1. Durability of Concrete Pipe

2. Durability of Concrete Pipe
The extreme durability has led to a lack of durability studies
Unlike CMP, corrosion not typically significant
Sewer lines and Sulfuric Acid are a major issue. Different producers have different methods to deal with durability in sewers
Precast concrete pipe has been around for thousands of years. It has come to be counted on and even taken for granted, at times, to be a material that lasts for over 100 years. Because of this, there have not been many studies of the durability of precast concrete pipe. We will discuss some of the studies that have been performed over the years.
Few things shorten the life of precast concrete pipe and corrosion is not typically one of those under normal circumstances. One factor that may cause corrosion of precast concrete pipe is that of sulfuric acid corrosion in sanitary sewers. This is a complex combination of factors, including BOD load, velocity in the pipe, pH, temperature and other factors, which can be mitigated by a variety of means. Our manufacturers which are present today would love to talk about that with you, because they offer a wide range of solutions. However, the vast majority of precast concrete pipe is built for storm drains and culverts, and that is what we will discuss the durability of precast concrete pipe in storm drains.

3. Introduction to Presentation
Based on a variety of information gathered from different studies.
Some references to other pipe materials, as the study used concrete pipe as baseline and studied durability of “alternative” products
There will be no single formula for predicting design life: Study will show that concrete storm drain pipe should last 100 years plus.
I will present you with a number of studies today that have been performed primarily regarding the durability of precast concrete pipe for storm drainage applications. Some of these studies include the durability of alternate drainage products, such as HDPE and cmp.
I’m sure you will agree that the service life of precast concrete pipe will be in excess of 100 years in the Las Vegas area.

4. Why Concrete Pipe What makes concrete pipe so durable? Low w/c ratio
Concrete Compressive strength
High density
Quality control measures
There have been examples of concrete pipe lasting for over 1,000 years. There are a number of reasons that precast concrete pipe lasts so long, including:
A low water cement ratio. Typically, precast concrete pipe is manufactured in a clean, organized manufacturing facility with what is called dry cast concrete. Pipe can be manufactured at a high rate with dry cast concrete. This is because very few forms are required to manufacture the pipe. Concrete is simply placed into a form and taken to the curing chambers to cure. The form is immediately stripped and returns to the pipe machine for the next pipe.
Dry cast concrete piper serves two purposes:
Allows the pipe to manufactured quickly and with very few forms.
Dry cast concrete is more durable due to high cement content, high density, low absorption and long life.

5. What are Other Engineers Doing?
The first question we might ask is:
What are engineers in other areas of the country using as a service life for precast concrete pipe.

6. The Army Corps spends a lot of money and has an aversion to risk.
U.S. Army Corps of Engineers No Engineering and Design Conduits, Culverts, and Pipes (31 March 1998)
The Army Corps spends a lot of money and has an aversion to risk.
They do more than dams and wetlands
This culvert design manual applies to all departments having civil works responsibilities.
The Corps of Engineers has a Design manual for corps drainage products. This manual serves as a guide for designers on material pipe selection and design procedures for trench/embankment earth loadings, and highway loadings.
Obviously, the corps is a conservative organization that believes in getting it right the first time. I will pass this around so you can look at the first few pages as I discuss this document.

7. Water resources and other civil works projects
U.S. Army Corps of Engineers No Engineering and Design Conduits, Culverts, and Pipes (31 March 1998)
Who are they?
Water resources and other civil works projects
Designing and managing the construction of military facilities for the Army and Air Force.
Providing design and construction management support for other Defense and federal agencies.
Basically, the corps designs and manages the construction of military facilities of the US Army and Air Force. I think most people here are familiar with the corps and the functions they perform, especially during times of combat. As a matter of fact, many members of the corps are currently in Iraq rebuilding the infrastructure of that country.

