Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016

79

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

VERCORS MOCKUP – FIRST EXPERIMENTAL RESULTS AND 

SYNTHESIS OF THE BENCHMARK 

 

Benoît Masson 

(1)

, Manuel Corbin 

(1)

 

 

(1) EDF SEPTEN, Villeurbanne, FRANCE 

 

 

 

 

 

 

 

Abstract 

EDF VERCORS is focusing on the behavior of a large prestressed concrete structure. 

VERCORS's concrete is studied by numerous researchers of COST project and EDF offers 

three benchmarks about civil works calculations: early age, aging and severe accident. This 

paper summarizes the results shown during the workshop (March 2016) following the first 

benchmark. The next benchmarks are scheduled in 2017 and 2021. 

 

1. Introduction 

As part of EDF’s continuous effort on the safety and life extension of its Nuclear Power 

Plants fleet, an experimental mock-up of a reactor containment building at 1/3 scale [Figure 

1] has been built at “EDF Lab Les Renardières” near Paris (France).  

 

Height from gusset 

to the top

 

[m]: 20.79 

 

Internal radius of 

cylinder

 

[m]: 7.30 

 

Thickness of cylinder 

[m]: 0.3 

 

Free volume inside 

containment [m

3

]: 

3160

 

Figure 1: VERCORS scheme 

 

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80

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

 

Materials of the model have been selected to be as much similar than the ones used for 

construction of full scale containments as possible, in terms of mechanical and thermal 

behavior as well. Concrete class is 34/37 MPa.  Nevertheless, the concrete mix microstructure 

cannot be perfectly scaled due to aggregates size.  

 

The prestressing tendons layout is exactly scaled, including any deviations around 

penetrations: tendons spacing is divided by three, and the ducts diameter is scaled as much as 

reasonably possible for the contractor ( 50mm). Every tendon has been cement grouted as in 

full scale structures, excepted instrumented ones (four vertical and two horizontal) in order to 

follow the prestress delayed losses, or to simulate tendons breaks. The prestressing tendons 

are composed of class 1860 MPa strands T15 (nominal cross section S = 139mm²). Each 

tendon has been tensioned at 1488 MPa at active extremities before anchorage slip, as in full 

scale structures. The number of strands composing each tendon is governed by the following 

design principle: the initial compressive state of concrete shall be equal to the one in the full 

scale containment walls, when tensioning phase is just over.  Consequently, at one third scale, 

tendons section is divided by nine, so that each tendon is made with 4 T15 strands, instead of 

37 T15 in the full scale structures.  

 

Steel class 500 MPa has been used for the reinforcement of concrete in the mock-up 

containment walls. Design principles for the reinforcement are the followings: rebars spacing 

and diameters are scaled to keep the same ratios   (%) as in full-size structures. In typical 

areas of the cylinder, reinforcement principles are alternatively HB 6/8 @6.7cm in horizontal 

direction at both inner and outer face, and HB 8/10 @0.75° in vertical direction. In the dome, 

reinforcement principles are also alternatively HB 8/10 @9.8cm at both faces. Stirrups are 

made with HB 5. Length of the rebars and the number of overlapping zones are not scaled for 

practical reasons. Concerning concrete cover, exact scaling is not possible due to the 

aggregates size. 

 

The mock-up is finely instrumented so that its behavior is monitored from the beginning of 

the construction. 

The monitoring system is composed with: 

 

1 meteorological station 

 

for the ambient air measure : 10 thermometers, 10 relative humidity sensors, 1 

atmospheric pressure gage, 1 flow meter 

 

12 pendulums (4 plumb lines with each 3 tables of aiming at different heights on 4 

vertical lines) 

 

4 vertical Invar wires  

 

336 Embedded strain meters  

 

211  Thermometers PT100 

 

2 km of optic fiber 

 

31 TDR (Time Domain Reflectometry) sensors  

 

30 « pulse » sensors (permeability measure) 

 

6 dynamometers for instrumented tendons 

 

160 strain gauges on rebars 

 

The mock up construction has been completed at the end of 2015 [Figure 2]. All over the 

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81

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

research program, several measurements will be collected every day on each sensor. 

Hundreds of samples of concrete have been prepared and tested to determine their material 

behaviors and parameters, including hydration, strengths, fracture energy and elastic 

properties, drying, shrinkage (autogenous and drying), creep (basic and drying) and 

permeability.

Figure 2: Picture of the VeRCoRs mock-up [11-12-2015] 

 

The main objectives of the project are to study:

 

the behavior at early age, 

 

the evolution of the  leak tightness under the effect of aging (drying effects are about 9 

times faster on the mock up because of scale effects),

 

the behavior under severe accident conditions for which the thermo-mechanical 

loading is maintained for several days.

 

The experimental campaign consists of a daily measurement (four measurements a day) of the 

whole sensors and in a periodic air pressure test (scheduled every 13 months) of the mock-up. 

During this test, the containment is pressurized at 5.2 bar absolute (pressurization at 200 

mbar/h and plateau at 5.2 bar abs during 24 hours before deflation at 150mbar/h), all sensors 

are interrogated each hour and the leakage is measured.  

 

EDF proposed in 2015 a first benchmark dedicated to early-age, mechanical and leak 

tightness behaviors. 

 

Two other benchmarks are planned in the future: 

 

In 2017, to assess the impact of two successive identical loadings (pressurization tests) 

on a concrete structure and to take into account the aging, in particular long term creep 

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