A CRTTICAL EVALUATION OF ASTM METHOD C 1 14, SECTION19 FOR THE DETERMINATION OF TOTAL CHLORIDE CONTENT OF

CURED CEMENT AND CONCRETE

Shahram Karimi

A thesis submitted in conformity with the requirements for the degree of Maser of Applied Science

Graduate Department of Chernical Engineering and Applied Cherni- University of Toronto

O Copyright by Shahrarn Karimi (300 1 )

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TITLE: A CRInCAL EVALUATION OF ASTM METHOD Cl 14, SECTION19 FOR THE DETERMINATION OF TOTAL CHLOEüDE CONTENT OF CURED CEMENT AND CONCRETE

AUTHOR: SHAHRAM KARiMI

DEGREE OF MASTER OF APPLIED SCIENCE

GRADUATE DEPARTMENT OF CHEMICAL ENGiNEERiNG AND APPLIED CHEMISTRY

üNIVERSITY OF TORONTO (200 1)

An assessrnent was made of the accuracy and precision of ASTM Method C 1 14 for the

anatysis of chlonde in cured cernent paste and concrete.

Cernent pastes with water-to-cement ratios of 0.45. containing known different amounts

of chIoride ranging from 0.0 to 8.0 percent by weight of dry cement. were prepared using

ASTM Type i Ordinary Portland Cement. The samples were alIowed to cure in a

hydrostat for 7 and 28 days with and without rotation and then were analyzed for total

chlonde content using ASTM Method C 114. Complete extraction of chloride fiom the

cernent specirnens was not achieved. showing the inability of the above method to bring

dl the chlorides into solution for analysis. For some of the samples contaîning hi&

chloride content the ASTM method under-reported the true values by as much as 70%.

ACKNOWLEDGMENTS -

1 would like to thank Professor Frank R Foulkes for his time. genuhe interest. and

invaluable guidance throughout this project. 1 wouid also like to thank my family for

their exceptional support and encouragement durùig the course of this study.

iv

TABLE OF CONTENTS

Abstract ................................................................... ................................................................... Ac knowledpents

Table of Contents ................................................................... List of Tables ..... ............................................................... List of Figures .. ................................................................. .

1.0 Introduction .......................................................... 1 . 1 Background .......................................................... 1 . 2 Objective ..........................................................

2.0 Litenture Review ................................................. 2.1 Portland Cernent

2.1.1 Definition ................................................ ........................................ 2.1.2 Manufacturing Process

............................... 2.1.3 Types of Portland Cernent ............. 2.1 -4 Chernical Composition of Portland Cernent

2 . I -5 Cernent Hydration ........................................ ............. 2.2 tntluence of Chloride Ions on Concrete Corrosion

...................................... 2.2.1 Sources of Chloride Ions .................................... 2.2.2 Binding of Chioride Ions

2.3.2.1 Types of Chioride Bonds ..................... ............ 2.2.2.2 Influence of C3A on Chioride Binding

2.2.2.3 Influence of Calcium Silicate Hydrate on Chloride .............................................. Binding

2.2.2.4 Effects of Associated Cation Type on Chloride .............................................. Binding

2.2.2.5 Influence of Sulfates on Chioride Binding ...... 2.3 Analysis of Chloride Content in Cured Cernent Pastes ............

2.3.1 Background ................................................ .... 3 . 2 Analysis of Cernent Pastes and Concrete for Chloride

3.0 Experhental Description ......................................................... 3-1 Overview

3.2 Materiais and Specimens ....................................... 3 2 . 1 Materials ................................................

................................................ 3.22 Cernent Samples 3 2.3 Equiprnent ................................................

3.3 Expecirnental Procedures ............................................. 3 3.1 Bais of Method ................................................ 3.3 2 Description of the Method ..............................

40 ResuIts and Discussion ..................... J . I Evaporable Water in Hydrated Cernent Pastes

4.2 Total Chloride Determination .......................................

. . 11 ... 111

iv vi vii

1 1 3

4 4 4 5 6 7 8 8 8 9 9

13

13 14 15 15 16

19 19 19 20 22 13 .. 22 22

29 29

Determination of the total chioride content of cernent slabs cured for 7 and 28 &ys ............................... 31 influence of Curing T i e on Total Chloride Detennination 36 infiuence of Rotation on Total Chlonde Determination .... 37 A Critical Analysis of the Data ............................... 43 The Influence of Acid Type and Concentration on Total Chloride Determination ...................................... 17 Cornparison of Berman's Method with the ASTM Method Cl14 ........................................................ 48 Effects of Heating, Digestion Time . and Sample Covering 49 Volatilization Losses by Heating ........................... 53

.................................................................. 3.0 Conclusions 54

6.0 Rscommendations ......................................................... 55

7.0 Réferences .............................................................. 56

Appendices Appendix A - General Data ....................................... 59

Appendix B - Tables of Some Measured Data ................. 60

.............................. Appendix C - Sample Calculations 63

LIST OF TABLES

Table f - Portland Cernent Types and Their Applications

Table 2 - Main Chernical Cornpounds of Portland Cernent

Table 2 - Chernical Composiiion of PortIand Cernent Type 1

Table 4 - A Cornparison of ASTM Method C 114 and Berman's Method for Total

ChIoride Analysis

Table 5 - Evaporable Water in Cured Cernent Spheres

Table 6 - Total Chloride Content of Hardened Cernent Slabs Cured for 7 days

Table 7 - Total Chloride Content of Hardened Cernent Slabs Cured for 28 days

Table 8 - Total Chloride Content of Hardened Cernent Spheres Cured for 28 days

Tabte 9 - Etïects of Acid Type and Concentration on Total Chloride Determination in

Cernent Pastes

Table 10 - Cornparison of Berman and ASTM Methods

Table 1 1 - EtTects of Different Parameters on the Total Chloride Extraction of Cernent

Table 12 - EtTects of Heating Tirne on Sodium Chloride Solution

Table AI - Common Vdues of Cornpound Composition of Portland Cements of Different Tges

Table .42 - Main Types of Portland Cernent

Table B 1 - Tables of Sorne Measured Dota

Table B2 - General Date for Cernent Slabs Cured for 28 Days

Table B3 - General Data for Cernent Spheres Cured for 28 Days

LIST OF FlCURES

Figure 1 - Passivated Steel in Concrete

Figure 1 - Corrosion CeIl in Concrete

Figure 3 - Free Chloride Concentration in Pore Solution as a Function of C3A Content

when Sodium Chloride is added at the Tiie of Mixing

Figure 3 - Effect of C3A Content on the Free Chloride Concentration of Pore Soiution in

Cernent Pastes

Figure 5 - Cernent Sampies are kept in Airtight Plastic Containers to Avoid Carbonation

Figure 6 - Fully Automated Titration Machine (QC-Titratem)

Figure 7 - Acid Extraction and Vacuum Apparatus

Figure 8 - Sample Potentiometric Titration Curve for Chloride in Cured Cernent Faste

Figure 9a - Actuai versus Experimental Chloride Content in Cernent Slabs Cured for 7

Days

Figure 9b - Percent Deviation Using ASïM Method versus Actual Chlonde Content for

Cement SIabs Cured for 7 Days

Figure Ion - Actual versus Experimental Chlonde Content in Cernent Stabs Cured t'or 28

Days

Figure [Ob - Percent Deviation Using ASTM Method versus Actual ChIoride Content for

Cernent SIabs Cured for 28 Days

Figure I 1 a - - Actual versus Experimentai Chloride Content in Cernent Spheres Cured

for 28 days

Figure 1 1 b - Percent Deviation Using ASTM Method versus Actual Chloride Content for

Cernent Spheres Cured for 18 Days

Figure 12a - Amal versus ExperimentaI Chioride Content in Different Cernent SampIes

Figure 1% - Percent Deviation Using ASTM Method versus Actual Chloride Content

Figure 13 - Caiibration Curve: Actual Total Chloride Content versus Totai Chloride

According ro ASTM Method for Cernent SIabs Cured for 7 days

Figure 14 - - Calibtation Curve: Actuai Total Chloride Content versus Totd Chloride

According to MTM Method for Cernent SIabs Cured for 28 days

viii

Figure 15 - Calibration Curve: Actuai Total Chioride Content versus Total Chioride

According to ASTM Method for Cernent Spheres Cured for 28 days (rotated for 24 h)

1.0 INTRODUCTION

1.1 Background

Concrete and steel are. by tàr, the most common raw materials used in construction

today, They sometimes compte but usually complernent each other. Reinforced

concrete is a prime example of such a beneficiai coexistence. Concrete is very strong in

compression but cannot withstand high tensile stresses: as a result, steel bars are

embedded within the concrete to produce a composite rnaterial that exhibits desirable

properties under both compression and tension. In r e m concrete provides a suitable

environment for steel by inhibithg the corrosion of embedded steel bars. This is

accomplished through the maintenance of a medium that is highly aikaline. due to the

presence of hydroxyl ions (OH3. This high alkaiinity encourages steel bars to passivate.

which in tum protects them h m comsion. The pH inside concrete is reported to be

around 13.0 and even higher [l?]. In addition. sound. goodquaiity concrete

significantly lowers the rate of dithion of aggressive ions such as chloride and sulfate

ions to the rnetal surface. thereby further reducing the risk of corrosion.

