| 1. What
is Roller Compacted Concrete? |
As
its name indicates,
roller  compacted
concrete (RCC) is a concrete which uses rollers to consolidate
the concrete into a durable surface.
|
| 2. How
is it different from
Conventional Concrete? |
RCC
has the same basic
ingredient as conventional concrete: cement, water, and aggregates. The
basic
difference is that RCC is a much drier mix with practically zero slump.
It is
drier, and looks and feels like damp gravel. It does not require any
forms,
dowels, reinforcing steel & finishing. Also, the method of
compaction is
different with the RCC being compacted by vibratory or pneumatic-tired
rollers.
|
| 3. How
is the mix for RCC
different from the mix of Conventional Concrete? |
|
The
objective of mix design is to produce an RCC mixture that has
sufficient paste
volume to coat the aggregates in the mix and to fill in the voids
between them.
Any of the basic RCC proportioning methods like those based on concrete
consistency testing, the solid suspension model, the optimal paste
volume
method, and soil compaction testing may be used for mix design.
Roller-Compacted
Concrete (RCC) uses aggregate sizes often found in conventional
concrete.
However, the blending of
aggregates will be different than that done in case of
conventional concrete. Crushed aggregates are preferable
in RCC mixes due to the
sharp interlocking edges of the particles, which help to reduce
segregation,
provide higher strengths, and better aggregate interlock at joints and
cracks.
Gap-graded mixes that are dominated by two or three aggregate sizes are
not
desirable for RCC. The content of fine particles required is typically
higher
than that of conventional concrete. Washed aggregates are not required
for this
type of concrete since a small quantity of non-plastic fines present
(2% to 8%
material passing a No. 200 sieve) can enhance its properties. This
produces a
mix that is stable during rolling.
Various
Standards /institutes like ACI
recommend particular gradings for different roller compacted structures
like
pavements. Generally use of dense, well-graded blends with a nominal
maximum
size aggregate (NMSA) not exceeding ¾-inch (19 mm) is
recommended in order to
help minimize segregation and produce a smooth finished surface.
The
moisture content in the mix should be such that the mix is dry enough
to
support the weight of a vibratory roller yet wet enough to ensure an
even
distribution of the cement paste.
Compared
with
conventional concrete, RCC pavement mixes have:
- A lower water
content
- A lower paste
content
- No
air-entrainment, although some admixtures may be used to increase
workability and control set time.
- More finer
aggregates
- Smaller
maximum size coarse aggregate.
|
| 4. Does
the RCC mix require curing? |
Curing
is very important
for RCC also. Since there is no bleed water in RCC
(due to much
lesser water content) , the main concern is to prevent its drying to
avoid
cracking resulting from drying shrinkage & to ensure
adequate
strength by allowing continuing hydration. Curing also helps in
avoiding
dusting of surface.
Normally surface of RCC is kept moist for 7 days, or
until a curing compound is applied. Due to more open texture surface of
RCC,
the curing compound application rates are 1.5 to 2 times the
application rates
used for conventional concrete. Due to large surface area of structures
like
RCC pavement curing techniques such as plastic sheeting and wet burlap
may not
be used due to higher cost involved.
|
5. Basic
Construction Sequence
for Roller Compacted Concrete
- Produced in a
pug mill or central batch plant
- Transported by
dump trucks
- Placed with an
asphalt paver : The thickness of layers generally varies from
8” to 10”
- May be
compacted by vibratory or pneumatic-tired rollers
|
| 6. Performance
of Roller
Compacted Concrete |
|
The
table below (source PCA)
illustrates the features & benefits of RCC:
|
Features
|
Benefits
|
High
flexural strength
(500 to 1000 psi) (3.5 MPa to 7.0 MPa)
|
Supports
heavy, repetitive loads without failure and spans localized soft
subgrade areas, which reduces maintenance costs and down time.
|
| High
compressive strength (4,000 to 10,000 psi) (28 MPa to 69 MPa)
|
Withstands
high concentrated loads and impacts from heavy industrial, military,
and mining applications.
|
| High
shear strength |
Eliminates
rutting and subsequent repairs. |
|
High
density, low absorption |
Provides
excellent durability, even under freeze-thaw conditions; eliminates
seepage through pavement.
|
| Low
water content, low water/cement ratio
|
Increases
strength, reduces permeability, and enhances durability and resistance
to chemical attack. |
| Aggregate
interlock |
Provides
high shear resistance at joints and uncontrolled cracks to prevent
vertical displacement or faulting. |
| No
steel reinforcing or dowels |
Speeds
and simplifies construction, reduces costs.
|
| No
forms or finishing |
Speeds
construction, reduces cost, minimizes labor.
|
| No
formed or sawed joints |
Speeds
construction, reduces cost. (To enhance appearance, joints can be sawn
into RCC pavement.) |
| Hard,
durable, light-colored surface |
Resists
abrasion, eliminates need for surface course and reduces cost. The
light color reduces lighting requirements for parking and storage areas.
|
Photograph
on the right is a sample cut from RCC pavement. It is seen
that this
sample is tightly compacted from top to bottom
|
 |
|
| 7. Limitations |
|
Aesthetics
- RCC does not have the same appearance as other types of concrete. It
is NOT
as pretty and smooth as regular concrete.
Rougher
Surface Texture - The mix design and construction methods
that make roller
compacted concrete so fast, easy, cheap, and durable also create a
surface
texture that gives it a characteristic coarse finish.
Limited
to low-speed traffic - Due to the nature of its surface,
RCC is not appropriate
for all types of traffic. Vehicles traveling at high speeds would
experience a
bumpy ride. That makes it better for applications where strength and
durability
are needed instead of speed.
|
| 8. Typical
application areas |
The
use of RCC for
pavements at industrial facilities such as port and intermodal
container
terminals is particularly appropriate because of the ability to
construct
low-cost concrete pavements over large areas.
- bulk material
storage
- general cargo
storage
- container
terminals
- road / rail
transfer facilities
- Ro-Ro terminals
- truck parks
- tank roads and
parking
- sewage sludge
stacking
- composting slabs
- Pre-casting
yards
|
 |
|
Parking Lot made with
Roller Compacted Concrete
|
 |
|
Container Handling
Depot made with Roller Compacted Concrete
|
