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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.
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Figure 50. Corrosion Probe
Figure 51. Vibrating Concrete
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Figure 52. Finishing Concrete Patch
Figure 53. Finishing Concrete Patch
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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.
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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
Recommended