NOTES - 04
EQUIPMENT
MANAGEMENT TIPS FOR THE CONSTRUCTION ENGINEERS
AND
PLANT & MACHINERY ENGINEERS
AN
INTRODUCTION TO CONSTRUCTION PLANT AND EQUIPMENT
AFTER
THE INTO MORE EQUIPMENT MANAGEMENT TIPS
THIS
IS APPLICATION OF YOUR KNOWLEDGE AND EXPERIENCE
A
LEARNING FROM THE FIELD WORK
A GENERAL CLASSIFICATION OF
EQUIPMENT
MORE EQUIPMENT
I. TRUCK MIXERS AND
AGITATORS
Truck mixers, also
known as transit mixers, consist essentially of mixed drum mounted on
conventional lorry chassis. The batched aggregate and cement are taken from
batching plant directly into mixer drum. Truck is provided with a water supply
tank with equipment for measuring the quantity of water entering into the drum
and a revolution counter indicating the extent of mixing. As soon as the mixer
drum is charged with its complete batch of materials from batcher plant, the
truck proceeds to concrete pouring point and mixing operation takes place
en-route, the water level and mixing control being operated by driver. When
length of haul is long, delivery of freshly mixed concrete at work is assured
by starting the mixing operation towards end of haul. Truck mixers are often
used as agitator bodies to carry concrete already, mixed at central mixing
plant, when there is likely to be a considerable period lag between the time of
mixing and time of placing. When so used, the drum is operated at lower speed
of rotation, imparting a mild mixing action designed to keep concrete alive.
Truck mixers used as agitators are capable of handling batches small as well as
large.
II. HANDLING AND
TRANSPORTING CONCRETE
The method used to
handle and place concrete should be selected to accomplish several objectives
including:
1. Economy
2. The prevention of
segregation
3. Final placing
before concrete attains initial set
There are many devices
to convey concrete from mixer to the forms, and they are used either singly or
in combination to suit different conditions. The more important are:
Hand Pans, Wheel
barrows and carts
Hoists
Jubilee Wagons
Dumpers and Lorries
Trucks, mixers and
agitators
Buckets
Chute
Belt conveyors
Pumps
Buckets: Buckets may
be divided in two groups - those used with material towers and those used with
power cranes, cables etc. The former, which are referred as tower buckets, vary
in size about 8 to 36 cu.ft. while latter, which are referred to as concrete
buckets, vary in size from about 0.5 to 8 cu.yd. Concrete buckets have bottom
gates which may be opened in such a manner that the concrete will flow
vertically downward. The gates on smaller buckets are operated manually, while
the gates on larger buckets are operated by compressed air or by some other
mechanical method. Gates should be designed so that they may be opened or
closed at will to regulate the flow of concrete.
Hoisting concrete with
crane versus a material tower - On some projects, such as multistory building,
it may be possible to use in crane or material tower to hoist the buckets of
concrete. Each has advantages which may make it more suitable than the other
under certain conditions:
The advantages of
crane and bucket are as follows:-
1. Greater mobility
permits the crane to deposit the concrete at different locations around the
structure provided. There is access to the building, thus reducing haul
distance with buggies.
2. The crane may be
used for other operations.
3. The cost of getting
a crane ready to operate shall be less than that of the tower.
The advantages of a
tower and bucket are as follows:-
1. The investment in
the tower and hoisting equipment will be less than that of the crane.
2. The method requires
less space in a congested location.
Chutes: This equipment
as ordinarily used, is one of the most unsatisfactory device for transporting
concrete. Use of Chutes is not prohibited, but the operations must be so
controlled that segregation and objectionable loss to a slump will be avoided.
To meet these conditions the following requirements must be fulfilled:
1. The Chute must be
on a slope sufficiently steep to handle concrete of least slump that can be
worked and vibrated and must be supported so the slope will be constant for
varying loads.
2. If more than few
feet long, the chute must be protected from wind and sun in order to prevent
slump loss.
3. Effective end
control that will produce a vertical drop and prevent separation of concrete
ingredients must be provided.
End control is of
primary importance as segregation results, not from length or slope of chute,
but from lack of such control.
Belt Conveyor
Belt conveyors, used
so advantageously in transporting many construction materials, have limited
field when applied to transport of concrete. The principle objection is the
tendency of concrete to segregate on steep inclines at transfer points, and as
the belt passes over the rollers. Considerable separation takes place as the
concrete is discharged from the belt, to counter act which, a down pipe
arrangement should be used. The usual width of belt conveyor is 24 inches and
speed of 250-300 feet per minute, such a belt can handle about 40 cu.yds. of
concrete per hour. The surface of belt is usually of rubber, with four or five
ply backing. The belt often gets grouted up by mortar and this difficulty may
be got over by passing the return belt through a trough of water, but with worn
belts, where the canvas is exposed by stripping off the rubber cover, the water
plays havoc in a short time.
