A Wireless Sensor for Monitoring Chloride Ingress in Concretesp.maintenance.transportation.org/Documents/MMC2009Session3B-3Sr… · A Wireless Sensor for Monitoring Chloride Ingress

A Wireless Sensor for Monitoring Chloride Ingress in Concrete

MMC09-028

12th AASHTO-TRB Maintenance Management Conference Annapolis, MDJuly 19-23, 2009

July 21, 2009

Contact [email protected](240) 228-6378(443) 841-8825 (mobile)

Rengaswamy (Srini) Srinivasan

Team and Acknowledgement

Bliss Carkhuff, Johns Hopkins University

Terry Phillips, Johns Hopkins University

Hassan M. Saffarian, Corrosion Sensors, LLC

July 21, 20092

Program Sponsor: Maryland State Highway AdministrationMDSHA Chief of Research: Allison R. Hardt

Miniature Wireless Smart Aggregates Embedded inBridge Decks

July 21, 20093

Figure 5 - Completed Smart Aggregate before final assembly

1” Diameter; Totally Wireless

Embeddable Sensor Overview

• Background

• Chloride Sensor

• Corrosion Sensor

July 21, 20094

• Corrosion Sensor

1. Corrosion rate2. Coating health monitor3. Water corrosivity

Overview of Corrosion in Concrete

TemperatureChloride

H2OpH

CO2O2

CP/stray current

Concrete

and

Surrogate Rebar

A.C. Impedance

Measurement

T κ

Note: This slide describes the various physical and chemical parameters that influence corrosion of rebar

July 21, 20095

Estimated

Corrosion Rate

CP/stray current

other

Conductivity/Temperature

to

Corrosion Rate Algorithm

microbesand

Rebar

StructureSensor 1

“Parametric ” Algorithm

to determine

Corrosion Rate

2 3 4 5 6 7 8 n

Actual

Corrosion Rate

Surrogate

Corrosion Rate

Impedance

to

Corrosion Rate Algorithm

T κ

Threshold Limits of Chloride in Concrete

• Allowed limit in concrete�

�0.05 %wt. (by mass of concrete)

�0.4 %wt. (by mass of cement)

− 0.85 g of salt (max) allowed in 1 L (or 1.7 kg) of concrete

or 1.89 lb/cu. yd.

July 21, 20096

• Limit of chloride when steel begins to corrode�

�Steel corrodes when the chloride content is 0.6 times the concentration of [OH¯ ]

− If the pH = 12.9, [OH¯ ] = 1x10-1.1 M; and [Cl¯ ] = 48 mM

� Missouri Department of Transportation (MoDOT) Report No. RDT-03-004, March 2003, p. 10.

� Hausmann, D. A. (1967) ‘Corrosion of Steel in Concrete: How does it occur?’

Materials Protection, 6: 19-23.

Composition of Concrete

Composition of concrete in a volume of 1m3:

Cement = 350 kg

Lightweight coarse aggregate = 473 kg

Lightweight fine aggregate = 168 kg

Normal weight fine aggregate = 550 kg

July 21, 20097

Normal weight fine aggregate = 550 kg

Water required for desired slump = 180 kg

Density = 1676 kg/m3

3750 lb/cu. yd.

139 lb/cu. ft.

Sensing Chloride:

• Sensing elements− Carbon Steel and Stainless

• Driving force− Difference in the galvanic potential

• Parameter monitored− Time traces of the potential difference− Time traces of the galvanic current

Chloride

Steel-Based Chloride Sensor

July 21, 20098

− Time traces of the galvanic current

Zero Resistance Ammeter(or) Voltmeter

Steel Sensor

Current Collector

Mortar Seal

Technique Name: Electrochemical Noise


Open

Zero Resistance Ammeter

Chloride

Current Collector

Mortar Seal

July 21, 20099

Time (second)

EN

Sig

nal


Steel Sensor


Close

Zero Resistance Ammeter

Chloride

Current Collector

Mortar Seal

July 21, 200910

Time (second)

