immobiliare centro nord s.p.a., 37050 belfiore (vr), …...immobiliare centro nord s.p.a., 37050...

Since its beginning, just after start-up onSeptember 2003, the new production sitehas reached in less than one month thefirst step of the required capacity of about1,400 sqm per day to cover the currentmarket demand capacity (1,050 sqm ofstandard hollow core stabs and 350 sqmof jumbo elements). The final capacityonly requires the installation of a secondmixer and a concrete bucket conveyoralready foreseen in the plant design.

The main innovations introduced in thenew production site concern a variety oftechnological, productive and environ-mental aspects:- Manufacture of hollow core slabs and

beams with depth up to 1,000 mm- Translating casting beds- Fixed cutting station with double saw

operation- Prestressing strand pre-cutting and the

new prestressing system and control- Discharge water recycling and treat-

ment system

The step forward in qualitycompared to traditional pro-duction plants lies in the manyinnovations included in the pro-duction cycle: operations thatare traditionally performed atthe same time in the whole pro-duction area are now locatedin different separate areas.

The result has been noteworthysavings in labour costs andadvantages connected withenvironmental well-being, witha reduction in cleaning costsdue to concentration of “dirty”operations in special areas,

CPI - Concrete Plant International – # 4 - August 2005 www.cpi-worldwide.com

Innovative technology for hollow core production

The new factory run by Immobiliare Gruppo Nord S.p.A.

Elements are produced withheights up to 1,000mm

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PRECAST CONCRETE ELEMENTS

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Immobiliare Centro Nord S.p.A., 37050 Belfiore (VR), Italy

The only one of its kind with a unique productiontechnology from the casting to the cutting of floorslabs with depths from 160 to 1200 mm: this is

the innovative production plant of the GruppoCentro Nord near Verona, Italy, covering an areaof 90,000 square metres.

05-Fertig_188-209_eng 19.08.2005 8:58 Uhr Seite 202

while traditionally the entire plant had tobe cleaned. All processes have beenhighly automated.

The products

Traditional and well-known hollow corefloors come in depths from 16 to 50 cm.Their daily manufacturing schedule callsfor the production of six beds of these hol-low core slabs (over 1,000 m2/day).

The large FORAP, PAV and MAGNUMpieces, whose depths vary from 60 to100 cm, are used as bridge slabs withspans from 14 to 24 metres and for heavyloads suitable for road building (viaductsand artificial tunnels), for commercial build-ings and underground works (under-ground car parks and services). They areproduced with a new slipformer suppliedby Nordimpianti System for special 1,000mm depth hollow core slabs.

FORAP elements are rectangular in sec-tion, with three large voids to limit weight;this makes their application more flexiblein the case of heavy loads. They are oftenused in underground constructions.PAV upside-down “T” beams for bridgesand viaducts have for years been thestrongpoint of Gruppo Centro Nord in theroad-building field.

MAGNUM elements are characterizedby a fairly light “U” section of prestressedconcrete closed at the top with a corruga-ted steel plate that supports the in situ cast-ing. These allow spans up to 18 m withlimited dead weight and not too heavyloads; they are therefore ideal for theerection of large shopping centres andmulti-storey car parks.Now produced with depths up to onemetre and with increased prestressing,their performance has been greatly im-proved and they are becoming more andmore interesting from an economical pointof view.

Every day two beds of these elements areproduced; this represents about 350m2/day and 40% of total production interms of turnover – an excellent exampleof the remarkable profitability of this kindof product.The range of products described abovecalls for the mixing of 240 - 260 m3 ofconcrete, class R 60 MPa, on average perday.

Longitudinal movements ofproducts with translatingcasting beds

The 350-metre long building has beendivided into two sections for different

manufacturing phases. In the first sectionthere are seven casting beds with a lengthof 150 metres; at their extremities thereare the anchoring blocks for the prestres-sing tendons designed for tensions up to500 tons each. In the second section, like-wise, there are seven curing beds with alength of 150 metres which are alignedwith the casting beds.

