Historic Mortars, the Chemistry Behind What Binds Our Built Environment

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by Randy Ruth of LimeWorks.us

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  • Portland cement used on railroad projects and water works even in lancaster in the 19th century
  • Historic Mortars, the Chemistry Behind What Binds Our Built Environment

    1. 1. HISTORIC MORTARS:THE CHEMISTRY BEHINDWHAT BINDS OUR BUILTENVIRONMENT
    2. 2. What is mortar? A mixture of various compounds including Lime and or Cements mixed with water and sand to bond or cover Masonry i.e. brick, stone, terracotta, stucco, and plaster. Mortar ≠ concrete or cement
    3. 3. Historic mortars Historic mortars  Gypsum  Great pyramids in Egypt  Interior plaster  Stone mortar  Lime  Primary building binder for 3000 years  Natural Cement  Portland Cement  Recent applications 1824 England and 1870 in U.S.
    4. 4. Types of historic lime mortars• Air Lime Cycle  Three basic types  Hi-calcium Lime  Dolomitic Lime  Magnesium Lime  Hexagonal plate crystal structure  Sets Via Carbonation  Impurities can produce hydraulic behavior  Burned @ 950 F
    5. 5. Types of historic lime mortars Natural Hydraulic lime Cycle  Two basic types  Argillaceous  Clay impurity  siliceous  Pure Silica  Hexagonal plate crystal structure  Sets Via Carbonation  Set Via Hydraulic reaction with Silica  Belite (di-calcium Silicate)
    6. 6. Types of historic lime mortars Pozzolanic Hydraulic lime Cycle  Needs a reactive silica source  Calcinated material  Brick, tile, fly-ash, Blast furnace slag, glass, silica fume….  Must be the right fineness  At least 180 microns  Hexagonal plate crystal structure  Sets Via Carbonation  Set Via Hydraulic reaction with Silica  Belite (di-calcium Silicate)  Varying minerals formed
    7. 7. Manufacture and mixingtechniques of historic mortars• 3000 B.C. – Roman Empire  Limestone burned in Ricks and stone kilns  Most often mixed and transported by hand in baskets  Primarily hot lime mixing  Quicklime mixed on site with sand  Laid fresh  Lime slaking for plaster and washes  Fresco
    8. 8. Manufacture and mixingtechniques of historic mortars• Fall of Rome – 1700’s  Vitruvious  1 lime : 3 sand introduced  Quicklime not hydrated lime  Pozzolanic mix designs for “Roman concrete”  Mixed very stiff and hand compacted  Used vitrified clay (tiles)  NHL used in Europe  “Roman Cement” lost  Basic lime mortar used and sourced locally
    9. 9. Manufacture and mixing techniques of historic mortars• 1700’s – 1870’s  1759-John Smeaton- Builds Eddy stone Lighthouse with NHL + pozzolan  1796-James Parker- Patent for artificial hydraulic lime, called “Roman Cement”  1818-Natural Cement found in Madison county, NY  1824-Joshph Aspdin- Patents Portland Cement in England  First cement to contain “Alite” Tri-calcium silicate  1868-First Shipment of Portland Cement to U.S  1871-First Portland Cement Plant opens in Coplay, PA
    10. 10. Manufacture and mixingtechniques of historic mortars• 1870’s – 1913 • 1880’s-experimentation with rotary kiln • 1896-first year U.S. Portland cement production exceeds importation • 1900-First year Portland cement Production exceeds Natural Cement • 1904-1913 – Rotary kiln’s become primary kiln design • Burned @ 2400 F
    11. 11. The debate has not changed1914 articlein”EngineeringNews”
    12. 12. Manufacture and mixingtechniques of historic mortars 1913-Present  Modern Portland Cement reigns in engineering projects  Slag Cement produced  Lime fades as primary binder around after WWII  1:1:6 mix becomes common  Beginning of restoration with high lime content mortars in 1960’s  Mid 1990’s – Beginning of lime renaissance
    13. 13. Compare and contrastCompressive strength The more hydraulic a mortar the greater its strength Lime mortars are slowest setting (carbonation & belite) Portland cement is fastest setting (Alite and Belite) Pozzolans consume free lime to gain strength
    14. 14. Compare and contrast Flexural strength The more free lime the greater a mortars flexibility High calcium and Natural Hydraulic limes have the most free lime thus greatest flexibility Pozzolans consume free lime to gain strength thus reduce healing ability
    15. 15. Compare and contrast Vapor permeability
    16. 16. Question & Answers

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