Distress, Evaluation, and Repair of Historic Concrete Jarkko Simonen, P.E. Wiss, Janney, Elstner...

Distress, Evaluation, and Repair of Historic Concrete

Jarkko Simonen, P.E.Wiss, Janney, Elstner Associates, Inc.

Introduction

• History• Common Distress Mechanisms– Corrosion– Freeze Thaw– Material problems

• Analysis or Evaluation Methods• Repair

Introduction

• Cement has a long history– Certain types of cement have been

used by the Babylonians, Egyptians, and Romans

– Portland cement 1824– Reinforced concrete 1867

• In the northwest one of the early examples of concrete construction is Fort Casey - 1890

• Generally the use of concrete became common after about 1900

Concrete Vintage Generalizations

Older Concrete (1900 to 1945)– Multiple layers– Placement in lifts– Higher w/c (lower f ’c)– Early reinforcing

systems– Carbonation– No air entrainment

Modern Concrete (1945 to present)– Homogenous pour– Improved placement– Lower w/c (higher f ’c)– Modern reinforcing– Carbonation– Air entrainment?– Admixtures

Introduction

Environment• Wet• Cold• CoastalDeterioration due to the environment• Corrosion• Freeze thaw

Corrosion

• Common in environments that contain salt and moisture• Distress manifests as

staining, cracking, and spalling of the concrete

Concrete provides a great environment for steel against corrosion

Concrete

Problem with rust• Corrosion of the rebar causes rust to form• Rust is 6 to 10 time less dense than steel • Increased volume causes concrete to crack

• Destroys natural passive oxide layer provided by portland cement paste

• Complicated chemical interactions• Hygroscopic

Effects of Chloride Contamination

Chloride Contamination

• Environment (soils, sea water)• Applied (deicing chemicals)• Integral (admixtures, aggregate, water)

CarbonationCarbonation

CO2 + H2O + Ca(OH)2 CaCO3 + H2Oatmospheric rain cement paste limestone water

CO2

NON-CARBONATEDCONCRETE

/ H O2

DEPTH OFCARBONATION

Carbonation

• Advances about 1 mm per year in normal concrete• Once carbonation

reaches steel, the steel is unprotected • Corrosion can affect

large areas

Freeze-thaw weathering regions (ASTM C33)

Freeze-thaw

• Damages the near surface region of concrete• Surface flakes off typically in horizontal layers• More aggressive if surface is exposed to chlorides

Air entrainment can be effective in mitigating freeze-thaw

ASR - Reaction between silica and hydroxyls (OH-) in the pore solution, forming silica gel. As the gel forms, it absorbs water and expands.

OH -

OH -

OH -

OH -

OH -

OH -

OH -

ALKALIS SILICA GEL (REACTION RIM)

SURROUNDINGPASTE

COARSEAGGREGATE

FINEAGGREGATE

ALKALIS SILICA GEL (REACTION RIM)

EXPANSIONCRACK

GEL ENTERINGCRACK

SURROUNDINGPASTE

COARSEAGGREGATE

FINEAGGREGATE

RADIALCRACK

Alkali Silica Reaction• ASR must have all three

components present to cause a problem‐ Reactive aggregates‐ Abundance of alkalis‐ Water

• In the northwest we have two out of three‐ Reactive Aggregates‐ Water‐ Generally cement has low

alkalinity• ASR aggravates F/T and corrosion

Assessment Methods

Field• Visual survey• Mechanical sounding survey• Corrosion assessment

‐ Half-cell potential measurements ‐ Linear Polarization Resistance Method

• Other non-destructive methods (rebound hammer, impact-echo, pulse velocity, etc.)

Assessment Methods

Laboratory• Chloride content• Depth of Carbonation (Phenolphthalein indicator)• Petrographic examination

Condition AssessmentsReferences• ACI 201.1R Guide to Making a Condition Survey of Concrete in Service• ACI 224.1R Causes, Evaluation and Repair of Cracks in Concrete

Structures• ACI 364.1R Guide for Evaluation of Concrete Structures Prior to

Rehabilitation• ACI 437.1R Strength Evaluation of Existing Concrete Buildings• ACI 546R Concrete Repair Guide• Technical Guidelines by International Concrete Repair Institute (ICRI)• Guide to Nondestructive Testing of Concrete• Others

Visual Survey• Identify distress mechanisms• Repair quantities• Repair locations/typesMechanical Survey• Identify hidden distress• Dislodge dangerous fragments• Gives you a better feel about the

concrete quality

Corrosion SurveysHalf cell surveys

– Identify potential areas of corrosion

– Repair quantities– Repair locations/types

Linear Polarization

– Corrosion rate/aggressiveness

NDT Investigative Techniques• Impact echo• Pulse velocity• GPR• Magnetic rebar locators

Laboratory Analysis

• Initial opinion of deterioration and conditions• Type of concrete exposure• Discuss testing with petrographer/chemist• Repair type being considered• Type of testing and expected results

Evaluation for Chlorides

Two methods• Cores• Drill/powder samples

Testing• ASTM C 1152: Acid-

Soluble Chloride in Mortar and Concrete

• ASTM C 1218: Water-Soluble Chloride in Mortar and Concrete

Evaluation for Carbonation

Petrography • ASTM C856: Standard Practice for

Petrographic Examination of Hardened Concrete – Freeze thaw– ASR– Finishing Problems– Identify substrate materials– Etc.

Repair

Concrete repair• Protection/Mitigation• Patch repairs• Reconstruction

Protection/Mitigation

• Coatings– Prevent moisture

• Electrochemical treatments– Cathodic protection– Chloride extraction– Re-alkalinization

• Other – Sealers

• Silanes• Siloxanes

– Migratory corrosion inhibitors

Patch Repairs

Considerations• Compatibility– Strength– Wear– Thermal

• Appearance– Color– Texture– Finish– Profile

Repairs should blend in

Blending Repairs

• Lift lines• Form board lines• Color• Texture

• Surface Preparation– Saw cuts– Rectangular

• Installation – Dry as possible

• Finishing• Curing

Samples and Mock-ups

• Cleaning• Coating removal• Color• Finish• Texture• Surface preparation• Design mix• All installation and finishing

procedures and• Techniques

Repair

Special Considerations with Historic/Architectural Concrete• Tasks are similar of work with other concrete• Options may be more limited• Rules of good concrete repair practice apply• Original design may need to be improved• Emphasis is needed on investigation, laboratory

analysis, samples, mock-ups, and trial repairs

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