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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 - direct economic benefit Saving in materials Reduced construction depth Reduced transport and erection cost. Overview.

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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 - direct economic benefit • Saving in materials • Reduced construction depth • Reduced transport and erection cost

  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 and DR 05252 • Case Studies • Future developments • 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. 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/

  5. International Use of H.P.C. • Used for particular applications for well over 20 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.

  6. 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 • Useage mainly in bridges rather than buildings • Joint government/industry group, BHP 2000 • 70-80 MPa concrete now common in France

  7. 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”

  8. 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

  9. Economics of High Strength Concrete

  10. 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

  11. Economics of High Strength Concrete

  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. Case Studies • Concrete strength: 50 MPa to 100 MPa • Maximum spans for typical 3 lane Super-T girder bridge with M1600 loading • Standard Type 1 to Type 5 girders • Type 4 girder modified to allow higher pre-stress force: • · Increase bottom flange width by 200 mm (Type 4A) • · Increase bottom flange depth by 50 mm (Type 4B) • · Increase bottom flange depth by 100 mm (Type 4C)

  16. Case Studies • · Compressive strength at transfer = 0.7f’c. • · Steam curing applied (hence strand relaxation applied at time of transfer) • · Strand stressed to 80% specified tensile strength. • · Creep, shrinkage, and temperature stresses in accordance with AS 5100. • · In-situ concrete 40 MPa, 160 mm thick in all cases. • · Assumed girder spacing = 2.7 m.

  17. Case Studies

  18. Case Studies - Summary • · Significant savings in concrete quantities and/or construction depth. • Grade 65 concrete with standard girders. • Grade 80 concrete with modified girders and Type 1 and 2 standard girders. • More substantial changes to beam cross section and method of construction required for effective use of Grade 100 concrete.

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

  20. Future Developments

  21. Summary • · Clear correlation between government/industry initiatives and useage of HPC in the bridge market. • Improved durability the original motivation for HPC use. • Studies show direct economic benefits. • HPC usage in Australia limited by code restrictions.

  22. Recommendations • · 65 MPa to be considered the standard concrete grade for use in precast pre-tensioned bridge girders and post tensioned bridge decks. • · 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. • · Investigation of higher strength grades for bridge deck slabs, using membrane action to achieve greater spans and/or reduced slab depth.

  23. Recommendations • · 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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