S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 1
CLASSIFICATION OF MAJOR EQUIPMENT
Construction equipment classification facilitates identifying equipment, verifying stock, locating spares, recording repairs, accounting costs, indexing catalogues, logging performance, monitoring effectiveness, estimating outputs, and planning procurements. There are many methods for classifying construction equipment. These include dividing the equipment into special purpose and general purpose machines; classifying equipment according to the alphanumeric code generally, conforming to the description of equipment; and categorizing equipment into its functional use. In particular, functional classification of major equipment is reflected in below:
Functional Classification of Construction Equipment
1.Earthwork Equipment
Excavation and lifting equipment—back actor (or backhaul, face shovels, draglines, grata or clamshell and trenchers.
Earth cutting and moving equipment—bulldozers, scrapers, front-end loaders
Transportation equipment—tippers dump truck, scrapers rail wagons and conveyors. Compacting and finishing equipment—tamping foot rollers, smooth wheel rollers,
pneumatic rollers, vibratory rollers, plate compactors, impact compactors and graders. 2. Materials Hoisting Plant
Mobile cranes—crawler mounted, self-propelled rubber-tired, truck-mounted. Tower cranes—stationary, travelling and climbing types.
Hoists—mobile, fixed, fork-lifts. 3. Concreting Plant & Equipment
Production equipment-batching plants, concrete mixers. Transportation equipment—truck mixers, concrete dumpers
Placing equipment—concrete pumps, concrete buckets, elevators, conveyors, hoists, grouting equipment.
Precasting special equipment—vibrating and tilting tables, battery moulds, surface finishes equipment, prestressing equipment, GRC equipment, steam curing equipment, shifting equipment.
Erection equipment.
Concrete vibrating, repairing and curing equipment, Concrete laboratory testing equipment.
4. Support and Utility Services Equipment
Pumping equipment.
Sewage treatment equipment. Pipeline laying equipment.
Power generation and transmission line erection equipment. Compressed air equipment.
Heating, ventilation and air-conditioning (HVAC) equipment. Workshop including wood working equipment.
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Aggregate production plant & rock blasting equipment Hot mix plant and paving equipment.
Marine equipment.
Large-diameter pipe laying equipment. Piles and pile driving equipment, Coffer dams and caissons equipment. Bridge construction equipment.
Railway construction equipment.
9.2 EARTH FACTOR IN EARTHWORK
The most important factor that determines the suitability of equipment for earthwork is the earth itself. The earthwork process is affected by the ground condition. The main ground characteristics which influence the performance of the equipment are the suitability of equipment, the digging effort, the resulting output, and the output measurement.
9.2.1 Equipment Suitability
The type of earthmoving equipment required varies with the nature of the soil and tasks to be performed. Typical job-related equipment used in building projects are given below:
(1) Excavating and lifting in soft earth
(a) Deep pits excavation — Clamshell and dragline. (b) Shallow pit excavation — Backhoes.
(c) Ground level excavation — Shovels.
(d) Shallow trenching — Trenchers, excavators (backhoes). (e) Wet soil excavation — Excavators (dragline or) grab. (2) Cutting: over areas
(a) Short-hauls (b)Long-hauls
(3) Loading and transporting excavated soil
(a)Loading soil — Loaders, shovels, excavators.
(b)Transporting soil — Tippers, dumpers, scrapers. rail wagons, conveyors. 9.2.2 Digging Effort
The digging effort of equipment depends upon the nature of the soil. For example, it is easy to dig in common earth than in stiff clayey soil. The typical soil factor which determines the
comparative equipment effort required in various types of soils can be taken as under
Nature of soil
Loam, sand, gravel Common earth Stiff clay, soft rock
Digging effort
Easy digging Medium digging Hard digging Soil factor 1.0 0.85 0.67
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9.2.3 Volume Conversion
The volume measure varies with the state of the soil. Three states of soil encountered in earthmoving operations are in-place
natual soil, loose excavated bulk soil, and compacted soil. The volume of soil in its in-place natural state is usually, referred to as the bank volume. It swells when heaped in a loose state after excavation, and shrinks when mechanically compacted.
9.2.4 Equipment Output
The equipment capability to perform an assigned earthwork task can been be determined from the on-site actual trials or can be accessed from its past performance records of
Operation under similar site conditions
The equipment's hourly output is determined by multiplying the earth quantity moved (Load) per cycle by the number of cycles per hour
Equipment actual hourly output = Actual load/cycle x cycles/hour
For example, a front-end loader on a given job moves a load of 1.5 m3 of loose soil in one cycle consisting of loading-lifting-travelling-unloading-return trip-sod ready for loading. If each cycle time is 1.2 minutes, then
Actual output per working hour = Load per cycle x cycles per hour « 1.5 m3 * 60 minutes/1.2 minutes = 75 m3 per hour.
But at the planning stage the actual on-site trials may not be feasible, and the past performance data may not always be available, or it may not be adequate as the site conditions vary from place to place and project to project. In the absence of these reliable performance methods, the equipment output norms can be derived from the performance data given in the manufacturer‘s manuals. This off-the-job equipment hourly ideal output data is reflected in these manuals in the form of charts, graphs, performance curves, and tables. This 'ideal output' is multiplied by 'correction factor' to determine the optimum output1.
Optimum output = Ideal output x Correction factor.
Correction factor depends upon the operating characteristics of the equipment and the site conditions like excavator swing factor, earth grade factor, soil factor, rolling resistance, traction factor, and so on. The ideal output and correction factor are covered in subsequent paragraphs under each equipment.
The equipment planned performance at site of work depends upon many situational factors that influence the output. These situational factors can be broadly grouped under two headings, i.e. controllable factors and uncontrollable factors. The output adopted planning purposes can be determined as under:
Planned output = Optimum output x Performance factor.
Nature of soil Bank volume Loose volume Compacted volume Common earth Sand Clay Rock (blasted) 1.00 1.00 1.00 1.00 1.25 1.12 1.27 1.50 0.90 0.95 0.90 1.30 ...
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9.3 EARTH EXCAVATING EQUIPMENT
Primary earth excavating equipment is the tractor-mounted excavator. Excavators operate in a stationary mode. They dump excavated materials on the sides, or directly into waiting tippers/dump trucks and they gradually, shift their position as the work progresses. Various types of earth excavating equipment are listed in Exhibit 9.2.
The excavating equipment is divided into four categories, viz. face shovels, backhoes, draglines and grab or clamshell Further, excavators can be rope-operated or hydraulically . Operated the type and size of the equipment depends upon the nature of the task, the type of soil, digging depth and the desired level of production.
