CATHODIC PROTECTION OF A

FOUR-LANE DIVIDED CONTINUOUSLY REINFORCED

CONCRETE PAVEMENT

' "Implementing research findings"

CATHODIC PROTECTION

OF A

FOUR-LANE DIVIDED

CONTINUOUSLY REINFORCED CONCRETE PAVEMENT

September 1987

Prepared By Andrew D. Halverson, P.E. Research Project Engineer

PHYSICAL RESEARCH SECTION OFFICE OF MATERIALS, RESEARCH AND STANDARDS

MINNESOTA DEPARTMENT OF TRANSPORTATION

The contents of this report reflect the views of the author who is responsible for the facts and the accuracy of the data presented. The contents do not necessarily reflect the official views or policy of the Minnesota Department of Transportation. This report does not constitute a standard specification or regulation.

FOREWORD

This study was initiated to further investigate the cathodic

protection continuously reinforced concrete pavements (CRCP).

An initial cathodic protection system has been in operation for

sev~n years on tw~ lanes of interstate highway. It was felt that

economies could be achieved by building a system that would

protect both roadways of a 4-lane, interstate highway. This

report is the first product of that study.

This report discusses the CRCP pavement problem in Minnesota and

describes the design and construction of the cathodic protection

system. Future reports will document the performance of the

system.

The author appreciates the invaluable assistance provided by

Kenneth c. Clear, the designer of the system~ Collins Electrical

Construction Company, the contractor; and the personnel of the

Minnesota Department of Transportation's Central Office and

Oakdale District Office who helped this project reach completion.

i

SUMMARY

1n 1982, the Minnesota Department of Transportation decided to

pursue the design and construction of a second cathodic

protection system for the protection of continuously reinforced

concrete pavement. Corrosion of the reinforcing steel in this

type of pavement has been a severe maintenance problem for the

Department. An initial cathodic protection research project has

been successful in, at least, retarding this corrosionl

The original cathodic protection system was placed off the right

hand shoulder of the southbound 2 lanes of a 4-lane freeway. It

protects those 2 lanes. The intention, for the second system,

was . to place the system in the median in order to protect 4

lanes. It was desirable to protect the greatest number of square

feet possible in order to achieve the least cost per square foot.

The Department contracted with a consultant for the design of the

system. This resulted in three separate designs, each 1800 feet

long, with separate power sources. There is a trench system with

the anodes placed in a 4 foot deep by 1 foot wide trench. There

is a shallow post hole system with the anodes placed in 12 foot

deep augered post holes, and, where soil ~esistivity required it:

there is a deep post hole system with the anodes placed in 15

foot deep augered post holes.

The pavement is grounded every 200 feet of each roadway.

iii

Construction b~gan in October of 1982. When the contr~ctor quit

oper~tions for the winter, all anodes were inplace as was the

system ground bei. The anodes in both post hole systems had not

been wired in to 'i <;:i rcui t and the rectifiers had not been placed.

This work was completed during the 1983 construction season.

Construction went well with the exception of one major problem.

The post holes were ~ugered in a fine sand. The sides of the

post hole had a tendency to collapse inwards. In addition, as

the contractor worked down a slight grade, the post holes were

reaching into the w~ter table. A casing had to be used to hold

the edge of the nole until the proper depth was reached and the

anode was placed.

Initial testing of the syst~ms has indicated that they will be

effective. Thi~ is based on readings taken on corrosion probes

that were pl~ced during construction of the system. The system

was ~ctivated in December of 1983. In August of 1984 one

rectifier was shut down due to failure of the circuit control

boards. The ~amai,ing two rectifiers were shut down in February

of 1985 for the same reason. The boards were repaired and

modified, and the system was reactivated in June of 1986. The

system performed adequately until June of 1987 when successive

failures of system components was experienced. Repairs are being

made and the syst9m will be evaluated when fully operational and

polarized.

iv

TABLE OF CONTENTS

Page -----Introouction 1

Background ~ 4J G • 0 • 0 Gee G @ e 0 •• G. e@ e .. 01. e" e ® ... G. e e .., e ill &Ieee@ e e e e e e e e & 3

Bxperimental Work 19

System Design

Construction 26

Findings and Conclusions 61

v

LIST OF FIGURES

Figure

1 Deterioration of continuously reinforced concrete

2 3 4 5 6 7 8 9

10 11

12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

pa v em e n t G 0 0 0 0 0 0 0 8 0 0 0 e 8 0 0 Gl 0 Gl @ 0 G 0 $ 0 G 0 S e G Gl & 0

