1. Batching, Mixing, Transporting, and Handling Concrete
Chapter 10-Batching, Mixing, Transporting, Handling-EB101-Design and Control of Concrete Mixtures-7th Canadian Edition-2002

2. Ordering / Specifying Concrete
CSA A23.1
Three Alternatives ―
Alternative (1) ― Common
Alternative (2) ― Prescription
Alternative (3) ― Performance
CSA A

3. Ordering / Specifying Concrete (1) Alternative (1) ― Common
Supplier responsible for proportions
Owner Specifies ―
Type of cementing materials
Class of exposure
Required structural strength
Nominal max. size coarse agg.
Air content
Admixtures
Any other properties required ie. Slump, flexural strength

4. Ordering / Specifying Concrete (2) Alternative (1) ― Common
Supplier Certifies ―
Plant, equipment and all materials used in concrete meet CSA A23.1
Mix proportions will produce concrete of spec. quality & yield
Strength meets CSA A23.1 requirements

5. Ordering / Specifying Concrete (1) Alternative (2) ― Prescription
Owner responsible for mix proportions and properties of mix
Owner Specifies ―
Types and amounts of cementing materials
Nominal max. size of coarse agg.
Proportions by mass of FA and CA per m3 of concrete
Range of air content
Admixtures
Slump at point of discharge
CSA A

6. Ordering / Specifying Concrete (2) Alternative (2) ― Prescription
Supplier certifies ―
Plant, equipment and all materials used in the concrete meet CSA 23.1

7. Ordering / Specifying Concrete (1) Alternative (3) ― Performance
Supplier responsible for concrete “as delivered”
Owner specifies ―
The class of concrete (to meet the appropriate exposure conditions)
Architectural, structural, and durability criteria

8. Ordering / Specifying Concrete (2) Alternative (3) ― Performance
Supplier certifies ―
Quality plan* ensures performance criteria will be measured and recorded
Concrete meets the specified performance criteria prior to supply
*plan is to designate slump or other measure of workability

9. Batching
Fig Control room for batching equipment in a typical ready mixed concrete plant. (69894)

10. Stationary Mixing Stationary Mixers Mixer Types ― up to 9 m3
Onsite or Central Mix R/M plant
Used for complete or shrink mixing
Mixer Types ― up to 9 m3
Tilting or non-tilting drum
Open top revolving blade or paddle
Typical complete mixing times
Minimum of 1 min. for up to 0.76 m3 or less mixer capacity plus 15 sec. for each additional m3 or fraction thereof.
Fig Concrete can be mixed at the jobsite in a stationary mixer― tilting drum type. (58642)
ASTM actually states that where no mixer performance tests are made, the acceptable mixing time for mixers having capacities of 1 yd3 (0.76 m3) or less shall be not less than 1 min. For mixers of greater capacity, this min. shall be increased 15 s for each cubic yard (cubic metre) or fraction thereof of additional capacity.

11. Ready Mixed Concrete Central-mixed concrete
mixed completely in a stationary mixer
delivered in
an agitator truck
a truck mixer operating at agitating speed
a nonagitating truck
Fig Central mixing in a stationary mixer of the tilting drum type with delivery by a truck mixer operating at agitating speed. (69926)

12. Central Mix Ready Mix Plant
Fig Schematic of a central mix plant.

13. Nonagitating Truck
Used for: Transport concrete on short hauls over smooth roadways. Common on highway paving jobs. Discharge time usually limited to 30 to 45 min.
Advantages: Can use ordinary metal box dump trucks. Cost of nonagitating equipment is lower than that of agitator trucks or mixers.
Watch for: Should only be used for low slump mixes. Possibility of segregation if haul roads rough. Height upon discharge is needed.
Fig Nonagitating trucks are used with central-mix batch plants where short hauls and quick concrete discharge allows the rapid placement of large volumes of concrete. (69897)

14. Agitator Trucks
Used for: Transporting concrete for all uses. Haul distances must allow discharge of concrete within 2 hours.
Advantages: Operate from central mix batch plants. Can extend haul distances over that of typical (nonagitating) dump trucks.
Watch for: Timing of deliveries should suit job organization. Concrete crew and equipment must be ready onsite to handle concrete.
Fig Agitator trucks are also used with central-mix batch plants. Agitation capabilities allow this type of truck to supply concrete to projects with slow rates of concrete placement and at distances greater than nonagitating trucks. (69898)