8. U. S. Army Corps of Engineers No
U.S. Army Corps of Engineers No Engineering and Design Conduits, Culverts, and Pipes (31 March 1998)
CONCRETE- Most studies estimated product service life for concrete pipe to be between 70 and 100 years. Of nine state highway departments, three listed the life as 100 years, five states stated between 70 and 100 years, and one state gave 50 years.
(2) STEEL - Corrugated steel pipe usually fails due to corrosion of the invert or the exterior of the pipe. Properly applied coatings can extend the product life to at least 50 years for most environments.
(3) ALUMINUM- Aluminum pipe is usually affected more by soil-side corrosion than by corrosion of the invert. Long-term performance is difficult to predict because of a relatively short history of use, but the designer should not expect a product service life of greater than 50 years.
(4) PLASTIC- Many different materials fall under the general category of plastic. Each of these materials may have some unique applications where it is suitable or unsuitable. Performance history of plastic pipe is limited. A designer should not expect a product service life of greater than 50 years.
Excerpt from Para. 1-4
Life Cycle Design
1998

9. U. S. Army Corps of Engineers No
U.S. Army Corps of Engineers No Engineering and Design Conduits, Culverts, and Pipes (31 March 1998)
“For major infrastructure projects, designers should use a minimum project service life of 100 years when considering life cycle design.”
“In general, concrete pipe can be expected to provide a product service life approximately two times that of steel or aluminum.”
What kind of pipe does the corps of engineers really specify. Well, also in that report, the corps states that major infrastructure projects should use a pipe service life of 100 years. It also states that concrete pipe provides twice the service life of steel or aluminum or plastic.
I challenge you to perform a life cycle analysis on all projects to determine the best alternative for pipe over the life of a project. In fact, I’ll even provide the software. The ACPA provides software called PipePac that has an easy to follow package called LCA for selecting pipe based on a life cycle cost analysis.
Call Randy or the ACPA for a copy.

10. Settlement of manholes or control structure.
U.S. Army Corps of Engineers No Engineering and Design Conduits, Culverts, and Pipes (31 March 1998)
Site Inspection
Surface settlement.
Surface water.
Dip in pavement.
Settlement of manholes or control structure.
What should inspectors look for when inspecting a flexible storm drainage product? Besides testing the backfill for proper installation densities, one should look for the possible trouble spots in an installation:
The Corps lists settling of the product as a possible problem. This occurs when the pipe deflects and the soil above that pipe deflects also. In concrete pipe, one should ensure that the pipe is placed on a proper bedding with adequate bearing strength to resist settling. Other than that, there are several options for the proper installation of precast concrete pipe.

11. Failures a. Leaking joints. b. Separated joints. c. Crushed pipe wall.
U.S. Army Corps of Engineers No Engineering and Design Conduits, Culverts, and Pipes (31 March 1998)
Failures
a. Leaking joints.
b. Separated joints.
c. Crushed pipe wall.
d. Perforated pipe wall.
e. Misaligned pipe sections.
f. Root penetration of pipe.
g. Material deposition.
h. Change in loading condition.
Other problems to look for according to the Corps include leaky and separated joints, crushed and perforated pipe wall, and other problems. These are all due to inadequate installation practices because typically the low bid contractor thinks he can install the flexible pipe in a manner similar to precast concrete pipe, which will result in joint failure. In concrete pipe, the structure comes to the job in the pipe, not on the soil, which relies less on a low bid contractor and more on the pipe manufacturer for project success.

12. U. S. Army Corps of Engineers No
U.S. Army Corps of Engineers No Engineering and Design Conduits, Culverts, and Pipes (31 March 1998)
To download a copy of the Corps of Engineers Drainage manual, go the following web site, which is included in your presentations.

13. American Association of State Highway and Transportation Officials (AASHTO) - Model Drainage Manual (1991)
Material selection shall include consideration of service life which includes abrasion and corrosion.
Culverts shall be located and designed to present a minimum hazard to traffic and people.
Another well known organization with a Drainage manual is AASHTO. AASHTO is a consortium of specification writers from DOTs of every state. They listen to industry but make allow no outside voters on their committees.
In 1991, AASHTO came out with a drainage manual to serve as a model for local DOTs and governing agencies when preparing their own drainage manuals. This includes sections on material selection as well as hydraulic and hydrologic design of storm drains and culverts.
The report recommends some interesting things that all designers should be doing. The report states that service life of the material should be considered including abrasion and corrosion. Also, the public safety should be a key when selecting a pipe material. Far too often, we forget as professional engineers, that are most important job is to protect the public welfare. We get lost in selection of the material based on cost and other factors. But what happens when a pipe fails and causes a sinkhole on a busy road, such as a freeway?

