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Joint-less Industrial Floor,MTD Hungaria, Nemesvamos

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General Floor CharacteristicsJoint-less Industrial Floor made of Shrinkage-Compensating Concrete

Joint-less: 'joint-less' doesn't mean that there are absolutely no joints in the floor. However joint-less floors have 80-90% less joints than conventional floors. Joints: joints need to be formed at certain locations,e.g.: where daily concrete pour is finished (this is called construction joint), orat critical floor locations where stress needs to be reduced.These joints are steel armored to protect joint edges from spalling and the prefabricated joint profiles inculde plate dowels for effective load transfer between the floorpanels separated by the joint.

Concrete: expansive concrete made with DENKA CSA #20, C30/37-XC1-32-F3

Subgrade: 35 cm crushed rock, E2=100-130 N/mm2

Floor thickness: 15 cm

Load bearing capacity: 12 ton/rack leg; 15 ton/m2

Floor flatness and levelness: FF35/FL20

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Floor DesignStructural Design

Industrial floors are multi-layered structures:

Sub-soilSub-gradeConcrete slab

For floor design sub-soil characteristics were taken into account, sub-grade and concrete slab was designed for the applied loads.

Design criterium: concrete slab remains crack-free.

Locating joints correctly is vital for crack free floors.

The employed flooring technology allows 40 meter joint spacing without any cracks (as opposed to 5-7 meter joint spacing, as in case of conventional flooring). Also, long and narrow floor sections can be built without cracking.

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Floor DesignJoint locations (indicated by black arrows below)

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Floor DesignJoint formation

Joint edges subjected to small hard wheels are prone to break (spall).

Any joint wider than appr. 1 mm will spall.

To avoid spalling we protect joint edges with steel (See below).

Effective load transfer in joints is necessary to aviod step formation between the two sides of the joint that would further deteriorate joint edges.

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Floor DesignSteel bar reinforcement

Properly sized and located steel reinforcement is key to effective shrinkage compensation. If shrinkage-compensating concrete is properly and elastically restrained, it induces compressive stress in the slab that is intended to approximately offset the tendency of shrinkage to induce tensile stress.

Taking into account the expansive potential of the concrete mix and the expected shrinkage, a small ratio of steel bar reinforcement was placed in the upper half of the slab.

Additional reinforcement was employed around re-entrant corners to avoid cracks.

Floor DesignConcrete mix design

Shrinkage-compensating concrete expands after setting. The expansion takes place in the first 7 days. After 7 seven days -when subjected to drying- it starts shrinking. If designed properly expansion equals or it is slightly higher than the ultimate shrinkage.

To confirm the above, the employed concrete mixture went under examination at the Budapest University of Technology and Economics for 28 days.

The following properties have been looked at:Expansion (ASTM C878)ShrinkageFresh concrete workabilitySlump loss over 1,5 hours

Length change

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Floor ConstructionSteel bar reinforcement

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Floor ConstructionSteel bar reinforcement at re-entrant corners

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Floor ConstructionJoint formation: steel armored joint with effective load transfer

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Floor ConstructionJoint formation: steel armored joint with effective load transfer

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Floor ConstructionPouring concrete

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Floor ConstructionPouring concrete

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Floor ConstructionPouring concrete

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Floor ConstructionPouring concrete

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Floor ConstructionDosing DENKA CSA #20 expansive agent at the ready mix concrete plant

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Floor ConstructionTaking concrete sample at the ready mix concrete plant

Fresh concrete quality was continously checked during construction.

The followings were tested:

Concrete temperatureSlump flowWater contentConcrete density

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Monitoring floor performanceConcrete expansion and shrinkage are measured with built in strain gauges

Strain gauge

Data acquisition system

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Results No cracksNo joint spallingSmall joint opening

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Results Floor performance data acquired by two built in strain gauges confirms that the floor behaves as expected:

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Results (The floor recieved epoxy coating for oil resistance)

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Results (The floor recieved epoxy coating for oil resistance)

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Results (The floor recieved epoxy coating for oil resistance)

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ResultsJoint

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Conclusions With no cracks and no joints to maintain the floor is practically maintenance-free.

No down timesNo maintenance cost

No headache

The floor next door is a conventional floor, with closely spaced joints (6 m). It is 6 months old and the joint deterioration typical of this kind of flooring already started and joint repair will be needed soon.

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