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Title:

Concrete

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Concrete maintaining the Quality Achieving durable exterior flatwork in residential construction – PowerPoint PPT presentation

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Date added: 23 March 2020
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Provided by: chbaedmont
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Tags: concrete | fume | silica

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Title: Concrete


1
Concrete maintaining the Quality
  • Achieving durable exterior flatwork in
    residential construction

2
Objectives
  • Review the exterior flatwork problem we face
  • Discuss the issues with achieving durable
    exterior flatwork
  • Technical summary
  • What can the homebuilding industry do?

3
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?

4
What it looks like
5
(No Transcript)
6
(No Transcript)
7
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)

8
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

9
Achieving Durable Exterior FlatworkTechnical
Review
  • Concrete
  • Placing
  • Finishing
  • Curing
  • Sealing Maintenance

10
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

11
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)

12
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

13
Curing
  • Essential for surface durability!
  • Must balance 3 critical elements

14
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
15
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

15
7/2/2015
16
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

17
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

18
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

19
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

20
Impact of Temperature on Concrete
11
19
29
57
72
7/2/2015
20
21
Long Term Strength Development
7/2/2015
21
22
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

23
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

24
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

25
The Challenge
After 1 year of strengthening the links in the
chain do you have
  • This
  • This

or
7/2/2015
25
26
Questions?
27
ARMCA Residential Committee
  • Committee reinstated in 2011
  • Looking for more representation
  • Home Builders
  • Finishers
  • If interested contact Ed Kalis _at_ ARMCA
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