9.3.1 Face Shovel
It operates from a flat surface, producing upward digging action, excavating and filling the bucket as it climbs after the bucket is filled, its upper part swings to the dumping position where the bucket is emptied in a waiting truck or on to a stockpile. Thereafter, it returns to its original position and starts the next cycle of excavation. It is capable of working in all types of dry soils. The
struck-bucket capacity of the face shovel struck-bucket varies from VI yd! (0.38 wft to 4/1/2 yd* (3 25 to3), and depending upon the size of the machine and bucket, its cutting length varies from 7 m to 10. 6 m 9.3.2 Backhoe
It is primarily used for excavating materials below its track level, i.e. excavation of small end Urge pits, bison* net and large trenches, backhoe are generally track-mounted but snail capacity equipment do have wheel-mounting to add to their mobility.
The backhoes are fitted with buckets having struck capacity varying from 1/2 Yd' (0.38 m) to 4 1/4 Yd3 (3.25 m9) and their corresponding digging depth capability is from 5 m to a maximum of 9.5 m. 9.3.3 Dragline
It is a rope-operated boom-fitted crane type machine. The bucket is thrown into the excavation area, and the cable-controlled hook is rotated, so that, the bucket gets filled by scraping the surface to be excavated. It is used for digging below the ground level specially, in loose soils or marshy and underwater areas with soft beds.
The dragline can operate in a depth approximately up to 1/3 of its boom length for broad sweeping type excavated work. Its boom length varies from 21 m to 36 m and the struck bucket capacity extends from 1/2 Yd3 (0.38 m3) to 4 Yd3 (3.06 m3).
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9.3.4 Grab or Clamshell
Like dragline, it is a rope-operated boom-fitted crane type machine having a grab or clamshell bucket the grab bucket has interlocking teeth to penetrate loose soil whereas the clamshell bucket has no teeth. These buckets are dropped with their sides open like open jaws on the soil to be grabbed, and thereafter, these jaws are closed by rope machines prior to hauling. These machines are used primarily for deep confined excavations such as shafts, wells and spoil heaps removal. The depth of the excavation can be roughly taken as 1/3 of the boom length. The range of the size of the grab bucket and its length of boom are similar to those of the dragline.
9.3.5 Output Planning Data
Planned output = Ideal output x Correction factor x Performance factor. ‗Ideal output in loose cubic meters (LCM):\
Ideal output = Bucket output/Cycle x Cycles/hour these are explained as under;
(a) Bucket output/cycle—a cycle of a bucket starts from the point it strides the excavation place to its return to the next excavation point after unloading the excavated materials at the specified place in the transporter or on a heap of loose excavated materials. The maximum loose material in cubic meter* (LCM) it can carry in its bucket per cycle is equal to its bucket struck capacity.
(b)Cycles/hour—the cycle time is the time taken by the cycle of bucket movements which includes load, swing, unload and return to start the cycle again.
Maximum number of cycles/hour * 60 minutes/cycle time in; minutes.
9.3.6 Correction Factors
These include the following and their implications on the equipment output are shown in Excavator Output Adjustment Factors for Secondary Tasks
Equipment Nature of Secondary Tasks Task Efficiency Shovel Movement from excavating place to unloading place:
a. Within vicinity 1.0
b. Little movement 0.6 to 0.9
c. Appreciable; movement or delays 0.4 to 0.6 Backhoe Trenching
a. Equal to bucket width 1.0
b. More than bucket width 0.7 to 0.9
Dragline a. Bulk excavation 1.0
b. Wide open ditches 0.7 to 0.9
c. Confined, restricted places 0.5 to 0.7
Clam shell a. Dry soil Pits 0.9
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 6 (a) Equipment conversion factor: It relates to the type of equipment employed.
Equipment Factor multiplier
Face shovel 1.00
Backhoe 0.80
Dragline 0.75
Grab 0.40
(b)Soil digging factor: It depends upon the digging effort. Digging
effort Factor multiplier
Easy digging Medium digging Hard digging
9.3.7 Procedure for Determining Output from Equipment Output
Planning chart the output of an excavating equipment, for planning purposes, can be easily determined from the equipment output planning table shown in Appendix 9.1. The procedure involved is explained with the following example:
Example Estimate the hourly production in bulk volume (LCM) of a backhoe with bucket capacity of
0.96 M3 employed on excavation of a foundation four meters deep in hard digging soil. The excavated earth is to be loaded in waiting dump trucks, placed at a swing angle of 75 degrees. The expected performance efficiency is 83%.
(a)Ideal output of loose soil in cubic meter (LCM) for an equivalent face shovel of bucket capacity of 0.96 m3 from Appendix 9.1.
(b)Backhoe output using equipment conversion factor of 0.8 operating at optimum depth
(c)Correction factors applicable are
—Soil factor for bard digging = 0. 67 —Load factor for loading into vehicle = 0.80
—Swing factor for 75 degrees = 1.05
Therefore, correction factor s 0.67 x 0. 80 x 1.06
(d) Performance efficiency Hence expected output/h
= Ideal output x correction factor x performance efficiency.
= B x C x D » 0.8A x C x D = 120 x 0.56 x 0 . 83 Say = 56 LCM/h. 1.0 0 0.8 5 0.6 7 = 150 LCM (approximate) = A x 0.80 = 120 LCM
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9.4 EARTH CUTTING AND HAULING EQUIPMENT
9.4.1 Bulldozers
The bulldozer is a versatile machine. It can be used for moving earth over distances upto 100 m, clearing and grubbing sites, stripping top unwanted soil, excavating to a shallow depth say upto 200 mm at a time, pushing scrapers, spreading soil for leveling areas, ripping bare soft rock, and maintaining roads. Bulldozers normally are Track-mounted, however there are four-wheeled dozers with large-powered engine. The wheel dozers exert higher bearing pressure as compared to track-dozers.
Dozers excavate and push earth with the help of a stiff welded steel blade fitted in front and controlled by two hydraulic cylinders. Blades are of four types. The straight S-blade is used for forward pushing of earth. U-blades have large capacity, and are used for pushing loose materials. Angle A-blades are used for pushing soil to one side rather than hauling it forward as is required in hill road formation cutting. Push P-blades are used for push loading a scraper. A dozer can also be fitted with a backhoe attachment for ripping hard soil and rock, and a winch for uprooting trees, skidding boulders and heavy materials.
Ideal output for dozing soft soil depends upon the engine power, straight-blade capacity and dozing distance. The ideal output of bulldozers is shown in Appendix 9.1.
This ideal output, measured in the bulk volume (loose soil), assumes forward dozing speed of 3 km/h, return speed of 6 km/h, maneuvering time of 0.15 minutes, easy going on generally level ground and dozing of (bank) materials using a straight S-blade. This ideal production is corrected to conform to varying conditions as under.
