Transcript Slide 1

Concrete and Masonry Construction
BSE 2294
Animal Structures and
Environment
Dr. Susan Wood Gay
Concrete has several properties that
make it well suited for a wide variety of
agricultural uses.
• Advantages:
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–
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Plastic when first mixed
Durable
Sanitary
Low maintenance
• Disadvantages:
– Heavy
– Expensive
– Low insulation volume
Concrete is composed of two
components: paste and aggregate.
• Paste
– Portland cement
– Entrained air
– Water
• Disadvantages
– Heavy
– Expensive
– Low insulation value
Cement plant in Iola, Kansas.
Portland refers to the type of cement
that is universally produced by all
manufacturers.
• Carefully controlled mixture of:
–
–
–
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Lime
Silica
Alumina
Iron oxide
• Burned and ground into fine
powder
Stone quarries on the Island of Portland.
Portland cement components
Portland
Cement
Clinker
Clay
Shale
Gypsum
Silica Sand
Limestone
Cement Rock
Oyster Shells
Coquina Shells
Marl Shells
Iron Ore
Marl River
Deposits
Portland cement manufacturing
Portland cement manufacturing
Portland cement manufacturing
Portland cement manufacturing
Portland cement is available in five
types as designated by ASTM.
Type
Description
I
Normal cement; suitable for general construction
II
Modified cement; low heat-producing for very large
concrete structures
III
High-early-strength cement; hydrates rapidly for cold
weather application
IV
Low-heated cement; lower heat of hydration than Type II
for large masses of concrete such as dams
V
Sulfate-resistant cement; resists damage due to the high
sulfate content of water
Entrained air is important for good
quality concrete.
• Uses less sand and water
• Reduces segregation
• Improves workability
• May be finished earlier
• Increases water tightness
• Resists freezing and thawing
• Resists surface scaling
One cubic yard of concrete can contain
400 to 600 billion air bubbles.
Normal portland cement is suitable for
most farm and general construction
work.
• 1 sack = 94 lbs or 1 ft3
• Dry storage is essential
• Do not use cement that contains
lumps
Common products for home concrete use.
Water for making concrete should be
clear, free of acids, alkalis, oils, and
organic matter.
Both the cost and quality of the
concrete are affected by the kind of
aggregate selected.
• Aggregate should be:
– Clean
– Hard
– Strong
• Sharp, rough, or flat aggregate
requires more cement-water
paste
Gravel Quarry in Southern Ontario.
• Fractured material severely
reduces strength
Aggregates size is determined by
screening material through a Number 4
sieve.
• Number 4 sieve
– ¼ inch openings
– 16 openings/in2
• Fine aggregate – passes
through a Number 4 sieve
• Coarse aggregate – does not
pass through a Number 4 sieve
Inclined aggregate screen.
The use of well-graded aggregates will
produce an economical mixture with
the least amount of cement.
• “Well-graded” – a variety of
materials ranging in sizes:
– Fine sand
– Coarse sand
– Small stones
• Allows small particles to fill voids
between large particles
• Use of aggregates from gravel
banks not recommended
Well-graded aggregate fit together so
perfectly that a minimum of paste is required.
The maximum size of aggregate used
depends on the size and shape of the
structure and the distribution of rebar.
Structure Type
Aggregate Size
Walls or columns
≤ 1/5 minimum dimension of the
member
Slabs
≤ 1/3 slab thickness
Reinforced concrete
≤ 3/4 space between rebar
Excessive amounts of silt or organic
matter prevents a secure bond
between the paste and aggregate.
A silt test can determine whether
aggregate should be washed.
• Glass jar
– 2 inches of aggregate
– 6 inches of water
• Shake vigorously and let stand
for one hour
1/8 in
2 in
• If more than 1/8 inch of silt has
settled at the top of aggregate –
wash or abandon
Silt
Aggregate
The silt layer is only 1/8 in; therefore the
aggregate is useable without washing.
An organic matter test can determine
whether aggregate should be washed.
• Glass jar
– ½ pint of water
– ½ pint of aggregate
– 1 teaspoon lye
• Stir and let stand for 3 to 4 hours
• Observe color
– Clear to light straw – use
– Dark straw – do not use
Free of
OM
Some
OM
Too much
OM
The samples on the left and in the middle are
useable; the sample on the right is not .
Slump is the measure of concrete
consistency.
Compressive Strength (psi)
Concrete strength is inversely
proportional to the amount of water
used.
7000
5 gallons/sack
6000
6 gallons/sack
5000
7 gallons/sack
4000
3000
2000
1000
0
7d
28d
90d
Moist-cure test at 70 degrees F.
The concrete mix depends upon the
desired application.
Kind of Work
Water to
Cement
Ratio
Maximum
Size of
Aggregate
Mass Ratio
(cement:
gravel:sand)
Concrete subjected to severe
wear, weather, or weak acid and
alkali solutions
5 gal/sack
¾ in
1:1.9:2.3
1½ in
1:1.7:3.1
Floors, driveways, walks, septic
tanks, storage tanks, structural
beams, columns, and slabs.
6 gal/sack
¾ in
1:2.5:2.8
1½ in
1:2.2:3.7
Foundation walls, footings, mass
concrete, etc.
7 gal/sack
¾ in
1:3.1:3.3
1½ in
1:2.8:4.2
Use the specific density of materials to
determine the masses of materials
needed for a specific concrete mix.
A 1:1.9:2.3 ratio mix = ?
The specific gravity (γ) of a substance
is a comparison of its density to that of
water.
1 cup water
1 cup lead
Each glass contains equal volume of material; however, the
glass with lead will weigh more than the glass with water.
The density of a material is calculated
by multiplying its specific gravity by
the density of water.
