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THE REHABILITATION OF THE ANTWERP RING ROAD

Innovative approaches and techniques

On May 31, 1969 the Ring Road “R1” around the city of Antwerp wasopened to traffic. The R1 is an urban motorway located atapproximately 3 km from the centre of the city. The 14 km long ringroad comprises the J.F. Kennedy tunnel in the southwest and theMerksem viaduct in the northeast. Several fully directionalinterchanges provide the link with 6 radial motorways tying into theR1. Due to the vicinity of the ring with regard to the city centre localaccess and exit ramps are provided as well.

The most recent rehabilitation works were executed between 1976and 1977. At that occasion some areas of the ring road were widenedup to 7 traffic lanes. After 35 years of service, the maximum trafficintensity on the R1 is nearing 200000 vehicles per day, which makes itto one of the most trafficked motorway links in Europe.

This situation has led to the need for a complete structuralrehabilitation of this motorway. The Directing Authority and Owner,the Department of Roads and Traffic of the Flemish Ministry of PublicWorks (in 2006 changed into the Infrastructure Agency of the FlemishMinistry for Mobility and Public Works) gave in 2001 the start for thedesign and execution of the project “Structural Rehabilitation of theAntwerp Ring Road”. It consisted not only of a pavement renewal butalso the renovation of 170 km of sub-surface drainagepipes and stormsewers, manholes, road appurtenances, bridges, utility tunnels forpipes and cables…

In addition to the pure technical works, a lot of attention also was paidto the establishment of an ambitious programme of “LessDisturbance” measures in and around Antwerp and to a maximumrecycling of the broken up materials, in favour of the environment.This comprehensive approach made it possible to execute the works ina record period of two times approximately five months.

The original pavement on the motorway consisted of asphalt on a baseof lean concrete or unbound coarse aggregates. After a thoroughcomparative study of the different alternatives, the main part of theexisting pavement was replaced with a new pavement structureconsisting of 23 cm continuously reinforced concrete (CRCP) supportedby a 5 cm thick bituminous asphalt inter-layer, 25 cm of cementstabilised asphalt rubble and 15 cm recycled crushed lean concrete. Afine textured exposed aggregate concrete surface was applied in orderto obtain an excellent skid resistance combined with a reduction of therolling noise.

The original pavement in concrete slabs in the Kennedy Tunnel wasreplaced with a new pavement of the same type with a similarfoundation as for the CRCP

The innovative techniques that have been used during the realisationof this ambitious project will undoubtedly contribute to a furtherdevelopment of CRCP in Belgium and other countries.

1. General description of the R1

1.1 Surrounding area

From the Kennedy tunnel up to the approach to the viaduct, the ringroad has been designed in a wide open cut below the general naturalground level. At the time of the original design this choice was madein order to maintain the crossing radial urban arteries and roads at thenatural terrain level. Furthermore urban planning considerationspertaining to the densely built-up urban area reinforced this conceptas well.

This excavation followed the former ring of military fortresses. Thiswas a logical choice considering the availability of a construction siteclear of buildings and thus avoiding expropriations.

Given the fact that the natural ground water level varied between 2and 4 m below the natural terrain level, an extensive and permanentsub-surface drainage system was realised in order to ensure that thegroundwater level in the wide open cut is lowered well below the subgrade of the ring road pavement. This drainage system along with thestorm water network has a total length of around 170 km.

1.2 Number of lanes and cross fall

The number of traffic lanes on the 7 km long section of the R1, whichis being executed in CRCP varies according to the location from 4 up toa maximum of 5 to 7.

The largest number of lanes occurs in the weaving sections of the exitsand entrances of the interchanges. In an attempt to accommodate theever-increasing traffic flows the R1 was widened in certain areas. Thisis the reason why at present no shoulders are available along certainparts.

Where compatible with the geometry a crowned cross section isapplied in order to ensure an adequate surface run-off. The minimumcross slope is 2.5%. Where geometrically required a superelevation isintroduced.

On the interchanges the number of traffic lanes varies from 1 to 2. TheKennedy Tunnel consists of 3 lanes in each direction.

The changing number of lanes has a considerable impact on the designof the CRC pavement.

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Localisation of the project

View at the surrounding area

2. Study and design

2.1 Existing situation

The limited maintenance and the very intense and heavy traffic (up to25 % heavy vehicles) had taken its toll after 30 years.

Serious deficiencies could be observed at several places such as:

• Cracking, ravelling, … of the asphalt,

• Cracked concrete slabs in the Kennedy Tunnel,

• Seriously damaged safety barriers,

• Deficient evacuation of storm water

• Local settlements of the shoulders due to leakage of sand intostorm sewers.

A lot of these deficiencies not only caused a serious disturbance of thetraffic but also presented a danger to the thousands of vehicles usingthe R1 daily.

As an example, a broken manhole cover resulted in a gigantic trafficchaos on the ring in 2003.

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1

2

3

4

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1-2 Cracked slabs in the Kennedy Tunnel3 Deficient water evacuation - deteriorated steel barriers4 Damaged asphalt surface5 Damaged asphalt surface and concrete barriers

2.2 Testing programme

Considering the large scale of the project and taking into account theinternational importance of this transport facility the technical studywas started by an extensive testing programme.

For the pavement part, this programme consisted of:

• A visual inspection

• Falling weight deflectometer measurements

• Research of drilled cores

The aim was to determine to what degree the rehabilitation workswere needed, as well with regard to the actual pavement as withregard to the substructure layers .

2.2.1 Visual inspection of the road surface

By means of the ARAN or “Automatic Road Analyser” of the RoadStructures Division of the Flemish Ministry of Mobility and PublicWorks, the R1 was subjected to a visual inspection, resulting in themapping of the damage patterns (cracks, holes, ravelling…). Based onthis visual inspection, the further testing programme was detailed.

2.2.2 Georadar

The georadar was used on the R1 to get a picture of the thickness ofthe different layers and to detect the possible weak zones.

