“properties of concrete” introduction. overview what is concrete made of? what is concrete used...
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““Properties of Concrete”Properties of Concrete”
IntroductionIntroduction
““Properties of Concrete”Properties of Concrete”
IntroductionIntroduction
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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?What is concrete made of?What is concrete made of?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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CONSTITUENTSCement 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
• Similar to Air Entrained Concrete slide• See how aggregate size impacts water
demand and amount of “paste” in the mix
Cement Water Air Fine Aggregate Coarse Aggregate
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ADMIXTURES
• increase set time• decrease set time• increase workability• adjust other
concrete properties
• reduce water demand
• entrain air• inhibit corrosion
•Plastic and hardened properties of concrete may be changed by adding admixtures•Admixtures are commonly used to:
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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 CONCRETEIs 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-cementratios from 0.25 to 0.70. The band indicates that eachcylinder contains the same amount of cement. Increasedwater dilutes the effect of the cement paste, increasingvolume, 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 What Is Concrete Used For?For?
What Is Concrete Used What Is Concrete Used For?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?Why Is Concrete Used?Why Is Concrete Used?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 Why Do We Reinforce Concrete?Concrete?
Why Do We Reinforce Why Do We Reinforce Concrete?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 CONCRETECURING OF CONCRETECURING OF CONCRETECURING 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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• Critical to durable concrete• Increases strength• Decreases permeability• Increases durability
Curing
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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!!!