The authors appreciate the financial support from the National Basic Research Program of China (973 Program) under the contract No. 2015CB655105, the Natural Science Foundation the contract No. 51308262, and the Natural Science Foundation of Jiangsu Province under the contract No. BK20131012.

Caution: Several of the chemicals, such as silver nitrate, potassium chromate, and concentrated sulfuric acid, used in the testing process are acutely toxic and corrosive. Please adopt appropriate safety measures while using them, including the wear of safety glasses, gloves, lab coat, etc.
1. Preparation of Paste Specimens
<ol>
	<li>Preparation of the mold
	<ol>
		<li>Use a brush to clean up a mold of size 70 mm &#215; 70 mm &#215; 70 mm, making sure that the inner surfaces of the mold are impurity-free.</li>
		<li>Brush mold-release diesel oil evenly on the inner surfaces of the mold using another brush.</li>
	</ol>
	</li>
	<li>Molding Paste Specimen
	<ol>
		<li>Use an electronic balance to weigh 1,000 g of water into a 1,500 mL plastic cup and 2,000 g of cement into a 3,000 mL plastic basin.</li>
		<li>Add 1,000 g water and 2,000 g of cement into a 5 L mixing pot sequentially. The water to cement ratio is 0.5.</li>
		<li>Put the mixing pot on the base of a cement paste mixer and fasten it after raising it to the stirring position.</li>
		<li>Mix at 65 rpm for 90 s.</li>
		<li>Let the mixture sit for 30 s. During this period, scrape off the paste on the inner wall of pot using a scraper knife and mix it into the rest of the pot. Mix at 130 rpm for 60 s.</li>
		<li>Remove the mixing pot from the mixer. Pour the well-mixed cement paste into the mold. Shovel the cement paste with a scraper knife and vibrate the mold for several seconds to compact the paste on a vibrating table.</li>
		<li>After filling up the mold, seal the mold surface with cling film to prevent moisture evaporation. Let sit for 24 h in the molding at 23 &#177; 2 &#176;C.</li>
	</ol>
	</li>
	<li>Curing
	<ol>
		<li>Remove the hardened paste specimens from the mold.</li>
		<li>Place hardened paste specimens in a curing room at 23 &#177; 2 &#176;C and 95% relative humidity for 60 d.</li>
	</ol>
	</li>
	<li>Cutting
	<ol>
		<li>Take specimens out of the curing room after 60 d.</li>
		<li>Fix the specimen on a high precision cutting machine and cut off 20 mm from the mold-free surface. The processed specimens of size 70 mm &#215; 70 mm &#215; 50 mm will be subjected to chloride ingression exposure afterwards.</li>
	</ol>
	</li>
	<li>Sealing with epoxy resin
	<ol>
		<li>Taking the cut-surface as the exposure surface, seal the other five surfaces of the specimen (70 mm &#215; 70 mm &#215; 50 mm) with epoxy resin using a brush. The volume of epoxy resin used for each specimen is about 30 mL. Harden the epoxy resin through air exposure for 24 h. 
		NOTE: Prepare specimens for chloride ingression exposure after the epoxy resin has hardened.</li>
	</ol>
	</li>
</ol>
2. Cyclic Wetting and Drying
<ol>
	<li>Add 0.35 kg of NaCI and 9.65 kg of deionized water into a 15 L plastic bucket for a NaCI solution with a mass ratio of 3.5%.</li>
	<li>With the exposure surface facing down, place specimens in a plastic box (50 cm &#215; 30 cm &#215; 20 cm) with two braces laid on the bottom. The brace can be stainless steel bars or plastic grid plates. The presence of the brace allows the exposure surface to take about 1.0 cm of space to the bottom of the box.</li>
	<li>Pour the 3.5% NaCI solution slowly into the plastic box and stop when the liquid level is about 1.0 cm above the exposure surface. Seal the box with a plastic film (about 0.25 mm thickness) to prevent concentration changes caused by evaporation. Then, put the plastic box in a room with constant temperature of 23 &#177; 2 &#176;C and humidity of 65 &#177; 2%.</li>
	<li>Starting from the time of pouring the NaCl solution, soak specimens for 24 h for the wetting process.</li>
	<li>Take specimens out of solution after wetting for 24 h, wipe off the residual solution with a towel gently, and put them in the same constant temperature and humidity room for 6 d, which is the drying process.</li>
	<li>After drying for 6 d, put specimens back into the NaCI solution again.</li>
	<li>Repeat steps 2.5 and 2.6 (7 d for one wetting-drying cycle) for a total of 12 cycles.</li>
</ol>
3. Grinding Powder Samples
<ol>
	<li>After 12 wet-dry cycles, fix the specimen on the base of high precision computer numerical controlled (CNC) grinding machine, which was converted from a milling machine by replacing the original cutter with a titanium alloy cutter.</li>
	<li>Place powder-collecting paper around the specimen on the base of a grinding machine before starting to grind.</li>
	<li>Start the high precision CNC grinding machine and wait until the system is loaded.</li>
	<li>Press the &#34;ZERO&#34; button and the subsequent &#34;X&#8594;0&#34;, &#34;Y&#8594;0&#34;, &#34;Z&#8594;0&#34; buttons to make the operation desk and milling cutter return to the coordinate origin automatically.</li>
	<li>Press &#34;Manual Data Input (MDI)&#34;, double click &#34;PROGRAM&#34;, input &#34;N3S1000&#34; and click &#34;INPUT&#34;, then press &#34;CYCLE START&#34; to start the main shaft. Note that &#34;N3S1000&#34; means the revolving speed of the shaft is being set at 1000 rpm.</li>
	<li>Load the main grinding program: Press &#34;MDI&#34;, click &#34;PROGRAM&#34; repeatedly to find &#34;PROGRAM (CATALOG)&#34; page, and select the appropriate program. Next, click &#34;EDIT&#34;, and press &#34;INPUT&#34; to load the main program. 
	NOTE: The main program can be personalized according to a specific grinding requirement, including settings of the total grinding depth, number of layers, thickness of each layer, and time interval between grinding two layers. For this protocol, the total grinding depth is 10 mm, and the number of layers is 20; the grinding thickness of each layer is 0.5 mm; and the time interval between grinding layers is 60 s. See the disclosure for details of program.</li>
	<li>Set the milling cutter position: First, click &#34;MANUAL OPERATION&#34; and then &#34;MAINSHAFT FORWARD&#34; to rotate the main shaft. Next, click &#34;HAND WHEEL&#34; and manually adjust the cutter to the ready-to-grind position (usually on the one third of the front-left surface of specimen). Finally, click &#34;SET&#34; and &#34;X&#34;, &#34;INPUT&#34;, &#34;Y&#34;, &#34;INPUT&#34;, &#34;Z&#34;, and &#34;INPUT&#34; buttons subsequently. Record the relative coordinates as the original space coordinates to finish cutter setting.</li>
	<li>Launch the main grinding program: Press &#34;START&#34;, then click &#34;AUTO&#34; and &#34;CYCLE START&#34; buttons subsequently. The machine starts grinding automatically as pre-programmed. 