The abovementioned passive film can be desuoyed either by carbonation through a

lowering of the pH of the pore solution or by ingress of aggressive ions mrch as chloride

ions into the cernent matrix. Once this passive film is destroyed, corrosion of the steel

can occur. leading to the formation of corrosion products - mostly iron oxides - which

rnay expand to occupy h m two to seven times the voIume of the original steel [3]. Such

expansion can produce intemal forces that can lead to cracking and spalling of the

concrete and, subsequently. to the demise of the whole structure since. it is now exposed

to the surmunding environment

The diffusion of aggressive chlonde ions into concrete structures has been the subjcct of

a great deal of research and debate during the past few decades, A search of the j o d s

Cernent and Concrete Research and American Concrete Institute of Materials Journui by

the author revealed that steel reinforcement corrosion by chloride ions has been cited in

about 30% of the articles since the eady 1980's. This trend wiil probably continue on

account of the ever-increasing use of deicing salts on roadways and bridge decks during

winter. especiaily in North America

To understand the problem and the methods of protecting the reinforcing steel from

chloride anack. it is necessary to study the mechanism of chloride ion d i f i i on into the

concrete. This involves determining the diffusion coetlicient of chioride ions into

hydrated cement pastes [4]. Before conducting such a study. one must be able to measuse

the chloride content of hardened cement paste or concrete with accuacy and certainty.

The most widely used method in North America utilizes ASTM Method C 114. section

19-chloride [SI. which in turn is based on Berman's Method [6] . According to this

method. the total chloride ion content of a sarnple is determined by digesting it in 1+I

nitric acid. filtering. and then canying out a potentiometric titration with silver nitrate

using a chloride-selective electrode. However. surprisingly. it is not clear whether such a

method or any other acid extraction method is capable of determining the me or total

chioride content of the sample [q.

Nevertheless. chIoride analysis is criticai wben conducting duability assessrnent of

exisring concrete structures such as bridge decks and marine strucnues [8]. It is aiso

important to be able to determine the cidoride contents of k h concrete and its

constituents for quality control purposes.

12 Objective

The objective of this research projet was to evaluate the accmcy and consistency of the

standard acid e-utraction method - ASTM Method C I 14. Section 19-chionde - to

determine total chioride content of c d cernent paste specimens.

2.0 LITERATURE REMEW

2.1 Portland Cernent

2.1.1 Definition

According to ASTM C 150. Portland Cernent is defined as "hydraulic cernent produced

by pulverizing clinken consisting essentiaily of hydraulic calcium silicates. usually

containing one or more of the f o m of calcium sulfate as an inter p u n d addition" [9].

2.1.2 Manufacturing Process

Portland cernent is produced by grinding and heating a mixture of calcium and silica

called calcining and sintering respectively. in appropriate forms and proportions up to

about 1500 O C in a rotary cernent kiln. which is a long and sIoping cylinder that rotates

slowly to mix its contents as they move through it. Cement kiIns consist of various zones

with ditkrent temperames to facilitate the occurrence of complex chemicai and physicai

reactions that are required to make the consituents rem with each other.'

The above process cm be done either with or without water. the former being called the

"wet process" and the latter the "dry process". About 70% of al1 plants running in the

United States utilize the dry process. while the remaining 30%. mostly older plants. use

the wet process. in which raw materials are mixed under wet conditions.'

2.13 TypesofPortiaadCement

Ordinary Portiand Cernent (OPC) is by far the most common type in use: in the United

States done. more than 83 million tons were produced in 1998 [IO]. in addition.

' Source: www.uvi.ed/San~hysic~SC13~~WeWSmcnirr/ChemO~ement.hml

4

different types of OPC are produced to meet Merent needs. The American Society for

Testing and Materials Iists eight types of cernent in ASTM C 150. A brief description of

each type and its uses is given in Tables 1 '. Al, and A2.

Table 1 - Portland Cernent Types and Their ~ ~ ~ l i c a t i o n s '

Cernent Type Applications

I Generai purpose cernent. no limits are imposed

II Used when moderate sulfate-resistance is required

[II

IV

v

Used when early high-strength is desired

Used when low heat of hydration is required

Used when high sulfate resistance is critical

Sirnilar to type 1 with an air-enuaining agent

Similar to type II with an air-entraining agent

IIIA Similar to type III with an airentraining agent

According to the US Department of Transportation based on data provided by the U.S.

Department of the tnterior'. more than 92% of the Portiand cernent produced in the

United States consists of types 1 and II. while type III accounts for 3.5%. Ordinary

Portland cement complying with ASTM type 1. supplied by Lafarge Canada was used to

'make the specimens in this work.

2.1.1 Chemical Composition of Portland Cernent

.nie right different types of Portland cernent descnkd in the previous section differ h m

one another in their chernical composition. As discussed earlier. the main constituents of

I Source: www.fhwado~gov/in~cturelmaterials~cemen~htmI

5

Portland cernent are lime, silica, al- and ùon oxide. These react with each other in

the cernent kiln to form more complex compounds. The amount of each cornpound

dictates the type and characteristics of the finished Portland cernent product. Four

complex compounds are considemi to be the major constituents of cernent; and are

denoted by the ASTM as tricalcium silicate, dicalcium silicate. tricalcium aluminate. and

tetracalcium alurninoferrite. and comprise 90% of the cernent by weight These

compounds are listed in Table 2. dong with their chernical fonnulae and abbreviated

symbols [IO].

Table 2 - Main Chemical Compounds of Portland Cernent

Name of Cornpound C hemical Formula Ab breviation

Tricalcium silicate 3Ca0.Si02 c3s

Dicalcium silicate 2Ca0.Si02 CIS

Tticalciurn durninate 3CaO.Ai2O3 C3A

Tetracdciurn alunino ferrite 4Ca0.Alz03.Fez03 C+AF

2.15 Cernent Hydration

Anhydrous Portland cement is a gray powder with particle sizes in the range of

1 ro 50 191. M e n it is disperseci in water. ail the rninerds (CjS. C2S. C j k and

C&F) tsact with the water to produce very insoluble precipitates of Calcium Silicate

Hydrates (C-S-H), calcium aluminate hydrates, and calcium sulfoaiuminate hydrate

(called ettringite). The reactions of the silicates are shown below.

In addition to the above compounds, C3A and C2A also produce calcium hydroxide.

Ca(OH)2. which is slightly soluble in water. Calcium hydroxide reacts with srnaII

amounts of sodium and potassium sulfates that are present s in the cement and results in

the tonnation of potassium and sodium hydroxides. both of which are very soluble in

water.

It cm be seen that during the fmt few hours of hydration. the aikalinity of the pore

solution is mainly due to the formation of calcium hydroxide: but as the hydration

progresses. the pH of the pore solution becomes deterrnined more by the production of

sodium and potassium hydroxides.

23 Influence of Chloride Ions on Concrete Corrosion

2.2.1 Sources of Chloride Ions

As mentioned in section 1.1, the high allralinity of the concrete provides embedded

reinforcement steeI with a corrosion-ke environment as long as the passive layer of

7-Fe203 is not disnirbed. However. it is well documented [ i l . 121 that the intrusion of

chloride ions into concrete can destroy this passive film and initiate corrosion. provided

that water and oxygen also are present, as shown in Figures 1 and 2 [4].

- * . . an- . 0"- . "": t 1 -

Figure 1 - Passivated steel in concreteC41 Figure 2 - Corrosion ce11 in Concrete[J]

Chioride ions can be introduced to the concrete either at the time of mixing. by the

addition of calcium chloride as an accelerator. or they may penetrate into the concrete

from outside sources. such as deicing salts used in winter months.

22.2 Binding of Chloride Ions

ChIorides in cement pastes or concrete are found in three forms: bound with the hydration

products. adsorbed to the surface of the hyâration products. or in the k state within the

pore solution. However, it should be noted that ody the tiee chlorides in cernent pastes

or concrete - water-soluble chlorides - c m contnhte to reinforcement corrosion [7. 131

2 2 3 Types of Chloride Boads

It is well known that chlorides. regardiess of their origin. can be bound to the hydrated

products in cernent pastes or concrete [14]. Many cesearches have shown that the binding

capacity of the hydrated cernent dictates the amount of chloride that can be taken out of

the solution: ix.. be bound to the cernent hydration products. In light of this, two types of

bonds have been identified: physical and chernicd bonds [15].

In a chemical bond. chloride ions are incorporated in the Iattice of the crystalline

hydration products and are held together by a chemical bond. Two such chloride-

containing products are calcium monochloroalurninate and calcium trichloroaluminate

[16]. The arnount of chloride ion that can be chemically bound to the hydration products

depends on tictors such as the type and composition of the cernent or concrete. the

presence of other anions and cations. pH orthe pore soIution. and the temperature.

Chloride ions also can be physicaily adsorbeci at the surface of the hydration products. In

general. it appears that such bonds are weaker than the chemical bonds described above.

However. it is not well known how chloride ions are panitioned within these three States.

223.2 Infiueace of Cd on Cbloride Binding

Many workers have commented on the role of C A in binding of chionde ions in cernent

or concrete [2. 15. 14, As mentioued above. the arnount of Cl- that can be bound

depends on the bidiig capacity of the hydrated cernent. This would translate into the

C A content of the cernent: the higher the C3A content, the higher the Cl- binding

capacity .

The reaction of C3A with water is rapid and exothedc. The litteration of a large arnount

of heat has an adverse effect on the concrete in t enu of workability: consequently. it is

important to retard this reaction by some means. This is usually done by adding gypsum

to the concrete mix prior to hydration in order to slow down the reaction [9].

