Conference PaperPDF Available

Overlay Ductal®: a durable solution for bridges retrofitting

Authors:
Overlay Ductal®: a durable solution for bridges retrofitting
Sébastien Bernardi, Damien Jacomo, Frédéric Boudry 1
Overlay Ductal®: a durable solution for bridges
retrofitting
Author(s) & Affiliation:
Sébastien BERNARDI, Ductal
®
Technical Head – LafargeHolcim
Damien JACOMO, Ductal
®
Business engineer – LafargeHolcim
Frédéric BOUDRY, Project Manager - Walo Bertschinger AG
Abstract:
The Chillon Viaduct, built by prestressed box girder segmental construction, was constructed in
the late 1960s. Recent examination of structural performance showed that punching of wheel
loads through the deck slab is prevailing, though structural safety requirements currently can be
fulfilled. Furthermore, the box girder concrete is prone to alkali silica reaction (ASR). The
chosen strengthening measure is adding a layer of ultra-high performance fiber reinforced
concrete (UHPFRC) additionally reinforced with steel rebars on the top surface of the deck slab,
also serving as waterproofing layer. A new 45 mm (1.7 in.) Ductal
®
bridge deck delivers an
effective response to these challenges.
Keywords: composite structure, Ductal
®
, overlay, retrofit, strain-hardening, thixotropic
1. Introduction
The Chillon Viaduct located on the Swiss National Highway on the East end of the Lake of
Geneva, was constructed in the late 1960s. The variable height box girder structure, spanning be-
tween 92 m (302 ft.) and 104 m (341 ft.) over a total length of 2 210 m (7 250 ft.), was built by
prestressed segmental construction with epoxy-glued joints which was a world novelty at the
time. Recent structural assessment showed that the governing failure mode at Ultimate Limit
State (ULS) is punching of wheel loads through the 18 cm (7 in.) thin deck slab, though
structural safety requirements currently can be fulfilled. Further investigations revealed that the
concrete is prone to alkali aggregate reaction (AAR). The latter is expected to lead to significant
concrete strength reduction in the future, with an associated reduction in punching shear
resistance.
As the replacement of the waterproofing on the deck slabs was planned for 2014-2015, its
combination with a strengthening intervention was investigated. It has been decided to
consolidate the viaduct by adding, on the previously hydro-jetted top surfaces of deck slabs, a 40
to 50 mm (1.6 to 2 in.) thin layer of Ultra High Performance Fibre Reinforced Concrete
(UHPFRC) which is additionally reinforced by steel rebars, on the top surface of the deck slab.
The choice of UHPFRC as a strengthening material, was motivated by its outstanding
mechanical properties, namely high tensile and compressive strengths and a its important
deformation capacity due to the high amount of incorporated steel fibres in the cement-based
matrix of the material, as well as by its very low porosity implying minimized moisture exchange
and ingress of aggressive chemical substances such as chloride ions from the surrounding
First International Interactive Symposium on UHPC – 2016
Overlay Ductal®: a durable solution for bridges retrofitting
Sébastien Bernardi, Damien Jacomo, Frédéric Boudry 2
atmosphere. Consequently, the latter property (low porosity) will have beneficial effects on a
further evolution of the AAR (because of lack of water supplies) and on corrosion of
reinforcement of steel rebars.
Figure 1. View of the Chillon viaduct
Figure 2. Construction of the viaduct with prestressed box girder segments
2. Background
The concept of application of strain-hardening UHPFRC for the rehabilitation of structural
members is schematically illustrated on Figure 3. A dense layer of UHPFRC with 25 to 60 mm
(1 to 2 in.) thickness is applied on the superstructure in zones of severe environmental and
mechanical loads (exposure classes XD2, XD3) and only where the UHPFRC fits the
requirements. The construction process becomes simpler, quicker, and more robust, with an
optimal use of composite construction. The waterproofing capabilities of UHPFRC exempt from
applying a waterproofing membrane. Thus, the asphalt pavement can be applied after only 7 days
of moist curing of the UHPFRC composite layer, in a wide range of climatic conditions. This
constitutes a very significant time saving with respect to the drying period of up to 3 weeks
necessary prior to the application of a waterproofing membrane for a usual mortar or concrete
and to their limited durability.
