Concrete admixtures are added ingredients beyond cement, water, and aggregates that are used to modify the properties of fresh and hardened concrete. The main types of admixtures are air entrainers, water reducers, set retarders, set accelerators, and plasticizers. Air entrainers add microscopic air bubbles that increase durability in freezing environments. Water reducers allow a reduction in water while maintaining workability, increasing strength. Set retarders delay setting for hot weather, while set accelerators increase early strength for cold weather. Plasticizers make low-slump concrete flowable. Admixtures are selected and dosed to achieve specific concrete properties for construction needs.

2. What Are They?
 Ingredients other than:
 Cement
 Water
 Aggregates
 Added before or during mixing.

3. Why Are They Used?
 To modify properties of fresh & hardened concrete
 To ensure the quality of concrete during mixing,
transporting, placing & curing
 To overcome certain unexpected emergencies during
concrete operations (ie, set retarders)
 to reduce the cost of concrete construction

4. How Applied?
 Most admixtures are supplied in a ready-to-use form
and added at plant or jobsite.
 Pigments and pumping aids are batched by hand in
VERY small amounts

5. Effectiveness
 Factors effecting results of use:
 Type & amount of cement:
○ Chemistry effects due to portland components
 Water content & Slump
○ Flowability will effect how well admixtures are
activated due to internal agitation actitivity
 Mixing time
○ Effects of admixtures are dependent on time
allowed to react.

6. 5 Typical Functions of Admixtures:
 Air entraining
 Water-reducing
 Retarders
 Set Accelerators
 Plasticizers (superplasticizers)
 Some other “specialty” types exist:
 Color, corrosion inhibitors, etc.

7. Air Entrainment
 The entrained air bubbles act as a physical buffer
against the cracking caused by the stresses due to water
volume augmentation in freezing temperatures.
 Developed in 1930s
 Today, recommended for all concretes exposed to
freeze/thaw cycles
 Imposes microscopic air cells that relieve internal
pressure of freezing water
 High resistance to cycles of wetting and drying
 High degree of workability
 High degree of durability

8. Water Reducers
 Internal lubricant
 Allows for reduction of water/cement ratio while
maintaining workability (increased strength)
 Can reduce water requirement at least 5-10%
 Obtain higher slump without adding water
 lower CO2 emissions and energy usage per volume of
concrete produced
 With this type of admixture, concrete properties are
improved and help place concrete under difficult conditions.
 Mid-range water reducers result in at least 8%
 Mid-range water reducers provide more consistent
setting times than standard water reducers.

9. Water Reducer: Pozzolith
 Performance:
 Improves workability at low w/c ratio
 Normal to retarded set times
 Helps eliminate “cold joints”

10. Set Retarders
 Set retarding concrete admixtures are used to delay
the chemical reaction that takes place when the
concrete starts the setting process. These types of
concrete admixtures are commonly used to reduce
the effect of high temperatures that could produce a
faster initial setting of concrete.
 Slows curing rate
 Used to counteract hot weather conditions that cause
increased rate of hardening.
 This makes placing and finishing difficult
 Pozzolith 961

11. Set Accelerators
 Accelerating concrete admixtures are used to increase
the rate of concrete strength development, or to reduce
concrete setting time. Calcium chloride could be named
as the most common accelerator component
 Increase curing rate for achievement of high early
strength
 Speeds up start of finishing operations
 Used for speeding curing rate in cold weather
concreting
 Pozzolith 122

12. Master Builders Pozzolith
 Performance:
 High early strength
 Accelerated setting time characteristics

13. Superplasticizers
 The main purpose of using super plasticizers is to
produce flowing concrete with a high slump in the
range of 7-9 inches to be used in heavily reinforced
structures and in placements where adequate
consolidation by vibration cannot be readily achieved.
The other major application is the production of high-
strength concreteat w/c's ranging from 0.3 to 0.4. It has
been found that for most types of cement, super
plasticizer improves the workability of concrete.
 Also known as high-range water reducers (HRWR)
 Reduce water requirement by 12-30%
 Can make low slump concrete flow like high-slump
mix
 Makes mix highly fluid and can be placed with little or
no vibration or compaction
 Effect lasts only 30-60 minutes and is followed by rapid