archimedes&#39; principle, Clark et al. adopted the drainage method to measure the residual sections of a corroded bar along its length, but displacement of the bar was manually controlled without significant accuracy in this case11. Li et al. improved this drainage method by using an electric motor to automatically control the displacement of a steel bar and measure results more accurately16. Finally, over the past few years, with the development of 3D scanning technology, this method has been used to measure the geometric dimensions of a steel bar17,18,19,20. Using 3D scanning, the diameter, residual area, centroid, eccentricity, moment of inertia, and corrosion penetration of a steel bar can be precisely acquired. Although researchers have used these methods in different experimental settings, there has not been a comparison and evaluation of the methods with respect to their precision, suitability and applicability.
Corrosion, particularly pitting corrosion, compared to generalized corrosion, not only changes the mechanical properties of corroded bars but also decreases the residual bearing capacity and service life of concrete structures. More accurate measurements of morphological parameters of corroded steel bars for the spatial variability of corrosion along bar length are imperative for more reasonable assessments of bar mechanical properties. This will help evaluate the safety and reliability of reinforced concrete (RC) structures damaged by corrosion more precisely21,22,23,24,25,26,27,28,29.
This protocol compares the five discussed methods for measuring the geometry and amount of corrosion of a steel bar. A single, 500 mm long and 14 mm in diameter, plain round bar was used as the specimen and subjected to accelerated corrosion in the lab. Its morphology and level of corrosion were carefully measured before and after using each method, including mass loss, a Vernier caliper, drainage measurements, 3D scanning, and X-ray micro computed tomography (XCT). Finally, the applicability and suitability of each were evaluated.
It should be noted that the ribbed bars embedded in concrete, not the plain bars exposed to air, are commonly used in concrete structures and subjected to corrosion. For ribbed bars, the Vernier caliper may not be as easily applied. Because these bars corrode in concrete, their surface penetration is more irregular compared to bars exposed to air11. However, this protocol is geared towards the applicability of analysis of different measurement methods on the same bar; therefore, it uses a naked plain bar as the specimen to eliminate the influence of ribs and concrete non-homogeneity on morphological parameter measurements. Further work on the measurement of corroded ribbed bars using other methods may be carried out in the future.

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applicability analysis of assessment methods for morphological parameters of corroded steel bars

The irregular and uneven residual sections along the length of a corroded steel bar substantially change its mechanical properties and significantly dominate the safety and performance of an existing concrete structure. As a result, it is important to measure the geometry and amount of corrosion of a steel bar in a structure properly to assess the residual bearing capacity and service life of the structure. This paper introduces and compares five different methods for measuring the geometry and amount of corrosion of a steel bar. A single 500 mm long and 14 mm diameter steel bar is the specimen that is subjected to accelerated corrosion in this protocol. Its morphology and the amount of corrosion were carefully measured before and after using mass loss measurements, a Vernier caliper, drainage measurements, 3D scanning, and X-ray micro-computed tomography (XCT). The applicability and suitability of these different methods were then evaluated. The results show that the Vernier caliper is the best choice for measuring the morphology of a non-corroded bar, while 3D scanning is the most suitable for quantifying the morphology of a corroded bar.

Figure 6 shows the diameters of the 500 mm long non-corroded bar specimen at angles of 0&#176;, 45&#176;, 90&#176;, and 135&#176; for each section along its length measured using Vernier calipers. The bars were then cut into three parts, as shown in Figure 1.
Figure 7 presents the cross-sectional areas of the non-corroded bar specimens alon...

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Applicability Analysis of Assessment Methods for Morphological Parameters of Corroded Steel Bars

This paper measures the geometry and the amount of corrosion of a steel bar using different methods: mass loss, calipers, drainage measurements, 3D scanning, and X-ray micro-computed tomography (XCT).

The irregular and uneven residual sections along the length of a corroded steel bar substantially change its mechanical properties and significantly ...

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6.3K Views.  Shenzhen University. This paper measures the geometry and the amount of corrosion of a steel bar using different methods: mass loss, calipers, drainage measurements, 3D scanning, and X-ray micro-computed tomography (XCT).

Video: Applicability Analysis of Assessment Methods for Morphological Parameters of Corroded Steel Bars

Potentiodynamic Corrosion Testing

Different metallic materials have different polarization characteristics as dictated by the open circuit potential, breakdown potential, and passivation potential of the material. The detection of these electrochemical parameters identifies the corrosion factors of a material. A reliable and well-functioning corrosion system is required to achieve this.
Corrosion of the samples was achieved via a potentiodynamic polarization technique employing a three-electrode configuration, consisting of reference, counter, and working electrodes. Prior to commencement a baseline potential is obtained. Following the stabilization of the corrosion potential (Ecorr), the applied potential is ramped at a slow rate in the positive direction relative to the reference electrode. The working electrode was a stainless steel screw. The reference electrode was a standard Ag/AgCl. The counter electrode used was a platinum mesh. Having a reliable and well-functioning in vitro corrosion system to test biomaterials provides an in-expensive technique that allows for the systematic characterization of the material by determining the breakdown potential, to further understand the material's response to corrosion. The goal of the protocol is to set up and run an in vitro potentiodynamic corrosion system to analyze pitting corrosion for small metallic medical devices.

