|
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.
( Click Here to know more about Roller Compacted Concrete)
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
Properties of RCC Mix can be summarized
as below:
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.
|