Chlorides in cernent react with calcium aluminates and, to a lesser extent, calcium

alumino femtes. to tom chloroaluminates and c hloro femte hydrates. The main product

king hnned is chIoroaluminate hydrate known as Friedel's salt.

3 CaO.AI2O3 .CaC12. 1 OH@. A similar reaction with tetracalcium alumino femte (C4AF)

resdts in the formation of calcium chioroferrite. ~C~OEQO;.C~CI~. 1 OHtO [l O]. Bakker

[1 51 has reported that calcium oxychloride. CaO.CaClZ2H20. also will be fonned. but

only at high chloride concentrations.

The generd consensus used to be that cements with high CjA content wodd be Iess

prone to chloride attack. Lambert et al [18] reported a noticeable reduction in chloride in

pore solution wïth increasing C3A content, when chioride is added at the time of mixing

(adrnixed chloride). Figure 3 is a graphical representation of the above study.

Figure 3 - Free chloride concentration in pore solution as a tiuiction of C3A content

when sodium chloride is added at the time of mixing [18]

Rasheeduzzafar et ai [2] has aiso noted a decrease in the arnount of fiee chloride ions in

the pore solution with increased C3A content in cernent paste sampies having a water-to-

cernent ratio ot'0.60 (Figure 4).

However. it should be borne in rnind that if sulphate sdts are present in the cernent mix.

CjA will react preferentially with them to produce trisulph0duItIi~te hydrate. The

remaining C3A will then react with chiorides. Sorne researchers [ 10. 161 have argued that

reaction with CjA is the dominant mechanism for the removal of chiorides fiom the pore

solution when chloride is added at the tirne of rnixing. because of the rapidity of the

reaction. In the case of extemal chloride ingress into cernent or concrete. a smaller

amount of chloroaluminate is fomed because Iess C3A is avaiIable.

Figure 4 - EtTect of C3A content on the t'ree chloride concentration of pore solution in cernent pastes [2]

According to Lambert et ai [18] and Delagrave [16]. other factors also contribute to the

removal of chlotide ions h m the mix water. Lambert et ai [18] have reported that

cements with no C3A have exhibited considerable chloride-binding capacity.

DeIpve [161 has reported on the data provided by other researches [3. 191 showing that

chlorides can also react with tricalcium sikate hydrates as well as with dicalcium silicate

hydrates to form insolubte complexes. These will be briefly discussed in the following

section.

23.23 Influence of Calcium Silicate Hydrate on Chloride Biading

Tricalcium aluminate plays a critical role in the binding of free chiondes in mix water to

fonn insoluble complexes, thereby reducing the risk of reinforcement corrosion-

However. other processes also have k e n found to remove kt: chloride ions h m the

mix water. One important mechanism is suggested by Ramachandran [3]. who states that

fiee chloride ions can interact with the C-S-H phase in three ways: they c m penetrate into

the C-S-H interlayer. bind to the hydrated calcium silicate iayen. or be bound in the C-S-H

layer. He has suggested that substantial arnounts of chloride ion. from the addition of

calcium chioride (CaCI?), can be removed h m the mix water via these- three modes.

However. other researchen have disputed Ramchandran's findings [18.20], Through the

application of high sampling technique. Diamond et al have shown that significant

arnounts of free chloride ions are retained in cernent paste sarnples with water-to-cernent

ratios ot'Od0 to 0.50. even aller long penods of hydration [18J. In general. there is a Iack

of understanding of how chloride ions interact with the C-S-H gel in the cernent paste or

concrete. There is also a limited quantitative knowledge regarding the above

mechanism(s) in the literature: therefore, the me effects of tricalcium and dicalcium

silicate hydrates rernain to be detemiined.

232.4 Effects of Associated Cation Type on Chloride Binding

The environmental conditions influence the cMoride binding capacity of cernent pastes

and concrete in different ways. The type and quanùty of sait that may tie present at the

time of mixing or may peuetrate the cernent matrix Vary from one environment to

another. The deicing sait used on roadways and bridge decks during winter months

consists mainly of sodium chloride, dthough other deicing agents such as calcium-

magnesium acetate (CMA) have shown promise [II]. Calcium chlonde has traditionally

been used as an accelerator in concrete structures to hcilitate setting. Buried concrete

structures might come into contact with subterranean water or soil. which contain

different types and quantities of salts. Marine structufes corne into contact with seawater

that is rich in sodium chloride with Iesser quantifies of KT ~a'*. M~'*. and SO/- [ L 71.

Numerous studies have shown that different cations will have different effects on the

chloride binding capacity of cement pastes or concrete. Arya et al [22] found that calcium

chloride will bind more than sodium chloride when added at the time of mixing. when

identical concentrations of both were used [Iq. Regourd [l3] has suggested that

magnesium sulfate (MgSO4) is the rnost harmful salt in seawater in terms of concrete

corrosion. According to him. magnesium chloride (MgCl>) is more active than sodium

chloride: thereby more h m can be expected from the hrmer saIt as far as attacking

cement is concerned.

2.2.2.5 Influence of Sulfates on Chloride Binding

The addition of sulfates to cernent pastes or concrete will lower the binding capacity of

the system. Hussain et ai [Z]. who measured the chioride uptake in cement pastes with

different C3A content and various sodium sulfate (NatSOa) concentrations, observeci that

a hi& sulfate cement bound less d o n d e than a Iow sulfate cernent. This can be

attributed to the preferential reacbon of suIfate with C;A phase. which will inhibit the

formation of Friedel's salt. Consequently, this wilI increase the concentration of chloride

ions in the pore solution.

In addition. both Hussain et J [23] and Hotden et J [24] have reported an increase in the

pH of the pore solution when sulphate ions were present at the tirne of mixing. An

increase in pH can be explained in terrns of charge neutrality. Hydroxyl ions (OH') will

enter the pore solution to balance the anions rernoved in the forrn of insoluble salt

complexes: this will result in an increase in the pH of the pore solution and.

consequcntly. will have an adverse effect on the chlotide binding [17].

23 Analysis of Cbloride Content in Cured Cernent Pastes

2.3.1 Background

Portland cernent concrete is one of the most versatile and widely used materials in the

constniction industry [9]. Its low cost. abundance. and ease of manufacture has made it

a pert'sct candidate for construction of buildings. pavements, dams. and bridge decks.

amongst others. The use of cementitious materials is very old. dating back to ancient

Egypt [IO]. The demand for concrete has been steadily increasing during the past 100

uears. and this trend will most Iikely continue in the future. However. the chloride-

induced corrosion of reinforcing steel ernbedded in concrete has become the subject of a

great deal of concern and research in the pst few decades. Whether it is a coastai

structure in the Middle East or a highway bridge deck in Canada the main mechanism of

tàilure has most ofien been damage related to reinforcement corrosion caused by the

ingress of chloride ions through the cernent rnatrix to the reinforcing steel [17].

Considerable effort has been devoted to solving this problem. and has created a great

need for developing an accurate and reliable meîhod to determine the chioride content of

hardened cement paste or concrete 1251.

Some anaiytical methods were in use about four decades ago. but there existed some

doubts in regard to their accuracy and precision; in addition, these older methods were

very time-consuming and labour extensive. In 1972. H. A. Berman [6] proposed a

method to determine the chloride content of hardened cernent pastes and concrete. that

cvcntually was adopted by the United States Feded Highwy Administration with some

modifications in 1974. and again in 1977 [251. A S W Method C 1 14. Section 19-

chloride is also based on the above method. with sorne minor moditications.

233 Anabsis of Cernent Pastes and Concrete for Chloride

As discussed earlier. chloride in cernent paste or concrete c m be found in two toms.

water-soluble and water-insoluble chioride. [n addition. water-insoluble or bound

chlorides are further divided into two sub-groups: chemically bound with the hydration

products and physically adsorbed to the calcium silicate hydrates (C-S-H) surface. It is

well established that onIy fixe chiorides can participate in corrosion: therefore. it would

seem logicai that only the amount of free chloride in concrete should be determined,

since onlv these chlorides can conrniute [O reinforcement corrosion. The U.S. Federal

Highway Administration laboratories have reported that 75 CO 80 percent of the total

chloride present in cured concrete is in the fonn of water-soluble chloride [26].

Consequently, nvo methods of chloride ion determination have k e n developed: free

chloride content and water-soluble chloride content.

Up to now. the most accurate method of determining the free chloride content in cernent

pastes or concrete has been the pore solution expression technique in which pore fluid in

the cernent paste or concrete is squeezed out under hi& pressure (300100 MPa) and then

analyzed for chioride content. The second method which determines water-soluble

chloride. involves dissolving or leaching out the fiee chloride in the pore solution.

Standard test methods for the determination of both types of chlonde exist [22].

However. it is recopized that the amount of chioride ions released into the solution

based of the latter method depends on severai factoa. süch as the amount of water added.

the duration of the extraction. the temperature of the system. and the methoci of agitation

[37.28]. tn addition although there are severai leaching techniques in use. none of thern

has produced accurate resuits over the range of chioride additions that was investigated

[271. Furthemore. it is known chat such methods will overestimate the Free chloride

content when applied to concrete exposed to e x t e d chloride such as deicing sdt [Y. 271.

With regard to pore solution expression. it has been found that it is more inaccurate when

appIied to concrete than when applied to cernent pastes [29]. Finally. when coxrete

specimens are dry. it becomes very dficult to obtain enough pare solution to c a q out

the experirnentd work [271.

in view of the above difficuities, it has becorne increasingiy cornmon practice to

determine the totd chioride content of cernent pastes or concrete in order to mess the

need for maintenance of existing concrete structures exposed to salt. and to insure that

new structures do not contain h a d LeveIs of chioride ions. ASTM Method C 114,

Sectionl9-chloride, recommends an acid digestion method in which the total chloride

contents of cernent pastes or concrete are measured.

