1 General The main consideration when con- structing roads on poor load-bear- ing subsoil is that every load deforms the soft soil layers; and the greater the load, the greater the deforma- tion. This deformation process con- tinues over years, depending on the thickness of the soil layers. The low shear resistance of poor loadbear- ing subsoils means that concen- trated loads should be avoided as far as possible, otherwise these layers will give at the sides. Com- pensating for this form of subsi- dence by laying new material leads to further settlement due to the additional burden. The conventional techniques of sub- soil improvement by complete or partial replacement of the soil are often time consuming and therefore costly. By employing lightweight materials, the weight of the road embankment – and with it the load on the subsoil – is reduced consid- erably. A largely subsidence-free method of construction is thus obtained when practically no additional loads are brought to bear – ie, by using extremely lightweight materials in the embankment such as blocks of Styropor foam (see figs. 1 and 2). Technical Information 24558 June 1991/September 1993 Styropor T 800 Highway construction/ Ground insulation Foams Styropor foam as a lightweight construction material for road base-courses ® = Registered trademark σ 0 σ 1 σ > σ 1 0 Conventional embankment structure increased surface pressure σ 0 EPS embankment structure non increased surface pressure σ 1 G = G = σ = σ 2 ~ 1 1 0 ~ G 1 G 2 Fig. 1 Comparison of conventional and EPS embankment structures.
Transcript
1 General
The main consideration when con-structing roads on poor load-bear-ing subsoil is that every load deformsthe soft soil layers; and the greaterthe load, the greater the deforma-tion. This deformation process con-tinues over years, depending on thethickness of the soil layers. The lowshear resistance of poor loadbear-ing subsoils means that concen-trated loads should be avoided asfar as possible, otherwise theselayers will give at the sides. Com-pensating for this form of subsi-dence by laying new material leadsto further settlement due to theadditional burden.
The conventional techniques of sub-soil improvement by complete orpartial replacement of the soil areoften time consuming and thereforecostly. By employing lightweightmaterials, the weight of the roadembankment – and with it the loadon the subsoil – is reduced consid-erably.
A largely subsidence-free method ofconstruction is thus obtained whenpractically no additional loads arebrought to bear – ie, by usingextremely lightweight materials inthe embankment such as blocks ofStyropor foam (see figs. 1 and 2).
Technical Information
24558 June 1991/September 1993
StyroporT800
Highway construction/Ground insulation
Foams
Styropor foam as a lightweight construction materialfor road base-courses
® = Registered trademark
σ0σ1
σ > σ1 0
Conventional embankment structure
increased surface pressure
σ0
EPS embankment structure
non increased surface pressure
σ1 ~G = G = σ = σ2~
1 1 0~
G1
G2
Fig. 1 Comparison of conventional and EPS embankment structures.
2
2 Experience to date
Experience with Styropor (EPS)foam boards used as frost protec-tion for roads and railways formedthe basis for the development of this construction technique. Thismethod of construction has beenapplied since the middle of the1960s, mainly in countries withsevere winters (eg, alpine regions,Canada and the Scandinavian coun-tries) where the deeply penetratingground frosts make it necessary toprovide costly frostproof subbasesfor roads and railways (see figs. 3and 4). With the appearance in 1984of a booklet “Road surfacing withthermal insulation layers made fromfoam plastics” by the German Insti-tute for Road & Transport Research(Soil Mechanics Working Group),“antifrost construction methods”can now be ranked alongside otherconventional construction tech-niques.
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
σv
σH
σv
σH
With the EPS method no horizontal forces act on the bridge abutmentand supporting walls (lighter design)
Fig. 2
Fig. 3 and 4 Frost protection in road and railway construction using EPS rigid foam boards.
The use of rigid EPS foam, not onlyfor protective antifrost layers in theform of insulating boards, but as aload-carrying substructure for roadsand bridge abutments in the form oflarge blocks, is based on this practi-cal experience and on the fact thatlightweight (ca. 20 kg/m3) Styroporfoam possesses high bending andshear strength for distributing bothdead weight and live loads; and sooffers higher efficiency than conven-tional building materials (fig. 5).
