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...

<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 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&#215;70mm&#215;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&#181;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...

Watch this Scientific Journal Video about Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way at JoVE.com

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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