7 7

maintenance has left these pavementsin deteriorated condition, and Germanyis making a huge effort to rebuild all ofthese highways to link all areas of thecountry, which they feel is vital to theireconomic growth.

A photograph of a 50-year-old (1930’s)jointed concrete pavement section onthe autobahn approaching Berlin fromMunich is shown in Figure 3.8. Thesewere the divided controlled-accesshighways that impressed manyAmericans returning from World WarII, including President Eisenhower, tosponsor the development of the USAInterstate highway system.

3.3 Germany

l Concrete Pavements in Germany

Germany has constructed manyconcrete pavements since the 1920’s,mostly on the autobahn (freeway)system and at airports. Bus stopsconstructed of concrete were observedin Berlin. The Study Tour observedfirsthand many original sections of theGerman autobahn system in the formereast Germany constructed withconcrete in the 1930’s. Many of theseoriginal pavements are carrying heavytraffic today, although they are quiterough and many of them are undermajor rehabilitation. Fifty years of no

Figure 3.8 Photo of a 1930’s German autobahn concrete pavement near Berlin.(Note cracking in outer truck lane of the 12-m (39-ft) slabs.)

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Approximately 30 percent of theformer west German autobahn and 82percent of the former east Germanautobahn are constructed with concretepavement (approximately 4,168 km(2588 mi) of concrete out of 10,900 km(6769 mi) total). The West Germanpavements constructed prior to 1970are jointed plain and jointed reinforcedconcrete, and only dowelled JPCP wasconstructed after 1970. Germanyfavors dowelled JPCP because of theextensive use of deicing salts and thepotential for corrosion of reinforcedpavements. Over the years, the designof the German concrete pavements haschanged considerably; however, thecurrent JPCP design has been builtextensively since the early 1970’s bothas new pavement and as overlays ofold concrete pavements.

An extensive research anddevelopment program has beenunderway in Germany for many years,at such institutions as the FederalHighway Research Institute (BAST)and the Munich Technical University toimprove concrete pavement materials,construction and design. Manyexcellent technical articles can be foundin the literature from this research.

Concrete pavements have also beenconstructed at airports in Germany.The Study Tour visited the newMunich II International Airport thatwas just opened in May, 1992. Thisairport was constructed with more than2 million square meters (2.4 millionsquare yards) of 36-cm (14.2 in)dowelled JPCP for runways, taxiwaysand aprons. For comparison, DullesInternational Airport has 1.2 millionsquare meters (1.4 million squareyards) of 38.1-cm (15-in) undowelled JPCP.

l Pavement Designs

Original Autobahn ConcretePavement Design. The followinginformation was obtained during ameeting of the Study Tour and Germanhighway officials in Berlin and alsofrom references 3 and 7.

Planning and initial construction of theGerman autobahn was started in the1920’s. The first German autobahnideas were based on car-onlyhighways, built in northern Italy byPiero Puricelli in the 1920’s. (7) Thefirst cross-section of a four-lanedivided highway was created in 1926,the word “autobahn” first appeared in1928 (7), and the design speed was 160km/h (100 mph) in non-mountainousareas. These pavements wereconceived as two lanes in one directionwith 7.5-m (24.5ft) pavement width.A policy statement on the principle ofperformance required of theconstruction industry and also oncontract and procurement procedureswas issued by Fritz Todt, InspectorGeneral of the German HighwayAdministration, in 1933:

“It is not always the lowest bid whichshould be given preference. Qualityis the most important criterion.” (7)

A decision was made about that timeto construct the autobahn highwaynetwork with concrete pavements. By1940 approximately 4000 km (2480 mi)of four-lane divided autobahnhighways were constructed. Duringthe war years the governmentprohibited using steel for any purposeother than military. A concretepavement research program wascarried out in the 1930’s with the

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construction of many test sections. Thegeneral design evolved as follows,although there are some variations ofthis design.

