batching, mixing and transportation of fresh concrete

Batching, Mixing, Transporting, and

Handling Concrete

Batching, Mixing, Transporting, and Handling Concrete

Stages in concrete making

n Batching.n Mixing.n Transporting.n Placing.n Compacting.n Finishing. n Curing.

04/13/2023Plain and Reinforced Concrete


BATCHING

04/13/2023 Plain and Reinforced Concrete

Batching is the process of measuring concrete mix ingredients by either mass or volume and introducing them into the mixer. To produce concrete of uniform quality, the ingredients must be measured accurately for each batch.

Percentages of accuracy of measurement of cementitious material ±1%, aggregates ± 2%, water ±1%, and admixtures ± 3%.


Equipment should be capable of measuring quantities within these tolerances for the smallest batch regularly used as well as for larger batches. The accuracy of scales and batching equipment should be checked periodically and adjusted when necessary.


BATCHING

Control room for batching equipment in a typical ready

mixed concrete plant.


Batching

Volume Batching.

All materials measured by volume.

Expressed in relative ratios

Difficult to ensure quality.



Batching

Weigh Batching

Materials quantities by weightSimple and accurate



Mixingn Hand Mixing

u Small jobsu Inferior mixingu Low quality

concreten Machine Mixing

u Good mixingu Large works

n concrete mixersH Tilting mixersH Non-tilting mixersH Reversing drum

mixersH Pan type or stirring

mixersH Transit mixer


Small pan mixer



Mixers Types


Maintenance of Mixers

n Well maintained mechanicallyn Place on firm and leveled platformn Drum and blades must be cleanedn Drum should be kept in tilting

position to avoid rain water collection

n The skip must rest on proper cushion such as sand bags



Stationary Mixing

n Stationary Mixersu Onsite or Central Mix R/M plantu Used for complete or shrink

mixingn Mixer Types ― up to 9m3

u Tilting or non-tilting drumu Open top revolving blade or

paddlen Typical complete mixing times

u Minimum of 1 min. for up to 1 yd3 or less mixer capacity plus 15 sec. for each additional yd3 or fraction thereof



Mixing Timen Mixer speed is 15 to 20 rpmn 25 to 30 revolutions are adequate.n Lesser mixing result in poor

concrete.n Over mixing is uneconomical.n Mixing beyond 2 mins does improve

strength of concrete.n Mixing time is mixer capacity

dependent.04/13/2023 Plain and Reinforced Concrete



Mixing time- affect on Strength



Mixing Time


Mixing time- affect on Strength



Ready Mix Concrete


Ready mixed concrete is proportioned and mixed off theproject site and is delivered to the construction area in afreshly mixed and unhardened state


Ready Mixed Concrete

n Central-mixed concrete u mixed completely in a

stationary mixer u delivered in

H a truck agitatorH a truck mixer operating

at agitating speed H a nonagitating truck



Ready Mixed Concrete

n Shrink-mixed concreteu mixed partially in a

stationary mixer and completed in a truck mixer

n Truck-mixed concrete u mixed completely in a

truck mixer



Truck Mixed Concrete

n 70 to 100 revolutions required for mixing,

mixing speed = 6 to 18 rpm

n After mixing, drum revolves at agitating speed, 2 to 6 rpm

n Discharge before exceeding 300 drum revolutions

n Discharge before 1½ hours



Ordering Ready Mixed Concrete

Specify:n Coarse aggregate sizen Slumpn Air contentn Basis for proportioning,

select Options A ,B, or C.




Option A—performance based:

Purchaser specifies:n Compressive strength

Concrete producer selects mix proportions.




Option B—prescription based:

Purchaser specifies mixture proportions including:

n Cement contentn Water contentn Admixture type and content




Option C—mixed option:

Purchaser specifies:n Compressive strengthn Cement contentn Admixture type and content

Concrete producer selects mix proportions.



Ready Mix Plant



Mobile Batcher Mixer

n Used for: Intermittent production of concrete at jobsite, or small quantities.

n Advantages: Combined materials transporter and batching and mixing system. One-man operation.

n Watch for: Good preventive maintenance program. Materials must be identical to those in original mix design.



Nonagitating Truck

n Used for: Transport concrete on short hauls over smooth roadways.

n Advantages: Cost of nonagitating equipment is lower than that of truck agitators or mixers.

n Watch for: Slump should be limited. Possibility of segregation. Height upon discharge is needed.



Agitator Trucks

n Used for: Transporting concrete for all uses. Haul distances must allow discharge of concrete within 1½ hours.

n Advantages: Operate usually from central mixing plants.

n 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:

n Spec. w/c-ratio is not exceededn Measured slump less than specifiedn Allowable mixing and agitating time

(or drum revolutions) are not exceeded

n Concrete is remixedu min. 30 rev. at mixing speedu until uniformity is within limits




n Transportingu Mortar panu Wheel barrowu Chutesu Dumperu Bucket and

Ropewayu Belt conveyoru Skip and Hoistu Pumping

Transporting and Handling



n Used for: Short flat hauls on all types of onsite concrete construction.

n Advantages: Versatile—ideal inside and on jobsites with changing placing conditions.

n Watch for: Slow and labor intensive.

Wheelbarrows and Buggies



Belt conveyor

n Used for: Conveying concrete horizontally or higher/lower level.

n Advantages: Adjustable reach, traveling diverter, variable speed.

n 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

n Used for: Conveying concrete horizontally or higher/lower level.

n Advantages: Conveyer arrives with concrete. Adjustable reach and variable speed.

n Watch for: End-discharge arrangements needed to prevent segregation and mortar on return belt. Belt cover needed in hot and windy weather.




Buckets

n Used with: Cranes, cableways, and helicopters.

n Advantages: Enables full versatility of cranes, cableways, and helicopters to be exploited. Clean discharge.

n Watch for: Select bucket capacity to conform to size of the concrete batch and capacity of placing equipment.





ocean construction site using a ferry



Rear DischargeFront Discharge




Cranes and Bucketsn Used for: Work above ground

level.n Advantages: Can handle

concrete, reinforcing steel, formwork, and sundry items.

n Watch for: Has only one hook. Careful scheduling between trades and operations is needed to keep crane busy




Pumps

n Used for: Conveying concrete from central discharge point to formwork.

n Advantages: Pipelines take up little space and can be readily extended. Delivers concrete in continuous stream. Pump can move.

n Watch for: Constant supply of freshly-mixed concrete is needed without any tendency to segregate.




Flexible Hose at End of Pump’s Rigid Pipeline




Pump Capacity Planning



Screw Spreaders

n Used for: Spreading concrete over large flat areas.

n Advantages: Concrete can be quickly spread over a wide area to a uniform depth.

n 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



batching, mixing and transportation of fresh concrete

Engineering

reinforced concrete

andhandling concrete

mixing timebatching

concrete makingbatching

improvestrength of concrete

lesser mixing result

andhandling concreteplain

andhandling concretespecify