Hot-Dip Galvanized Reinforcing Steel

A Construction Perspective

Purpose of the Seminar

The purpose of this seminar is to educate engineers,

DOT personnel, contractors, and other specifiers about

the benefits of using hot-dip galvanized reinforcing steel

in concrete projects..

Why would contractors want to use HDG ASTM A767 C1

• Will not be damaged during transportation/installation. NO TOUCH UP

• Shorter lap lengths. LESS STEEL

• Field durability. CAN SIT IN THE SUN

• Meets 75-100 Design-Build Criteria. ACCEPTED BY NYSDOT

• Already in use in NY State. 25+ years of experience with NYSTA bridges.

Learning Objectives

• Upon seminar completion, you will be able to:

• Discuss the hot-dip galvanizing process

• Identify reasons specifiers choose hot-dipped galvanized (HDG) reinforcing steel (corrosion protection, durability, longevity, availability, sustainability, and cost)

• Understand construction and design issues affecting HDG reinforcing steel performance in concrete

Hot-Dip GalvanizingSurface Preparation, Galvanizing, Inspection

Why Galvanize Steel for Corrosion

Protection?

•Durable Barrier Coating

•Cathodic Protection

•Long Life

•Maintenance Free

•Economical

Hot-Dip Galvanizing Process Overview

Barrier Protection

Barrier protection resists

corrosion by isolating the

steel from electrolytes in

the environment

Barrier Protection

• Tenacious Bond• Metallurgically

bonded to steel (3600 psi.)

• Abrasion resistance• Zn-Fe Alloy layers

are harder than base steel

• Ductile Coating• Pure Zn layer bends

w/o cracking

Cathodic ProtectionGalvanic Series of

Metals

ZINC = ANODE

STEEL = CATHODE

This arrangement of metals determines

what metal will be the anode and cathode

when the two are put in a electrolytic cell

(dependent on salt water as electrolyte).

Zinc Patina

ZincZinc OxideZinc HydroxideZinc CarbonateZinc Carbonate

Galvanizing Protection

• Barrier Protection from

external electrolytes

• Cathodic Protection from

Zinc protecting steel

• Zinc patina is passive and

impervious making it a

critical part of HDG’s long-

lasting protection

Why Protect Rebar?

Corrosion of Black BarFe

FeO

Fe3O4

Fe2O3

Fe(OH)2

Fe(OH)3

Fe(OH)3‧3 H2O

0 1 2 3 4 5 6

Volume (cm3）

Veteran’s Memorial Bridge

Visible Signs of Rebar Corrosion

Staining

Spalling Compl

ete

Failure

Crack

ing

STONEHAM ARCH BRIDGE

HGD REBAR IN DECK, ARCHES AND

SUBSTRUCTURE

Stoneham, QC • 2012

I-85/I-385 GATEWAY

PROJECT

Greenville, SC • 2018

Design & Specification

Specifying HDG Reinforcing Steel

➢ ASTM A767

➢ 5.9 mils (150 µm) -Class 1

➢ 3.4 mils (86 µm) - Class 2

➢ Fabricated and straight lengths (60’)

➢ ASTM A123➢ 3.9 mils (100 µm)

➢ Connected to steel fabrications

➢ ASTM A1094 (CGR)➢ not batch HDG

➢ 2.0 mils (50 µm)

➢ Straight lengths (60’)

Bending Before Galvanizing

• Large as possible bend radii

• Avoid embrittlement of steel by cold working

• Smooth bends and hooks

• Use table in ASTM A767

Bending After Galvanizing

• ASTM A767 Class I

• No bend radius limit

• Bend slowly to minimize flaking or cracking

• Not cause for rejection

• Coating can be repaired according to ASTM A780

• ASTM A767 Class II, A123, A1094

• No bend radius limit

• Little/no coating damage during bending

• Coating can be repaired to ASTM A780 as needed

Rebar Durability & Corrosion Resistance

• Abrasion Resistance

• No special handling

• Metallurgical bond (~3,600 psi)