Slab: Uniform thickness, 20-25 cm (8-10 in) JPCP (some thinner and thicker),mostly two-layer construction. Topslab layer is 9 cm (3.5 in) thick andcontains high-quality aggregate (3-cm(1.2-in) maximum size). The lower slablayer is 13 cm (5 in) thick and containslocal gravel aggregates (5cm (2-in)maximum size).

Width of traffic lane = 3.75 m (12.3 ft)(two lanes in one direction)

Joints: Spacing for plain jointedconcrete sections = 8-12 m (26.539 ft)

. Spacing for jointed reinforced sections= 1230 m (39-98 ft) (stopped in 1937)

Typical expansion joint spacing12-18 m (39-59 ft). (Note: It wascommon practice to systematicallyincrease the joint spacing from slab toslab in increments of 1 m (3.3 ft) or so,with periodic return to the firstspacing.)

Dowels 35.6 cm (14 in) long, 2.2cm(0.875 in) diameter round steel dowelswith a sleeve on one end.

Dowels spaced 30.5 cm (12 in) nearcenter of slab with closer spacingtoward edge.

Longitudinal joints tied (3.75-m (12.3-ft)lane width).

use different quality aggregates in eachlayer. The upper layer used only high-quality aggregate as judged bycompressive strength and wear tests(typical types were granite, basalt andquartzite) and the elimination ofimpurities and flat particles. Asomewhat inferior aggregate (localgravel) was used for the lower layerfor economic reasons.

Aggregate gradation was closelycontrolled through use of several sizerequirements. It appears that a fairlyuniform dense aggregate gradationresulted from this specification.

Flexural strength requirementsincluded 3.7 MPa (540 psi) minimumand 4.4 MPa (640 psi) average.Compressive strength requirementswere 32 MPa (4,700 psi) minimum and39 MPa (5700 psi) average. Strengthswere tested with specimens madeduring construction and by means oftests on cores made at approximately60 days. (3)

Very dry (zero-slump) concrete with awater/cement ratio usually of 0.45 orless. No air entrainment admixturewas used.

Foundation:

Considerable effort made to reduce thedamaging effects of frost heave andexcess moisture. This was done byplacing longitudinal drains to interceptground water flowing towards thehighway or to lower the ground watertable, and by placing layers of granularmaterials (often sand was used)

Concrete: Most pavements wereconstructed in two courses for ease incompaction of very dry concrete and to

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between the slab and the subgrade.Often the grade line was raised 0.9 m(3 ft) or more above the natural groundlevel, and in cuts the roadway wasexcavated below grade and backfilledwith selected material. (3) In the Berlinarea, the concrete pavement was oftenplaced on the sand subgrade.

Shoulders: Usually 0.38 m (1.25 ft)wide inner (left) and 2.2 m (7.33 ft)wide outer (right). Pavement included17.8 cm (7 in) of concrete capped with7.6 cm (3 in) of AC for colordelineation. In cases where dark-colored concrete was used in the trafficlanes, plain concrete was used in thetop course of the paved shoulder stripfor color delineation. (3)

Construction: Usually two lanesformed at same time with a tiedweakened-plane longitudinal joint.The concrete base for the shoulder stripwas constructed before the pavementslab and was used as a base uponwhich to mount the rails carrying theheavy construction equipment used inthe mixing, placing, and finishingoperations. Tamping and somevibration of the concrete wasperformed. (3)

Many original sections of the Germanautobahn are still in place and servingheavy traffic in the former EastGermany, whereas the former WestGermany has previously rehabilitatedmost of the old pavements. The StudyTour had the unique opportunity toobserve many of these old pavementsduring the trip from Munich to Berlinand also on the freeway loopsurrounding Berlin (Berliner Ring).They are fairly rough, due mainly tothe many transverse cracks that havespalled and faulted. No obviouspumping was observed and the 50-year-old concrete showed no durabilityproblems. A large reconstruction effortis currently underway in the formerEast Germany and the concrete fromthese pavements is being recycled intoeither lean concrete base or the upperlayer of the granular blanket.

