HIGHWAY

INSULATION

COMMERCIAL

STYROFOAM BrandHighload InsulationOne of man’s best laid plans.

Wherever underlying soils are sus-ceptible to frost, roadways will sufferfrost heaving and spring break-up. Thedamaging effects of this frost actionplay havoc with traffic on major arter-ies as well as pose a monumental cashoutlay to repair year in, year out.

To combat this recurring engineer-ing nightmare, Dow Chemical CanadaInc. introduced the concept of high-way insulation in 1959, with the firstCanadian installation appearing in 1962.

Essentially this concept requiredDow to draw on its resources anddevelop a rigid board insulation with acombination of properties which wouldprevent sub-soil frost action. With that,they manufactured STYROFOAM*Brand Highload Insulation, a TYPE 4extruded polystyrene rigid foamboard. When properly installedbetween the sub-soil and gravel base, STYROFOAM Brand HighloadInsulation reduces heat loss from thefrost-susceptible subgrade so thatfrost heaving and spring break-up are held at bay. Since its inception,STYROFOAM Brand Highload Insulationhas been successfully reducing frostand thaw damage on countless road-ways in Canada, the U.S.A., Japan andthroughout Europe. These widescalefield applications have also demon-strated that STYROFOAM BrandHighload Insulation is equivalent orbetter than conventional measuresand often more economical thanreplacing the subgrade with costlynon-frost-susceptible base materials.

HIGHWAY INSULATION IN SEASONAL AREAS

Frost action on roadways isinevitable. This frost action includes“frost heave” and “spring break-up”.

“Frost heave” is the upward move-ment of pavement as a direct result ofice lenses forming in the frost-suscep-tible subgrade. As freezing starts inthe subgrade, a suction force developsand draws water up through the soil tothe freezing face. This moistureexpands as it freezes, creating moresuction. As the process continues andice lenses are formed, the upwardpressure causes heaving in the surface of the pavement.

“Spring break-up” occurs whenwarm spring temperatures start tothaw the ice lenses from the surfacedownward. Since the lower soil zonesare still frozen, drainage is restrictedand super-saturated soil conditionsresult. The soil’s bearing capacity isgreatly reduced, forming a very weakfoundation that can result in alligatorcracking and rutting in flexible pave-ments. In rigid pavement, crackingdevelops in the slabs.

SOLUTIONS TO THE PROBLEMThree factors are responsible for

frost action.1) Frost-susceptible soil2) Freezing soil temperatures3) Water supply at or near the

freezing frontTo reduce frost action, one

or more of these factors must be reduced or removed. Over theyears, several different techniqueshave been found useful in minimizingor alleviating the problem to somedegree:1) Removing pockets of frost-

susceptible soil and using extra-thick base courses to spread theload during spring thaw. This canbe expensive and may not providecomplete protection.

2) Providing adequate drainage forfree water through ditching.

3) Placing a layer of insulation in theembankment section to keep sub-grade soil temperatures abovefreezing.

2

*Trademark licensed from The Dow Chemical Company

FIGURE 1: FROST HEAVE

Pavement SurfaceRuts

Gravel Base

Frozen

Unfrozen

Moisture

FIGURE 2: SPRING BREAK-UP

Pavement SurfaceGravel Base

Frost-susceptible SoilIce Lenses

Capillary WaterFreezing Temperatures

Water Table

The third concept calls for an insulation material, which combines animportant range of properties uniqueto STYROFOAM Brand HighloadInsulation. Installed between the sub-soil and gravel base, STYROFOAMBrand Highload Insulation preventsheat loss from the frost-susceptiblesubgrade so that ice lenses are notformed. Thus, frost heaving andspring break-up are held at bay.

3

FLEXIBLE PAVEMENT

RIGID PAVEMENT

Bituminous Concrete Surface

Gravel Base

STYROFOAM Brand Highload Insulation

Frost-Susceptible Soil

Water Table

Portland Cement Concrete Surface

Gravel Base

STYROFOAM Brand Highload Insulation

Frost-Susceptible Soil

Water TableTABLE 1: SPECIFICATIONS

TABLE 2: SPECIFICATIONS

NOTE: (1) For 25mm or 1 inch thickness.

NOTE: (1) At 5% deformation or yield, whichever comes first. Suitable safety factors must be employed to limit long-term creep and fatigue deformation.(2) For 25mm or 1 inch thickness.