14. American Association of State Highway and Transportation Officials (AASHTO) - Model Drainage Manual (1991)
The material selected shall be based on a comparison of the total cost of alternate materials over the design life of the structure which is dependent upon the following:
durability (service life),
structural strength,
hydraulic roughness,
bedding conditions,
abrasion and corrosion resistance, and
water tightness requirements.
The selection of the material should be based on the total cost of the alternate materials over the design life of the structure.
Let’s think about that. So far, we have AASHTO and the Corps of Engineers recommending that we select our pipe based on the cost over the design life of the project. Yet, many times we refuse to perform a life cycle cost analysis.
Perhaps, if we had selected materials based on the cost of the design life of the project for the last 50 years, we wouldn’t be in the situation that we are in in this country --- of having to replace so much or our rotting infrastructure.

15. American Association of State Highway and Transportation Officials (AASHTO) - Model Drainage Manual (1991)
“The material selection shall consider replacement cost and difficulty of construction as well as traffic delay.”
The selection shall not be made using first cost as the only criteria.”
First cost shall not be the only criteria. They are telling you to run an LCA analysis that includes replacement cost, as well as the cost of construction delays which Joe Perrin will discuss in a moment.

16. “Culvert alternatives shall be selected which satisfy: topography, and
American Association of State Highway and Transportation Officials (AASHTO) - Model Drainage Manual (1991)
“Culvert alternatives shall be selected which satisfy:
topography, and
design policies and criteria.
Alternatives shall be analyzed for:
environmental impact,
hydraulic efficiency, and
risk and cost.
Culverts shall be analyzed based on design policies and RISK!!!
What are we risking when we have a pipe failure:
Sinkholes,
Replacement costs
Damaged reputations
Lawsuits
License revocation

17. construction and maintenance costs,
American Association of State Highway and Transportation Officials (AASHTO) - Model Drainage Manual (1991)
The chosen culvert shall meet the selected structural and hydraulic criteria and shall be based on:
construction and maintenance costs,
risk of failure or property damage,
traffic safety,
environmental or aesthetic considerations,
political or nuisance considerations, and
land use requirements.
Here are some of the other criteria:
Maintenance costs, risk of failure, safety.

18. Missouri Highway and Transportation Department – Division of Materials and Research, Life Expectancy Determination of Zinc-Coated Corrugated Steel and Reinforced Concrete Pipe Used in Missouri, (December 1990)
“The field evaluation included 2,255 CSP and 1,642 RCP stratified by age to obtain as representative nonbiased sample as possible ...
Those pipe in need of replacement are 45.6% of the CSP and 0.3% of the RCP surveyed.”
In 1990, the show me state came out with it’s own durability study. It was quite an extensive study, based on a field evaluation of 2,255 Corrugated metal pipe and 1,642 reinforced concrete pipe.
Basically, what the study evaluated was the amount of each pipe that needed to be replaced. It came back with a return of 45.6 per cent replacement of the camp and only 0.3 % of the reinforced concrete pipe.

19. Missouri Highway and Transportation Department – Division of Materials and Research, Life Expectancy Determination of Zinc-Coated Corrugated Steel and Reinforced Concrete Pipe Used in Missouri, (December 1990)
“Reinforced Concrete Pipe (RCP) has shown to be more durable and significantly outlasts Corrugated Steel Pipe (CSP).”
“RCP appears to be more-cost effective, despite the lower, initial installation cost of CSP.”
“Despite its lower, initial installation cost, CSP most likely would have to be installed one to four times during the life of one RCP.”
I can’t help but share with you some of the quotes from the Missouri study. Rcp is more durable than corrugated metal pipe.
RCP appears to be more cost effective, despite the lower initial cost of the alternate product.
CMP will have to be installed one to four times as many times as rcp. Why do it? Why not install a product you won’t have to come back and replace for many years.

