B08_Section_J_Attachment_5_Petrographic_Investigation.pdf

A Twining Company

Petrographic Investigation of One Mortar Sample From Fort Jefferson National Monument Located in Dry Tortugas National Park, Florida

Prepared for Mr. David B. Woodham, PE Atkinson-Noland & Associates, Inc.

Boulder, Colorado

Prepared by Meredith Strow Report No. 227812.d 27 May 2022

2800 Wilderness Place, Suite A Boulder, CO 80301

T: 303.938.0166 www.drpcinc.com http://www.drpcinc.com

Fort Jefferson Counterscarp Wall Petrography Page 1

1.0 INTRODUCTION

Mr. David B. Woodham, PE of Atkinson-Noland & Associates, Inc. (ANA) located in Boulder, Colorado requested DRP, A Twining Company (DRP) to perform petrographic examination on one mortar sample extracted from a counterscarp wall at Fort Jefferson National Monument located in Dry Tortugas National Park, Florida. The purpose of the investigation is to evaluate the composition and condition of the mortar in the submitted sample. On 3 May 2022 Mr. Woodham delivered one mortar sample to DRP labelled Sample #4. The sample was assigned DRP sample number 26YD13399.

Fort Jefferson was constructed between 1845 and 1876 such that no information regarding the original project materials are available. The location of the structure on a remote island in the Gulf of Mexico provides exposure to heat, salt, destructive weather systems and water. No information was provided regarding the field condition of the sample that was submitted for petrographic examination.

2.0 SCOPE OF WORK

The testing involved petrographic examination according to ASTM C856 [ ]. This report 1 describes the findings of the investigation. Appendix A contains the notes, photographs and micrographs from the petrographic examination. Appendix B summarizes the procedures used to perform this scope of work.

3.0 FINDINGS

Details of the sample composition and condition are provided below. The figures referenced herein are located in Appendix A.

• General Observations. The sample is an irregularly shaped piece of mortar measuring ~80 x 75 x 50 mm (3 ⅛ x 3 x 2 in.) (Figure A1). Two surfaces are gray to dark gray globular surfaces and the remaining surfaces are irregular, fractured surfaces such that the sample represents a partial thickness of the mortar within the wall (Figures A1-A3).

• Cracks and microcracks. No cracks are present in the sample. Few randomly oriented <25-75 µm (<1-3 mil) wide microcracks are observed in the body of the paste in thin section (Figure A4).

• Paste. The paste on two exterior surfaces is gray to dark gray (Munsell Soil Color GLEY 1 4-5/N) and remainder of the mortar exhibits an off white to very light beige color (Munsell

Standard Practice for Petrographic Examination of Hardened Mortar. Annual Book of ASTM Standards, Vol. 4.02., ASTM 1 C856-20.

Report No. 227812.d 27 May 2022

Fort Jefferson Counterscarp Wall Petrography Page 2

Soil Color 7.5YR 9.5/1). Paste throughout the sample is very soft to soft (Mohs <2-2.5) with a rough texture and dull luster (Figure A5). The paste consists of natural cement and lime (Figures A6-A9). The amount of observed residual cement is estimated at <5% by volume of paste. The amount of observed lime lumps is estimated at <5% by volume of paste. No distinct calcium hydroxide is observed in the paste. The paste throughout the sample exhibits high to very high capillary porosity (Figure A10).

• Aggregate. The aggregate is a natural gravel and sand with a ~12.5 mm (½ in.) nominal top size (Figure A11). The aggregate is carbonate in composition, consistent with beach aggregate, and comprises of various limestones, calcite and coral fragments. No evidence of ASR or ACR is observed. No low w/c mortar coatings, deleterious coatings or encrustations are observed on particles.

• Voids. The mortar is non-air-entrained with total air content estimated at less than 3%. Voids are free of secondary deposits.

