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Properties of ConcreteIntroduction
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Overview

• What is concrete made of?
• What Is Concrete Used For?
• Why Is Concrete Used?
• Why Do We Reinforce Concrete?
• Curing of concrete

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What is concrete made of?
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What is concrete made of?

• Concrete is basically a mixture of two
  components
• Paste
• Aggregates
• Paste (Portland cement, water, and air)
• Aggregates (sand, gravel, crushed stone)

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CEMENT

• Cement (Dry powder of very fine particles) is a
  building material made by grinding calcined
  limestone and clay into a fine powder
• Portland Cement chemical composition
• Limestone, shale and clay
• CaO (lime)
• Al2O3 (Alumina)
• SO3 (Sulfite)

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CEMENT

• When mixed with water, forms a paste
• it undergoes chemical changes (chemical
  reaction-Hydration)
• Glue paste coats all the aggregates together
• hardens and forms a solid mass

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WATER

• Water good for drinking is good for concrete

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WATER

• needed for two purposes
• chemical reaction with cement
• workability
• only 1/3 of the water is needed for chemical
  reaction
• extra water remains in pores and holes
• results in porosity
• Good for preventing plastic shrinkage cracking
  and workability
• Bad for permeability, strength, durability.

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AGGREGATES

• cheap fillers
• hard material
• provide for volume stability
• reduce volume changes
• provide abrasion resistance

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AGGREGATE

• Aggregate are divided into two groups
• Fine - AASHTO M-6 or ASTM C-33
• Coarse - AASHTO M-80 or ASTM C-33
• Fine aggregate consist of natural or manufactured
  sand with particle size up to 3/8 inch
• Coarse aggregate particles are retained on the 4
  sieve and range up to 6 inches

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COARSE AGGREGATE
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FINE AGGREGATE
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CONSTITUENTS

• paste 25 to 40
• portland cement 7 to 15 by Vol.
• water 14 to 21 by Vol.
• Aggregates 60 to 75
• coarse aggregates
• Fine aggregates
• Admixtures

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CONSTITUENTS

• Cement Water Air Fine Aggregate
  Coarse Aggregate

Cement paste constitutes about 25 to 40 volume
of concrete
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AIR ENTRAINED CONCRETE

• Why the difference between line 1 and line 2?
• Line 1, small size CA, increased H2O and cement
• Line 2, larger CA, less H20, air, cement

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NON-AIR ENTRAINED CONCRETE
Cement Water Air Fine Aggregate Coarse
Aggregate

• Similar to Air Entrained Concrete slide
• See how aggregate size impacts water demand and
  amount of paste in the mix

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ADMIXTURES

• Plastic and hardened properties of concrete may
  be changed by adding admixtures

• Admixtures are commonly used to

• increase set time
• decrease set time
• increase workability
• adjust other concrete properties

• reduce water demand
• entrain air
• inhibit corrosion

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ADMIXTURES

• chemical
• retarders
• accelerators
• water reducing
• air entraining
• mineral
• fly ash
• silica fume
• slags

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QUALITY OF CONCRETE

• Quality of concrete depends on quality of paste
  and quality of aggregates
• each particle of aggregate is completely coated
  with paste
• All spaces between aggregate is filled with paste

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QUALITY OF CONCRETE

• Is determined by
• W/C Ratio
• Advantage of reducing water
• Increased compressive and flexural strength
• lower permeability
• increased resistance to weathering
• reduced shrinkage cracking tendencies
• The less water used, the better quality of
  concrete, provided it can be consolidated
  properly.

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Ten cement-paste cylinders with
water-cement ratios from 0.25 to 0.70. The band
indicates that each cylinder contains the same
amount of cement. Increased water dilutes the
effect of the cement paste, increasing volume,
reducing density, and lowering strength.
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FORMS

• A form is the mold for setting concrete into a
  desired shape

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What Is Concrete Used For?
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What Is Concrete Used For?

• Construction Material
• Art Work

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Picture of Bench
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Why Is Concrete Used?
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Why Is Concrete Used?

• Economics
• Inexpensive, readily available
• Material Properties
• Long Lasting
• Molded into a desired shape
• Great insulator
• Hard

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Material Properties (cont.)

• Great Compressive Strength (up to 8000 psi and
  even more than that)
• Poor Tensile Strength (almost 0)
• Reinforcement methods ()

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Why Do We Reinforce Concrete?
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Why Do We Reinforce Concrete?

• Prevent cracking due to tension forces

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Question

• What is the difference between tension and
  compression?

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Question

• Why would concrete never be used in tension?

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How Do We Reinforce Concrete?

• Steel rebar
• Excellent in tension, poor in compression

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CURING OF CONCRETE
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CURING OF CONCRETE

• Over time concrete will cure, which is a
  hardening process.
• Concrete has a 28 day curing time, this is the
  amount of time it takes to be considered
  completely cured

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Curing

• Critical to durable concrete
• Increases strength
• Decreases permeability
• Increases durability

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Curing Concrete

• How concrete is cured
• Ponding or Immersion
• Spraying or Fogging
• Wet Coverings
• Impervious Paper
• Plastic Sheets
• Membrane-Forming Curing Compounds

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Questions?

• Remember
• Use Common Sense
• Temperature effects on your body have very
  similar effects on concrete
• If you are not sure, ASK!!!