The mobile casting plate and its specialseparating system represent the innovativeheart of this plant and are protected byinternational patents which are the pro-perty of Gruppo Centro Nord.

Separating, casting, curing and cuttingoperations, and fast reuse of the prestress-ing units ensures two production opera-tions per day and bed. The operationsthat are traditionally performed at thesame time in the whole production areaare now Iocated in different areas.

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www.cpi-worldwide.com CPI - Concrete Plant International – # 4 - August 2005

The 350 m long hallis subdivided into

the production area(front) and the

curing area (rear)

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Dr. Eng. Giorgio Della Bella, born inMilan in 1939. Degree in CivilEngineering by “Politecnico diMilano” year 1965. Technical GeneralDirector of “Gruppo Centro Nord”,Italy. Chairman of “Assap”

(International Association of Hollow Core Producers)since 1981


The result have been noteworthy savingsin labour costs and advantages associa-ted with environmental aspects, with areduction in cleaning costs due to concen-trations of “dirty“ operations in limitedareas, while traditionally the entire planthad to be cleaned.

The idea consists of separating the statio-nary, traditional casting bed from itsupper part: the casting plate. The mobilecasting plate of steel is lying on its bedduring the casting stage, but it can be raised by a multitude of wheels on theinside of the bed and moved longitudinally.

The axles of each casting bed can be raised simultaneously for a few centime-tres by means of small oleodynamic cylin-ders, while the curing bed axles are fixedand have coated wheels to support theconcrete element without damaging itsintrados.

Each monolith produced, 1.2 metres inwidth and slightly less than 150 metres inlength, is cast on the steel plate composedof a series of sheets welded head to head.The seven casting plates are mobile andrun longitudinally to and from the curingbeds.

In the casting phase the plate lies on thecasting bed where it remains until the con-crete has reached the minimum requiredstrength for the application of prestressing.

Following this, the steel plate, togetherwith the just hardened concrete element,is transferred from the casting bed to thecuring bed, passing over the intermediatesteel plate bending device.

The purpose of the latter is to separate thesteel plate from the concrete piece bybending the plate gradually downwardsso as to lead it onto a horizontal planebelow the curing bed.

As soon as the concrete piece has beentransferred, the empty plate returns to thecasting bed, once again crossing the bend-ing device.

This transfer offers the possibility of remov-ing the element from the casting bedquickly so as to be able to use it onceagain for a new cast in the shortest possi-ble time. This also permits a high degreeof flexibility in the manufacturing processby separating casting, curing and cuttingoperations.

The piece can in fact remain as a whole inthe curing stage prior to cutting it into sin-gle slabs. Thus we have the two-foldadvantage of being able to make twocasts per day on each of the seven bedswhile the cutting of the element, and thusthe prestressing of the single slabs, is post-poned until the concrete has reached agood degree of hardness and strength.

In this way, both the camber and the dif-ferences in camber that are often observedin installed hollow core floors are limited.The results obtained with this plant are farsuperior to all expectations.

It is interesting to observe the expressionsof surprise and admiration when visitorswitness these operations, since nothing ofthis kind has ever been seen in the field ofconcrete prefabrication.

Machine for the positioningof long elements for cutting

When the concrete has hardened com-pletely on the curing bed, the 150 m longpiece must be moved horizontally somedistance at a time for cutting it into singlesections by the transversal cutter at thefixed cutting station.

Transversal or oblique cutting lines havealready been designed to obtain the sin-gle slabs. The element must be movedcarefully to align the cutting line preciselywith the cutter’s diamond disk.