	NOTE: During the grinding process, powder will be accumulated on the collecting paper which is pre-spread on the base of machine. After grinding each layer, the milling cutter will rise away from the specimen and remain stationary in the X, Y, Z directions for 60 s as programmed. Collect a powder sample during the 60 s break and re-spread the collecting paper. 
	CAUTION: Though the milling cutter stops moving in the X, Y, Z directions, it is still rotating. Attention should be paid to avoid touching the milling cutter with any body parts to avoid injury. Besides, it is necessary to use a mask and gloves due to the dust generated during grinding process.</li>
	<li>Shut down the machine after finishing grinding.</li>
</ol>
4. Detecting Chloride Content7
<ol>
	<li>Preparation of solution
	<ol>
		<li>Potassium chromate solution
		<ol>
			<li>Dissolve 5 g of potassium chromate in 20 mL of deionized water. Add 10 mg of silver nitrate. Shake well and let sit for 24 h. 
			CAUTION: Potassium chromate and silver nitrate are toxic. It is necessary to wear rubber gloves and a mask while using them.</li>
			<li>Filter the solution into a conical flask with a funnel and filter paper and move it into a 100 mL volumetric flask. Add deionized water until reaching the 100 mL calibration mark. The potassium chromate indicator of 5% concentration is obtained.</li>
		</ol>
		</li>
		<li>Prepare 0.5% phenolphthalein solution: Dissolve 0.5 g of phenolphthalein in 75 mL of ethyl alcohol. Add 25 mL of deionized water and shake well.</li>
		<li>Prepare dilute sulfuric acid: Dissolve 5 mL of concentrated sulfuric acid (98.3%) in 100 mL of deionized water. 
		CAUTION: Concentrated sulfuric acid is very corrosive. It is necessary to wear rubber gloves, a mask, and goggles while using it.</li>
		<li>NaCI standard solution
		<ol>
			<li>Heat about 2 g of pure sodium chloride under 200 - 300 &#176;C in a crucible with an electric furnace, and stir with a glass rod during the process until there are no sounds of salt cracking (devoid of water).</li>
			<li>After cooling in a desiccator, take 1.169 g of NaCI crystals, dissolve in a 1,000 mL volumetric flask with 100 mL deionized water. Add deionized water until reaching the 1,000 mL calibration mark. An NaCl standard solution of 0.02 M is obtained. Calculate the concentration of the NaCl standard solution with the equation below: 
			<img alt="Equation 1" src="/files/ftp_upload/56268/56268eq1.jpg" /> 
			where, CNaCl is the standard concentration of NaCl solution, mol/L; V is the volume of solution, L; M is the molar mass of NaCl, 58.45 g/mol; m is the mass of NaCl, g.</li>
		</ol>
		</li>
		<li>Silver nitrate solution
		<ol>
			<li>Dissolve 1.7 g of silver nitrate in 100 mL of deionized water with a 200 mL breaker. Move it into a 1,000 mL brown volumetric flask and add deionized water up to the 1,000 mL calibration mark.</li>
			<li>Pipette three 10 mL (V1) units of 0.02 M standard NaCI solution into three conical flasks. Add 10 drops of potassium chromate indicator in each with a dropper.</li>
			<li>Titrate the solution from step 4.1.5.2 with the prepared silver nitration from step 4.1.5.1. Stop when the solution becomes reddish and the red color does not fade away. Record the volume of consumed silver nitration solution (V2). Calculate the standard concentration of silver nitration solution with the equation below, and take the mean value of three testing results. 
			<img alt="Equation 2" src="/files/ftp_upload/56268/56268eq2.jpg" /> 
			Where, CAgNO3 is the concentration of silver nitrate solution, mol/L; V1 is the volume of NaCl solution, 10 mL; V2 is the volume of silver nitrate solution consumed, mL.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Water-soluble chloride content
	<ol>
		<li>Grind every sample obtained in section 3 in a mortar until it can be sifted through an 80 &#181;m sieve. Heat and dry the sifted samples at 105 &#176;C for 2 h in an oven.</li>
		<li>Take 2 g of each dried sample, put them in 100 mL plastic bottles, add 50 mL (V3) of deionized water with a 50 mL measuring pipette, and seal the bottles with caps. Shake the bottles violently to guarantee that the sample and deionized water are well-mixed.</li>
		<li>Fasten plastic bottles on an automatic vibrator and vibrate for 24 h to dissolve the water-soluble chloride from samples.</li>
		<li>Filter the solution in bottles after vibrating for 24 h with funnels and filter paper. Pipette two 10 mL (V4) units of filtrated solution from every bottle into two conical flasks.</li>
		<li>Add two drops of phenolphthalein solution to each conical flask to make the solution present purplish red. Neutralize the solution to colorless with dilute sulfuric acid.</li>
		<li>Add 10 drops of potassium chromate indicator into the colorless solution and titrate immediately with silver nitrate solution. Shake the conical flask manually during titrating to make sure that the chloride ions react with silver nitrate quickly and completely. Stop titrating when the solution becomes reddish and the red color does not fade away. Record the volume of consumed silver nitrate solution (V5).</li>
		<li>Calculate the content of water-soluble chloride with the equation below and take the mean value of the two testing results. 
		<img alt="Equation 3" src="/files/ftp_upload/56268/56268eq3.jpg" /> 
		where, Cw is the water-soluble chloride content in the paste sample, % cement; ms is the mass of powder sample, 2 g; V3 is the volume of deionized water used to dissolve sample, 50 mL; V4 is the volume of filtrated solution extracted at each nitration, 10 mL; V5 is the volume of silver nitrate solution consumed at each nitration, mL; Mcl is the molar mass of Cl, 35.5 g/mol.</li>
		<li>Plot water-soluble chloride profiles after getting the chloride content at different depths of paste specimens.</li>
	</ol>
	</li>
</ol>
5. Accuracy Test of Grinding Thickness
<ol>
	<li>Set five grinding thicknesses: 1.0 mm, 0.5 mm, 0.2 mm, 0.1 mm, and 0.05 mm in the main grinding program. Grind with each thickness five times.</li>
	<li>Measure the thickness of specimen before grinding (H1) and after grinding (H2) with a vernier caliper, and calculate the practical grinding thickness with the equation below. Do not take the specimen down from the machine during measuring to guarantee the reliability of measurement. 
	<img alt="Equation 4" src="/files/ftp_upload/56268/56268eq4.jpg" /> 
	Where, P is the practical grinding thickness, mm; H1 is the thickness of specimen before grinding, mm; H2 is the thickness of specimen after grinding, mm.</li>
</ol>