EN

Sig

nal


Steel Sensor

Testing in Concrete, Round #1 (Site #1)

Concrete Pour: 7/23/07; Cure Time: 30 days; Chloride test start: 8/23/07

1600

Note: This data was collected on a freshly poured concrete that was first cured for one month. Next, water withVarious amounts of salt (as indicated in the graph) was added to top surface of the concrete. At the time ofthe measurement, there was 0.5-inch of water with salt “standing” on the top surface of the concrete. Theamplitude of the current that we registered (200-1600 nA) were unusually large for the 10-50 mM salt waterThat was standing on the concrete surface. This made us to suspect that the concrete might have beencontaminated with salt water (when it was poured) or its pH was too low (<12). Therefore we repeated thisTest using concrete from a different pour; the results are compared in the next several slides.

July 21, 200911

0 20 40 60 80 100 120 140 1600

400

800

1200

50 mM Chloride

30 mM Chloride

10 mM Chloride

Cu

rre

nt (n

A)

Time (second)

0 mM Chloride

EN

Sig

nal



In Aqueous Solution of pH 13

Note: This data helps to understand the data in the last slide. The data shown in this slide were collected in aqueous medium,not concrete. The pH of the medium was controlled using Ca(OH)2 and NaOH. The current at pH 12.2 is high, demonstratingthe effect of low pH on the current (increased rate of corrosion of rebar). We suspected the pH of the concrete (in the last slide) was low.

60

250.0

In Aqueous Solution of pH 12.2

July 21, 200912

0.0 mM

20 mM

33 mM

50 mM

0 50 100 150 200 250-30

-20

-10

0

10

20

30

40

50

60

Cu

rre

nt (n

A)

Time (second)0 50 100 150 200 250

0.0

50.0

100.0

150.0

200.0

Srini & Amy

December 12, 2006

0.0 mM

20 mM

33 mM

50 mM


1000

1250

1500

Ave

rage

EN

Sig

na

l (n

A)

0 mM Chloride

50 mM Chloride

30 mM Chloride

10 mM Chloride

Data: Average of 4 sensors at each chloride concentration

Concrete had cracks

Was pH <12.0?Did concrete mix had salt?

July 21, 200913

0 100 200 300 400 500 600

0

250

500

750

Ave

rage

EN

Sig

na

l (n

A)

Time (hour)



-10

-5

0

0 mM

10 mM

Mean = -4.34 nA

300 hours after exposureNote: this is the second attempt mentioned earlier. Note,the amplitude of currents are much lower.

July 21, 200914

-20 0 20 40 60 80 100 120 140 160-30

-25

-20

-15

-10

Mean = -26.3 nA

Mean = -18.36 nA

Mean = -14.64 nA

Cu

rren

t (n

A)

Time (second)

10 mM

30 mM

50 mM



-10

-5

0

-5

0

300 hours after exposure 1650 hours after exposure

O mM Chloride0 mM Chloride

Note: The amplitude of currents did not go up further,even as we increased the chloride concentration,because the pH of the concrete was perhaps >12.

July 21, 200915

-20 0 20 40 60 80 100 120 140 160-30

-25

-20

-15

-10

Cu

rre

nt (n

A)

Time (second)-20 0 20 40 60 80 100 120 140 160

-30

-25

-20

-15

-10

Cu

rren

t (n

A)

Time (second)

10 mM Chloride

30 mM Chloride

50 mM Chloride

300 mM Chloride

600 mM Chloride

1200 mM Chloride



0

40

80

A

ve

rag

e E

N S

ign

al (n

A)

0 mM Chloride

50 mM to 1.2 M Chloride


10 mM to 0.3M Chloride

Note: Overall, the concrete at the second site did show little sign of chloride induced activity. This was possible, onlyif its pH was high, say >12.

