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 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 Coastal Deterioration 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)

Carbonation CO 2 + H 2 O + Ca(OH) 2 CaCO 3 + H 2 O atmosphericraincement pastelimestonewater

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.

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 Assessments References 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/types Mechanical Survey Identify hidden distress Dislodge dangerous fragments Gives you a better feel about the concrete quality

Corrosion Surveys Half 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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