3.0 EXPERlMENTAL DESCRIPTION

3.1 Overview

The experimental program consisteci of two phases:

Phase 1 - sample preparation

Phase II - determination of the chioride content of each specimen

Phase 1 involved the preparation of hÿo sets of samples: cement spheres (30 mm in

diameter) and cement slabs ( 3 7 x 3 7 ~ 7 mm). The cernent spheres were prepared in such a

manner as to minimize segregation by slowly rotating thern (2 revolutions per minute) for

34 hours after casting.

Phase 11 included analysis of al1 the specimens containine different amounts of chloride.

utilizïng either Berman's Method [6] or ASTM Method C I 1 4 Section 19-chloride [j].

A great deai of effort went into analyzing the samples and interpreting the results. The

objective of this phase was to determine the accuracy and precision of the above

methods. particularly the latter.

3.2 Materials and Specimens

3.2.1 Materials

The raw materials were obmined at the start of the program and were used throughout the

course of the work. The ordinaq Portland cernent (OPC) was supplied by Lafarge

Canada ( meeting ASTM Type 1 specifications)- The chernical composition of the above

material is shown in Table 3.

Analyticd reagent grade sodium chloride (NaCl, 99.9%) and silver nitrate (AgNO3.

mrets A.C.S. specifications) and deionized water ( 4 0 MSLm) were used to prepare

aqueous solutions for testing and to add to the mix water to prepare cernent samples.

Sodium chloride was dried at LOS O C for 24 hours prior to making solutions.

Table 3 - Chernical composition of Portland cement Type 1 (suppiied by Lafarge Canada)

Comwnent Weieht ( O h )

Compound Composition C S (tricalcium silicate) CLS (dicalcium silicate) C:A (tricalcium aluminate) CaA F (tetracalcium aluminot'emte)

3 2 2 Preparation of Cement Samples

For a pure OPC sampIe. 10 g of PortIand cernent was mixed with 4.5 g of deionized

water. to create a sample with a water-to-cernent ratio of 0.45. The cernent paste was

mixed thoroughly to produce a uniform sample, and then placed h i d e plastic molds.

Three sets of cement pastes were prepared:

1. The tint set was cast in plastic rnolds (37x37~7 mm) with the tnix water

containing chlorides at each of the concentrations given in Table 5 (page 30).

This set was used to evaluate the influence of the chioride concentration and

curing time in the determination of the fiee chloride content. A11 the samples

were cured in a hydrostat (100% relative humidity) for seven days at room

temperature (about 22 O C ) .

2. The second set was prepared in the same manner as the above set but they was

cured for 28 days.

3. The third set consisted of a senes of cernent pastes identical to the previous set

but was cast in 30 mm diameter plastic molds and rotated at about 3 rpm for 14

hours to minimize segregation. This series was used to evaiuate the influence

of rotation in the determination of the free chlonde content in addition to the

goals stated above.

The cernent sarnples were dried at 105 O C for 24 hours and were weighed to the nearest

0.001 g using a - Acculab VI mode1 - balance. The sarnples were cnished in an

enclosed metal box using a hammer and then were finely ground using a mortar and

pstle. Al1 powder cernent samples were stored in airtight plastic containers to avoid

carbonation (Figure 5 on page 23).

3 3 3 Equipment

The potentiometric titrations were performed using a computer-controlled burette -

Burivar 12, model MS-9A9 - with an Orion silver/sulfide combination electrode -

model 90-06. The accuracy of the instrument is + 0.01 mV and has an automatic

temperature compensation probe (Figwe 6 on page 23).

33 Experimental Procedures

33.1 Basis of the method

ASTM Method C 114. Section 19-chlotide involves the extraction of chloride ions

through an acid digestion process from c m d cement pastes or concrete. The total

chloride content of the sample is determined fiom analyzing the obtained aqueous

solution and is cxpressed as a percentage by weight of the dry sample: Le., cement or

concrete. This is based on the assumption that al1 chloride complexes (mainly

chloroalurninates) present in the sample wilI decompose upon the addition of nitric acid

and readily will come into the solution as k e chloride ions.

33.2 Description of the method

The method used for the determination of the total chloride contents of various ground

powders was similar to that outIined in ASTM Method Cl 14. Section 19-chloride. A

bnef description of this method is provided here. as weH as a comparison of the above

-

Figure 5 - Cernent samples kept in airtight plastic containers to avoid carbonation

Figure 6 - Fully Automateci Titration Apparatus (QC-Titrate?

method with its predecessor. Berman's method (Table 4). Complete descriptions of the

above methods have been given elsewhere [5,6].

After adequate grindimg, the samples were first dried at 105 OC to constant mass and

allowed to cool in a desiccator. They were then sieved through a 3 1 5-micron sieve and

only material passing the sieve was kept for analysis. Five grams of sample was placed

in a 250 mL beaker and dispersed with 75 mL of deionized water.' Twenty-five

milliliten of dilute (I+I) nitric acid was immediately and slowly poured into the beaker

and the solution was stirred with a glass-stining rod to break up any lumps. Three

milliliters of hydrogen peroxide (30% solution) then was added to the mixture if the smell

of hydrogen sulfide was strong. The beaker was covered with a watch glass and allowed

to stand for 1 to 2 minutes. after which it was placed on a preheated hot plate and brou@

just to a boil. The covered sample then was removed from the hot plate and was allowed

to cool until it was saîè to handle for filtering,

A 500-mL Büchner funne1 and fiItration Rask was used to tilter the solution: vacuum was

applied to facilitate the filtration (Figure 7). The filtering procedure was as follows:

Ali the glassware was rinsed with deionized water prior to filtration.

A 9-cm coarse filter paper was placed inside the h e l and was washed with four

25-mL doses of deionized water.

The washings were discarded and the flask was rinsed with a srnail portion of

deionized water.

I ASTM CI 14 requires 5 g samples for marerials having an expected chloride content of l e s than about 0.15% chloride and propomonally smaller samples for materials having higher chloride contents.

Table 4 - A cornparison of ASTM Method C 1 14 and Berman's Method for total chloride analysis

1 to 3 gram samples.

Add 10 mL distilled water and stir.

Add 3 mL o f concenaated HN03 and air.

Dilute with hot water to 50 mL.

If necessary. add more acid:

Methy l oranse indicator -. red solution

Heat the solution at medium heat and boil for ont

minute (to avoid losing volatile chlorine).

Filter into a 150-mL beaker. Use double filterç:

medium and hi& pomsity.

Decant the clear solution and wrtsh

the tilter paper with hot distilled water 5 to 10 tirnes

and allow the tiltrate to cool to room tempefanue.

Titrate potentiomemcally with

0.0 i M or 0.025 M AgN03 solution.

10. %CI is calculated using:

V: Volume o f AgNO; added

M: Moralin o f AgNO: solution

W: Weight o f the sarnple (3)

ASTM Method C 114 -Seetion 19. chloride (1997)

5g cement or log concrete.

Add 75 mL water.

Add 75 mL o f dilute (Itl) HNOl and stir.

If can srnet1 H2S. add 3 ml H a .

Add 3 dmps o f methyl orange indicator and stir. Covcr the

beaker and allow to stand for 1 to 2 minutes. If solution

turns yellow or yellow-orange, add more ( l+ 1) acid until

solution is faint pink or red. Then add 10 more drops.

Heat the solution rapidly. while covered to boiling. Do mot

boil for more than few seconds.

Wash a corne-textured tilter four times with 25-mL

increments o f watcr into a flask under suction.

Wash the tlask and filter the sample solution. Rinse the

beaker and the filter paper twice with small ponions of

water. Transfer the f i l m e to a 150-mL beaker and rime the

flask once with water. Cool the filmte to roorn temprnrurr

The volume should not exceed 175 mL. To the cooIed

sample add 1.00 mL o f standard 0.05 M NaCI.

Titrate potentiometrically with 0.05 M AgN03 solution.

IO. Use the formula k l o w to calculate %CI:

V,: Volume o f AgNOl used for sample titrarion V?; Volume o f AgN03 used for blank litration* M: Morality o f AgNO3 solution W: Wcight o f the sample (g) 0.10: milliequivalents o f NaCl added

(O2mL x 0.05 N)

* refer to ASTM C I 14 for biank prepmion [SI.

Figure 7 - Acid Extraction and Vacuum Apparatus

0 The suction apparatus was assembleci and the solution was filtered under vacuum.

Once the solution went through, the residue was rinsed twice with small portions

of distilled water.

0 The tiltrate was poured back into the original beaker and the flask was rinsed hto

the beaker. The final volume was 160-180 mi..

a The beaker was covered with a watch glas and was placed in a 25 OC water bath

to cool.

Two milliliters of standard 0.0500 M NaCl solution was added CO the cooled sample.

which then was titrated potentiometrically with standardized 0.0500 M silver nitrate

iA2NOI) solution using the automaleci titracor. QC-Titratorr\'. The titration set un is

shown in Figure 7 and a sample titration cuve is presented in Figure 8. The end point of

the titration was reached when the change in mV pet volume of titrant added was at the

ma~imum.

It should be noted that two standard samples containing 0.0500 M chloride solutions were

used to calibrate the instrument every time rneasurements were taken.

