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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
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