Dozer optimum output = Dozer ideal output x Correction factor Output planning data = Dozer optimum output x performance factor
Where, correction factor leads to the following effect.
(a) Blade factor—multiply ideal output by the blade factor value.
Type of blade Blade factor
S blade 1.0
A blade 0.75
U blade 1.25 (used only for loose soil).
(b) Transmission system—For direct drive, take 80% of the ideal output which is based on the power shift system. Direct drive system output = 0.8 power shift system
output.
(d)Grade factor—The manufacturer's manual provides the data for a change of output with varying slope, but for planning purposes it can be taken as under.
(e)Nature of slope Effect on output (%)
(f) Downhill working Increase 2.5 x grade (%) (g)Uphill working Decrease 2 x grade (%).
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 8 Example Determine the output of a bulldozer having 215 HP engine, fitted with . blade rated capacity
4.40M . The dozer is employed for excavating a hard clayey arc
with average haulage of 50 meters, on a ground with down slope of 10%. It has dire drive transmission, and its expected performance is 50 minutes per hour.
Solution Output/h = Ideal output/h x correction factor x performance factor.
(a) Ideal output/h for 50 meter haulage of
215 HP dozer with 'S' blade of capacity ... , „, .
A A-T,_3 r _ A- _ j _ « , * 160 LCM approximate)
4.40 m from Appendix 9.1.
(b) Correction factors applicable ore:
—Soil factor for hard digging = 0.67
—Blade factor for A blade ■ 0.61
—Grade factor for 10 % down grade = 1 + 2.5 x 10%
(assistance) = 1-25
—Transmission factor for direct drive = 0.8 —Swell factor of clayey soil = 1.3
Therefore correction factor
= 0.67 x 0. 65 x 1. 25 x 0. 8 x ^ = 0.42
(C) Performance factor for 50 min/hour working = 0.83 (D)Therefore expected output in BCM = AxBx C
= 160 x 0.42 x 0.83 = 55.8. Say 56 BCM
9.4.2 Scraper
It is the equipment commonly used for scraping, loading, hauling and discharging including spreading large quantities of earth over long distances; say around three Km. It can scrape
soils in layers of 15 cm to 30 cm in depth. Basically, a scraper has a soil container or bowl mounted on two wheels. It digs into the earth after the forward portion of the container is lowered, and it collects the earth as the scraper moves forward. Unloading and spreading takes place in controlled layers in the discharge area with the aid of a tractor plate while the unit keeps on moving. Scrapers come in many sizes varying from 8m3 to 50 m3. There are two main categories of scrapers—(I) towed scrapers and (ii) motorized scrapers. They are shown in Exhibit 9.4.
(I) Towed scrapers these are pulled by a tractor or a bulldozer capable of 300 HP or more. Although the loading cycle may take hardly two to three minutes, its travelling speed is slow. Its main advantage over the motorized scraper is that it can operate in small areas
And can scrape in heavy soil areas. Towed scrapers are best suited for medium distances Up to 400 m. Towed scrapers range from 8 m3 to 30 m3.
(If) Motorized scrapers Several types of motorized scrapers with heaped capacity ranging from 15 m3 to 50 m3 are available to suit varying job requirements. These include single engine scraper, double engine scraper and elevating scraper.
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 9 (a) Single engine scraper requires a pusher bulldozer to provide the necessary attractive force.
Generally one medium-sized crawler tractor is sufficient to serve four to five scrapers.
B , Cycle time of each scraper
Scrapers per pusher = ■~ ? -- R—-— Cycle time of pusher
Example Cycle time of a scraper is 6 minutes and a pusher to fill a scraper is 1.5 minutes. Calculate the number of scrapers which a pusher can serve. Determine the number of pushers to serve 10 scrapers.
Solution Number of scrapers per pusher = =6/1.5 =4
Number of pushers for 10 scrapers = No. of scrapers o 10/4 =3
No. served by one pusher 9.4.3 Loader Shovel
This machine, also called as the front-end loader, can be used as earth loader, earth transporter over short distances, and earth excavator in loose soil. It can operate like a face shovel and bulldozer. It is available with wheel mounting and track mounting.
The loader shovel can also be fitted with a benefactor attachment. This benefactor type loader can be used for light excavation like manholes, drain trenches, small pits, etc. and for loading of materials into tippers. The ideal output data for loader shovel is given in Appendix 9.1.
The quantity of materials that can be hauled by the loader depends upon its bucket capacity. Loader bucket capacities are specified by the manufacturer either in terms of heaped capacity or struck capacity. However, planning can be based on the loose soil struck opacity of the bucket, and the heaped capacity (loose soil) can be converted into struck capacity LOOSE* soil) as under
Bucket struck capacity • Bucket heaped capacity x Fill-factor where fill factor can b e taken as
Nature of soil Bucket fill factor 0.95, 0.95 0.80 0.70
Common earth, Sand and gravel, hard clay, blasted rock 9.4.4 Hauling Equipment
The type of earth hauling equipment primarily depends upon the haulage distance. A rough Guideline for selecting equipment based on haulage distance is given in Table 9.3
Table 9.3
Guidelines for Selecting Equipment Based on Haulage Distance (in metres)
Type of Equipment Range of Haulage
Distance
1. Front-end loader track Up to 80
2. Front-end loader (wheeled) Up to 200
3. Bulldozers Up to 80
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 10 5. Elevating self-loading
scrapers
100-1000
6. Single engine scrapers 500-1500
(dozer pusher arrangement) 7. Double engine motorised
scrapers
2000 and
above (push pull arrangement)
8. Tippers and dump trucks 800 and
above
Mostly the excavated earth is hauled in heavy duty rubber-tired tippers, lorries, and rear-opening dump trucks. Over long distances these vehicles vary in capacity from 5 m3 to 30 m3 dumpers. Tipping lorries are employed for transporting materials over level grounds where as dumpers are used for moving large quantities of materials across rough areas. Generally, front-end loaders and excavators are used to load tippers and dumpers.
The number of haulage vehicles required can be calculated as under.
Haulage vehicle required = 1 + (Cycle time per trip of vehicle) Load filling time of vehicle
example Construction of a military helipad at an altitude of 2400 m involves 80,000 m? (loose) of
area excavation in soft soil. This task is to be completed in 200 working hours. The company entrusted with the execution of the task has two dozers each with an output of 220 no'/h under job conditions. It also holds wheel loaders and 22 m dump trucks. One loader can load in trucks about 120 m3 of excavated soil per hour. The dump truck cycle time for disposal of excavated materials is 35 minutes. This includes 7 minutes of loading time by a loader team consisting of 2 loaders. Estimate the output of front-end loader for loading excavated soil heap into dump trucks and determine approximately the number of dozers, loaders and dumpers required to complete the task on time.
