1. Chemical Admixtures for Concrete Pipe
Ed Mansky
Grace Construction Products
Febuary 11, 2014
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2. Concrete Admixtures Learning Objectives
Provide an introduction of chemical admixtures for use in concrete
Discuss definitions, uses, benefits, and cautionary measures

3. Introduction Definition
A material other than water, aggregates, hydraulic cement, and fiber reinforcement, used as an ingredient of a cementitious mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mixing
Through chemical and physical actions, admixtures interact with the hydrating cementitious system to change the characteristics of the fresh or hardened state of concrete.
SCM is considered a mineral admix (supplementary cementitious materials)

4. Introduction
A modern wetcast concrete is more than a mixture of cement, aggregate and water
ADMIXTURES and MINERAL COMPONENTS are becoming as ESSENTIAL as PORTLAND CEMENT when making modern concrete
Today Concrete without mineral components or admixtures is found in museums
Admixtures enhance the properties of concrete and mortar in the plastic and hardened state. Effectiveness in concrete will depend on its concentration and the effect of the various constituents in the concrete mixture.
Very unusual to make concrete w/o an admix with wetcast – because of enhanced performance and/or economic considerations 4

5. Introduction Major reasons for using admixtures are:
To reduce the cost of concrete construction
To achieve certain properties in concrete more effectively than by other means
To maintain the quality of concrete during the stages of mixing, transporting, placing, and curing in adverse and varying weather conditions
To overcome certain emergencies during concreting operations
Keep in mind that no admixture of any type or amount can be considered a substitute for good concrete practice
Key slide. Highlight of the benefits of using admixtures
Productivity gains. Materials savings. Process improvements.

6. Introduction
Admixtures can be used to modify various fresh and hardened concrete properties:
Fresh state
Hardened state
decrease water content
increase workability
reduce segregation
reduce the rate of slump
loss
improve pumpability
improve placeability &
finishability
modify the rate of bleeding
retard or accelerate
setting time
improve freeze / thaw resistance
improve impact & abrasion resistance
inhibit expansion due to ASR
inhibit corrosion
reduce shrinkage cracking
reduce permeability
produce colored concrete
produce cellular concrete
Admixtures provide an important component to improving the performance of concrete.

7. Chemical Admixture Types
Water-reducing admixtures (plasticizers)
Retarding admixtures
Accelerators
Corrosion inhibitors
Air-entraining admixtures
Lubricants or surfactants
There are many kinds of chemical admixtures that can function in a variety of ways to modify the chemical and physical properties of concrete.

8. Water Reducers
Among the most common admixtures used in precast and pipe production is water reducers. There are many types, and it is imperative that producers understand their function to be sure they are gaining the maximum advantage when using them.
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9. Water Reducers and High Range Water Reducers (HRWR / Superplasticizers)
WRDA and Supers are of many differing chemistries and compositions and understanding how they work is important to concrete production.

10. Water Reducing Admixtures
Overview
Can be used to reduce water content, improve slump or both
Three groups: low-, medium- and high-range
How it works
Reducing flocculation and improves water efficiency
Effects on Concrete
Increased strength
Increased slump and workability
Keeps particles separated creating less friction between the particles and superior cement hydration. 5% - 12% for low range, high range reducer provide as much as 30% reduction in water. Mid range, while not recognized by ASTM C494 provide water reduction in the area between low and high range reducers. . Added benefit is a slight retarding affect, which can enhance workability time as well as result in increased 28 day strengths.

11. Water Reducer and High Range Water Reducer
Definition (ACI 116)
Admixtures that either increase slump of freshly-mixed mortar or concrete without increasing water content OR maintain slump with a reduced amount of water, the effect being due to factors other than air entrainment
Water reducers also referred to as Type A, D, E, F, & G per ASTM C 494.

