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Roller-Compacted Concrete

 A Different Kind of Concrete

Roller-compacted concrete, or RCC, takes its name from the construction method used to build it. It's placed with conventional or high-density asphalt paving equipment,then compacted with rollers.

RCC has the same basic ingredient as conventional concrete: cement, water, and aggregates, such as gravel or crushed stone.

But unlike conventional concrete, it's a drier mix—stiff enough to be compacted by vibratory rollers. Typically, RCC is constructed without joints. It needs neither forms nor finishing, nor does it contain dowels or steel reinforcing.

These characteristics make RCC simple, fast, and economical.

Tough, Fast, Economical

These qualities have taken roller-compacted concrete from specialized applications to mainstream pavement. Today, RCC is used for any type of industrial or heavy-duty pavement. The reason is simple. RCC has the strength and performance of conventional concrete with the economy and simplicity of asphalt. Coupled with long service life and minimal maintenance, RCC's low initial cost adds up to economy and value.

Roots in Logging

RCC got its start in the Seventies, when the Canadian logging industry switched to environmentally cleaner, land-based log-sorting methods. The industry needed a strong pavement to stand up to massive loads and specialized equipment. Yet economy was equally important: log-sorting yards can span 40 acres (16 hectares) or more. RCC met this challenge and has since expanded to other heavy-duty applications.

Durability—even under severe loads—
gave RCC pavements their start for
log-sorting yards.

Today, RCC is used when strength, durability, and economy are primary needs:
Port, intermodal, and military facilities; parking, storage, and staging areas;
streets, intersections, and low-speed roads.

RCC's economy of scale made it ideal for roads, parking, and staging areas at the Honda Plant in Lincoln, Alabama. At 140 acres, it's the largest RCC pavement project to date.

No Rutting, No Pot Holes

The high strength of RCC pavements eliminates common and costly problems traditionally associated with asphalt pavements.
RCC pavements:

• Resist rutting
• Span soft localized subgrades
• Will not deform under heavy, concentrated loads
• Do not deteriorate from spills of fuels and hydraulic fluids
• Will not soften under high temperatures

Unique Mix, Unique Construction

RCC owes much of its economy to high-volume, high-speed construction methods.Large-capacity mixers set the pace. Normally, RCC is blended in continuous-mixing pugmills at or near the construction site. These high-output pugmills have the mixing efficiency needed to evenly disperse the relatively small amount of water used.

Dump trucks transport the RCC and discharge it into an asphalt paver, which places the material in layers up to 10 inches (250 mm) thick and 42 feet (13 m) wide.

Compaction is the most important stage of construction: it provides density, strength, smoothness, and surface texture. Compaction begins immediately after placement and continues until the pavement meets density requirements.

Curing ensures a strong and durable pavement. As with any type of concrete, curing makes moisture available for hydration—the chemical reaction that causes concrete to harden and gain strength. A water cure sprays or irrigates the pavement to keep it moist. A spray-on membrane can also be used to seal moisture inside.

When appearance is important, joints can be saw cut into the RCC to control crack location. If economy outweighs appearance, the RCC is allowed to crack naturally.

Once cured, the pavement is ready for use. An asphalt surface is sometimes applied for greater smoothness or as a riding surface for high-speed traffic.

Economy. Performance. Versatility.

For RCC, economy was the mother of invention. The need for a low-cost, high-volume material for industrial pavements led to its development.

Low cost continues to draw engineers, owners, and construction managers to RCC. But today's RCC owes much of its appeal to performance: The strength to withstand heavy and specialized loads; the durability to resist freeze-thaw damage; and the versatility to take on a wide variety of paving applications. From container ports to parking lots, RCC is the right choice for tough duty.

DOWNLOAD FREE BOOKS ON NOMINAL TOPICS OF R.C.C CONCRETE

R.C.C CONCRETE SPECIFICATIONS 


R.C.C BEAM DESIGN 


R.C.C FRAME STRUCTURE 


TECHNICAL SPECIFICATIONS 


R.C.C CONCRETE BASICS 


EARTH QUAKE REHABILITATION WORKS 

METRIC MEASUREMENTS, some useful approximations

10 millimetres (mm) 0.4 inch (in)
25 mm 1 in
100 mm 4 in
300 mm 1 foot (ft)
1 metre (1000 mm) 3 ft 3.37 in
1 square metre (1 m2) 10.76 ft2 or 1.2 yard2 (yd2)
1 cubic metre (1 m3) 35 ft3 or 1.3 yd3
1 litre 1.75 pint (pt)
4.5 litres 1 gallon
1 kilograms (kg) 2.2 pounds (lb)

