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All you wanted to know about roofing slate and you were afraid to ask
Some questions (and answers) about roofing slate
by Victor Cárdenes
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NSA 2016 Annual Meeting, March 3-6 Philadelphia
• What is a roofing slate? (from a geological point of view)
• Who many types of roofing slates exist?
• What about pyrite?
• What about carbonates?
• What about ribbons?
• Some remarks about standards
• How are the slates from Europe/China/Brazil?
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TWO DIFFERENT TERMS!
- ROOFING SLATE: Commercial term, refers to any rock able to be split and used for roofing
- SLATE: Geological term, refers to a specific type of rock
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What is a roofing slate?
Not all slates can be used for roofing, and not all roofing slates are slates
Roofing slates are metamorphic rocks
4
MUDP
RES
SU
RE
TE
MP
ER
ATU
RE
TIM
ESLATE
PHYLLITE
LOW-GRADE SLATE
SCHIST
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CLEAVAGE 1) Sedimentation 2) Lithostatic compression
3) Tectonic compression
a) b)Cleavage
Mud
Sand
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Cleavage allows splitting
Pneumatic chisel
Hammer and chisel
Alignment of the mica minerals
0.1 mm
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Cleavage vs. flexural strength
Mayen, Germany
Minas Gerais, Brazil
Otta, Norway
Penrhyn, WalesValentia, Ireland
Lugo, Spain
Cle
avag
e
Flexural strenght
203000
405800
608700
MPaPSI
0 6001100
400750
200400
°C°F
Pressure vs. Temperature
META
MO
RPH
ISM
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Who many types of roofing slates exist?
Low-grade slate Slate
Phyllite Schist
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10
TONS Millions $
Low-grade slate25.0%
Slate73.0%
Schist1.0%
Phyllite1.0%
Low-grade slate38.0%
Slate60.0%
Schist1.0%
Phyllite1.0%
Estimation of the total volume of roofing slate production depending on the type of rock
Source: Personal data and United Nations COMTRADE Database
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Roofing slates are also classified by their color
Three color families: - Black Gray (B) - Green (G) - Red-Purple (R)
Mayor mineral components • Quartz • Mica • Chlorite Accessory components (<2%) Iron sulphides (pyrite): B, G Organic matter (carbon): B, g Iron oxides (hematite): R
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The combination of the rock type and the color family establishes the classification for roofing slates
Roofing slate lithotypes
LOW GRADE SLATES
0SLATES
1SCHISTS
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PetrographiccodeColor
code
BLACK-GRAYB
GREENG
PURPLE-REDR
B0Black-gray low grade slates
B1Black-gray slates
Black-gray phyllites
B2 B3Black-gray schists
G0Green low grade slates
Green slatesG1 G2
Green phyllites
Green schistsG3
R0Purple-red low grade slates
R
Purple-red slates1 R2
Purple-red phyllitesR3
Purple-red schists
PHYLLITES
2
Octahedron
“Dollar”
Fossils
Framboids
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What about pyrite?
Iron Sulphides: Pyrite (FeS2) and Pyrrhotite (FeS1-x)
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Sometimes, these minerals might cause trouble
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How works oxidation?
SO2 H O2
Oxidation is triggered by weather conditions
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Oxidation grades according to EN 12326-2
T1 T2
pyrite cube aggregate
pyrrhotized shell
pyrite cubeT3
Initial stage Color change Rust marks Corrosion
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Estimation of the incidence of oxidation
T1
T2
T3
60%
40%
<0.1%
Oxidation is mainly an aesthetical problem
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Type of slate and oxidation
Three color families: - Black Gray (B) - Green (G) - Red-Purple (R)
Mayor mineral components • Quartz • Mica • Chlorite Accessory components (<2%) Iron sulphides (pyrite): B, G Organic matter (carbon): B, g Iron oxides (hematite): R
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Has oxidation any solution?
So far, different solutions have been tested
Cleaning and application of protective coating
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Has oxidation any solution?
So far, different solutions have been tested
Application of coating treatment during the fabrication process
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Ankerite: CaFeCO3
Calcite: CaCO3
Siderite: FeCO3
Dolomite: MgCaCO3
What about carbonates?
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Gypsification (Fading) CaCO3 + SO2 CaSO4 2H2O
1x
10x
100x
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Calcite Gypsum
SO2 H O2
Gypsification is also triggered by weather
33% increase
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Slaty cleavage
Gypsum
Detachment
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Fading Calcite and dolomite white fading (CaCO3 ) (MgCaCO3)
Ankerite and siderite red fading (CaFeCO3 ) (FeCO3)
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Sedimentation
River network
A) Normal mud sedimentation B) Occasional sand sedimentation C) Mud sedimentation again
What about ribbons?
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1) Sedimentation 2) Lithostatic compression
3) Tectonic compression
a) b)Cleavage
Mud
Sand
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4 ft.
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Some remarks about standards
EN 12326 ASTM C 406 IS 6250 GB/T 18600
1999 1932 1981 2009
European Union USA India China
Mechanical behavior Flexural strength
Water Absorption
Permeability
Freeze-Thaw
Thermal cycle
Acid exposure
Carbon and carbonate content
Petrography
(*)Qualititative classification
COUNTRY
Sampling
Formatting
Weathering behavior
Petrological characterization
YEAR
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European Standard EN12326
- 13 test methods - Developed from former
national standards - CE mark - Petrology
Petrographic examination
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American Standard ASTM C406
- 3 test methods - Lifespan - No oxidation tests
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Indian Standard IS 6250
- 6 test methods - Inspired in the former BS - Last revision 1981!
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Chinese Standard GB/T 18600
- 5 test methods - Inspired by other standards - Quality and lifespan
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Thank you for your attention Any questions?
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