Just the Facts III: Concrete vs. HDPE Booklet - Ontario Concrete

JUST THE FACTSCONCRETE PIPE

VS. HDPE

Ju s t t he FACTS !

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Contents

Current Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Corrugation Growth and its Effect on Manning’s "n" . . . .4

Deflections, Deformations, Line and Grade Problems . . . .5

Long Term Pipe Durability . . . . . . . . . . . . . . . . . . . . . . .6

Joints and Maintenance Connections . . . . . . . . . . . . . . .7

Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Conflicts with Underground Utilities . . . . . . . . . . . . . . . .9

Wall Buckling and Crushing . . . . . . . . . . . . . . . . . . . . .9

Design Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Site Storage and Handling . . . . . . . . . . . . . . . . . . . . .11

Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

DRAINAGE PIPE PERFORMANCE

AND DESIGN COMPARISON

CONCRETE VS. HDPE

CURRENT STANDARDS

In the province of Ontario, standards generally used are a combination ofthe Ontario Provincial Standards (OPS) and Canadian StandardsAssociation (CSA). For HDPE pipe, it is not as simple as referencing docu-ments from these organizations. A review of the current standards relatedto the materials used in manufacturing, as well as the installation of HDPEpipe, provides designers and specifiers with the need to reference otherdocuments such as ASTM and AASHTO.

A COMPILATION OF THE CURRENT STANDARDS, FOR HDPE NON-PRESSURE PIPE PRODUCTS INCLUDES:

OPSS 1840: Material Specification for Non-Pressure PolyethylenePlastic Pipe Products – this standard provides general guidance appropri-ate standards for materials and quality assurance.

CAN/CSA-B182.6: Profile Polyethylene Sewer Pipe and Fittings – this stan-dard covers open profile, 100 mm to 1200 mm, and closed profile, 450 mmto 1200 mm, diameter sewer pipe

ASTM F894: Standard Specification for Polyethylene (PE) Large DiameterProfile Wall Sewer and Drain Pipe – this standard covers requirements andtest methods for materials, dimensions, workmanship, ring stiffeners, flatteners,joint systems and a form of marking for large diameter, 10 to 120 in. (250 to3050 mm) profile wall polyethylene pipe for use in low pressure and gravityflow applications

ASTM F405: Standard Specification for Corrugated Polyethylene (PE) Pipeand Fittings – this standard covers requirements and test methods for corru-gated polyethylene (PE) pipe and fittings for nominal sizes 3 to 6 in. (75 to150 mm)

ASTM F667: Standard Specification for Large Diameter CorrugatedPolyethylene Pipe and Fittings – this standard covers requirements and testmethods for materials, etc. for nominal sizes 8 to 24 in. (200 to 600 mm)

AASHTO M252: Standard Specifications for Corrugated PolyethyleneDrainage Pipe – this specification covers the requirements and methods fortesting of corrugated polyethylene (PE) pipe, etc. for 75 mm to 250 mm diam-eter

AASHTO M294: Standard Specification for Corrugated Polyethylene Pipe,300 to 1200 mm diameter – this specification covers the requirements andmethods for testing of corrugated polyethylene (PE) pipe, etc. for 300 mm to1200 mm diameter

Ju s t t he FACTS !

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A COMPILATION OF THE CURRENT STANDARDS, BY CONCRETEPIPE PRODUCT INCLUDES:

OPSS 1820: Material Specification for Circular Concrete Pipe –this standard provides general guidance appropriate standards for materi-als and quality assurance

CAN/CSA-A257.1: Circular Concrete Culvert, Storm Drain, Sewer Pipeand Fittings – this specification covers nonreinforced circular concrete pipeand fittings 100 mm to 900 mm in diameter

CAN/CSA-A257.2: Reinforced Circular Concrete Culvert, Storm Drain,Sewer Pipe, and Fittings – this specification covers reinforced circular con-crete pipe and fittings 300 mm to 3600 mm in diameter

CAN/CSA-A257.3: Joints for Circular Concrete Sewer and Culvert Pipe,Manhole Sections, and Fittings Using Rubber Gaskets – this standard spec-ifies the design and performance requirements for flexible watertight joints

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“Smooth inside wallHDPE pipe develops

ridges in the liner when installed. Thisdeformation of theliner is caused bybackfill loads that

force the corrugated outer

portions of the pipe todeform the liner.”

RCP - Smooth Wall

HDPE - Smooth Wall

CORRUGATION GROWTH AND ITSEFFECT ON MANNING’S "N"

Selection of the proper value for thecoefficient of roughness of a pipe isessential in evaluating the flowthrough culverts and sewers. Anexcessive value is uneconomical andresults in over sizing of pipe, while onthe other hand a low value can resultin hydraulically inadequate pipe.

Numerous laboratory studies havebeen conducted in an effort to deter-mine Manning’s n. Results of theselaboratory studies including work atUtah State University confirmMannings "n" laboratory values of0.009 to 0.010 for concrete pipeand 0.009 to 0.015 for smoothinside wall polyethylene pipe.

