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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 - durability and workability Reduced permeability High workability Good resistance to segregation

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slide2

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
slide3

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
slide4

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
slide6

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/

slide7

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.
slide8

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.
slide9

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
slide10

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”
slide11

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
slide12

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
slide13

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.
slide15

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.
slide16

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?
slide17

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”
slide20

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

slide22

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.
slide24

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
slide25

Future Developments

  • Strength-weight ratio becomes comparable to steel:
slide27

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.
slide28

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.

slide29

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