Roller-Compacted Concrete
Concrete Basics
Home > Roller-Compacted Concrete  The
use of roller-compacted concrete (RCC) originated in Canada during
the mid-1970s when dry land log sorting became mandatory for the
forest industries of British Columbia. RCC, a durable paving material
that carries heavy loads, is now developing as a fast, economical
construction method for dams, off-highway pavement projects, heavy-duty
parking and storage areas, and as a base for conventional pavement.
RCC is a stiff, zero-slump concrete mixture with the consistency
of damp gravel comprised of local aggregates or crushed recycled
concrete, portland cement, and water. The mixture is placed and
roller compacted with the same commonly available equipment used
for asphalt pavement construction. The process requires no forms,
finishing, surface texturing, or joint sawing and sealing.
RCC has a low water content, requiring
it to be mixed in a continuous flow system, usually a pugmill, instead
of a ready mixed truck. A dump truck transports freshly mixed RCC
to the construction site where workers place the mixture in layers,
called lifts, using a conventional asphalt spreader. Lifts, which
range from 8-12 inches (20-30 cm) in thickness, are then compacted
using vibratory steel-wheel and pneumatic tire rollers. Immediately
after workers complete compaction, water is applied as a fine mist
to cure the concrete.
 Because
of its low water-cement ratio, RCC typically has high strengths
similar to, or even greater than, conventional concrete. RCC's high-strength
properties combined with ease of construction and high rate of production
often make RCC more economical than a flexible pavement. Additionally,
more than 20 years of exposure on logging roads in cold climates
have demonstrated that RCC has adequate resistance to freezing and
thawing.
Popular for Paving
Due to its advantages as a comparatively low cost, durable paving
material, RCC has steadily moved to more general uses. In the early
1990s, many municipalities began using RCC as a base for composting
facilities. RCC provides all-weather access for trucks and heavy
equipment, supplies a firm base for composting operations and allows
the facility to control drainage. Additionally, paved composting
facilities produce a more acceptable and valuable compost because
they prevent contamination of compost by dust and gravel.
RCC is also emerging as a common base
for conventional highway and street pavements. Even though RCC is
not a smooth pavement, a layer of asphalt may be used to cover the
surface and smooth out the roadway. In Edmonton, Alberta, the city
paved a two-lane, 1,800-foot-long (550 m) stretch of a street with
8 inches (20 cm) of RCC over a 6-inch (15 cm) cement stabilized
subgrade.
New Era in Dam Construction
 Concrete
has played an increasingly important role in the construction and
rehabilitation of dams in North America during the last 25 years
as a result of the applications of RCC technology to dam construction.
Since its first use for a gravity dam in the United States in 1982
by the U.S. Army Corps of Engineers in the construction of the Willow
Creek Dam in Oregon, RCC has grown to 76 gravity dams and more than
190 spillway/overtopping protection structures and other miscellaneous
water resource applications.
An RCC dam is designed much the same
way as a conventional concrete gravity dam is designed: the dam
material is built up to a height and depth that allows the section
to resist the forces the water is expected to exert upon it by its
weight. Typically, in RCC dam construction, contractors produce
a no-slump concrete mix and spread it in 1-foot-thick (300 mm) layers
from abutment to abutment atop a rock foundation that stretches
across the waterway to be dammed. Because the RCC mix is too dry
to be effectively combined in ready mix trucks, the concrete is
usually mixed at a temporary plant erected near the dam site and
transported by conveyor belt, front-end loader, or dump truck to
the placement site. The newly placed layer of RCC, called a lift,
is compacted with a vibratory roller.
The RCC construction method gained popularity during the 1980s
because it proved to be less expensive than conventional methods
of dam construction, including rockfill and earthfill construction.
RCC is less expensive, in part, because it is faster.
 Continuous
placement of RCC is normally specified on dam projects to minimize
cold joints between the horizontal concrete layers that could inhibit
bonding of the concrete layers to each other. As a result a typical
work schedule consists of two, 10-hour work shifts, six to seven
days a week. RCC dam projects also can be completed more quickly
than embankment dam projects because they require less volume of
material. In addition, RCC dams allow for savings on the construction
of spillways, outlet conduits, river diversion schemes, and related
features that can be designed to be shorter and less material-intensive
than with earth or backfill dam construction. More
on RCC pavements.
 RCC
has also become a widely accepted material for upgrading existing
embankment dams to accommodate currently accepted possible maximum
probable flood levels, which are often higher than the maximum flows
anticipated when the dams were originally designed. RCC can be used
to overlay the downstream slope of the existing embankment dam to
protect the dam from erosion if the structure is overtopped by water.
RCC's placement in horizontal layers means that RCC overlays often
take on a stair-stepped form on the sloped, downside face of the
dam. More
on RCC for water resources.
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