2.1 Economy
The price of rigid EPS is much lowerthan that of other foam materials,but compared with conventionalmaterials used in road substruc-tures, it is considerably more expen-sive. However, a simple cost com-parison is not enough – the alterna-tive construction methods must bealso considered. Dependent uponthe local conditions, constructingwith Styropor offers a definite tech-nical and economically interestingsolution – mostly for existing struc-tures (eg, bridges, supporting walls,pipe ducts) where subsidence is tobe avoided. Experience from abroadhas shown that in certain cases acost reduction of 50% can beachieved over conventional buildingtechniques. Styropor also offersobvious advantages if, for instance,material has to be transported tothe construction site over long dis-tances or special conditions have tobe met on environmental grounds.
3 Styropor – rigid EPS
EPS is the standard abbreviation forExpanded Polystyrene. The stan-dard used for rigid EPS foam as aninsulating material in the buildingand construction industry is DIN 18164, part 1. Styropor EPS foamhas been produced worldwide forover 40 years, and is mainly used inthe construction and packagingindustries.
3
Starting with the Styropor granulate,which contains a blowing agent, themanufacture of EPS foam takesplace in three stages: Pre-expand-ing, intermediate storage andmoulding (fig 6). During the firststage the granulate is heated andmade to expand – rather like pop-corn when it is made (fig. 7). Theblowing agent used is pentane, anaturally occurring hydrocarbon.The pentane expands the Styroporgranules into individual foam parti-cles five times their original volume.Next, the pre-expanded material isstored to allow air to diffuse into itand the blowing agent partly to dif-fuse out. Finally, the pre-expandedmaterial is placed in a mould andfurther expanded so that the foamparticles fuse together. The result isa compacted foam material whosevolume consists mostly of airtrapped in many microscopicallysized cells.
The special manufacturing processmakes it possible to vary the densityof the Styropor foam. Because theproperties of the material largelydepend on its density, the foam canbe made with application-specificproperties: from insulating boards tolightweight construction material.
Fig. 5 Construction of an embankment using EPS (Hardinxveld-Giessendam, NL).
Fig. 6 The processing stages in the production of EPS foam: raw material(left), pre-expanded particles, moulded foam.
4
AAAAA
AAAAAAAAAAAAAAAAAA
Styropor Production
Styrene withadditives
Water Blowing agent(pentane)
PolymerizationWater
Styropor Deliveryto thecustomer
Steam
Styroporraw material
Pre-expand
Steam
Transport screw
Mould Steam
SteamIntermediatestorage
Styropor foam
Fig. 7
Table 1 The most important physical properties of Styropor foam
Physical properties Test standard Unit Test result
Application types Part PS 15 SE PS 20 SE PS 30 SE
Application types DIN 18 164, Part 1 W WD WS + WD
Minimum density DIN 53 420 kg/m3 15 20 30
Building material class DIN 4102 B 1, difficultly B 1, difficultly B 1, difficultlyflammable flammable flammable
Thermal conductivityMeasured value at + 10 °C DIN 52 612 W/(m · K) 0.036–0.038 0.033–0.036 0.031–0.035
Calculated value according to DIN 4108 W/(m · K) 0.040 0.040 0.035
Saturated aliphatic hydrocarbons, surgical spirit, white spirit –
Paraffin oil, Vaseline + –
Diesel oil –
Petroleum spirit –
Alcohols (eg, methanol, ethanol) + –
Silicon oil +
+ Resistant: the foam remains unaffected even after long exposure.+ – Limited resistance: the foam may shrink or suffer surface damage on prolonged exposure.– Not resistant: the foam shrinks or is dissolved.
5
Styropor FH is a grade for makingfoam with enhanced resistance to aromatic-free hydrocarbons com-pared with other Styropor grades.
The suitability of this product for a specific application must betested in each case.
3.1 Physical properties
The most important properties ofrigid Styropor foam are described inTables 1 and 2.