Excavation quantity /Output/h x Working hour 80,000 / 220 x 200 S{8ay)
=Excavation/h by dozers / Loader output/h =No. of dozers x dozer output/h / Loader output/h
_ 2 x 220 / 120
- 4 = 2 loader teams, each team consisting of 2 dozers.
(c) Dumpers required = 1 + / Loading time
For each loading team of 2 front end loaders = 1+(35/7)=6
Total dumpers required = 2 x 6 = 12. Dumper cycle time Solution
(a) Dozers required =
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Types of Rollers Nature of Soil 100
% 100%
HOW THE TRANSPORTATION DISTANCE AFFECT THE SELECTION OF EARTH
HAULING EQUIPMENT?
The type of earth hauling equipment primarily depends upon the haulage distance. A rough
guideline for selecting equipment, based on haulage distance is given in Table below.
Hauling Distance of Equipment
S.No.
Type of Equipment
Range of Haulage Distance (in Meters)
1
Front-end loader track
Up to 80 Meters
2
Front-end loader (wheeled)
Up to 200 Meters
3
Bulldozers
Up to 80 Meters
4
Towed scrapers
100~300 Meters
5
Elevating self-loading scrapers
100~1000 Meters
6
Single
engine
scrapers(dozer
pusher
arrangement)
500~1500 Meters
7
Double
engine
scrapers(push
pull
arrangement)
2000 Meters and above
8
Tippers and dump trucks
800 Meters and above
Haulage vehicle required = 1 + (Cycle time per trip of vehicle) Load filling time of vehicle
9.
5 EARTH COMPACTING AND GRADING
EQUIPMENT
The compacting process increases the density of soil by reducing air void space. Consolidation, on the other hand, increases soil density by reducing water voids. Consolidation is a long-term process spread over years, whereas compaction can be achieved in a few hours. Compaction improves bearing strength, permeability and compressibility. Compacting equipment combine their static weigh with tamping, vibration, impact and kneading action to
produce the desired compacting effort. Compaction equipment requirement
varies with soil characteristics and compacting effort. Exhibit 9.5 shows the type of compacting effort and equipment required to compact different soils. The compacting equipment can be broadly
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 12 classified into tamping foot rollers, pneumatic tired rollers, vibratory rollers, impactors, plate vibrators, and smooth steel-wheel rollers.
9.5.1 Segmented Pods and Tamping Rollers
A tamping roller consists of one or more hollow steel cylindrical drums with rows of steel •tads like sheep's feet mounted on it As the roller is towed with a crawler tractor, these studs punch into the soil and compact it by tamping and kneading action. Generally, the compaction gets carried out to a depth of 150 mm. The cylinder drum can also be filled with water or sand to add extra weight while compacting.
9.5.2 Smooth Wheeled Rollers
These rollers have one or more smooth steel wheels, and the latest variety rollers are self-propelled. The self-propelled tandem and 3-wheeled rollers are used for finishing compaction of layers up to 150 mm of sand, gravel and water bound macadam used in base courses. Smooth wheeled rollers are employed for compacting bituminous materials specially the top layers in road surfacing operation. Smooth wheeled rollers are classified either by type or weight or both. Various types of rollers include 3-wheel two axles, 2-wheel tandem and 3-wbeel tandem The weight of the rollers can also be increased by ballasting with water, sand, or pig iron. Rollers are designated in terms of static weight and ballasted weight, i.e. 15/20 tons means that the static weight of the roller is 15 tons and the maximum weight when ballasted is 20 tons. In order to indicate the pressure exerted, these rollers are also designated by specifying the minimum weight per linear width of roller, i.e. 60 kg/cm width.
9.5.3 Pneumatic Rollers
Pneumatic rollers are available in light, medium and heavy weights. They compact soil by a kneading action. The weight of the equipment can be nearly doubled with ballasting using water, sand or pig iron, and the ground pressure can be maintained as desired by controlling the weight of the ballast, the number of the wheels, the width of the tyres and the tyre pressure. The pneumatic tired rollers are rated in terms of tyre pressure (ground contact pressure) per unit area. It may be noted that the load on the tyres determines the depth is which compaction is possible, where as both the tyre pressure and the tyre load are important for achieving compaction near the surface. (See Table 9.4.)
9.5.4 Vibratory Rollers and Compactor*
Vibration improves compaction and save time when compared with the static weight method of compaction. Vibrations set the rim roller in oscillation, and these in turn transmit vibrations to the soil. Vibrations are induced by installing a rotating eccentric weight inside the roller drum. Vibratory rollers combine the static weight with dynamic forces. Maximum compacting effort is produced when the resonance frequency of the roller and soil coincide. Generally, the rating for the vibratory compactor is stated as total applied force' expressed in tons and it is the numerical sum of the dynamic forces plus static weight. The vibrating frequency is specified as cycles/minute. Vibration frequencies range from 1400 to 3000 cycles per minute. Further, a slow displacement speed of say 2.5 to 4 km/h produces a better effect than speedier movement.
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 13 'Vibratory compactors are of various types and sizes. These include smooth drum vibratory rollers and tamping foot vibratory rollers. These are widely used for compacting non-cohesive soils.
9.5.5 Production Output of Roller Compactors
The nature of soil dictates the type of compacting equipment required, and the dry density which can be achieved. After the compacting equipment is selected, its average output can
be calculated as under:
Compaction in m3/hr = WSTEC / P
where W = Width compacted per pass (M) S - Compactor speed in M/h T = Thickness of compacted layer in m3 E = Job efficiency factor C = Compacting factor P = Number of passes required—varies from 4 to 6 and the approximate value of the compacting factor for the changing state of soil. In the absence of actual data, the compacting factor
9.5.7 Graders
These are used to grade earthen road formations and embankments to their finished shape within specified limits by trimming the surface. The graders can also be used for forming ditches, mixing and spreading soils, backfilling and scarifying ground.