<ol>
	<li>Byang, H. O., Jang, S. Y. <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+material+and+environmental+parameters+on+chloride+penetration+profiles+in+concrete+structures.">Effects of material and environmental parameters on chloride penetration profiles in concrete structures.</a> Cem. Concr. Res. 37 (1), 47-53 (2007).</li><li>Mehta, P. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Concrete: structure, properties and materials. , 105-169 (1986).</li><li>Khelidj, A., Loukili, A., Bastian, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+study+of+the+hydro-chemical+coupling+inside+maturing+concretes:+effect+on+various+types+of+shrinkage.">Experimental study of the hydro-chemical coupling inside maturing concretes: effect on various types of shrinkage.</a> Mater. Struct. 31 (9), 588-594 (1998).</li><li>Nielsen, E. P., Geiker, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chloride+diffusion+in+partially+saturated+cementitious+material.">Chloride diffusion in partially saturated cementitious material.</a> Cem. Concr. Res. 33 (1), 133-138 (2003).</li><li>He, F., Shi, C., Yuan, Q., Chen, C., Zheng, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AgNO3-based+colorimetric+methods+for+measurement+of+chloride+penetration+in+concrete.">AgNO3-based colorimetric methods for measurement of chloride penetration in concrete.</a> Constr. Build. Mater. 26 (1), 1-8 (2012).</li><li>Collepardi, M., Turriziani, R., Marcialis, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Penetration+of+chloride+ions+into+cement+pastes+and+in+concretes.">Penetration of chloride ions into cement pastes and in concretes.</a> J. Am. Ceram. Soc. 55 (10), 534-535 (1972).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> JTJ 270-98. Testing Code of Concrete for Port and Waterwog Engineering. , 202-207 (1998).</li><li>Chang, H., Mu, S., Xie, D., Wang, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+pore+structure+and+moisture+distribution+on+chloride+"maximum+phenomenon"+in+surface+layer+of+specimens+exposed+to+cyclic+drying-wetting+condition.">Influence of pore structure and moisture distribution on chloride "maximum phenomenon" in surface layer of specimens exposed to cyclic drying-wetting condition.</a> Constr. Build. Mater. 131 (1), 16-30 (2017).</li><li>Lu, C., Gao, Y., Cui, Z., Liu, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+Analysis+of+Chloride+Penetration+into+Concrete+Subjected+to+Drying-Wetting+Cycles.">Experimental Analysis of Chloride Penetration into Concrete Subjected to Drying-Wetting Cycles.</a> J. Mater. Civil. Eng. 27 (12), 1-10 (2015).</li><li>Xu, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Properties of Chloride Ions Transportation in Concrete under Different Drying-wetting Cycles. , (2012).</li><li>Zhao, T., Fan, H., Cao, W., Wang, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Concrete+powder+grinding+machine.">Concrete powder grinding machine.</a> China patent. , (2012).</li></ol>