PRECAUTIONS: This product is combustible and should be properly installed. For specific instructions, see Dow literature available from your supplier or from Dow.

Compressive Strength(1) (min)ASTM D1621-73

275kPa(40psi)

415kPa(60psi)

690kPa(100psi)

480kPa(70psi)

590kPa(85psi)

860kPa(125psi)

275kPa(40psi)

310kPa(45psi)

350kPa(50psi)

CAN/ULC S-701-97 – (Type 4)

480kPa(70psi)

585kPa(85psi)

690kPa(100psi)

9650kPa(1400psi)

15170kPa(2200psi)

25510kPa(3700psi)

Tensile Strength (Typical)ASTM D1623-78 (Method A)

CAN/ULC Classification

Flexural Strength(2) (Typical)ASTM C203-91

Compressive Modulus (Typical)ASTM D1621-73

Highload 40 Highload 60 Highload 100PROPERTY

Shear Strength (Typical)ASTM C273-61

FIGURE 3: INSULATED PAVEMENT CONCEPT

PROPERTY

†Thermal resistance. Minimum R-value or RSI(1) ASTM C-518-91, C-177-85

Linear thermal coefficient ofexpansion ASTM D696-79

Capillarity

0.87 (m20C)/w

6.3 x 10 mm/m/ ˚C

NONE

35 ng/Pa•s•m2

less than 0.7

74 ˚C

5.0 ft2 hr˚F/BTU

3.5 x 10-5 in/in/ ˚F

NONE

0.6 perms

less than 0.7

165 ˚F

Water vapour permeance(1) (max)ASTM E96-90

Water absorption (% by volume)(max)•ASTM D2842-90

Maximum operating temperature

METRIC IMPERIAL

-2

DESIGNTECHNOLOGY

To bring the concept of the insu-lated pavement to life, Dow developeda structural computer program basedon the Elastic Layer Theory, to be used with standard rigid and flexiblepavement design methods. The inves-tigation method assigned values ofelastic modulus and Poisson’s ratio to each pavement layer and subgradeclass. Stresses, strains and deflectionsin the layers were then calculated for a circularly distributed wheel load.

A pavement section was thendesigned using conventional practices

based on loading and soil conditions. By applying the Elastic Layer Theory to the simulation, the resultant stresses, strains and deflections weredetermined. An insulation layer wasthen added. By comparing results,along with known fatigue properties of the system, insulated pavementdesigns were selected which limitedstress on the insulation within a rea-sonable safety factor. It’s important tonote that where insulation is installedaccording to a correct design, it elimi-nates frost action in the subgrade. Thisexcludes the extra material normallyused to combat frost action in conven-tional designs, and the structurallydesigned section stands as therequired pavement thickness.

To determine the thickness andwidth of insulation required in a section to prevent subgrade freezing, a thermal analysis of the system wasnecessary. To do this, Dow developed

a thermal computer program based on a numerical technique known as theFinite Difference Method. Soil and climatological data were also intro-duced to determine the insulationthickness. In addition, the TwoDimensional Finite Element thermalprogram was used in design sectionswhere frost penetration through theembankment sides was critical.

The results of the programs compared favourably with field datagathered from instrumentation of several test sites.

As a guide, the computer analysesthat have been performed were basedon the following data:

CLIMATOLOGICAL DATA1) Mean annual air temperature for

the site (assumed to be averagevalue for all past years available).

2) Design air thawing index for thesite (assumed to be average for allpast years available).

3) Design air freezing index for thesite (assumed to be the maximumvalue for any given 10-year period,or assumed to be average of 3highest values for any 30-year period, if available).

4

FIGURE 4: STRESSES AND STRAINS ANALYZED IN A LAYERED STRUCTURE

Contact Stress

Asphaltic ConcreteLayer (E1.µ1)

h1

h2

h3

Subgrade (E4.µ4)

E = Young’s Ratioµ = Poisson’s Ratioa = Contact Radius

Total Deflection

Tensile Stressor Strain

Granular Base and SubbaseCourse Layer (E2.µ2)

Compressive Stress on theInsulation

STYROFOAM HighloadBrand Extruded PolystyreneFoam Insulation (E3.µ3)

Compressive Strain Stress ofDeflection in Subgrade

GEOTECHNICAL DATA1) Characteristic soil profiles from

ground surface to depth of at least3 metres (10 ft.) – preferably to adepth of 6 metres (20 ft.) whereavailable – below subgrade eleva-tion. Profiles were representative of foundation soil conditions along the route.