The motor grader is the equipment mostly used for grading and finishing of large areas. Motor graders generally have engines
up to 300 HP and the latest models are provided with hydraulically controlled attachments. These attachments include an excavation blade similar to the bulldozer, scarified, ripper and backhoe. The blade of the motor grader has replaceable cutting edges. These blades come in flat, curved and serrated styles. Motor graders are fitted with articulated frames for increasing maneuverability. Motor graders are now available with automatic grade controls for achieving the desired grading. Grading distance of 500 meters and above give optimum output. For shorter distances, task efficiency gets reduced:
Distance in meters 50 100 200 500 Task efficiency 0.4 0.6 0.8 1.0
Graders' optimum output for finishing is measured in M?/hour on an area basis or km/hour on an linear basis:
Output in m2 /hour = W.S.E / P
where,W = Width graded per pass S = Average speed in m/h E = Job efficiency factor P = Number of passes (generally 4 to 6)
Example Calculate the time required to grade and finish 30 km of road formation with width equal to
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 14 successive two passes as 6 km/h, 8 km/h and 10 km/h respectively. Assume machine efficiency based on operator's skill, machine characteristics and working conditions as 75%
Average speed = 2x6 + 2x8x2x10 /6 = 8 km/h
Area to be graded per hour
_ Width graded per pass x Average speed x Machine efficiency / Number of passes _ W x 8 x 1000 x 0.75 / 6 =
Numbers of hours required to grade and finish 30km long and 3W wide area = total area / Area/hr
= (30x1000x3W) / (Wx8x1000x0.75) +6* *= (denominator) =90 hours.
9.5.8 Equipment selection criteria
Equipment selection criteria depends upon the following factors:
1. Compacting equipment – nature of materials, depth of fill, daily workload, and working conditions
2. Grading Equipment – Nature of maeterials, daily workload, finished accuracy and working conditions.
9.6 CONCRETING PLANT AND EQUIPMENT
Concrete is produced by combining basic materials like cement, aggregate and water into a homogeneous, suitably designed, plastic mix that solidifies into structural and non-structural building members. The process of production of concrete involves batching, mixing, transportation, placing, consolidating and curing.
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9.6.1 Concrete Batching and Mixing Equipment
Batching is the process of proportioning cement, aggregates, water and admixture, by weight or volume. Prior to mixing. The equipment used for batching and mixing can be divided into three categories via mobile concrete mixers. Commonly called concrete mixers: centralized batching and mixing plant : and mobile truck mixers which are covered under concrete transportation
9.6.2 Mobile concrete mixers
These mixer have a conical or circular rotating drum with baffle fitting inside. These are mounted on pedestals with facilities for batching of various concreting materials. There are three types of concrete mixers, viz. tilting drum mixers, non-tilting' drum mixers and reverse drum mixers. Tilting drum mixers discharge the concrete by tilting the drum. Tilting mixers are used for producing very small quantities of concrete or mortar mixes.
Non-tilting drums are suitable for requirements say up to 10 m3/b. These have a hopper fitted outlet on the top for loading and another chute-fitted outlet on the bottom for discharge. The reverse-drum mixers mix in one direction and discharge in the opposite direction.
The mobile concrete mixers vary in size from as slow as 100 liters to 400 liters or QW per cycle. The
size of the concrete mixers denotes the volume of concrete that can be mi^ in a single cycle, and usually it is expressed in cubic feet or cubic meters, or the ratio©/ the concreting materials volume to the wet concrete volume, for example 21/14 means a concrete mixer having maximum capacity to
hold dry concreting materials up to 21 cubic feet capable of producing wet concrete of 14 cubic feet. Concrete mixers are available as static units and trailer-mounted towed units.
9,6.3 Central Batching Plant
A central batching plant includes all types of equipment and materials necessary to provide input to the mixers and to deliver output to the concrete transporting system. Batching plants can be divide into two categories, viz. medium size or low profile batching plants, and large volume or high profile batching plants. Generally medium size batching plants have a rated capacity of 25 m3/h to 60 m3/ h and are used for producing concrete for building construction projects where as batching plants having higher capacity, say 120 m3/h, are employed for heavy construction or are used in the ready-mix concrete supply business.
Experience dictates that for planning purposes, the average output of the central concrete batching plants be taken as 60% to 70% of the hourly rated capacity for each working hour so as to cater for various correction factors specially idle-time on account of non-utilization period and repairs.
9.6.4 Transportation Equipment
Equipment used for transportation of concrete, from mixer to placing site, depends upon
the distance involved and the volume of concrete to be placed. Wheelbarrows, with limited capacity say 0.04 m3, and small motorized dumpers, with capacity up to 1.0 or1 are used for transporting and placing small quantities of concrete.
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 16 Concrete transit mixers are employed for transporting large quantities of concrete over long distances. These mixers have a rotating drum mixer mounted on a truck. These transit mixers transport wet concrete from the mixer to the placing site, and their rotating drums carrying capacity varies from 3 m to 9 m concrete. Concrete specifications restrict the time from loading to discharge of the concrete mixer as one hour without retarders, provided the drum is kept rotating to agitate the wet mix. For long distances, say exceeding two hour's travel time, the dry mix can be transported in specially designed truck-mixers, and the concrete is manufactured at the placing site by mixing these materials with water.
The number of truck-mixers required for transporting concrete can be worked out by evaluating the cycle-time. Consider a typical mixer cycle-time data of 6 m3 truck-mixer, given below:
Loading time for 6 m3 truck-mixer = 14 minutes Travel time of loaded truck-mixer to site = 7.5 „ Average waiting time at site = 7.5 „
Discharge time at site using concrete pump = 15 „ Travel time for return trip = 5 „
Total cycle time = 49 minutes
Therefore truck-mixers required for continuous supply
Cycle time , . (cycle time \ DISCHARGE ) + 1 (spare) =49/50 +1 = 5 No‘s
□ 9.7
CRANES FOR MATERIAL HOISTING
Cranes are predominantly used for handling including lifting, lowering and swing shifting of small to heavy loads. Cranes come in many types such as crawler-mounted mobile
cranes, self-propelled rubber-tired wheels, telescopic jib cranes, truck-mounted strut-jib cranes and tower cranes. The commonly used cranes are shown in Exhibit 9.8.
9.7.1 Mobile Cranes
In wide spread project sites, mobile cranes provide the best means for lifting and shifting
of small to heavy loads. These cranes can move over level firm surfaces as well as on rough terrains. Mobile cranes are of the following types:
1. Crawler-mounted cranes These cranes spread their dead load over larger area through their long tracks, and as such are useful while working in unprepared surfaces. The boom of these cranes comes in sections which are joined by pin connections. The straight boom thus formed can lift loads over a radius of 30 to 40 metres. In order to overcome the ground obstruction to the inclined boom, a fly-jib (say, 18 meters in length) is attached to the top of the end boom
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 17 2. Self-propelled rubber-tired wheels cranes These cranes have greater mobility
over hard surfaces and are in great demand for shifting and transporting light loads over short distances, and for off-loading of medium to heavy loads. Self-propelled
cranes can be broadly divided into three categories:
(a) Strut-jib cranes for shifting small loads at a distance, where ground obstruction restricts the utility of the crane.