Formwork

Formwork gives concrete its SHAPE.
Formwork provides a mould, into which concrete is placed.
When concrete has hardened the formwork is removed.
Formwork must be:
ACCURATE
STRONG, and
WELL MADE.
Formwork that is not will leak from the joints, may sag, bulge or
move and, especially in large construction, will not be safe.
The surface of the forms in contact with concrete affects how
concrete will look. If the final look of the concrete is important choose
a material which will leave the surface texture wanted.
PLACEMENT Be sure that formwork is placed so it can be removed. If formwork is placed
in awkward positions or tight corners it may be difficult to remove when the concrete had
hardened.
It is helpful if formwork is:
SIMPLE to build,
EASY to hand, and
RE-USEABLE.
Formwork sections should be of simple design, not too big and of standard sizes if they
are to be re-used.
MATERIALS Formwork is normally made from steel or timber. Timber is easy to make
into formwork while steel will allow a greater number of re-uses.
Formwork can be made on site or bought from formwork suppliers. Special forms made
from various materials can be purchased for forming waffle slabs, circular columns and
other special profiles.



REMOVAL TIMES Form Oil should be applied to the inside of the formwork to stop it
sticking to the concrete and make removal easier. Coat BEFORE the reinforcement is put
in place. Formwork may be left in place to help curing.
See CHAPTER 10 Curing Concrete
Removal time may vary according to the weather,
In cold weather, concrete may take longer to gain strength than in warmer weather,
therefore removal times will be longer.
In normal conditions (around 20°C) 7 days is long enough to leave the forms in place
unless the concrete is suspended when other conditions apply.

Reinforced Concrete

The steel found in many concrete structures is called REINFORCEMENT.
Reinforcement helps concrete resist TENSILE and SHEAR forces, and helps control
CRACKING in concrete.
CONCRETE PROPERTIES
Normal Concrete:
HIGH compressive strength
VERY LOW tensile strength
VERY LOW shear strength
Reinforced Concrete:
VERY HIGH compressive strength
VERY HIGH tensile strength
VERY HIGH shear strength
WHY USE REINFORCEMENT?
As a force is applied to concrete there will be
compressive, tensile and shear forces acting
on the concrete. Concrete naturally resists
compression (squashing), very well, but is
relatively weak in tension (stretching).
Horizontal and/or vertical reinforcement is
used in all types of concrete structures where
tensile or shear forces may crack or break
the concrete. HORIZONTAL reinforcement
helps resist tension forces. VERTICAL
reinforcement helps resist shear forces.




Below are some examples of reinforcement use:
In a SUSPENDED (off-the-ground) concrete slab,
horizontal reinforcement resists tension and vertical
reinforcement (in say supporting beams) resists
shear forces.
In a SLAB-ON-GROUND, reinforcement increases
the tensile strength and helps control the width of
shrinkage cracks.
See CHAPTER 16 Cracking in Concrete
It does not prevent cracks but controls the width that cracks can open.
Uses of reinforcement include:
Increasing the spacing of control joints
Odd shaped slabs
Slabs with re-entrant corners.
REINFORCEMENT POSITION
The position of reinforcement will be shown in the plans. Reinforcement must be fixed in
the right position to best resist compressive, tensile and shear forces and help control
cracking.
The reinforcement in trenches and slabs rests on
BAR CHAIRS and must be securely fixed to the
bar chairs so it won’t move when concrete is
placed around it.
Concrete Cover The reinforcement must be placed so there is enough concrete covering
it to protect it from rusting.
Typical covers are shown in the diagram. To ensure durability, both the concrete cover and
strength should be shown in the plans.