Here, we present a protocol to set up and run an in vitro potentiodynamic corrosion system to analyze pitting corrosion for small metallic medical devices.

Different metallic materials have different polarization characteristics as dictated by the open circuit potential, breakdown potential, and passivation ...

Environment

Metal Corrosion and the Efficiency of Corrosion Inhibitors in Less Conductive Media

Material corrosion can be a limiting factor for different materials in many applications. Thus, it is necessary to better understand corrosion processes, prevent them and minimize the damages associated with them. One of the most important characteristics of corrosion processes is the corrosion rate. The measurement of corrosion rates is often very difficult or even impossible especially in less conductive, non-aqueous environments such as biofuels. Here, we present five different methods for the determination of corrosion rates and the efficiency of anti-corrosion protection in biofuels: (i) a static test, (ii) a dynamic test, (iii) a static test with a reflux cooler and electrochemical measurements (iv) in a two-electrode arrangement and (v) in a three-electrode arrangement. The static test is advantageous due to its low demands on material and instrumental equipment. The dynamic test allows for the testing of corrosion rates of metallic materials at more severe conditions. The static test with a reflux cooler allows for the testing in environments with higher viscosity (e.g., engine oils) at higher temperatures in the presence of oxidation or an inert atmosphere. The electrochemical measurements provide a more comprehensive view on corrosion processes. The presented cell geometries and arrangements (the two-electrode and three-electrode systems) make it possible to perform measurements in biofuel environments without base electrolytes that could have a negative impact on the results and load them with measurement errors. The presented methods make it possible to study the corrosion aggressiveness of an environment, the corrosion resistance of metallic materials, and the efficiency of corrosion inhibitors with representative and reproducible results. The results obtained using these methods can help to understand corrosion processes in more detail to minimize the damages caused by corrosion.

The testing of processes associated with material corrosion can often be difficult especially in non-aqueous environments. Here, we present different methods for short-term and long-term testing of corrosion behavior of non-aqueous environments such as biofuels, especially those containing bioethanol.

Material corrosion can be a limiting factor for different materials in many applications. Thus, it is necessary to better understand corrosion processes, ...

Experimental Protocol to Determine the Chloride Threshold Value for Corrosion in Samples Taken from Reinforced Concrete Structures

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these structures. Corrosion of the embedded reinforcing steel is the most frequent cause for degradation. While it is well known that the ability of a structure to withstand corrosion depends strongly on factors such as the materials used or the age, it is common practice to rely on threshold values stipulated in standards or textbooks. These threshold values for corrosion initiation (Ccrit) are independent of the actual properties of a certain structure, which clearly limits the accuracy of condition assessments and service life predictions. The practice of using tabulated values can be traced to the lack of reliable methods to determine Ccrit on-site and in the laboratory.
Here, an experimental protocol to determine Ccrit for individual engineering structures or structural members is presented. A number of reinforced concrete samples are taken from structures and laboratory corrosion testing is performed. The main advantage of this method is that it ensures real conditions concerning parameters that are well known to greatly influence Ccrit, such as the steel-concrete interface, which cannot be representatively mimicked in laboratory-produced samples. At the same time, the accelerated corrosion test in the laboratory permits the reliable determination of Ccrit prior to corrosion initiation on the tested structure; this is a major advantage over all common condition assessment methods that only permit estimating the conditions for corrosion after initiation, i.e., when the structure is already damaged.
The protocol yields the statistical distribution of Ccrit for the tested structure. This serves as a basis for probabilistic prediction models for the remaining time to corrosion, which is needed for maintenance planning. This method can potentially be used in material testing of civil infrastructures, similar to established methods used for mechanical testing.

We propose a method to measure a parameter that is highly relevant for corrosion assessments or predictions of reinforced concrete structures, with the main advantage of permitting testing of samples from engineering structures. This ensures real conditions at the steel-concrete interface, which are crucial to avoid artifacts of laboratory-made samples.

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these ...