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Production of elements with a total length of150m (top of pictures). As soon as a suffi-cient strength has been reached, a com-plete, 150 m long “prefabricated element”is moved to the curing facility (lower part ofpictures). At the same time, the steel plate isseparated from the concrete by slightly bending it and moving it under (!) thecuring facility. As soon as the entire 150metres have reached the curing facility, thesteel plate is moved back to the productionunit. This way the next production cycle canbe started immediately


In the planning stage, this operation wasthe cause of more than one worry sincethere was no precedent in any industrialsector for the moving of masses in theorder of 100–150 tons with precisionarrest at a tolerance level of ± 10 mm.Movement of the element now takes placeby means of a special positioning ma-chine – an operation which has tuned outto be fully successful.

By means of hydraulically powered rub-ber wheels, the machine moves, accele-rates, slows down and brings to a stop theelements weighing even more than 150tons with an unbelievable delicacy andprecision.

This machine is already designed to workautomatically with optical recognition ofcutting lines.

The cutting station and theupside-down cutter

The final section of the building, behindthe curing area, is dedicated to the fixed

www.cpi-worldwide.com CPI - Concrete Plant International - August 2005

A special machine ensures optimal positioning of the elements for the subsequent cuttingoperation


and isolated cutting plant where the longconcrete monoliths are cut to size into sin-gle slabs as they move step by step fromthe curing bed to the cutting station.

In traditional plants, the diamond disk cut-ting machines moves along over the entirelength of the cured piece on the castingbed and cuts it into single slabs, thus pro-ducing a great deal of cement mud, dustand loud noise.

Cut slabs have to be removed by a liftingdevice to free the casting bed. In the newplant the cutting machines work in a singleplace set aside specifically for this pur-pose and isolated from the rest of theplant; single slabs are transferred to anexternal area for storage, sliding on rol-lers that eliminate all need for lifting.

It must be taken into account that the dia-meter of a diamond cutting disk must bealmost three times the depth of the pieceto be cut. Thus a piece 600 mm in depthrequires a ø 1.7 m disk and a piece1,000 mm in depth requires a ø 2.8 mdisk, a size no longer feasible both interms of the cost of diamond disks and thesize of the cutting machines.

Since the new plant was designed for theproduction of slabs up to 1,200 mm indepth, cuts are made with two diamonddisks: one cuts half the thickness from

above and the other cuts the other halffrom below by means of a novel upside-down cutting machine specifically de-signed and produced by Nordimpianti.In this way we have succeeded in keepingsizes and costs of cutting disks and ma-chines within reasonable limits.

This innovative cutting method was madepossible simply by having the piece to becut slide on rollers from the curing bed tothe fixed cutting area. In traditional plants,

the cutting operation from the bottomupwards is impossible.

The entire cutting section was designedfor the future installation of two more cut-ting machines.One will be for longitudinal cuts both ontop and bottom of the monoliths and theother will be another special machinecapable of cutting the heads of floor slabsof greater depth to create Gerber-typesaddles.


The cutting station is equippedwith two blades to ensure thatcutting can be carried outfrom above and below

Under the curing facility, already prepared prestressing strands already cut to length arewaiting. As soon as they are needed, they are pulled out of the zinc pipes to the produc-tion unit. This way, any problems that might occur when pulling the strand from the coilare prevented. As soon as a strand is needed and the zinc pipe is empty, it is replaced with the nextstrand cut to length so that the required prestressing strands are available at all times


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Tendon laying

The laying of prestressing tendons is per-formed in a very special plant consistingof a bundle of normal zinc pipes belowthe curing beds as long as the distancebetween the two tendon-anchoring heads.

A normal tendon-inserting machine is placedat one end of the pipe bundle while theother end is at the anchoring head.

Tendons are inserted in the machine andpushed through all the pipes until theirextremities emerge from the other end.When needed, a conventional tendon-lay-ing machine pulls the strands out of thezinc pipes onto the aligned casting bed.Because the strands are precut with thecorrect length needed, and because they

are positioned straight in the zinc pipesbelow the curing area, the pulling opera-tion onto the casting beds can be carriedout is operated rapidly. As soon as a zincpipe is unloaded, a special strand push-ing machine loads it again with a strandof the correct diameter and length.

