Concrete and Masonry Section 13 Unit 39

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Concrete and MasonrySection 13Unit 39
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Introduction

• Most buildings have concrete and/or masonry
  components.
• The ability to use concrete and masonry materials
  is an essential skill for construction and,
  repair and maintenance of buildings.

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Concrete
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Concrete

• Concrete is a mixture of stone aggregates, sand,
  Portland cement, and water that hardens as it
  dries.
• Concrete does not dry, it goes through a chemical
  reaction called hydration.

Agricultural Mechanics, Herren
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Concrete - cont.
Concrete is truly a versatile building material.
It can be formulated with very specific
performance characteristics in mind and include
lightweight, heavyweight, porous,
fiber-reinforced, mass, high-performance and
cellular concretes.

• Advantages
• Fireproof
• Insect rodent proof
• Decay resistant
• Storm resistant
• Wear resistant
• Waterproof (water resistant)
• Strong

• Attractive
• UV resistant
• Doesnt require expensive equipment.
• Available locally
• Low original and maintenance costs
• Sanitary and easy to keep clean
• Recyclable

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Concrete - cont.

• Disadvantages
• Labor intensive
• Requires moving a lot of weight
• Requires forms
• Dense material
• Special skills required to place and finish

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Seven (7) Characteristics of Concrete
2. Resists attack by water
1. Durable
3. Resists manures and most chemicals.
4. Fire resistant
5. Very strong in compression
6. Weak in tension
7. Resistant to freezing and thawing
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Characteristic 1 Durability
Def The ability of concrete to resist weathering
action, chemical attack and abrasion while
maintaining its desired engineering properties.
Concrete ingredients, their proportioning,
interactions between them, placing and curing
practices, and the service environment determine
the ultimate durability and life of concrete.
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Characteristic 2 Resists Attack by Water
Two characteristics watertightness and
permeability.
Watertightness the ability of concrete to hold
back or retain water without visible leakage.
Permeability the amount of water migration
through concrete when the water is under pressure
or the ability of concrete to resist penetration
by water or other substances.
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Characteristic 2 Resists Attack by Water -cont.
The same properties of concrete that make it less
permeable also make it more watertight.
Low permeability concrete requires a low
water-cement ratio. Moist curing also reduces
permeability.
Factors that affect permeability and water
tightness include

• Permeability of the paste
• Permeability and gradation of the aggregate
• Quality of the paste
• Quality of the paste--aggregate transition zone
• Relative proportion of paste to aggregate

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Characteristic 3 Resists manures and most
chemicals.

• Good quality concrete is resistant to the acids
  of manure.
• Concrete is very alkaline, pH is usually greater
  than 12.5.
• Resistance can be increased with surface
  treatments.
• Concrete is susceptible to deterioration by
  sulfates.

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Characteristic 4 Fire Resistant

• Concrete provides the best fire resistance of any
  building material.
• It does not burn, it cannot be 'set on fire' like
  other materials in a building and it does not
  emit any toxic fumes, smoke or drip molten
  particles when exposed to fire.
• Concrete and its mineral constituents enjoy the
  highest fire resistance classification.

The strength of concrete will deteriorate with
high temperatures.
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• The compressive strength depends on
• The strength of the aggregate
• Proportion of aggregate sizes
• Type of Portland cement
• Purity of water
• Uniformity of mixture
• Procedures used in placing, finishing and curing

Characteristic 5 Strong in Compression
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Compressive Strength Influenced by Water/cement
Ratio
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Characteristic 6 Concrete is weak in tension
Does this table and picture show why steel
reinforcement is use in concrete?
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Characteristic 7 Concrete is resistant to
freezing and thawing

• The resistance decreases as the permeability
  increases.
• When concrete spaces are 91 or more full of
  water, freezing will damage the concrete.
• When water freezes to ice it occupies 9 more
  volume than that of water.
• Air entrained concrete is less permeable.
• Example of freezing damage

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Concrete Constituents
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Concrete Constituents
Concrete a mixture of aggregate and Portland
cement paste.
Aggregate usually sand, gravel and/or crushed
stone.
Paste Portland cement and water
Process the paste binds the aggregates into a
rocklike mass as the paste hardens because of the
chemical reaction (hydration) of the Portland
cement and water.
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Proportion of Constituents

• Basic concrete mix
• Air 6
• Portland cement 11
• Coarse aggregate 41
• Fine aggregate 26
• Water 16

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Admixtures

• Admixtures are materials other than cement,
  aggregate and water that are added to concrete
  either before or during its mixing to alter its
  properties, such as workability, curing
  temperature range, set time or color.
  (http//www.toolbase.org/)

Admixtures cannot compensate for bad practice
and low quality materials.
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Admixtures - cont.