The georadar is a non-destructive physical monitoring method thatallows mapping of the shallow substructure in a rapid way and withhigh resolution. The principle is the following: a transmitting antennasends an electro-magnetic wave propagated from the pavementsurface into the substructure. Any inhomogeneity in the structure, e.g.the interface between the asphalt layer and the base layer, will reflecta part of the electro-magnetic energy of the transmitted wave. Thereflected part of the wave is registered at the surface by a receiverantenna. The non-reflected part penetrates deeper in thesubstructure.

2.2.3 Falling Weight Deflectometer (FWD) measurements

FWD measurements allow determining the bearing capacity of thepavement structure.

The deflection of the road surface is measured at known distances ofan impulse load, created by a falling mass. The peak value of thisimpulse load is simulating the peak load under the wheel of a fullyloaded truck.

Young's modulus for a newly laid lean concrete is situated around15000 MPa. The FWD measurements on the R1 for the existing leanconcrete base often gave much lower values.

2.2.4 Drilled cores

For both the main lanes and the traffic lanes on the interchanges, aseries of cores (respectively 70 en 36) were drilled out of the existingpavement. The sample locations were based on the visual inspectionresults of the ARAN and on the reflection results of the Georadar.

This research focused on:

• The composition of the different layers and the expectedcharacteristics for recycling.

• Verifying the quality of the existing base.

Considering the fact that a maximum recycling of the demolishedmaterials was aimed at, all cores were tested on the presence of tar. Innone of the bituminous layers any tar was found.

The cores also revealed a good bond between the asphalt pavementand the lean concrete base, which had consequences on the milling orthe breaking up of the asphalt.

2.2.5 Conclusion

Based on this testing programme and considering the requiredminimum lifetime of 35 years it was concluded that it was necessary torenew the existing pavement structure over its full depth rather than apartial or complete replacement of the asphalt layers only.

2.3 Choice of type of pavement

2.3.1 Generalities

An important part of the study pertained to the choice of the type ofpavement material.

Considering the limited space because of the requirement to maintaintraffic on at least 1 lane and due to the relatively small radii of thealignment curves it was immediately decided to use asphalt for thepavement of the ramps of the interchanges.

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Results of the georadar measurements

Young's modulus (MPa) of the lean concrete obtained by FWD-mea-surements

For the new pavement on the actual Ring Road a thoroughcomparative study was made of the type of new pavement structure tobe used, i.e. asphalt pavement versus continuously reinforced concretepavement (CRCP).

At first a Life Cycle Cost Analysis was made. This involves an economicappraisal. Subsequently a Multi Criteria Analysis was made in order totake into account in the appraisal the non-budgetary aspects as well

2.3.2 Life Cycle Cost Analysis

In the Life Cycle Cost Analysis the Net Present Value Method over aninfinite horizon was used, i.e. it was determined how much money onehas to reserve now for the construction today and the maintenanceand the re-construction in the future.

The comparison indicated that, at the moment of initial construction,an asphalt pavement is less expensive than a CRCP. On the long term,taking also into account future rehabilitation and re-constructioncosts, the NPV over an infinite horizon appeared to be comparable andslightly beneficial for CRCP.

2.3.3 Multicriteria analysis

Upon performing the Multi Criteria Analysis besides economicalaspects other aspects were considered as well such as amongst othersnoise, recycling, comfort, safety, execution time, winter maintenanceetc.

A score is assigned to each type of pavement for each of the criterions.Furthermore, a weight factor is allocated to each criterion, taking inaccount the particular circumstances of the R1.

This analysis resulted in an overall score of CRCP that was slightlybetter than that of an asphalt pavement. Because of the smalldifference in the scores a sensitivity analysis was performedsubsequent to the MCA. This revealed that the overall score for theasphalt pavement alternative would become better than that of theCRCP only when the criterion of the execution time is assumed to haveabsolute priority.

2.3.4 The choice for continuously reinforced concrete (CRC)

Based on this comparative study the decision was made to renew thepavement on the actual Ring Road using CRCP with the exception ofthe asphalt pavement on the viaduct and in a short zone between theKennedy tunnel and the first under-bridge.

Indeed, the longer lifetime and the very little maintenance requiredfinally tipped the balance in favour of CRCP. The scale of the works andof the accompanying traffic alleviating measures was so enormousthat this kind of intervention, with such a socio-economic impact,should not be repeated too soon.

Unlike the pavement on the Ring plain concrete was used in theKennedy tunnel. This choice was made because of the difficultcircumstances regarding the supply of fresh concrete. Furthermore aCRCP would have required relatively expensive terminal systems atboth ends of the tunnel shaft.

This well studied and well planned investment will not only yield aneconomic profit on the long term but will also result in less disturbanceof traffic and of the environment.

2.4 Basic design options

The basic technical options mentioned hereinafter were of directinfluence on the design and concept of the new CRCP.

1. A densely built-up area adjoins the R1 on both sides. Although theR1 is mostly situated in a deep open cut it was neverthelessdecided to take extra measures to abate the noise produced by theintense traffic. Therefore a noise-reducing concrete pavementsurface was opted for.

2. In order to abate the detrimental influence of the edge effect thewidth of the concrete pavement is increased beyond the edge ofthe outer traffic lane

3. Longitudinal joints between concrete pavement and asphaltpavement are avoided as much as possible. Such joints, which arediscontinuities in material as well as in method of execution, areoften subject to premature deterioration especially when they areintensely trafficked by heavy vehicles.

4. Regardless of the changing number of traffic lanes on the R1, it ispurposely opted for to construct the pavement in CRCP over thefull width of the carriageway, i.e. from the median up to andincluding the auxiliary lanes and/or the shoulders. This allows topermanently transform the paved shoulder into an additionaltraffic lane in the future or to use it as a temporary lane duringaccidents or works. Furthermore this option helps to comply withbasic design options N°s 2 and 3 above.

