PORTLAND CEMENT CONCRETE - Materials for Civil and Construction Engineers - page 296

The addition of fibers to concrete reduces the workability. The extent of
reduction depends on the aspect ratio of the fibers and the volume concen-
tration. Generally, due to construction problems, fibers are limited to a max-
imum of 2% by volume of the mix. Admixtures can be used to restore some
of the workability to the mix.
Since the addition of fibers does not greatly increase the strength of con-
crete, its use in structural members is limited. In beams, columns, suspended
floors, etc., conventional reinforcing must be used to carry the total tensile
load. Fiber-reinforced concrete has been successfully used for floor slabs,
pavements, slope stabilization, and tunnel linings.

■ 7.6.10 Roller-Compacted Concrete

Based on the unique requirements for mass concrete used for dam con-
struction, roller-compacted concrete (RCC) was developed. This material
uses a relatively low cement factor, relaxed gradation requirements, and a
water content selected for construction considerations rather than strength.
RCC is a no-slump concrete that is transported, placed, and compacted with
equipment used for earth and rockfill dam construction. The RCC is hauled
by dump trucks, spread with bulldozers, and compacted with vibration
compactors. Japanese experience using RCC in construction found several
advantages:

1. The mix is economical, because of the low cement content.
2. Formwork is minimal, because of the layer construction method.
3. The low cement factor limits the heat of hydration, reducing the need
for external cooling of the structure.
4. The placement costs are lower than those for conventional concrete
methods, due to the use of high-capacity equipment and rapid place-
ment rates.
5. The construction period is shorter than that for conventional concrete.

In addition, experience in the United States has demonstrated that RCC
in-place material costs are about one-third those of conventional concrete.
The two primary applications of RCC have been for the construction of dams
and large paved areas, such as military tank parking aprons.

■ 7.6.11 High-Performance Concrete

While the current specifications for concrete have provided a material that
performs reasonably well, there is concern that the emphasis on strength in
the mix design process has led to concrete that is inadequate in other per-
formance characteristics. This has led to an interest in developing specifi-
cations and design methods for what has been termed high-performance
concrete (HPC). The American Concrete Institute (ACI) defines HPC as con-
crete that meets special performance and uniformity requirements, which
cannot always be obtained using conventional ingredients, normal mixing