• Common admixtures
• Retarding admixtures
• Accelerating admixtures
• Super plasticizers
• Water reducing admixtures
• Air-entraining admixtures

• Additional admixtures
• Bonding,
• Shrinkage reduction,
• Damp proofing and
• Coloring.

• Addition of fiber to concrete makes it tough and
  fatigue resistant. Such type of admixtures are
  used extensively in important engineering
  projects.

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Types of Cement
Different types of Portland cement are
manufactured to meet many different applications
of concrete.
Types I IA are the most common.
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Air Entrained
Developed during the 1930s
Produced by using air-entraining cement or by
using an air-entraining admixture.
Recommended for nearly all concretes that are
exposed to freezing and thawing, and deicing
chemicals.
Spalding is a characteristic of using concrete
without air entrainment.
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Properties of Air Entrainment

• Increased freeze-thaw resistance
• Increased deicer-scaling resistance
• Improved sulfate resistance
• Equivalent Strength
• Improved workability

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Aggregate
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Aggregate

• Concrete should include at least two different
  sizes of aggregate--fine and coarse.
• Fine 1/4 inch or less (not to include fines)
• Coarse 1/4 to 2 inch
• Standard practice is to crush stone and the use
  screens to separate the sizes.
• The correct proportion of fine aggregate and
  coarse aggregate can then be mixed together.
• Aggregate should be 60 to 80 of the volume.
  (cheapest material).
• Stream bank aggregate must be tested for
  excessive silt and clay. (page 557, Fig 39-2)

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Aggregate-cont.
Aggregate diameter must not exceed 1/3 of slabs
that do not use rebar.

• Aggregate diameter must not exceed 1/5 of void in
  forms were rebar is used.

The largest recommended aggregate size is 2
inches for most applications.
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Purchasing Concrete
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Purchasing Introduction

• For large jobs in is common practice to have the
  concrete delivered to the site.
• The cost of having concrete delivered is
  determined by
• Quantity
• Mix
• Minimum charge
• Unload fee
• Mileage fee

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Purchasing Concrete - Quantity Needed

• Quantity needed
• Concrete is sold by the cubic yard (yd3).
• To determine the quantity need calculate the
  volume in cubic inches (in3) or cubic feet (ft3)
  and convert to cubic yards (yd3 or just yd).
• 27 ft3 1 yd
• 46656 in3 1 yd
• Common practice to add 5 to 10 for waste and
  volume errors.

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Purchasing Concrete Quantity - Example

• Determine the yards of concrete that will be
  required to pour a driveway that is 26 feet wide,
  120 feet long and 6 inches thick.
• Solution

• Adding 10.

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Purchasing - Mix

• Two factors which determine the ideal mix.
• Environment
• Intended use

• Environmental factors
• Soil phosphates
• Freeze thaw
• De-icers

• Use factors
• Maximum Load
• Vibration

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Purchasing Basic Mix
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Purchasing Slump

• The inches of slump indicates the water-cement
  ratio and the quality of the concrete.

Slump is determine through a slump test.
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Slump - Test

• A slump test is conducted using an Abrams cone,
  slump cone.
• A slump cone is 8 inches in diameter at the
  bottom, 4 inches in diameter at the top and 12
  inches tall.

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Slump Test cont.

• Steps
• Moisten cone
• Place cone on moist, smooth non absorbent level
  surface that is larger the the lugs on the cone.
• While standing on the lugs, fill the cone 1/3 and
  uniformly rod 25 times.
• Fill the cone 2/3 full and rod the 25 times
  insuring the rod just penetrates the first layer.
• Over fill the cone and rod 25 times
• Strike off the excess with the rod.
• Slowly lift the cone vertically and place on
  surface beside concrete.
• Place rod across the top of the cone and the
  concrete and measure the distance from the bottom
  of the rod to the surface of the concrete.
• This distance is the inches of slump.

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Mixing Concrete
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Introduction

• Small jobs can be mixed at the site.
• Concrete weights over 4,000 pounds per cubic
  yard.
• Therefore, it is important to determine amount of
  concrete first, because even a small volume of
  concrete can require moving a lot of material.
• Using Quikcrete is a popular option to reduce the
  work.