July 21, 200916

-200 0 200 400 600 800 1000 1200 1400 1600 1800-200

-160

-120

-80

-40

0

Ave

rag

e E

N S

ign

al (n

A)

Time (hour)

1st addition2nd additionMore salt (x2)

3rd additionMore salt (x10)

Site #1 versus Site #2

1200

1600

50 mM Chloride

30 mM Chloride

-10

-5

0

Cu

rren

t (n

A)

Site #2 Site #1

O mM Chloride

July 21, 200917

0 20 40 60 80 100 120 140 1600

400

800

10 mM Chloride

Cu

rren

t (n

A)

Time (second)

0 mM Chloride

-20 0 20 40 60 80 100 120 140 160-30

-25

-20

-15

Cu

rren

t (n

A)

Time (second)

10 mM Chloride

30 mM Chloride

50 mM Chloride


Site # 1: w/ pores/cracksSite #2: Free of Pores

• Pore-free, crack-free concrete seal• Allows chloride to percolate slowly

July 21, 200918

-200 0 200 400 600 800 1000 1200 1400 1600 1800-1400

-1200

-1000

-800

-600

-400

-200

0

Cu

rre

nt (n

A)

Time (hour)

0 mM Chloride



10 mM to 0.3M Chloride

1st addition

2nd additionMore salt (x2) 3rd addition

More salt (x10)

0 100 200 300 400 500 600

0

200

400

600

800

1000

1200

1400

Cu

rre

nt

(nA

)

Time (hour)

0 mM Chloride

50 mM Chloride 30 mM Chloride

10 mM Chloride

Test Results from Coring Concrete from Bridge Decks


Site #1: Salt is too high; pH is too low

Site #1

Allowed LimitsSalt: 1.89 lb/cu. yd.pH: ~12Density: 140 lb/cu. ft.

July 21, 200919

Salt is low; pH is high; Density is high

Site #2

Chloride Sensors Summary

• The sensor predicted

– Problems at Site #1

– Found Site #2 concrete was good

July 21, 200920

– Found Site #2 concrete was good

Steel-Based Corrosion Sensor

Impedance Meter

Chloride

Current Collector

Mortar Seal

Embeddable Wireless Corrosion Rate Meter for Concrete

July 21, 200921

Impedance Meter

Steel Sensor

0 200 400 600 800 1000 12000

200

400

600

800

1000

1200

100 Hz 0.05 Hz

-ZIm

ag

inary (

oh

m)

ZReal

(ohm)

Solarton 1260

MW-EIS

(TEDCO)

Results from theEmbeddable Wireless Corrosion Rate Meter for Concrete

3

4

5

75

100

125 0 mM Chloride

10 mM Chloride

100 mM Chloride

Corr

osio

n R

ate

(m

il / year)

µm

/ y

ear)

• Closed Symbols� Concrete is wet

• Open Symbols� Concrete is dry

or drying

July 21, 200922

0 50 100 150 200 250 300

0

1

2

0

25

50

Time (hour)

Corr

osio

n R

ate

(m

il

Corr

osio

n R

ate

(µ

m

or drying

Sensor Instrumentation: EIS and EN

Schematic

Voltage Bufferor

Transimpedance AmplifierµController

R.f. Transmitter

Antenna

EIS: ImpedanceEN: Electrochemical Noise

July 21, 200923

InductivePickupCoil (or)Battery

SurrogateRebar

Electrode

Power and ClockManagement

A/DAnalogSwitch

Miniature Wireless Instrument Embedded inBridge Decks

July 21, 200924

Status of the Embeddable Sensor for Concrete

• Monitors chloride ingress– Technique used: Electrochemical Noise

• Measures corrosion rate– Technique used: Full Spectrum Electrochemical Impedance Spectroscopy

July 21, 200925

– Technique used: Full Spectrum Electrochemical Impedance Spectroscopy

• Monitors coating health– Technique used: Full Spectrum Electrochemical Impedance Spectroscopy

• Small, and communication and power are wireless– Therefore fully embeddable