Continuously reinforced concrete pavement ~·· Tension failure ••••• • •••••••••• Tension failure Deteriorating concrete Deteriorating concrete •• Deteriorating concrete Deteriorating concrete •• Tension failure in portland cement concrete overlay ... Gl e ••••• e •• ® e ••• e •••• e e •• e. e •••• Gl 1111 e •• e e

Galvanic corrosion cell ••••••••••.••••••••••••••••••• Cathodic protection of a continuously reinforced concrete pavement eeeeeeeeeeeeeeeeeeeeee eeeeeee

Trench type cathodic protection system Dur iron anode ............. e •••• e •••• e

Post hole cathodic protection system Cannister and anode for post hole system Pavement at cathodic protection site Infrared thermography •••••••• Infrared thermography ••••• Rectifier for I-35W Trench type cathodic protection system Shallow post hole system Deep post hole system Typical system ground I-35E cathodic protection system site Locating reinforcing steel Concrete milling machine Milling concrete •••••••• Milled concrete •••••••••• Removing·concrete around the steel Cleaning the reinforcing steel Cadwelding •••••••• • ••••••• Completed cadwelds ••••• • •••• Testing cadwelds ••••••• Drilling under bituminous shoulder Opening ground bed trench ••••••••• Trenching for ground bed header cable Lead wire with polyvinyl-chloride conduit Splice of ground lead to header cable Instrumentation test leads •••••••••• Test station ••••••••••••••••••••• Test station buried beside shoulder Sandblasting ground connections Airblasting ground connections Concrete-mobile Grouting patch area

vii

2 3 5 5 6 6 7 7

9 10

11 12 12 13 14 15 16 16 17 22 23 24 25 28 28 29 29 30 30 31 31 32 32 33 33 34 34 36 36 37 37 38 38 39 39

Figure

46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78

Grouted patch and ground lead Vibrating concrete ••••••••• Finishing concrete •••••••• Patch with membrane sealer Corrosion probe ••••••••••••••• Vibrating concrete •••••• Finishing concrete patch Finishing concrete patch Finishing concrete patch Corrosion probe patch and saw-cut Excavating trench system Excavating trench system Cadwelded anode lead wire Forming splice kit ••••• Filling mold w~th epoxy Curing splice kit Completed s·pl ice kit Testing splice ki~ High-speed auger drilling post holes High-speed auger drilling post holes Lowering cannister into post hole Backfilling with coke breeze Anode lead wire ••••••• Predrilling post holes Low-speed auger ·~···· Casing ..•.•..•.• Drilling in casing Wet soil from post hole Splice kit ..... ., .......... . Testing splice kits 3-inch rigid metallic conduit under Preparing to pull cables ••••••• Rectifier for I-35E system

viii

pavement

40 40 41 41 43 43 44 44 45 45 46 46 47 47 48 48 49 49 51 51 52 52 S3 53 54 54 55 55 57 57 58 58 59

INTRODUCTION

The deterioration of continuously reinforced concrete pavement

(CRCP) is a serious problem ·in tile State of Minnesota. This

deterioration is primarily the result of chloride induced

corrosion of the reinforcing ~teel and is similar to the problem

afflicting concrete bridge decks.

It can generally be stated that the produc that build up on the

surface of the reinforcing steel, as a result of corrosion,

occupy a great deal more volume than the steel from which they

were formed. As these materials build up, they produce stress in

the concrete matrix. Due t9 its low tensile strength and brittle

nature, the concrete fails and cracks. The crack propagates to

the surface, and spalling and potholing result (Figure 1).

The distress in CRCP is visible throughout the year in the form

of old patches of the pavement surface, and the spalls and

potholes are a particular problem in the spring.

-1-

TRANSVERSE CRACKS

Figure 1. Deterioration of Continuously Reinforced Concrete Pavement.

-2-

BACKGROUND

The first continuously reinforced concrete pavement (CRCP) in the

State of Minnesota was constru~ted in 1983 on Interstate 35 near

Faribault in the southern part of the State. This was a test

freeway nearly eleven miles long. The pavement was section of

not jointed. It contained a high percentage of reinforcing

steel, either 0.5, 0.6, or 0.7 percent. Tt was intended that,

with temperature change, the pavement would develop many small,

closely spaced cracks held tight by the reinforcing steel; this

would eliminate the need to saw, seal, and maintain pavement

joints (Figure 2). The cracks developed as expected but a

maintenance-free pavement was not the result.

