Concrete Design
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Transcript of Concrete Design
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CEE300/TAM324Aggregates and concrete
Aggregates
Understand and interpret important physical properties
Concrete and cement
Understand concrete as a composite material
Understand the fundamental concepts about portland
cement cementFrom last lecture:* Aggregates are granular particulates, working together
as a group* For civil engineering applications, aggregates are normally
comprised of naturally occurring rocks and common minerals (silicates, aluminates, carbonates, etc.): ceramics
* Hardness, strength, chemical stability and gradation are important properties
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Rock types - Igneous Formed on cooling of lava
(melted rock)
Mainly quartz, feldspar, pyroxene,
silica glass
Extrusive versus intrusive
effect?
Rock examples– Granite (intrusive)
– Diorite (intrusive)
– Rhyolite (extrusive)
– Basalt (extrusive)
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Rock types - Sedimentary
Formed by weathering of existing rocks
Deposition: mechanical or chemical Consolidation: physical or chemical
Mainly quartz, calcite, clay
Rock examples- Gravel, sand, silt, clay (mechanical
deposition, physical consolidation)- Sandstone, shale (mechanical deposition, chemical consolidation)- Limestone (chemical deposition,
chemical consolidation)
Often laminar, usually weak and porous
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Rock types - Metamorphic
Formed by alteration (pressure and temperature) of existing rock
Mainly quartz, calcite, mica, feldspar, pyroxene
Rock examples– Marble (metamorphosed
limestone)– Slate (low-pressure
metamorphosedshale)
– Phyllite, schist, gneiss (high- pressure metamorphosed shale)
– Quartzite (metamorphosedsandstone)
Often laminar, usually dense and strong
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Recall gradation curves
50 mm
Size (log)
% p
assi
ng
0.15 mm
100
0
Lack of particles within this size range
Well graded
(combined coarse and fine aggs)
Uniformly graded
Gap graded
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Aggregate particle shape
(Gravel and natural sand)Increasing water demand and compaction effort
(Crushed stone & manufactured sand)
Aggregate surface texture also has an effect on bond and water demand“glassy” to “rough”
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Physical properties ofaggregatesStrength
Aggregates should not be weaker than design load or the strength of strength of concrete
Generally not a problem:Crushing strength of aggs = 100 to 200+ MPa
Compressive strength of concrete = 25 to 50 MPa
Porosity
The nature and amount of pores and voids affect certain properties
Impermeable pores (Vi)
Solid (Vs)
Absorption
Moisture content
Specific gravity
Density of a single aggregate piece!
Used in mix design computations
Permeable pores (Vp)
Expressed as a ratio of density of solid to that of water (1000 kg/m3)
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Pores, voids and moisture absorption
drySaturated surface-dry(permeable pores wet)
wet
pore
void
Draws in water
Gives out water
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Inter-relation between gradation, voids and bulk density
Containers with volume
V
Uniformly graded Well graded
* High void content within aggregate sample.
* Lower bulk density of sample (m1/V)
m1 mass of
agg. sample
m2
* Lower void content within aggregate sample.
* Higher bulk density of sample (m2/V)
“Density” of the entire aggregate sample (many pieces), as opposed to specific gravity of a single piece
Void content = volume of voids (non-solids) / total volume
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What is concrete?Graded mineralaggregates serve as inert and stable filler for cement matrix
The cement “paste” matrix is a mixture portland cement (pc) and water
Chemical or mineral admixtures may be added to obtain needed properties
Constituents:
Cement paste (22-30% by vol.)
Aggregate* (70% by vol.)
air (1-8% by vol.)other
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A view inside pc concrete
PC concrete made with siliceous rounded gravel
PC concrete made with crushed limestone
How are these two materials different?
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Concrete as a composite material
strength permeability
shrinkage creep
Properties of concrete
Properties ofcement matrix
Thus cement properties are important!
Portland cement -- definitioncement: cohesive or adhesive material that bonds fragments together
inorganic cements: typically comprised of mineral oxides
hydraulic cements: set and harden, even under water, by virtue of a chemical reaction with water (hydration)
portland cement