First International Interactive Symposium on UHPC – 2016
Overlay Ductal®: a durable solution for bridges retrofitting
Sébastien Bernardi, Damien Jacomo, Frédéric Boudry 3
Figure 3. Concepts of application of the local strengthening of structures with UHPFRC
Cast-on site applications require strain-hardening UHPFRC able to withstand the
development of eigenstresses due to restrained shrinkage, without cracking. Their rheology can
be adjusted from self-compacting to thixotropic for application on inclined substrates. Their
tensile response must be validated on specimens representative of the application (fiber
orientation and rheology). When it is required, the combination of the protective properties and
deformation capability of UHPFRC with the mechanical performance of reinforcement bars
(normal or high grade) provides a simple and efficient way of increasing the stiffness and load-
carrying capacity. Reinforcement bars also help mitigate the variability of the tensile response of
UHPFRC over large surfaces. These concepts have been validated by means of extensive
research aimed at characterizing UHPFRC materials and the structural behavior of composite
reinforced UHPFRC structural members, as well as numerous successful applications in
Switzerland and abroad, since 2004.
Figure 4. Bending and shear tests on composite slabs reinforced with strain-hardening UHPFRC
Figure 5. Examples of applications with strain-hardening UHPFRC
UHPFRC
First International Interactive Symposium on UHPC – 2016
Overlay Ductal®: a durable solution for bridges retrofitting
Sébastien Bernardi, Damien Jacomo, Frédéric Boudry 4
3. Testing Methods
The UHPFRC designed for the overlay application responds to the following general
requirements: high compressive and tensile strengths, strain hardening in tension, very low
permeability, self-compacting fresh mix with the ability to be cast with a slope of 7%.
3.1. Rheology
The lever used to modify the self-compacting behavior to a rheo-thinning behavior is the
admixture. The simple slope test (Figure 6) allowed us to identify the best solution and to
evaluate the robustness with temperature (5 to 35 °C so 41 to 95 °F).
Due to the mechanical casting method developed by the company Walo Bertschinger
AG, scale-up tests have also been performed to check the compatibility between the Ductal® mix
and the process and its influence on the fibres orientation.
Figure 6. Slope test and scale-up test with the casting machine
3.2. Tensile behavior
High tensile strength as well as strain hardening and softening are characterising properties of
UHPFRC. The uniaxial tensile behavior was determined using 4 points bending tests on thin
plates measuring 500x100x30 mm (19.7x3.9x1.1 in.) and a back analysis method afterwards.
Complementary direct tensile tests have also been carried out on dogbone specimens.
Figure 7. Bending and direct tensile tests on strain-hardening Ductal® specimens
First International Interactive Symposium on UHPC – 2016
Overlay Ductal®: a durable solution for bridges retrofitting
Sébastien Bernardi, Damien Jacomo, Frédéric Boudry 5
4. Results
During the 2 phases of the Chillon project, a huge amount of tests have been carried out by
different laboratories:
fresh state: density, air content, slump and slope maintain
hardened state: compressive and bending tests, bonding tests (adhesion between Ductal® and
the existing concrete on the deck), Young’s modulus, water absorption and air permeability
Tables 1 summarizes the main characteristic of the thixotropic Ductal® evaluated under samples
produced at the R&D Center and also on the job site (casted plates and plates cut on the deck).
The performances of this new Ductal® product comply with the project specifications (class UA),
coming from the Swiss technical recommendations.