On long stretches of
belts, the concrete tends to and stiffen especially in hot, dry or windy
weather. To counteract this, the belt may be covered, with light sheet metal
covers. This also applies to long length of chutes.
Pumps
Pumping concrete
through steel pipelines is one of the most satisfactory methods of transporting
concrete and has been successfully employed on almost every part of
construction including tunnels, bridges, and multistoried buildings. Its
advantage lies in fact that other concrete transporting plants such as borrows,
skips, hoists, towers etc. are eliminated. A very considerable saving in time
and labor is also affected.
Wide varieties of
pumps are available for placing concrete. These pumps can handle all kinds of
mixers and pumping distances varying from 250 to 2000 feet horizontally and 75
to 400 feet vertically. The pumps may be mounted on trucks, trailers or skids.
Truck mounted pump and
boom combination is proving particularly effective in saving labor and
eliminating pipeline handling and set up times and costs. Hydraulically
operated and articulated booms come in various lengths up to nearly 100 feet.
Three types of pumps
are available, namely:
1. Piston 2. Pneumatic
3. Squeeze type
At the end of the run
of pump the pipeline must be cleared of concrete by inserting plunger or sponge
'ball' at pump end and forcing it through under air pressure. After concrete is
cleared, the pipe line is washed out to leave a smooth, clear surface ready for
following day's work.
Concrete discharged
from pipelines is normally very good. The pressure required to force the
concrete along the pipe line tends to expel much of air in the mix. There is
also practically no segregation; in fact, concrete that segregates badly cannot
be handled satisfactorily by pumping.
Compaction
As concrete is being
placed it should be compacted thoroughly and uniformly by means of hand tools,
vibrators, finishing machines to secure dense structure, close bond with
reinforcement and smooth surfaces.
The primary advantage
of vibrating is that it permits the use of dryer concrete, which has a higher
strength because of reduced water content. The advantages of vibrating concrete
are as follows:
1. The reduced water
permits a reduction in the cement and fine aggregate because less cement paste
is needed.
2. The lower content
reduces shrinkage and voids.
3. Dryer concrete
reduces the cost of finishing the surface.
4. Mechanical
vibration can replace three to eight hand peddlers.
5. Lower water content
increases the strength of concrete.
6. The dryer mix
permits the removal of some forms more quickly which may reduce the cost of
forms.
Vibrators are of the
following four general types:
Internal, 'spud' or
'needle' vibrators which consists of a metal spud or rod which may be inserted
into newly placed concrete and which vibrates while it is being withdrawn.
Surface vibrators
which are mounted on screeds or platforms and are chiefly used for
consolidating road slabs, floors etc.
External or 'form'
vibrators which are attached to form work and external shuttering of walls,
columns etc. The forms transmit the vibrating action to the concrete.
Vibrating tables which
are used for making precast products. Most of the high-frequency vibrators now
available give at least 3600 impulses per minute and some of them produce
frequencies of two or more times this number of impulses. They may be
electrically driven, or they may be operated from petrol engine or
air-compressor.
An immersion type
vibrator should be inserted vertically, at points 10 to 30 inches apart and
slowly withdrawn. However, in shallow or inaccessible concrete some
consolidation can be obtained by using the vibrator in a sloping or horizontal
position. Vibrating period of 5 to 15
seconds for each penetration is usually sufficient.
Good small vibrator
can handle from 5 to 10 cubic yards per hour, even in restricted places, and
one large two-man heavy duty type can handle approximately 60 cubic yards per
hour in spacious forms. Spare units and parts should always be on hand to take
care of breakdowns and necessary repairs.
Re-vibration has been
found to be beneficial rather than detrimental, provided the concrete is again
brought to a plastic condition. Re-vibration may be accomplished by immersion
type vibrators, by form vibration, by transmission of vibration through the
reinforcement system.
The following
precautions are recommended while using immersion pokers :-
a. Keep the whole
length of poker immersed in concrete.
b. Never run the
vibrator when not in concrete.
c. Avoid sharp bends
in flexible pipes.
d. If flexible tube
begins to twist and jump, stop the machine at once. Examine the bearing and
grease them if necessary. It is essential to keep bearing well packed with
grease.
e. When using the
pneumatically operated type, supplying air to a motor in vibrating head, always
clear the air line before starting work. To do this, pass the air, with the
vibrating head disconnected.
