116 CHAPTER FIVE
non-air-entrained concrete and from 0.54 to 0.35 for air-entrained concrete.
These values are for a specified 28-day compressive strength in lb/in^2 or
MPa, of 2500 lb/in^2 (17 MPa) to 5000 lb/in^2 (34 MPa). Again, refer to the ACI
Codebefore making any design or construction decisions.
Maximumw/cratios for a variety of construction conditions are also listed in
the ACI Code. Construction conditions include concrete protected from exposure
to freezing and thawing; concrete intended to be watertight; and concrete exposed
to deicing salts, brackish water, seawater, etc. Application formulas for w/cratios
are given later in this chapter.
JOB MIX CONCRETE VOLUME
A trial batch of concrete can be tested to determine how much concrete is to be
delivered by the job mix. To determine the volume obtained for the job, add the
absolute volume Vaof the four components—cements, gravel, sand, and water.
Find the Vafor each component from
(5.2)
where Vaabsolute volume, ft^3 (m^3 )
WLweight of material, lb (kg)
SGspecific gravity of the material
wudensity of water at atmospheric conditions (62.4 lb/ft^3 ; 1000 kg/m^3 )
Then, job yield equals the sum of Vafor cement, gravel, sand, and water.
MODULUS OF ELASTICITY OF CONCRETE
The modulus of elasticity of concrete Ec—adopted in modified form by the ACI
Code—is given by
(5.3)
With normal-weight, normal-density concrete these two relations can be simpli-
fied to
(5.4)whereEcmodulus of elasticity of concrete, lb/in^2 (MPa); and specified
28-day compressive strength of concrete, lb/in^2 (MPa).
fc47002 fc MPa in SI units
Ec57,000 2 fc lb/in^2 in USCS units
0.043wc1.5 2 fc MPa in SI units
Ec 33 wc1.5 2 fc lb/in^2 in USCS units
VaWL
(SG)Wufc