During the visit to a reconstruction siteon the A10, described below, a piece ofold concrete pavement was obtainedand submitted to the ConstructionTechnology Laboratories (CTL) foranalysis. The official petrographicanalysis is given in the Appendix and asummary is provided here.

1.All placing, finishing, and preliminarycuring operations were completedunder sunshades that spanned theentire pavement. Woven-reed curingmats were left in place for 3 weeks andwere kept continuously wet duringthat period.

The sample is a hard, dense,good-quality concrete consistingof siliceous and calcareousaggregates in a portland cementpaste. The paste-aggregate bondis tight and the concretefractures through coarse and fineaggregate particles.

Surfaces were dense and compact, withthe coarse aggregate either just belowthe top or actually exposed to somedegree. No thick layer of mortarexists. (3)

2. Estimated water-cement ratio,based on paste properties, is lessthan 0.35. Large residual cementparticles (unhydrated portlandcement clinker, UPC's) are abundant.

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3. The concrete is not air entrained.Estimated air content is 1 to 2percent. Most air voids aresmall and lined or filled withsecondary deposits, mostlyettringite.

Some reasons for the goodperformance of these pavements:

J Lower traffic loadings during earlylife,

J Relatively mild climate,

J Highly durable concrete (achievedby care in proportioning uniformgradation mixes; 3-cm (1.2-in)maximum size, high-quality, hard top-course aggregate; consolidation byvibration; dry mix with lowwater/ cement ratio; 21-day watercuring and protection from sun andwind with a cover; no deicing saltsused for many years),

J Thick granular layer between slaband subgrade for frost protection andsome bottom drainage (sometimes thislayer included fine sand and was notadequate),

J Backfilling with select material ofvery soft soil,

J Ground water moisture control, and

J Dowelled joints.

The long joint spacing (12 m (39 ft) inthe Berlin area and especially whensteel mesh was not used) appears to bethe only major deficiency noted for thisdesign, and resulted in manytransverse cracks that spalled andfaulted in the truck lane.

Current German Concrete PavementDesign. Following World War II, theconcrete pavement designs variedconsiderably between West and EastGermany. Prior to 1970, the WestGerman design included jointed wiremesh-reinforced pavement with a jointspacing of 7.5 to 10 m (24.5 to 33 ft),including expansion joints at 60- to100-m (197- to 328-ft) spacing. (1) Dueto various problems, this design waschanged to a jointed plain concretepavement beginning in 1970. (1) Thisdesign has been improved since thattime, evolving into the currentautobahn highway JPCP design cross-section shown in Figure 2.4. Somedetails of this design are as follows.

JPCP Slab:

2226 cm (8.7-10.2 in) thick, dependingon truck traffic volume in design lane(see design catalog, reference 2). Top7-cm (2.8-in) layer contains high-quality crushed aggregate for freeze-thaw durability and friction. The w/cratio for both layers must be equal.

0.5 m (1.6 ft) widening for both trafficlanes.

Full 11-m (36-ft) width pavingthickness for future traffic controlduring rehabilitation (four lanes oftraffic can be accommodated).

Shoulder: Tied concrete shouldersboth lanes (avoids differential frostheave that occurred on AC shoulders).(1)

Concrete: Exceeding 5.5 MPa (798 psi)in center-point loading (about 10-15percent greater than third-pointloading).

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Base: 15-cm (6-in) cement-treated orlean concrete, exceeding 9 MPa (1305psi), usually about 12 MPa (1740 psi)compressive strength after three daysof wet curing, base bonded to slab,joints (or notches) provided in base (35percent thickness) just beneath joints inslab. (Figure 2.5)

Some use of 25-cm (10 in) cement-treated base with cement-stabilizedsubgrade .

10-cm (4in) bitumen-treated base alsoused sometimes.

Subbase: Granular blanket, 30 to 90cm (1236 in) thick, depending on frostpenetration and bearing capacity, lessthan 5 percent 0.063-mm (0.0025 in)fines allowed before compaction (lessthan 7 percent fines after compaction).

Transverse Joint: 5.0-m (16.5ft)spacing.