Each profile included strata depthsdescribed according to symbols, soil description, terminology andfield identification procedures ofthe United Soil ClassificationSystem of the AASHTO System.

2) Measured and recommended bestvalues assumed as bearing capacityindices at subgrade elevation foreach soil profile.

3) The range and recommended bestvalues for the in situ dry density andmoisture content (expressed as %of dry density) for each subgradesoil stratum.

4) Predicted in-place dry densities and moisture contents of the highway embankment materials.

HIGHWAY DESIGN DATA1) Type, thickness, width and descrip-

tion of pavement, base course and sub-base.

2) Design maximum single-axle loadlimit and tire pressure.

3) Estimated number of heavy trucksper year on design lane and aver-age gross weight of heavy trucks.

4) Design life of highway.

COST OPTIMIZATION DATAComparative non-insulated frost

action free design with estimated unitprices for construction.

HELPFUL BUT NONESSENTIALDATA1) Mean annual ground temperature

at 0 to 9 metres (0-30 ft.) – depthbelow ground surface, or bestapproximation.

2) Depth of frost penetration for a particular soil profile at the sitewith the mean annual air tem-perature, air thawing index and airfreezing index for the year or yearsthat the depth was determined.

CONSTRUCTION METHODSInsulated pavement construction

can utilize conventional road-buildingequipment and techniques.

The subgrade should be shapedand compacted in accordance withnormal specifications prior to place-ment of insulation. On this surface,insulation boards 600mm x 2400mm(24 inches x 96 inches) thickness areplaced in staggered fashion with longaxis parallel to the centre line andpinned to underlying soil with woodenskewers approximately 150mm x 6mm(6 inches x 1/4 inch) diameter. Whenplacing the first row of board downthe highway centre, a stringline is themost convenient way to ensurestraight alignment. Placement ofboards progresses from the centre out and extends 1.2m (4 ft.) into theshoulder. Care should be taken toobtain tight joints and to stagger alltransverse joints.

When going from an insulated toan uninsulated pavement section, atransition zone is required to provide agradual change in embankment thermal properties. This zone consistsof a step-down pattern of insulationthicknesses to allow greater subgradeheat loss at each end of the insulated section. The insulation thickness step-down (or reduction) in thesezones is 25mm (1 inch) and each step-down is carried for 4.9m (16 ft.).For example, an insulated pavementemploying a 75mm (3 inch) thick STYROFOAM Brand HighloadInsulation layer would have two insula-tion step-downs in each of its transitionzones. The insulation would first bereduced to a 50mm (2 inch) thicknessfor 4.9m (16 ft.) and then reduced to a 25mm (1 inch) thickness for another4.9m (16 ft.).

FLEXIBLE PAVEMENT SECTIONIn constructing flexible pavements,

the insulation is covered by enddumping, spreading, and compacting agranular-material lift to a compactedthickness of 0.15 meters (6 inches) mini-mum. Coarse aggregate causes noappreciable damage to the insulationsurface. Once this layer is compacted tothe required density, the strength ofSTYROFOAM Brand Highload Insulationextruded polystyrene foam allows sub-sequent lifts of granular material andasphalt concrete to be placed in thenormal manner.

NOTE: Care should be taken to preventvehicles, heavy equipment, etc., frombearing directly on the insulation sincedamage can result.

RIGID PAVEMENT SECTIONFrom the structural aspect of design,

concrete slabs can be poured directly on the insulation. However, since theprobability of surface icing occurringincreases with proximity of insulation to road surface, a base course is oftenplaced on top of insulation before theslab is poured. The phenomenon of surface icing is covered in detail in the“Differential Icing” section of thisbrochure.

OVERLAYSIn some cases, instead of building

an entirely new pavement, it’s more economical to construct an insulatedflexible or rigid overlay. In these applications, the appropriate thicknessof insulation is placed directly onto theexisting pavement and kept in place bybonding it to the pavement with anadhesive, or by placing small piles ofgranular material on the insulationboards immediately after installation.The properly designed overlay can thenbe placed on top of the insulation in the same manner described in previous paragraphs.