Table 1. Results of the characterization for the Ductal® mix
Characteristics Unit Thixotropic Ductal®
Slope control (%) up to 10
Total shrinkage at 90 days µm/m (10-6) 500
Compressive strength at 28d MPa (ksi) 125 (18)
Limit of elasticity under tension at 28d MPa (ksi) 8.0 (1.2)
Post-cracking resistance at 28d MPa (ksi) 9.0 (1.3)
Young’s modulus at 28d GPa (ksi) 45 (6530)
Water porosity at 90d (%) 6
(very high durability)
Diffusion coefficient of chloride ions
at 90 days 10-12 m2.s-1 (sq ft.s-1)
0.1 (1.1)
(very high durability)
Apparent gas permeability at 90 days 10-18 m2 (sq ft) 0.5 (5.3)
(very high durability)
Figure 8. Fresh Ductal® poured on a 7% sloped rough plate (dimensional control)
First International Interactive Symposium on UHPC – 2016
Overlay Ductal®: a durable solution for bridges retrofitting
Sébastien Bernardi, Damien Jacomo, Frédéric Boudry 6
Figure 9. Direct tensile behavior of strain-hardening Ductal®
5. Discussion
The constitutive law in tension obtained with the 2 methods, direct tensile tests and back analysis
from bending tests, gave similar results for the strain-hardening phase. It confirms the good
reliability of the back analysis approach, based on the relationship between the curvature and the
deflection but only valid in the elastic domain (Figure 10).
Figure 10. Principles of the curvature-based formulation
About the rheology, the robustness has been validated during the design phase, and 3
different mixes implemented in the automatic mixing plant, to take into account of the ambient
temperature. A simple adjustment of the superplasticizer guaranteed the appropriate workability
and adequacy with the casting process.
Stress
Strain-hardening Strain-softening
Elastic behavior
fUtu = 9 MPa
fUte = 8 MPa
ε
Utu = 3.8
0
/00
ε
Ute = 0.18
0
/00
ε
Ut
σ
Ut
First International Interactive Symposium on UHPC – 2016
Overlay Ductal®: a durable solution for bridges retrofitting
Sébastien Bernardi, Damien Jacomo, Frédéric Boudry 7
6. Conclusions
The concept of application of strain-hardening UHPFRC for the improvement of existing
structures has been applied successfully on Chillon viaduct. This project is the biggest overlay
project in the world right now, with industrial quantities of Ductal® cast per day (up to 80 m3),
over several weeks (6 in 2014 and 5 in 2015) to reinforce a twin 2.1 km long highway viaduct.
Exceptional execution methods developed for this project have demonstrated the effectiveness of
the reinforced UHPFRC strengthening solution. The robustness of the established formula has
reduced the hazards during the construction, particularly the workability of UHPFRC with the
temperature.
Combination of UHPFRC with rebars offers an efficient way to produce highly durable
reinforced UHPFRC tensile membranes to reinforce existing structures.
Figure 11. Implementation of thixotropic Ductal® on Chillon viaduct's deck
First International Interactive Symposium on UHPC – 2016
Overlay Ductal®: a durable solution for bridges retrofitting
Sébastien Bernardi, Damien Jacomo, Frédéric Boudry 8
7. References
Buitellar P., Braam R., “Heavy Reinforced Ultra Thin White Topping of High Performance
Concrete for Re-strengthening and Rehabilitation of Structures and Pavements”, 2004.
Denarié E., “Full scale application of UHPFRC for the rehabilitation of bridges – from the lab to
the field”, Deliverable SAMARIS D22, 2006.
Denarié E., Šajna A., “Composite UHPFRC-concrete construction harden structures to last”',
CCC-2009: The 5th Central European Congress on Concrete Engineering, Baden, Austria,
Edited by Austrian Society for Concrete and Construction Technology, September 2009, pp. 80-
83.
Denarié E., “Recommendations for the tailoring of UHPFRC recipes for rehabilitation”,
Deliverable ARCHES D06, 2009.
Šajna A, Denarié E, Bras V., “Assessment of a UHPFRC bridge rehabilitation in Slovenia, two
years after application”, 3
rd
International Symposium on Ultra-High Performance Concrete,
Kassel, Germany, 2012, pp. 937-944.
Brühwiler E. and Denarié E, “Rehabilitation and strengthening of concrete structures using
Ultra-High Performance Fibre Reinforced Concrete”, Structural Engineering International,
Volume 23, Number 4, November 2013, pp. 450-457.
Zwicky D. and al., “Essais sur dalles “Chillon” renforcées au BFUP armé”, Technical report (in
french), University of Applied Sciences HEIA-FR, iTEC, Fribourg, Switzerland, 2013.