TRANSPORTATION
EQUIPMENTS
I. The movement of
plant from one site to another is a problem that confronts all plant users at
frequent intervals. All concerned staff should be fully trained to carry out
their part of operation to ensure that it runs smoothly. Bad reconnaissance or
misleading can easily lead to damage to or loss of plant and machinery.
II. For land
movements, self propelled, wheeled machines equipped with large diameter of
pneumatic tyred wheels, such as graders and motorized scraper, can move across
country or by roads under their power speeds. When moving by road their speeds
and daily distance of move should be restricted e.g. for a grader 160 kilometer
is a reasonable limit. Machines mounted on road type pneumatic tyres sprung
trailer chassis can be towed on roads.
III. All other
machines must be carried, though crawler tractors can, if unavoidable, travel
for limited distance on their own tracks preferably across country. If forced
to travel on road, crawler tractor should wear track pads and move on soft
verge as much as possible to minimize the damage they will do to road surfaces
and will incur themselves owing to vibration, and their daily journey should be
restricted to 40 km or less.
IV. Before planning
road movement of equipment, a detailed reconnaissance is essential covering:
a. Loading points b. Routes
c. Halting points
d. Dispersal areas.
It is better to
consult police, P.W.D. and RTO at early stage of planning.
V. Route
reconnaissance should include the following:
a. Road width
b. Road surface
c. Radius of bends
d. Up gradients
e. Down gradients
f. Overhead clearance
g. Other traffic
h. Suitable halting
places
VI. Whole planning
a. Choose a route for
large awkward vehicles avoiding dense traffic during rest hours.
b. Avoid travel by
night for heavy conveys
c. Provide route card
to every driver
VII. Transporters
In transport, we have
a. Trucks
b. Trailers
Machinery may be
transported on trucks with either flat bed or dump bodies. This gives better
maneuverability but involves the longer and heavier ramps or dependence on
banks. It has the disadvantages of labor for handling the ramps, danger in
using them and greater height of machine when loaded.
Most of excavating
machines are not designed to travel under their own power on highways,
particularly for long moves and are carried from job to job on machinery
trailers. These are manufactured in a wide variety of sizes and types of which
only a few are described here.
- A semi trailer has
rigid drawbar supported by towing truck.
This may carry the
direct weight of more than half the trailer and load, if the wheels are in the
rear, or only serve to stabilize against rocking if the axle is under the
middle of the load.
- Full trailers are
usually supported in front by swiveling axle and connected to truck by
comparatively light draw tongue.
Any trailer can and
should be equipped with brakes, light operated from truck or tractor's cab.
Trailer must have a
deck or carrying space large enough to support or hold the machine to be
carried. It must be strong enough for the job, and must provide loading and
unloading with minimum of difficulty and danger. It should be pulled by a truck
or tractor, amply powerful to climb any grade it may meet and have brakes
adequate for stopping it going down. In general, a trailer should be purchased
which is of sufficient size for biggest and heaviest machine to be regularly
carried.
Another factor is size
and weight of ramps. Maneuverability may be critical. From this stand point,
semi trailers are too much preferred.
VIII.TRANSPORTING
The amount of load on
rear trailer tyres used or those of trolly or tractor, can be adjusted by
placing the machine towards the front or rear of the deck. Placement will also
be affected by the need to rest the bucket blade and the direction in which the
boom is to be carried.
A dipper stick bucket
may be tacked under the boom or the deck, rested on the gooseneck or between
rear tyres or if tractor is a dump truck in its body. Long booms are usually
faced to the rear and carried low, with the bucket or hook resting on the deck.
It may be necessary to have the operator stay with a large shovel in transit to
raise, lower or swing the boom to avoid obstacles.
When the machine is
correctly positioned, it is left in gear with clutch engaged and the brake
locked. The ramps and the blocks are loaded on to the deck and machine secured
against sliding by the blocks or chains or both.
Many machines are
moved without any chaining or blocking, particularly for short trips. Crawler
tractor tends to stand very well. Shovels, because of their height, are less
stable. Rubber tyred vehicles tend to bounce and creep blocking is recommended
for all machine transportation, since minor accidents may become a serious one
if it slides off a trailer.
In most states, truck
and trailer widths are limited to eight feet. Wider vehicles must obtain
special permits. Drivers of full trailers should be sure of their routes so as
not to get into a blind street. The average driver cannot come back such a
distance, or turn it around in restricted quarters.