Cracking and Reinforcement Reinforcement alone WILL NOT STOP cracking, but helps
control cracking. It is used to control the width of shrinkage cracks.
See CHAPTER 16 Cracking in Concrete
Concrete Reinforcement Bond To help control the width of cracks, or their location (at
joints), there must be a strong bond between concrete and reinforcement. This allows the
tensile forces (which concrete has a very low ability to resist) to be transferred to the
reinforcement.
To help achieve a strong bond:
The reinforcement should be CLEAN (free from flakey rust, dirt or grease).
The concrete should be PROPERLY COMPACTED around the reinforcement bars.
Reinforcing bars and mesh should be located so that there is enough room between
the bars to place and compact the concrete.
To improve the transfer of tensile forces to the steel,
the reinforcement is often anchored by:
BENDING,
HOOKING, or
LAPPING the bars.
Types of Reinforcement Two types of steel
reinforcement used are mesh sheets or loose bars.
Loose bars are normally deformed, while mesh may
be made from either smooth or deformed bars.
Typical bar diameters are 12, 16, 20 and 24 mm.
Typical mesh sizes are SL42, 52, 62, 72 and 82. The
SL stands for Square mesh Low Ductility and the
numbers represent meanings as well. For example
for SL42 the 4 is the nominal bar size and the 2
refers to the wire spacing (200 mm).
Fibre Reinforcement Synthetic fibres can be added to concrete to aid in minimising early
age plastic shrinkage and can reduce the presence of excessive bleedwater. However,
synthetic fibres are not a replacement for fabric or steel reinforcement. In slab on ground
construction the control joint spacing is the same as plain concrete.
Steel fibres are used for the above and to improve the toughness of concrete. However
they can be used to control drying shrinkage cracking over limited spacings and for oddshaped
slabs. They also increase the flexural, or bending, strength of concrete.

Cracking in Concrete

Random cracking in concrete is not desirable, it can make
your concrete look ugly and lead to structural weakness
of the concrete.
Reinforcement and joints are used to control
cracking. Bad cracking leaves the reinforcement
exposed to air and moisture, which may cause it
to rust and weaken concrete.
See CHAPTER 11 Joints in Concrete and
See CHAPTER 17 Reinforced Concrete
TYPES OF CRACKS
Two types of cracks happen in reinforced concrete:
PRE-SETTING CRACKS Cracks that happen BEFORE concrete hardens,
while it is still workable.
HARDENED CRACKING Cracks which happen AFTER concrete hardens.
PRE-SETTING CRACKS
Pre-setting cracks are cracks which form during placing, compaction and finishing caused
by movement of concrete before it is dry.
There are three types of pre-setting cracks:
PLASTIC SETTLEMENT cracks
PLASTIC SHRINKAGE cracks, and
Cracks caused by MOVEMENT OF THE FORMWORK.
Pre-setting cracks can be prevented by looking for them as they happen, while the
concrete is still setting.
If they are detected early on they can be easily fixed by re-compacting, re-trowelling or
re-floating the concrete surface.




Plastic Settlement Cracks
When do they form? They form soon after
concrete is placed, while it is still plastic. They
get bigger as concrete dries and shrinks and
tend to follow the lines of reinforcement.
Prevention
Revibrate the concrete.
Re-trowel the surface.
Look for cracks as the concrete is
setting. At this stage they can easily
be fixed.
Plastic Shrinkage Cracks
When do they form? On very hot days or in low humidity and moderate winds. Cracking
is more common in summer but may occur during winter.
See CHAPTER 12 Hot and Cold Weather Concreting
Plastic shrinkage cracks appear in lines,
roughly parallel or in a crazed haphazard
way. They are usually 300–600 mm long but
may be between 25 mm and 2 m in length.
Prevention
Dampen the subgrade and forms and protect
concrete from the wind.
Keep all materials cool on hot days.




Place, compact and cure as quickly as possible on hot days so concrete won’t dry out.
Once the concrete has been compacted, screeded and floated apply a uniform spray film
of EVAPORATIVE RETARDANT (Aliphatic Alcohol) to prevent rapid loss of surface
moisture, then continue with finishing.
Try to place at the cooler times of the day.
Repair Cracks may be closed by reworking
the plastic concrete.
Formwork Movement
If formwork is not strong enough it may bend or bulge. Formwork movement may happen
at any time during placement and compaction.
Prevention Make sure formwork is strong.
If the concrete collapses, strengthen the formwork and re-vibrate the concrete.
Thermal Shock
Applying cold water, as curing, over concrete on a hot day can result in cracks from the
sudden contraction.
Prevention Use warm water.
CRACKS AFTER HARDENING
Cracks after hardening may be caused by drying shrinkage, movement or settling of the
ground, or placing higher loads on the concrete than it was designed to carry.
Little can be done with cracks after hardening. Careful and correct placement helps
prevent serious cracking after hardening.
Only uncontrolled cracks are a possible problem. Cracks at control joints or controlled by
steel reinforcing is expected and acceptable.