Denarié E., Jacomo D., Fady N., Corvez D., “Rejuvenation of maritime signalization structures
with UHPFRC”, 2
nd
International Symposium on Ultra-High Performance Fibre-Reinforced
Concrete, Marseille, 2013, 157-166.
Chanvillard, G. and Corvez, D., “Explicit back analysis method for quick determination of direct
tensile strength of plate structural members”, International Symposium on UHPC in Marseille,
November 2013.
Cahier Technique SIA 2052, “Béton fibré ultra-performant (BFUP) - Matériaux,
dimensionnement et exécution”, Projet, Avril 2014.
Dobruský S., Chanvillard G., “Modified force-bases fiber beam formulation tailored for inverse
analysis of both strain hardening and strain softening cementitious composites”, 3
rd
International
RILEM Conference on Strain Hardening Cementitious, Delft, November 2014.
8. Acknowledgements
The authors wish to express their gratitude to Gérard Molinès and Julien Verne from
LafargeHolcim, for their rigorous and accurate work provided in the development of the Ductal
®
mix and the technical support on the field.
First International Interactive Symposium on UHPC – 2016
... This includes the use of UHPC for thin bonded overlays for concrete pavements. Bernardi et al. [6] reported successful use of UHPC in thin overlay of 45 mm in thickness reinforced with 3.25% steel fibers for bridge deck rehabilitation in Switzerland in 2014. The overlay repair included reinforcing rebar and UHPC to strengthen the existing deck that was damaged from alkali silica reactivity. ...
Article
This paper evaluates the efficiency of various shrinkage mitigation approaches in reducing autogenous and drying shrinkage of ultra high performance concrete (UHPC). This included the use of various contents of CaO-based and MgO-based expansive agents, shrinkage-reducing admixture, and pre-saturated lightweight sand. Workability, compressive strength development, autogenous and drying shrinkage were evaluated for UHPC mixtures subjected to moist curing periods of 1, 3, and 7 d. Test results indicate that the use of lightweight sand was shown to be more effective in mitigating shrinkage than enhancing compressive strength. The replacement of natural sand by 60% of lightweight sand, by volume, was found to reduce autogenous shrinkage from 530 to 35 µm/m at 91 d. The coupled effect of using 60% lightweight sand and either CaO-based expansive agent, MgO-based expansive agent, or shrinkage-reducing admixture can reduce autogenous shrinkage at 91 d by up to 600 µm/m and drying shrinkage by up to 700 µm/m. In some combination, the use of shrinkage mitigating admixtures was found to reduce the 91-d compressive strength ranging from 8 to 20 MPa, even when 60% lightweight sand was employed. The initial moist curing period had positive effect on mitigating total shrinkage. The incorporation of 10% CaO-based expansive agent in UHPC with 60% lightweight sand subjected to 7 d of moist curing exhibited the best overall performance with 91-d autogenous shrinkage of 110 µm/m in expansion and 91-d total shrinkage (autogenous shrinkage after 1 d plus drying shrinkage) of 580 µm/m (also in expansion).
... Basic Chararteristic Properties of the UHPC Overlay Mix(9) ...
Article
Deterioration of existing bridge decks, which usually originates with the deck cracking on the top surface, is a common problem in North America. It causes frequent repair of the decks to limit further damage resulting from water/chloride ingress. Superior engineering and durability properties facilitate the use of ultra-high performance concrete (UHPC) as an attractive alternative for a deck overlay, minimizing both deck deterioration and maintenance costs. Recently developed UHPC thixotropic mix designs, which are different from commonly used self-leveling UHPC, enable UHPC overlay to be used on decks with slopes and meet specific crowning requirements. The use of a UHPC thixotropic mix design with 3.25% of steel fibers was successfully evaluated under laboratory conditions by applying it on sloping deck surfaces with appropriate roughness between the normal concrete (NC) and UHPC. The feasibility of applying this technology in the field was then investigated on a small bridge for the first time in North America in May 2016. This paper presents the details about the laboratory evaluation, field implementation of UHPC overlay, and lessons learned from this first UHPC overlay project in North America.