The following properties are of mostsignificance in road construction:
– closed cell structure, which meansvery low water absorption
– frost resistant and rotproof– no breeding ground for pests,
mould or putrefying bacteria– biologically harmless (no danger
to ground water, no ozone-damaging blowing agent)
– good performance under sus-tained static and dynamic loading.
3.1.1 Mechanical performance
EPS foam is a thermoplastic whichexhibits visco-elastic behaviourwhen under load. This is why thecompressive stress at 10% com-pressive strain is quoted (DIN53421) instead of the compressionstrength. This value lies well withinthe plastic region (the compressedmaterial does not return to its origi-nal shape) and therefore is not usedwhen designing.
The compressive stress/compres-sive strain curves in fig. 8 show thatstress increases linearly until thelimit of the elasticity is reached at1.5 % to 2 % of strain, according tothe density of the material. As perma-
nent material deformation begins,the value of strain climbs morerapidly; however there is no definitebreak separating the elastic and pla-stic regions of the curve.
6
15
10
5
0
7
5
0
5
0
Str
ain
in %
1 10 100 500
days
1
Compressive stress
0.035 MPa
0.030 MPa
0.015 MPa
Compressive stress 0.07 MPa
0.05 MPa0.03 MPa
Compressive stress 0.1 MPa
0.08 MPa0.06 MPa
Density 14.5 kg/m3
Density 23.5 kg/m3
Density 32.5 kg/m3
Fig. 9 The behaviour of Styropor foam under sustained loading for various loads and densities.
When designing for permanentloads, values must therefore bechosen which lie below the 2 %strain limit (fig. 9). Rigid EPS foamwith a density of 20 kg/m3 can sus-tain loads in the region of 0.025 to0.050 N/mm2 (2.5 – 5 t/m2).
3.1.2 Behaviour towards chemicals
EPS foam is resistant to alkalis,soaps, dilute acids and salts (seeTable 2). Organic solvents attack thefoam to a greater or lesser extent.The long-term effects of the sol-vents contained in petrol and dieselfuel are the foam’s shrinkage or partial dissolution.
Experience has shown that theupper layers of material that coverthe foam are enough to protect itfrom small amounts of escaped fuel.When there are larger amounts offuel involved (eg, a ruptured roadtanker), the foam can be replaced atthe same time as the contaminatedearth is removed; this work wouldhave to take place in any case – onenvironmental grounds.
Covering the foam substructure withPE sheeting gives it additional pro-tection; however, this is not normallynecessary.
3.1.3 Behaviour towards livingorganisms
Rigid EPS foam offers microorgan-isms no habitat. It does not rot orturn mouldy. Bacteria in the soil donot attack the foam. Animals candamage it by burrowing, but manyyears of road building experiencehave shown that they do not preferit to other conventional insulatingmaterials. EPS foams have no envi-ronmentally damaging effects anddo not endanger water (crushedEPS waste is used in agriculture tobreak up and drain the soil).
7
4 Experience in other countries
The first large stretch of road to userigid EPS foam as a substructurewas build in Norway in 1972 (fig. 10).This development was initiated bythe Norwegian Road ResearchLaboratory in Oslo which, for manyyears, has evaluated the use of rigidEPS foam board as an antifrostlayer in road and railway construc-tion. Although positive results aboutthis method of embankment con-struction were published, interestwas initially confined to Scandinavia.It was in 1985, at an internationalroad building conference in Oslo,that this construction method firstcaught the attention of experts fromcountries in which difficult soil con-ditions are common and where sig-nificant economic advantages wereto be gained by the use of EPSfoam rather than conventional mate-rials (eg, in the polder areas of Holland, in southern France, USA,Canada and in Japan).
In the meantime, numerous data isavailable from research institutes indifferent countries on the theory andpractical use of EPS in construction.
4.1 Areas of application
EPS is mainly used in the followingareas of road construction:
Substructure on poor load-bearingsubsoils
Reduced loads on subsoil. Themost common application so far.
Backfill at bridge abutments
To reduce the earth pressure (caused by horizontal forces) anddifferential settlement at bridgeabutments.