(b) Cantilever-jib crane provides greater clearance under the jib for heavy and bulky loads.
(d) Telescopic-jib crane provides flexibility in adjusting distances and heights of lifts. It has greater mobility on roads than other self-propelled cranes.
9.7.2 Estimating Crane Output
The crane's capacity to handle loads from one location to another is given by: Crane output/Hour = Load/cycle x cycles/hour.
Calculation of the output and cycle time depends upon many variables, and it can best be determined by referring to machinery manuals and site trials.
It is important that manufacturers' manuals must be referred to in order to determine the tipping load at a given radius and the safe working load of the crane. Generally the safe working load varies from 67 to 75% of the theoretical crane tipping load.
For initial planning purposes, the cycle time can be computed as outlined below. However, the data indicated is for illustration purposes only:
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 18
Estimating Crane Output
The crane's capacity to handle loads from one location to another is given by:
CRANE CAPACITY: Crane output/hour = Load/cycle × cycles/hour
Calculation of the output and cycle time depends upon many variables and it can, at best, be
determined by referring to machinery manuals and site trials.
It is important that manufacturers manuals must be referred to in order to determine the tipping load
at a given radius and the safe working load of the crane. Generally, the safe working load varies
from 67 to 75% of the theoretical crane tipping load.
For initial planning purposes, the cycle time can be computed as outlined in Table However, the
data indicated is for illustration purposes only.
Crane Cycle Time Computation
S. No.
Activity (medium-sized crane)
Time
in
minutes
1.
Hooking load at ground level
1.0 minute
2.
Raising load from ground level to a height of 30 meters at 60 metres/minute
0.5 minute
3.
Slewing through 120 degrees at 60 degree/minute
0.5 minute
4.
Travelling on rails for 45 meters at 30 metres per minute
1.5 minute
5.
Moving trolley at jib level for unloading and positioning by 15 metres at 15
metres per minute
1.0 minute
6.
Unhooking load
1.0 minute
7.
Lowering load by 5 metres at 60 to 100 meters/minute, and resting at the
proper place
1.0 minute
8.
Raising hook by 5 meters (overlapping)
0.0 minute
9.
Slewing to original loading position
1.0 minute
10.
Moving trolley at jib level to loading position
0.5 minute
11.
Travelling on rails to original loading position
1.5 minutes
12.
Lowering hook
0.5 minute
Total cycle time after disregarding effect of small overlapping activities
11.0 minutes
Th
erefore, the above crane, operating with a job efficiency of 44 mins/hr and shifting a 5 ton load in each cycle, shall handle 5 ton load × cycles in one hour (of 44 minutes).= 5 × 44 min / 11 min = 20 tons/hr
It may be noted that the rated crane capacity is equal to the maximum load-lifting capacity at the minimum operating radius.
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 19
10.2 COST CONSIDERATIONS
The economic use of equipment is related to its employment cost. Hourly plant employment cost forms the basis for the cost estimation of work executed by the plant. The plant employment cost can be determined by computing plant owning and operating costs as follows:
Equipment employment cost = Owning cost + Operating cost.
There are many factors, determinate as well as indeterminate, which affect the plant owning and operating costs. Some of these factors include the state of the plant (old or new) and its capitalized cost, the source through which the capital is to be raised in case of a new purchase, the site delivered price, the implication on corporate taxes for the new purchase, the company's policy regarding capitalization, the economical plant life in years, the resale value after a useful life, the number of hours of operational employment contemplated in a year, the past performance records in the case of an old plant, the job conditions, the skill of the operator, and the repair and maintenance facilities including timely supply of spares. The main factors affecting the owning and operating costs are explained below. These are followed by a simplified approach with examples for estimating these costs. There is no substitute for experience while evaluating the plant employment costs. Therefore, the method of estimation of the hourly plant cost given in succeeding paragraphs should be taken as simplified guidelines to be modified by the experienced estimator according to the situation
10.2.1 Equipment Owning Costs
It represents the cost of ownership of the equipment. These costs are incurred by the owner whether the equipment Is used or not. The equipment owning costs include: (a) Depreciation cost.
(b) Cost of capital invested. (c) Taxes and insurance.
Depreciation cost Depreciation is the loss in market value of the plant over a period of time, resulting from usage, wear and tear or age. There are several methods of calculating the annual depreciation that should be charged to the project to cover the plant capital cost. These include the straight line method, sinking fund method, declining fund method, sum of digit method and experience of owning and operating a similar plant. Exhibit 10J2 outlines various methods of determining depreciation. Depending upon the company policy, market trends and nature of usage, an appropriate method of depreciation can be adopted.
The straight line method is most commonly used for depreciation estimation. The information required is the delivered- at -site purchase cost including attachments, the residual or resale value after use, and the equipment's usage life period. The tyre replacement cost is not included in the depreciation estimation as it is dealt under operation costs.
Annual depreciation = Delivered price – Residual value ownership period In year
Depreciation per usage hour = Annual Depression
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 20 Consider an example of a crawler tractor. Its purchase price is $100,000 and the assessed resale value after using for 5 years is 25% of the delivered price. This equipment is planned to operate 2000 hours per year.
Delivered price = $100,000.
Residual value = 25% of $100,000 = = $25,000. Annual depreciation = $ 100000-25000 / 5 = $ 15000.
Investment costs The costs cover interest on the money invested in equipment/plant, taxes of all types, insurances, licenses and storage expenses. Rates for these costs vary with owners and locations. However, these can be estimated based on the prevailing rates at the project location. Hourly Investment = Average investment x Annual interest rate
Annual usage hours = (N+1) Delivered price x I 2N x Annual usage hours where,
N = Ownership years t,,,,,,, I= Rate of interest.
10.2.2 Equipment Operating Costs
The cost of operating the equipment/plant includes fuel costs, routine maintenance costs, major repair costs, operators' costs, tyre replacement costs, and overhead costs.
Fuel costs Most of the construction plants at project sites use combustion ignition engines as the prime mover. These engines require fuel. The requirement of fuel at full load can be approximately estimated from the engine fly wheel horsepower CHP rating.
Cost of fuel consumed in one hour = Cost per litre x Hourly fuel consumption. Hourly fuel consumption = Hourly fuel consumption at full load x Operating factor.
The fuel price per litre, delivered at the site, is obtained from the local suppliers as it varies from place to place. The rate of consumption depends upon the type of engine (diesel or petrol), the state of the engine and the working conditions.