2.5cm-diameter (1 in) dowels,unevenly spaced across section asshown in Figure 2.7, plastic coatingwith thickness greater than 0.3 mm(0.012 in) covers the total length ofdowels, no oil used.

Automatic dowel placement, nobaskets.

Saw depth: 0.25-0.30 slab thickness.

Sealant: Compression seal.

Longitudinal Joint: Saw depth: 0.40-0.45 slab thickness.

Tie: Deformed 20-mm-diameter (0.8in) steel tie bar, plastic coating with

thickness greater than 0.3 mm(0.012 in) covers center 20 cm (8 in).

Spacing of ties: three bars per 5 m(16.5 ft) of slab at centerline joint, fivebars per 5 m (16.5 ft) of slab atlane/ shoulder joint.

Sealant: Compression seal.

Subdrainage: Variations in subdrainshave been used. The latest cross-section (Figure 2.4) shows a porousconcrete layer beneath the shoulderthat provides a flow channel to alongitudinal subdrain which thenempties at regular intervals into alateral pipe and finally into a largerlongitudinal pipe. The systemobserved on the A10 project includedcatch basins at regular intervals thatwere connected to the longitudinalsubdrain (and were extended verticallyto the surface of the shoulder and acatch basin with a surface grate tocollect surface water) as shown inFigure 3.9. These catch basins wereconnected to the deeper manholewhich was connected to a longitudinaldrain pipe.

Porus concrete layer under shoulder: a15-cm (6-in) layer of porous concrete isbeing evaluated beneath the concreteshoulder to promote drainage of thetreated base layer.

Surface: Textured by light longitudinalbrush (burlap drag) to produce low-noise surface with some macrotexture.Hard aggregate provides friction.

Cross slope: 2.5 percent uniformacross lanes.

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Figure 3.9 Construction site on the A10 south of Berlin showing catch basins at edgeof slab that are connected to longitudinal pipe under the lean concrete baseand connected to the manhole shown on the left.

Bridge Ends: End lug is placed morethan 15 m (49 ft) from backwall ofstructure and then an AC surface overa CTB are placed to the backwall, asshown in Figure 3.10.

A four-year warranty system exists forconcrete and asphalt pavements,during which the contractor isresponsible for repair of any problemsthat develop.

The government relies on the warrantyand on the contractor protecting hisreputation if problems develop. Asmall amount of money is withhelduntil final acceptance at the end of thewarranty period. If major problemsdevelop, the project is not accepted and

the contractor is warned that furtherrepairs may be needed. Originally thisoccurred more often; now it seldomoccurs. If the project is not accepted itaffects the contractor’s reputation andit is considered in future contractawards. Since performance onprevious contracts is considered inawards, the contractor’s reputation isimportant.

The words “emergency lane” are usedto describe the shoulder because thesepavements are constructed to a full11-m (36-ft) width so that during anyfuture rehabilitation, four lanes oftraffic can be carried on one side of thedivided highway.

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bridge

Figure 3.10 Bridge approach design for JPCP in Germany.

Projects constructed without dowelbars have faulted significantly. Manyof these are in the former EastGermany where the governmentprohibited dowels. Dowels are neededin the German climate and traffic tocontrol faulting.

A plate load test in which pressure isrepeatedly applied to and removedfrom the soil in stages is conducted inthe field to ensure that a minimumbearing elastic modulus is achieved ontop of the subgrade (minimum is 45MPa (6,525 psi)) and on top of thegranular blanket layer (minimum is 120MPa (17,400 psi)) for concretepavements. (8)

The German pavement design catalogis an excellent method to communicatethe details of the pavement design to

the field. (2) There is now a newcatalog for rehabilitation alternativesalso. The Study Tour rode over severalsections of the design and alsoobserved a construction site. It wasobserved and reported from varioussources that this design is performingvery well under heavy traffic.

The catalog provides for a directcomparison between concrete andasphalt designs. The granular blanketis the same for both concrete andasphalt pavements to control frostheave, provide uniform support and toprovide some bottom drainage. TheAC pavement layers are built on top ofthis, as are the concrete base and slab.

