CIA Biennial Conference Melbourne October 2005

High Performance Concrete in Bridge Decks Opportunities for Innovation

Introduction

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Increasing international use of HSC in bridges Mainly in response to durability problems; de icing salts; freeze-thaw conditions

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Focus of this paper - direct economic benefit

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Saving in materials Reduced construction depth

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Reduced transport and erection cost

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

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

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 /

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.

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

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”

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

Economics of High Strength Concrete

Spacing, m Section AAASHTO Type I AAASHTO Type II AAASHTO Type III AAASHTO Type IV NU1100 NU1350 3.4

90 90 83 83 83 83 0.6 in diameter strands 2.7

83 90 83 83 76 76 2.1

83 90 83 83 76 69 1.5

83 83 76 83 76 69 3.4

76 76 76 62 62 62 0.5 in diameter strands 2.7

76 76 69 62 Table 1 Maximum effective girder compressive strength, after Kahn and Saber (34) 62 62 2.1

69 76 69 62 62 62 1.5

69 76 62 62 62 55

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

Economics of High Strength Concrete

AS 5100 Provisions for HSC

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Maximum compressive strength; 65 MPa Cl. 1.5.1 - Alternative materials permitted

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Cl 2.5.2 - 18 MPa fatigue limit on compressive stress - conservative for HSC

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Cl 6.11 - Part 2 - Deflection limits may become critical

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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.

AS 5100 and DR 05252

Clause AS 5100 DR 05252 1.1.2

1.1.2

1.5.1

Subject Concrete srength and density range AS 5100 25-65 MPa, 2100-2800 kg/m3 Use of alternative materials Alternatives allowed Provisions DR 05252 20-100 MPa, 1800-2800 kg/m3 Clause removed 2.2

2.5.2

6.1.1

(b,c) 6.1.2

6.1.7

6.1.8

6.4.3.3

8.1.2.2

8.2.7.1

8.2.8

8.6.1(a) 9.1.1

2.2

3.1.1.2(b) Tensile strength 3.1.2

3.1.7

3.1.8

3.4.3.3

8.1.3

8.2.7.1

Strength reduction factors Fatigue provisions Modulus of elasticity Shrinkage Creep Loss of prestress due to creep Rectangular stress block Shear strength of beams excluding shear reinforcement 8.2.8

Minimum shear reinforcement 8.6.1(a) Minimum steel area in 9.1.1

tensile zone Minimum tensile steel in slabs Phi reduced for k u > 0.4

Phi reduced for k u > 0.375

Maximum stress under fatigue loading = 18 MPa Not included From compressive strength or tests From flexural or tensile tests, upper and lower bound factors applied if compressive strength used Proportional to square root fc Default basic shrinkage strain independent of concrete strength Basic creep factor constant for f'c >= 50 MPa Revised for higher strength grades Autogeneous and drying shrinkage calculated separately, both related to concrete strength Basic creep factor increased for f'c = 40, 50 MPa; reduced for f'c >= 80 MPa Default creep factor uses prestress Default creep factor reduced to force before time-dependent losses.

80% of AS 5100 value Stress = 0.85f'c Shear strength proportional to f' c 1/3 Stress = (1.0-0.003f'c)f'c with limits of 0.67 and 0.85

f' c 1/3 limited to 4 Mpa, ie no increase in shear strength for f'c > Independent of concrete strength 64 MPa Increased area for f'c > 36 MPa 3k s (A ct /f s ) Independent of concrete strength Cl 8.1.4.1 (minimum strength requirements) applied Increased area for f'c > 30 MPa approx

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.

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)

Case Studies

  Compressive strength at transfer = 0.7

f’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.

Case Studies

1 2 3 4 5 4A 4B 4C Type Depth mm 750 1000 1200 1500 1800 1500 1500 1500 A mm2 454,084 491,409 531,021 573,592 616,426 680,172 592,772 618,612 Precast I mm4 3.280E+10 6.675E+10 1.043E+11 1.756E+11 2.658E+11 1.971E+11 1.798E+11 1.840E+11 Yc mm 389 515 613 776 946 627 760 743 Section Properties A mm2 Composite I mm4 887,584 924,909 7.685E+10 1.412E+11 964,521 2.112E+11 1,007,092 3.357E+11 1,049,926 4.886E+11 1,113,672 4.383E+11 1,026,272 3.488E+11 1,052,112 3.632E+11 Yc mm 604 779 913 1,122 1,331 998 1,106 1,088 Max No Strands 50 50 50 50 50 82 62 74

Super-T Maximum Span

55 50 45 80 MPa 40 35 65 MPa 50 MPa 30 25 18.00

20.00

22.00

24.00

26.00

28.00

30.00

Maximum Span, m

32.00

34.00

36.00

38.00

Type 1 Type 2 Type 3 Type 4 Type 5

Super-T Maximum Span

85 80 75 70 65 60 55 50 45 33 50 MPa 34 80 MPa 35 65 MPa 36 37

Maximum Span, m

38 39 40 Type 4 Type 4A Type 4B Type 4C

Case Studies - Summary

 Significant savings construction depth.

in concrete quantities and/or • 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.

Future Developments

• Strength-weight ratio becomes comparable to steel: Strength-Weight Ratio 45 40 35 30 25 20 15 10 5 0 Structural steel Concrete High strength concrete Lightweight HSC

Future Developments

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.

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.

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 standards – Education of designers, precasters and contractors – Collect and share experience and