WHEN FIELD PERFORMANCE OF MASONRY DOES NOT CORRELATE WITH LAB TEST RESULTS

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WHEN FIELD PERFORMANCE OF MASONRY DOES NOT CORRELATE WITH LAB TEST RESULTS

Peter R. Meijer, AIAPeter Meijer Architect, PC

Outline

BackgroundHistory of DeficienciesBrick ManufacturingVisual ObservationField TestingLab Testing

Background

Historic High School

5

Grant Baseball Team 1926Alterations Over Time

6

SE corner of school (No Date)

Alterations Over Time

7

Grant Baseball Team 1951

Alterations Over Time

8

Old Gym 1963-64

Alterations Over Time

9

Multi-light wood windows

Terra cotta moldingsMasonry Details

10

Terra cotta friezes and cornicesMasonry Details

11

Brick details and blind windows

Original window size & proportionMasonry Details

12

Cast-Iron details

Terra cottadetailsMasonry Details

13

History of Deficiencies

Comparative Photographs

15

Comparative Photographs

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Comparative Photographs

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Comparative Photographs

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Brick Manufacturing

Brick Manufacturing

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Brick Composition

BrickmakingMiningPreparationMoldingDryingFiringBrick CompositionClay chemical compound of silica, alumina and metallic oxides (color)WaterAdditives - sand

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Brick Products

Image: National Building Museum

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Common Deficiencies

Common Deficiencies Poor construction

Material composition

Weather

Human intervention

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Common DeficienciesCOMMON SOURCE OF EFFLORESCENCEPrincipal Efflorescing Salt Most Probable SourceCalcium sulfateCaSO42H2OBrickSodium sulfateNa2SO410H2O Cement-brick reactionsPotassium sulfate K2SO4Cement-brick reactionsCalcium carbonate CaCO3 Mortar or concreteSodium carbonate Na2CO3 MortarPotassium carbonate K2CO3 MortarPotassium chloride KCl Acid CleaningSodium chloride NaCl Sea WaterVanadyl sulfate VOSO4 BrickVanadyl chloride VOCl2 Acid CleaningManganese oxide Mn3O4 BrickIron oxide Fe2O3 or Fe(OH)3Iron in contact or brickw ith "black core" orblack heartCalcium hydroxide Ca(OH)2 Cement

Efflorescence low firing

Salts:Carbonates - mortarSulfates - brickChlorides - additives

Typical:Sodium (Na)Potassium (K)Calcium (Ca)

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Common Deficiencies

Cracking Poor firing; Fast cooling

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Common Deficiencies

Discoloring Impurities

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Common Deficiencies

Deformities Poor Firing

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Common Deficiencies

High Porosity volume relation

volume of voids : volume of the total

Permeability

High Absorption weight relation

weight dry : weight wet

Capillary suction

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Visual Observations

Exterior Visible Damage

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Exterior Visible Damage

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Exterior Visible Damage

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Exterior Visible Damage

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Exterior Visible Damage

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Multiple Surface Deficiencies

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Exterior Visible Masonry Damage

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Historic Document Review:Wall Construction

Wall Construction

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Wall Construction

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Wall Construction

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Wall Construction

National Terra Cotta Society, Terra Cotta Standard Construction, 1927

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Wall Construction

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Wall Construction

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Field Testing

Wall lets

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Wall lets

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Wall lets

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Field Testing

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Field Testing

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Lab Testing

BIA TABLE 4Physical Properties in Brick Specifications

Lab Testing

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Lab Testing

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All three samples showed silica as the binding mechanism, thus do not appear to have had an applied coating. The sampling fracture planes, following the surfaces in these samples, suggests the silica may have been recrystallized and hardened by subsequent atmospheric exposure

Masonry Coatings FTIR Evaluation

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. precipitated calcium carbonate (probably calcite) and opal-hydrous silica Clay minerals were not observed. A few encapsulated frustules (shells) of diatoms and fibers from fabrics were also recovered within the deposit in a manner suggesting rain and/or service water allowed dissolved calcium and silica from the mortar to seep laterally onto this surface and mineralize

Lab Testing: Surface Salt Deposition

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Mortar Sample

High magnication photo shows more detail on the porosity within the cementing matrix. This type of porosity looks as though it formed after formulation of the mortar and could be due to dissolution of unstable granular components. If so, then the increased porosity of the interior of the mortar may be related to water movement through the mortar .Electron Microscopy

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Mortar Sample

the total porosity of the interior of this mortar sample is about 3X that of the outer edge of the sample. The reduced porosity of the outer edge of the mortar could be a function of smearing of the exposed joint during finishing of the mortar. External pressure on the mortar surface would probably reduce the porosity of a thin zone. Electron Microscopy

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Mortar Sample

The primary difference between the edge mortar and the internal mortar is related to the amount of porosity in the cement matrix. The edge mortar shows only about 3% porosity, whereas the interior cement has nearly 8% porosity

The lime : aggregate ratio of this sample is about 48:52, or nearly 1:1, after removing minor amounts of porosity . Electron Microscopy

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Brick Sample #2

Yellow-stained K-feldspar represents remnants of patching material that entered irregularities in the brick failure surface. The brick shows scattered large voids and planar void traces that often connect larger voids. The dark spots are areas of enhanced oxidation. The sandy material at the left edge of the brick represents lime mortar, rich in volcanic sand, that fills joints between the bricks.Electron Microscopy

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Electron Microscopy

Brick sample #3 The brick is transected by numerous planar and irregular voids that are often interconnected and provide pathways for water percolation through the brick, as well as possible locations for freeze/thaw damage. The center of the thin section shows a zone with complex interconnected porosity (blue areas) that may have developed during firing of the clay (shrinkage cracks). The common occurrence of large planar voids contributes to an increased risk of brick failure along these surfaces.

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Conclusions

Failure mechanism inherent in manufacturing process. Likely due to poor bonding of clay during extrusion.Low IRA is good and due to small diameter capillaries within brick. However, there is a correlation between small diameter capillary and susceptibility to expansion failures.Salts in cement based mortars are leaching into the masonry over long periods of time. Upon drying, expansion of the salts within capillaries causing excessive force.Some micro-climate freeze thaw may be occurring

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Next Steps

Recommendations

Control water100% repointing with lime based mortarReplace all failed brick unitsNo sealers due to high maintenance requirementFurther invasive openings at structural steel locations

63

Key Points

Use your knowledge and ALL the visual cluesAVOID leaping to a conclusionDevelop THEORIES for the damageSystematically TEST the theoriesConduct FIELD evaluationConduct LAB testsAre the RESULTS what you expectedIt takes TIME

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Thank You

Peter R. Meijer, AIAPeter Meijer Architect, PC

Maximum ColdWater Absorption,%MaximumFive-Hour BoilingAbsorption, %Maximum SaturationCoefficient

Average of 5 brickIndividualAverage of 5 brickIndividualAverage of 5 brickIndividual

C 62GradeSW17.020.00.780.80

MW22.025.00.880.90

NWNo limitNo limitNo limitNo limit

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