PC-TitratlON PLUS

Sample Name ~aport D a k W û 3 2 ~ 1 7:18 PM Operator: A

GO.OS-SL28-2 Sample Number: 3926 Run Number 223

Equation Name Equation ResuR Un&

C 1 vel lcon~5.453'1000/svol 40.6048 ppm

prcnt (vel'tcon35.453'100)1(1000'swght) 0.0001 %CI

eP vel 4.00W mL

svol 5voI

tmn tcon

175.0000 mL Figure 8 - Sample Potentiometric

0.0500 Titration Curve and Output Data

4.0 RESULTS AND DISCUSSION

1.1 Evaporable Water in Hydrated Cernent Pastes

Water can be found in two foms in hydrated cernent pastes: evaporable water in the pore

solution and non-evaporable water as part of the hydrated cement products.

Hardened cement spheres were dned in an oven at IO5 "C for 24 hours after a 28-day

cure to determine their evaporable water content. It was found that evaporable water

comprised about 17% of the total mass of the specimens. Therrnogravimemc analysis is

required to detennine the percent of non-evaporable water of the cured cement samples

through loss on ignition. in which samples are heated at a rate of 35 OC per minute up to a

temperature of 1000 "C [30]. i-iowever. this was beyond the scope of this thesis. The

results are summarized in Table 5.

4.2 Total Chloride Determination

There is no doubt that the corrosion of reinforcing steel bars embedded in concrete

structures such as bridges. pavements. and marine structures has become a costly problem

in North Amerka. To address this. much work has been done throughout the wodd to

find solutions to prevent concrete deterioration in new structures and to mitigate the

problem in existing ones. The high performance concretes currently k ing recommended

for structures in which the presence of chloride is expected are characterized by low

permeability and diffisivity. The fim step to rneaswe the permeability and diffiisivity of

such concrete systerns is to determine their chioride dimision coefficients. To do this

successfully. a fast and reliabte rnethod is needed to determine the total chloride content

Table 5 - Evaporable Water in Cured Cernent Spheres

Set NaCl in Rotation Curing Weight (g) mixiraccr Tirne P d Before Afier A h After % Evaporablr ?/o Loss due

[Ml (hour) (day) Curing Drying Crushing Powderdrying water to cmhing

of the specirnens. Berman's method has traditionaily been used to do this: more recentiy.

ASTM has introduced a procedure for the detemination of the total chloride content of

cernent pastes and concrete which is based on Berman's method, with few rninor

modifications ( t ek to Table 4). Bot. rnethods chirn to achieve cornplete extraction of

chlorides h m cernent pastes and concrete to an accuracy of 0.5 percent of the arnount

present in the original sample [6].

A series o f cernent samples was prepared and chIoride ions were introduced into the mix

by dissolving known quantities of NaCl in the mix water. After pteparing the samples

according to the procedure outlined in section 3-22, their totai chloride contents were

determineci usine ASTM Method C 114. Section 19-chloride. as described in section

3.3.2. The results are presented in Tables 6 through 8.

4.2.1 Determinaiion of Total Chloride Content o f Cernent Specimens Cured for 7

and 28 Days

The tirst set of samples consisteci of 14 cernent slabs ( 3 7 x 2 7 ~ 7 mm) containing different

arnounts of chloride. ranging fnim 0.00 to 5-00 M. added at the time of mixing into the

mix water as NaCI. Afier wet curing in a 100% relative hurnidity container for 7 days.

total chloride contents were determined following the standard method de~cnbed in

section 3.3.2. The results are presented graphically in Figures 9a and 9b and nurnerically

in Table 6.

From Figure 9a. it is apparent that cornplete extraction of chlorides From the cernent

pastes was not achieved, The first trend that c m be seen is a _mdud reduction in the

percentage of r'ctracted chloride as the chloride content of the sarnple increases. The

tiltered extracts contained ody 4l to 97 percent of the total chloride; this signifies a

chloride loss of more than 55% at the highest concentration of 5 M NaCl. or 8% chloride

by weight of dry cernent. [t c m be hypothesized that an incomplete decornposition of

chloride-complexes such as chIoroaIuminate hydrates (Friedel's salt) has led to such

deviations from actuai vdues: this will be discussed in more detail in the fol~owing

sections. The second mnd (Figure 9b) is a very sharp increase in the rate of chloride loss

at iower concentrations, which is benveen 0.006 to 0.012 g CYg dry cernent. rhere is no

obvious explmation for this trend but it may be due to the formation of complexes that

-*-Adual Values

Slabs - 7 days

Figure 9a - Actual versus Experirnental Chloride Content in Cernent Slabs cured for 7 days

0.00 0.01 0.02 0.03 0.U 0.05 0.06 0.07 0.08 0.09

Actual Chloride Content {g Cri g dry cernent)

Figure 9b- Percent Deviation Ushg ASTM Method versus ActuaI Chioride Content for

Cernent Slabs Cured for 7 days (Error bars represent 1 standard deviation)

Table 6 - Total Chloride Content of Hardened Cernent Slabs Cured for 7 Days

Sam pie NaCl Chlofide Content (g) Name Concentraion (M) Acîuai Experïrnenîal %Deviation Avg. %Deviation %Chloride

NO.OO-SL07-1 NO.OOSL07-2 NO.OOSL07-3

F0.02-SLO7-1 F0.02-SLO7-2 F0.02-SLO7-3

G0.05SL07-1 GO.05-SLO7-2 G0.05SL07-3

H0.10-SL07-1 HO. 1 O-SL07-2 HO. 1 O-SLO7-3

10.20-SL07-1 10.20-SL07-2 t0.20-SLO7-3

J0.30-SLOf -1 J0.30-SL07-2 J0.30-SL07-3

K0.40-SL07-1 K0.40-SLO7-2 K0.40-SL07-3

LO.50-SL07-1 LO.50-SL07-2 LO.50-SLO7-3

M0.70-SL07-1 MO. 70-SL07-2 M0.70-SLO7-3

Al .00-SL07-1 Al .00-SL07-2 Al .00-SL07-3

62.00-SL07-1 82.00-SL07-2 82.00-SLO7-3

C3.00-SL07-1 C3.00-SL07-2 C3.OOSLO7-3

04.00SLO7-1 04.00-SLO7-2 04.00-SL07-3

€5.00-SL07-1 E5.00-SLO7-2 ES.W-SL07-3

O 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Actual Chloride Content (g CI 1 g dry cernent)

Figure I Oa - Actual versus Experimental Chtoride Content in Cernent Slabs Cured for 18 Days

slabs - 28 days

1

4.0 6 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Actual Chloride Content (g Cïlg cernent)

Figure IOb - Penient Deviation Using ASTM Method versus Actual Chloride Content for Cernent

Slabs Cured for 28 Days

Table 7 - Total Chloride Content of Hardened Cernent Slabs Cured for 28 Days

Sampie NaCl WMde Content (g) Name Concentraian [MI Achat Enierimental %Deviaion Ava. %Deviation %Chloride

N0.00.SL28-1 NO.OO-SL28-2 NO.OO-SL28-3

FO.02-SL20-1 FO.02-SL28-2 FO.02-SL28-3

G0.05SL28-1 G0.05-SL28-2 G0.05SL28-3

HO.lO-SL28-1 HO. 10-sua-2 HO. 10-SL28-3

10.20-SU81 10.20-sL28-2 10.20-SL07-3

J0.30-SU81 J0.30-SL28-2 J0.30-SL28-3

K0.40-SL28-1 K0.40-SL28-2 K0.40-SL28-3

LO.50-SL28- 1 L0.50-SL28-2 L0.50-SL28-3

M0.70-SL28-1 M0.70-SUC2 M0.70-SL28-3

A l .MISL28-1 A l .o@SL28-2 A l .00-SL28-3

B2.00-SL28-1 BZOO-SU82 B2.MISL28-3

C3.00-SL2&1 c3.00-SL28-2 c3.00-sL28-3

D4.00-sua-1 D4.00-sua2 D4.00-SL28-3

E5.OO-SL28-1 E5.MISL28-2 ES.OOSL28-3

are v e l hard to decompose, even with nitric acid, when the chloride concentration is

low. but more readily decornposable when chloride ions are abundant within the cernent

mauix.

The second series of tests was conducted on cernent slabs similar to the first series but

cured for 28 days, Figures 10a and lob and Table 7. respectively. present the -mphical

and numerical data for these slabs. The trends are similar to those observed for 74.

curing timss.

Figures 12a and 1Zb show the intluence of curing time on chloride extraction and

recovep fiom spheres cured for 28 days. It can be seen that. as in the case of slabs. as the

curing period increases. the percent chloride recovery decreases.

4.23 Influence of Curiag Time on Total Chloride Determination

Figures 9a and 10a show the percent deviation of the total chloride using the ASTM

method versus the actual chloride content for the above-mentioned series. As mentioned

above. the percent chloride extraction decreases as the actuai chloride content increases.

