Austroads Bridge ConferencePerth September 2005

High Performance Concrete

in Bridge Decks

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

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

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

What is High Performance Concrete?

Table B80/3.1 Wet Curing Requirements (Part)

Exposure Other requirements

classification Minimum Maximum Minimum

cement w/c ratio strength for

content (by mass) durability

(kg/m 3 ) f c.min(d)

(MPa)

A 320 0.56 25

B1 320 0.5 32

B2 370 0.46 40

C 420 0.4 50

U In accordance with Annexure B80/6

w/c denotes total water to total cement ratio

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 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.

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.

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

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

• 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

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.

AS 5100 and DR 05252Subject

AS 5100 DR 05252 AS 5100 DR 052521.1.2 1.1.2 Concrete srength and

density range25-65 MPa, 2100-2800 kg/m3 20-100 MPa, 1800-2800 kg/m3

1.5.1 - Use of alternative materials Alternatives allowed Clause removed

2.2 2.2 Strength reduction factors Phi reduced for ku > 0.4 Phi reduced for ku > 0.375

2.5.2 - Fatigue provisions Maximum stress under fatigue loading = 18 MPa

Not included

6.1.1(b,c)

3.1.1.2(b) Tensile strength From compressive strength or tests From flexural or tensile tests, upper and lower bound factors applied if compressive strength used

6.1.2 3.1.2 Modulus of elasticity Proportional to square root fc Revised for higher strength grades6.1.7 3.1.7 Shrinkage Default basic shrinkage strain

independent of concrete strengthAutogeneous and drying shrinkage calculated separately, both related to concrete strength

6.1.8 3.1.8 Creep Basic creep factor constant for f'c >= 50 MPa

Basic creep factor increased for f'c = 40, 50 MPa; reduced for f'c >= 80 MPa

6.4.3.3 3.4.3.3 Loss of prestress due to creep

Default creep factor uses prestress force before time-dependent losses.

Default creep factor reduced to 80% of AS 5100 value

8.1.2.2 8.1.3 Rectangular stress block Stress = 0.85f'c Stress = (1.0-0.003f'c)f'c with limits of 0.67 and 0.85

8.2.7.1 8.2.7.1 Shear strength of beams excluding shear reinforcement

Shear strength proportional to f'c1/3 f'c

1/3 limited to 4 Mpa, ie no increase in shear strength for f'c > 64 MPa

8.2.8 8.2.8 Minimum shear reinforcement

Independent of concrete strength Increased area for f'c > 36 MPa

8.6.1(a) 8.6.1(a) Minimum steel area in tensile zone

3ks(Act/fs) Cl 8.1.4.1 (minimum strength requirements) applied

9.1.1 9.1.1 Minimum tensile steel in slabs

Independent of concrete strength Increased area for f'c > 30 MPa approx

Clause Provisions

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.

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?

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”

Results of quality control of SCC

Concrete finish achieved on the Higashi-Oozu Viaduct girders

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

Stolma Bridge, Norway, High Strength Lightweight Concrete

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.

The Confederation Bridge, Canada, HPC for Durability

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

Future Developments

• Strength-weight ratio becomes comparable to steel:

0

5

10

15

20

25

30

35

40

45

Structural steel Concrete High strengthconcrete

Lightweight HSC

Strength-Weight Ratio

Future Developments

SummaryClear 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.

Recommendations65 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 encouragedThe 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.

RecommendationsInvestigation 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