Batching, Mixing, Transporting, and Handling Concrete - Design and Control of Concrete Mixtures - page 181

Table 10-1. Methods and Equipment for Transporting and Handling Concrete (Continued)

Type and range of work for

Equipment which equipment is best suited Advantages Points to watch for

Nonagitating Used to transport concrete on Capital cost of nonagitating equipment Concrete slump should be limited.

trucks short hauls over smooth is lower than that of truck agitators or Possibility of segregation. Height is

roadways. mixers. needed for high lift of truck body

upon discharge.

Pneumatic guns Used where concrete is to be Ideal for placing concrete in freeform Quality of work depends on skill of

(shotcrete) placed in difficult locations and shapes, for repairing structures, for those using equipment. Only ex-

where thin sections and large protective coatings, thin linings, and perienced nozzlemen should be

areas are needed. building walls with one-sided forms. employed.

Pumps Used to convey concrete Pipelines take up little space and can Constant supply of freshly-mixed

directly from central discharge be readily extended. Delivers concrete concrete is needed with average

point at jobsite to formwork or in continuous stream. Pump can move consistency and without any

to secondary discharge point. concrete both vertically and horizon- tendency to segregate. Care must

tally. Truck-mounted pumps can be be taken in operating pipeline to

delivered when necessary to small or ensure an even flow and to clean

large projects. Tower-crane mounted out at conclusion of each operation.

pump booms provide continuous Pumping vertically, around bends,

concrete for tall building construction. and through flexible hose will con-

siderably reduce the maximum
pumping distance.

Screw spreaders Used for spreading concrete With a screw spreader a batch Screw spreaders are normally

over large flat areas, such as of concrete discharged from a bucket used as part of a paving train.

in pavements and bridge or truck can be quickly spread over They should be used for spreading

decks. a wide area to a uniform depth. The before vibration is applied.

spread concrete has good uniformity
of compaction before vibration is used
for final compaction.

Tremies For placing concrete under- Can be used to funnel concrete down Precautions are needed to ensure

water. through the water into the foundation that the tremie discharge end is

or other part of the structure being always buried in fresh concrete,

cast. so that a seal is preserved be-

tween water and concrete mass.
Diameter should be 250 to 300 mm
(10 to 12 in.) unless pressure is
available. Concrete mixture needs
more cement, 390 kg/m 3 (658
lb/yd 3 ), and greater slump, 150 to
230 mm (6 to 9 in.), because
concrete must flow and consolidate
without any vibration.

Truck agitators Used to transport concrete for Truck agitators usually operate from Timing of deliveries should suit job

all uses in pavements, struc- central mixing plants where quality organization. Concrete crew and

tures, and buildings. Haul dis- concrete is produced under controlled equipment must be ready onsite

tances must allow discharge of conditions. Discharge from agitators to handle concrete.

concrete within 1 1 ⁄ 2 hours, but is well controlled. There is uniformity

limit may be waived under and homogeneity of concrete on dis-

certain circumstances. charge.

Truck mixers Used to transport concrete for No central mixing plant needed, only Timing of deliveries should suit job

uses in pavements, struc- a batching plant, since concrete is organization. Concrete crew and

tures, and buildings. Haul dis- completely mixed in truck mixer. Dis- equipment must be ready onsite

tances must allow discharge of charge is same as for truck agitator. to handle concrete. Control of con-

concrete within 1 1 ⁄ 2 hours, but crete quality is not as good as with

limit may be waived under central mixing.

certain circumstances.

Wheelbarrows For short flat hauls on all types Very versatile and therefore ideal in- Slow and labor intensive.

and buggies of onsite concrete construction, side and on jobsites where placing

especially where accessibility conditions are constantly changing.

to work area is restricted.