2.5 Recycling

It was a major purpose of the rehabilitation project to apply recyclingof broken-up materials to the maximum possible. This was a logicalconsequence of the very large quantities of broken-up and recyclablematerials, of the envisaged short construction period, and last but notleast, of the decision not to create additional traffic flows by haulingbroken-up materials and by supplying new materials.

Due to these circumstances a detailed study was made of theopportunities for recycling. The envisaged service lifetime of the newpavement structure, the very large quantities of recyclable materialsand the experiences in Belgium and abroad were taken into account inthis study.

Recycling in itself is not new but the large scale that was at stake wasnew and unique in Belgium.

As a result of the recycling study the existing asphalt pavement wasrecycled

• Partly in the new bituminous pavement mixes

• Partly in the new cement bound coarse granular base. In order toarrive at a continuous gradation and at a maximum density of thebase after compaction, it was necessary to add 15 % to 20 % sand.

The existing road base, which mainly consisted of lean concrete andlocally of coarse aggregate, was broken-up and recycled in thegranular new sub-base.

2.5.1 Recycling of the existing asphalt pavement in cement bound asphaltrubble

There is a growing interest in the use of asphalt rubble as aggregate ina cement treated base and some applications were alreadyimplemented in the Netherlands, France, Germany and the UnitedStates, mostly with satisfying results. The Belgian experiences with thistype of base layer “cement bound asphalt rubble” (CBAR) are ratherlimited, however, the principle is well known.

The product consists of a homogeneous mix of sand, aggregates (inthis case asphalt rubble), batching water and a binder. Belgianstandard specifications only provide cement as a binder for the use inbase layers. A cement content of 4% (of the dry mass) allows achievingthe required compressive strength of 3 MPa after 7 days. After 28 days,the compressive strength must reach 5 MPa.

For the R1 project, the use of a mixing plant was compulsory.

Adding about 15 to 20 % of sand to the crushed asphalt rubble ismostly necessary in order to obtain a continuous grading of themixture and a maximum density of the base layer after compaction.

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The material requirements of asphalt rubble for bases are less strictthan for warm reuse in bituminous mixtures. Homogeneity is lesscrucial and more concrete rubble is allowed in the mix.

A CBAR base is in general comparable to a hydraulically boundaggregate base concerning strength development and Young'smodulus of elasticity. However, the presence of a bituminous mortaryields, to some extent, a temperature-dependent visco-elasticbehaviour, positively influencing the flexibility of the layer.

• Because of the temperature dependency of bitumen, the CBAR'scompressive strength decreases with increasing temperature: e.g.a temperature raise from 20°C up to 40°C involves a halving of thestrength.

• Resistance against plastic deformation is 10 times higher than forasphalt, eliminating any problem of rutting. CBAR has a greaterinitial stability than soil-cement, making it possible to overlay itwith asphalt almost immediately. However, on the longer term, itsstrength development is less.

• The residual bituminous binder contributes to the flexibility of thebase. The crack sensitivity will be smaller than for other cement-bound bases. Stresses induced by drying, hardening and thermalshrinkage are reduced by relaxation more easily.

2.5.2 Recycling of concrete rubble

According to the Standard Specifications in Flanders (SB 250) crushedconcrete rubble can be used as coarse aggregate for sub-bases and foralmost all kind of bases (unbound granular, cement bound, leanconcrete, roller compacted concrete).

In the R1 project, unbound concrete rubble (originating from theexisting lean concrete base and from concrete road appurtenances)was reused in the sub-base.

2.6 Standard concept for CRCP in Belgium

The concept of the CRCP for the R1 is based on the standard practice inBelgium, applied since the end of the 1990's for concrete motorwaysand which was based on the first large scale experiences with CRCP inthe beginning of the 1970's.

It consists of a CRC (20 to 23 cm) laid upon a bituminous inter-layer (4to 6 cm) and a lean concrete base.

The position as well as the diameters of the reinforcing steel isdependent on the thickness of the CRCP to be constructed. Thelongitudinal reinforcing steel amounts to a percentage 0.75 %.

For the pavement of the R1 the longitudinal steel (BE 500 S) consists ofdeformed bars diameter 20 mm spaced at 0.18 m c.t.c. They have aminimum length of 14 m and are placed on top of the transversereinforcing steel. When splicing longitudinal steel the minimum lap is35 bar diameters (35 x 20 = 700 mm of 0.70 m) with a skewed splicepattern and whereby having more than one splice in the sametransverse plane is kept to a minimum.

The transverse reinforcement (BE 500 S) consists of diameter 12 mmdeformed bars. They are spaced at 0.70 m and are supported on steelchairs, which are placed on the bituminous interlayer.

The transverse reinforcing bars are placed at an angle of 60 degrees tothe longitudinal steel. When placed at a right angle it is expected thatthe bars could be crack-inducing and could thus influence the crackpattern.

Tie bars diameter 16 mm are placed across each longitudinalconstruction joint. These tie bars have to be placed by drilling holes ata right angle to the longitudinal joint at half the thickness of the CRCPand by subsequently chemically anchoring the tie bars. The spacing canvary from 0.80 m to 0.85 m so as to avoid interference with thetransverse steel bars.

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Recycling from the old in the new pavement structure

2.7 Dimensioning of CRCP

The thickness design of the pavement was made according to thestandard “Road structures, Version 2” (Ref.) of the Ministry of PublicWorks of Flanders, Belgium. This method is based on thedetermination of the traffic expected to use the pavement, expressedin terms of cumulative 100 kN equivalent standard-axle loadapplications during the design period.

From this the Pavement Class and the corresponding slab thicknessdesign are derived. The main variables in the method concern the CBR-value of the sub grade, the lane distribution factor, the traffic volumeand the percentage of heavy trucks (up to 25 % for the R1), the designspeed and the design period.

