Batching, Mixing, Transporting, and Handling

Concrete

Batching, Mixing, Transporting, and Handling Concrete

Stages in concrete makingn Batching.n Mixing.n Transporting.n Placing.n Compacting.n Finishing. n Curing.

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

BATCHING

04/22/2023 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%.

Batching, Mixing, Transporting, and Handling Concrete

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.

04/22/2023 Plain and Reinforced Concrete

BATCHING

Control room for batching equipment in a typical ready

mixed concrete plant.

Batching, Mixing, Transporting, and Handling Concrete

Batching

Volume Batching.All materials measured by volume.Expressed in relative ratiosDifficult to ensure quality.

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Batching

Weigh Batching

Materials quantities by weightSimple and accurate

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Mixingn Hand Mixing

u Small jobsu Inferior mixingu Low quality concrete

n Machine Mixingu Good mixingu Large works

n concrete mixersH Tilting mixersH Non-tilting mixersH Reversing drum

mixersH Pan type or stirring

mixersH Transit mixer

04/22/2023Plain and Reinforced Concrete

Small pan mixer

Batching, Mixing, Transporting, and Handling Concrete

04/22/2023 Plain and Reinforced Concrete

Mixers Types

Batching, Mixing, Transporting, and Handling Concrete

Maintenance of Mixersn 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 collectionn The skip must rest on proper cushion

such as sand bags

04/22/2023 Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Stationary Mixing

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

n Mixer Types ― up to 9m3 u Tilting or non-tilting drumu Open top revolving blade or paddle

n Typical complete mixing timesu Minimum of 1 min. for up to 1 yd3

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

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

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.

04/22/2023 Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

04/22/2023 Plain and Reinforced Concrete

Mixing time- affect on Strength

Batching, Mixing, Transporting, and Handling Concrete

04/22/2023 Plain and Reinforced Concrete

Mixing Time

Batching, Mixing, Transporting, and Handling Concrete

Mixing time- affect on Strength

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Ready Mix Concrete

04/22/2023Plain and Reinforced Concrete

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

Batching, Mixing, Transporting, and Handling Concrete

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

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

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

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

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

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Ordering Ready Mixed Concrete

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

Options A ,B, or C.

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Ordering Ready Mixed Concrete

Option A—performance based:

Purchaser specifies:n Compressive strength

Concrete producer selects mix proportions.

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Ordering Ready Mixed Concrete

Option B—prescription based:

Purchaser specifies mixture proportions including:

n Cement contentn Water contentn Admixture type and content

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Ordering Ready Mixed Concrete

Option C—mixed option:

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

Concrete producer selects mix proportions.

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Ready Mix Plant

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

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.

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Nonagitating Truckn 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.

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Agitator Trucksn 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.

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling 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 exceededn Concrete is remixed

u min. 30 rev. at mixing speedu until uniformity is within limits

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Batching, Mixing, Transporting, and Handling Concrete

04/22/2023 Plain and Reinforced Concrete

n Transportingu Mortar panu Wheel barrowu Chutesu Dumperu Bucket and

Ropewayu Belt conveyoru Skip and Hoistu Pumping

Transporting and Handling

Batching, Mixing, Transporting, and Handling Concrete

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

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Batching, Mixing, Transporting, and Handling Concrete

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.

Transporting and Handling

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

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.

Transporting and Handling

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Bucketsn 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.

Transporting and Handling

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

04/22/2023 Plain and Reinforced Concrete

ocean construction site using a ferry

Transporting and Handling

Batching, Mixing, Transporting, and Handling Concrete

Rear DischargeFront Discharge

Transporting and Handling

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

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

Transporting and Handling

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Transporting and Handling

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Pumpsn 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.

Transporting and Handling

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Flexible Hose at End of Pump’s Rigid Pipeline

Transporting and Handling

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

04/22/2023 Plain and Reinforced Concrete

Transporting and Handling

Batching, Mixing, Transporting, and Handling Concrete

Pump Capacity Planning

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

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.

Transporting and Handling

04/22/2023Plain and Reinforced Concrete

Batching, Mixing, Transporting, and Handling Concrete

Work Above Ground Level

Transporting and Handling

04/22/2023Plain and Reinforced Concrete