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Concrete Engineering International Spring 2006 • 45

Two bridge deck overlay replacementprojects that were under way in theNetherlands during the summer of

2005 represented the culmination of majorresearch efforts into solving problems withfatigue damage to steel deck bridges. Projectsto rehabilitate the Hagenstein Bridge on theA27 near Vianen and the Moerdijk Bridge onthe A16 near Breda, saw the first large-scaleapplication of a new concrete overlay systemthat is intended to solve problems with fatigueon such structures.

Research and developmentA major research project has been carriedout over the last six years, including a pilotproject in 2003, to try to develop a new high-performance concrete (HPC) wearing coursefor orthotropic steel bridges which can alsoextend the service life of the total construc-tion by solving fatigue problems in specificdeck details. The resulting solution is verypromising, since it turns the deck plate into amuch more rigid construction with a higher‘plate factor’ due to the monolithic compos-ite interaction between the reinforced high-performance concrete (RHPC) overlay andthe steel deck plate. The overlay, with a min-imum thickness of 50mm, has been found toextend the service life of the orthotropicbridge deck by a matter of decades withoutadditional maintenance.

Developments in concrete over the past fewdecades have resulted in HPC of 100–155MPaand even ultra-high-performance concrete(UHPC), which can be higher than 400MPa.Much higher strengths can be achieved by afurther densification of the cement matrix com-bined with an additional pressure and heattreatment during setting and hardening. ButHPC and UHPC are also very brittle, so it is nec-essary to use a large amount of aggregate inthe matrix and, if possible, reinforcement withfibres and reinforcement bar. This compositeor hybrid material is known as ‘compact rein-forced composite’ (CRC) and the CRC principlemakes it possible to accurately predict thebehaviour of structures of all sizes under differ-ent loadings, especially when scaling up fromsmall models. Heavily reinforced ultra-high-performance concrete seems to haveextremely good fatigue resistance even undercontinuous high loads.

Overlay propertiesOne of the first large applications of rein-forced high-performance concrete (RHPC)overlay was as a white topping on damagedpavements and industrial floors and in cargoships. The properties of the overlay make itpossible to place it as an ‘independent’ top-ping, or wearing course, on a cracked and/orpolluted sub-base, or even on an under-dimensioned sub-base made from differentmaterials, such as asphalt concrete, concrete,wood, ceramics or steel. One or more layersof welded mesh reinforcement are includedand the concrete mixture contains both steelfibres and acrylic fibres based on a specialcomposite of pre-blended materials.

The standard setting time of the mixture ismore or less equal to that of a traditionalconcrete mixture and, similarly, depends ontemperature and relative humidity, althoughaccelerators can shorten the setting time.After curing for approximately 24 hours at20°C, the overlay is ready for use. Due to thelarge amount of welded mesh reinforcementand steel fibres, the hardened overlay is ableto withstand a certain amount of restraineddeformations from the base without theoccurrence of large surface cracks.

RHPC overlay is a combination of an HPCstrength class C110 (based on special pre-blended materials and reinforced with bothsteel fibres and acrylic fibres) and welded

mesh reinforcement. The mesh reinforce-ment is placed on an 8mm diameter barused as a spacer. Therefore, the total amountof reinforcement is approximately 24kg/m2

of traditional reinforcement and 5kg/m2 ofsteel fibres. The total thickness of the RHPCoverlay is, in this case, 50mm and the con-crete cover on the reinforcement is thereforeonly 18mm. If the thickness of the layer wereto be increased, the reinforcement could beadjusted as necessary. To replace the exist-ing wearing course with an RHPC overlay, thebonding between the steel deck plate (thick-ness 10–12mm) and the overlay is of crucialimportance to secure total deck rigidity anda uniform monolithic behaviour under all cir-cumstances. The best bonding method wasthe use of a two-component, epoxy-basedadhesive with broadcast bauxite aggregate.After hardening of the epoxy, the overlay iscast and the surface shot-blasted. No addi-tional wearing course is applied.

The Moerdijk Bridge In addition to research on relatively smallsamples, it was also necessary to performtests on full-scale structural elements underdifferent loading conditions. Several associ-ated projects at different institutes, such asthe civil engineering division of the Ministryof Transport, Contec, Delft University ofTechnology and TNO Building & Construction

TRANSPORT & INFRASTRUCTURE

Concrete evidenceFatigue cracks are a major problem for orthotropic steel bridge decks, and cracks in the steel deck plate

are of particular concern given their effect on traffic safety. This article reports on a new overlay system that promises to address some of these problems.

