1. High Performance Concrete
Austroads Bridge Conference
Perth September 2005
High Performance Concrete
in Bridge Decks
               

2. Introduction Increasing international use of HSC in bridges
Mainly in response to durability problems; de-icing salts; freeze-thaw conditions
Focus of this paper - durability and workability
Reduced permeability
High workability
Good resistance to segregation
Use of cement replacement materials
Reduced ductility and fire resistance
Greater susceptibility to early age cracking
               

3. Overview What is High Performance Concrete?
International use of HPC in bridges
Use of HPC in Australia
Economics of High Strength Concrete
HSC in AS 5100
Specification of High Performance Concrete
Case Studies
Conclusions
Recommendations
               

4. What is High Performance Concrete?
"A high performance concrete is a concrete in which certain characteristics are developed for a particular application and environments:
Ease of placement
Compaction without segregation
Early-age strength
Long term mechanical properties
Permeability
Durability
Heat of hydration
Toughness
Volume stability
Long life in severe environments
               

5. What is High Performance Concrete?
               

6. Information on H.P.C.
· “Bridge Views” –
· “High-Performance Concretes, a State-of-Art Report ( )” -
· “A State-of-the-Art Review of High Performance Concrete Structures Built in Canada: ” -
· “Building a New Generation of Bridges: A Strategic Perspective for the Nation” -
               

7. International Use of H.P.C.
Used in Japan as early as 1940
Used for particular applications for over 30 years.
First international conference in Norway in 1987
Early developments in Northern Europe; longer span bridges and high rise buildings.
More general use became mandatory in some countries in the 1990’s.
Actively promoted for short to medium span bridges in N America over the last 10 years.
               

8. International Use of H.P.C.
Japan
100 MPa concrete developed in 1940
Three rail bridges constructed in High Strength Concrete in 1973
Durability became a major topic of interest in early 1980’s
Self-compacting concrete developed in 1986 to address durability issues, and lack of skilled labour
Annual 400,000 m3 used in 2000.
               

9. International Use of H.P.C.
Scandinavia
Norway
Climatic conditions, long coastline, N. Sea oil
HPC mandatory since 1989
Widespread use of lightweight concrete
Denmark/Sweden
Great Belt project
Focus on specified requirements
France
Use of HPC back to 1983
Usage mainly in bridges rather than buildings
Joint government/industry group, BHP 2000
70-80 MPa concrete now common in France
               

10. International Use of H.P.C.
North America
HPC history over 30 years
Use of HPC in bridges actively encouraged by owner organisation/industry group partnerships.
“Lead State” programme, 1996.
HPC “Bridge Views” newsletter.
Canadian “Centres of Excellence” Programme, 1990
“A State-of-the-Art Review of High Performance Concrete Structures Built in Canada: ”
               

11. Use of H.P.C. in Australia
Maximum concrete strength limited to 50 MPa until the introduction of AS 5100.
Use of HPC in bridges mainly limited to structures in particularly aggressive environments.
AS 5100 raised maximum strength to 65 MPa
Recently released draft revision to AS 3600 covers concrete up to 100 MPa
               

12. Economics of High Strength Concrete
Compressive strength at transfer the most significant property, allowable tension at service minor impact.
Maximum spans increased up to 45 percent
Use of 15.2 mm strand for higher strengths.
Strength of the composite deck had little impact.
HSC allowed longer spans, fewer girder lines, or shallower sections.
Maximum useful strengths:
I girders with 12.7 mm strand - 69 MPa
I girders with 15.2 mm strand - 83 MPa
U girders with 15.2 mm strand - 97 MPa
               

13. AS 5100 Provisions for HSC Maximum compressive strength; 65 MPa
Cl Alternative materials permitted
Cl MPa fatigue limit on compressive stress - conservative for HSC
Cl Part 2 - Deflection limits may become critical
Cl Tensile strength - may be derived from tests
Cl 6.1.7, Creep and shrinkage provisions conservative for HSC, but may be derived from test.
               