Valleyside roads
To reconstruct the slide areas of valleyside roads that have failed.
Fig. 10 An embankment in Norway built of EPS.
ROAD EMBANKMENTSReduced loads on subsoilcompared to conventionalembankment. Most commonapplication so far.
($ 0.11 N/mm2 at 10% strain)according to DIN 53421. For sustained loading, values can berelied upon which are 20 – 25 % ofthis measured value.
– Bending strength ($ 0.22 N/mm2
according to DIN 53423).
The above tests are carried out on a representative sample of foamspecimens.
The absorption of water (eg, groundwater) is simply used to calculate thedead weight and has no effect onthe mechanical properties of thefoam.
8
Long-term experience in Norwayhas shown that even under unfa-vourable conditions the volume ofwater absorbed does not rise above10%. (For determining settlement, aweight of 1.0 kN/m3 is used).
The flame resistance of EPS blockscomplies with material class B 1DIN 4102 P. 1 (difficultly flammable).The foam block must be stored forat least 2 weeks between manufac-ture and use.
4.3 Method of construction work
The following information on con-struction work is based on practicalexperience in the use of EPS tech-niques in different European coun-tries:
The first layer of foam blocks isplaced on a compacted levellingcourse. The amount of unevennessin the levelling course must not bemore than 10 mm in 4 m; this guar-antees a flat enough surface for lay-ing the foam. All the layers of foamare positioned with a joint packingcompound.
The coefficient of friction betweenthe foam blocks is approximately0.5. To avoid slippage when manylayers are built, the blocks arebound to each other using either
2 spike grids or 2 spots of PURadhesive per block (see fig. 11).Until now, heights of up to 8 m havebeen achieved. It is important todetermine the height of the watertable. Any lifting forces which occuras a result of the water level reach-ing the foam blocks must be com-pensated for.
Structures bordering the carriage-way (eg, guard rails) may be an-chored into the 10 cm-thick con-crete layer that is usually placedabove the EPS course to distributecompression. If such a layer of con-crete is not used, an anchorage canbe achieved by concreting in trans-verse beams between the Styroporblocks at set intervals to produce aformwork.
Steep-sided embankments (see fig. 12) can be drained of water bycreating openings in the EPS sub-structure. Water channels can becut into the foam blocks with achain saw. Small holes and gapsbetween the blocks do not damagethe substructure.
The sub-base course on top of theEPS substructure is always depos-ited ahead the of the advancingmachinery. Compacting the loosesub-base course can be achievedwith the usual equipment. Becauseof the vibrational damping behaviourof the EPS substructure, the sub-base course is, as a rule, layeddown in several relatively thin layersand compacted by static means(eg, with a road roller as opposed toa pounding machine).
Fig. 11 Fixing the EPS blocks together by means of a spike grid.
Fig. 12 Draining a steep-sided embankment.
4.4 Design
When designing the road, the EPSsubstructure is viewed as a stratumwith an elastic modulus of 5000 kN/m2. In Holland, dimension-ing was carried out based on this“linear elastic” multi-layer modelwith the aid of a computer programcalled CIRCLY; this proved to beaccurate in practice.
In Norway, because of the manyyears of practical experience thathas been gained, dimensioning is
9
carried out on a “half empirical”basis. Here the thickness of thematerial above the EPS substruc-ture is between 35 cm and 60 cmdepending on the projected volumeof traffic that will use the road.
As observations have shown up tonow, there is no risk of early frostformation on the road surface if thelayer above the EPS is thicker than35 cm.
5 Prospects
In Norway, around 50000 m3 of EPSfoam block are used annually forroad construction (see fig. 13). InHolland – mainly in the area of thepolders – this construction tech-nique has been increasingly used asan economic alternative since 1985.In 1988, on just one constructionproject alone (Capelle a/d Ijssel),35000 m3 of EPS foam were usedto build an embankment.
In the period 1990 –1991 in Sweden,between the towns of Stora Högaand Ljungskile (about 100 km northof Gothenburg) part of the Euro-straße 6 was converted to a four-lane highway. Here 40000 m3 of
EPS foam were used owing to diffi-cult soil conditions.
