HW5

Question 1

Define workability of concrete.

Answer 1

Workability, according to ASTM C125, describes effort required to manipulate
freshly mixed concrete without loss of homogeneity.

Question 2

Define cohesiveness

Answer 2

Cohesiveness describes the tendency for a concrete mix to bleed (where water
moves out of the mix) and/or segregate (where aggregates segregate from the
matrix).

Question 3

What is the difference between bulk specific gravity and dry rodded unit weight
of an aggregate

Answer 3

Bulk specific gravity is the density of the material normalized by the density of
water (This is a unitless value). Dry rodded unit weight is the density of a given
material after it has undergone a standardized method of compaction

Question 4

Give two examples where high workability of concrete is required for
construction

Answer 4

(1) A highly congested reinforcement cage; (2) Pumping is required to place
concrete; (3) Complex formwork (This list is not exhaustive)

Question 5

If the slump of your mix is too low for a certain application, how would you
correct for this?

Answer 5

To increase the slump of a mix, the amount of water in the mix should be
increased (keeping the same water-cement ratio).

Question 6

What is the definition of “absorption capacity” of aggregates?

Answer 6

Absorption capacity is the total amount of moisture required to bring aggregate
from oven-dry to saturated surface dry condition

Question 7

What do we mean by “free moisture” of an aggregate?

Answer 7

Free moisture means the amount of excess water in a given batch of aggregates
beyond saturated surface dry condition (water that the aggregate will give to the
mix. Note that if this number is negative, aggregates will take water from the mix,
this is called ‘effective absorption’).

Question 8

Would you expect a difference in absorption capacity in case of igneous rock such
as basalt compared to sandstone? Please explain

Answer 8

Yes, igneous rocks, such as basalt have a much lower porosity than sandstone and
should therefor exhibit a lower absorption capacity

Question 9

What is the range in value of the dry-rodded unit weight of coarse aggregates
commonly used in normal weight concretes?

Answer 9

From Lecture: 100-140 lb/cuft