• Secondary Deposits. The paste partially to fully carbonated throughout the sample (Figure A12). Few regions in thin section show non-carbonated paste. Layers of calcium carbonate are observed on the outer surfaces of the mortar (Figure A13). Other than calcium carbonate in the form of paste carbonation and secondary layers on exterior surfaces, no secondary deposits are observed.

4.0 CONCLUSIONS

The findings from this scope of work indicate the Sample #4 consists of carbonate aggregate with a 12.5 mm (½ in.) nominal top size bound in a non-air-entrained natural cement and lime paste binder. Binder composition is consistent with historical natural cement, such as Rosendale cement. The sample is friable with paste that is very soft (Mohs <2) and off white to very light beige color (Munsell Soil Color 7.5YR 9.5/1). Exterior surfaces show gray to dark gray color (Munsell Soil Color GLEY 1 4-5/N). Paste capillary porosity is very high and the paste is highly absorptive. Partial to full carbonation of the paste is observed in the majority of the sample. The aggregate fraction aggregate comprises of various limestones, calcite and coral fragments.

This concludes work performed on this project to date.

Meredith Strow Principal Petrographer

Report No. 227812.d 27 May 2022

Fort Jefferson Counterscarp Wall Petrography

Appendices

Appendix A Sample #4 Petrography (ASTM C856) Appendix B Procedures drpcinc.com

APPENDIX A: Fort Jefferson Counterscarp Wall Petrography Report No.: 227812.d Sample ID: Sample #4 (26YD13399) Date: 27 May 2022

1. RECEIVED CONDITION

ORIENTATION &

DIMENSIONS

Sample is an irregular portion of mortar taken from a counterscarp wall; sample measures ~80 x 75 x 50 mm (3 ⅛ x 3 x 2 in.) (Figure A1).

SURFACES

Two surfaces are dark gray to black globular surfaces and the remaining surfaces are irregular, fractured surfaces such that the sample represents a partial thickness of the mortar within the wall (Figure A1, Figure A2).

GENERAL CONDITION The sample was received in one piece (Figure A1, Figure A3).

2. EMBEDDED OBJECTS

GENERAL None present. No reinforcement (steel bar, wire mesh, fibers) is observed.

3. CRACKING

MACROSCOPIC None present.

MICROSCOPIC Few randomly oriented <25-75 µm (<1-3 mil) wide microcracks are observed in the body of the paste in thin section (Figure A4).

4. PASTE OBSERVATIONS

POLISHED SURFACE

Paste on two exterior surfaces is gray to dark gray (Munsell Soil Color GLEY 1 4-5/ N) and remainder of mortar exhibits an off white to very light beige color (Munsell Soil Color 7.5YR 9.5/1). Paste throughout the sample is very soft (Mohs <2) with a rough texture and dull luster (Figure A5). Paste exhibits high absorbency; water droplets are quickly absorbed by the paste.

THIN

SECTION

The paste consists of natural cement and lime (Figures A6-A9). The amount of observed residual cement is estimated at <5% by volume of paste. The amount of observed lime lumps is estimated at <5% by volume of paste. No distinct calcium hydroxide is observed in the paste.

CAPILLARY POROSITY The paste throughout the sample exhibits high to very high capillary porosity (Figure A10).

5. AGGREGATE

PHYSICAL PROPERTIES

The aggregate is a natural gravel and sand with a ~12.5 mm (½ in.) nominal top size (Figure A11). The particles range from equant to elongated in shape with sub-rounded to sub-angular edges and smooth to rough surfaces. Aggregate distribution is fairly uniform and gradation is fairly even.

ROCK TYPES

The aggregate is carbonate in composition and comprises of various limestone, calcite and coral fragments, consistent with beach sand (Figure A11). Limestone particles are commonly fossiliferous. No particles are potentially susceptible to alkali-silica reaction (ASR) or alkali-carbonate reaction (ACR).

OTHER FEATURES No evidence of ASR is observed. No evidence of ACR is observed. No deleterious coatings or encrustations is observed. No low w/c mortar coatings is observed.

6. VOIDS

VOID SYSTEM The mortar is non-air-entrained with total air content estimated at less than 3%. The mortar exhibits no notably large entrapped voids.