12. Water Reducer and High Range Water Reducer
How they work
Superplasticizers, may reduce the water requirement by more than 30%, without the side effect of excessive retardation. By dispersing the cement grains and allowing superior hydration to take place, much improved strengths are a result.
Without Admixture
With Admixture

13. Water Reducer and High Range Water Reducer
How they work
Superplasticizers, may reduce the water requirement by more than 30%, without the side effect of excessive retardation. By dispersing the cement grains and allowing superior hydration to take place, much improved strengths are a result.
Water reducers and superplasticizers can have a dramatic effect on the workability of concrete. Slump increases without the addition of water.
Without Admixture
With Admixture

14. How Conventional Type A Water Reducers Work+
Water
Cement
When cement is mixed with water, cement grains cluster together to form “flocs”, which trap water inside them. This trapped water is not available to contribute to the workability of the plastic concrete, and causes non-uniform cement hydration.
Cement grains naturally cluster together to
form flocs, which trap water inside them

15. - Floc Busting Action of Water Reducers
1. Water Reducer coats the cement grains
Freed Water
Cement -
2. Water Reducer imparts negative charge to cement grains
Water reducers separate cement flocs into individual grains through the mechanism of electrostatic repulsion. Trapped water is released, and that water now available to increase workability and contribute to cement hydration
3. Like charges repel cement grains away from each other

16. - - - The Result: + admix = +
Cement flocs are broken up and water is evenly dispersed
The Result:
Increased Water Cut (Lower W/C Ratio): Lower water/cement ratio means improved product strength and quality, “insurance policy”
Improved Workability: Concrete that is easier to place and finish, with no sacrifice in quality
Freeing of the trapped water through the use of dispersents allows more cement surface areas to be contacted by water for improved hydration and improves the workability of the concrete mix.

17. Effect of Water Reducer
Water Reducer (disperses materials for better flowability)
Explanation Flocculation versus de-flocculation
w/o admix, cement “Flocks” together. With the admix, the particles are dispersed.
No Water Reducer (Materials are clinging together) 17

18. COMB POLYMERS Cement Dispersion by Steric Repulsion Comb Teeth Water
Hooking units,
Comb Backbone +
Cement + + + + +
Cement
The newest Mid Range / High Range Water Reducers are a formulated comb polymer blend.
Comb polymers have highly engineered polymer backbones to which are attached pendant polymer strings (comb teeth)
The backbone has a positive charge and therefore is attracted to the cement grain. The “teeth” then stretch out and repel each other through physical force which is called steric repulsion
The “teeth” are also hydrophylic, drawing water into the cement grain and ensuring increased rate of hydration. Because hydration is faster, set times are shorter while maintaining superior workability times.
Slump retention is good because the “teeth” keep the cement grains apart during the hydration process and maintain workability for a longer period of time.
Therefore, this technology has two great advantages over the conventional mechanisms. Excellent water reduction with longer slump life and shorter set times.
Comb polymer
Steric (physical) Repulsion Force

19. How Superplasticizers Work- video
This video demonstrates how water reducers and the newest superplasticizers work. Previous technologies allowed for water reduction and improved strengths through a mechanism of particle repulsion caused by electrical charges on the cement grains. New technologies of polycarboxylate admixtures allow for superior workability and cement dispersion through a completely different mechanism that involves engineered polymers and a more physical particle repulsion mechanism.

20. Why Water Reduction? Provides dispersion of cement particles Strength
reduces water demand while maintaining slump (workability) thus increases concrete strength
Benefit
lower concrete permeability
can reduce concrete costs with less cementitious material if used correctly
Wrap up. How and why water reduction is important to concrete production.

21. Classification
Normal water reducer TYPE A (decreases the water requirements by about 5 – 10%)
Ca or Na salts of lignosulfonic acid
salts of hydroxycarboxylic acids
Carbohydrate
Gluconates
Mid-range water-reducing (decreases the water requirements by about 6 – 12%) …. no ASTM
Complex aqueous solution of lignosulfonates with accelerating admixtures
Polycarboxylate ether with set and strength enhancing ingredients
Superplasticizer TYPE F&G (decreases the water requirements by about %)
Sulfonated melamine formaldehyde
Sulfonated naphtalene formaldehyde
Polycarboxylates
Chemistry for each of the admixture ranges vary due to water requirements; low range typically use lignins, gluconates. mid-range refined lignins or polycarboxylate, and high range is refined polycarboxylates or melamines or naphtalenes derivitives.
Most admixes are carbohydrate based

22. Effects on Properties of Fresh Concrete
The use of water reducer / superplasticizer:
Increases slump
Improves flow
Improves placeability
Improves pumpability
Improves finishability
Improves formed surfaces
Can have an effect on air content and setting
Setting times can be extended, workability times can be extended, and air entrainment admixture dosage generally has to be recalibrated.

23. Slump Flow Test - SCC
The ultimate in workability enhancement. Self Consolidating Concrete. Made possible by admixture developments.