Thesis
A number of research concerns have arisen in the concrete research community on the fire resistance of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) beams, despite their improved mechanical properties at ambient temperature. The traditional experimental approach to performance-based fire resistance estimation comes with a lot of economic and physical constraints. The recent improvements in both computational power and algorithms suggest that a numerical approach to performance-based fire resistance estimation has the capability to solve some of these challenges. By building on the principle of the finite element method, in this study, finite element models of UHPFRC beams exposed to elevated temperatures in a fire were developed in a finite element software package ABAQUS. The developed finite element models were validated against experimental results reported in a previous experimental study on UHPFRC beams which were pre-loaded under load ratios of 0.2, 0.4 and 0.6 then subjected to 60-minutes ISO 834 fire in a furnace. The finite element model predicted the thermal and mechanical responses of UHPFRC beams which were in good agreement with results reported on the experimental beams. Subsequently, the finite element models were used in a parametric study to investigate the fire resistance of UHPFRC beams under nine different load ratios (0.1-0.9) and different heating regimes, that is, the ISO 834, and the hydrocarbon temperature-time curves and fire resistance ratings were estimated at 0, 30 or 60-minutes for the beams considered. It is hoped that the proposed finite element models be used directly for performance-based fire safety design of UHPFRC beams as a cost-effective numerical tool and be employed in parametric studies to develop simple prescriptive design rules.
Conference Paper
p>The superior mechanical and durability properties of ultrahigh-performance concrete (UHPC) offer significant potential advantages when used as an overlay material—a common method for extending the service life of concrete bridge decks. Providing high compressive strength, improved environmental resistance, and increased service-life expectancy compared to conventional concretes, UHPC mixture proportions can be adapted using local materials. Flexural testing of a high-performance concrete (HPC; 66 MPa) prestressed channel beam bridge girder was conducted to investigate the use of nonproprietary UHPC (120 MPa) developed using materials primarily local to New Mexico, USA, for bridge deck overlays. The girder was first subjected to cyclic loading (minimum 1000 load-unload cycles to deflection-based service load conditions) to establish baseline performance and behavior. The girder surface was then textured, and a 25 mm nonproprietary UHPC overlay was cast. Cyclic loading was repeated for the girder-overlay system before loading the system to failure to investigate post-cracking flexural behavior. The UHPC overlay developed satisfactory bond with the HPC substrate without a bonding agent and exhibited no visible signs of distress or debonding after cyclic loading. Comparative analyses indicated increased stiffness and capacity for the girder- overlay system.</p
Technical Report
Full-text available
A large number of bridges in the nation are rated as structurally deficient and require immediate retrofits or replacements that will impose a significant financial burden on bridge owners. A fast, cost-efficient, and reliable retrofit solution is needed to tackle this problem. Typical bridge deck deterioration starts with shrinkage cracks, and additional cracks may occur due to traffic loads and time-dependent effects, which are worsened by freeze-thaw cycles over time. These cracks then lead to water and chloride penetration into the concrete deck, causing rebar corrosion and further damage to the superstructure. A potential solution, suggested in a previous study, is to apply a thin layer of ultra-high-performance concrete (UHPC) on top of normal concrete (NC) bridge decks. Because UHPC has a higher tensile strength and low permeability, cracking as well as water and chloride ingression can be minimized, which in turn will extend the lifespan of the bridge. Moreover, UHPC is also deemed to have a higher fatigue resistance than NC. In this study, a new UHPC mix to accommodate surface crowning was developed by a material supplier and tested in the laboratory. Using this new mix, the thin UHPC overlay concept was successfully implemented on a county bridge in Iowa. The implementation involved state and county engineers, a local contractor, and a material supplier. The bridge overlay was periodically monitored, and thus far there have been no concerns regarding the performance of the UHPC overlay or the bond at the interface between the UHPC and NC layers. In addition to the field implementation, three concrete slabs with and without a UHPC overlay were tested in the laboratory. The results showed that a UHPC overlay in the positive moment region increased the strength by 18% while showing a more ductile response. In the negative moment region, although wire mesh was used, its effectiveness was not significant due to its small steel area. The effectiveness of the wire mesh could be improved by increasing the amount of steel area within the overlay, but its impact on the UHPC-NC interface bond needs to be evaluated.