20. Illinois Department of Transportation - IDOT Pipe Committee Report (July 1994)
“There is an element of risk involved when a piping system is dependent upon backfill materials and procedures.
The committee feels it is appropriate to mitigate this risk by differentiating where rigid and flexible pipes are allowed.
This approach is not to say that flexible pipes are expected to fail. Rather, it is a means to address the risks, system wide, associated with a piping material that is very dependent upon proper construction procedures for its performance, in the case of plastic pipes; and as a means to address the differences in long-term durability, in the case of CMP’s.”
So, what do we coming back to:
There is a risk involved when installing flexible pipe. The MODOT study says just that, there is risk in performance because it is very dependent on proper construction.

21. Illinois Department of Transportation - IDOT Pipe Committee Report (July 1994)
Reinforced Concrete Pipe is required for pipe culverts on all roadways with more than 3,000 vehicles per day.
Reinforced Concrete Pipe is required for storm sewers on roadways with more than 1,500 vehicles per day.
In 1994, the Illinois DOT felt it necessary to evaluate their specifications and determine which products should be allowed in critical and non-critical roadways.
They put a committee together and evaluated the performance of concrete and flexible pipe. In a nutshell, their recommendation was to allow rcp for all roadways and flexible pipe for only non-critical roadways.

22. Wisconsin Department of Transportation - Evaluation of the Department’s Guidelines and Specifications for the Use of Alternative Storm Sewer Materials
“The consequences of having to replace a failed (storm) sewer pipe are usually serious. Typically this would require expensive reconstruction and rerouting of traffic.”
“Rigid Pipe (i.e., Concrete Pipe) is more tolerant of poor backfill compaction than flexible pipe (i.e., plastic and metal)”.
“Given reduced staff levels, it is not realistic to expect continuous inspection of storm sewer installations.”
Wisconsin DOT also chimed in with a study in What they said was that concrete pipe is more tolerant of poor installation than flexible pipe materials. Due to the inadequate personnel to conduct inspections on pipe projects, concrete pipe should be used.

23. Wisconsin Department of Transportation - Evaluation of the Department’s Guidelines and Specifications for the Use of Alternative Storm Sewer Materials
“Where the design year traffic volume exceeds 4,500 ADT, the new materials may be specified for storm sewer located outside of traffic lanes”
i.e., Concrete Pipe only under Traffic Lanes with more than 4,500 cars per day
Only concrete pipe should be used for high traffic areas greater than 4,500 cars per day.

24. Other Specifications of Interest
Kansas Department of Transportation
Urban Drainage and Flood Control District, City and County of Denver
Georgia Department of Transportation
Kentucky Department of Transportation
Pennsylvania Department of Transportation
We have more examples of specifications you may want to look at. Contact Randy for a copy of these to see what other areas of the country are doing for selecting drainage pipe materials.

25. RCP is considered 100 year design life
Pennsylvania Department of Transportation - Alternate Pipe Selection Criteria Based Upon Type of Installation
RCP is considered 100 year design life
CMP can have increased design life if metal gauge is increased. Most DOT’s CMP gauge tables would equate to a 25 year design life in PDOT spec.
HDPE shown as 50 year design life. Not allowed under the pavement. Deep burial not allowed.
As many of you may know, PennDot is a leader in storm drainage design and usage. The current Chairman of the AASHTO Culvert Committee is from Pennsylvania.
PENNDOT gives concrete pipe a 100 year design life, while cmp and HDPE receive much lower service lives.

26. Colorado T-Rex Pipe Investigation
84” RCP Pipe was removed as freeway reconstructed
Pipe Age – 44 Years
Original Pipe Class – Class I
D-Load Testing
Initial D-Load (.01 crack) – 2,414 lb/ft/ft (in excess of Class IV)
You may have heard of the rather large roadway installation called T-Rex through downtown Denver by the Colorado DOT. As part of that installation, some of the existing storm drainage pipe was taken out and abandoned as called for in the specifications.
The DOT decided to perform a study on that pipe to see the shape it is in at the end of the service life and the possible design life of the pipe.
It was a good opportunity to see if the long service life claims of concrete pipe manufacturers proved true. Another claim worth investigating is whether concrete pipe grows stronger with age. In this case, 84” pipe was remove and tested in a d-load apparatus. The pipe was originally manufactured as a Class I pipe, which has a d-load requirement of 800 lb/ft/ft. After 44 years of use, the pipe was tested and results indicated a current d-load of 2,414, which three times greater than required.