The authors have nothing to disclose.

The grinding error of the high precision CNC milling machine is controlled within 0.04 mm and the standard deviation is less than 0.03 mm (Table 1)8. It proves that this milling method has a high degree of accuracy and stability in the measurements of chloride contents as a function of depth, contributing to a better illustration of real chloride distribution in the specimens.
When the testing interval is 0.5 mm, with the depth from exposure surface inc...

The chloride induced corrosion of reinforcing steel is one of the major causes jeopardizing the service life of reinforced concrete structures exposed to an aggressive environment (e.g., marine environment or deicing salts environment). The chloride distribution can be used for investigations of the chloride penetration rate, the amount of steel corrosion, and predictions of the service life. Therefore, a precise chloride distribution is of great significance for the durability research of concrete structures.
Mechanisms or combined actions of multi-mechanisms are responsible for chloride transport in concrete under specific environments1. In submerged parts of marine structures, pure diffusion is the only mechanism driving chloride ingress2, which causes the chloride content to decrease with increasing depth. Concrete is in a non-saturated state3 when subjected to a wetting-drying environment such as a marine tidal zone or a deicing salt environment. In such conditions, the process of chloride ingress becomes very complicated and both diffusion and capillary suction operate in chloride transport4. Thus, the chloride distribution under wetting-drying conditions is probably more complicated than in a submerged condition. Therefore, the chloride distribution under cyclic wetting-drying conditions needs to be studied more precisely.
The chloride distribution in cement-based materials is usually represented by a chloride profile. The accuracy of a chloride profile mainly depends on two aspects: the accuracy of chloride content and the accuracy of chloride distribution along the depth. Regarding the chloride content test, the basic principle is based on the chemical reaction between (Cl-) and (Ag+)5,6, though different standards require different specific operations. The exact chloride content can be acquired as long as specific operations are followed. However, the accuracy of the chloride distribution along the depth relies mainly on the accuracy of the sampling position. The methods already known for obtaining power samples at different depths of specimen are an electric drill, a normal grinding machine, and a profile grinder. Unfortunately, they all share a disadvantage as the accuracy is low when the grinding thickness or sampling interval is small. Thus, the requirement of investigating chloride distribution in the surface layer of specimens under cyclic wetting-drying condition is not met. Therefore, a new method that can allow a smaller sampling interval (e.g., less than 0.5 mm) and reduce error to the minimum (e.g., less than 0.05 mm) is needed.
The detailed protocol here offers a more accurate way to get a chloride profile by improving the precision of chloride distribution along the depth.