2.8 Characteristics of the concrete

A fine texture of the pavement surface renders good results withregard to noise abatement. The best abatement result is attainedwhen the exposed aggregate granules are spaced at 5 to maximum 10mm. In order to comply with Design option 1, two measures weretaken. As surface finish an exposed aggregate concrete was applied. Inaddition to this a fine concrete mix was utilized. This mix complies withthe following specifications:

• The stone grading to be used is 4/7, 7/14 and 14/20 mm. Theamount of 4/7 aggregate has to be at least 20% of the totalgranular mix (sand and coarse aggregate). The percentage of sandwas kept as low as possible for as far compatible with an adequateworkability.

• The water/cement ratio is less than 0.45

• The minimum amount of cement is 400 kg/m3

• The use of an air-entraining agent is compulsory

2.9 Over width of the outer traffic lane

The stresses in a concrete slab are increased considerably when theload is located near the edge of the slab. This so called edge effect hasbecome even more critical due to the increased loads of the trucktraffic (especially trucks with triple axles and overloaded vehicles).

One of the detrimental consequences of the edge effect is that itincreases the potential of punch-outs along the edge of the outertraffic lane.

These high stresses can be decreased by constructing the CRCP with anextra width (see Design Option N° 2) where the shoulder consists ofasphalt pavement or where no shoulder is available. By this measurethe distance between the wheel track and the edge of the pavement isincreased.

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Dimensioning : the R1 belongs to the highest pavement class due tothe great amount of heavy traffic

Belgian standard concept for CRCP reinforcement

The edge effect in the outer traffic lane can also be avoided byexecuting the shoulder pavement in concrete as well.

On the R1 the latter solution has been adopted with the exception ofa few isolated areas where a narrow shoulder was paved in asphalt. Inthese areas the CRCP on the mainline was executed with an extrawidth of 0.70 m (including the edge striping).

2.10 CRCP lanes with variable width

The ends of the auxiliary lanes to and from the ramps of theinterchanges and the local ramps have mostly a variable width. Apavement of variable width can more easily be constructed in asphaltthan in CRCP. However, because it was opted for to avoid longitudinaljoints between asphalt and concrete in the travelled way, the auxiliarylanes were executed in CRCP for as far as they were adjacent to theCRCP of the mainline of the R1. In this way basic design options N°s 3and 4 were complied with in that only transverse joints occur betweenthe asphalt pavement on the ramps on the one hand and the CRCPalong the mainline on the other hand. Furthermore these joints arekept as short as possible.

As a consequence of this decision the CRCP had a variable width at theends of the entrance and exit lanes. Both straight and curvedvariations of width occur.

For short and transversally small variations in width, it is possible toconstruct the CRCP with a constant width while indicating the varyingwidth of the travelled way by traffic striping. This method is also usedfor asphalt pavements.

For long and transversally large variations in width, the solution ofconstructing the CRCP with a variable width was chosen.

This solution is perfectly realizable in practice provided the phasingand the placement of the reinforcement and the concrete are wellprepared in advance and are given the needed attention duringexecution.

Considering the function of the longitudinal steel the alignment of thelongitudinal bars of the ramp lane(s) deviating from the mainline waskept parallel to the horizontal geometry of these lanes. When thewidth of the CRCP slab becomes too large (± 5m) a spontaneousshrinkage-bending crack will originate in a longitudinal direction.Therefore, a longitudinal saw cut was made from a width of morethan 5 m on. The saw cut is stopped where the width becomes lessthan 5 m. At this location additional transverse reinforcement barswere placed (at half the normal spacing, i.e. 0.35 m in lieu of 0.70 m) inorder to minimize the risk of a spontaneous developing of alongitudinal crack beyond the end of the saw cut.

Additional tie bars (at half the normal spacing i.e. 0.40 m in lieu of 0.80m) along the longitudinal construction joint between the CRCP of themainline and the CRCP with variable width, were deemed necessary tolimit the risk of opening of the longitudinal joint.

The alignment of the longitudinal reinforcement bars of the triangulararea between the main lanes and the ramp was taken parallel to thatof the main lanes.

Consequently these bars abut the joint with the ramp at an angle. Inorder to avoid that this situation would induce cracks, 2 additionallongitudinal bars are placed along this joint with the CRCP on theramp.

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Schematic plan of the reinforcement at an entrance/exit lane

Detailed view of the reinforcement steel at on entrance lane.

2.11 Terminals for CRCP

2.11.1 General

The ends of the CRCP slabs are subjected to changes in length mainlyas a result of changes in temperature. The length over which themovement at the ends occurs, the so-called active length is dependenton the friction between the slab and the underlying bituminous layer,on the temperature changes, etc. and amounts to about 100 to 200 m.

The middle part of the concrete pavement is immobilized since beyondthe active length the friction forces exceed the driving force, which isthe thermal movement.

The movements at the extremities can cause damage to bridges,tunnels or adjacent pavements and they can generate uncomfortableand sometimes dangerous irregularities in the road surface. Hence, itis important to control the movements at the end of a CRC pavement.

There are two possible solutions to cope with these terminalmovements:

• the movement of the end is restrained by using end anchorages

• the movement of the end is accommodated by using a terminal joint

2.11.2 Anchoring abutments

An anchorage abutment is designed so that it can resist the forces thatresult from restraining the movement of the active length of theconcrete. For this purpose the end of the concrete slab is equippedwith transverse or longitudinal lugs, which are anchored in the subgrade. The degree to which the anchorage abutment resists the forcesdepends on the number and the dimensions of the lugs. Consequentlyit is possible to design the abutment such that the residual movementis practically nil.

The lugs are realized by excavating their shape in the sub grade and byplacing the reinforcement and the concrete without the use of anyside forms.

2.11.3 Terminal joints

Unlike an end anchorage treatment terminal joints allow the freemovement of the ends of the concrete. Figure 8 shows the details ofthe terminal joint designed for the R1 project. This design is animprovement of a formerly applied concept in Willebroek, Belgium.

The free expansion and contraction of the CRCP end is accommodatedby means of a standard expansion joint used for bridges. The neoprenejoint strap is attached to the metal clamps, which are anchored to areinforced concrete beam on each side of the joint.