For more information go to http//www.nrmca.org/a
boutconcrete/
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Quikrete
http//www.quikrete.com/OnTheJob/ProductSelector.a
sp
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Mixing Concrete

• Characteristics of good mix
• Each aggregate particle is covered with cement
  paste
• Each aggregate particle is bound to others
• Cement paste
• Water--cement ratio must be exact proportions.
• Water in aggregate must be accounted for and
  deducted from water added to mix.
• Water--cement ratio must be adjusted for
  different service conditions.

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Concrete Mixes

• The proportions of water, Portland cement, fine
  aggregate and course aggregates are not the same
  for all concrete jobs.
• When mixing concrete it is common to express the
  mix (receipt) as a proportion. For example

1 1 ft3 (sack) of Portland cement 2
2 ft3 of fine aggregate 2-1/4 2.25 ft3 of
coarse aggregate

• The proportions can be used on a volume or weight
  basis

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Proportions

• The proportions must be changed to meet the
  service conditions.

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Mixing--cont.

• The amount of water in the aggregate must be
  included in the calculations.
• Effect of water in aggregate. (Fig 39-3)

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Water vs. strength
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Effect of Adding Water

• Adding 1 gal of water to 1 yd3 of concrete
• Increases slump 1 inch
• Decrease compressive strength by 200 psi
• Increases shrinkage by 10
• Increases permeability by up to 50

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Estimating Materials - By Volume

• Determine the amount of materials that will be
  required to pour a concrete slab that measures 12
  ft x 10 ft x 3 in. A 1-2.1/2-3.1/2 mix will be
  used.
• Step one determine the volume required.

• Adding the 10

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Estimating Materials - By Volume - cont.

• Step two determine the yield of one batch of the
  receipt.

• Because the aggregate mixes together, the yield
  by volume will only be about 2/3s of the total
  volume.

• Step three determine the number of batches
  required.
• 33 cubic feet of concrete is required, each one
  sack batch will yield 4.62 cubic feet.
• The number of batches

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Estimating Materials - By Volume - cont.

• Step four determine the Portland cement, fine
  aggregate and coarse aggregate.

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Concrete Mixes--cont.

• When concrete ingredients are measured using
  weight, density conversions must be used.
• Portland cement 94 lb/ft3 (100 lb/ft3 often
  used)
• Fine aggregate 100 lb/ft3
• Coarse aggregate 110 lb/ft3

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Estimating Materials - By Weight

• Determine the amount of materials that will be
  required to pour a concrete slab that measures 18
  ft x 12 ft x 4 in. A 1-2.-3.1/2 mix will be
  used.
• Step one determine the volume required.

• Adding the 10

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Estimating Materials - By Weight - cont.

• Step two determine the yield of one batch.

• Step three determine the number of batches.

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Estimating Materials - By Weight - cont.

• Step four determine the amount of cement, fine
  aggregate and coarse aggregate.

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Workable Mix

• Workability of concrete refers to the consistency
  of the wet concrete.
• Wetter concrete is more workable, but the higher
  the water content--the poorer the quality of the
  concrete.
• Characteristics of a workable mix
• Portland cement thoroughly mixed
• Aggregate fully covered
• Aggregates evenly distributed
• Minimum amount of water
• Uniform color and consistency
• Can be mixed, moved and placed with a shovel or
  spade

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Curing rate

• Concrete gains strength rapidly at first but
  continues to cure for years.
• Industry standard is to compare strength at 28
  days.

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Preparing Concrete Forms
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Concrete Forms

• Form a metal or wooden structure that confines
  the concrete to the desired shape or form until
  it hardens.
• The more complex the shape of the concrete--the
  more complex the forms.
• Normal concrete weights between 100 150 lb/ft3,
  therefore any forms supporting the weight of
  concrete must be well engineered.
• Forms can be constructed from dimensioned lumber
  and plywood, or in some cases, metal forms can be
  purchased or rented.

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Concrete Forms Information

• Use soft, clean straight lumber.
• Sharpen stakes evenly.
• Space stakes appropriately.
• Use a level to set the forms for the desired
  slope.
• Do not drive nails into concrete space.

• Insure stakes do not extend above the tops of the
  forms.
• Construct the inside surface of the forms to
  create the desired shape in the finished
  concrete.
• Coat all surfaces that will be in contact with
  the concrete.

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Concrete Forms--Wall Example
Board Tie
1 Boards or 3/4 Plywood
Brace
Stud
Spreader Block
Stake
Wire Tie
Wale
Concrete Footing
Agricultural Mechanics Fundamentals
Applications Herren--Fig 39-7
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Concrete Forms--Slab Example
Control Joint
Concrete
Straightedge
Form
Wall Stake
Packed Damp Sand
Agricultural Mechanics Fundamentals
Applications Herren--Fig 39-7
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Concrete Joints

• Three (3) types of joints are used for concrete.
• Isolation joints allow expansion and contraction
  of a concrete slab without generating potentially
  damaging forces within the slab itself or the
  surrounding structures

• Control (Contraction) joints this type of joint
  allows only for contraction or shrinkage of the
  slab, as can be anticipated during the curing
  process

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Concrete Joints-cont.

