chapter 3 rigid pavement - DOT On-Line Publications - Department ...

L
2
R'RWA TECEXICAL ADVISORY T 5080.17
July 14, 1994
Microsilica has been used as an
addition to concrete up to
15 percent by weight of cement,
although the normal proportion is
10 percent. With an addition of
15 percent, the potential exists
for very strong, brittle concrete.
It increases the water demand in a
concrete mix; however, dosage rates
of less than 5 percent will not
typically require a water reducer.
High rep.lacement rates will require
the use of a high range water
reducer.
Microsilica greatly increases the
cohesion of a mix, virtually
eliminating the potential for
segregation. However, the cohesion
may cause mixes to be sticky and
difficult to finish. It may be
necessary to specify a higher slump
than normal to offset the increased
cohesion and maintain workability.
In addition, microsilica in the mix
greatly reduces bleeding;
therefore, mixes which contain
microsilica tend to have a greater
potential for plastic shrinkage
cracking. It is imperative to use
the proper curing methods to
prevent the surface water from
evaporating too quickly.
4. PROPORTIONING. Most of the concrete placed in highway
facilities in the United States are under severe
exposure conditions. State highway agencies specify a
recipe for concrete mixes which includes minimum cement
content, maximum water-cement ratio, air content range,
and minimum strength. These requirements are necessary
to -- achieve - durability, as well as strength.
a. The maximum aggregate size should be as large as
possible. This reduces total aggregate surface
area and results in lower cement demand. The
3.10.11