The concrete beam on the asphalt pavement side is supported on steelbeams driven vertically in the ground. This support system is intendedto ensure a proper load transfer across the joint and to avoid possibledifferential settlements or movements as a result of braking andacceleration forces.

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Cross-section of the terminal joint used at the R1

Cross-section of an anchoring lug

View of the reinforcement steel of the terminal joint

The concrete heel beam on the concrete pavement side is anchored tothe CRCP and is supported on a concrete foundation. The top surfaceof this foundation is to be finished smooth and covered with a bondbreaker to allow free movement of the heel beam over the top surfaceof the foundation.

Upon contraction of the concrete pavement the movement of the heelbeam should not be hindered. Therefore a void is foreseen on thebackside of the heel beam to accommodate contraction.

In principle the terminal joint should be watertight. Water that mighthave infiltrated in the joint accidentally is discharged to the stormwater network by means of a drain at the lowest points of the crosssection of the carriageway.

2.11.4 Types of terminal systems used for the R1

In the USA both the terminal joint solution (e.g. wide flange beam)and the terminal treatment using anchorage abutments are usedthroughout various states.

In Belgium the Standard SB 250 specifies only the anchorageabutments. Notwithstanding this specification the terminal jointtreatment (detailed in Figure 8) was used at both ends of the CRCP onthe mainline (4 through traffic lanes plus a shoulder) of the R1, mainlybecause of the satisfying earlier experience with this kind of joint andthe substantially lower price.

Considering the fact that in Belgium the use of the terminal joint typetreatment is rather new, a monitoring programme is set up and startedin order to record the movements and behaviour of the joint undervarying climatic conditions and traffic circumstances.

As opposed to the terminal treatment of the CRCP on the main lanesone has no choice regarding the type of treatment of the ends of theCRCP of the auxiliary lanes. Indeed, it is necessary that the behaviourof the CRCP on the auxiliary lanes be as much as possible the same asthat of the adjoining CRCP on the mainline.

As the CRCP of the main lanes is not subjected to longitudinal cyclicmovements at the location of the intermediate auxiliary lanes, it wasnecessary to utilize anchorage abutments to restrain their ends. Thenumber of transverse lugs was designed so that the residualmovement was limited to 4 mm. This was considered acceptable andresulted in terminal anchor abutments having 4 lugs each. (Thissolution is shown on Figures 2, 5, 6, and 7.)

In addition to these anchor abutments the doubling of the number oftie bars in the longitudinal joints between the mainline CRCP and theCRCP on the entrance and exit lanes helps to avoid opening up ofthese joints.

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View at the anchoring abutment consisting of four lugs

Placement of the double reinforcement layer above the anchoringabutment

Dimensions of theanchoring abutment

General view of thelocalisation of termi-nal constructions

3. Construction

3.1 Time schedule

The international importance of the R1 along with the extremely highaverage daily traffic volumes necessitated to keep the constructionperiod as short as possible. This construction period was limited to 140calendar days during construction period 1 for the Outer Ring and to150 calendar days during construction period 2 for the Inner Ring.

In addition to these short construction periods a working time of 16hours per day, 7 days a week was imposed for the rehabilitation workson the mainline. The rehabilitation works in the Kennedy tunnel hadto be carried out continuously, 24 hours a day, 7 days a week.

Along with the pavement rehabilitation works, 170 km of storm watersewers and drainage pipes, 9 utility tunnels under the R1 and manybridges had to be rehabilitated within the same construction periodsmentioned above. This comprehensive programme of rehabilitationworks required an integrated organization and coordination in orderto realize both qualitatively and quantitatively the works within therequirements of the specifications.

3.2 Construction Site

A separate temporary haul road was built over the entire length of theproject. This road was also intended for use by emergency vehicles andcrossed the ramps of the interchanges by means of temporary gradeseparations.

In order not to overload needlessly the surrounding roadway networkthe provision of two construction plants on the construction site itselfhad to be foreseen. These plants were utilized to recycle the broken upmaterials and to supply the concrete.

A continuous blinding screen on the median ensured a visualseparation between all through traffic detoured on one carriagewayand the construction operations on the other carriageway.

3.3 Phased construction of the CRCP

The selected regulation of traffic during execution along with theenvisaged basic design options necessitated a well thought-outphasing and organization of the works and resulted in a constructionmethod of the CRCP, which was phased both longitudinally andtransversally.

The placement of the CRCP for the R1 had to be split-up in a number ofphases, which was greater than usual for CRCP. Several circumstancesmentioned above caused this situation. The main aspects anddifficulties of this method of construction are described hereinafter.

3.4 Zones of constant width

It was impossible to execute the pavement at once over its full width.Not only the great total width of the carriageway but also thepresence of reinforcement inherent to casting CRC made thisimpossible.

In principle the 4 through lanes were cast (from the median towardsthe outer edge) in widths of 2 lanes (2 x 3.75 m) or 1 lane plus ashoulder. Subsequently the adjoining entrance and exit lanes werecast. The casting widths varied according to the number of lanes, thepresence of a shoulder in CRC and/or the necessity to foresee awidening of the outer lane at those locations where no shoulder wasavailable or where the shoulder pavement was of asphalt.

3.5 Zones of variable width

As described above the R1 has many entrance and exit lanes. At theends of these lanes the CRCP had to be placed with variable widthsfrom narrow to wide. This required not only a well prepared sequenceof supply and placement of the concrete but also a detailed plan ofconstruction joints with all related special arrangements of reinforcingbars and tie bars.

All sections having a variable width were also cast by slip-form paver.

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View of the concrete batching plant

3.6 Longitudinal leave-outs

Due to the requirement that all ramps of the interchanges had toremain open to traffic at all times, it was inevitable that the traffic hadto cross at grade the carriageway where the rehabilitation works werein progress. As a result of this the execution of the CRCP could not berealized in one continuous longitudinal operation from the beginningto the end of the mainline pavement. It was necessary to leave a gapof about 300 m long and to temporarily end the newly placed CRCP bya transverse construction joint. Four suchlike leave-outs spread over adistance of about 7 km had to be realized.

