Practice Question: Volume of Water for Concrete Mixture
NCEES Civil PE Specification VII.C.: Concrete
Problem
Given a required water-cement ratio of 0.5, you are preparing a concrete mix to place the 1-foot-thick square spread footing pictured below.
If 5 sacks of cement are used in the mixture, what volume of water is required? Assume each bag of cement weighs 94 pounds.
Assume a specific weight of water of 62.4 pounds per cubic foot.
CORRECT 😃
INCORRECT 😟
% Students Correctly Answered:
71.6%
Solution
Answer: C) 3.8 cubic feet
Volume of Footing:
$$ V_{footing}=1\ ft\ast4\ ft\ast4\ ft=16\ ft^3 $$
Weight of Cement:
$$ W_{cement}=5\ast94\ lb=470\ lb $$
Water-Cement Ratio:
$$ w_{cr}=0.5 $$
Weight of Water required:
$$ w_{cr}=\frac{W_{water}}{W_{cement}} $$
$$ W_{water}=0.5\ast470\ lb=235\ lb $$
Volume of Water Required:
$$ V_{water}=\frac{W_{water}}{\gamma_{water}}=3.8\ ft^3 $$