VOID FILLINGS Voids are free of secondary deposits.

7. SECONDARY DEPOSITS

PHENOLPHTHALEIN The paste partially to fully carbonated throughout the sample (Figure A12). Few regions in thin section show non-carbonated paste.

SECONDARY DEPOSITS

Layers of calcium carbonate are observed on the outer surfaces of the mortar (Figure A13). Other than calcium carbonate in the form of paste carbonation and secondary layers on exterior surfaces, no secondary deposits are observed.

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FIGURES

(a)

(b)

Figure A1. Photographs of the sample in as-received condition showing (a) an oblique view of the sample showing outer surfaces and (b) oblique view of the sample showing interior surfaces. The red and blue dots in

(a) show the orientation of the saw cuts used to prepare the sample. The yellow scale is ~150 mm (6 in.) long;

small and large divisions are in centimeters and inches, respectively.

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(c)

(d)

Figure A1 (cont’d). Photographs of the sample in as-received condition showing (c) exterior surface and

(d) interior surface of the sample. The red and blue dots in (c) show the orientation of the saw cuts used to prepare the sample. Small and large divisions on the yellow scale are in centimeters and inches, respectively.

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(a)

(b)

Figure A2. Photographs showing detail of the (a) exterior surface and (b) interior surface of the sample. Scale in both images shows millimeter increments.

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Figure A3. Photograph of the polished surface prepared from the sample. The yellow scale is ~150 mm (6 in.)

long; small and large divisions are in centimeters and inches, respectively.

Figure A4. Fluorescent transmitted light thin section photomicrograph showing randomly oriented microcracks (red arrows) in the paste.

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(a)

(b)

Figure A5. Images showing detail of paste. (a) Photograph of the polished surface showing overview of paste in the outer portion of the sample (exterior surface at top of image). Scale shows millimeter increments.

(b) Reflected light photomicrograph showing detail of paste in the body of the sample.

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(a)

(b)

Figure A6. Transmitted light photomicrographs of thin section showing detail of the paste in (a) plane-polarized and (b) cross-polarized light. Red arrows in (a) indicate residual cement particles. Yellow arrows in

(b) indicate lime lumps.

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(c)

(d)

Figure A6 (cont’d). Transmitted light photomicrographs of thin section showing detail of the paste in

(c) cross-polarized light with the gypsum plate inserted and (d) cross-polarized light with the quarter wave plate inserted.

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Figure A7. Plane-polarized transmitted light photomicrograph showing residual cement particles (red arrows) in thin section.

Figure A8. Reflected light photomicrograph showing lime lumps (yellow arrow) on the polished surface of the sample.

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(a)

(b)

Figure A9. Transmitted light photomicrographs of thin section showing detail cement particle (encircled red) and lime lump (encircled yellow) in (a) plane-polarized and (b) cross-polarized light.

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(a)

(b)

Figure A10. Transmitted fluorescent light photomicrographs of thin section showing detail of paste in two different regions in the middle of the sample. The black areas correspond to aggregate that has very low or effectively zero percent porosity and the bright green circles are air voids filled with epoxy that have 100% porosity. The variations in green between these end members reflect variations in the capillary porosity or micro-density of the paste.

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(a)

(b)

Figure A12. Images dewing detail of aggregate. Reflected light photomicrographs of the polished surface showing overview of the (a) coarser aggregate particles (red arrows) and (b) finer aggregate particles in the sample.

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(c)

(d)

Figure A11 (cont’d). Images dewing detail of aggregate. Cross-polarized transmitted light photomicrographs showing detail of aggregate particles in thin section.

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Figure A12. Photograph showing overview of phenolphthalein-stained surface of the sample. Scale shows millimeters.

Figure A13. Cross-polarized transmitted light thin section photomicrograph showing calcium carbonate layers (encompassed by red bracket) on the exterior surface.

