CIA Biennial Conference Melbourne October 2005 High Performance

CIA Biennial Conference Melbourne October 2005 High Performance Concrete in Bridge Decks Opportunities for Innovation

Introduction • Increasing international use of HSC in bridges • Mainly in response to durability problems; deicing salts; freeze-thaw conditions • Focus of this paper - direct economic benefit • Saving in materials • Reduced construction depth • 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 2/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

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 • 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 05252

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 M 1600 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 4 A) · Increase bottom flange depth by 50 mm (Type 4 B) · Increase bottom flange depth by 100 mm (Type 4 C)

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

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.

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

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