Two-Lift Paving - Design Viewpoints

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A Two-Lift concrete Paving (2LCP) workshop was organized as a part of the Texas Department of Transportation (TxDOT) project 0-6749: Feasibility Study of Two-Lift Concrete Paving (2LCP). This workshop was conducted at the J. J. Pickle Research Campus (PRC), The University of Texas at Austin, Austin, TX on May 23rd, 2013. Dr. Jiong Hu, Texas State University, Research Supervisor, and Dr. David Fowler, The University of Texas at Austin, Co-Research Supervisor, co-chaired the workshop. The workshop offered the option of attending in person or remotely through webinar. Fifty-one attendees were present remotely or in person; 28 in person and 23 persons remotely.

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Two-lift pavingDesign aspects

Luc Rens, C.E.FEBELCEM – Consulting Engineer

l.rens@febelcem.be

EUPAVE – Managing Director

May 23, 2013, Two-Lift Paving Workshop, Austin, Texas

Classic continuous reinforced concrete in Belgium

Belgian standard design for concrete motorways 1 lift - single run of the slipform paverSimple and reliable construction methodExposed aggregate concrete surfaceStones : PSV ≥ 50 - no recycled materials

1996 - Herne : Test sections of low-noise surfaces

TWO-LIFT PAVING - BELGIAN EXPERIENCE

2002

N511 – Estaimpuis

Double layered CRCP with different top layers

TWO-LIFT PAVING - BELGIAN EXPERIENCE

E34/N49

Category : main road (at most places transformed into motorway)

Traffic volume (March 2007):23 000 vehicles a day in the direction from Antwerp to Zelzate25% heavy traffic

Construction in 2 phases: Direction from Antwerp: 2007 Direction to Antwerp: 2008

E34/N49 – Two lift continuously reinforced concrete

Construction in two layers: optimum noise reduction at surface due to fine exposed aggregate concrete in top layer Continuously reinforced concrete Recycled aggregates in the lower course – aggregates

from existing concrete road

Recycled aggregates: from existing road –quality controlled by COPRO

Concrete mix specifications

Specifications for the top layer:- aggregate 4/6,3 (PSV 50) – no reclaimed material allowed- coarse sand – no reclaimed material allowed- CEM III/A 42,5 N LA 425 kg/m³- W/C 0,45- air entrained – air void content 5%

Specifications for the bottom layer:- aggregate 4/6,3 : no reclaimed material allowed- aggregate 6,3/20 – 20/32 : reclaimed crushed concrete,60 to 100%- coarse sand – no reclaimed material allowed- CEM III/A 42,5 N LA 375 kg/m³- W/C 0,45- air entrained – air void content 3 %

Structure of two-layered CRCP

Continuous longitudinal reinforcement at 8 cm from surface

Placing of the concrete “wet on wet” by two slipform pavers (maximum time interval of 2 hours)

EXECUTION

Surface finishing = fine-grained exposed aggregate concrete

EXECUTION

RECLAIMED AGGREGATES IN PAVEMENT CONCRETE

Experiences in other countries

Austria

• Double-layered jointed plain concrete since 1990

• 21 cm + 4 cm

• Motorway programme (A1 – A2)

• Reuse in the lower course of 65 % of recycled crushed concrete from the old pavement

• Asphalt layer between base and concrete pavement

Germany

• Has taken over the Austrian technique

• Geotextile between base and concrete pavement

• The Netherlands, Belgium…

N49 : after 3 years in service… (May 2011)

N49 : after 3 years in service… (May 2011)

N49 : after 3 years in service… (May 2011)

Horizontal cracks at the height of the reinforcement

Shrinkage crackOver total depth

Horizontal crack

Vertical crack ends at the reinforcement

What is different?

Older realisations with double layered CRCP:Herne (1996) – Estampuis (2002)

What is different on the E34/N49?

- Rebars are higher in the concrete layer: 8 cm from surface at the N49 and 13 cm in Herne?

- Traffic intensity is much higher and the concrete has been exposed to traffic much sooner

- Time of execution: warm summer for the N49, normal spring in Herne

- Use of recycled aggregates in the bottom lift

Research and investigation

Inspection of cores Bond steel – concrete Microscopic examination Ultrasonic tomography

Ultrasonic tomography : measurement at a crack

Concrete properties determined on bottom layer (after 4 years in service)

Core Volumic density Compressive strength

1 2350 kg/m³ 80,32 N/mm²2 2360 kg/m³ 82,55 N/mm²

3 2360 kg/m³ 88,45 N/mm²

We are still looking for the answers…

How did the horizontal cracks occur?

Due to the too large opening of the initial transverse cracks?

Due to the use of reclaimed aggregates in the bottom layer of the concrete? (because of additional shrinkage and/or lower strength)

Due to the two layers? Differential shrinkage?

Changes in design for recent worksites of two-lift CRCP

Changes in design– No RCA– No air entrainer in

bottom layer– Induced cracking– Long. steel 1cm

lower

Risk for punch-outs

What could be the solutions ?ACTIVE CRACK CONTROL ?

Short crack inducer – At the edge of the pavement– 40 cm wide– 3 cm deep– Spaced at 1,20 m (4 ft)

Test strips of double layered concrete (JPCP) for industrial areas

Wet-in-wet application –excellent bond

Recycled aggregates in base layer

TiO2 in top layer

Thank you for your kind attention

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