HIGHWAY INSULATION - Dow Chemical...DESIGN TECHNOLOGY To bring the concept of the insu-lated...
Transcript of HIGHWAY INSULATION - Dow Chemical...DESIGN TECHNOLOGY To bring the concept of the insu-lated...
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.
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*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.
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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
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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).
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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.
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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.
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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.
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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.
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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
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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.
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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
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