<table><tbody><tr><td>Cement</td><td>Jiangnan Xiaoyetian</td><td>P.II. 52.5</td><td></td></tr><tr><td>Potassium chromate, 99.7%</td><td>Tianjin Kemiou</td><td>HG391887</td><td>Toxic</td></tr><tr><td>Ethyl alcohol</td><td>Sinopharm</td><td>XK10009257</td><td></td></tr><tr><td>Silver nitrate, 99.8%</td><td>Sinopharm</td><td>7761888</td><td>Toxic</td></tr><tr><td>Phenolphthalein, 99.5%</td><td>Tianjin Fuchen</td><td>XK1301100017</td><td></td></tr><tr><td>Concentrated sulfuric acid, 98.3%</td><td>Shanghai Lingfeng</td><td>XK1301100085008</td><td>Highly corrosive</td></tr><tr><td>Sodium chloride, 99.7%</td><td>Xilong Scientific</td><td>XK1320100153</td><td></td></tr><tr><td>Diesel oil</td><td>China Petroleum</td><td>0#</td><td></td></tr><tr><td>Epoxy resin</td><td>Yifeng Chemical</td><td>E44-6101</td><td></td></tr><tr><td>Deionized water</td><td>Beijing Liyuan</td><td>PUW-10N</td><td></td></tr><tr><td>CNC Milling meachine</td><td>Foshan Xiandao Digital Technology</td><td>C31E</td><td></td></tr><tr><td>Cement paste mixer</td><td>Wuxi Construction and Engineering</td><td>NJ160</td><td></td></tr><tr><td>High precision cutting machine</td><td>Buehler</td><td>2215</td><td></td></tr><tr><td>Mixing spot</td><td>Wuxi Construction and Engineering</td><td>JJ-5</td><td></td></tr><tr><td>Scraper knife</td><td>Jinzheng Building Materials</td><td>CD-3</td><td></td></tr><tr><td>Cling film</td><td>Miao Jie</td><td>65300</td><td></td></tr><tr><td>Mold (70mm&amp;times;70mm&amp;times;70mm)</td><td>Jingluda</td><td>ABS707</td><td></td></tr><tr><td>Plastic box</td><td>Fangao Household</td><td>32797</td><td></td></tr><tr><td>Stainless steel brace</td><td>An Feng</td><td>316L</td><td></td></tr><tr><td>Paper</td><td>Deli</td><td>A4</td><td></td></tr><tr><td>Oven</td><td>Shanghai Huatai</td><td>DHG-9070A</td><td></td></tr><tr><td>Automatic vibrator</td><td>Lichen</td><td>HY-4</td><td></td></tr><tr><td>Vibrating table</td><td>Jianyi</td><td>GZ-75</td><td></td></tr><tr><td>plastic film</td><td>Miao Jie</td><td>65303</td><td></td></tr><tr><td>Vernier caliper</td><td>Links</td><td>601-01</td><td></td></tr><tr><td>Electronic balance</td><td>Setra</td><td>BL-4100F</td><td></td></tr><tr><td>Plastic bottle</td><td>Lining Plastic</td><td>454</td><td></td></tr><tr><td>Brush</td><td>Huoniu</td><td>3#</td><td></td></tr><tr><td>Mask</td><td>UVEX</td><td>3220</td><td></td></tr><tr><td>Gloves</td><td>Ammex</td><td>TLFGWC</td><td></td></tr><tr><td>Plastic cup</td><td>Maineng</td><td>MN4613</td><td></td></tr><tr><td>Desiccator</td><td>Shenfei</td><td>GZ300</td><td></td></tr><tr><td>Filter paper</td><td>Hangzhou Wohua</td><td>9614051</td><td></td></tr><tr><td>Dropper</td><td>Huaou</td><td>1630</td><td></td></tr><tr><td>Breaker</td><td>Huaou</td><td>1101</td><td></td></tr><tr><td>Funnel</td><td>Huaou</td><td>1504</td><td></td></tr><tr><td>Measuring cylinder</td><td>Huaou</td><td>1601</td><td></td></tr><tr><td>volumetric flash</td><td>Huaou</td><td>1621</td><td></td></tr><tr><td>Conical flash</td><td>Huaou</td><td>1121</td><td></td></tr><tr><td>Pipette</td><td>Huaou</td><td>1633</td><td></td></tr><tr><td>Burette</td><td>Huaou</td><td>1462</td><td></td></tr><tr><td>Mortar</td><td>Huaou</td><td>YBMM254</td><td></td></tr><tr><td>80&amp;micro;m sieve</td><td>Shanghai Dongxing</td><td>KJ-80</td><td></td></tr><tr><td>Crucible</td><td>Oamay</td><td>GYGG</td><td></td></tr><tr><td>Electric furnace</td><td>Tyler</td><td>SX-B06</td><td></td></tr></tbody></table>