1. Petrol engine fuel consumption per hour * =0 .22 liters x rated HP x load factor 2. Diesel engine fuel consumption per hour *= 0 .15 liters x rated HP x load factor
Routine maintenance costs Maintenance costs include the cost of lubricating oil, grease, filter, batteries, minor repairs, and the labour involved in performing maintenance. The quantity of lubricating oil required for lubrication can be calculated from the manufacturer s manual showing the number of hours after which the oil changing is needed. Depending upon the operating conditions, the oil changing generally varies from 50 to 200 engine running hours. Generally, the maintenance costs including service, labour (mechanic) and minor repairs vary with the type of
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 21 equipment involved and the project environment and these can be approximately calculated as proportion of hourly fuel coat as follows. '
Operating conditions Hourly maintenance cost
Favorable 1/4 Fuel cost
Average 1/3 Fuel cost
Unfavorable 1/2 Fuel cost
Major repair costs These costs vary with the type of equipment, the condition of the plant, the prices of spare parts, the maintenance charges and the operating conditions, Generally, the cost of repairs including cost of spare parts and labour can be roughly taken as equal to the depreciation cost x repair factors. For special purpose equipment such as the rock-crushing plant, the wear and tear is more and needs detailed estimation. Similarly, for electrically operated plants such as the concrete weight-batching and mixing plant, the repair cost is less than the depreciation cost.
Repair cost = Depreciation cost x Repair factor.
Repair costs vary appreciably, with the age of the equipment. The repair cost in the first year of acquiring the new equipment is far less than say in the fifth year of its operation. An approximate year-wise repair cost can be estimated using the following relationship:
- . . . ,
Repair cost during nth year = n x Value to be depreciated
Digit sum of equipments file in years
for example, if the total value of depreciation of wheeled equipment (repair factor -0.76) works out as $75,000 and its life is 5 years; then the repair cost during each year of operation (working 2000 hours per year) can be estimated as under:
Total repair cost = Total depreciation x Repair factor = $75,000 x 0.75 = $56,250.
Tyre costs for wheeled equipment It is not easy to forecast the tyre life due to a large
number of interacting variables. In fact there is no accurate method of determining tyre life. The tyre manufactures provide indication of tyre life but these should be taken as guidelines only. The tyre life should be assessed by experienced plant engineers, m the absence of such a facility, Table 10.5 following can be used to estimate tyre life
Hourly tyre replacement cost = 1.15 x tyre price x no of tyres Tyre life in hours
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 22
10.2.3 Method of Estimation of Owning and Operating Costs
Hourly owning and operating cost of an equipment can be calculated, moving step listed:
The step-by-step approach followed is self explanatory. Exhibit 10.3
Construction Equipment Costing Hourly Owning And Operating Cost Estimate Ownership Data
Machine Nomenclature Crawler Tractor
A. Rated horsepower 250
B. Ownership period (years) 5
C. Estimated Usage (Hours/years) 2000 D. Ownership Usage (Total Hours) 10,000
(Confifa'on-SeveiB/Average/Moderate) Severe Owning Costs
E. Delivered Price 100,000
F. Tyres Original Cost Nil
G. Delivered price less tyres (E-F) 100,000
H. Residual Value at Replacement 25% 25'000
(Expressed as % of G)
I. Value to be Depreciated (G-H) ___ 75000
J. Depreciation per hour (I/D) 7.5
K. Interest Cost per hour (B+1)xE x rate 4.8 rate- 16%
2Bx D
L. Taxes & Insurance per hour (B+1)xE x rate 1.2 rate- 10
2Bx D
M. Owning Cost per hour (J + K + L) 13.5 Operating Costs
N. Pole (Consumption diesel = 0.227 liters x4.50 2.25 O. Oil, Lubricant, Filters etc. OV x Service factor) Nil P. Tyre Replacement Cost (= F/tyre life) 712
Q. Repairs <J x Repair Factor) Nil
R. Special Wears 13.87
S. Total Operating Cost per hour (Sum of N to R) T. Total Owning sad Operating Cost (M+ s) 27.37
Manpower Costs „
U. Operator Costs per hour 10
V. Helpers Cosu per hour nil
W. Total Crew Cost per hour ______
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 23
10.5 SUMMARY OF EQUIPMENT SELECTION CONSIDERATIONS
Selection of an equipment or plant system to perform an assigned task depends upon many interrelated factors. These factors, mostly covered in Chapters 9 and 10, are outlined below:
10.5.1 Task Considerations Nature of task and specifications.
Daily or hourly forecast of planned production. Quantity of work and time allowed for completion. Distribution of work at site.
Interference expected and interdependence with other operations. 10.5.2 Site Constraints
Accessibility to location. Maneuverability at site. Working space restrictions. Altitude and weather conditions. Working season and working hours.
Availability of local resources of manpower, materials and equipment. Availability of land, power supply and water supply for workshop and camp. Availability of equipment hiring, repair and maintenance faculties, locally. Availability of fuel, oil and lubricants.
10.5.3 Equipment Suitability
Type of equipment considered suitable for the task.
Make models and sizes of special purpose, and general purpose equipment that can handle the task. Production capability, serviceability condition and delivery time of each equipment t
Equipment already owned by the contractor.
Usefulness of the suitable equipment available for other and future tasks 10.5.4 Operating Reliability
Manufacturer's reputation.
Equipment components, engine-transmission, brakes, steering .operator's cabin Use of standard components.
Warranties and guarantees. Vendor's after-sale service.
Operator's acceptability, adaptability and training requirements. Structural design.
Preventive maintenance programme. Safety features.
Availability of fuel, oil and lubricants. 10.5.5 Maintainability
Ease of repair and maintenance.
Vendor's after-sale service, repairs, spares and maintenance. Availability of spare parts.
Standardization consideration. 10.5.6 Economic considerations
Owning costs. Operating costs.
Re-sale or residual value after use. Replacement costs of existing equipment. 10.5.7 Commercial Considerations
Buy second-hand or new equipment. Rent equipment.
Hire-purchase equipment. Purchase or lease.
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 24
Concreting
► Concrete is a construction material composed of cement (commonly Portland cement) as well as other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate such as gravel, limestone, or granite, plus a fine aggregate such as sand),
water, and chemical admixtures.