The pavement design used for the newMunich II International Airport isgiven under the description of projectsvisited.

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l Concrete Material and Construction

An extensive research program wasstarted in the 1930’s into cements andconcrete mixtures that included theconstruction of many test sections. Adetailed description of the old 1930’sautobahn concrete mixtures is given inreference 3. Reasons for the excellentdurability of the old autobahn concreteare previously given.

Current German concrete requirementsare as follows:

J 4 to.6 percent entrained air,including air void systemrequirements.J Water/cement ratio < 0.42 toprovide dense mixture.J 340 kg/m3 (573 pounds/yd3))cement.J Mixing time is 45 seconds minimum.J Graded aggregates.J Aggregates must pass freeze-thawand alkali-silica reaction tests.J Freeze-thaw tests are run onaggregates for 300 cycles in aggressivesolution and loss cannot 0.2 percentmaximum.J If reactive aggregates are present,low-alkali cement (less than 0.6 percentalkali) is specified. If problems stillexist, the aggregate is changed.J No flyash is used in highwaypavement.J Germany uses the center-pointloading flexural beam test, which theyfound to be 10-15 percent higher thanthe third-point loading test. Aminimum of 5.5 MPa (800 psi) for thecenter-point loading flexural strength at28 days, which corresponds to about4.9 MPa (711 psi) in third-pointloading.

J Compressive strength is measuredwith a 3-cm cube. The minimumstrength is 35 MPa (5075 psi).

J It was stated that some AC can beused in recycled concrete mixtures.

J Air void content and void systemquality control are specified inreference 2. Tests are conducted thefirst day of production and again ifthere is any doubt as to air content.The bubble spacing must be less than0.2 mm (0.008 in) and the microporesmust be at least 1.8 percent.

The air void system may be tested inequipment viewed by the Study Tourat the Cement Research Facility inDusseldorf. The equipment labelled“DBT” costs about $20,000 and ismanufactured by a Danish company.It relies on Bernoulli’s principle thatlarger air bubbles, representing airvoids, rise to the surface faster. Asmall tube sample, 2.5 cm (1 in) indiameter, of fresh concrete is takenfrom the newly placed slab, placed inthe equipment, and the amount of airper time period is measured. Thisequipment can produce results inabout 20 minutes on the air voidcontent and spacing and can be usedon the construction site. It reportedlycorrelates well with linear traverseresults on hardened concrete.

Some ASR distress has recentlydeveloped on the northern BerlinerRing autobahn pavement due to high-alkali cement used on project (in theformer East Germany). The EastGerman government dictated thesource of the aggregate and cement forthis project. No “D” cracking problems

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were observed, probably due to the useof only high-quality hard aggregates inthe slab surface.

Various construction items:

J The use of a “tent” to protect thenewly placed concrete from rain andsun may provide a significant effect.This procedure also would reduce thetemperature and thermal gradient ofthe fresh concrete, which would reducedetrimental curling of the slab. This isstill being done today as discussedunder the Munich airport projectdescription.

J Curing is done with either watersprinkling or wax-based curingcompounds.

J The two-lift construction of the slabresults in smoother profile as well as amore economical mixture where high-quality stone is expensive.

Cement-treated base compressivestrength requirement is a minimum of9 MPa (1305 psi) to provide resistanceto erosion.

Germany believes strongly in bondingthe lean concrete base or CTB to theslab to reduce curling and erosion.This is accomplished by notching thebase 35 percent of its thicknessimmediately after placement exactlybeneath the transverse and longitudinaljoints of the concrete slab.

l Rehabilitation

A new rehabilitation catalog isavailable. Selection of the

rehabilitation alternative depends onthe following criteria: (6)

J Traffic restrictions duringreconstruction,J Possibility of the use of recycledmaterials,J Adequate clearance for bridges,J Required improvements of cross-slope and other geometrics,J Required widening of the crosssection (lane or shoulder), andJ Economics.