Figure 2. Continuously Reinforced Concrete Pavement

-3-

Construction of CRCP as a standard practice began in Minnesota in

1967 and,

completed.

through the late sixties, over 200 route miles were

Total lane-miles of CRCP is much higher, since the

roads are multi-laned freeways which include additional mileage

of ramps at interchanges.

By 1970, the construction of CRCP had been discontinued. Initial

failures were already apparent. The failures were tension

failures, evident in the form of open cracks where reinforcing

steel had ruptured (Figures 3 and 4). Already, corrosion was

revealed at these locations, and this reduced the

cross-sectional area of the reinforcing steel2

By 1974, the oldest pavements began to exhibit isolated cases of

spalling and shallow potholing. During 1975, maintenance

operations to patch open holes became frequent, and, by 1976, the

maintenance reached a significant level (Figures 4-8).

In 1977, the Minnesota Department of Transportation initiated a

performance and condition review and a research investigation to

examine the state-of-the-art for rehabilitation of deteriorated

CRCP. As part of the research: a critical section of pavement

on Interstate 94 received a bituminous overlay; a marginally

critical section of Interstate 35W was rehabilitated by removing

the upper portion of the surface and any delaminated areas, and

by overlaying with a low-slump, concrete overlay; and another

section of Interstate 3SW was placed under cathodic protection.

-4-

Figure 3. Tension Failure

Figure 4. Tension Failure

-5-

Figure 5. Deteriorating Concrete

Figure 6. Deteriorating Concrete

-6-

Figure 7. Deteriorating Concrete

Figure 8. Deteriorating Concrete

-7-

The critical section of Interstate 94 was ~t its junction with

Trunk Highway 280 near the Minne~polis/St. Paul city limits.

This section of ~pproximately one mile in length was overlaid

with a 2-inch thick bituminous surface. An overlay of this type

will eventually separate from the portland cement concrete, ~nd

merely serves to temporarily improve the riding quality of the

pavement. These overlays can begin to become ~ patching problem

in one year, depending upon the severity of the weather.

However, it is rel~tively easy to remove and replace a thin

overlay to maintain the riding quality. A thick overlay will

last longer, but it is more difficult to remove and replace.

The marginally critical section of pavement was on Interstate 35W

north of County Road J in Blaine. This section of pavement is

less than one mile long on the northbound lanes of the highway.

The pavement was milled to varied depths. Delaminated areas were

then removed, and a 2- to 3-inch portland cement concrete overlay

was placed. One portion of the overlay had joints cut through it

and through the reinforcing steel to make it, in effect, a

jointed pavement. After five years of testing, the overlay has

not yet delaminated, but several tension failures have developed

(Figure 9).

The cathodically protected section of pavement is a 1,000 foot

section of Interstate 35W in Blaine. It was built on the

southbound lanes, adjacent to the portland cement concrete

overlay. The concept of cathodic protection of a highway

pavement is new, but cathodic protection has been used on

pipelines, bridges, and, more recently, on other structures.

-8-

Figure 9. Tension Failure in Portland Cement Concrete Overlay

Briefly, the theory behind cathodic protection recognizes that

the corrosion of reinforcing steel in concrete is an

electrochemical process. The process requires an anode, a

cathode, a conductor, and an electrolyte (Figure 10). Portland

cement concrete is naturally highly alkaline. As an electrolyte,

such as chloride from deicing salts, penetrates the concrete; the

natural passivity of the concrete is upset and a galvanic

corrosion cell is created with ion transfer beginning in the

electrolyte (the destabilized concrete) and electron transfer in

the conductor (the reinforcing steel). Borrowing a technique

from the pipeline industry, we impress a current, from a

rectifier to a buried, remote anode, to neutralize the corrosive

current by polarizing the steel, making it entirely a

current-receiving cathode (Figure ll).

-9-

. · CONCMITII! ( II!LII!CTROL YTIE ) d, ·~:(1' ·: .. ...... , ...

. ••. • . • • ·"' .... . . II'' . .. ....•. IONIZA TBON '! o ! ·.' ·. j, ~ .

. · ... t ... . ~ .... ···:

RIEBNFORCIN8 STEIL

Figure 10. Galvanic Corrosion Cell

The 1,000 foot section of I-35W is divided into two designs for

cathodic protection. One-half of the section is protected with a

trench-type cathodic protection system, and the other half is

protected with a post hole system.