5

DESIGN CHARTS

HIGHWAY INSULATION IN PERMAFROST AREAS

Permafrost is a perennially frozenground condition, and it can encom-pass all soil types, from coarse ice tofree gravel to clays to silts containinglarge volumes of ice. When construct-ing pavements in permafrost areas,engineering problems are thermalproblems.

Because the thermal state of theground can be significantly altered byonly minor variations in site conditions,thawing of high-ice-content soils mayresult, leading to a super saturated soil condition that greatly reduces the load-carrying capacity of the soil.Since the top soil in these cold areas iscomposed of organic materials, it hasextremely poor engineering propertiesin its thawed state.

6

FIGURE 5: AVERAGE PENETRATION OF FROST BENEATH STYROFOAM BRAND HIGHLOAD INSULATION IN PAVED HIGHWAYS

0.50m

0m

100mm

Level of Pavement Surface

Level of STYROFOAM Brand HighloadInsulation

STYROFOAM Brand HighloadInsulation Thickness

90mm75mm65mm50mm40mm25mm0mm

1.00m

500

1000

1500

2500

3000

1.50m

2.00m

2.50m

3.00m

3.00m BASED ONVAL GAGNE TEST SITE

RESULTS 1972-1977(JOINT PROJECT-O.M.T.C. & DOW)

ME

TRIC

2000 DEGREE DAYS CELCIUS

1'6"

3'

4'

5'

6'

7'

8'

9'

10'

0'

4"3.5"3"2.5"2"1.5"1"0"

Level of Pavement Surface

Level of STYROFOAM Brand HighloadInsulation

STYROFOAM Brand HighloadInsulation Thickness

900

1800

2700

4500

5400

9'10" BASED ONVAL GAGNE TEST SITE

RESULTS 1972-1977(JOINT PROJECT-O.M.T.C. & DOW)

IMP

ER

IAL

3600 DEGREE DAYS FAHRENHEIT

FIGURE 6: PERMAFROST: PERENNIALLY FROZEN GROUND

NORTH(CONTINUOUS PERMAFROST)

PERMAFROST ACTIVE LAYER

SOUTH (DISCONTINUOUS

PERMAFROST)

0.3M(1’)

460M(1500’)

0.6-0.9M(2’-3’)

SOLUTIONS TO THE PROBLEMTo overcome these difficulties, the

ice-rich soil can either be eliminatedduring construction or preserved in itsfrozen state. Eliminating permafrostand replacing it with non-frost suscep-tible material may be economical indiscontinuous zones where there arepermafrost pockets of limited size andnumber. In most cases, however, it’snot economical. This is especially truein continuous zones where permafrostis much deeper and widespread. Here,a common procedure is to build anembankment with a sufficient amountof granular material to preserve thepermafrost and provide a structurallysound base in order to support summer traffic.

Conventional methods of roadwayconstruction across permafrost onlyprovide a sufficient overlay to supportvehicle loadings during the most critical climactic period. This minimumis usually much less than the thicknessof granular overlay necessary to prevent degradation of the permafrost.This means that a considerableamount of differential road settling willoccur as indicated in Figure 7.

Two current factors increase thepotential for using STYROFOAM BrandHighload Insulation for permafrostareas. First, the costs for obtainingnon-frost susceptible fill for embank-ments are increasing. Second, theincreasing number of gravel highwaysbeing paved with asphalt concreteposes problems of great depth ofthaw into permafrost due to theasphalt’s heat-absorption properties.

STYROFOAM Brand HighloadInsulation is an economical alternativeto conventional embankment insula-tion methods. When placed in the cor-rect location within the embankment,it can prevent the thawing of per-mafrost during the summer months.This protection enables the frost-sus-ceptible soil to retain the structuralproperties needed to support traffic asshown in Figure 8.

CONSTRUCTION METHODSAs in the seasonal areas, construc-

tion of an insulated pavement sectionin permafrost areas can be accom-plished with conventional road-buildingequipment and techniques.

In preparing the subgrade forinstallation of STYROFOAM BrandHighload Insulation, site clearanceshould be done by hand to keep disturbance of the ground cover to aminimum. The required sub-basematerial should then be spread on topof the subgrade with a light crawler-

type tractor and compacted to the satisfaction of the engineer.