γsand/gravel = 2.65
ρH2O = 62.4 pcf
ρsand/gravel = (2.65)(62.4 pcf) = 165.4 pcf
γcement = 3.15
ρcement = (3.15)(62.4 pcf) = 196.6 pcf
Concrete Volume Example #1
Determine the volume of a one-sack batch of concrete for a
storage tank. The maximum size of aggregate is ¾ inch.
Concrete Volume Example #2
Determine the amount of concrete needed for a feeding floor 35
ft by 120 ft by 4 in thick. Include 5% for error.
The actual yield of concrete is 60% of
the volume of the total volume of
materials.
Concrete Yield Example
Determine the yield of a 7 gal/sack concrete mixed using a
maximum aggregate size of 1½ inches.
The purpose of mixing is to achieve a
uniform distribution of the ingredients
and allow for air entrainment.
• Mixing times:
– One minute for ≤ 1 yd3
– One minute plus 15 s/yd3 for
large batches
• Mixing order (truck mixers):
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Water
Little aggregate
Cement
Balance of aggregate
Brand new cement mixing truck.
Forms should be ready and in place
before the concrete is mixed or before
the ready-mix arrives.
• Form materials:
– Plywood
– Steel
– Sheathing
• Forms should be:
– Clean
– Tight
– Tied together to prevent bulging
Form for concrete column consisting of
plywood and rebar.
Before pouring concrete, the job site
must be properly prepared.
Remove the soft spots and fill them
with soil, gravel, or crushed rock.
Grade area to approximate slope.
Excavate the site about three or more
feet then backfill with compact material
to prevent foundation sinking.
Construct forms for footing, foundation,
and/or floor slab.
Wood forms should be oiled with form
oil or used crankcase oil prior to
concrete placement.
Immediately after the concrete is in
place, it is struck off with a straight
edge board, known as screeding.
Soon after screeding, the surface may
be floated (smoothed) with a darby or
bullfloat.
Forms may be removed from fittings or
foundations in 24 hours; slabs and
beams need in four to five days.
Curing is the time needed to complete
the chemical reaction between
portland cement and water.
Compressive Strength (psi)
Fresh concrete develops 40% of its
potential strength during the first 14
days of curing; 70% during the first 28.
7000
5 gallons/sack
6000
6 gallons/sack
5000
7 gallons/sack
4000
3000
2000
1000
0
7d
28d
90d
Moist-cure test at 70 degrees F.
Curing is a hydration process;
therefore, concrete must not be
allowed to dry out during curing.
• Continuously sprinkle with water
• Cover with:
– Damp sand
– Damp straw
– Plastic film
Plastic film over freshly poured slab.
Concrete must be protected from
freezing or excessive heat during the
curing process.
• Optimum temperature ~ 75 °F
• Process slows down as
temperature decreases
• Curing stops at 32 °F
• Permanent damage if freezing
occurs with first 24 hours
Reinforcing materials improve the
strength of concrete structures by
carrying tensile loads.
• Transfer of tensile forces
• Materials
– Wire mesh
– Reinforcing bars (rebar)
– Synthetic fibers
Placing rebar and wire mesh prior to pouring.
Wire mesh is a common reinforcing
material for concrete.
• Advantages:
– Can be formed into various
shapes
– Tensile strength of 60,000 to
70,000 psi
• Disadvantages:
– Difficult to install
– Expensive
– High labor
Wire mesh form.
Rebar is ribbed steel bars installed in
foundation concrete walls, footers,
and other poured structures.
• Advantage:
– Very high tensile strength
(70,000 to 90,000 psi)
• Disadvantages:
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Difficult to install
Expensive
High labor
Cannot weld
Rebar in sealer.
Synthetic fibers are replacing welded
wire mesh, especially in residential
slabs.
• Advantages:
– Easy to install
– Reduce plastic shrinkage cracks
• Disadvantages:
– Very low tensile strength
Nylon fibers for concrete reinforcement.
Walls constructed with concrete blocks
bonded together with mortar are
described as masonry construction.
• Advantages:
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Durable
Fire resistant
Low maintenance
Relatively inexpensive
• Disadvantages:
– More porous than concrete
– More subject to cracking than
concrete
Construction of concrete block wall.
The ASTM has developed a set of
specifications for masonry blocks.
• Compressive strength:
– Type A – 1000 psi (below grade)
– Type B – 700 psi (above grade)
• Water absorption limited to 15
lb/ft3
• Moisture content ≤ 40%
Concrete blocks must meet ASTM standards.
• Free from defects
Actual sizes of concrete blocks are 3/8
inch less than nominal size in each
direction.
7 5/8 in
7 5/8 in
15 5/8 in
All dimensions should be planned to
be in multiples of blocks or halfblocks.
• Minimize cutting and fitting
• Horizontal dimensions
– Half blocks
– Whole blocks
• Vertical dimensions
– Whole blocks only
Setting concrete blocks.
Concrete blocks are available in
several shapes.
Block
Dimensions
(in x in x in)
Stretcher
8 x 8 x 16
Corner block
8 x 8 x 16
Half block
8x8x8
Sash block
8 x 8 x 16
Jamb block
8 x 8 x 16
Bull nose
8 x 8 x 16
Partition
4 x 8 x 16
Stretchers are used for the bulk of the
wall.
Corner blocks have one square end for
wall corners.
Half blocks are used in alternate rows
at openings.
Sash blocks have vertical grooves in
one end for metal sashes.
Jamb blocks have 2 in by 4 in
openings cut out at one end for a door
jamb or wooden window sash.
Bull nose blocks have one rounded
corner for smooth wall openings.
Partition blocks are for inside walls
subject to small loads.
Masonry Block Example
Determine the number of blocks required for the back wall of a
machinery shed. The wall is 40 ft long and 16 ft high.