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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Option B:

It is a prescription based. The purchaser

specifies:

Mixture proportions, including:

Cement.

Water.

Admixture contents.

ASTM C 94

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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


Frankfurt

Europe‘s

largest

batching

plant for

readymix

concrete.

With full

infrastructure

system for

aggreagtes

and sand.

Batching plants

Tower Stationary Plants


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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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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