The trench system has a Duriron anode placed 3-l/4 feet deep in a

4-foot deep trench. Anodes are placed every 50 feet and lie

within a l-l/2 foot deep lift of conductive, metalurgical, coke

breeze (Figure 12). An anode from the I-35W trench system is

shown in Figure 13.

-10-

I ~

IN COKE

~\,UN'I/

CURRENX

Figure 11. Cathodic Protection of Continuously Reinforced Concrete Pavement.

CRCP

Figure 12. Trench type Cathodic Protection System

Figure 13. Duriron Anode

-12-

The post hole system also has the anodes 50 feet apart. However,

the anodes are placed in a 10-foot ~eep, augered, post hole

(Figure 14) • The anodes are contained in an R-inch ~iameter,

4-l/2 foot long, galvanized, sheet metal canister. The can is ter

is filled with coke breeze (Figure 15), and the post hole

back-filled with.coke breeze to a depth of six feet.

Figure 14.

T 6'

!' ~'r",, r,';-t,;~ ~''///t 1

1t

It ~~·

I I 'I • fl / I .; /I

r i '\\'-~ ,, \\\' \.'-\\ \' ' . \ ' TRENCH

1'-1

1

Post Hole Cathodic Protection System

-13-

is

TOTAL ASSEMBL V WEIGHT 95 LBS.

GALVANIZED SHEET MET A l ..,.,-.--..-....~-~

BODY

ANODE COMPACTED IN

CONDUCTIVE BACKfill

Figure 15. Canister and Anode for Post Hole System

-14-

Visual observation of the cathodically protected pavement has

revealed less surface distress and patching than is evident on

adjacent, unprotected pavement (Figure 16). During 1982, there

was increased interest within the Department to take another look

at cathodic protection on a larger scale. In addition, in the

summer of 1982, the Department contracted with Donahue and

Associates to conduct an investigation of selected segments of

CRCP using infrared thermography. This investigation, which

included the original cathodically protected pavement, revealed

numerous, significant areas of delamination on unprotected

pavement but only minor areas of delamination on the cathodically

protected pavement (Figures 17 and 18). A detailed evaluation of

the infrared thermography results is included in reference 1.

Figure 16. Pavement at Cathodic Protection Site

-15-

Figure 17. Infrared Thermography

Figure 18. Infrared Thermography

-16-

The rectifier for the I-35W system is illustrated in Figure 19.

Figure 19. Rectifier for I-35W

-17-

EXPERIMENTAL WORK

In 1982, at the request of the Department's Oakdale District

Office, efforts began to design and construct one mile of

cathodic protection for a segment of CRCP. The segment chosen

was a four-lane divided section of I-35E north of St. Paul.

The Department contracted with Mr. Kenneth Clear of Kenneth C.

Clear Inc., Concrete Materials and Corrosion Specialists, to

design the system.

This section of the report will be divided into two sections.

The first will describe the design of the system; and the second

will describe its construction.

System Design

The section of Interstate 35E to be cathodically protected is

located in the City of Vadnais Heights, north of St. Paul. The

section begins at a bridge over LaBore Road Connection and the

Burlington Northern Railroad (Bridge Number 9567) and ends at the

White Bear Lake city limits.

The roadway was constructed in 1970. The continuously reinforced

concrete pavement is 8 inches thick. It contains 0.7 percent

steel by cross sectional areao The reinforcing steel consists of

tied bars. The average daily traffic is 29,300.

Test results from a 1980 CRCP inventory revealed that there is

about 2.3 inches of concrete cover over the reinforcing steel.

-19-

Chloride contents, as determined by drill dust samples, are about

3,990 parts per million (ppm) from 0 to 1/2 inch depth; 2,550 ppm

from 1/2 to 1 inch: 1,960 ppm from 1 to 1-1/2 inches, 1,070 ppm

from 1-1/2 to 2 inches; and 630 ppm from 2 to 2-1/2 inches.

Electrical potentials were taken with a copper/copper sulfate

half-cell. All readings taken revealed active corrosion.

Delamination detection was done using a Delamtect. This revealed

less than 1 percent delamination. This was corroborated by

infrared thermography done in 1982 and 1983.

Efforts to build a cathodic protection system began in April 9,

1982. It was decided that this second pavement protection system

should be built in the median of the freeway in order to protect

both roadways. A consultant agreement for design and testing was

signed in May.

