PORTLAND CEMENT CONCRETE - Materials for Civil and Construction Engineers - page 298

SUMMARY

The design of durable portland cement concrete materials is the direct re-
sponsibility of civil engineers. Selection of the proper proportions of portland
cement, water, aggregates, and admixtures, along with good construction
practices, dictates the quality of concrete used in structural applications.
Using the volumetric mix design method presented in this chapter will lead
to concrete with the required strength and durability. However, the proper de-
sign of portland cement concrete is irrelevant unless proper construction pro-
cedures are followed, including the appropriate mixing, transporting, placing,
and curing of the concrete. To ensure that these processes produce concrete
with the desired properties, a variety of quality control tests are performed
by civil engineers, including slump tests, air content tests, and strength-
gain-with-time tests.
While the vast majority of concrete projects are constructed with conven-
tional materials, there are a variety of important alternative concrete formula-
tions available for specialty applications. These alternatives are introduced in
this chapter; however, the technology associated with these alternatives is rel-
atively complex, and further study is required in order to fully understand the
behavior of these materials.

QUESTIONS AND

PROBLEMS

7.1 The design engineer specifies a concrete strength of 5500 psi. Deter-

mine the required average compressive strength for
a. a new plant where s is unknown
b. a plant where for 22 test results
c. a plant with extensive history of producing concrete with

s = 500 psi

s = 400 psi

d. a plant with extensive history of producing concrete with

s = 600 psi

7.2 A project specifies a concrete strength of 24.1 MPa. Materials engi-

neers will design the mix for a strength higher than that to account
for variabilities.
a. Calculate the required average compressive strength of the mix de-
sign if the mixing plant has a standard deviation of
b. Using the ACI code equation, estimate what would be the modulus
of elasticity of this concrete at the required compressive strength.

s = 3.8 MPa.