detecting the water-soluble chloride distribution of cement paste in a high-precision way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

The original data and statistical results about the accuracy of grinding thickness are collected (Table 1)8. Mean and error are used to reflect the accuracy and standard deviation&#160;(SD) is used to reflect the consistency of this method.
The water-soluble chloride content of testing interval 0.5 mm (Figure 1) and 2.0 mm (Figur...

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Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

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9.5K Views.  Southeast University. A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

Video: Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

Dynamic Electrochemical Measurement of Chloride Ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

Chemistry

Measurement of Ion Concentration in the Unstirred Boundary Layer with Open Patch-Clamp Pipette: Implications in Control of Ion Channels by Fluid Flow

Fluid flow is an important environmental stimulus that controls many physiological and pathological processes, such as fluid flow-induced vasodilation. Although the molecular mechanisms for the biological responses to fluid flow/shear force are not fully understood, fluid flow-mediated regulation of ion channel gating may contribute critically. Therefore, fluid flow/shear force sensitivity of ion channels has been studied using the patch-clamp technique. However, depending on the experimental protocol, the outcomes and interpretation of data can be erroneous. Here, we present experimental and theoretical evidence for fluid flow-related errors and provide methods for estimating, preventing, and correcting these errors. Changes in junction potential between the Ag/AgCl reference electrode and bathing fluid were measured with an open pipette filled with 3 M KCl. Fluid flow could then shift the liquid/metal junction potential to approximately 7 mV. Conversely, by measuring the voltage shift induced by fluid flow, we estimated the ion concentration in the unstirred boundary layer. In the static condition, the real ion concentrations adjacent to the Ag/AgCl reference electrode or ion channel inlet at the cell-membrane surface can reach as low as approximately 30% of that in the flow condition. Placing an agarose 3 M KCl bridge between the bathing fluid and reference electrode may have prevented this problem of junction potential shifting. However, the unstirred layer effect adjacent to the cell membrane surface could not be fixed in this way. Here, we provide a method for measuring real ion concentrations in the unstirred boundary layer with an open patch-clamp pipette, emphasizing the importance of using an agarose salt-bridge while studying fluid flow-induced regulation of ion currents. Therefore, this novel approach, which takes into consideration the real concentrations of ions in the unstirred boundary layer, may provide useful insight on the experimental design and data interpretation related to fluid shear stress regulation of ion channels.

Mechanosensitive ion channels are often studied in terms of fluid flow/shear force sensitivity with patch-clamp recording. However, depending on the experimental protocol, the outcome on fluid flow-regulations of ion channels can be erroneous. Here, we provide methods for preventing and correcting such errors with a theoretical basis.

Fluid flow is an important environmental stimulus that controls many physiological and pathological processes, such as fluid flow-induced vasodilation. ...

Biochemistry

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 ...