Peter Buitelaar, Contec ApS, Denmark, René Braam, Delft University of Technology Concrete Structures Group, The Netherlands and Niek Kaptijn, Ministry of Transport, Public Works and Water Management, The Netherlands

Figure 1: The overlay is placed under cover to provide protection from adverse weather conditions.

(Photos:Peter B

uitelaar,Contec A

pS.)

CEI Pages 33 48 Spring 06 8/3/06 4:36 pm Page 45

46 • Concrete Engineering International Spring 2006

Research, were carried out to investigate anddocument the material’s properties andbehaviour and this research is still ongoing.

Tests proved that the intended applicationof RHPC overlay was a very promising solu-tion for rehabilitation of orthotropic steelbridge decks: both durability and strengthwere found to be adequate. In the summerof 2005, the Dutch ministry started the reha-bilitation of two major bridges. The MoerdijkBridge on the A16 near Breda betweenRotterdam and Antwerp is believed to havethe most intense traffic spectrum in westernEurope with more than 100,000 vehiclescrossing per day and some 2.5 million heavygoods vehicles per lane each year.

A total area of 16,000m2 was rehabilitatedfrom May to November 2005, and the samearea will be undergoing rehabilitation duringthe summer of 2006. Engineering and super-vision is being carried out by the civil engi-neering division of the Dutch ministry andthe main contractor is TBI Beton-enWaterbouw Haverkort. Subcontractors Bruil-Ede and Cobeton are responsible for placingthe heavily reinforced, high-performanceconcrete, which is being supplied by Contec.

The bridge is being rehabilitated because itis suffering from cracks which have beencaused by fatigue in the deck plate and inthe weld between the deck plate and thethrough-wall. The deck plate on this bridge isuneven, resulting in a thickness of overlaybetween 47 and 100mm, making it neces-sary to place the reinforcement on supports.Some extra reinforcement is also necessaryin the locations where the deck is thickest.Traffic is still using the other lanes while therehabilitation takes place.

The Hagenstein BridgeTime restrictions are the issue for the othercontract – the Hagenstein Bridge on the A27near Vianen, located on the motorwaybetween Breda and Almere. A total area of4200m2 was rehabilitated during July 2005in just 14 days. The second phase, a similartotal area, will be rehabilitated during July2006. Client, engineering and supervisionare the same on this project as on theHagenstein Bridge, but the contractor wasStrukton Betonbouw. Again, the high-per-formance concrete was supplied by Contec.

The use of RHPC as bridge deck surfacing

is a good alternative to conventional asphaltsurfacing. Replacement of the mastic asphaltsurfacing with RHPC reduces the stresses inthe deck plate by approximately 80% andthe stresses in the longitudinal weldbetween deck plate and trough web byapproximately 60%. Therefore, it is a veryeffective solution for fatigue problems, suchas those found in bridge deck structures.

It was not possible for the contractorsworking on the bridge to achieve therequired maximum flatness of 3mm over 3musing a vibrating screed. The skid resistancewas also less than on the pilot project. Thecomplexity of the job (namely the bridge inuse with significant movements) in combina-tion with the relatively new method of reha-bilitation, made placing more difficult thanexpected. A very thin wearing course on topof the RHPC may be necessary to reach theflatness and skid resistance of the surface.

ConclusionMore tests undertaken at the Delft Universityof Technology, with regard to the placeability,shrinkage and use of internal curing com-pounds, are showing promising results forplacing with slipform pavers on future reha-bilitation projects. In 2005, RHPC was placedon the Voorst viaduct, located on the A1/E30motorway in the Netherlands, to strengthenthe existing structure and to upgrade thecapacity from a dual carriageway to a three-lane motorway with an additional traffic lanein each direction as a rush-hour lane. TheRHPC was placed using a slipform paver forthe first time on an actual job. �

TRANSPORT & INFRASTRUCTURE

� Acknowledgement:This article has been adapted from an articlethat was first published in Bridge Design &Engineering magazine, issue no. 40, thirdquarter 2005 and is published withpermission. See www.bridgeweb.com

Figure 2: The properties of the overlay make it possible to place it as an ‘independent’topping, or wearing course.

Figures 3 and 4: Deck deformations shown in the finite-element model.

Figure 5: The completed overlay.

Replacement of the mastic asphalt surfacing with RHPC reduces the stresses inthe deck plate by approximately 80% and the stresses in the longitudinal weld

between deck plate and trough web by approximately 60%.‘’

CEI Pages 33 48 Spring 06 8/3/06 4:37 pm Page 46