The test results were very similar for both curing times at lower chloride contents (up to

0.036 g Cl ! g dry cernent). but started to deviate from each other when the chioride

content increased to 0.044 g Cl 1 g dry cernent and beyond. Acid extraction of cernent

specimrns cured for 7 days were recovered 44 to 97 percent of the actuai chloride. while

those that were cured for 28 days only recovered 29 to 94 percent of the actuai chioride

added at the time of mixing. This signifies a chloride l o s of about 71% at the highest

chloride content of 0.403 g CI 1 g dry cernent. while the corresponding figure for the

7day cured samples is about 56%. This m be attributed to the reaction of k e chloride

ions in the pore solution with the cement hydration pmducts. particularly tncalcium

aluminate. to form chlorocomplexes such as Friedel's sait. It is generally accepted that

concrete or cernent continues to cure well after hydration kgins and may take years to

cornplete. Therefore. it is possible that the above reactions continue to occur atier 7 days.

consequently immobilizing more chioride ions h m the pore solution. If the acid

extraction is not successtùl in recovering al1 the chtonde ions. a p a t e r error will be

associated with the cernent samples that were cured for a longer period; i.e. 28 days.

4.23 Influence o f Rotation on Total Chloride Determination

The third set consisted of a series of cernent pastes identical to the second set but cast in

30 mm diameter plastic molds and rotated at about 2 rpm for 24 hours to minimize

segregation. This series was used to evaluate the intluence of rotation on the

determination of the total chloride content. in addition ro assessing the accuracy and

precision of .ASTM Method C 1 14. Section 19-chIoride.

.A cornparison of the results obtained for this set of samples with those of the previous

sets - cernent slabs cured for 7 and 28 days - indicates similatities in terms of

extracted chloride over the whoIe range of chloride content of 0.0 to 8.0%.

O 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

A-1 Chknd. Content (g CI 1 g dry cernent)

Figure I l a - .4ctual versus hperimental Chloride Content in Cernent Spheres Cured for 28 Days

0.00 0.01 0.02 0.03 0.M 0.05 0.M 0.07 0.08 0.M Acanl Chloride Content (g CI 1 g dry cement)

Figure I I b - Percent Deviation Using ASTM Method versus Actual Chlonde Content for Cernent

Spheres Cured For 28 Days

Table 8 - Total Chloride Content of Hardeneci Cernent Spheres Cured for 28 Days

NO.00-SP28-1 N0.00-SF'28-2 NO.OMP28-3

F0.02-SP28- 1 FO.02-SP28-2 FO.02-SP28-3

G0.05SP28-1 G0.05-SP28-2 G0.05-SP28-3

Ho.10-SP28-1 Ho. 10-SF'28-2 HO. 10-SPZ8-3

10.20-SP28-1 10.20-SP28-2 10.20-SP28-3

J0.30-SP28-1 J0.30-SP2ô-2 J0.30-SP28-3

K0.40-SP28-1 K0.40-SP28-2 KO.GSP28-3

LO.50-SP28-1 L0.50-SP28-2 LO.50-SP28-3

M0.70-SLO7-1 M0.70-SLO7-2 M0.70-SLO7-3

A1.OO-SL07-1 Al .00SLO7-2 A1 .OGSL07-3

02.004 ~ 0 7 - 1 B2.00-SLO7-2 82.00-SL07-3

C3.00-SLO7-1 (3.00-SLO7-2 C3.00-SL07-3

04.00SL07-1 04.00-SL07-2 û4.00-SL07-3

E5.WL07-1 E5.00SL07-2 E5.OITSL07-3

Acid extraction of cement spheres cured for 28 days recovered 34 to 96 percent of the

total chloride that was added to the rnix at the tirne of mixing.

The agreement found between results obtained for this series and the previous two series

indicates the inability of ASTM Method C 114, Section 19-chloride to extract al1 the

chloride from hardened cernent samples. The decomposition in niuic acid is the most

widely used rnethod for chloride extraction for several reasons: it is very fast compared

with other methods. the procedure is very simple to follow. it is economical. and it has

been claimed to be very accurate and precise [6]. The main objective of this part of the

study was to examine this l a s claim. which the results have show to be invalid.

The results presented in Figures 12a and 12b and in Tables 7 and 8 show that the amount

of acid-soluble chloride extracted fiom cernent samples rotated h r 24 hour exceeds the

arnount of acid-soluble chloride extracted h m cernent samples that have not k e n

rotated. This cm be clearIy seen especially in sarnples with chloride contents greater than

about 1 .O%. There is no obvious explanation for this trend. but the results ernphasize the

complexity of the hydration and chioroaIuminate and other chloro-complex formation

mechanisms within the cernent rnatrix. The fact that the amount of acid-soluble chlorides

increases when cernent specirnens are mtated tends to emphosize the significance of the

pore structure of the cernent matrix. which controls the accessibility of chioride ions to

the reaction sites. If the marked reduction of acid-sduble chloride is due to insoluble

chloro-complex rormation, then by rotating the specirnens. chioride ions are restricted in

their movements since pore structures are formed differently than when the specirnens are

not rotated. When cernent samples are not rotated, segregation will occur. in which

mixture components separate and different phases wiII be formed within the cernent

matrix. As a result, pore structure geornetry will be affecteci and larger pores and

capillary voids tend to be formed. Chloride ions. in tum. will have more access to

reaction sites and. thecefore. cm be bound more easily and freely to the cement hydration

products. Furthemore, the above results show that chloride binding capacity and other

important characteristics of the cement are not soleIy based on cernent composition but

also can be affected by other factors, such as the pore structure of the cernent.

Segrcgation is defined "as separation of the constituents of a heterogeneous mixture so

that their distribution is no longer uniforrn". in wet cernent. this is rnanifested by the

separation of grout (cernent and water) h m the mix [IO]. This will directly influence the

formation of pore structures within the cernent matrix and. consequently. will affect other

cernent characteristics, such as pore solution chemistry.

-*-Actual Chloride Content- -*Cement slabs, aired for 7 days, not rotated

O 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

ActuaI Chloride Content (g CI 1 g dry cernent)

Figure 13a - Actual versus Expen'rnental Chioride Content in different Cernent Sarnples

+ Cement siabs. cured for 7 days. n u faakd

8 Cernent shbs. curad for 28 days. n u rUatecl

Cement spheres. cured far 28 W. mrated for 24

0.0 0.M 0.01 0.02 0.03 0.01 0.05 0.08 0.07 0.M 0.09

k tua l Chloride Content (g CI 1 g dry cernent)

Figure 1 Zb - Percent Deviation Using ASTM Method versus Actual Chloride Content

Total Chloride According to ASTM Method for Cernent Spheres

42.4 Critical Analysis of the Data

The fact that the total quantity of chloride was not extracted in al1 the above experiments,

even at the lowest chioride content of 0.006 g Cl 1 g dry cernent. shows the inability of

ASTM Method Cl 14, Section 19-chloride to bring al1 the chlorides into solution for

analysis. Three graphs (Figures 13 -15) have been constmcted based on the results

obtained in the previous sections. These graphs can be used as caiibration curves when

the actual total chloride content in a cured sample of Type 1 OPC is not known. The

ASTM Method is relatively accurate when the chloride ievel is low: Le.. less than 0.02 g

CI / g cernent. However. the results deviate from actual levels when chloride levels start

to rise beyond 0.02 g Cl'/g cement.

tt is worth noting that the above rnethod or any other chloride extraction method.

consists of two distinct parts: complete extraction of chlorides fiom the sample and

accurate determination of the total quantity of the extracted chloride. The latter step is

usually pert'ormed with an autornated titrator. as in this research project. or a pH meter

and an appropriate chloride ion-selective electrode. It is the former step that requires an

understanding of the complexity of the problem. According to Berman [6], Lolivier [3 11

and Koelbel et al [32] both reported low results (low chloride extraction) even aller

several hours of heating with 1+8 and 1+4 iiN03. respectively. when using a method

similar to ASTM C IM. This has been mainiy attributed to the Iow concentrations of

HN03 used to digest the cernent samples. although several factors can be responsible for

this. The iniluences of a number of such factors have k e n investigated and the results

are presented in the following sections.

0.000 0.005 0.010 0.015 0.020 0.025 0.OM 0.035 0.010

Total Chloride Content Based on ASTM Method (g CI 1 g dry cernent)

Figure 13 - Calibration Curve: Actual Total Chioride Content versus Total Chloride Accordhg to ASTM Method for Cernent Slabs Cureci for 7 Days

0.000 0.005 0.010 0.0 15 0.020 0.025

Total Chloride Content Bosed on ASTM Method (g Cl / g dry cernent)

Figure 14 - Cdibration Curve: Actual Total Chioride Content versus Totd Chloride According to ASTM Method for Cernent SIabs Cured for 28 Days

0.000 0.005 0.010 0.015 0.020 0.025 0.030

Total Chloride Content Ba& on ASTM Method (g CI 1 g dry cernent)

Figure 15 - Calibration Curve: Actuai Total ChIoride Content versus Total Chloride

According to ASTM Method for Cernent Spheres Rotated for 24 h and Cured for 28 Days

42.5 The Influence o f Acid Concentration on Total Chloride Detemination

A series of tests was conducted on identical cernent samples containing known amounts

of chloride (added to the mix water) folIowing Berman's method. Al1 the parameters

were kept constant. but the type and quantity of the acid used for digestion were varied to

evaluate their intluence on the total chloride determination.

Table 9 presents the results of the above test perfomed on samples containing 1.1%

chloride ions (0.01 1 g Cïlg sample). Complete chloride recovery fiom the above

samples was not achieved by doubling, or even. tripling the amount of ni& acid.

Similar results were obtained when nimc acid was replaced by suifùric acid. It is

concluded that the specitied amount of acid required by the method is suficient. and that

the addition of more acid will not bring more chlorides into the solution.