Preparation of Aligned Steel Fiber Reinforced Cementitious Composite and Its Flexural Behavior

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the Earth&#39;s magnetic field, for manufacturing a cementitious composite reinforced with aligned steel fibers. Aligned steel fiber reinforced cementitious composites (ASFRC) were prepared by applying a uniform electromagnetic field to fresh mortar containing short steel fibers, whereby the short steel fibers were driven to rotate in alignment with the magnetic field. The degree of alignment of steel fibers in hardened ASFRC was assessed both by counting steel fibers in fractured cross-sections and by X-ray computed tomography analysis. The results from the two methods show that the steel fibers in ASFRC were highly aligned while the steel fibers in non-magnetically treated composites were randomly distributed. The aligned steel fibers had a much higher reinforcing efficiency, and the composites, therefore, exhibited significantly enhanced flexural strength and toughness. The ASFRC is thus superior to SFRC in that it can withstand greater tensile stress and more effectively resist cracking.

This protocol describes an approach for manufacturing aligned steel fiber reinforced cementitious composite by applying a uniform electromagnetic field. Aligned steel fiber reinforced cementitious composite exhibits superior mechanical properties to ordinary fiber reinforced concrete.

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the ...

Determining Tribocorrosion Rate and Wear-Corrosion Synergy of Bulk and Thin Film Aluminum Alloys

The increasing complexity and severity of service conditions in areas, such as aerospace and marine industries, nuclear systems, microelectronics, batteries, and biomedical devices, etc., impose great challenges on the reliable performance of alloys exposed to extreme conditions where mechanical and electrochemical attack co-exist. Finding ways for alloys to mitigate the combined attack of wear and corrosion (i.e., tribocorrosion) under such extreme conditions is thus highly critical for improving their reliability and service lifetime when used in such conditions. The challenge lies in the fact that wear and corrosion are not independent of each other, but rather work synergistically to accelerate the total material loss. Thus, a reliable method to evaluate the tribocorrosion resistance of metals and alloys is needed. Here, a protocol for measuring the tribocorrosion rate and wear-corrosion synergy of Al-based bulk and thin film samples in a corrosive environment under room temperature is presented.

Here, we present a protocol to measure the tribocorrosion rate and wear-corrosion synergy of thin film and bulk Al alloys in simulated sea water at room temperature.

The increasing complexity and severity of service conditions in areas, such as aerospace and marine industries, nuclear systems, microelectronics, ...

Full-field Strain Measurements for Microstructurally Small Fatigue Crack Propagation Using Digital Image Correlation Method

A novel measurement approach is used to reveal the cumulative deformation field at a sub-grain level and to study the influence of microstructure on the growth of microstructurally small fatigue cracks. The proposed strain field analysis methodology is based on the use of a unique pattering technique with a characteristic speckle size of approximately 10 &#181;m. The developed methodology is applied to study the small fatigue crack behavior in body centered cubic (bcc) Fe-Cr ferritic stainless steel with a relatively large grain size allowing a high spatial measurement accuracy at the sub-grain level. This methodology allows the measurement of small fatigue crack growth retardation events and associated intermittent shear strain localization zones ahead of the crack tip. In addition, this can be correlated with the grain orientation and size. Thus, the developed methodology can provide a deeper fundamental understanding of the small fatigue crack growth behavior, required for the development of robust theoretical models for the small fatigue crack&#160;propagation in polycrystalline materials.

Microstructurally small fatigue crack growth behavior is investigated using a novel methodological approach combining crack growth rate measurement and strain-field analysis to reveal the cumulative deformation field at sub-grain level.

A novel measurement approach is used to reveal the cumulative deformation field at a sub-grain level and to study the influence of microstructure on the ...

Quantifying the Relative Thickness of Conductive Ferromagnetic Materials Using Detector Coil-Based Pulsed Eddy Current Sensors

Thickness quantification of conductive ferromagnetic materials by means of non-destructive evaluation (NDE) is a crucial component of structural health monitoring of infrastructure, especially for assessing the condition of large diameter conductive ferromagnetic pipes found in the energy, water, oil, and gas sectors. Pulsed eddy current (PEC) sensing, especially detector coil-based PEC sensor architecture, has established itself over the years as an effective means for serving this purpose. Approaches for designing PEC sensors as well as processing signals have been presented in previous works. In recent years, the use of the decay rate of the detector coil-based time domain PEC signal for the purpose of thickness quantification has been studied. Such works have established that the decay rate-based method holds generality to the detector coil-based sensor architecture, with a degree of immunity to factors such as sensor shape and size, number of coil turns, and excitation current. Moreover, this method has shown its effectiveness in NDE of large pipes made of grey cast iron. Following such literature, the focus of this work is explicitly PEC sensor detector coil voltage decay rate-based conductive ferromagnetic material thickness quantification. However, the challenge faced by this method is the difficulty of calibration, especially when it comes to applications such as in situ pipe condition assessment since measuring electrical and magnetic properties of certain pipe materials or obtaining calibration samples is difficult in practice. Motivated by that challenge, in contrast to estimating actual thickness as done by some previous works, this work presents a protocol for using the decay rate-based method to quantify relative thickness (i.e., thickness of a particular location with respect to a maximum thickness), without the requirement for calibration.