IX. The following
points need attention when plant is carried on trailers:
a. The overall height,
width, and load classification of plant when loaded must be within the limits
of roads and bridges. In case of doubt, consult PW dept., RTO or police
department. Load high machines such as excavators on low loaders. In some cases
a degree of dismantling may be necessary to reduce dimensions.
b. Carry all parts
removed from machine on same vehicle as the machine.
c. The operator should
travel with his machine in a position where they can see the machine and
communicate with the driver e.g. immediately behind the drivers cabin.
d. Tyre pressure of
transporter and trailers should be checked at clock hour halt when tyres are
cool. Trailer brakes must be adjusted to act before those of towing vehicles.
e. Mark projecting
loads by flags in day and by lamps in night. Loads wider than the vehicle
should be placed front and rear.
X. BULK CEMENT
CARRIERS
Special road rail
steel containers are also employed for carrying bulk cement. These may be
mounted on flat railway wagon and can be transported on to lorries. Each
container holds 3.5 tons of cement and about 200 tons can be loaded per hour.
Hinged lid at the top is clamped down after the cement is poured in. At
destination the container is lifted from wagon or lorry by crane and contents
are dropped in an elevated bin by opening two hinged doors which form its base.
In air activated
containers, unloading of the containers is accomplished by connecting two
flexible hose lines to containers, one for compressed air and one for carrying
cement into consignee's storage bins. The containers may also be bodily lifted
by means of crane and transported to lorries, if so required.
CONCRETE
CONSTRUCTION EQUIPMENT
COMPARATIVE COSTS
Cost of alternatives
Intangible factors
Contract requirements
- speed of construction - quality
Factors in costing :
some aspects
Labour
Plant
Temporary works
Influence in
surrounding operations
Basic Data required:
Total quantity of
concrete
Construction period
Unit labor output
Unit plant output
Knowledge of balancing
equipment
Particular Site
requirements
Method of Costing:
1. From Construction
Program, assess the time available for concreting.
2. Estimate the
required output of concrete per unit time (week or day or hour)
3. Choose mixing,
transporting and placement equipment (capacity and numbers) to suit.
4. Check for
possibility of cheaper alternatives.
5. Assess the manpower
required to suit.
6. Assess the raw
materials storage and replenishment requirements.
7. Assess the
temporary works required.
8. Investigate if
re-handling of materials is involved.
9. Consider intangible
factors.
10. Compile the cost.
Checklist of Temporary
works
- Adequacy of ground
conditions to receive equipment
- Specification for
service roads
- Layout of service
roads
- Requirements for
crossing works/reinforcement etc.
- Requirements of
barges/floating craft
·
Cost of temporary works Vs. other alternatives
·
Batching and Mixing equipment for concrete
1.
Concrete mixers - capacity range 200 to 2000 liters
2.
Concrete mixer with built-in weighting arrangement - capacity 200 to 500 liters
3.
Batching plant with composite batching and mixing facilities-capacity range 15
cu.m. per hour to 200 cu.m. per hour.
a. Mobile batching
plant
b. Stationary batching
plant
c. Dry batching plant
4.
Truck mixers - capacity range 1 cu.m. to 10 cu.m.
a. with separate
primeover
b. with power take-off
from the truck engine
5.
Trailer mounted mixers
6.
Truck mixers with batching facilities
7.
Truck mixers with batching and belt conveyer discharge facilities
8.
Truck mixers with batching and hydraulic crane boom discharging facilities
9.
Separate weigh batching systems Concrete Transportation equipment
1. Mortar pans
2. Wheel barrows
3. Powered wheel
barrows
4. Concrete
dumpers-capacity range 0.5 cu.m. to 2 cu.m.
5. Large capacity
dumpers-capacity 4 to 6 cu.m.
6. Truck mixers (as
per earlier description)
7. Fork lifts
8. Rail mounted
trolleys
9. Monorail systems
10. Chutes
11. Concrete placers
(belt conveyers)
12. Concrete pumps
13. Pneumatic placers
14. Concrete placer
booms
15. Premises
16. Tower cranes
17. Mobile cranes
18. Cableways
19. Helicopters
Tower Cranes
A wide variety of
capacities and mounting systems available. Tower cranes may be mounted on fixed
foundations, truck chassis, crawlers, trailers, rail tracks, etc. Tower cranes
can also be of climbing type.
The maximum free
standing height without any anchoring of the mast above the base is about 40 m.
For greater heights, the mast is anchored at about 10 m to 15 m intervals.
The normal range of
boom length is between 20 to 50 m. The load carrying capacity at the extreme
end ranges between 0.5 to 3 tons and at minimum radius between 5 to 20 tons.
The operator's cabin
may be located either at the top of the mast or at the base of the mast.
The tower crane cannot
be operated at very high wind speeds.
The latest improvement
in tower crane technology incorporates an articulated boom so that greater
heights with free standing mast can be covered. Articulated booms also
facilitate operation in confined locations.
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