Expression of Cementitious Pore Solution and the Analysis of Its Chemical Composition and Resistivity Using X-ray Fluorescence

The goal of this method is to determine the chemical composition and electrical resistivity of cementitious pore solution expressed from a fresh paste sample. The pore solution is expressed from a fresh paste sample using a pressurized nitrogen gas system. The pore solution is then immediately transferred to a syringe to minimize evaporation and carbonation. After that, assembled testing containers are used for the X-ray fluorescence (XRF) measurement. These containers consist of two concentric plastic cylinders and a polypropylene film which seals one of the two open sides. The pore solution is added into the container immediately prior to the XRF measurement. The XRF is calibrated to detect the main ionic species in the pore solution, in particular, sodium (Na+), potassium (K+), calcium (Ca2+), and sulfide (S2-), to calculate sulfate (SO42-) using stoichiometry. The hydroxides (OH-) can be calculated from a charge balance. To calculate the electrical resistivity of the solution, the concentrations of the main ionic species and a model by Snyder et al. are used. The electrical resistivity of the pore solution can be used, along with the electrical resistivity of concrete, to determine the formation factor of concrete. XRF is a potential alternative to current methods to determine the composition of pore solution, which can provide benefits in terms of reduction in time and costs.

This protocol describes the procedure to express fresh pore solution from cementitious systems and the measurement of its ionic composition using X-ray fluorescence. The ionic composition can be used to calculate pore solution electrical resistivity, which can be used, together with concrete electrical resistivity, to determine the formation factor.

The goal of this method is to determine the chemical composition and electrical resistivity of cementitious pore solution expressed from a fresh paste ...

Fabrication of a Dipole-assisted Solid Phase Extraction Microchip for Trace Metal Analysis in Water Samples

This paper describes a fabrication protocol for a dipole-assisted solid phase extraction (SPE) microchip available for trace metal analysis in water samples. A brief overview of the evolution of chip-based SPE techniques is provided. This is followed by an introduction to specific polymeric materials and their role in SPE. To develop an innovative dipole-assisted SPE technique, a chlorine (Cl)-containing SPE functionality was implanted into a poly(methyl methacrylate) (PMMA) microchip. Herein, diverse analytical techniques including contact angle analysis, Raman spectroscopic analysis, and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis were employed to validate the utility of the implantation protocol of the C-Cl moieties on the PMMA. The analytical results of the X-ray absorption near-edge structure (XANES) analysis also demonstrated the feasibility of the Cl-containing PMMA used as an extraction medium by virtue of the dipole-ion interactions between the highly electronegative C-Cl moieties and the positively charged metal ions.

The fabrication protocol of a dipole-assisted solid phase extraction microchip for the trace metal analysis is presented.

This paper describes a fabrication protocol for a dipole-assisted solid phase extraction (SPE) microchip available for trace metal analysis in water ...

Bioengineering

Quantification of Metal Leaching in Immobilized Metal Affinity Chromatography

Contamination of enzymes with metals leached from immobilized metal affinity chromatography (IMAC) columns poses a major concern for enzymologists, as many of the common di-and trivalent cations used in IMAC resins have an inhibitory effect on enzymes. However, the extent of metal leaching and the impact of various eluting and reducing reagents are poorly understood in large part due to the absence of simple and practical transition metal quantification protocols that use equipment typically available in biochemistry labs. To address this problem, we have developed a protocol to quickly quantify the amount of metal contamination in samples prepared using IMAC as a purification step. The method uses hydroxynaphthol blue (HNB) as a colorimetric indicator for metal cation content in a sample solution and UV-Vis spectroscopy as a means to quantify the amount of metal present, into the nanomolar range, based on the change in the HNB spectrum at 647 nm. While metal content in a solution has historically been determined using atomic absorption spectroscopy or inductively coupled plasma techniques, these methods require specialized equipment and training outside the scope of a typical biochemistry laboratory. The method proposed here provides a simple and fast way for biochemists to determine the metal content of samples using existing equipment and knowledge without sacrificing accuracy.

We present an assay for easy quantification of metals introduced to samples prepared using immobilized metal affinity chromatography. The method uses hydroxynaphthol blue as the colorimetric metal indicator and a UV-Vis spectrophotometer as the detector.

Contamination of enzymes with metals leached from immobilized metal affinity chromatography (IMAC) columns poses a major concern for enzymologists, as ...

