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

Summary

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

Abstract

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.

Introduction

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 enviro....

Protocol

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

1. Preparation of the mold
   1. Use a brush to clean up a mold of size 70 mm × 70 mm × 70 mm, making sure that the inner surfaces of the mold are impurity-free.
   2. Brush mold-release diesel oil evenly on the inner surfaces of the mold using another brush.

Results

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 (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 (Figure 2

Discussion

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.......

Materials

List of materials used in this article

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