The design resulted in three separate systems, each with its own

source of power. There are a trench system and two post hole

systems. Each of these is 1,800 feet long, and each has five

zones with independent electrical control.

The entire 5,400 feet has a continuous ground bed. System

grounds were made to the reinforcing steel every 200 feet on both

the northbound and southbound roadways.

The trench system was placed in a 4-foot deep by 1-foot wide

trench. Nine inches of conductive meta1urgica1 coke breeze was

placed in the trench and compacted* The 2-inch by 60-inch

Duriron anodes were placed 60 feet apart. There are 6 anodes per

-20-

zonee A zone is 360 feet longs The anodes are covered with 9

inches of coke breeze which was also compacted. The remainder of

the trench was backfilled with excavated material (Fig~re 20).

The post hole cathodic protection system immediately north of the

trench system is a shallow post hole system. The anodes were

placed in 12-inch diameter post holes that were 12 feet deep.

The post holes were 36 feet apart. There are ten anodes per

zone. The 1-1/2 inch by 60-inch anode is contained in an 8- h

diameter, galvanized metal canister that is 7 feet longo The

anode is backfilled with coke breeeze within the canister, and

the canister is backfilled with coke breeze within the post hole

(Figure 21).

The northerly-most system is a deep post hole system. The anodes

were placed in 12-inch diameter post holes augered 15 feet deep.

The post holes were 17 feet apart. There are 20 anodes per zoneo

The l-l/2 inch by 60-inch anodes are contained in a 10-inch

diameter, galvanized metal canister that is 7 feet longs The

anode is backfilled with coke breeze within the canister and the

canister is backfilled with coke breeze

(Figure 22)o

thin the post hole

As mentioned previously, the system is grounded every 200 feet.

A ground wire is attached to both the transverse and the

longitudinal reinforcing steel. This wire leads to a ground bed

header wire in a collector trench that is 4 feet off the edge of

the pavemento The header cable is continuous along the

northbound and southbound roadways (Figure 23)e

-21-

I 1\.)

N I

BACKFILL EXCAVATED MATERIAl: AND COMPACT

<t. TRENCH AND MEDIAN

{SOD 3' WIDE.

2" x 60" ANODE WITH N0.6 A WG SEVEN STRANDED COPPER WIRE {FACTORY INSTALLED)

-+--+---PLACE 0.75' UNCOMPACTED METALLURGICAL COKE BREEZE AND COMPACT. PLACE ANODE &

~ A WG INSULA TED WIRE. PLACE ADDITIONAL

0.75' OF UNCOMPACTED COKE AND COMPACT.

Figure 20. Trench Type Cathodic Protection System

I [\J

w I

CONST. TRENCH

FIElD SPliCE N0.6 TO N0.2 A WG INSUlA TED

FIElD BACI<:Fill •1-/ WITH COKE BREEZE

1.5" x ANODE IN 8" DIAMETER

FillED CANISTER

Figure 21. Shallow Post Hole System

~ POST HOLE & MEDIAN

2.0'

BACKFill POST HOlE WITH AUGERED MATERIAl

AWG SEVEN WIRE

INSTAll ED TO ANODE IN

1 DIAMETER AUGERED HOlE

I N .1::-1

--------~., ·'\'-.;,\-,:\\ . --------

BACKFILL POST HOLE WITH AUGERED MATER

1

IAL

5.0'

1.0'

1.0'

Figure 22a Deep Post Hole System

ft. Of POST HOLE & MEDIAN

I

~ L: ~ v::

:':\: , .. ·,.·. ::-

·.•

,. ···'

.~·. ~~£ :·::

.,

b,:· .2 .;....

2.0' MAX.

\_

').~

COLLECTOR TRENCH "DEEP

E N0.6 WIRE TO CONTINUOUS 2 A WG INSULA TED CABLE

N0.6 A WG SEVEN OPPER WIRE (FACTORY 0 ANODE IN CANISTER}

LL WITH COKE BREEZE

ODE IN 10" DIAMETER CANISTER

~2" DIAMETER AUGERED POST HOLE

I ['..) \.}1

I

...1

CADWELD THROUGH

FROM 5/8"

LONGITUDINAl BAR

TO 5/8"

