unit 6 Flashcards
______ makes the Concrete Workable and molded into the Desired Shape.
Water
The amount of water in concrete controls many fresh and hardened properties in concrete including
workability, compressive strengths, permeability, water tightness, durability and weathering, drying
shrinkage, and potential for cracking. (t or f)
t
The ratio of the amount of water, minus the amount of water absorbed by the aggregates, to the
amount of cementitious materials by weight in concrete is called the _____________________.
water-cementitious ratio
The w/cm ratio equation is?
w/cm= (weight of water – weight of water absorbed in the aggregates) divided by the weight
of cementitious materials.
Upon _________, the paste or glue consisting of the cementitious materials and water binds the
aggregates together.
hardening
Increasing the w/cm ratio also improves other hardened concrete properties by increasing the
density of the paste which lowers the permeability and increases water tightness, improves durability
and resistance to freeze-thaw cycles, winter scaling and chemical attack. (t or f)
f (decreasing)
Designers select maximum w/cm ratios and minimum strengths primarily based on exposure
conditions and durability concerns – not load-carrying capacity requirements. (t or f)
t
For different exposure
conditions, use the code required maximum w/cm ratios and minimum strengths to reduce the
permeability of the concrete. Doing so will decrease the concrete’s resistance to weathering. (t or f)
f (increase the concrete’s resistance to weathering.)
The most important factor affecting the amount of drying shrinkage and the subsequent potential
for cracking is the ___________________.
water content or the amount of water per cubic meter of concrete
concrete shrinkage increases with lower water contents (t or f)
f (higher)
About half of the water in
concrete is consumed in the chemical reaction of hydration and the other half provides the concrete’s
workability. (t or f)
t
Except for the water lost to bleeding and absorbed by the base material or forms, the
remaining water that is not consumed by the hydration process contributes to drying of shrinkage. (t or f)
t
The ease of mixing, placing, consolidating and finishing concrete is called __________.
workability
The ____________o f the mixture is the single most important factor that affects workability.
water
content
Adding more water to the concrete increases workability but more water also increases the potential
for segregation (settling of coarse aggregates particles), increased bleeding, drying shrinkage, and
cracking in addition to decreasing the strength and durability. (t or f)
t
If measured slumps are less than allowed by the specifications, slumps may be adjusted by a ____-
time addition of water.
one
in adding water onsite the water is should not exceed the maximum water content for the batch as established by the accepted
concrete mixture proportions (t or f)
t
in adding water onsite it is important that the concrete has been discharged from the mixer except for slump testing (t or f)
f (no concrete has been discharge)
in adding water onsite All water additions shall be completed within __ minutes from the start of the first water
addition.
15
in adding water onsite Water shall be injected into the mixer with such pressure and direction of flow to allow
for proper distribution within the mixer. (t or f)
t
in adding water onsite The drum shall be turned an additional __revolutions or more at mixing speed to ensure
a homogeneous mixture
30
Before adding water on the site, the allowable amount of water that can be added must be known. (t or f)
t
This amount should be printed on the delivery ticket or be determined after the pre-construction
meeting and be agreed upon by parties. (t or f)
f (during the pre-construction meeting)
______ is the key component in concrete.
Water
