Effects Of Pollution On Treated Limestone Rough Draft
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Evaluation of Pollution Uptake on Consolidated Limestone Mary F. Striegel NCPTT
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Transcript of Effects Of Pollution On Treated Limestone Rough Draft
Evaluation of Pollution Uptake on Consolidated Limestone
Mary F. StriegelNCPTT
Air Pollution
Sulfur dioxideNitrogen dioxidePesticidesVolcanoes
Erosion of stone profiles Loss of polish Progressive illegibility of inscriptions Dramatic disintegration
Pollution: An integral part of weathering
Limestone and Marble
LimestoneSedimentary rock Calcium Carbonate fossils
MarbleMetamorphic rock
Acid Rain and Buildings
Chemical weathering- Acidic dissolution of the carbonate minerals Calcite -calcium carbonate Dolomite- calcium magnesium carbonate
What are Stone Strengtheners / Consolidants ?
Pollutants interact with stone, hastening deterioration and loss of surface integrity
Consolidants can be added to increase strength and protect remaining binder
A chemical that holds old decaying stone together
Irreversible
A method of last resort
Protection of Calcerous Stones
• Film forming sealers (drying oils, waxes, plant resins)
• Acrylics• Epoxies
• Stearates• Silicones• Fluoropolymers
• Others (fluorosilicates, fluorides, barium hydroxides, oxalates, lime watering)
Entrapment of moistureClouding /discoloration
Inability to remain attached tocarbonate materials
The Ideal stone Strengthener
Strengthen the stone
Protect against moisture and Pollution
Health / safety and impact on the environment
Issues to Consider
Application techniques
Compatibility with substrate
Durability of treatment
Performance / strengthening value
Depth of Penetration
Effect on appearance
Effect on porosity and permeability
Research focus
Evaluate the success of 4 different stone strengtheners
Trade Name Chemical Family
Eponex 1510 Hydrogenated bisphenol A-epichlohydrin based epoxy resin
Acryloid B-72 Acrylic copolymer
OH 100 Alkoxysilane
HCT Hydroxylating Conversion Treatment
Chemical Structures ?
Methods
Initial analysis Laser Profilometry Colorimetry Fourier Transform Infrared Spectroscopy (FTIR)
Consolidate / Treatment Environmental Chamber
Ion Chromatography Colorimetry FTIR
(a) Laser Profilometry
Methods
Using a laser a surface profile Measurement of each stone is taken
Examples of parameters: Roughness, void volumes, ratio of texture aspects, flatness of distribution
Methods
Record color change of stone samples
Determine magnitude of color change at various intervals throughout experiment
Observation of any color change as a result of the treatment
Track the aging of the treatment
(b) Colorimetry
( c) Fourier Transform Infrared Spectroscopy
Molecules absorb infrared energy at certain frequencies dependent on the types of bonds present
Spectra or graph produced is a fingerprint for the molecules on the surface of the stone
Methods
Methods
Extract solutionat column start
Running column witheluent creating the separation
Testing / separation of ionic species into columns based on the speed by which they travel through a liquid eluent
Examples: chloride, bromide, sulfate,Phosphate, nitrate and weak organic acids
(d) Ion Chromatography
Methods
(e) Application of Treatments
Dipping
Spraying
Ace polyethylene sprayer
Methods(f) Environmental Chamber Exposure
Must provide stable, reproducible, controllable conditions
Temperature typically 25 ºC
Humidity typically 75% RH)
Wind speed typically 40 dm/sec)
SO2 exposure dosage typically 50 ppb
Record reliable data for each, every 3seconds for 10 days
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OH 100 Before Treatment
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OH 100 After Treatment
Roughness of the core (Sk) =20 µm Roughness of valleys (Svk) =29 µm Void volume of valleys (vvv) =0.00612 µm3/ µm2
Roughness of the core (Sk) =17.7 µm Roughness of valleys (Svk) =31 µm Void volume of valleys (vvv) =0.0071 µm3/ µm2
Porosity (dominant factor)
Surface roughness (deep valleys correlate directly with increasing velocity)
Results
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HCT spray Before
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HCT spray After
Roughness of the core (Sk) =22 µm Roughness of valleys (Svk) =27.1 µm Void volume of valleys (vvv) Vvv =0.00998
Roughness of the core (Sk) =18.3 µm Roughness of valleys (Svk) =29.2 µm Void volume of valleys (vvv) =0.00636 µm3/ µm2
Results
ResultsIon Chromatography
Sulfate ions
ResultsSO2 Deposition Velocities
SO2
Stone
Water film
ra –aerodynamic resistance
rb-boundary layer resistance
rc water + rc stone(Surface resistance)
Deposition velocity = Vd = flux / [SO2] = 1 / r total
= 1 / ra + rb + rc
Surface resistance (rc) of materials can be determined if the aerodynamic and boundary layer Resistance (ra +rb) to gas transfer is known
Results
Deposition velocities
-0.5
0
0.5
1
1.5
2
2.5
3
HCT D
IP
OH10
0
Eponex
Unt
reat
ed
HCT S
pray
B72
Treatment
De
po
sit
ion
Ve
loc
ity
(c
m/s
)
Treatment Deposition Velocity
(cm/s)
STDeV
HCT DiP 2.45 0.19
OH100 0.01 0.05
Eponex 1510 0.05 0.03
Untreated 0.27 0.06
HCT spray 1.72 0.15
Acryloid B-72 0.04 0.16
Results
Ongoing Research
Hydrophilicity
Chemical change on treated stone
SEM Image from the Weiss research Group
Attenuated Total Reflection (ATR) FTIR spectroscopy to study the chemical nature of treated stones.
Acknowledgements
National Park Service NCPTT MRP Staff NSU