24. Effects on Properties of Hardened Concrete Due to Lower w/cm Ratio
When using water reducer / HRWR
Compressive strength increases
Permeability decreases
Chloride resistance increases
Frost resistance improves
Increases sulfate resistance
Increases resistance to abrasion
In nut shell by creating lesser void areas, lesser chance for outside elements creating problems. Lower w/c translate to higher strength. However, additional cost, modification with air entraining, less responsive with some cements.
Features above are due to lower w/c

25. Retarding & Set Stabilizing
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26. Retarding Admixtures and/or Set Stabilizers
How it works
Decreases the rate of cement hydration (C3S)
Admixture absorbs into calcium hydroxide atoms and temporarily inhibit their growth into larger crystals
Effects on Concrete
Delays Initial set
Extends workability time
Two types; Type B retarder and Type D water reducer and retarding also provide a retarding effect. Both types offset unwanted effects of high temperatures / high cement contents, like acceleration of set and reduction of 28 day strengths.

27. Accelerators
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28. Accelerators How they work Why accelerate concrete?
Increases rate of cement hydration (C3S)
Why accelerate concrete?
Shorten the setting time
Quicker early strength
Reduce bleeding
Earlier finishing
Improved initial protection against freezing
Earlier use of structure / piece
Reduction of protection time to achieve a given quality
The admixture stimulates the calcium compounds in the cement. Accelerators are not anti-freezing agents, therefore concrete must be protected in freezing weather. Other types of accelerators would be silicates, alkali hydroxide, nitrates, and bromides.
Some accelerators are used to reduce set time only w/o increase in early strength, others are used specifically to increase early strength.
Be sure to verify if accelerator contains chloride or not

29. Accelerating Admixtures
2 Classes of Accelerating Admixtures:
Set Accelerator
Strength Accelerator (Early Age)
Calcium Chloride is a well known accelerator, but BEWARE, it should not be used in reinforced concrete
Several non-chloride, non-corrosive accelerators are available, but generally most are not as effective as calcium chloride
Calcium Chloride is not recommended for use in reinforced concrete due increased corrosion of the reinforcement in its presence. 29

30. Calcium Chloride Very effective & economical accelerator
Cautions when using chloride-bearing admixture
DO NOT use in ANY reinforced concrete
high potential to cause corrosion
calcium chloride should not exceed 2% in non reinforced concrete
calcium chloride should not exceed 1% when concrete contains uncoated aluminum conduit
can cause discoloration issues (dark and light gray spots, especially on hard trowled finishes)
Should not be used where sulfate resistance is required. Should be dissolved in a portion of mixing water before batching (reduce lumps that may disfigure concrete later). Should be dispensed separately in the mix from air entraining admixtures.
Be sure local specs allow this type of accelerator 30

31. Time of Set Control Retarding vs Accelerating
Use of admixes get you to where you want to be…either accelerated or retarded set times.
Always a compromise

32. Corrosion Inhibitors
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33. Corrosion Inhibitors How it works Effects on Concrete
Passive film enhances the protection of reinforcing steel from corrosion in the concrete
Generally, corrosion inhibitors are not needed to protect steel reinforcing, due to the passivating effect of the high pH in the concrete.
Effects on Concrete
May accelerate initial set
May improve early age strength
Typically concrete pH is around 12 to 13 during the initial hydration phase. These admixtures are added to concrete during batching and they protect embedded reinforcement by delaying the onset of corrosion and also reducing the rate of corrosion after initiation.

34. Corrosion Inhibitors Control Corrosion of Steel Reinforcement
Dosage dependent on anticipated chloride level
Corrosion inhibitors were developed to prevent / reduce the effects of chloride induced corrosion.
Chlorides introduced from deicing salts or seawater lead to corrosion of embedded steel in concrete. (Insert): The damage to this concrete parking structure resulted from chloride-induced corrosion of steel reinforcement. (50051).
Not uncommon to use gallons of corrosion inhibitor – depends upon anticipated chloride exposure and resulting corrosion.

35. Air Entraining
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36. Air Entraining Admixtures ASTM C260
Overview
Create stable system of microscopic air bubbles
How it works
Microscopic air bubbles gives water a place to expand during freezing conditions
Effects on Concrete
Increased resistance to freeze-thaw damage
Improved workability of fresh concrete
Every 1% air entraining potentially reduces the concrete strength by up to 5-10%
The admixture acts like a slight friction reducer this adds to effectiveness of the workability of fresh concrete.