• Construction joints Construction joints can be
  horizontal or vertical and are formed when
  placement of the concrete is interrupted for some
  reason.
• It may be the end of a day's work or
• May be that some other work needs to be completed
  before resuming the placement.
• New concrete is placed against concrete that has
  solidified or skimmed over.

Butt
Dowel
Key
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Reinforcing Concrete

• Concrete is strong in compression, but weak in
  tension.
• Reinforcement is used to increase the tension
  strength.

• The type, size and spacing of the reinforcement
  is determined by the thickness of the slab and
  the designed load.
• Fibers are also being used to reinforce concrete.

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Pouring, Finishing, and Curing Concrete
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Pouring (Placing)

• Concrete should be placed--not poured.
• Concrete must be placed as closes to the final
  location as possible.
• Heavy--labor intensive to move.
• Moving causes the aggregate to segregate.
• Inspect forms and bracing before starting the
  placing.
• Insure all of the tools and help are available
  and ready before starting.
• Starts to harden in 15 minutes
• Once in place and hardening process has
  started--its there.
• Ensure concrete does not dry out.
• Dampen the soil/sand base before placing.
• Protect top surface after placing.

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Finishing Concrete

• The number of processes and type of process used
  is determine by the desired finished surface.
• Trowel
• Broom
• Exposed aggregate
• Grooved
• Stamped
• Burlap
• Etc.
• The finishing process has at least Four (4)
  steps.
• Screeding
• Floating
• Final surface
• Edging jointing

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(1) Screeding (2) Floating Concrete

• The process used is determined by the use of the
  concrete and the desired finished surface.

• 1. Screeding
• Screeding is striking off the concrete surface to
  insure it is level with the forms
• Pushes large aggregate below the surface
• Starts the smoothing process
• Can be accomplished with a straight board
• 2. Floating
• Brings fine aggregate and cement paste to the
  surface
• Produces smoother surface
• Uses a wooden or magnesium float

• Floating should not be attempted until the
  concrete has hardened to the point that stepping
  on it makes a very faint imprint.

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(3) Finishing Concrete

• Many options are available for the finished
  surface of concrete.

• Molded
• Individual
• In forms
• Stamped
• Exposed aggregate
• Colored
• Smooth surface
• Rough surface
• Other

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(4) Edging Jointing

• Part of the finishing process may also be edging
  and jointing

Edging
Edging forces the large aggregate away from the
corner and rounds the corner.
Reduces breakage on the edge.
Jointing
The groove cut or formed or cut in the surface
helps control the location of the cracks.
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Curing Concrete
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Curing Concrete

• Concrete hardens through a chemical process.
• Initial strength is reached in a week.
• Must be protected during this time

• Potential problems.

• Solutions

1a. Dampen base/forms before placing
1. Drying out
1b. Cover with plastic or canvas
2a. Insulate the surface
2. Excessive heat
2b. Dampen the surface
3a. Dont place on frozen ground
3. Freezing temperature
3a. Dont place when freezing temperature is
expected
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Curing Rate
28 Days
Days
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Effect of Curing conditions
of 28 Days
Days
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Masonry
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Introduction

• Masonry is Any type of construction using brick,
  stone, tile or concrete units held in place with
  Portland cement.
• Masonry units are held in place with mortar
• Mortar Portland cement, sand and water
• Other materials may be added.

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Masonry Construction

• Disadvantages
• Strength, durability and water resistance of
  finished product dependent on strength,
  durability and water resistance of masonry units.
• Labor intensive
• Different skills required than for wood frame or
  concrete.

• Ancient method of construction.

• Advantages
• Fireproof
• Insect and rodent proof
• Decay resistant
• Storm resistant
• Wear resistant
• Water (proof) resistant
• Strong
• Attractive
• Can be installed without expensive equipment
• Available locally
• Low original and maintenance costs
• Recyclable

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Masonry Units

• Building bricks
• Pavers
• Custom bricks
• Stone

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Masonry Units-cont.

• Concrete blocks (Fig 39-15)

• Light weight blocks

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Additional Topics

• Estimating number of block needed
• Constructing footers
• Mixing mortar
• Laying block

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Questions