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Ready Mix Concrete-Batching, Mixing, Transporting, and Handling

Ready Mix Concrete-Batching, Mixing, Transporting, and Handling

While Ordering Ready Mixed Concrete Following Points is to be specified:

  • Coarse aggregate size
  • Slump
  • Air content
  • Basis for proportioning, select Options A ,B, or C.
Option A—performance based:

Purchaser specifies:

  • Compressive strength
Concrete producer selects mix proportions.

Option B—prescription based:

Purchaser specifies mixture proportions including:
· Cement content
· Water content
· Admixture type and content
Option C—mixed option:

Purchaser specifies:
n Compressive strength
n Cement content
n Admixture type and content
Concrete producer selects mix proportions.

Batching

Fig. 1. Control room for batching equipment in a typical ready mixed concrete plant.

Fig. 1. Control room for batching equipment in a typical ready mixed concrete plant.

Stationary Mixing

  • Stationary Mixers
    • Onsite or Central Mix  R/M plant
    • Used for complete or shrink mixing
  • Mixer Types ? up to 9m3
    • Tilting or non-tilting drum
    • Open top revolving blade or paddle
  • 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 thereof
Ready Mixed Concrete

  • Shrink-mixed concrete
    • mixed partially in a stationary mixer and completed in a truck mixer
  • Truck-mixed concrete
    • mixed completely in a truck mixer
Fig.2. Concrete can be mixed at the jobsite in a stationary mixer.

Fig.2. Concrete can be mixed at the jobsite in a stationary mixer.

Ready Mixed Concrete

  • Shrink-mixed concrete
    • mixed partially in a stationary mixer and completed in a truck mixer
  • Truck-mixed concrete
    • mixed completely in a truck mixer
Fig. 3. Truck-mixed concrete is mixed completely in a truck mixer.

Fig. 3. Truck-mixed concrete is mixed completely in a truck mixer.

  • Central-mixed concrete

    • mixed completely in a stationary mixer
    • delivered in
      • a truck agitator
      • a truck mixer operating at agitating speed
      • a non-agitating truck
Fig. 4. Central mixing in a stationary mixer of the tilting drum type with delivery by a truck mixer operating at agitating speed.

Fig. 4. Central mixing in a stationary mixer of the tilting drum type with delivery by a truck mixer operating at agitating speed.

Ready Mix Plant

Fig: 5. Ready Mix Plant

Truck Mixed Concrete

  • 70 to 100 revolutions required for mixing,
Mixing speed = 6 to 18 rpm
  • After mixing, drum revolves at agitating speed, 2 to 6 rpm
  • Discharge before exceeding 300 drum revolutions
  • Discharge before 1½ hours
Mobile Batcher Mixer

  • Used for: Intermittent production of concrete at jobsite, or small quantities.
  • Advantages: Combined materials transporter and batching and mixing system. One-man operation.
  • Watch for: Good preventive maintenance program. Materials must be identical to those in original mix design.
Fig. 6. Mobile batcher measures materials by volume and continuously mixes concrete as the dry ingredients, water, and admixtures are fed into a mixing trough at the rear of the vehicle.

Fig. 6. Mobile batcher measures materials by volume and continuously mixes concrete as the dry ingredients, water, and admixtures are fed into a mixing trough at the rear of the vehicle.

Non-agitating Truck

  • Used for: Transport concrete on short hauls over smooth roadways.
  • Advantages: Cost of non-agitating equipment is lower than that of truck agitators or mixers.
  • Watch for: Slump should be limited. Possibility of segregation. Height upon discharge is needed.
Fig 7. Non-agitating trucks are used with central-mix batch plants where short hauls and quick concrete discharge allows the rapid placement of large volumes of concrete.

Fig 7. Non-agitating trucks are used with central-mix batch plants where short hauls and quick concrete discharge allows the rapid placement of large volumes of concrete.

Agitator Trucks

  • Used for: Transporting concrete for all uses. Haul distances must allow discharge of concrete within 1½ hours.
  • Advantages: Operate usually from central mixing plants.
  • Watch for: Timing of deliveries should suit job organization. Concrete crew and equipment must be ready onsite to handle concrete.
Fig .8. Truck agitators are also used with central-mix batch plants. Agitation mixing capabilities allow truck agitators to supply concrete to projects with slow rates of concrete placement and at distances greater than non-agitating trucks.

Fig .8. Truck agitators are also used with central-mix batch plants. Agitation mixing capabilities allow truck agitators to supply concrete to projects with slow rates of concrete placement and at distances greater than non-agitating trucks.
Remixing Concrete

Water may be added at jobsite provided:
  • Spec. w/c-ratio is not exceeded
  • Measured slump less than specified
  • Allowable mixing and agitating time (or drum revolutions) are not exceeded
  • Concrete is remixed
    • min. 30 rev. at mixing speed
    • until uniformity is within limits
Transporting and Handling

Wheelbarrows and Buggies

  • Used for: Short flat hauls on all types of onsite concrete construction.
  • Advantages: Versatile—ideal inside and on jobsites with changing placing conditions.
  • Watch for: Slow and labor intensive.
Fig. 9. Versatile power buggy can move all types of concrete over short distances.Fig. 9. Versatile power buggy can move all types of concrete over short distances.
Fig. 9. Versatile power buggy can move all types of concrete over short distances.