37. Air-Entraining Admixtures
Definition
Are used to produce concrete that is resistant to the effects of freezing and thawing and to improve workability V
Pic just to show how it creates tiny bubbles.
Polished section of air-entrained concrete as seen through a microscopic

38. Air-Entraining Admixtures
Significance of freezing and thawing
The most potentially destructive weathering factor is freezing and thawing while the concrete is wet, particularly in the presence of de-icing chemicals used for snow and ice removal
Contrary to fresh concrete which can be protected, we can’t avoid the exposure of mature concrete to alternating freezing and thawing
Due to freezing and thawing, hardened concrete can suffer both internal as well as surface damage. Internal damage can lead to loss of strength and structural integrity.
The de-icing salts lower the freezing point of water and therefore create more freeze/thaw cycles

39. Mechanism of Frost Damage
Hydraulic pressures
Caused by the 9% expansion of water upon freezing
Growing ice crystals displace unfrozen water
If a capillary is above critical saturation (91.7% filled with water) hydraulic pressures results as freezing progresses
At low water contents, no hydraulic pressure should exist
Critical saturation begins at 91.7%
Water is forced ahead of the advancing freezing front
Water expands 9% on freezing
Internal hydrostatic pressures can disrupt the concrete

40. Effect of Entrained Air
Surface Damage
2% air
4% air
6% air
Difference between 2-6% =Dramatically improved Durability with air entrainment - even if it may not as strong
ASTM C 672: Samples are monitored visually and for loss of mass over a period of 50 or more cycles of freezing and thawing in presence of salts

41. Mechanism of Air Entrainment
Hydrophobic end is attracted to air within bubbles + -
Aggregate
Surface tension reduced – stable bubbles
Air
Charges around bubbles lead to repulsive forces between bubbles (prevent coalescence) + -
Cement + -
Cement + -
Aggregate
Bubbles adhere to cement & aggregate particles – cohesion of mix improved
AEA’s do not add air to the concrete…they make the air that is already there…STABLE

42. Un-wanted air in Concrete (Wetcast)
How much air should be in concrete (no admixtures)?
Less than 3%
How much air should be in concrete with no AEA admixture, only WR or other admixture?
Less than 3%
If you have MORE than 3% AIR in concrete with NO admixtures… it’s a cement issue
If you have MORE than 3% AIR in concrete with just WR (no AEA) … it’s an admixture issue or a cement issue
The above assumes that the quality of the water is OK, bad water can cause air issues (too much-too little)

43. Many factors effect the development of air entrainment.
Entraining Air
Many factors effect the development of air entrainment.
Mixing time
Materials
Sequencing
Temperature
Mixing Action
Equipment
Dosage Rates
Admixtures
*Almost everything!
It hasn’t been until recently that technology has been developed so that we can better understand what is going on in the mixer with regards to the development and amount of entrained air. We can now see the effectiveness of mixing, sequencing, materials, mix time etc and how it can effect the generation and amount of entrained air in a mix.

44. Lubricants and Surfactants
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45. Lubricants & Surfactants (Drycast)
How it works
Decreases surface friction and therefore aids in stripping forms
Increased reaction to vibration
Improved moisture retention
Effects on Concrete
Can improve appearance
Improved water tolerance
Increase in surface paste

46. Dry Cast admixes Productivity improvement Reduction in cracking Improved surface swipe Sharper joints / reduced repair
Rheology modifiers (mix lubricants) can enhance the mechanical consolidation of concrete mixes, speeding production and reducing the stickiness of the mixes. They can also improve the hydration characteristics of low water content mixes and reduce moisture loss due to evaporation. Improved surface finishes and leak proof joints can be a benefit of using these types of products.

47. ASTM Specs
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48. Current Admixture Standards
ASTM C 494
ASTM C 260
ASTM D 98
ASTM C 869
ASTM C 1141
ASTM C 1017
ASTM C 937
ASTM C 979
Chemical Admixtures
Air-entraining Admixtures
Calcium Chloride
Foaming Agents
Admixture for Shotcrete
Flowing Concrete
Grout Fluidifier
Pigments
Summary of ASTM standards for concrete admixtures. Within some of specs are many sub-specs, such as ASTM C494 has Type A-G categories.

49. QUESTIONS?

50. Thank You