Concrete

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Concretemaintaining the Quality

• Achieving durable exterior flatwork in
  residential construction

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Objectives

• Review the exterior flatwork problem we face
• Discuss the issues with achieving durable
  exterior flatwork
• Technical summary
• What can the homebuilding industry do?

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Residential Exterior Flatwork

• Concrete work subcontracted to a finishing
  company
• Exterior concrete looks great when home is turned
  over
• Homebuilder hears from unhappy home owner after
  1st or 2nd winter
• What is the problem? What caused it? Who is
  responsible?

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What it looks like
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What causes it

• Inadequate or no curing and/or
• Inappropriate finishing and/or
• Inappropriate concrete and/or
• Incorrect or no sealing maintenance
• In combination with exposure to freezing
  temperatures water ( de-icing chemicals)

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What do we do?

• Must treat achieving durable exterior flatwork as
  a chain of important events
• Each link must be executed correctly to prevent
  deterioration
• Industry partners must work together
• Suppliers cannot make a bullet proof concrete

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Achieving Durable Exterior FlatworkTechnical
Review

• Concrete
• Placing
• Finishing
• Curing
• Sealing Maintenance

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Concrete

• Alberta Building Code Canadian Standards
  Association require
• C-2 Exposure (de-icing chemicals freeze/thaw)
• 32MPa (or 30MPa where indigenous aggregates do
  not achieve 32MPa)
• 0.45 w/cm
• 5-8 fresh air (3 hardened air with spacing
  factor not exceeding 0.23mm)
• ARMCA Recommends DURA-MIX
• above requirements and
• 300kg/m3 of cement minimum

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Placing

• Subgrade should be dampened and not frozen
• For more consistent set and improved workability
• CSA A23.1 requires concrete to be placed within
  120 minutes from batching
• Prolonged mixing results in loss of air, slump
  compressive strength
• Water should not be added to increase slump above
  100mm
• Additional water significantly reduces freeze
  thaw resistance
• Slump over 100mm should be achieved with a high
  range water reducer (superplasticizer)

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Finishing

• Minimize handling and do not over vibrate
• Allow bleed water to evaporate before finishing
• Do not use steel trowels (Fresno) or power
  trowels on air entrained concrete
• CSA A23.1 Steel trowel finish should not be
  applied to air-entrained concrete
• Blistering or scaling might occur if trowel
  finish is applied
• Use a magnesium float and concrete broom

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Curing

• Essential for surface durability!
• Must balance 3 critical elements

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Methods of curing

• There are two ways to cure concrete
• 1) add water to the surface to replace the water
  that is evaporating
• 2) seal the concrete to prevent the water from
  evaporating
• Note adding water to the surface is NOT adding
  water that will be worked into the concrete
  mix--that would weaken it.

Wet Curing Blankets
Liquid Curing Membrane
Ponding Method
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CSA Curing Table 20
Description 3 d at gt 10 C or for a time
necessary to attain 40 of specified strength
Name Basic
Level 1
7 d at gt 10 C and for a time necessary to attain
70 of specified strength. When using silica
fume concrete additional curing procedures shall
be used See Clause 1.3.13.
Additional
2
A wet-curing period of 7 d. The curing types
allowed are ponding, continuous sprinkling,
absorptive mat or fabric kept continuously wet.
Extended
3

• Note (2) recommends concrete be allowed to air
  dry for at least one month after curing before
  exposure to de-icing chemicals
• C-2 Exposure requires Level 2 curing

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7/2/2015
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Hot Weather/Severe Drying

• When surface evaporation is more than
  0.50kg/(m2/h) the concrete must be protected
• Hot temperatures /or windy conditions _at_ low
  relative humidity
• Evaporation retardant (Confilm, Profilm etc) is
  recommended
• Apply as soon as possible
• Do not use as a finishing aid

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High Evaporation Days

• ARMCA website has a tool to calculate evaporation
  rate
• Input values concrete temperature, air
  temperature, relative humidity and wind velocity
• July September 2011, of days where protection
  was required
• Calgary July 29 Sept 24
• Red Deer July 20 Sept 23
• Edmonton July 20 Sept 26

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Cold Weather

• Concrete must not freeze before it has reached
  3.5MPa!
• Concrete needs a significant portion of design
  strength to withstanding freeze thaw cycles
• Concrete must be allowed to dry out mature
  before first winter
• Use of winter heat (warm concrete
  accelerators) does not replace required curing

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Cold Weather Construction

• Local municipalities require cold weather
  construction practices for pavement placed after
  September 30th
• CSA A23.1 Level 2 curing required
• 7 days at a minimum of 10 C or the time required
  to attain 70 of 28 day strength

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Impact of Temperature on Concrete
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7/2/2015
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Long Term Strength Development
7/2/2015
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Sealing Maintenance

• Properly seal the concrete 28 days after concrete
  placement before exposure to traffic
• Penetrating sealers (silane or siloxane) are
  recommended and should be reapplied at least
  every 3yrs
• Concrete placed after Sept 15 should be sealed
  the following spring
• Concrete should be cleaned yearly
• Snow and ice should be removed as it accumulates

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De-icing Chemicals

• Avoid whenever possible
• All increase the number of freeze thaw cycles
  some attack the concrete matrix
• Especially damaging in the first winter when
  concrete hasnt reached its full strength
• Sand is the recommended product to improve
  traction on ice
• Most of the de-icing chemicals present on
  driveways come from tire transfer from city roads
• If all the links in the chain are executed
  correctly exterior flatwork can withstand
  exposure to standard de-icing chemicals

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Achieving Durable Exterior FlatworkHomebuilder
Influence

• Insist on DURA-MIX test concrete before placing
• Insist on certified journeyman finishers
• Insist finishers use appropriate curing methods
  for the environmental conditions
• Provide home owners with the appropriate
  information regarding sealing maintenance

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The Challenge
After 1 year of strengthening the links in the
chain do you have

• This

• This

or
7/2/2015
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Questions?
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ARMCA Residential Committee

• Committee reinstated in 2011
• Looking for more representation
• Home Builders
• Finishers
• If interested contact Ed Kalis _at_ ARMCA