CE 264 (Admixture) Exam
Study Guide
Admixtures - ANSWER ingredients other than portland cement, water, and aggregates
that may be added to concrete
Admixture - ANSWER to impart a specific quality to either the plastic (fresh) mix or the
hardened concrete (ASTM C494)
1. type, brand and amount of cement ;
2. water content
3. aggregate shape
4. gradation and proportions
5. mixing time
6. slump
7. temperatures of concrete and air - ANSWER The effectiveness of admixture depends
upon these factors:
1. air entrainers
2. water reducers
3. retarders
4. hydration controller admixtures
5. accelerators
6. specialty admixtures - ANSWER Admixtures are classified by the following chemical
and functional physical characteristics:
1. to reduce the cost of concrete construction
2. to achieve certain properties in concrete more effectively than by other means
3. to ensure quality of concrete during the stages of mixing, transporting, placing, and
curing in adverse weather conditions
4. to overcome certain emergencies during concrete operations - ANSWER The
Portland Cement Association (PCA) identifies four major reasons for using admixtures
(Kosmatka et al., 2011):
, Air entrainers - ANSWER produce tiny air bubbles in the hardened concrete to provide
space for water to expand upon freezing
Critical saturation - ANSWER Upon freezing, water expands in volume by 9%. If the
percent saturation exceeds 91.7%, the volume increase generates stress in the
concrete.
Hydraulic pressure - ANSWER Freezing water draws unfrozen water to it. The unfrozen
water moving throughout the concrete pores generates stress, depending on length of
flow path, rate of freezing, permeability, and concentration of salt in pores.
Osmotic pressure - ANSWER Water moves from the gel to capillaries to satisfy
thermodynamic equilibrium and equalize alkali concentrations. Voids permit water to
flow from the interlayer hydration space and capillaries into the air voids, where it has
room to freeze without damaging the parts.
Internal stresses - ANSWER reduce the durability of hardened concrete, especially
when cycles of freeze and thaw are repeated many times.
Critical saturation
Hydraulic pressure
Osmotic pressure - ANSWER three mechanisms contribute to the development of
internal stresses in the concrete
0.2% to 3% - ANSWER entrapped air voids represent approximately how much % of the
concrete volume
1mm - ANSWER All concrete contains entrapped air voids, which have diameters of
1% and 7.5% - ANSWER The entrained air voids are not connected and have a total
volume between
14 billion bubbles per cubic meter - ANSWER Concrete mixed for severe frost conditions
should contain approximately
Frost resistance - ANSWER improves with decreasing void size, and small voids reduce
strength less than large ones.
fineness of air voids - ANSWER is measured by the specific surface index, equal to the
total surface area of voids in a unit volume of paste.
23,600 m2 /m3 (600 in.2 /in.3 - ANSWER The specific surface index should exceed
_______ for frost resistance
air entrainment - ANSWER provides other important benefits to both freshly mixed and
hardened concrete.
improves concrete's resistance to several destructive factors, including freeze-thaw
Study Guide
Admixtures - ANSWER ingredients other than portland cement, water, and aggregates
that may be added to concrete
Admixture - ANSWER to impart a specific quality to either the plastic (fresh) mix or the
hardened concrete (ASTM C494)
1. type, brand and amount of cement ;
2. water content
3. aggregate shape
4. gradation and proportions
5. mixing time
6. slump
7. temperatures of concrete and air - ANSWER The effectiveness of admixture depends
upon these factors:
1. air entrainers
2. water reducers
3. retarders
4. hydration controller admixtures
5. accelerators
6. specialty admixtures - ANSWER Admixtures are classified by the following chemical
and functional physical characteristics:
1. to reduce the cost of concrete construction
2. to achieve certain properties in concrete more effectively than by other means
3. to ensure quality of concrete during the stages of mixing, transporting, placing, and
curing in adverse weather conditions
4. to overcome certain emergencies during concrete operations - ANSWER The
Portland Cement Association (PCA) identifies four major reasons for using admixtures
(Kosmatka et al., 2011):
, Air entrainers - ANSWER produce tiny air bubbles in the hardened concrete to provide
space for water to expand upon freezing
Critical saturation - ANSWER Upon freezing, water expands in volume by 9%. If the
percent saturation exceeds 91.7%, the volume increase generates stress in the
concrete.
Hydraulic pressure - ANSWER Freezing water draws unfrozen water to it. The unfrozen
water moving throughout the concrete pores generates stress, depending on length of
flow path, rate of freezing, permeability, and concentration of salt in pores.
Osmotic pressure - ANSWER Water moves from the gel to capillaries to satisfy
thermodynamic equilibrium and equalize alkali concentrations. Voids permit water to
flow from the interlayer hydration space and capillaries into the air voids, where it has
room to freeze without damaging the parts.
Internal stresses - ANSWER reduce the durability of hardened concrete, especially
when cycles of freeze and thaw are repeated many times.
Critical saturation
Hydraulic pressure
Osmotic pressure - ANSWER three mechanisms contribute to the development of
internal stresses in the concrete
0.2% to 3% - ANSWER entrapped air voids represent approximately how much % of the
concrete volume
1mm - ANSWER All concrete contains entrapped air voids, which have diameters of
1% and 7.5% - ANSWER The entrained air voids are not connected and have a total
volume between
14 billion bubbles per cubic meter - ANSWER Concrete mixed for severe frost conditions
should contain approximately
Frost resistance - ANSWER improves with decreasing void size, and small voids reduce
strength less than large ones.
fineness of air voids - ANSWER is measured by the specific surface index, equal to the
total surface area of voids in a unit volume of paste.
23,600 m2 /m3 (600 in.2 /in.3 - ANSWER The specific surface index should exceed
_______ for frost resistance
air entrainment - ANSWER provides other important benefits to both freshly mixed and
hardened concrete.
improves concrete's resistance to several destructive factors, including freeze-thaw