Installation of boards of STYROFOAM Brand HighloadInsulation on this surface follows the same procedure described forseasonal areas. In cases where wooden skewers cannot penetrate topin the insulation to the underlyingfrozen sub-base, steel spikes of thesame length can be used. The thermalshort created by the spikes will causeno appreciable thawing in the sub-base.

7

FIGURE 7: CONVENTIONAL EMBANKMENT

FIGURE 8: INSULATED EMBANKMENT

Original Road Profile

Insulating Road Profile Due to

Permafrost Thaw

STYROFOAM BrandHighload Insulation

Extruded PolystyreneFoam Insulation

Active Layer

Ultimate Permafrost Table

Ultimate Permafrost Line

Original Permafrost Line

Active Layer

Embankment

Subsidence Dueto Thaw of Ice

Ground Surface

Permafrost Table

Non-frost Susceptible Embankment Fill

Ground Surface

Original Permafrost Table

HISTORY ANDDEVELOPMENT

Early in 1959, The Dow ChemicalCompany and Purdue University under-took a joint investigation of insulatedpavements. The University’s School of Civil Engineering had considerablebasic knowledge on frost penetrationin soils. This information was used tofurther develop a mathematical tech-nique for predicting rate and depth offrost penetration in pavement systems.

Purdue also produced a structuralanalysis procedure for insulated pave-ment systems. Dow later developed athermal analysis method. The combi-nation of these two analytical methodsinto the computer design programs isdescribed in greater detail in the“Design and Technology” section.

Extensive laboratory evaluations of many insulation materials and theirfindings led researchers to select STYROFOAM Brand extruded poly-styrene foam as uniquely qualified tomeet all requirements. From that base,STYROFOAM Brand HighloadInsulation was specially developed forhighway insulation. This extrudedfoam has a dense, tough surface skin.It possesses very high compressivestrength and very high thermal resis-tance. It has low water absorption, itwill not sustain mould growth or decay,and it has no food value for plant oranimal life. These permanent properties

together with ease of handling andinstallation make STYROFOAM BrandHighload Insulation ideally suited foruse in a soil environment beneath a highway.

Since inception in 1962, a numberof test sites have been continuouslymonitored. This data is used in studiesfor refining the procedure and techniques of highway insulation.

PERFORMANCEIn order to measure how the prop-

erties of STYROFOAM Brand HighloadInsulation react to prolonged periodsof use, comprehensive testing has beendone in the field and in laboratory simulations.

Two basic types of laboratory tests were performed to project thelong-term thermal performance ofSTYROFOAM Brand HighloadInsulation. The first was a simple soaking test. Samples of the insulationwere submerged for varying time periods and then removed to monitortheir properties. Test results showedvery little water pickup and very littlereduction in thermal resistance. Nextcame an accelerated freeze/thaw test which showed very little increasein water pickup and reduction in thermal resistance after extensivefreezing and thawing.

8

FIGURE 9: WATER ABSORPTION VS YEARS OF SERVICE FOR CANADIANAND U.S. HIGHWAY FIELD INSTALLATIONS

YEARS OF SERVICE

WA

TER

AB

SOR

PTI

ON

(%

BY

VO

LUM

E)

00

1

2

3

4

5

6

7

8

9

10

11

12

13

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

25mm (1.0") STYROFOAM40mm (1.5") STYROFOAM50mm (2.0") STYROFOAM60mm (2.5") STYROFOAM75mm (3.0") STYROFOAM

Moisture absorption performancewas also examined under field condi-tions. Samples of STYROFOAM BrandHighload Insulation were taken fromvarious highways after several yearsservice. Again, very little moisturepickup was recorded. These testresults are displayed in Figure 9 wherethe insulation’s water pickup is shown as a function of the years of service.

The results in Figure 9 are excellentfor the type of STYROFOAM BrandHighload Insulation used in the past. However, current grades of STYROFOAM Brand HighloadInsulation have improved properties,including lower water absorption and a thermal resistance value of: RSI = 0.87 (R=5.0).