Here, we present a protocol to quantify the relative thickness (i.e., thickness as a percentage with respect to a reference) of conductive ferromagnetic materials using detector coil-based pulsed eddy current sensors, while overcoming the calibration requirement.

Thickness quantification of conductive ferromagnetic materials by means of non-destructive evaluation (NDE) is a crucial component of structural health ...

Crack Monitoring in Resonance Fatigue Testing of Welded Specimens Using Digital Image Correlation

A procedure using digital image correlation (DIC) to detect cracks on welded specimens during fatigue tests on resonance testing machines is presented. It is intended as a practical and reproducible procedure to identify macroscopic cracks at an early stage and monitor crack propagation during fatigue tests. It consists of strain field measurements at the weld using DIC. Images are taken at fixed load cycle intervals. Cracks become visible in the computed strain field as elevated strains. This way, the whole width of a small-scale specimen can be monitored to detect where and when a crack initiates. Subsequently, it is possible to monitor the development of the crack length. Because the resulting images are saved, the results are verifiable and comparable. The procedure is limited to cracks initiating at the surface and is intended for fatigue tests under laboratory conditions. By visualizing the crack, the presented procedure allows direct observation of macrocracks from their formation until rupture of the specimen.

Digital image correlation is used in fatigue tests on a resonance testing machine to detect macroscopic cracks and monitor crack propagation in welded specimens. Cracks on the specimen surface become visible as increased strains.

A procedure using digital image correlation (DIC) to detect cracks on welded specimens during fatigue tests on resonance testing machines is presented. It ...

Co-localizing Kelvin Probe Force Microscopy with Other Microscopies and Spectroscopies: Selected Applications in Corrosion Characterization of Alloys

Kelvin probe force microscopy (KPFM), sometimes referred to as surface potential microscopy, is the nanoscale version of the venerable scanning Kelvin probe, both of which measure the Volta potential difference (VPD) between an oscillating probe tip and a sample surface by applying a nulling voltage equal in magnitude but opposite in sign to the tip-sample potential difference. By scanning a conductive KPFM probe over a sample surface, nanoscale variations in surface topography and potential can be mapped, identifying likely anodic and cathodic regions, as well as quantifying the inherent material driving force for galvanic corrosion.
Subsequent co-localization of KPFM Volta potential maps with advanced scanning electron microscopy (SEM) techniques, including back scattered electron (BSE) images, energy dispersive spectroscopy (EDS) elemental composition maps, and electron backscattered diffraction (EBSD) inverse pole figures can provide further insight into structure-property-performance relationships. Here, the results of several studies co-localizing KPFM with SEM on a wide variety of alloys of technological interest are presented, demonstrating the utility of combining these techniques at the nanoscale to elucidate corrosion initiation and propagation.
Important points to consider and potential pitfalls to avoid in such investigations are also highlighted: in particular, probe calibration and the potential confounding effects on the measured VPDs of the testing environment and sample surface, including ambient humidity (i.e., adsorbed water), surface reactions/oxidation, and polishing debris or other contaminants. Additionally, an example is provided of co-localizing a third technique, scanning confocal Raman microscopy, to demonstrate the general applicability and utility of the co-localization method to provide further structural insight beyond that afforded by electron microscopy-based techniques.

Kelvin probe force microscopy (KPFM) measures surface topography and differences in surface potential, while scanning electron microscopy (SEM) and associated spectroscopies can elucidate surface morphology, composition, crystallinity, and crystallographic orientation. Accordingly, the co-localization of SEM with KPFM can provide insight into the effects of nanoscale composition and surface structure on corrosion.

Kelvin probe force microscopy (KPFM), sometimes referred to as surface potential microscopy, is the nanoscale version of the venerable scanning Kelvin ...

Stress-Strain Characteristics of Steels

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
The importance of materials to human development is clearly captured by the early classifications of world history into periods such as the Stone Age, Iron Age, and the Bronze Age. The introduction of the Siemens and Bessemer processes to produce steels in the mid-1800s is arguably the single most important development in launching the Industrial Revolution that transformed much of Europe and the USA in the second half of the 19th century from agrarian societies into the urban and mechanized societies of today. Steel, in its almost infinite variations, is all around us, from our kitchen appliances to cars, to lifelines such as electrical transmission networks and water distribution systems. In this experiment we will look at the stress-strain behavior of two types of steel that bound the range usually seen in civil engineering applications - from a very mild, hot rolled steel to a hard, cold rolled one.