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Introduction

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

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Introduction

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  1. 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

  2. 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

  3. 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

  4. What is High Performance Concrete?

  5. Information on H.P.C. · “Bridge Views” – http://www.cement.org/bridges/br_newsletter.asp · “High-Performance Concretes, a State-of-Art Report (1989-1994)” - http://www.tfhrc.gov/structur/hpc/hpc2/contnt.htm · “A State-of-the-Art Review of High Performance Concrete Structures Built in Canada: 1990-2000” - http://www.cement.org/bridges/SOA_HPC.pdf · “Building a New Generation of Bridges: A Strategic Perspective for the Nation” -http://www.cement.org/hp/

  6. 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.

  7. 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.

  8. 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

  9. 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: 1990-2000”

  10. 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

  11. 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

  12. AS 5100 Provisions for HSC • Maximum compressive strength; 65 MPa • Cl. 1.5.1 - Alternative materials permitted • Cl 2.5.2 - 18 MPa fatigue limit on compressive stress - conservative for HSC • Cl 6.11 - Part 2 - Deflection limits may become critical • Cl 6.1.1 - Tensile strength - may be derived from tests • Cl 6.1.7, 6.1.8 - Creep and shrinkage provisions conservative for HSC, but may be derived from test.

  13. AS 5100 and DR 05252

  14. 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.

  15. 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?

  16. 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”

  17. Results of quality control of SCC

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

  19. Case Studies · Stolma Bridge, Norway, High Strength Lightweight Concrete · Completed 1998, balanced cantilever, main span 301m · Cube strength 69 MPa, density 1900-1950 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

  20. Stolma Bridge, Norway, High Strength Lightweight Concrete

  21. 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 10-13 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.

  22. The Confederation Bridge, Canada, HPC for Durability

  23. 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

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

  25. Future Developments

  26. 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.

  27. 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 80-100 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.

  28. 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

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