Article
Full-text available
An original concept is presented for the durable rehabilitation and strengthening of concrete structures. The main idea is to use ultra-high performance fibre reinforced concrete (UHPFRC) complemented with steel reinforcing bars to protect and strengthen those zones of the structure that are exposed to severe environmental influences and high mechanical loading. This concept efficiently combines the protection and resistance properties of UHPFRC and significantly improves the structural performance of the rehabilitated concrete structure in terms of durability. The concept has been validated by means of field applications, demonstrating that the technology of UHPFRC is now well developed for cast in situ and prefabrication using standard equipment for concrete manufacturing. This novel technology is a step forward towards more sustainable structures.
Conference Paper
Full-text available
It is now common to characterize the tensile behaviour of fibre-reinforced concrete by bending tests rather than by direct tensile tests. Then it is fairly common today to apply reverse analysis to extract the tensile constitutive equation of the material. For the case of thin plates showing a bending hardening behaviour, a new explicit method (which does not need any numerical solver) allowing performing reverse analysis into equivalent strain is proposed which starts with an experimental moment-deflection relationship to get tensile stress-strain constitutive relationship. The great advantage of this explicit approach is to be easy to program and it allows to quickly manually adjust a constitutive material relationship on the experimental results without any data pre-treatment. Two specific application cases are presented showing how this methodology could accelerate the use of UHPFRC in real applications making easy the analysis of characterization tests.
Conference Paper
Nonlinear behavior of reinforced concrete, either by fibers or rebars, has been studied over decades. In this paper, classical models for flexural behavior are discussed and an improved model is proposed. It is based on a modified force-based formulation where the progressive loading is driven by the curvature of the nonlinear hinge, allowing capturing the softening behavior. In order to describe the structural deflection during this softening part, as the curvature outside the nonlinear hinge decreases, damage constitutive equation should be introduced. Rather using the classical damage model proposed by Mazars, a macroscopic damage model at the level of moment-curvature curve is proposed which reduces the full calculation of the beam mechanical equilibrium to only one numerical loop as soon as the cross-section equilibrium is known. Hypothesis of this new model (damage modeling, localization problem and shear contribution to deflection) are discussed showing the powerfulness and benefits.
Assessment of a UHPFRC bridge rehabilitation in Slovenia, two years after application
  • A Šajna
  • E Denarié
  • V Bras
Šajna A, Denarié E, Bras V., "Assessment of a UHPFRC bridge rehabilitation in Slovenia, two years after application", 3 rd International Symposium on Ultra-High Performance Concrete, Kassel, Germany, 2012, pp. 937-944.
Béton fibré ultra-performant (BFUP) -Matériaux, dimensionnement et exécution
Cahier Technique SIA 2052, "Béton fibré ultra-performant (BFUP) -Matériaux, dimensionnement et exécution", Projet, Avril 2014.
Composite UHPFRC-concrete construction – harden structures to last CCC-2009: The 5th Central European Congress on Concrete Engineering
  • E Denarié
  • A Šajna
Denarié E., Šajna A., " Composite UHPFRC-concrete construction – harden structures to last " ', CCC-2009: The 5th Central European Congress on Concrete Engineering, Baden, Austria, Edited by Austrian Society for Concrete and Construction Technology, September 2009, pp. 80- 83.
Recommendations for the tailoring of UHPFRC recipes for rehabilitation
  • E Denarié
Denarié E., "Recommendations for the tailoring of UHPFRC recipes for rehabilitation", Deliverable ARCHES D06, 2009.
Full scale application of UHPFRC for the rehabilitation of bridges -from the lab to the field
  • E Denarié
Denarié E., "Full scale application of UHPFRC for the rehabilitation of bridges -from the lab to the field", Deliverable SAMARIS D22, 2006.
Essais sur dalles "Chillon" renforcées au BFUP armé
  • D Zwicky
Zwicky D. and al., "Essais sur dalles "Chillon" renforcées au BFUP armé", Technical report (in french), University of Applied Sciences HEIA-FR, iTEC, Fribourg, Switzerland, 2013.