Paving the leave-outs was accomplished differently during the firstconstruction period (works for the outer ring in 2004) as opposed toduring the second construction period (works for the inner ring in2005).

For the outer ring the new CRCP was executed such that eachsubsequent casting width (e.g. 1, 2, 3) was executed over the fulllength of the mainline pavement before the next casting width (e.g. 4,5, 6) was placed. After having completed in such a way the new CRCPover its full width the at grade traffic at the leave-outs wassubsequently detoured over the new CRCP followed by the paving ofthe leave-outs. This phasing of the placement of the CRCP made itnecessary to temporarily terminate the CRCP by two transverseconstruction joints, one at each end of the leave-out. Other transverseconstruction joints in between were end of the day construction joints.

During the paving works for the inner ring, the contactor adapted thephasing of the CRCP and the working hours so that the number oftransverse construction joints, which are always delicate zones in thefinished pavement, was reduced to the minimum attainable under thegiven circumstances. In between two consecutive leave-outs the CRCPwas first placed over its full width (e.g. 1, 2, 3). Subsequently the at

grade traffic was detoured over the new CRCP and only then theslipform paver was moved to the next section where the same castingphasing was applied (e.g. 4, 5, 6). This method resulted in only onetransverse construction joint per leave-out. In order to further reducethe number of transverse joints the contractor eliminated the end ofthe day transverse construction joints by executing the paving works ina continuous operation 24 hours a day. This adapted method ofexecution of the CRCP has proven to entail a better pavement surfacefinish.

Both methods of construction required at all times a detailedscheduling and coordination of the placement of both the reinforcingsteel and the concrete. Furthermore the traffic on the leave-outs couldonly be briefly interrupted outside peak hours to allow the passage ofthe slip-form paver across the leave-out. The adapted method forplacing the CRCP during the second construction period resulted in adecrease of the number of these passages as well.

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Phased construction : overview of the different phases of concreting in the first(2004) and the second (2005) period

3.7 Precautions at leave-outs

At the leave-outs a period of 7 days on the average elapsed betweenthe pours of the concrete. It was necessary to restrain the movementof the free ends of the newly placed CRC on both sides of the leave-outs in order not to distress the bond between the bituminousinterlayer and the CRCP. This restraining precaution is necessary untilthe moment of paving the leave-outs.

Restraining could have been realized by means of anchor lugs. Becauseof the high construction cost of anchor lugs a cheaper solution (whichwas temporary anyhow) was chosen. The solution consisted placingover the full width of the concrete a moist layer of sand, 0.50 m thickand 50 m long insulating on both ends of the CRCP adjoining theleave-outs. This layer insulates the concrete and restrains thetemperature changes and thus the movements too. A length of 50 mwas considered adequate because of the limited variation of thetemperature that could be expected within this temporary situation. Aplastic foil is placed under the sand to protect the newly placedconcrete. The sand layer has to be kept moist and should be kept inplace until 1 day or less before paving the leave-out. Removal of thesand shall be done with care in order not to damage the pavementsurface.

Once the paving of the leave-outs had begun it was sometimesnecessary to remove the sand in order to allow the passage of the slip-form paver and the supply of the concrete. It was therefore in suchcircumstances permitted, as an exceptional measure, to remove thesand over a limited width and during a short period providedmeanwhile the concrete surface was moistened regularly in order tolimit the temperature changes as much as possible.

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General view of a leave out in the CRCP with an insulating sandlayer at the ends

Closer view of the insulating sand layer to prevent the movement at the end of the CRCP

3.8 Placement of the concrete

Subsequent to the placement of the bituminous interlayer and thereinforcing steel the concrete was cast using a CMI Model HVW 2000slip-form paver capable of placing CRC widths of up to about 10 m.

The paver was equipped to cast concrete slabs with variable width. Thecasting was done from narrow to wide because the reverse would havecaused heaping of the concrete in front of the paver.

Considering the fact that the surface regularity of the track for thecaterpillar of the slip-form paver is of great influence on the surfaceregularity of the finished concrete, stringent requirements wereapplicable for the quality of this track. The track needs to have anadequate bearing capacity, has to be sufficiently rough and has tocomply with the same surface finish tolerances as the CRCP surfaceitself.

Open bin trucks were used to transport the concrete from the siteplants to the paver. Tarpaulins are required upon warm weatherconditions.

After application of the surface retarder, the concrete is protectedagainst drying out or rain by means of a plastic sheet. The next day thesurface mortar layer is washed out. Subsequently the longitudinaljoints are saw cut and chamfered. Then the joint sealant is placed.

The concrete is finally protected against drying by application of acuring compound.

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Slipform paver in action with a working width of 7 m

Placement of the transverse reinforcing steel

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View of the skewed slicing of the reinforcing steel bars The slipform paver is guided by stringlines

View of the slipform paver and the extra manual vibration of the concrete alongthe edges

General view of the concrete worksite

Protection of the surface by a plastic sheet

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Drilling of the holes for the tie-bars

Spraying of the setting retarder immediately after concreting Sealing of the longitudinal joint

Installation of the dowels for the JPCP in the Kennedy Tunnel

Sawing of the longitudinal joints

Paving in the Kennedy Tunnel

Removal of the surface mortar by brushing

4. Linear road appurtenances

4.1 Concrete gutters

An effective evacuation of the rainwater was a prime issue for the R1project considering the fact that a large number of lanes are cross-sloping towards the same side of the road.

In case of a classic gutter with water gulleys the water runs off thesurface towards these gulleys. However, if the latter is blocked, thewater will accumulate on the adjacent pavement surface.

For that reason a slot drain was chosen along the edge of thepavement next to the central reserve. This kind of drain rapidlyreceives the run-off water from the pavement surface and collects itthrough an underground cylindrical channel, evacuating the watertowards the nearest connection to the sewers network..