STYROFOAM Brand HighloadInsulation has also been subjected tocontinuous and repeated load applica-tion tests to simulate dead and liveloading conditions found in the field.From these tests and others, the creep (long term deformations due todead loads) and fatigue (long termdeformations due to live loads) lives of STYROFOAM Brand HighloadInsulation were established. Deadloads on STYROFOAM BrandHighload Insulation should be limitedto one third of the rated compressivestrength of the insulation product.Allowable live load stresses on STYROFOAM Brand HighloadInsulation depend on the number ofrepeated loads expected. For lessthan 103 loadings, design so that thestress on the STYROFOAM BrandHighload Insulation does not exceedone half the rated compressivestrength of the insulation. For 106 loadcycles, design to one eighth of therated compressive strength; for 108

load cycles, use one tenth of the ratedcompressive strength to limit fatiguedeformation. More information on the creep and fatigue properties ofSTYROFOAM Brand HighloadInsulation can be obtained from yourDow Sales Representative.

PERFORMANCE OF INSULATED HIGHWAYS

To show the type of overallperformance that can be expected ofinsulated roadways, data from one sea-sonal and one permafrost test sectiontypify the success of STYROFOAMBrand Highload Insulation.

The seasonal region test for a highway in Val Gagne, Ontario, is

9

5252015 10152025 5 10152025 5 10152025 5 10152025 5 10152025 5 10152025 5 10152025

NOVEMBER

(-22)

(-4)

(14)

(32)

(50)

(68)

(86)

-30

-20

-10

0

Temperature

Temperature Below 75mm (3") Layer ofSTYROFOAM* Brand Plastic Foam

( of Highway)

Temperature Above 75mm (3") Layer ofSTYROFOAM* Brand Plastic Foam

( of Highway)

10

20

30 mm75 (3")

460 (18")

75 (3")

100 (4")

AsphaltConcrete

AsphaltConcrete(Old)

GravelBase

OldEmbankment

TC: Thermocouple

TC1

Subgrade

TC2

O

FO

C

19731973 1973 1974 1974 1974 1974 1974

OCTOBER DECEMBER JANUARY FEBRUARY MARCH APRIL MAY

CL

CL

FIGURE 10: THERMAL PERFORMANCE OF AN INSULATED PAVEMENT IN A SEASONAL AREA(1)

VAL GAGNE, ONTARIO, 1973-1974 AIR INDEX = 2100 DEGREE-DAYS C. (3780 DEGREE-DAYS F.)

demonstrated in Figure 10. As thegraph shows, very little freezing tookplace below the STYROFOAM BrandHighload Insulation. In this case, nofrost action occurred in the frost-susceptible subgrade.

These results typify the perfor-mance of foam-insulated highways in seasonal areas.

To demonstrate the thermal performance of an insulated highwayembankment in the permafrost region,a test site was installed near Inuvik,N.W.T. Figure 11 shows that resultsfrom this site compare favourably withearly predictions and calculations. Theyindicate that, in properly designedinsulated pavement sections, the sub-grade will remain frozen throughoutthe warm summer months.

The structural performance of ahighway insulated with STYROFOAMBrand Highload Insulation in a seasonal

area was studied using Benkelmanbeam deflection tests.

An examination of the dataacquired from these tests shows the falldeflection of the pavement is slightlygreater in the insulated section than inthe control. However, deflections in thecontrol increased significantly duringthe spring thaw indicating a loss ofsubgrade support. During this sameperiod, deflections in the insulated sections remained well below those inthe control and showed only a slightincrease over the fall values.

10

2

1

1971 1972 1973 1974

WINTER SITE 90mm (3.5") INSULATIONPIONEER FILL PLACED

TEST SECTIONS CONSTRUCTED

ORIGINAL GROUND SURFACE LAYER OF INSULATION

FILL ADDED

WINTER SITE 50mm (2.0") INSULATION

SUMMER SITE 115mm (4.5") INSULATION

1975 1976 1977 1978

0

2

1

0

2

1

1

0

80

DE

PTH

OF

THA

WM

ETE

RS

INC

HE

S

40

0

80

40

0

80

40

40

0

460mm (18")

GRAVELBASE

GRAVELSUB-BASE

SUBGRADE

HI

600mm (24")

90mm (3.5")

LAYER OF INSULATION

THAWED FROZEN

LAYER OF INSULATION

TEST SECTIONS CONSTRUCTED

FIGURE 11: THERMAL PERFORMANCE OF AN INSULATEDEMBANKMENT IN A PERMAFROST AREA(1)

INUVIK N.W.T. 1971-1978 AIR FREEZING INDEX = 4690 DEGREE-DAYS C. (8442 DEGREE-DAYS F.)

