Soil and Concrete in Construction

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Soil and Concrete in Construction

• CE 477 Summer Session 1, 2009

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Definitions

• Soil - Dirt (pardon my language) consisting of
  soil particles and void spaces between particles.
  Void spaces may contain liquid (often water) or
  gas (generally air) phases. The soil particles
  may be mineral or organic. We will focus on
  predominately mineral soils with negligible
  organic matter.

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Soil Components

• Phases
• Solid Mineral particles
• Voids (pore space)
• Liquid Soil water solution, primarily H2O
• Gas Primarily air

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Phase Diagrams
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Definitions

• Unit Weight (?) total weight of soil/total soil
  volume
• Dry unit weight (?d) weight of soil
  solids/total soil volume
• Water content (? or ?) weight of water/weight
  of soil solids
• Void ratio (e) volume of voids/volume of soil
  solids
• Porosity (n) volume of voids/total soil volume
• Specific gravity (Gs) Dry unit weight/unit
  weight of water

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Soil Moisture States

• Saturated All pore spaces filled with water.
• Air dry Variable, at equilibrium with
  atmospheric air (humidity)
• Oven dry All pore spaces filled with air (no
  water), 105C oven, 24 hours
• Gravimetric moisture content
• (Ww-Wd)/Wd
• Volumetric moisture content
• VH2O/Vs

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Soil Density States

• In-Situ (Bank) Soil as it naturally occurs,
  undisturbed in source
• Loose Soil that has been picked up (fluffed),
  as it occurs after excavation and before
  compaction
• Compacted Soil that has been placed and
  compacted to a design density or unit weight

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Soil Compaction terms

• Swell factor loose dry unit weight/bank dry
  unit weight (generally lt 1)
• Swell percent 100 (bank unit wt/loose unit wt
  1)
• Shrinkage factor compacted dry unit weight/bank
  dry unit weight
• Shrinkage percent 100 ((compacted unit wt-bank
  unit wt)/compacted unit wt

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Required compaction density
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Example
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Portland Cement Concrete

• Constituents
• Aggregate
• Fine (sand)
• Coarse (gravel)
• Intermediate
• Cementious Material
• Portland Cement
• Fly ash (Pozzolanic material)
• Slag
• Water
• Admixtures
• Accelerators
• Water reducers
• Etc.
• Air

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Criteria

• Cost
• Strength
• Durability
• Workability
• Special requirements
• Chemical exposure
• Extreme temperatures
• Etc.

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Common Specifications

• Strength 28 or 90 day compressive
• Workability Slump, aggregate gradation

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Slump
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Central Mixed Concrete

• High production
• Contractor has direct control
• Shorter hauls

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Hoover Dam
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Transit Mix Concrete

• Medium to small jobs
• Long-term operation
• Economic for smaller jobs
• Quality control, timing are problems

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Transit Mix Concrete
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Effect of water/cement
Higher w/c higher slump, workability
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Concrete Mix Description

• Cement Fine Aggregate Coarse Aggregate
• Water Cement (Gallons H2O Sack cement)
• 1 sack 94 lb
• Entrained Air by volume
• Admixtures, generally volume per cubic yard

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Moisture of Aggregate

• Saturated surface dry (SSD) Moisture content
  of dry materials such that they will not absorb
  or contribute water to mix
• Moisture contents are stated relative to SSD
  condition
• Corrections for moisture in aggregate must be
  made to added water

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Example