The following types of rehabilitationare currently being performed on theGerman autobahn pavements. (6)

JPCP Overlay with Interlayer: Theexisting concrete pavement is fracturedinto pieces less than 0.5 m (1.6 in) insize. Then a 10-cm (4-in) interlayer ofeither lean concrete (notched) or ACmaterial is placed on top of the existingconcrete pavement. A JPCP overlay isthen placed to the same thickness as anewly constructed pavement (i.e., 26cm (10.2 in) for the heaviest trafficclass).

JPCP Overlay with Thick FabricInterlayer: The existing concretepavement is fractured into pieces lessthan 0.5 m (1.6 ft) in size. Then ageotextile interlayer is placed on top ofthe existing concrete pavement. Aslightly thicker JPCP overlay is thenplaced on top of the fabric (i.e., 27 cm(10.6 in) for the heaviest traffic class).The debonding with the underlyinglayer and the additional elasticity ofthe geotextile fabric requires a thickerslab. However, the softer fabricmaterial may also reduce curlingstresses in the JPCP overlay.

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Total Width Reconstruction: Theentire pavement is completely removedand a new JPCP with untreatedcrushed permeable base constructed.This pavement type is new forGermany; however, it makes it possibleto recycle up to 100 percent of the oldpavement. The JPCP thickness isincreased (i.e., 30 cm (12 in) for theheaviest traffic class).

Lane Reconstruction. A cross-sectionis shown in Figure 2.10. A porousconcrete base is recommended havinga void content of more than 20 percentand compressive strength exceeding 15MPa for a thickness of 40 cm (15.7 in).The permeability coefficient requiredfor this base’ is less than lOA m/s. Thenew JPCP is placed directly on thislayer but is constructed thicker (i.e., 30cm (12 in) for the heaviest traffic class).The new lane is tied securely to theadjacent slab by five corrosion-protected bars (Zcm-diameter (0.8 in))per 5-m (16.5ft) slab).

AC Overlay: A 12-cm (4.7-in) ACoverlay is sometimes placed where arehabilitation life of six to eight years isd e s i r e d .

l Noise Pollution

A major concern about traffic noiseexists in Germany as in other Europeancountries. Until recently, most of theconcrete pavements were textured withtransverse tining, which was very goodfor friction and hydroplaning butcaused considerable road noise andvibrations. It was found that thistexture produced 3 dB(A) greaterrolling noise than AC pavements andwas not allowed to be used in urbanareas. If, however, a longitudinal

burlap drag was used along with thesmaller top-size aggregates, the noiselevel was about the same as a porousAC surface. This change was recentlymade in the construction specifications.Germany has experimented withvarious exposed aggregate surfaces butbelieves that the longitudinal burlaptexture along with high-quality hardaggregates in the upper slab willprovide low noise and good friction.

l Project Sites Observed

New Munich II International Airport.The Study Tour visited the newlyopened airport and observed some ofthe 2 million square meters (2.4 millionsquare yards) of concrete pavements aswell as having a presentation on theconstruction of the pavements. Figure3.11 shows a photo of a runway underconstruction. The JPCP constructed atMunich II Airport is defined asfollows: (4, 5)

Slab: 36 to 40-cm (14.2 to 15.8-in)JPCP constructed in two layers.40 cm (15.8 in) on ramps only.

Top 14 cm (5.5 in) includes crushedgranite for better freeze-thaw resistanceand friction.

Bottom 22-24 cm (8.7-9.5 in) used localgravel aggregate.

Double course construction wasachieved in a single pass of a slipformpaver in 15 m (49 ft) width.

Runway cross-section varied, withcentral 30 m (98 ft) being 36 cm (14.2in) and outer 15 m (49 ft) on each sidethinning to 26 cm (10.2 in). The totalwidth is 60 m (197 ft).

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Figure 3.11 Photo of runway under construction at the new Munich InternationalAirport. (Note the “tent” coverings placed behind the paver to providecuring protection to the surface for seven days.)

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Dowels and tie bars were placed on Tie bars were placed automatically intop of the lower layer. outer longitudinal joints.