(1) DATA PROVIDED BY INTERDEPARTMENTAL COMMITTEE ON HIGHWAY INSULATION.

Gravel

CONVENTIONAL

Ashphalt Conc

Heat Flow

Frost-SusceptiSoil

Gravel

INSULATED

Heat Flow

STYROFOAM BrandHighload Insulation

Frost-SusceptibleSoil

Ashphalt Concrete

FIGURE 12: WINTER HEAT FLOW IN CONVENTIONAL AND INSULATEDPAVEMENT SECTIONS

DIFFERENTIALICING

Introducing insulation into thedesign of a highway embankment hasthe effect of controlling the sub-soilthermal regime as shown in Figure 12.However, this insulating layer alsoalters temperature distribution in the embankment section above theinsulation. This can result in warmer orcolder pavement surface temperaturesin an insulated highway section, compared to those on adjacent non-insulated sections. This temperaturedifference between insulated andnon-insulated pavement sectionsallows one surface to support forma-tion of ice while the adjacent surfacedoes not.

This discontinuous or “differential”icing phenomenon also occurs overconventional non-insulated highwaysin practically all areas subject to freezing and thawing conditions. Itsfrequency largely depends on meteo-rological conditions and the thermalproperties of the highway section. As yet, no practical basis has beenestablished so quantitative frequencypredictions can be made in insulatedor non-insulated sections.

SUGGESTED WAYS OFREDUCING DIFFERENTIAL ICING1) Lowering the insulated foam in the

pavement section to allow for athicker cover to act as a heat sinkover the foam.

2) Putting in thinner sections of insulation to allow more heat topass through the insulation duringcritical times.

11

FIGURE 13: TYPICAL INSULATED CULVERT

Road Bed

Culvert

Granular Fill

STYROFOAM Brand HighloadInsulation Under Culvert

Frost-Susceptible Soil

SUGGESTED PRECAUTIONSIt is suggested that an insulated

section should not be started in the following locations:1) The middle of a curved portion

of the road.2) At the top of a hill.

3) Near a major intersection.

4) Near a railroad crossing.Differential icing is not confined

solely to intermittently insulated highways. It can occur on bridges,overpasses, shaded areas, areas ofsevere wind exposure, and whereabrupt changes in soil and ground-water conditions occur.

OTHER APPLICATIONSSTYROFOAM Brand Highload

Insulation has been field tested andfound effective for numerous otherapplications. One is the insulation ofculverts. Cold air blowing through theculvert in the winter can freeze the soil,severely damage the culvert, and createa bump in the pavement surface above.Differential heaving at a culvert or anyother drainage structure crossing the roadway pavement can be minimized or alleviated by the use of STYROFOAMBrand Highload Insulation as shown in Figure 13.

Other insulation applicationsinclude: airport pavements, railroadbeds, embankment lightweight fill, shallow buried utility lines, founda-tions, and transmission line towers.

Printed in U.S.A. *Trademark of The Dow Chemical Company Form No. 178-00540-0201X McK†A business unit of The Dow Chemical Company and its subsidiaries McKAY 169547

The Dow Chemical Company

200 Larkin Center

1605 Joseph Drive

Midland, MI 48674

NOTICE: No freedom from any patent owned by Dow or others is to be inferred.Because use conditions and applicable laws may differ from one location toanother and may change with time, Customer is responsible for determiningwhether products and the information in this document are appropriate forCustomer’s use and for ensuring that Customer’s workplace and disposal prac-tices are in compliance with applicable laws and other government enactments.Dow assumes no obligation or liability for the information in this document. NOWARRANTIES ARE GIVEN; ALL IMPLIED WARRANTIES OF MERCHANTABILITYOR FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY EXCLUDED.

COMBUSTIBLE: Protect from high heat sources. For more information, consultMSDS and/or call Dow (1-800-268-4840). In an emergency, call (1-519-339-3711). Local building codes may require a protective or thermal barrier. Contactyour local building inspector for more information.

COMMERCIAL

In the U.S., call1-800-441-4369

In Canada, call1-800-268-4840

English

1-800-363-6210French

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