27. T-Rex Investigation
Here is a photo of the pipe shortly after removal.

28. T-Rex Investigation
Here is a more close up photo of the concrete pipe, which is in fairly good condition and looks like it could be re-used if allowed.

29. T-Rex Investigation
For those of you concerned with abrasion in concrete pipe, here is a look at the invert of an 84” concrete pipe after 44 years of use. It has had plenty of water and bed load rushing through the pipe, but because of it’s high hardness due to low w/c ratios the pipe has not abraded much at all. This indicates the pipe will last well in excess of the claim of 100 years by the concrete pipe industry.

30. T-Rex Investigation
Here is a photo of the pipe in a d-load test apparatus. Did I mention the pipe tested to a d-load of 2414 lb/ft/ft?

31. Ohio Culvert Durability Study
Completed 1982 – After a ten year investigation
Extremely Technical 173 Page Report
1,616 Culverts Studied
Reinforced Concrete and Corrugated Metal Pipe were included
Another extensive study comparing alternate storm drain pipe materials was a study conducted by the Ohio DOT in This was a report that compared the performance of over 1616 concrete and cmp pipe.

32. Ohio Culvert Durability Study
FHWA requested culvert surveys as it became evident that service life of CMP was seriously affected by the trend of designing to minimum gauge thickness (based solely on structural considerations)
FHWA Technical Advisory T “Corrugated Metal Pipe Durability Guidelines” March 21, 1978
The designer must make a determination that two or more products or materials are equal to perform their intended function for the design life of the product.
What brought this study about? It was a mandate by the FHWA that says the designer must make a determination that two or more materials are equal to perform the intended function for the design life of the product.
For pipe, that would be conveying the water through the pipe with no failure or constrictions.

33. Ohio Culvert Durability Study
Investigation Procedures
Investigation started in 1971
Culverts 42” and larger were used
Culverts selected randomly
Samples divided by age
1940 and older
1941 to 1950
1951 to 1960
1961 and newer
The investigations started in 1971 and ran for ten years.
The samples were divided for groups of ten years.

34. Ohio Culvert Durability Study
General Data Considerations:
Pipe Size
Pipe Type
Manufacturer, if available
Type of Pipe Protection
Wall Thickness
General Topography
Date and Time
The data included the pipe type, size, manufacturer, etc.

35. Ohio Culvert Durability Study
Durability Considerations:
Depth of Flow
Velocity
Abrasiveness
Protection Rating
Pipe Material Rating
Test Readings (pH, resistivity, etc.)
Cores from Metal Pipe Culverts
Hydraulic/Structural Considerations (Sag or deflection, joint problems, etc.)
The study was very comprehensive, including the parameters shown above for each product.

36. Ohio Culvert Durability Study
Most Important Factor in Pipe Corrosion:
Low Water pH
Abrasive Bedloads
Abrasion not a concern for rcp in typical installations
According to the Ohio study, what are the most important factors in pipe corrosion.
Low water pH – for concrete pipe, a pH as low as 4 with a pipe slope of 2.5 % resulted in a 100 year service life.
A 16 gage corrugated steel pipe with a pH of 7 will last 20 years.
Another concern is abrasion. For concrete pipe, this is not much of a concern for normal situations. For high bed loads, we do recommend a velocity of less than 20 fps, though.

37. Ohio Culvert Durability Study
For cmp, the pipe overall score was varied with very few scoring an excellent score.

38. Ohio Culvert Durability Study
The study compared the gage thickness of cmp with the expected service life and established the table above.

39. Ohio Culvert Durability Study
Of the 519 concrete culverts studied, only nine were rated in poor conditions.

40. Ohio Culvert Durability Study
Concrete Pipe Culverts:
Rating
No.
Percent
Poor 9
1.7
Fair 33
6.3
Good
115
22.2
Very Good
302
58.2
Excellent 60
11.6
519
100
This table summarizes the performance of the concrete pipe in the OHIO study. Over 92% rated Good, Very Good or excellent.
Can anyone tell me the difference between the pipe used today and back then. Concrete pipe is manufactured in modern facilities with dry cast concrete and f’c values greater than 5,000 psi.
If the concrete pipe of the 40’s lasted this long, how long will today’s?

