Question

Problem 2:
Initial mixture proportions for a concrete with the following requirements and properties is needed:
28 Day Design Strength = 4000 psi
It is for a parking lot deck and columns, so it is not in contact with sulfates from soil or saltwater
Slump should be 4”
Aggregate properties are:
Coarse Fine
SGSSD 2.60 2.55
Absorption (%) 0.8% 1.9%
Fineness Modulus N/A 2.90
Nominal Size ¾” x #8 N/A
Dry Rodded Unit Weight (lbs/ft3) 91.3 N/A
Description Rounded Gravel N/A
No reliable records for the relationship between w/c and compressive strength are available for the
specific cement and aggregate combination being used, so use Table 12-3 or Figure 12-3 for the
relationship between compressive strength and w/c.
Not using any chemical admixtures other than air-entrainment, determine the mixture proportions (per yd3
of concrete with aggregates in the SSD state if the freeze/thaw exposure classification is
a) Class F0 (not exposed to freezing and thawing, but use a minimal amount to improve workability
or just in case it is exposed to frost once in awhile…for example San Luis Obispo)
b) Class F3 (exposed to freezing and thawing while wet and exposed to de-icing chemicals…typical
of a parking structure in New York, Minnesota, Illinois, Indiana, Massachusetts, etc.)
c) Compare your proportions for the two, and what governed the w/c?

Answer 1

Mix design with given specfications for both class F0 and F3 exposure condition is shown below.

Comparing both the mixes,

For class F3 exposed mix, cement content is increased and fine aggregates content is decreased compared to class F0 exposed mix.