Batching, Mixing, Transporting, and Handling Concrete

Batching, Mixing, Transporting, and

Handling Concrete

Batching, Mixing, Transporting, and Handling Concrete

Ordering Ready Mixed Concrete

Specify: Coarse aggregate size Slump Air content Basis for proportioning,

select Options A ,B, or C.

ASTM C 94ASTM C 94



Option A—performance based:

Purchaser specifies: Compressive strength

Concrete producer selects mix proportions.

ASTM C 94ASTM C 94



Option B—prescription based:

Purchaser specifies mixture proportions including:

Cement content Water content Admixture type and content

ASTM C 94ASTM C 94



Option C—mixed option:

Purchaser specifies: Compressive strength Cement content Admixture type and content

Concrete producer selects mix proportions.

ASTM C 94ASTM C 94


Batching


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 yd3 or less mixer capacity plus 15 sec. for each additional yd3 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


Ready Mixed Concrete

Central-mixed concrete mixed completely in a

stationary mixer delivered in

a truck agitator a truck mixer operating

at agitating speed a nonagitating truck


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

ASTM C 94ASTM C 94


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.


Nonagitating Truck

Used for: Transport concrete on short hauls 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.


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.


Remixing Concrete (1)

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

ASTM C 94 (AASHTO ASTM C 94 (AASHTO M 157)M 157)


Transporting and Handling

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.

Wheelbarrows and Buggies


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.



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.



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.



Rear Discharge Front Discharge



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



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.



Flexible Hose at End of Pump’s Rigid Pipeline



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.



Work Above Ground Level



Videos 1/3

Stationary MixersBatching


Videos 2/3

Nonagitating MixersTruck Mixer Types


Videos 3/3

Agitators

Documents

Batching, Mixing, Transporting, and Handling Concrete