Belt conveyor

  • Used for: Conveying concrete horizontally or higher/lower level.
  • Advantages: Adjustable reach, traveling diverter, variable speed.
  • Watch for: End-discharge arrangements needed to prevent segregation and mortar on return belt. Belt cover needed in hot and windy weather.
Fig. 10. The conveyor belt is an efficient, portable method of handling concrete. A drop chute prevents concrete from segregating as it leaves the belt; a scraper prevents loss of mortar. Conveyor belts can be operated in series and on extendable booms of hydraulic cranes.

Fig. 10. The conveyor belt is an efficient, portable method of handling concrete. A drop chute prevents concrete from segregating as it leaves the belt; a scraper prevents loss of mortar. Conveyor belts can be operated in series and on extendable booms of hydraulic cranes.

Truck mounted conveyors

  • Used for: Conveying concrete horizontally or higher/lower level.
  • Advantages: Conveyer arrives with concrete. Adjustable reach and variable speed.
  • Watch for: End-discharge arrangements needed to prevent segregation and mortar on return belt. Belt cover needed in hot and windy weather.
Fig. 11. A conveyor belt mounted on a truck mixer places concrete up to about 12 meters (40 feet) without the need for additional handling equipment.

Fig. 11. A conveyor belt mounted on a truck mixer places concrete up to about 12 meters (40 feet) without the need for additional handling equipment.
Buckets

  • Used with: Cranes, cableways, and helicopters.
  • Advantages: Enables full versatility of cranes, cableways, and helicopters to be exploited. Clean discharge.
  • Watch for: Select bucket capacity to conform to size of the concrete batch and capacity of placing equipment
Fig. 12. Concrete is easily lifted to its final location by bucket and crane.

Fig. 12. Concrete is easily lifted to its final location by bucket and crane.

Fig. 13. In comparison to conventional rear-discharge trucks, front-discharge truck mixers provide the driver with more mobility and control for direct discharge into place.Fig. 13. In comparison to conventional rear-discharge trucks, front-discharge truck mixers provide the driver with more mobility and control for direct discharge into place.

Fig. 13. In comparison to conventional rear-discharge trucks, front-discharge truck mixers provide the driver with more mobility and control for direct discharge into place.

Cranes and Buckets

  • Used for: Work above ground level.
  • Advantages: Can handle concrete, reinforcing steel, formwork, and sundry items.
  • Watch for: Has only one hook. Careful scheduling between trades and operations is needed to keep crane busy
Fig. 14. The tower crane and bucket can easily handle concrete for tall-building construction.

Fig. 14. The tower crane and bucket can easily handle concrete for tall-building construction.

Pumps

  • Used for: Conveying concrete from central discharge point to formwork.
  • Advantages: Pipelines take up little space and can be readily extended. Delivers concrete in continuous stream. Pump can move.
  • Watch for: Constant supply of freshly-mixed concrete is needed without any tendency to segregate.
Fig.15. A truck-mounted pump and boom can conveniently move concrete vertically or horizontally to the desired location.

Fig.15. A truck-mounted pump and boom can conveniently move concrete vertically or horizontally to the desired location.

Flexible Hose at End of Pump’s Rigid Pipeline

Fig. 16. View of concrete discharging from flexible hose connected to rigid pipeline leading from the pump. Rigid pipe is used in pump booms and in pipelines to move concrete over relatively long distances. Up to 8 m (25 ft) of flexible hose may be attached to the end of a rigid line to increase placement mobility.

Fig. 16. View of concrete discharging from flexible hose connected to rigid pipeline leading from the pump. Rigid pipe is used in pump booms and in pipelines to move concrete over relatively long distances. Up to 8 m (25 ft) of flexible hose may be attached to the end of a rigid line to increase placement mobility.

Screw Spreaders

  • Used for: Spreading concrete over large flat areas.
  • Advantages: Concrete can be quickly spread over a wide area to a uniform depth.
  • Watch for: They are normally used as part of a paving train. They should be used for spreading before vibration is applied.
Fig. 16. The screw spreader quickly spreads concrete over a wide area to a uniform depth. Screw spreaders are used primarily in pavement construction.

Fig. 16. The screw spreader quickly spreads concrete over a wide area to a uniform depth. Screw spreaders are used primarily in pavement construction.

Work Above Ground Level

Ready mix Concrete PlacingReady mix Concrete Placing

Fig. 17. A pump boom mounted on a mast and located near the center of a structure can frequently reach all points of placement. It is especially applicable to tall buildings where tower cranes cannot be tied up with placing concrete. Concrete is supplied to the boom through a pipeline from a ground-level pump. Concrete can be pumped hundreds of meters (feet) vertically with these pumping methods.

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3 Comments

  1. The Constructor says:
    16/12/2009 at 14:13

    Ready Mix Concrete-Batching, Mixing, Transporting, and Handling: Ready Mix Concrete-Batching, Mixing, Transport.. http://bit.ly/89f9vl

  2. Jayesh Bhagat says:
    20/01/2010 at 16:03

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  3. Jayesh Bhagat says:
    20/01/2010 at 21:33

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