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Transcript of 6 ready mixed concrete 1
Ready-mixed concrete
CVLE 519
Concrete Technology
Dr. Adel El Kordi
Civil and Environmental Engineering Department
Faculty of Engineering
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INTORDUCTIONReady Mix Concrete which is popularly called as RMC.
The first ready mix factory which was built in 1930’s.
The consumption of cement in the form of RMC is about 5% in
India, where as in developed countries it’s about 70%.
DefinitionReady Mixed Concrete is proportioned and mixed off
the project site and is delivered to the construction
area in a freshly mixed and unhardened state.
But why to use RMC ?
1- Can serve a wide area
2- The plants are located in areas zoned for industrial use
3- Better quality concrete is produced
4- Elimination of storage space for basic materials at site
5-Elimination of hiring of plant and machinery
6- Wastage of basic materials is avoided
7- Time required is greatly reduced.
8- Noise and dust pollution at site is reduced
9- Labor associated with production of concrete is
eliminated
History of RMC?
Ready mix concrete was first patented
in Germany in 1903 its
commercial delivery was not possible
due to lack of transportation needs.
The first commercial delivery was made
in Baltimore USA in 1913.
The first revolving drum type transit mixer
was developed in 1926.
In 1931, a RMC plant was set up for
the construction of Heathrow airport,
London.
Ready Mix Plant
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A Aggregate delivery
B Aggregate receiving hopper
C Aggregate storage
D Conveyor belt
E Cementitious material storage
F Weigh hopper
G Cement delivery
H Mixer
I Admixtures
J Ready mix truck with returned
concrete
K Recycled water
L Reclaimed aggregates
M Pump
N Water storage
O Concrete loaded in ready-mix truck
P Control Room
Ordering Ready Mixed Concrete - The American Society for Testing and Materials
(ASTM C 94)
Specify:
1. Coarse aggregate size
2. Slump
3. Air content
4. Basis for proportioning,
select Options A ,B, or C.
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Ready mixed concrete is proportioned and
mixed off the project site and is delivered
to the construction area in a freshly mixed
and unhardened state.
Ordering Ready Mixed Concrete
Option A:
It is a performance based. It requires the purchaser to specify
The compressive strength only.
while the concrete producer selects the mixture proportions needed to obtain the required compressive strength.
Durability defects ????
ASTM C 94
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Ordering Ready Mixed Concrete
Option B:
It is a prescription based. The purchaser
specifies:
Mixture proportions, including:
Cement.
Water.
Admixture contents.
ASTM C 94
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Ordering Ready Mixed Concrete
Option C—mixed option:
Purchaser specifies:
Compressive strength.
Cement content.
Admixture type and content.
Concrete producer selects mix proportions.
ASTM C 94
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Most specifications require that batching be done by mass
rather than by volume ASTM C 94. Water and liquid
admixtures can be measured accurately by either volume or
mass. Volumetric batching ASTM C 685 is used for concrete
mixed in continuous mixers. Specifications generally
require that materials be measured for individual batches
within the following percentages of accuracy:
• Cementitious material ±1%.
• Aggregates ± 2%.
• Water ±1%.
• Admixtures ± 3%.
BATCHING
Batching
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• All concrete should be mixed until it is uniform in
appearance, with all ingredients evenly distributed.
• Mixers should not be loaded above their capacities and
should be operated at the mixing speed recommended
by the manufacturer.
• Structural low-density concrete can be mixed the same
way as normal-density concrete when the aggregates
have less than 10% total absorption by mass or when
the absorption is less than 2% by mass during the first
hour after immersion in water. For aggregates not
meeting these limits, mixing procedures are described
in PCA (1986).
MIXING CONCRETE
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• Concrete is sometimes mixed at the jobsite in a
stationary mixer or a paving mixer.
• Stationary mixers include both:
1- Onsite mixers.
2- Central mixers in ready mix plants.
• The onsite mixers are available in sizes up to 9.0 m3
and can be of the tilting or non tilting type or open-top
revolving blade or paddle type.
• The mixing period should be measured from the time
all cement and aggregates are in the mixer drum,
provided all the water is added before one-fourth of the
mixing time has elapsed (ACI 304R-00).
Stationary Mixing
Stationary Mixing
Typical complete mixing times
Minimum of 1 min. for up to 1 m3 or less mixer capacity plus 15 sec. for each additional m3 or fraction.
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1- Onsite mixers
Twin-Shaft mixerPan mixer with or
without turbo
2- Central mixers in ready mix plants
For more information: Tel: 0049-2325-987-0 / Fax: 0049-2325-987-660 or E-mail : [email protected] / Internet: www.Schwing.de
Batching plants
HN –Stationary Plants
HN 2,25
100 m³/h Compacted
concrete output
HN 3,0 120 m³/h Compacted
concrete output
For more information: Tel: 0049-2325-987-0 / Fax: 0049-2325-987-660 or E-mail : [email protected] / Internet: www.Schwing.de
Frankfurt
Europe‘s
largest
batching
plant for
readymix
concrete.
With full
infrastructure
system for
aggreagtes
and sand.
Batching plants
Tower Stationary Plants
For more information: Tel: 0049-2325-987-0 / Fax: 0049-2325-987-660 or E-mail : [email protected] / Internet: www.Schwing.de
Fully automated Stetter batching
plant with 3 mixers.
Maximum output 300 m3/h in
tandem operation.
Batching plants
Tower Stationary Plants
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@Types of Ready Mixed Concrete
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1. Central-mixed concrete is mixed completely in a
stationary mixer and is delivered either in:
• Truck agitator.
• Truck mixer operating at agitating speed.
• Non agitating truck.
Nonagitating truck
Types of Ready Mixed Concrete
Truck agitator or Truck mixer
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Truck Mixers
Wear protection (30 x 8 mm) on top of the spiral
protects both sides of the spiral and gives a higher
rigidity against deflection of the spiral
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2. Shrink-mixed concrete is mixed partially in a stationary
mixer and completed in a truck mixer.
Truck Mixers
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3. Truck-mixed concrete is mixed completely in a truck mixer
by using Weight Plant.
Weight Plant
Mobile Batcher Mixer
Mobile volumetric mixers are
special trucks that batch by
volume and continuously mix
concrete as the dry concrete
ingredients, water, and
admixtures are continuously
fed into a mixing.
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For more information: Tel: 0049-2325-987-0 / Fax: 0049-2325-987-660 or E-mail : [email protected] / Internet: www.Schwing.de
Batching plants
Mobile Plant M2
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Types of Concrete Trucks
1- Nonagitating Truck
Used for: Transport concrete
on short distance over smooth
roadways.
Advantages: Cost of
nonagitating equipment is
lower than that of truck
agitators or mixers.
Watch for: Slump should be
limited. Possibility of
segregation. Height upon
discharge is needed.
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Types of Concrete Trucks
2- Truck Mixer - ASTM C 94
a. 70 to 100 revolutions required for mixing, mixing
speed = 6 to 18 rpm.
b. After mixing (all revolution after 100), drum
revolves at agitating speed, 2 to 6 rpm.
c. Discharge before exceeding 300 drum revolutions.
d. Discharge before 1½ hours.
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3- Agitator Trucks
a. Transporting concrete for all uses. Distances must allow
discharge of concrete within 1½ hours.
b. Operate usually from central mixing plants.
c. Timing of deliveries should suit job organization.
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