Generally accepted recommenda-tions for design include a safety fac-tor of 20% to 30%, to account for dif-ferences between laboratory andactual installed conditions. Misalignment of joints, debris in theline, maintenance hole transition loss-es and other obstructions account forthe necessary safety factor. These rec-ommended safety factors are inde-pendent of the type of pipe beingused. In Ontario, the MOE guidelinessuggest a Manning’s "n" of 0.013 forall smooth walled pipe.

Smooth inside wall HDPE pipe devel-ops ridges in the liner when installed.This deformation of the liner is causedby backfill loads that force the corru-gated outer portions of the pipe todeform the liner. This well-known anddocumented phenomenon is known

Ju s t t he FACTS !

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“A general lack of pipestiffness is the biggest

contributor to deflectionand deformation

problems. Line andgrade irregularities are

due to a lack of longitudinal stiffness in

the pipe.”

900mm HDPE - Smooth Wall.

Vertical Deflection.

as corrugation growth. Unfortunately,no laboratory testing which has beenendorsed by the standards applica-ble in Ontario has been conducted toassess the effects of increased rough-ness of the pipe liner. The depth of theliner corrugations has been measuredup to 19 mm, which is comparable tocorrugated metal pipe. Designersneed to account for this increasedroughness when sizing drainagepipe. The true installed value ofManning’s "n" should be closer tothat of corrugated metal pipe.

DEFLECTIONS, DEFORMATIONS,LINE AND GRADE PROBLEMS

The difficulty of installing HDPE pipeis often evidenced by the many typesof deformations that show up in thefinished installations. Vertical deflec-tions are primarily a result of the pipebeing installed without adequate sidesupport to withstand the loads fromoverburden, which can be enhancedwhen moving trench boxes. A gener-al lack of pipe stiffness is the biggestcontributor to deflection and defor-mation problems. Line and gradeirregularities are due to a lack of lon-gitudinal stiffness in the pipe. Thelonger lengths of pipe, approximately6 m, require close control of beddingmaterial, grade and compaction dur-ing installation, or high and low spotsor deflection may occur.

In contrast, the 2.44 m concrete pipelengths allow close control of line andgrade, which fits easily into a stan-dard trench box. The weight of con-crete pipe resists lateral movementduring backfill operations and thewall thickness prevents deformation.

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“...research has shown that the lack of stress crack resistance of the polyethylene resin used to manufacture HDPE

pipe leads to this long term problem.”

Cracked HDPE Liner.

Cracked HDPE Liner.

LONG TERM PIPE DURABILITY

A recent NCHRP Study indicatedstress cracks and liner tears occur inHDPE pipe with time. The cracks gen-erally occur at the junction where theliner is welded to the outer corruga-tions. The main cause of the cracks isa combination of residual stressesbuilt into the pipe from the manufac-turing process and stresses inducedby poor installation and changingsoil conditions. This research hasshown that the lack of stress crackresistance of the polyethylene resinused to manufacture HDPE pipeleads to this long term problem. Theraw materials used to manufactureHDPE pipe can be tested forEnvironmental Stress Crack Resistance(ESCR), but many HDPE pipe manu-facturers do not choose to do so.There is no established method ofrepairing a torn or cracked HDPEpipe.

Concrete pipe is designed to the0.3mm crack, in accordance withCSA. Cracking of concrete pipe tothis standard indicates the design isappropriate and the steel is workingas designed to maintain the shapeof the pipe.

Ju s t t he FACTS !

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“If HDPE pipe joints are torn during

installation, leaks are a likely result. There is

not an established repair method for

torn joints.”

Joint Failure. Bedding Material Washed In.

Failed HDPE Joint.

JOINTS AND MAINTENANCE

HOLE CONNECTIONS

If HDPE pipe joints are torn duringinstallation, leaks are a likely result.There is no established repairmethod for torn joints. Compactionof pipe at maintenance holes can bedifficult. Due to the nature of mainte-nance hole installation, proper com-paction around the pipe can be diffi-cult and vertical deflections are likelyto result. The use of flexible boots aresuggested as the most appropriatemethod of connection between arigid maintenance holes and flexiblepipe. Grouting of this connection willnot work.

Concrete pipe joints that are dam-aged during installation can berepaired in accordance with estab-lished methods. There is little differ-ential deflection when a properlyinstalled concrete pipe enters a rigidmaintenance hole. The maintenancehole and the pipe should be subject-ed to the same bedding characteris-tics.

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“Fire can ruin the structural integrity

of the HDPE pipe and, in some cases,

there is nothing left except the soil

around the pipe.”

Floating 1050mm Pipe.

Culvert Fire.

FLOTATION

Flotation needs to be addressed dur-ing the design of buried pipelines.The lack of weight and stiffness ofHDPE pipe makes this an importantdesign consideration in areas with ahigh water table. If HDPE pipe can-not be restrained with overburden,anchoring devices should be used.

Because of the heavy weight andstiffness of concrete pipe, flotation isgenerally not an issue.