• Uniform Protection, Complete Coverage

• No holidays, no UV degradation

• Sacrificial action – cathodic protection

Coating grows

perpendicular

to the surface

= uniform

coverage

Development of Zinc Compounds

• Before Concrete Sets

• Calcium Zinc Hydroxyzincate

• Help fill voids at concrete/rebar interface

• Makes area less permeable

• Reduces penetrationn of aggressive chlorides

• After Concrete Sets• Zinc Oxide

• Loose, powdery minerals, less voluminous than rust

• Migrate away from rebar, preventing pressure buildup and eventual spalling

• Add to rebar’s bond strength in concrete

JESUP BRIDGE

Jesup, IA • 2013

Zinc’s Initial Reaction in Fresh Concrete

➢Reaction begins immediately upon contact with wet cement solution (highly alkaline)

▪ Hydrogen Evolution (H2)

▪ Calcium Hydroxyzincate (CHZ)

➢Ceases once concrete hardens

➢Surface film stabilizes the zinc

▪ Second level of barrier protection

Reducing Hydrogen Evolution

➢Hydrogen from zinc/concrete reaction stops once concrete sets

➢ASTM A767 and A1094 require HDG chromate passivating of rebar after galvanizing

➢ASTM A123 does not require chromate passivation

THE TIOGA BRIDGE

• PA Rte15 over Mill

Creek, NB • 1974

Economic Advantages

• Initial Cost Benefits

• Overall material and application costs

• Time savings in construction

• Life-Cycle Cost Savings

• Total cost throughout project life

• Includes maintenance costs and time value of money (interest/inflation)

• Often HDG initial cost IS life-cycle cost

• Life-Cycle Costs for Rebar are Complicated

• Core studies (coating on bar, chloride level)

• Deck replacement or concrete failures

• User Costs (future impact to motorists for detours and lane closures) MUST be considered in today's focus on the economy and the environment

Cost Comparison vs Black Bar

Source: NYSDOT Bridge Manual

In Place Cost Ratio

Ind

ex

to

Bla

ck

Bar

1.10 1.201.00

2.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

Black Epoxy HDG -1 Stainless

Effective Service Life

20

50

100

125

0

20

40

60

80

100

120

140

Black Epoxy HDG-1 Stainless

Serv

ice L

ife i

n y

ears

Effective Cost/Service Life

0.05

0.02

0.01

0.02

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Black Epoxy HDG-1 Stainless

Co

st v

s Lif

e R

ati

o

BB

Epoxy

HDG-1

SS

0

20

40

60

80

100

120

140

0.00 0.50 1.00 1.50 2.00 2.50 3.00

Serv

ice L

ife in

years

Cost Index to Black Bar

Service Life to Cost

LIFE AND COST DIMINISHING RETURNS

New York State Thruway Authority

• Authority was concerned about the durability of epoxy in the field during storage and placement

• Conducted an extensive study of epoxy reinforcing steel vs. hot dipped galvanized reinforcing steel.

• Switched to 100% galvanized reinforcing steel for bridges in 1995.

• Still require A767 Class 1 today.

GOVERNOR MARIO M.

CUOMO BRIDGE

Tarrytown,

NY• 2017

Installing Galvanized Rebar

• Same as black bar

• Overlap lengths

• Handling procedures

• Field bending possible

• Touch-up field cut ends

Pennsylvania Route 66 Bridge

In the FieldWelding• Use a slower welding rate

• Maintain proper ventilation

Overlap Lengths

• Identical to uncoated steel rebar

Storage, Handling, and Installation

• Stored outside with no coating degradation

• No special handling or installation required due to coating durability

Handling guide on galvanizedrebar.com

Summary

Assessment Question

•What is the specification for Hot Dipped Galvanized Rebar

1.ASTM A767

2.ASTM A123

3.ASTM A1094

Assessment Question

•What are requirements for handling HDG rebar?

1.Same as Black

2.Same as Epoxy

Assessment Question

• What are two products formed when highly alkaline porewater reacts with Zinc?

1.Calcium Hydrozincate

2.Hydrogen• Minimize by

• Chromate

• Limit Retarder

Assessment Question

What is the required coating thickness of ASTM A767 Class 1 #4 bar?

1.50 microns

2.86 microns

3.129 microns

4.150 microns

Assessment Question

• What is the Expected Functional Service Life of ASTM A767 Class1 rebar?

1.30 years

2.50 years

3.85 years

4.100 years