Table 9 - Effects of Acid Type and Concentration on Total Chloride Determination in Cement Pastes

Sample Sample Weight Nitric Acid Sulfuric Acid Digestion tirne* Unrecovered Chloride Number (g) ( m u (mu (min) (%)

3716 1 .OO** 0.04 5717 1 .OO** 0.09

3 733 1 .O0 3 .O0 10 28.86

5734 1 .O0 3 .O0 1 O 28.57 * Digestion time refea to the t h e that the sample was digested by the acid before heating. ** These m p l e s consisteci of 1.00 mL of 0.70 M NaCl in water (no cernent) and were used as references.

4.2.6 Cornparison of Berman's Method with the ASTM Method Cl14

Many workers have attributed low chloride determinations to the incomplete recovery of

chlorides fiom hardened cement paste and concrete or chloride loss through chlorine

volatilization upon heating the mixture [6, 8, 3 1. 321. A series of experiments was

pertbrmed on identical tiardened cement pastes with a known quantity of chioride to

evaluate the influence of severai factors involved in the chloride extraction process.

Cement spheres. 30 mm in diameter. containing 0.3 1% chloride ions were cast according

to the method outiined in section 3 . 2 2 The spheres were rotated for 24 hours at about 2

rpm and then were cured for 27 days in a hydrostat, AAer drying in an oven at 105 O C for

24 hours. their total acid-soluble chloride contents were detennined as described by

ASTM C 1 14. Section 19-chloride and Berman with several modifications.

The acid-soluble content of the first series of sarnples was determined according to the

above methods: i.e. ASTM Method C 114. Section 19-chloride and Berman's method.

without any modifications, The chloride content measured through these methods served

nvo purposes: to compare the two methods in terms of their accuracy and precision, and

also to serve as a guide and reference for future studies. The Results of the chloride

analyses perhrmed on these sarnptes are shown in Table 10. A good agreement was

observed between the results obtained with both techniques. The average amount of

unrecovered or lost chloride was found to be 15.2% and 15.3% for the Berman and the

ASTM C 144 methods. ~spectively.

Table 10 - Comparison of Berman and ASTM Metfiods

Sample Method Digestion Filtered Convered Heated Unrecovered Standard Number Time (min.) Chloride (%) Deviation

64 Benrian - 3 Yes Yes Yes 15.09 65 Bennan 2 Yes Yes Yes 14.39 84 Benrian - 7 Yes Yes Yes 16.01 0.8 1

Average 15.16

66 ASTM 2 Yeç Yes Y s 15.18 67 ASTM - 3 Yes Yes Y s 15.12 85 ASTM 2 Yes Y a Y= 15-58 0.25 Average 15.29

1.2.7 Effixts of Heatiag, Digestion Time, and Sample Covering

As mentioned above. if the container is not properly covered, volatile chlorine can be lost

when the mixture is heated. The next set of experiments was designed to investigate the

influence of heating. digestion time. and proper cover on total chloride recovery.

The results tiom this part of the study are surnrnarized in TabIe I I . It can be seen that

digestion time has Iittle effect on the total chloride extraction. provided the mixture is

digested for at least two hours. Ln addition. a cornparison of the above results with those

presented in Table 10 shows that if the mixtures are allowed to digest for at least two

hours. the influence of heating wiil be minimal.

Some workers have claimed that the elimination of the filtration step in the total chIoride

extraction wilI not significantly affect the outcorne [8]. The elimination of this step is

desirable for several reasons. First. it simplifies the procedure. since filtering requires not

only extra time but a h extra care to perform. Second. it reduces the risk of producing

Table 1 1 - Effects of Different Parameters on the Total Chloride Extraction o f Cernent Pastes

Sample Methcd Digestion Filtered Covered Heated Unrecovwed Nurnber T h e Chlori& (%)

ASTM 2 days Yes ASTM Z ~ Y S _ Yes

, , - 7 .

- - .,.+ :-

h a n 2 d a ~ Yes Berman 2 days Yes

Berman 2 hours Yes Berman 2 hours Y s

GSTM i h w r s Yes ASTM l h m Yes

Bennan 1 hours No &man 2 hotus No

ASTM 2 hours No ASTM 2 hours No

&man* 2 min Yes Berman* 3 min Yes

ASTM* 1 min Yes ASTM* 1 min Yes

Yes Y s

Yes Ys

Y s Y e

Yes Yes

Y 6 Yes

Y 6 Yes

Y s Y s

Yes Yes

No No

, - -

No No

No No

No No

Y s Ys

Yes Y s

Yes Yes

Yes Yes

A- -Y= Is.64 * ReBus used to colIect any condensate that may have formai.

erroneous results by insuflicient washing of precipitates or incomplete filtration OP the

mixture [a]. However. it is important to remember that the soiid residue present in the

digested concrete mixture cm affect the outcome of the titration; i.e.. the end point

determination. It has been suggested that the solid matter can affect the ionic activity in

solution by ionic adsorption [8]. However. the titration cm proceed if the solution

contains only a srna11 amount of solid residue- [SI.

A series of tests was conducted to determine the effects of the elimination of the filtration

step on the total chioride extraction pmess outiined by the two test methods. The results

fiom this part of the mdy (Table I l . sample numbers 82.83.86, and 87) confumed the

ASTM's tinding that a smail arnount of solid residue will not interfere with the titration.

The amot.int of chloride loss was found to be 15.7% for both rnethods. These are in good

agreement with the results of the previous determinations for which the solutions were

tiltered.

Berman [6] and ASTM [5J both have suggested that chloride can be lost through

volatilization during the extraction process if the beaker containing the solution is not

pmperly covered: a watch glas is ofien used to minimize loss of chlonne.

In the next series of experiments, the chloride extraction process was canied out in a

closed system (Figure 7). This set up served two purposes: it significantiy reduced the

risk of Iosing volatile compounds during digestion with nitric. and also was helpful in

condensing some of the vapours formed during the heating stage. However. it is worth

mentioning that if chloride is lost due to formation of chlorine upon cernent digestion. the

latter cannot be condensed back into liquid form. This is due to the fact that the boiling

point of liquid chlorine is about 34.6 'T at atmospheric pressure [33]. The arnount of

unrecovered chioride was found to be 15.2% and 15.6% for the Berman and ASTM C

1 14 methods. respectively (sample numbers 92-97). It was concluded that the original set

up is sukEcient in recovering and trapping the chloride in cernent upon digestion, and that

any losses must be accounted for elsewhere.

As discussed above. chiorides, regardless of their origùi. can be bound to the hydrated

products in cement pastes or concrete 1141. Tricaicium aluminate (C3A) is. by far. the

best candidate to irnmobilize aggressive chioride ions that are present in the cement

matrix at the tirne of mi.xing or when they diffuse into it at a later stage. Although severai

chloride complexes are known to be produced the main product k ing formed is

chloroalurninatr: hydrate known as Friedel's sait. The assumption is that upon the

addition of nitric acid and heating the mixture. ail these complexes will decornpose and

chloride ions will pass into solution. if that were the case. the total chloride content of

any cernent sarnple couid be deterrnined by a simple titration. However. chioride losses

have been known to occur. and many workers [6.25] have commented on the inaccuracy

of the most available methods for determining chloride content in cernent pastes or

concrete. They have amibuted the above problem to either chloride l o s h o u &

formation of volatile chlorine upon acid digestion or incomplete extraction-

.& series of 5.0 M aqueous NaCl solutions (Portland cernent not present) were prepared

and heated (90-100 O C ) for varying pends OF time to determine the eKects of heating

time on volatilization losses when no cernent is present and. rherefore- no ~hloride

complexes are forrned, This eliminated one of the sources of e m r - incomplete

chloride emaction due to chloride cornplex formation. Identicai 2.0 M aqueous sodium

chioride solutions were heated for 5 seconds and 5 minutes and then were titrated

following the ASTM Method. It was found that upon heating the solutions for 5 seconds

and 5 minutes. the chionde losses were about 0.23% and 0.66%. respectively. A set of

siniilar samples also was prepared and titrated sithout heating and the chioride loss was

found to be mund 038%. The resdts are summatized in Table 12 and it c m be seen

that the amount of chloride that wilI be Iost upon heating the solution is insignificant.

Therefore. it can be hypothesized that the main source of 2rror observed in these

experiments is attributable to an incompIere chioride extraction. and chis is, most Iikety.

due to chloride cornplex formation.

Table II - Effects of Heating Time on Sodium Chioride Solution

Sample Method Fittered Covered Heated Unrecovwed Average N u m k Chloride (?id Unrec. Chloride (KI

3899 ASTM No Yes No 3899 ASTM No Yes No

3 897 ASTM 30 Yes Yes-5 seconds 0.1 3903 ASTM No Yes Ys-Ssecorids 0.44 0.23

3898 ASTM No Yes Yes - 5 minutes I .O4

3904 ASTM No Ys Yes - 5 minutes 0.28

5.0 CONCLUSIONS

1. The potentiometric titration procedures - ASTM Method C 1 14. Section 19-chloride

and Berman's Method -are precise but not accurate. particularly when the chlonde

concentration is higher than 0.01 g Cl-/g dry cement.

2. Although chloride wili be lost as volatile chiorine upon acid digestion and heating.

the main source of error is an incomplete chlonde extraction. The latter is. most

likely. due to compkex formations that will not compktely decompose in nitric or

sulfuric acids.

3. When chlonde is added to the mix water. the higher the concentration in the mix

water. the higber the final amount of unrecovered chioride.

4. The addition of more niaic acid does not bring more chloride ions into solution.

5. Elimination of the filtration step does not affect the titration, provided as the solution

contains only a small amount of solid residue.