FIRE

HDPE pipe is a petroleum basedproduct. It is flammable and is notrequired to contain a fire retardant.Fire can ruin the structural integrityof the pipe. In some cases, the pipematerial is consumed by fire leavingnothing except the soil around thepipe. There are documented casesof fire in storm sewers and culvertscaused by burning debris.

Concrete is not flammable. Therehave been cases of burning itemssuch as leaves, grass in a concretepipe, with no damage to the pipe orinconvenience to the public.

Ju s t t he FACTS !

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“Concrete pipe is not affected by a disturbed soil

envelope because the strength

of a concrete pipe is engineered into

the product.”

Trenched Power Cable.

Failed Pipe Wall Buckling.

CONFLICTS WITHUNDERGROUND UTILITIES

Utility trenching and boringmachines will damage most plasticpipe, including HDPE. There is noindication to the operator of themachine that a pipeline has beencompromised. Even activity in theeasement that doesn’t damage thepipe outright, can cause long termproblems by disturbing the backfillenvelope that is integral to a flexiblepipes strength.

Concrete pipe can also be dam-aged by utility trenching and boringequipment, but the operator knowssomething has been hit. The dam-age can be fixed and/or the routealtered. Concrete pipe is much lesslikely to be affected by a disturbedsoil envelope because the strengthof a concrete pipe is engineeredinto the product.

WALL BUCKLING ANDCRUSHING

Wall buckling most often occurs atthe spring line of the installed HDPEpipe, although localized wall buck-ling can occur elsewhere. In deepfill situations, wall buckling canprogress to the point where the wallactually crushes or tears. A generalcollapse of the pipe may eventuallyoccur when wall crushing is present.

Concrete pipe is not affected by thisfailure mechanism.

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“Concrete pipe canbe custom designed for each installation,

accounting for differences in loads,

supporting soils, and traffic over the pipe.”

Concrete Pipe.

Concrete Pipe Installation.

DESIGN FLEXIBILITY

HDPE pipe does not have design flex-ibility because it is not a customengineered structure in the same wayas concrete. A polyethylene pipeinstallation is determined to beappropriate when deflection, buck-ling and bending calculations arewithin acceptable limits. The successof the installation is almost totallydependent on the care taken by theinstaller, the quality of the beddingmaterials and the insitu soil.

Concrete pipe can be customdesigned for each installation,accounting for differences in loads,supporting soils, and traffic over thepipe. Concrete pipe can bedesigned to utilize a very good back-fill or even an uncompacted backfill.Special wyes, tees, bends, and tran-sition pieces can be produced to thesame strength as the pipe.

Ju s t t he FACTS !

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“HDPE pipe has little structural strength and is therefore

subject to damage if handled improperly.

Nylon slings or cushioned cables

are recommended.”

Handling Concrete Pipe

Shipping Concrete Pipe

HANDLING AND STORAGE

The transport of HDPE pipe to the jobsite is generally done using flat bedtrucks, delivered in a loose or pal-letized form, depending on the typeand quantity of pipe. HDPE pipe haslittle structural strength and is there-fore subject to damage if handledimproperly. Nylon slings or cush-ioned cables are recommended. Thepipe should be set aside on the jobsite, in a flat area free of large rocks,rough surfaces and debris.Damaged pipe cannot be repaired.The pipe should also be locatedaway from construction traffic. Thepipe is subject to degradation by thesun’s ultra violet rays and should notbe stored on site for an extendedperiod of time.

Concrete pipe is a very durableproduct. The pipe is generally deliv-ered to site on flat bed trucks andunloaded using a boom or hydrauliclift. Concrete pipe resists gougingand if chipped, can be repairedusing well-known procedures. Thepipe can be stored on site for extend-ed periods of time, with no deterio-ration as it is not susceptible todegradation by ultra violet rays.

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“Reinforced concrete pipe utilizes conventional

materials with known and understood properties.

Aggregates, cement and reinforcing steel

are the basic raw materials used in

reinforced concrete pipe.”

MATERIAL

Reinforced concrete pipe utilizes con-ventional materials with known andunderstood properties. Aggregates,cement and steel are the basic rawmaterials used in reinforced concretepipe. There are variations withinthese basic materials, but the engi-neering properties of each are wellknown and may be easily measured.

Polyethylene, as a material compo-nent, is less familiar and more diffi-cult to evaluate. There are many for-mulations of polyethylene and thephysical properties can be manipu-lated to achieve the desired result.Unfortunately, some of the propertieshave opposing effects. For example,a formulation with a high modulus ofelasticity is desirable to give the pipegreater stiffness. But, high modulus ofelasticity materials can be suscepti-ble to stress cracking. Selecting alower modulus that is crack resistantwill require more wall area toachieve suitable section properties.This would require additional resin tobe used in the manufacture of thepipe, which, it appears, the industryis unwilling to do.

Ju s t t he FACTS !

Aggregates, cement and reinforcing steel are thebasic raw materials used in reinforced concrete pipe

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