Concrete: Contractor subcontracts totesting lab that produces certified mixdesign.

Concrete strength for both layers wasgreater than 6 MPa (870 psi).Specifications required the mean ofthree center-point-loaded beams to begreater than 6 MPa (870 psi) at 28 days.Typically, the mean strength exceeded7 MPa (1015 psi).

Continuous two drum plant used toachieve production of 200 cubic meters(262 cubic yards) per hour.

Water/cement ratio = 0.40 to 0.45.

340 kg/m3 (573 pounds/yd3) cement.

Air content measured once per hour inlaboratory.

Cores were taken and density wasmeasured (contractor specifies density).

Slab would be removed if strength ordensity deficiency existed.

Paving width = up to 15 m (49 ft) forthree 5 m (16.5 ft) slabs.

Joints: 5 by 5 m (16.5 by 16.5 ft)square slabs, transverse jointsdowelled, longitudinal joints tied andshaped with a sinusoidal verticalprofile.

Dowels were placed automatically inall transverse joints.

Joints were sawed within 8 to 10 hours.

Neoprene compression seals were usedin joints.

Base: 20-cm (8-in) cement-treated basewas constructed and immediatelynotched through about 35 percent of itsthickness exactly beneath the joints inthe concrete slab.

An attempt was made to bond cement-treated base to concrete slab throughcleaning and wetting surface.

Subbase: A thick granular blanket wasplaced between the subgrade and thecement-treated base course.

Curing: The concrete was moist-curedfor seven days under a “tent” as shownin Figure 3.11 and then curingcompound was placed.

Profile: A high-speed profilometerwas used to measure profile. Less than3 mm (0.12 in) gap was permittedbeneath a 4-m (13-ft) leveling beam.

Al0 Autobahn (Berliner Ring south ofBerlin). This project involved thecomplete reconstruction of a four-lanedivided autobahn highway concretepavement, originally constructed in1939, into a new JPCP. The followingitems describe the design andconstruction.

Traffic: Traffic was routed on to oneside where a 20-cm (Sin) unjointedlean concrete strip about Cm-wide (13ft) was added to the original slab sothat four lanes of traffic could becarried on one side. The lean concreteis expected to last through the

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eight-month construction duration andthen be recycled with the old concrete.Very heavy truck traffic exists on thishighway.

Pavement: The old concrete pavementwas fractured with a drop hammer.Then a large back hoe was used to pickup large pieces and load onto trucks tohaul to crusher. The concrete wascrushed and sized into stockpiles.

Slab: 26-cm (10.3 in) JPCP constructedin two layers.

Top 7 cm (2.75 in) contains crushedgranite for better freeze-thaw andf r i c t i o n .

Bottom 19 cm (7.5 in) contains localgravel aggregate.

Longitudinal burlap drag texture in thehard aggregate surface for low noise.

Joints: 5-m (16.4 ft) slabs, transversejoints dowelled, longitudinal joints tied.

Plastic-coated dowels were placedautomatically in all transverse joints ina nonuniform pattern (clustered inwheel paths of the truck lane).

Compression seals were used intransverse and longitudinal joints.

Reservoir saw-cutting: after the firstsaw cut, an elastic band was placed tofill the narrow cut across the twotraffic lanes, and a knot was tied ineach end to keep the band tight. Thiswas done to keep slurry from thesecond saw cut from flowing into crackand infiltrating the base and drainagefilter.

The first saw cut was 6.5 cm (2.6 in)deep (one fourth of the slab thickness).Observation of a section of completedslab showed that all joint had crackedthrough at joints giving gooduniformity of cracks. All joints wereplaced above notches in the leanconcrete base.

Shoulder: Tied concrete shoulder onouter lane.

Concrete: Contractor subcontracts totesting lab that produces certified mixdesign.

Concrete flexural strength for bothlayers was greater than 5.5 MPa (798psi) at 28 days (center-point loading).

Conventional paver was used forslipforming pavement. An unusualfeature was “T” shape of the vibrators.

Base: 20-cm (7.9-in) lean concrete baseslipformed.