BAR

(DOUBLE

REMOVE

3.5"~ j

4'-0" -------

~~~~~S~H~O~U~lD~E~R3~·--o_· ____ _j l L

~ 112" DIA. x 9" P.V.C. CONDUIT

PlACE N0.8 WIRE IN VA Fl. DEPTH ,.,,...-rotua TRENCH

Figure 23. Typical System Ground

Al

COllECTOR TRENCH 2" WIDE x 18" DEEP

fiElD SPLICE TO NO. 1 AWG & INSUlATE WElD

Power is supplieo to each system by a rectifier. Each unit has a

240-volt alternating current input. The rectifiers for the

trench and shallow post hole systems have an output of 50-volt

direct current at 32 amperes for each of the five zones. The

rectifier for the deep post hole system has an output of 80-volts

at 32 amperes per zone.

The oeep post hole system was designed because of high soil

resistivities at the project location. The project is located on

fill section through a swampy area. The trench and shallow post

hole systems are lower in elevation than the deep post hole

system. They are also located in the fill in the swamp. Their

soil resistivities are similar and are much lower than the deep

post hole system which is on an ascending grade. The deep post

hole system was designed to get to a wetter soil with lower

resistivity.

Construction

The contract for the cathodic protection system was put out for

bids in August 1982. The contract was let at a low bid of about

$131,000. Rectifiers were purchased by the State at a cost of

about $38,000 ann were to be installed by the contractor. Thus,

the total cost of the system was $169,000, or about 70 cents per

square foot. The contract was let September 10, 1982.

The contractor began work on October 11, 1982 by establishing

traffic control. The contract allowed ten working days during

which the passing lanes of each roadway could be closed for

-26-

construction (Figure 24). After those ten days, only temporary

lane closures were allowed.

The first thing the contractor did was establish the system

ground bed. System grounds were made to the longitudinal and

transverse reinforcing steel at 200 ft. intervals. Transverse

steel was found by the contractor by use of a cable locator

(Figure 25). A small milling machine was then brought in to

grind the concrete to the depth of the steel (Figures 26-28).

The contractor elected to use this method in lieu of sawinq the

edges of the area to be removed and then using a jackhammer to

remove the concrete to the depth of the reinforcing steel. Once

the milling machine reached the level of the reinforcing steel,

jackhammers were used to further expose the steel; the steel was

cleaned using an electric drill with a wire brush; and a number

eight stranded copper wire was cadwelded to the longitudinal and

then the transverse reinforcing steel (Figures 29-32). Each

cadweld was tested for soundness with a hammer (Figure 33). A

hole was drilled through the soil and under the 4-foot wide

bituminous shoulder on the median side of each roadway to an

18-inch deep collector trench (Figure 34). The trench was

originally opened up, at each ground connection, with a backhoe

equipped with a narrow bucket (Figure 35) and was later completed

with a trenching machine (Figure 36). The ground wire could then

be passed under the shoulder without damage to the shoulder. A

9-inch section of l/2-inch polyvinyl-chloride conduit was placed

around the wire to counteract any shear effects at the edge of

the concrete pavement (Figure 37).

-27-

Figure 24. I-35E Cathodic Protection System Site

Figure 25. Locating Reinforcing Steel

-28-

Figure 26. Concrete Milling Machine

Figure 27. Milling Concrete

-29-

Figure 28. Milled Concrete

Figure 29. Removing Concrete Around the Steel

-30-

Figure 30. Cleaning the Reinforcing Steel

Figure 31. Cadwelding

-31-

Figure 32. Completed Cadwelds

Figure 33. Testing Cadwelds

-32-

Figure 34. Drilling Under Bituminous Shoulder

Figure 35. Opening Ground Bed Trench

-33-

Figure 36. Trench for Ground Bed Header Cable

Figure 37. Lead Wire with Polyvinyl-Chloride Conduit

-34-

A number 1 AWG insulated cable with high molecular weight

polyethylene insulation was placed in each collector trench and

is continuous through the length of the trench. The number 8 AWG

ground lead, from the reinforcing steel, was cadwelded to the

number 1 header cable and enclosed with an epoxy encapsulation

kit manufactured for direct burial (Figure 38).

Each collector trench also contains three number twelve twisted

wires (Figure 39) These are to be used as test leads for

potential readings. The test leads terminate in test stations

buried along the shoulder (Figures 40 and 41). This design makes

it possible to take electrical potentials on the surface of the

pavement without running long lead wires and without running

wires across the pavement.

The system grounds were patched with concrete.

the reinforcing steel was sandblasted and