14. AS 5100 and DR 05252
               

15. AS 5100 and DR 05252
Main Changes:
Changes to the concrete stress block parameters for ultimate moment capacity to allow for higher strength grades.
· More detailed calculation of shrinkage and creep deformations, allowing advantage to be taken of the better performance of higher strength concrete
· Shear strength of concrete capped at Grade 65.
· Minimum reinforcement requirements revised for higher strength grades.
· Over-conservative requirement for minimum steel area in tensile zones removed.
               

16. Specification of High Performance Concrete
· Recommended Practice Z13; "Performance Criteria for Concrete in Marine Environments”.
Z07; “Durable Concrete Structures”
Differentiate between performance criteria for different stages”
Design
Concrete pre-qualification
Quality control during construction
Correlations between chloride ion permeability test results and concrete permeability misleading?
               

17. Case Studies Higashi-Oozu Viaduct, Japan – Self Compacting Concrete
Unsatisfactory surface finishes with conventional concrete
Noise and vibration from plant
Self compacting concrete chosen for these reasons
Material cost increased by 4%, labour cost decreased by 33%, overall saving of 7%
               
SCC still regarded as a special concrete due to higher cost and additional quality control requirements”

18. Results of quality control of SCC

19. Concrete finish achieved on the Higashi-Oozu Viaduct girders

20. Case Studies
· Stolma Bridge, Norway, High Strength Lightweight Concrete
· Completed 1998, balanced cantilever, main span 301m
· Cube strength 69 MPa, density kg/m3
· Aggregate expanded clay or shale
· W/C ratio down to 0.33
· Durability of LWAC structures in Norway investigated extensively over the last 15 years
· LWAC expected to withstand the design life of more than 100 years with comfortable margins
               

21. Stolma Bridge, Norway, High Strength Lightweight Concrete

22. Case Studies The Confederation Bridge, Canada, HPC for Durability
13-km long bridge across the Northumberland Strait Canada. Opened in 1997
Very aggressive environment
Corrosion protection adopted was high performance concrete in combination with increased concrete cover to the reinforcement
Other measures rejected because of high cost/benefit ratio
Diffusion coefficient 4.8 x m2/s at six months - 10 to 30 times lower than conventional concretes.
Low diffusion and increased cover expected to provide 100 year design life.
               

23. The Confederation Bridge, Canada, HPC for Durability

24. Case Studies
Virginia Department of Transport, Specifying for Durability
VDOT plan to obtain low permeability concrete by testing for resistance to chloride penetration.
Four week accelerated curing method is specified
Results similar to those obtained after six months of curing at 73°F (23°C).
Specified maximum Coulomb values are between 1,500 and 3,500.
These requirements were adopted for all HPC projects after 1997
The low-permeability provisions will become a part of an end-result specification
The new specifications addressing durability directly are expected to result in long-lasting and cost-effective bridge decks
               

25. Future Developments
Strength-weight ratio becomes comparable to steel:
               

26. Future Developments
               

27. Summary
· Clear correlation between government/industry initiatives and usage of HPC in the bridge market.
Improved durability the original motivation for HPC use.
Optimum strength grade in the range 60 – 90 MPa, based on cost of initial construction.
Consideration of improved durability and whole of life costing shows further substantial cost savings
HPC usage in Australia limited by code restrictions.

28. Recommendations
· 65 MPa to be considered the standard concrete grade for use in precast pre-tensioned bridge girders and post tensioned bridge decks.
· Mix designs to be optimised to ensure maximum benefit from higher strength grades.
· The use of super-workable concrete to be encouraged
· The use of MPa concrete to be considered where significant benefit can be shown.
· AS 5100 to be revised to allow strength grades up to 100 MPa as soon as possible.
· Optimisation of standard Super-T bridge girders for higher strength grades to be investigated.

29. Recommendations
· Investigation of HPC for bridge deck slabs to enhance durability
· Active promotion of the use of high performance concrete by government and industry bodies:
Review of international best practice
Review and revision of specifications and standards
Education of designers, precasters and contractors
Collect and share experience