Concrete…
maintaining the
Quality
Achieving durable exterior flatwork in
residential construction
Objectives
Review the exterior flatwork problem we face
 Discuss the issues with achieving durable
exterior flatwork

Technical summary
 What can the homebuilding industry do?

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?

What it looks like…
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)
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

Supplier’s cannot make a bullet proof concrete
Achieving Durable Exterior
Flatwork…Technical Review
Concrete
 Placing
 Finishing
 Curing
 Sealing & Maintenance

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
Placing

Subgrade should be dampened and not frozen


CSA A23.1 requires concrete to be placed within
120 minutes from batching


For more consistent set and improved workability
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)
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

Curing

Essential for surface durability!
Must balance 3 critical elements
Time
Temperature
Moisture
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
CSA Curing –Table 20
Level
1
Name
Basic
Description
2
Additional
7 d at > 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.
3
Extended
A wet-curing period of 7 d. The curing types
allowed are ponding, continuous sprinkling,
absorptive mat or fabric kept continuously wet.
3 d at > 10 °C or for a time necessary to attain
40% of specified strength
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
4/13/2015
15
Hot Weather/Severe Drying

When surface evaporation is more than
0.50kg/(m2/h) the concrete must be protected


Hot temperatures &/or windy conditions @ low relative
humidity
Evaporation retardant (Confilm, Profilm etc) is
recommended


Apply as soon as possible
Do not use as a finishing aid
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:
 Red Deer:
 Edmonton:

July – 29 : Sept – 24
July – 20 : Sept – 23
July – 20 : Sept – 26
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
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
Impact of Temperature on Concrete
11
6
3 2
Time to Initial Set
70 F (21 C)
19
8
60 F (16 C)
50 F (10 C)
11
40 F (4 C)
Time to Final Set
8
3
14
30 F (-1 C)
15
10
29
5
19
0
4/13/2015
3
Time to 500 psi
(3.5MPa)
6
20
57
38
30
Hours
72
47
40
50
60
70
80
20
Long Term Strength Development
Temperature of Concrete
vs
Time to 75% Design Strength
8
70 F (21 C)
60 F (16 C)
14
50 F (10 C)
18
25
40 F (4 C)
55
30 F (-1 C)
0
4/13/2015
10
20
Days
30
40
50
60
21
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
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
hasn’t 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
Achieving Durable Exterior
Flatwork…Homebuilder 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
The Challenge…
After 1 year of strengthening the links in the chain do you have:
This
4/13/2015
or
This
25
Questions?
ARMCA Residential Committee
Committee reinstated in 2011
 Looking for more representation

Home Builders
 Finishers


If interested contact Ed Kalis @ ARMCA