15. Ready Mixed Concrete Shrink-mixed concrete Truck-mixed concrete
mixed partially in a stationary mixer and completed in a truck mixer
Truck-mixed concrete
mixed completely in a truck mixer
Fig Truck-mixed concrete is mixed completely in a truck mixer. (1153)

16. Truck Mixed Concrete CSA A23.1
70 to 100 revolutions of drum required for mixing, at a mixing speed of 6 to 18 rpm
All revolutions after100 drum should rotate at agitating speed of 2 to 6 rpm
Time limit between batching and complete discharge at job site is 2 hours
and if more than 90 min. since batching, concrete subjected to C-1, C-2, and F-1 exposure must be retested for air content
While not a requirement of CSA A23.1, it is recommended that the concrete be discharged before 300 revolutions of the mixer drum
The 2 hour time limit on complete discharge begins after the introduction of water to the cement and aggregates or the cement to the aggregates.
Mixing at high speeds for about 1 or more hours will result in strength loss, temperature rise, excessive loss of entrained air, and accelerated slump loss.
Always operate mixers and agitators within the limits for volume and speed of rotation recommended by the manufacturer.

17. Mobile Batcher Mixer
Volume Mixing : dry materials, water and admixtures are fed into a mixing trough and mixed by an auger system. Concrete must meet ASTM C 685.
Used for: Intermittent production of concrete at jobsite, or small quantities.
Advantages: Combined materials transporter and batching and mixing system. One-man operation.
Fig 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. (54087)

18. Remixing Concrete (1) CSA A23.1
Water may be added at jobsite provided:
Measured slump less than specified
No more than 60 min. have elapsed from batching to start of discharge
Only enough water added to bring slump up to specified
No more water added than lesser of 16 L/m3 or 10% of mixing water
Spec. w/cm is not exceeded
Indiscriminate addition of water to make concrete more fluid lowers the quality of the concrete.

19. Remixing Concrete (2) CSA A23.1 Water may be added:
On instruction of Producer when supplied by Alternative 1 and 3 and by Owner when Alternative 2
If additional water is added:
Mixer turned at mixing speed a min. of 30 rev. after water added or until concrete uniformity requirements of Standard are met.
The later addition of water and remixing to retemper the mixture can result in marked strength reduction.
When the slump of superplastized concrete falls below the specified due to delay, it should be retempered with superplastizing admixtures only ― not water.

20. 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 labour intensive.
Fig Versatile power buggy can move all types of concrete over short distances. (54088)

21. Transporting and Handling
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 The conveyor belt is an efficient, portable method of handling concrete. A dropchute 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. (69896)

22. Transporting and Handling
Truck Mounted Conveyors
Used for: Conveying concrete horizontally or higher/lower level.
Advantages: Conveyor 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 A conveyor belt mounted on a truck mixer places concrete up to about 12 metres (40 feet) without the need for additional handling equipment. (53852)

23. Transporting and Handling
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 Concrete is easily lifted to its final location by bucket and crane. (69687)

24. Transporting and Handling
Fig Ready mixed concrete can often be placed in its final location by direct chute discharge from a truck mixer. (54955)
Fig In comparison to conventional rear-discharge trucks, front-discharge truck mixers provide the driver with more mobility and control for direct discharge into place. (70006)
Rear Discharge
Front Discharge

25. Transporting and Handling
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 The tower crane and bucket can easily handle concrete for tall-building construction. (69969)

26. Transporting and Handling
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 if required.
Watch for: Constant supply of freshly-mixed concrete is needed without any tendency to segregate.
Fig A truck-mounted pump and boom can conveniently move concrete vertically or horizontally to the desired location. (69968)

27. Transporting and Handling
Flexible Hose at End of Pump’s Rigid Pipeline
Fig 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. (69966)

28. Transporting and Handling
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 The screw spreader quickly spreads concrete over a wide area to a uniform depth. Screw spreaders are used primarily in pavement construction. (69895)

29. Transporting and Handling
Fig For work aboveground or at inaccessible sites, a concrete bucket can be lifted by helicopter. (Source: Paschel)
Fig 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 metres vertically with these pumping methods. (49935)
Working Above Ground Level

30. Videos 1/3
Stationary Mixers

31. Videos 2/3
Truck Mixer Types
Nonagitating Mixers

32. Videos 3/3
Agitators