Increasing international use of HSC in bridges

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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

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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

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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

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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 Bui
lding a New Generation of Bridges A Strategic
Perspective for the Nation -http//www.cement.o
rg/hp/
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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 1990s.
• Actively promoted for short to medium span
  bridges in N America over the last 10 years.

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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

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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

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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

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Economics of High Strength Concrete
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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

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Economics of High Strength Concrete
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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.

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AS 5100 and DR 05252
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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.

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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)

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Case Studies

• Compressive strength at transfer 0.7fc.
• 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.

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Case Studies
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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.

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Future Developments

• Strength-weight ratio becomes comparable to
  steel

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Future Developments
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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.

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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.

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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