The cylindrical channel provides a greater storage capacity in case ofheavy rainfall thus reducing the risk that the storm water wouldoverflow on the pavement. As opposed to a classic gutter the slotdrain can be safely driven on by vehicles because its top surface is flatand finished at only 1 to 2 cm below the pavement surface. Theabsence of gulleys reduces the chance of blockages and consequentlyreduces the need for maintenance and the related disturbance of thetraffic.

Classic open gutters were placed along the edge of the shoulderswhere accessibility for maintenance does not cause a significanthindrance to the traffic. In addition, in case of a storm flood or blockedgulleys, the water can accumulate on the hard shoulder beforeencroaching upon the pavement.

4.2 Road restraint systems

4.2.1 Cast in situ concrete safety barrier

Because of the very intense and heavy traffic on the R1, concrete safetybarriers of the American type F were opted for. This type of barriershad earlier been constructed in Belgium on the motorway A10 (E40)between Groot-Bijgaarden en Affligem. The F barrier exists in a high(H = 1,07 m) and in a low (H = 0,81 m) version. For the R1 the high typeF was applied because of the following two major advantages:

• A higher containment level for trucks thanks to the special shapeand the height of the barrier. In other words, it is practicallyexcluded for a car, a bus or a truck to encroach on the oncominglane and so cross-over accidents are eliminated.

• Drivers are highly protected against blinding by oncoming traffic.

Other numerous advantages of concrete barriers of course are also stillvalid, i.e.:

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View of the concrete safety barrier and the slot drain

Cross-section of the F-Barrier

• The stable and rigid behaviour (no barrier deflection, no barrierdisplacement, no damage under design impact loads) avoidingcollisions with constructions such as lighting posts and bridgecolumns;

• A maintenance free design lifetime of 50 years. The absence ofmaintenance is important as this avoids hindrance by road worksin the future and enhances safety and mobility.

• A high construction rate;

• The low life-cycle cost;

• The environmental-friendly aspect (no painting or protectivecoating, no leaching, completely recyclable...).

In the USA, the F-barrier has been tested according to the NCHRPReport 350 (National Cooperative Highway Research Program).According to these testing criteria, this barrier meets Test Level 5,corresponding to the following crash tests:

• Car - 100 km/h - Impact angle 20° - Mass 820 kg

• Light truck - 100 km/h - Impact angle 25° - Mass 2.000 kg

• Heavy truck - 80 km/h - Impact angle 15° - Mass 36.000 kg

These criteria differ somehow from those of the European StandardEN 1317-2 but based on a comparative interpretation one canconclude that the F-type should comply with containment level H4.

However, the implementation of the series of standards NBN EN 1317in the Belgian Standard Specifications will soon impose therequirements of the European test criteria.

The STEP-barrier, developed in the Netherlands, offers an excellentalternative for the in situ cast safety barrier. This type of barrier alreadyhas been constructed in Belgium along the motorway A8 (E429) Brussels-Tournai and on the N49 (E34) Antwerp-Knokke at Assenede.

The Step barrier's crash test results mention a containment level H2and a working width W2 (W _< 0,8 m). A containment level H2 indicatesthat the system has been subject to the following impact tests:

Test TB11 - Car - 100 km/h - Impact angle 20° - Mass 900 kg

Test TB51 - Bus - 70 km/h - Impact angle 20° - Mass 13.000 kg

The impact severity level, related to the vehicle occupant's safety, iswithin class B (Acceleration Severity Index ASI _< 1,4).

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Cross-section of the step-barrier

View of the step-barrier along the motorway A8

4.2.2 Precast concrete safety barrier

At the (emergency) crossing points in the central reserve, the cast insitu safety barrier was interrupted and replaced by prefabricatedconcrete barrier elements. DELTA -BLOC provides a wide range ofprecast safety barriers, all of them tested in accordance with theEuropean standards, in several classes of containment level, workingwidth and shock index. The type of DELTA-BLOC used on the Ring ofAntwerp is a New Jersey profile, 1,00 m high, containment level H2,working width W5 en impact severity level B.

Some advantages of prefabricated elements are the high concretequality that can be achieved in a controlled indoor environment andthe speed of installation and replacement on site.

In addition, they offer the possibility to be installed as an ultra safeworksite protection during road construction and to be used in a finalconfiguration afterwards.

Another interesting field of application for the DELTA-BLOC barriersare the bridges and viaducts for which a barrier has been developed ofcontainment H4b, the highest class, working width W7 and impactseverity B. The light anchoring of the system in the pavement,designed to rupture at impact loading, yields a good protectionwithout causing any damage to the bridge deck.

Also for the STEP-profile mentioned earlier, a prefabricated version isavailable on the market and complies with EN1317-2 (H2 - W5 - B).

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Delta-bloc of H4b containment level installed on a bridge (siegtal bridge in Siegen, Germany)

Delta-bloc on the Antwerp ring road

5. Conclusions

The rehabilitation works of the outer Ring of Antwerp have beensuccessful both in the technical field and in the field of trafficalleviating measures. This pioneering experience will certainly beuseful for the inner Ring and for the future comparable rehabilitationproject.

On the pure technical level, very useful experience has been gainedwith the large-scale execution of CRCP with variable widths. The sameapplies to the design and construction of a new type terminal jointaccommodating the movement of the CRCP ends.

One advantage of this project consisted of the fact that it was split-upinto two construction periods, spread over two years and each ofwhich comprised comparable types and amounts of works. Thisenabled both the owner and the contractor to improve the executionmethods and the quality of the works. The findings in the design andexecution of this ambitious project will certainly contribute to thefurther development of the CRCP technique in Belgium and elsewhere.

Last but not least the experience with the rehabilitation of thepavement of the busy Antwerp Ring Road has proven that a highquality of CRCP can be obtained under difficult circumstances providedthat the phasing and important details of construction are well studiedbeforehand and are continuously monitored during construction.