6. The arnount of acid-soluble chIorides increases when cernent specimens are rotated.

This emphasizes the significance of the pore structure of the cernent rnatrix, which

controls the accessibility of chloride ions to the reaction sites.

7. As curing time increases. the amount ofacid-soiubk chIorides will decrease.

1. ASTM Method C 114. Section 19-chloride must be corrected by the use of a

calibration factor for cured OPC sarnples containing greater than 0.08 g Cl-lg dry

cement.

2. Csments with different mcalcium aluminate (C;A) content should be tested to

evaluate the effets of C;A content on chloride binding.

3 The role of calcium silicate hydrate (CSH) on chloride binding should be

investigatcd.

4. The efTects of various cement extenders such as silica fume and fly ash on chloride

binding should be studied.

5. The use of calcium chloride instead of sodium chloride. as well as the use of different

watsr-to-cernent ratios should be investigated.

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h h e e d d a r . Hussain. S.. and Al-Saadoun. S.. "Effect of Tricalcium Aluminate Content of cement on Chloride Bindiig and Comsion of Reinforcing Steel in Concreten. ACI A4aterial.s journal, 89. 1992. pp. 3-1 2

Ramachanduran. V. S.. M&erials and Structure. 6 197 1

Karimi. S.. -'Development of a Rapid Method to Determine Chioride Diffusion Coetticient in Cured Cernent Pastes-. B.A.Sc. Thesis. University of Toronto. 1997

'-Standard Test Methods for Chemical Analysis of Hydnuiic Cernent (CI L4-97). section 1 9-Chloride". .4nnual Book of .-fST.bf SrandarciS. 01.01. ASTM. Philadelphia. 1997. pp. 1 1 1 - 1 12

Berman. H. A.. "Determination of Chionde in Hardened PortIand Crment Pas~e. Monar. and Concrete". Journal of Materials. JMLSA. f. 1972. pp. 330-335

Dhir. R. K.. Jones. M. R.. and Ahmed. E. H.. "Determination ofTotal and Soluble C hlorides in Concrete". Cernent and Concrete Reseurch. 20. 1990. pp. 579-590

Climen~ M. A., Viqueira. E., de Vera. G.. and Lopez-Atalaya M. M.. ".halysis of Acid-soluble Chiotide in Cernent. Mom. and Concrete by Potentiomevic Titration without Filtration Steps". Cernent und Concrete Research. z. 1999. pp. 893.889

Mehta. P. K.. foncrete: Structure. Properties, and Materials". Second Edition, Prentice Hall. New Jersey. 1993. pp. 180-194

Neville. A. M.. "Properties of Concrete". Founh Edition. Prentice Hall- Essex- England. 2000. pp. 68-75

Lem. J.. -'Effects of Chlonde Ion in Cernent Paste Solution on the Comsion of Embedded Iron. MASc. Thesis, University of Toronto. 1993.

Locke. C. E.. -Proceedings of 8" International Congres on Metallic Corrosion-. NRC. Toronto. 1984

"Pertbrmance of Concrete in Marine Environment". -4merican Concrete Insfitute. Publication SP-65. Detroit. 1980- pp. 226-240

14. Luping. T., and NiIsson, L., Thloride Binding Capacity and Binding [sotherms of OPC Pastes and Mortars". Cernent and Concrere Research. U, i 993, pp. 247- 353

SchiessI. P.. "Corrosion of Steel in Concrete", 1" Edition. New York. 1988. pp. 22-49

Delagrave. A.. Marchand, J., Ollivier. J.. and Julien. S.. Thloride Bindmg Capacity of Various Hydrated Cement Paste Systems". .-ithtanced Cemenr Based .Llu~eriais. 0 1997. pp. 28-35

McGrath. P., Private Communications. 1996

Lambert. P.. Page. C. L.. and Short, N. R.. "Pore Solution Chernisl of the Hydrated System TricaIcium Silicate/Sodium ChloriddWatef'. Cernent and CBnCrert! Research. IS, 1985. pp. 675-680

Beaudoin. J. J. and Ramachandran. V. S.. -Interaction of Chlonde and C-S-W. Cémenf und Concrere Research. 20.1990. pp.875-883

Diarnond, S.. "Chloride Concentrations in Concrete Pore Solutions Resulting h m Catciurn and Sodium Chloride Admixtures". Crmenr, Concrefe, und .-lggregutt~.~. & 1986

Santagata. M. C. and Collepardi. M., "The Effect of CMA Deicers on Concrete Properties". Cemenr and Concrete Research, 30.2000. pp. 1389-1 394

.-a. C.. BuenfeId. N. R. and Newman. J.. B.. "Factors Influencing Chloride- Binding in Concrete". Cernent and Concrere Reseurch. a. 1 990. pp. 29 1-300

Hussain. S. E.. R a s h e e d d a r . and Al-Gahtani. A. S.. -influence of Sulfates on Chioride Binding in Cernent". Cemenr and Concrere Reseurch. 24- 1994. pp. 8-24

Holden, W. R., Page. C. L.. and Short. N. R.. 'The Inheuce of Chiorides and Sulphates on Durabiïitf. Corrosion of Reinforcement in Concrete Construction. 1983

Clear. K. C. and Hanigan. E. T,, "Sampling and Testing for Chloride Ion in Concrete". FederaI Highway Administration Washington. D. C.. Matexiais Division. 1997. pp. 1-22

B i s h m S. W.. "Rapid, Accurate Method for Determining Water-Sotuble Chionde in Concrete, Cernent. Mortar. and Aggregate: Application to Quantitative Study of Chloride Ion Distribution in Aged Concrete". ACI .tlaterials Jownal. 88.1991, pp. 165-270

Haque. M. N. and Kayyali, O. A., " F m and Water Soluble Chloride in Concrete", Cernent and Concrere Research, 25- 1995. pp. 53 1-542

Cox. T. R. G., The Distniution of Chioride in Concrete". Conc., 20- 1986, pp. 9- I 1

Sandberg. P.. "Studies of Chloride Binding in Concrete Exposed in a Marine Environment". Cernent and Concrere Research. 29, 1999. pp. 473-477

Chan. G. W.. T h e Use of Rapid Scan Voltammeûy to Study the Effects of Adding Silica Fume and Commercial Corrosion inhibitors to Cured Cernent Pastes Containhg Embedded Iron Exposed to Chloride". M.A.Sc. Thesis. University of Toronto, 1996

Lolivier. J.. -Determination of Chloride in Hardened Concrete" (in French). International Symposium on Admixtures in Mortars and Concrete. Brusseb. 1967. RILEM-.ABEM. Report VI1 1. x. pp. 197-21 1

Koelbel. G.. Louvrier. J., and Voinovitch. 1.- Chimie =Inafytique. 50. 1968. pp. 1 78-1 86

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APPENDIX A - General Data

Table Al - Common Values of Compound Composition of Portland Cements of Different Types [IO]

Cernent Value Compound Composition (%) No. of

CiS CzS C3A CAF CaSOa Free Ca0 Me0 Ignition Los Samoles

Mau. T p e 1 Min.

M a n

Mau. Type II Min.

M m

Mau. Type Ill Min.

Mean

Mau. Tye IV Min.

M a n

Max. T'pe V Min.

M a n

Table .42 - Main Types of Portland Cernent [1 01

Rapid-hardeiing Putland E . . rapi&hardening Pbrtland Ultra high carly strength Partland Low h a Putland Maiifid canait

S u i f e-resisting Putland

Portland blastthaœ

Tye III

White Putland -

Table B 1 - Generai Date For Cernent Slabs Cured for 7 Days NaCl m e n t Valurne Average vol. Standard Theoreücaf Adual Con'n Weight of AgN03 of AgN03 Dviation A m 3 Amount of NaCl

Pl (mg) Added (ml) added (ml) Volume (mL) in sample (g)

Table BZ - General Date for Cernent SIabs Cured for 28 Days NaCl cernent Vdume Aveiage vol. Standard Theoretical Adual Con'n Weight of AgN03 of &NO3 Dviation AgN03 Amount of NaCl

Pl (mg) Added (ml) added (ml) Volume (ml) in sample (g)

Table B3 - General Data for Cernent Spheres Cured for 28 Days NaCl cernent Vdume Average vol. Standard Theoretical Actual Con'n Weight of A@03 of &NO J hnation W O s Arnount of NaCl

[M] (mg) Added (rnL) added (ml) Volume (mL) in sarnple (g)

APPENDIX C - S a m ~ l e Calculations

Determination of Evapourrtble Water

Frorn Table 5: Weight of the cement sphere before drying = 21.957 g

Weight of the cernent sphere f i e r dqing = 20.745 g

% Evapourable water = r(24.957-20.745)/(24-95n]x 1 00% = 16.88%

Calibration of ASTM Metbod C 114

Consider Cernent samples that have been prepared by mixing 4.45 g of cernent with 2 mL of 2 M NaCl solution. The arnount of chloride is therefore:

This is the known (actud) value of chloride in the sample.

After curing for 28 days. the saniples were titrated with 0.05 M A g O 3 solution:

moles Cl- = moIes AgCl= C x V C = Concentration of AgN03 (M) V = Volume of AgN03 (mL)

Volume of silver nitrate added = 67.3 mL

Concentration of Silver nitrate = 0.05 M

Moles CI- = (0.0672 L)x(0.05 mol.&) = 0.003360 mol Cl'

Chioride content = (0.003360 mol Cl-)x(35.453 @mol) = 0.1 i24 g Cl-