In this way the pipe bundle is always load-ed with strands of different diameters inthe right position for stressing them toge-ther on the casting bed and anchoring.

Prestressing and control system

Another innovative apparatus is thesystem for stressing the tendons: it is a per-fect merger of electronic, oleodynamicand IT engineering.

The plant of stressing jacks is truly functio-nal: it consists of a pair of large oleodyna-mic cylinders assembled on a complexself-propelled unit which, by means ofremote controls, moves transversally toface each of the stressing heads of theseven casting beds.

Remote-controlled by the operator, it per-forms all stressing operations with extremedelicacy and reliability.

Stressing of the tendons on a bed takesplace simultaneously and the central con-trol computer records all operations tocompare them with the requirements ofthe job as given in the order.

Each of the two tendon anchoring blocksat the ends of the casting beds is equipped with jacks that regulate the ten-sion of the steel throughout the heat curingperiod of the concrete piece.At the end of a cycle they slowly releasethe prestressing tendons at both ends ofthe casting bed at the same time.The oil pressure in the jacks is continuallymonitored on the control panel and acomputer records variations every fewminutes and supplies a graph of the ten-sion on the prestressing steel on each bedthroughout the heat treatment. �

The Simem mixing tower… … and the Skako mixer are optimally harmonized

The movable prestressingunit can pull up to 500 t

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Since the computer also records the tem-perature of the concrete at the intrados ofthe piece during the same time interval, itis possible for the first time in the field ofheat-cured prestressed concrete to ana-lyse the tension development in the rein-forcement together with the temperaturesduring the heat cycle. The graphs alsosupply data on the time and degree ofconcrete shrinkage in the curing phase.

Concrete mixing

The completely automatic concrete mixingtower is a masterpiece of cooperation bet-ween the Italian company Simem and theDanish company Skako.

Simem supplied the metal structure of thetower over 30 m in height, including thesystem of introducing and raising theaggregate, the cement silo, and thecement distribution system.

Together with Skako, Simem also de-signed and supplied the feeding hoppersof the mixer and the self-propelled hopperthat receives the mixed concrete and pla-ces it in the concrete slave hopper moun-ted on a special bridge trolley.

Skako supplied and installed the systemfor aggregate measurement, a two cubicmetre Apollo mixer of the latest genera-

tion and the complete electric, electronicand IT systems for perfect, completelyautomated control of the entire mixingplant, starting from discharge of aggre-gates from the conveyor system to the fee-ding of the slipformer or the extruder. Theresult is a perfect concrete mix. To achievethe final design of the plant, an additionalmixer has been included in the planning.Batching orders are remotely given by thecasting machine operator. Thus the con-trol room is entered only to start the ope-ration of the plant, to change the batchingratios and to intervene when a cement oraggregate silo is empty.

Water reuse

When designing the plant, special atten-tion was paid to the working environmentand quality. Water and sludge from pro-duction facilities, from the channels pass-ing alongside, and at the ends of the cast-ing beds and cleaning area are re-cycled and reprocessed, separating dirtywater and clean aggregates.

Rain water from all storage areas is alsosent to a big underground transversalreservoir channel that is 170m long, 5mwide and 3m high, with suitable capacityfor the most severe rainfall in order toallow de-oiling, neutralization, separationand clarification of the water to be reused

in the plant or to be discharged to theagricultural channel beside the plant.

Conclusion

The success of the many innovative fea-tures in the new production centre de-scribed above has underlined that thesubstantial investment made has turnedout to be an economic success.The plant’s productivity at a highest possi-ble level has been confirmed, even in theface of strong competition.

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Water recycling was of special importance to ICN


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Further information:

Immobiliare Centro Nord S.p.A.Via Castelletto, 537050 Belfiore (VR), ITALYT +39 045 6149279F +39 045 [email protected]


immobiliare centro nord s.p.a., 37050 belfiore (vr), …...immobiliare centro nord s.p.a., 37050...

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