In the last 3 – 4 years, in the extre-mely difficult subsoil conditions ofJapan (about 70% of Japan con-sists of impassable mountains, alarge part of the rest is moor andbog), success has also beenachieved with EPS constructiontechniques based not only on expe-rience from abroad, but also frommuch of the country’s own basicresearch (figs 14 and 15).
Simulations of sustained trafficloads are being carried out tounderstand the performance of theentire structure, with the aim ofobtaining a reliable method fordesigning different variations ofsuperstructure.
These findings, as well as the prac-tical experience gained from abroad,are gathered together in a study onlight-weight building materials by aworking party from the GermanRoad and Transport Research Asso-ciation. Before drawing up a set ofregulations, it is planned in themeantime to publish a paper en-titled “Advice for the use of light-weight building materials in earth-works, Part 1: Rigid EPS foam”*.
* German: “Hinweise zur Anwen-dung von Leichtbaustoffen im Erd-bau, Teil 1: EPS-Hartschaumstoffe”.
6 Summary
The low resistance to shear ofunstable soils that are subjected toexcessive loads, leads to settlementand deformation which can oftentake place over many years.
Road construction – especially inthe connecting areas around exist-ing structures – frequently requiresmeasures to be taken that involvethe soil being replaced, but, ongrounds of cost and environmentalprotection, these are becomingincreasingly more difficult.
A largely subsidence-free construc-tion is obtained when practically noadditional loads are applied to theunstable subsoil; this means thatthe weight of the embankmentshould be extremely small. Styroporrigid foam (EPS) fulfils this require-ment. Styropor was first employed
Fig. 13 Reconstructing a subsided mountainside road near Sougdahl inNorway using EPS.
Today, the German Institute forRoad Research is testing the EPSbuilding technique using full scalemodels.
Fig. 14 EPS substructure (18000 m3) at an abutment of the Kasai NagisaBridge, Tokio.
(mainly in Scandinavia) in the mid-1960’s as a frost protection layer inroad and railway construction. Theyears of positive experience whichfollowed formed the basis for thedevelopment of a technique ofbuilding roads upon unstable sub-soils using EPS. This constructionmethod then won a place in road-building technology when, startingwith Norway in 1972, blocks of EPSwere used as a lightweight materialfor the first large stretch of highway.EPS was later used in other coun-tries where difficult sub-soil condi-tions predominate, such as the pol-der area of Holland, in southernFrance, the USA, Canada andJapan. Also in Germany in areaswhere poor soil conditions exist, theEPS method of construction will beused increasingly as an economicalternative.
Bibliography
[1] Norwegian Road ResearchLaboratory: “Plastic Foam inRoad Embankments” Schrift Nr. 61, Aug. 87
[2] Stichting Bouw Research, Rot-terdam: “Wegen op PS-hard-schuim” Schrift Nr. 176, 1989
[3] EPS-Construction MethodDevelopment Organization,Tokio 1989: “Technical Reportsof Construction Method usingEPS”
[4] F. Hohwiller, EPS-Hartschaumals Leichtbaustoff im Straßenun-terbau, “Straßen- und Tiefbau”,Heft 1/2.91
Note
The information submitted in thispublication is based on our currentknowledge and experience. In viewof the many factors that may affectprocessing and application, thesedata do not relieve processors fromthe responsibility of carrying outtheir own tests and experiments;neither do they imply any legally binding assurance of certain proper-ties or of suitability for a specificpurpose. It is the responsibility ofthose to whom we supply our prod-ucts to ensure that any proprietaryrights and existing laws and legisla-tion are observed.
10
AAAAAA
AAAAAA
1985 1986 1987 1988 19890
10
20
30
40
50
60
70
80
90
100
EPS volumes in m3 (1000’s)
MiscellaneousPipelines
Golf courses
Parks andlandscaping
Roadsubstructures
Year
0.5 1.36.4
30.8
93.6
Fig. 15 Chart showing the development of EPS foam block in earthworksin Japan.