Notched within 20 minutes to about 35percent of its thickness exactly beneaththe joints in the concrete slab as shownin Figure 2.5.

The goal is to bond the lean concrete tothe concrete slab through cleaning andwetting the surface. The base iswatered three to four times per day.

Dowels and tie bars were placed in thelower layer.

Lanes were widened 0.5 m (1.6 ft).

The slab has a 2.5 percent cross-slopefor good drainage.

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Figure 3.12 Thick granular blanket placed beneath lean concrete base in Germany.

Subbase: A granular layer exceeding30 cm (11.8 in) was placed directly onthe subgrade. Figure 3.12 shows thethick granular layer placed beneath thelean concrete base.

Profile: The new two-layer pavement

legal maximum single-axle load was 10tons (22,000 pounds) up to 1989.Today it is 11.5 tons (25,300 pounds)and it will probably be 13 tons(28,700 pounds) in 1993. A largeamount of truck traffic exists on botheast-west and north-south autobahn inGermany.

rides very well.

Subdrains: The subdrainage systemwas detailed under the description ofthe current German cross-section.

. Traffic Loadings

Traffic loadings are very heavy todayon the German autobahn. Thisnetwork is only 1.7 percent ofGermanys total highway length, butcarries 27 percent of its traffic. Atypical autobahn has an ADT of 40,000with 25 percent heavy trucks. The

* Summary for Germany

The perfomance of the post-1970jointed plain concrete pavements inGermany can only be described asexceptionally good. There are very fewproblems with the current design andit is competing economically withasphalt pavement.

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The reasons for the good performanceinclude the following:

J Variably spaced doweled joints,

J Bonding of the concrete slab to thecement-treated base or lean concretebase to reduce erosion and pumping atthe interface and to reduce curling,

J A high-quality base that is resistantto erosion,

J Good-quality aggregates in theconcrete, especially in the surface,

J The thick granular layer above thesubgrade,

J The concrete’s resistance to freeze-thaw damage due to careful air voidcontrol during construction, and

J The two-pipe surface and subsurfacedrainage system.

A long pavement life with lowmaintenance is expected. JPCP hasbeen built as new pavement and asoverlays.

l German References

1.

2.

3.

4.

5.

6.

Eisenmann, J., D. Birmann andG. Leykauf, “Research Results onthe Bond Between CementTreated Subbases and ConcreteSlabs,” International Seminar onDrainage and Erodibility at theConcrete Slab-Subbase-ShoulderInterfaces, Paris, France, March,1983.

Beton, StraBenbau und Trag-schichten, Bauberatung Zement,1992. (Specifications for Germanpavements.)

Jackson, F. H. and H. Allen,“Concrete Pavements on theGerman Autobahn,” PublicRoads, Volume 25, No. 4, June1948.

Zachlehner, A., “Presentationabout the Construction ofConcrete Pavements at the NewMunich Airport,” June 6, 1992,Munich, Germany.

Brochure on Construction ofNew Munich II Airport byHeilit+Woerner Bau-AG (thetechnical managers of theproject), KlausenburgerstraBe 9,D-8000 Munchen 80, Germany.

Leykauf, G., “Design forRenewal of Old ConcretePavements in Germany,” paperprovided to US TECH byMunich Technical University,Munich, 1992.

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7. Reuter, Hans-Reinhard andHans-Ulrich Gruschow, “Historyof Autobahn Construction,”Paper provided to US TECHStudy Tour, Brandenburg Officeof Autobahns, Berlin, Germany,1992 (translation from German).

8 . Plate Load Test, Din 18134, June1990 Edition, GermanConstruction Industry StandardsCommittee, Beuth Verlag, Berlin.

9. “Richtlinien fur dieStandardisierung des Oberbauesvon Verkehrsflachen,” 1986(German standards provided toUS TECH Study Tour, 1992).

10. “Zusatzliche TechnischeVertragsbedingungen undRichtlinien fur Tragschichten imStrassenbau,” 1986 (Germanstandards provided to US TECHStudy Tour, 1992).