Preparation of Expanded Chitin Foams and their Use in the Removal of Aqueous Copper

Chitin is an underexploited, naturally abundant, mechanically robust, and chemically resistant biopolymer. These qualities are desirable in an adsorbent, but chitin lacks the necessary specific surface area, and its modification involves specialized techniques and equipment. Herein is described a novel chemical procedure for expanding chitin flakes, derived from shrimp shell waste, into foams with higher surface area. The process relies on the evolution of H2 gas from the reaction of water with NaH trapped in a chitin gel. The preparation method requires no specialized equipment. Powder X-ray diffraction and N2-physisorption indicate that the crystallite size decreases from 6.6 nm to 4.4 nm and the specific surface area increases from 12.6 &#177; 2.1 m2/g to 73.9 &#177; 0.2 m2/g. However, infrared spectroscopy and thermogravimetric analysis indicate that the process does not change the chemical identity of the chitin. The specific Cu adsorption capacity of the expanded chitin increases in proportion to specific surface area from 13.8 &#177; 2.9 mg/g to 73.1 &#177; 2.0 mg/g. However, the Cu adsorption capacity as a surface density remains relatively constant at an average of 10.1 &#177; 0.8 atom/nm2, which again suggests no change in the chemical identity of the chitin. This method offers the means to transform chitin into a higher surface area material without sacrificing its desirable properties. Although the chitin foam is described here as an adsorbent, it can be envisioned as a catalyst support, thermal insulator, and structural material.

This study describes a method to expand chitin into a foam by chemical techniques that require no specialized equipment.

Chitin is an underexploited, naturally abundant, mechanically robust, and chemically resistant biopolymer. These qualities are desirable in an adsorbent, ...

Porosity in Cement Paste

The porosity of concrete is a measure of the void spaces within its structure. These spaces impact its strength and durability significantly. When water and cement interact, a chemical reaction called hydration creates a semi-solid paste. This paste includes combined water, making up approximately 23% of the cement&#39;s dry mass, and gel water, which fills minuscule voids known as gel pores, accounting for about 28% of the cement gel volume.
The balance of water to cement in the mix is critical&#8212;it influences the extent of hydration and, thereby, the porosity and strength of the cured concrete. In an ideal hydration process, extra space not occupied by solid hydration products forms capillary pores, representing around 18.5% of the original cement volume. As the concrete cures, continuous hydration can fill the capillary pores with hydration products, increasing the density of the material.
For complete hydration and optimal strength, the curing process must be managed carefully. It allows for additional hydration, reducing porosity by filling the capillary spaces with more stable hydration products and, as a result, densifying the paste. This meticulous process is crucial for achieving durable, high-quality concrete that is less susceptible to environmental and mechanical degradation.

As fresh cement paste sets, it transitions from a fluid state to a solid mass, entrapping water in various forms, such as gel water, capillary water, and ...

Strength of Concrete

KEY TERMS AND CONCEPTS

Soundness of Cement

The soundness of cement refers to the ability of cement paste to retain its volume after setting. Unsound cement can lead to expansion and structural damage due to the presence of free lime, magnesia, and calcium sulfate. Free lime hydrates very slowly, expanding and causing unsoundness, which is difficult to detect because it intercrystallizes with other compounds. Magnesia also reacts with water, forming crystals that can disrupt the cement&#39;s structure. Calcium sulfate can create ettringite, which leads to expansion if not adequately consumed during the setting process.
The standard tests for cement soundness are Le Chatelier&#39;s and autoclave tests. Le Chatelier&#39;s test primarily detects unsoundness from free lime, and the autoclave test measures the unsoundness from free lime and magnesia. If expansion is more than 0.8% of the original length after autoclaving, the cement may be considered unsound. Unsoundness from free lime is rare, with magnesium-related issues more prevalent in US-produced cement due to the raw materials used.

Occasionally, after the cement paste sets, the free lime, magnesia, and calcium sulfate may hydrate, causing a destructive expansion in the hardened ...

Testing Water Quality

When the quality of water for concrete preparation is uncertain, its impact on the setting time of cement and compressive strength of mortar is assessed by comparison with de-ionized or distilled water benchmarks. American Society for Testing and Materials (ASTM) C1602 requires the setting times to be within 90 minutes of the control, British Standard (BS) 3146:1980 allows a 30-minute variance in the initial setting, while British Standards European Norm (BS EN) 1008 specifies initial setting time must be not less than 1 hour and final setting time less than 12 hours, within a 25 percent variability from the results with distilled water. Mortar cubes made with test water must achieve at least 90 percent of the compressive strength of those with distilled water.
Testing for impurities, such as chlorides, sulfates, total solids, alkalis, etc, is critical, as concentrations must not exceed established limits to ensure concrete quality. When seawater is utilized, the concrete&#39;s long-term compressive strength must not be over 15 percent lower than that of freshwater-prepared concrete. Moreover, performance tests simulating natural wetting and drying are employed to check for potential staining, a necessary step to verify the water&#39;s suitability for curing without compromising the concrete&#39;s appearance.

If the quality of water available for preparing concrete is uncertain, its suitability is determined by comparing the setting time of cement and the ...