41. Ohio Culvert Durability Study
Because of Extremely Long Service Life of Concrete Pipe: Predictive equations based on pipes located in acid coal mine drainages
Service life in excess of 300 years for water pH levels of 7.0.
Service life in excess of 100 years for water pH levels of 4.0 and above.
Service lives of concrete pipe were predicted in excess of not 100, not 200, but 300 years for normal installations of culverts and storm drains.

42. Ohio Culvert Durability Study
Years to Poor =
(0.349(pH)1.204)7.758
(Slope)0.824
This graph was generated by the Ohio Durability study. It shows the service life of precast concrete pipe based on the pH and the slope of the pipe. It shows that even when the pH is around 4, which is an extreme condition for a storm drain, concrete pipe can last up to 100 years.
Also, if you extrapolate out the graph, concrete pipe will last in excess of 300 years for normal installations. Did I already mention that?

43. Can Concrete Pipe be excavated and re-used?
We’ve already seen that concrete pipe can last over 100 years and we’ve already seen the shape the pipe is in when removed after 44 years. So, why not re-use the pipe when plans call for removal of a pipe system?

44. Ottawa, Canada Environmental Cleanup of Coal Tar Site
110 meters of RCP installed in 1964
Horizontal Elliptical Pipe 43” x 68”
33 years in aggressive environment
Pipe was cleaned, gasketed, and re-installed
Cost Savings to City of $54,500
We have two examples of the re-use of concrete pipe. One is in Ottawa and the other in Gloucester, Canada. Leave it to those kooky Canadians to think of this. By the way, Canada is way ahead of the US when it comes to pipe material selection based on LCA.
In Ottawa, concrete pipe was removed, cleaned and replaced at an environmental clean-up site, saving the City $54,000.

45. Ottawa Re-Use
Here is a picture of the pipe covered in coal tar being removed from the site.

46. Ottawa Re-Use
The pipe was then cleaned and re-gasketed.

47. Ottawa Re-Use
Next the pipe was re-installed.

48. Gloucester, Canada Environmental Cleanup involving hydrocarbons
45 meters of 54” RCP
Re-install changed loading on pipe from trench to embankment
Contractor requested strength tests
Pipe was removed, steam cleaned, fitted with new gaskets and re-installed.
Another environmental cleanup spawned the re-use of concrete pipe. In this case, pipe was remove and tested and proved to still be strong enough to handle the load.

49. Gloucester, Canada Strength Tests indicated that:
Pipe had gone from 2,000 lb/ft/ft (Class IV) to 4,000 lb/ft/ft (excess of Class IV)
Actual need was 1,350 lb/ft/ft (Class III)
The safety factor of pipe was 2.96 (in addition to design safety factors)
In fact, once again the pipe grew stronger with age. In this case, the pipe went from 2,000 to 4,000 lb/ft/ft and only required 1350, resulting in a factor of safety of nearly three.
Not bad for old pipe.

50. Aggressive Factors to Precast Concrete Pipe
Abrasion
Not significant for normal flows , 20 fps
Sulfates
US BUREC – No problems in precast rcp
Resistance by w/c ratio < 0.40
Fly ash increases sulfate resistance
Typically not a concern for precast concrete pipe
Let’s talk about two areas of concern to concrete pipe durability. A lot of people will tell you that abrasion is a problem in concrete pipe. Most of those people sell a product other than concrete pipe. The reason they say this is based on tests that are extremely un-realistic. For normal installations of concrete pipe, abrasion is simply not a concern. For unusual circumstances of extremely high velocities and bed loads, the designer can take precautions to avoid any possible abrasion problems.
Sulfates are also raised as a possible point of weakness for concrete pipe. This is because many engineers have experienced sulfate problems with cast-in-place concrete. The difference is that concrete pipe is not made with normal concrete. Concrete pipe is made with dry-cast concrete, which is sulfate resistant due to high durability from high cement content and hardness. This is echoed by the Burec which states there are no known problems with sulfates and concrete pipe on their projects.