Before patching,

then cleaned with

compressed air (Figures 42 and 43). The holes were grouted and

patches were then placed using concrete supplied by a concrete

mobile (Figures 44-48). Patches were sprayed with a membrane

curing compound (Figure 49).

A corrosion probe was placed in both roadways in each system in

the passing lane near the centerline. The probe consists of a

6-inch piece of reinforcing steel with a number eight stranded

wire attached. The steel is cast in salt-bearing concrete.

The probe was placed at the level of the reinforcing steel in the

pavement and the wire was passed through a saw cut to the edge of

-35-

Figure 38. Splice of Ground Lead to Header Cable

Figure 39. Instrumentation Test Leads

-36-

Figure 40. Test Station

Figure 41. Test Station Buried Beside Shoulder

-37-

Figure 42. Sandblasting Ground Connections

Figure 43. Airblasting Ground Connections

-38-

Figure 44. Concrete-Mobile

Figure 45. Grouting Patch Area

-39-

Figure 46. Grouted Patch Area

Figure 47. Vibrating Concrete

-40-

Figure 48e Finishing Concrete

Figure 49. Patch With Membrane Sealer

-41-

the pavement and then to the collector trench in the same manner

as the system grounds. Each corrosion probe also has its own

ground wire. The probe was patched along with the grounds

(Figures 50-55). The wire was sealed in the saw cut with epoxy.

Test stations are also provided for each corrosion probe.

The trench system was installed in a 4-foot deep by 1-foot wide

trench excavated with a backhoe (Figures 56 and 57). The trench

system was wired into five zones with six anodes in each zone

cadwelded to a continuous length of number 2 AWG insulated cable

between the anodes and the rectifier (Figure 58).

cover each weld.

Splice kits

The splice kits consist of a plastic sheath that is placed around

the cadweld (Figure 59). This sheath is then filled with a

two-part epoxy that is shipped in a container that has two

compartments. The materials are combined by breaking the

partition between the two components, the materials are mixed,

and the epoxy is poured into the sheath (Figure 60). The epoxy

is then allowed to harden (Figures 61 and 62) and the splice kits

were tested with a holiday detector to ensure their effectiveness

(Figure 63). The holiday detector is, ordinarily, used to check

epoxy coated reinforcing steel and consists of two electrical

leads, a power source, and a bell. One lead has a sponge which

is wetted. One lead is made electrically continuous with the

anode, either by direct connection or through the soil. The

wetted sponge is passed over the splice kit and if there is a

leak, the bell will sound.

-42-

Figure 50. Corrosion Probe

Figure 51. Vibrating Concrete

-43-

Figure 52. Finishing Concrete Patch

Figure 53. Finishing Concrete Patch

-44-

Figure 54. Finishing Concrete Patch

Figure 55. Corrosion Probe Patch and Saw-cut

-45-

Figure 56. Excavating Trench System

Figure 57. Excavating Trench System

-46-

Figure 58. Cadwelded Anode Lead Wire

Figure 59. Forming Splice Kit

-47-

Figure 60. Filling Mold with Epoxy

Figure 61. Curing Splice Kit

-48-

Figure 62. Completed Splice Kit

Figure 63. Testing Splice Kit

~49-

Construction of the trench system went well.

The construction of the post hole systems was another matter

however. The contractor first worked on the oeep system. He

used a high speed drill to auger the fifteen feet (Figures 64 and

65). The soil was a very fine sand. The sides of the post hole

tended to collapse inwards and this eventually became quite a

problem. The anodes and canisters were lowered into the post

holes by a choker using another truck with a boom (Figure 66).

The canisters were then backfilled with coke breeze (Figure 67).

Wet conditions late in the fall of 1982 prevented the contractor

from digging the trench to place the cable for connecting the

anodes (Figure 69).

As was mentioned previously,

contractor started at the

the soil posed a problem. The

highest part of the project. As he

drilled each hole he worked his way lower and came nearer the

water table. The sides of the holes would not hold and the

contractor had to switch to a much slower auger. Eventually, the

holes were pre-drilled with a higher speed auger (Figure 69) and

completed at low speed in a casing (Figures 70-72). Two zones of

the deep post hole system were also accepted at a shallower

depth, and the anodes were, eventually, partly submerged in water

(Figure 73).

When he stopped work for winter, the contractor completed all but

the lead wires for the anodes for the two post hole systems and

the placement of the rectifiers. The rectifiers had not been

delivered at that time.

-50-

Figure 64. High-speed Auger Drilling Post Holes

Figure 65. High-speed Auger Drilling Post Holes