PARTIES INVOLVED

The successful achievement of this challenging rehabilitationrequired an intense co-operation between all different partiesinvolved. In the first place, there is the public authority: the Ministryof the Flemish Community represented by the ROADS AND TRAFFICSDIVISION OF ANTWERP (since 2006 depending from theInfrastructure Agency of the Department Mobility and Transport).

During the study and design phase a project group was createdconsisting of experts in different techniques coming from the RoadAdministration (local and central services) , from the BELGIAN ROADRESEARCH CENTRE (BRRC) and from the multi-disciplinaryengineering company TECHNUM, the latter also being in charge ofthe Design and Tender Documents.

During the execution TECHNUM was in charge of the review andapproval of the construction drawings and rendered technicalassistance to the Road Authorities.

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The successful contractors group was VAN BROEKHOVEN - VAN GORP- WEGEBO, an association of three Belgian road contractors, all threebelonging to the Belgian Colas-group. In the meanwhile, VanBroekhoven and Van Gorp have merged into one new company VBG.The concreting works were mainly executed by WEGEBO.

A great part of the construction drawings had to be prepared by thecontractor before and during the works for which he made anappeal to engineering company ARCADIS-BELGIUM.

For the supervision of construction, a team of the engineeringcompany GRONTMIJ assisted the staff of the Road Administration.

In addition, quality supervision was set up by the Certification andControl Organism for Road Construction COPRO.

The consultants TRITEL and LIBOST were in charge of the study forthe implementation of the “Less Disturbance” plan

LESS DISTURBANCE

The greatest challenge of the R1's rehabilitation - even more thanthe aim to find the best technical solutions - was to make theseworks possible on a traffic artery carrying at some locations up to200.000 vehicles a day. That's why many people feared total trafficchaos and the Antwerp business community was extremely worriedwhen experts had predicted an economic loss of 900 million euro.

Therefore, together with the preparation of the works, aprogramme of accompanying alleviating measures was developedunder the name “Less Disturbance” project. The goal was to keep thetraffic flow on the Ring at a certain level and in the same time tomaintain the accessibility of the Antwerp conurbation. The measuresfocused on public and private transport with the emphasis on multi-modality. For each euro spent on the rehabilitation works, a eurowas spent for “Les Disturbance”. However, some of the measureswere permanent in nature such as the procurement of extra tramsand busses.

Measures for car and lorry traffic

The capacity of the R1 was reduced to about 60 % during therehabilitation works. In order to achieve free traffic flow, a separationwas made between through traffic and destination traffic. All thelocal entries and exits to the ring road were closed. Trough traffic(traffic travelling from one motorway to another) was thus kept onthe Antwerp ring road. Traffic whose origin or destination wasAntwerp was encouraged to use the Singel, which is an urban ringroad that runs parallel to the R1 ring road and encircles the citycentre. In order to achieve free traffic flow on the Singel, 35intersections were redesigned or had their traffic signals modifiedand 5 temporary bridges were constructed. Thanks to the optimiseduse of the Singel, 25 % of the lost capacity was recovered. Applyingother measures, particularly promoting other transport modes such astrams, buses, trains and cycles, catered for another 15 %.

New signing was installed on the access roads to Antwerp, clearlyindicating the difference between Ring and Singel. The signing inAntwerp itself was based on a subdivision in city zones and on thenames of the city gates that have been reintroduced on the exitroads.

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Extra signing to announce the worksite

A temporary bridge on the Singel

A considerable proportion of the daily traffic on the Antwerp ringroad consists of long distance traffic. Long distance travellers wereencouraged to avoid the ring road and use alternative roads byadditional signing that was installed at far distance. This wholeprogramme was also communicated to the Belgian and internationaltransport federations.

Measures in favour of public transport

Several actions were undertaken to encourage the people to changethe car for the public transport or the cycle:

• Increased capacity on the existing railway lines, engagement ofextra trains, new stations and extension of the car parks near thestations.

• Increased transport supply of trams and buses, creation of free buslanes and new park & ride areas.

• Development of a cycle network in Antwerp with extra directionalsigning, road markings and cycle parking spaces.

The strongest point: effective communication

All imaginable initiatives were taken in the field of communication inorder to inform the general public, the professional and socio-culturalorganisations and the local political authorities regarding themeasures planned in the framework of the “Less Disturbance” project.

The total cost of these communication initiatives 3,1 million euro.

Some of the actions:

• Information via the website www.antwerken.be.

• Involving the spoken and the written press.

• Co-operation with national and international transportfederations.

• Creation of “Less Disturbance” contact points made up with“accessibility managers” who are connected to key groups fromthe industry and the (local) administrations.

How it ended

Before their start, the rehabilitation works were totally unacceptablefor a lot of people: the economic life in Antwerp would be paralysedand the city tourism would be reduced to zero. An effort andinvestment, never seen before, in accompanying alleviatingmeasures and communications made it turn out differently. Thenuisance due to the works was accepted and was most of the timepredictable. The business community appreciated the way the workswere performed and thanked the organisers. The population alsohas shown its satisfaction.

Effective management from the beginning of the project withapplication of concrete measures, good preparation and activecommunication show that works on major road systems can beperformed with a relatively slight impact on all parties.

Text based on the article “Accompanying measures for rehabilitationof the Antwerp ring road” by Griet Somers, Accessibility Manager,“Less Disturbance” Contact Point, Flanders Region, Belgium & PatrickDebaere, Project Leader, Ministry of the Flemish Community,Belgium, in the PIARC-magazine ROUTES-ROADS, n° 329, 2006.

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Information on the website concerning the access roads to Antwerp

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Pictures :Ministry of the Flemish Community, Contractor Van Broekhoven-VanGorp-Wegebo, Manu Diependaele, Ken Moons, Omnibeton & DeltaBloc Europe GmbH, Paul Van Audenhove

Authors :Manu Diependaele & Dries De Groof,Technum Engineering CompanyLuc Rens, FEBELCEM0

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