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Appendix B: Fort Jefferson Counterscarp Wall Petrography Report No.: 227812.d Procedures Date: 27 May 2022

PROCEDURES

Petrographic Examination (ASTM C856) The petrographic work was done following ASTM C856 [ ] with sample preparation done at DRP in the following manner. After writing the unique 1 DRP sample number on the sample near its received label, the sample was measured and inspected visually and with a hand lens. The orientation of the saw cuts used to prepare the sample was then indicated on the top surface of the sample with blue and red dots. The sample was then photographed in their as-received condition.

A slab representing a longitudinal cross section of the sample was cut from the central portion of each sample using a Raimondini Zipper-105®, a 14-inch diameter water-cooled saw. This produced three (3) longitudinal sections of the sample. These sections were rinsed and oven dried in a Gilson® Bench Top laboratory oven at ~43°C (~110°F). After drying, each piece was labelled with the appropriate DRP sample number. One piece was set aside for phenolphthalein staining and the other was set aside for thin section preparation.

The central slab was then lapped and polished on a Diamond Pacific® RL-18 Flat Lap machine.

This machine employs an 18-inch diameter cast iron plate onto which Diamond Pacific® Magnetic Nova Lap discs with progressively finer grits are fixed. The Nova Lap discs consist of a 1/16 in. backing of solid rubber containing magnetized iron particles that is coated with a proprietary Nova resin-bond formula embedded with industrial diamonds of specific grit. The slab preparation involved the use of progressively finer wheels to a 3000 grit (~4 µm) final polish following procedures outlined in ASTM C457 [ ]. An aqueous lubricant is used in the 2 lapping and polishing process. The polished slab was examined visually and with a Nikon® SMZ-25 stereomicroscope with 3-158x magnification capability following to the standard practice set forth in ASTM C856.

Phenolphthalein was applied to a freshly saw-cut surface from the sample to assess the extent of carbonation, along with thin section analysis. Phenolphthalein is an organic stain that colors materials with pH of greater than or equal to ~9.5 purple. Portland cement concrete generally has a pH of ~12.5. Carbonation lowers the pH of the paste below 9.5, so areas not stained by phenolphthalein are an indicator of carbonation. The depth of paste not stained by phenolphthalein was measured from each exposed surface.

A petrographic thin section was prepared by cutting a billet from the remaining longitudinal section from the sample. Outlines marking the area of the billet were drawn with a marker on the saw-cut surface after visual and microscopical examination of saw-cut and polished surfaces.

The billet was labeled with the unique DRP number assigned to the sample then fixed to reference glass with a clear ultra-violet light-activated glue. After the glue hardened, the billet

Standard Practice for Petrographic Examination of Hardened Concrete. Annual Book of ASTM Standards, Vol. 4.02., ASTM 1 C856-20.

Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete, Annual 2

Book of ASTM Standards, Vol. 4.02, ASTM C457-16.

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Appendix B: Fort Jefferson Counterscarp Wall Petrography Report No.: 227812.d Procedures Date: 27 May 2022 was trimmed and then fixed to a slide with a clear UV activated glue. The billet was then ground and and impregnated with an epoxy that contained fluorescent dye. The impregnated billet was then ground and polished to a thickness of 20-25 µm using a PELCON® automatic thin section machine. The thin section was examined with a Nikon® E-Pol 600 petrographic microscope equipped to provide a 20-1000x magnification range following the standard practice set forth in

ASTM C856.

W/CM & Capillary Porosity Estimation Estimation of the w/cm of the paste is obtained from consideration of the color, texture and luster of the paste observed in reflected light, the hardness (Mohs) of the paste measured using calibrated probes, the packing of cementitious materials and the size and abundance of calcium hydroxide observed in plane and cross-polarized transmitted light, and the green tone of images obtained using fluorescence microscopy. In cases where pervasive carbonation occurs, the original w/cm cannot be estimated quantitatively. Image analysis methods of photomicrographs obtained in transmitted fluorescent light can be used to obtain quantitative measurements of the relative capillary porosity of the paste in such samples.

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