-51-

Figure 66. Lowering Cannister Into Post Hole

Figure 67. Backfilling with Coke Breeze

-52-

Figure 68 Anode Lead Wire

Figure 69 Predrilling Post Holes

~53-

Figure 70. Low-speed Auger

Figure 71. Casing

-54-

Figure 72a Drilling in Casing

Figure 73. Wet Soil from Post Hole

-55-

When work resumed in the summer of 1983, the contractor made the

cadweld connection of the number 8 AWG anode lead to the number 2

AWG header cable for each anode of the post hole systems. A

splice kit was used to cover each cadweld (Figure 74), and each

splice kit was again checked with a holiday detector (Figure 75).

A 3-inch rigid metallic conduit was passed under the roadway to

carry the cables from the median to the rectifiers which are

located on the back slopes (Figures 76 and 77). This is grounded

into the system to protect it from corrosion.

Also, in the summer of 1983, the designer tested the rectifiers

and determined the power levels at which the system would be

operated. All systems were finally activated in November and

December of 1983 (Figure 78).

The rectifiers for the trench system and the shallow post hole

system are capable of 50 volts direct current and 32 amps for

each of the five zones of each system. The rectifier for the

deep post hole system is slightly more powerful due to the higher

soil resistivity in this zone. This rectifier is rated at 80

volts direct current and 32 amps for each of the five zones. The

input for all rectifiers is 240 volts.

-56-

Figure 74. Splice Kit

Figure 75 Testing Splice Kits

~57~

Figure 76. 3-Inch Rigid Metallic Conduit Under Pavement

Figure 77. Preparing to Pull Cables

-58-

Figure 78. Rectifier for 1-35E System

-59-

FINDINGS AND CONCLUSIONS

With the exception of the soil problem, the construction of the

cathodic protection system went well. The contractor was the

same one that built our original pavement protection system, but

he was still hot familiar with this type of work. If more

projects are let there are certainly going to be more efficient

ways found to build them.

The use of a cable locator and a milling machine in establishing

the system ground worked very quickly and very well. Drilling

under the shoulder for the ground lead was an excellent idea.

However, when the trench was not backfilled promptly, the sides

collapsed at several locations and the shoulder was damaged.

The handling of the coke was difficult. This was delivered in

100-pound sacks on pallets. The material was stockpiled when

delivered and had to be handled more than once before it was

finally placed.

The cadwelding required some trial and error, but w~nt very well

after that. The splice kits all checked out well with the

holiday detector and only one failed to set properly.

was removed and replaced.

That one

The rectifiers were ordered in late September of 1982 and they

arrived late in April of 1983. One unit was damaged during

handling by Mn/DOT, and was returned in July for inspection and a

-61-

new cabinet. The repaired unit was received in November and was

promptly placed.

The entire system was activated in December of 1983. In August

of 1984, one rectifier was shut down due to failure of the

circuit control boards. The remaining two rectifiers were shut

down in Februafy of 1985 for the same reaason. The boards were

repaired and modified. The system was reactivate~ in June of

1986. It performed adequately until June of 1987. At that time,

a current-rectifying bridge circuit failed in one zone of the

deep post hole sywtem. Subsequently, three circuit cards failed.

Repairs are being made.

Init~al testing of the system has indicated that the corrosion

probe cari be polarized. This reveals that the reinforcing steel

can be too. Extensive testing of the system is planned.

We are looking a~ cathodic protection as one possible solution to

our CRCP problem. When we review the recent CRCP inventory, we

see that, of all of the projects surveyed, the reinforcing steel

is at the minimum depth, all sections have chlorides in excess of

the amount that induces corrosion, most sections have wide

cracks, there is active corrosion on all CRCP, and most sections

exhibit delaminations. Once again, we are talking of more than

200 route miles of CRCP, and, at least four times that number of

lane miles. Any such decision will be influenced by the cost and

effectiveness of the system.

-62-

REFERENCES

1. Hagen, M. G., Experimental Repair Methods for Continuously

Reinforced Concrete Pavement, Investigation No. 200, Office

2.

of Research and Development, Minnesota

Transportation, August 1985.

Department of

Hughes, P. C., Evaluation of Continuously

Concrete Pavement, Investigation 184,

Materials, Minnesota Department of Highways, 1970.

-63-

Reinforced

Office of