This document provides an overview of basic concrete technology, including definitions of concrete and its components, the importance of water content, effects of air entrainment, causes of cracking, types of green concrete, uses of helix steel fibers, considerations for slump, and recommendations for contractor-specified slump. It discusses how concrete is composed of paste and aggregates, how water is critical for strength and durability, benefits of entrained air, and factors that influence cracking, air content, and slump.

1. Basic Concrete Technology
 What is Concrete?
 Importance of water
 Air in Concrete
 Cracking
 Green Concrete
 Helix Dosing
 Slump
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2. What is Concrete?
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3. What is Concrete?
 Two components
 Paste (cement, water and air)
 Aggregates (sand and rock)
 Hardening process by hydration
 Chemical reaction with water
 Does not harden by drying
 Normal weight concrete
 2200 to 2400 kg/m3
 Lightweight concrete
 As low as 240 kg/m3
 High density concrete
 Up to 6000kg/m3
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4. Critical Influences on Concrete Quality
 Environment
 Temperature, humidity, wind, rain/snow
 Water Content
 Use of SCMs
 Admixture use
 Cracking tendencies
 Shrinkage, restraint, moisture loss
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5. Importance of Water
 For a given set of materials, the strength of concrete depends solely
on the amount of water for a given amount of cement
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6. Damaging Effects of Adding Water
 Higher w/cm = lower strength
 Reduced durability, higher permeability
 Increased bleed water
 Delayed finishing
 Increased shrinkage and cracking
 Increased likelihood of surface blemishes and discolouration
 Scaling
 Blisters
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7. Air in Concrete
 Entrapped Air
 All concrete has it
 Typically <2% of volume
 Irregular shape/size, normally 1mm and larger
 Does not contribute to freeze-thaw durability
 Super P’s will often increase levels of entrapped air
 Entrained Air
 Microscopic spherical bubbles in paste normally 10 to 1000 micron
 Typically 3 to 8% of volume
 Intentionally created with admixtures
 Affects various properties of concrete
 Air entrained concrete typically 2 to 9% lower strength per percentage
point of air
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8. Why Add Air?
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9. What Affects Air Content?
 Cementitious materials
 Amount of material
 Type of material, cement, ash
 Aggregates
 Changes in gradation of both coarse and fine aggs
 Material finer than 160 micron
 Water
 Mixing, too much or not enough
 Time
 Temperature
 Vibration
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10. Cracking
 Concrete Shrinks
 Drying
 Chemical
 Thermal
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 A crack forms when tensile
stress exceeds tensile
strength
 Unrestrained slab = No Cracks
 Restrained slab = Cracks

11. Controlling Cracking
 Jointing
 Correct use of reinforcing steel
 Design detailing
 Incorrect application can cause restraint
 Larger aggregate size
 Well graded aggregate blend
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12. Green Concrete
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Concrete, Cement and CO2

13. Green Concrete
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SCMs

14. Helix Dosage
• For a given structural design an appropriate Helix dosage can be
prescribed to remove most, if not all, of the rebar in a structural
element
• In the Canadian market, Helix dosage prescriptions are provided in
kg/m3
• Helix is supplied in 10 kg cartons
• The concrete supplier will generate an appropriate truck load quantity
of concrete to ensure a full number of boxes is consumed in each
truck
• This avoids partial boxes and potential dosing errors

15. Helix Dosage Example
 Customer requires 34 m3 of concrete
 Dosage prescription is 6.3 Kg/m3
 34 m3 X 6.3 Kg/m3 = 214.2 Kg of Helix or 22 Boxes
 3 T/L’s @ 6 Boxes/9.4 m3 truck = 6.38 Kg/m3
 1 T/L @ 4 Boxes/6.0 m3 truck = 6.67 Kg/m3
 Total 34.2 m3 delivered @ 6.43 Kg/m3

16. CSA 4.3.2.3.2 - Tolerances in slump or slump flow
• Tolerances for slump shall be within the following applicable ranges:
– (a) when the specified slump is less than 80 mm, the allowable variation shall be +/-
20 mm;
– (b) when the specified slump is 80 mm to 180 mm, the allowable variation shall be
+/- 30 mm; and
– (c) when the specified slump is greater than 180 mm, the allowable variation shall
be +/- 40 mm.
– Tolerance for slump flow shall be +/- 70 mm.

17. Slump Tolerances
• Slump tolerances exist to account for variability that the concrete
supplier faces in aggregate moisture content, environmental
conditions (temperature and humidity), and transit time.
• Concrete mixes are designed to achieve specified strengths @ 28 days
with the specified slump (i.e. conventional mixes target an 80 mm
delivered slump)

18. Helix and Slump
 As a rule, the addition of any fibre to a concrete mixture will tend to
“stiffen” the mix
 Even though Helix exhibits the highest degree of workability of any
steel fibre, it is not exempted from this rule
 The conventional job site wisdom of “just give it a little drink” must be
avoided by any responsible contractor

19. “Give it a little drink?” - Source: NRMCA CIP 26

20. Helix and Slump Recommendations
 Flat work – 110-120 mm Slump
 ICF – 130-150 mm Slump to avoid material hangup on webs and rebar
(if present)
 Water reducers / Super Plasticizers are available to increase slumps up
to 200 mm (and beyond for) conventional concrete mixes
 Water reducers / Super Plasticizers are your cheapest form of
insurance when it comes to concrete performance and strength

21. Contractor Specified Slump Recommendation
 Have an open and honest discussion with your pump and placing
crews as to the slump they require and convey that requirement to
your concrete supplier.
 Remember that one way or another, the pump and placers will get the
slump they desire – either with water reducers/super plasticizers or
with water
 A workable mix reduces pump and placer time and as such also
reduces cost
 Remember the there is a difference between low price and low cost.
(with or without fibres)