Major concreting equipment 1. Mixing equipment
Portable concrete mixer Batching plants 2. Transporting equipment Transit mixers Concrete dumpers 3. Delivery equipment Concrete pumps Hoist and buckets 4. Compacting equipment
Needle vibrators Surface vibrators
Concreting plant and equipment
The process of production of concrete involves batching, mixing, transportation and pumping of concrete
Batching is the process of proportioning cement, aggregates water and admixture by weight or volume prior to mixing
The equipment used for batching and mixing can be divided into three categories 1. Mobile concrete mixers
2. Centralized batching and mixing plant 3. Mobile truck mixers
1. Mobile concrete mixers
These mixers have a conical rotating drum with baffle fittings inside
These are mounted on pedestals with facilities for batching of various concreting materials There are 3 types of concrete mixers
Tilting drum mixers Non tilting drum mixers Reverse drum mixers\
Tilting drum mixers discharge the concrete by tilting the drum which is used for producing very small quantities of concrete
Non tilting drums are suitable for requirements say up to 10cum/hr.These have a hopper fitted outlet on the top for loading and another chute fitted outlet on the bottom of discharge
The reverse drum mixers mix in one direction and discharges in other directions The mobile concrete mixers will vary in size from 100 liters to 400 liters per cycle
The size of the concrete mixers denotes the volume of concrete that can be mixed in a single cycle and usually it is expressed in cum or the ratio of the concreting materials volume to the wet concrete volume.
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 25 The hourly output of a concrete mixer can be calculated by multiplying production in cum
per batch into the number of batches per hour. 2.Central batching plant
A central batching plant includes all types of equipment and materials necessary to provide input to the mixers and to deliver output to the concrete transporting system.
Batching plants are divided into 2 categories medium sized or low profile batching plant and large volume or high profile batching plant.
Medium sized batching plant have a rated capacity of 25cum/hr to 60cum/hr and used for producing building construction projects where as batching plant having higher capacity say 120cum/hr are employed for ready mix concrete business.
For planning purpose the average output of the central concrete batching plants be taken as 60 to 70% of the hourly rated capacity so as to cater for various correction factors specially idle time on account of non utilization period and repairs.
Transporting equipment
► Equipment used for transportation of concrete from mixer to placing site depends upon the distance involved and the volume of concrete to be placed.
► Wheel barrows with limited capacity 0.04cum and small motorized dumpers with capacity up to 1 cum are used for transporting small quantities of concrete
Transit mixers
Concrete transit mixers are employed for transporting large quantities of concrete over long distances.
These mixers have a rotating drum mixer mounted on a truck.
These transit mixers transport wet concrete from the mixer to the placing site and their rotating drum carrying capacity varies from 3cum to 9cum of concrete.
Concrete specifications restrict the time from loading to discharge of concrete as one hour without retarders provided the drum is kept rotating to agitate the wet mix.
For long distances say exceeding 2 hrs travel time the dry mix can be transported in specially designed truck mixers and the concrete is manufactured at the placing site by mixing these materials with water.
The number of truck mixers required for transporting concrete can be worked out by evaluating the cycle time.
Concrete transport truck
Special concrete transport trucks (in–transit mixers) are made to transport and mix concrete from a factory/plant to the construction yard.
They are charged with dry materials and water, with the mixing occurring during transport. (Although, more modern plants load the truck with 'Ready Mixed' concrete.
With this process, the material has already been mixed, and then is loaded into the truck. The ready mix truck maintains the material's liquid state, through agitation, or turning of the drum, until delivery.)
The interior of the drum on a concrete truck is fitted with a spiral blade. In one rotational direction, the concrete is pushed deeper into the drum.
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 26 This is the direction the drum is rotated while the concrete is being transported to the building
site.
This is known as "charging" the mixer. When the drum rotates in the other direction, forces the concrete out of the drum.
From there it may go onto channels to guide the viscous concrete directly to the job site. If the truck cannot get close enough to the site to use the channels, the concrete may be
discharged into a concrete pump connected to a flexible hose, or onto a conveyor belt which can be extended some distance (typically ten meters).
A pump provides the means to move the material to precise locations, multi-floor buildings, and other distance prohibitive locations.
Rear discharge" trucks require both a driver and a "man" to guide the truck and chute back and forth to place concrete in the manner suitable to the contractor.
Newer "front discharge" trucks have controls inside the cab of the truck to allow the driver to move the chute in all directions.
Concrete mixers generally do not travel far from their plant, as many contractors require that the concrete be in place within 90 minutes after loading.
If the truck breaks down or for some other reason the concrete hardens in the truck, workers need to enter the barrel with jackhammers; dynamite is still occasionally used to break up hardened concrete in the barrel under certain circumstances.
Six-axle Advance Ready Mix truck Volumetric Concrete Mixer Front discharge truck
A rear–discharge concrete transport truck Off road mixer truck
Ready mixed concrete
Ready mixed concrete can be ordered in several ways
Recipe batch – The purchaser specifies the responsibility for the proportioning of the concrete mixture
Performance batch - The purchaser specifies the requirements for the strength of concrete. Part performance and part recipe – The purchaser specifies minimum cement the required
admixtures, and the strength requirements, allowing the producer to proportion the concrete mixture within the constraints.
Ready mixed concrete is supplied to sites in specially designed truck mixes which is basically a mobile mixing drum mounted on a lorry chasis.
Truck mixes can be employed in one of three ways
1. Loaded at the depot with dry batched materials plus the correct quantity of water, the truck mixer is used to complete the mixing process in the depot before leaving the site. During transportation the mix is kept agitated by the revolving drum.
2. Fully or partially mixed concrete is loaded into the truck mixer at the depot. During transportation the mix is agitated by the drum revolving in 1 to 2 revolutions per minute. On arrival the mix is finally mixed by increasing the drum revolution to between 10 and 15 revolutions per minute.
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 27 3. When the time taken to deliver the mix to the site may be unacceptable the mixing can take place on the site by loading the truck mixer at the depot with dry batched materials and adding the water upon arrival on site.
To obtain maximum advantage from the facilities ,the supply instruction should contain the following
Type of cement
Types and minimum size of aggregates Test and strength requirements
Testing methods
Slump or workability requirements Volume of each separate mix specified Delivery programme
Placing of concrete
Once the concrete arrive at the site ,it must be moved to its final position without segregation and before it has achieved its initial set
Methods include Buckets
Motor propelled buggies Chutes Belt conveyers Concrete pumps Concrete bucket Conveyer belt Pumping concrete
Concrete Batch Mixing Plant with Transit Mixer
Concrete Batch Mixing Plant: Weigh Batcher
C.C. Mixer
Handling & Transporting Equipment: Bucket Handled By Crane
Concrete Pump Lift Dumper
Ker Laying Machine Concrete Paver Canal Laying Pavers: Pin / Poker Vibrator Surface / Plate Vibrator
S.R.P* 5TH TERM- CONSTRUCTION EQUIPMENT MANAGEMENT Page 28
Buckets
Permit concrete placement at the lowest practical slump
Gates should be designed so that they can be opened and closed at any time during the discharge of concrete.
Segregation must be avoided Buggies
Hand buggies and wheel barrows are capable of carrying 4 to 9 cft of concrete. Recommended for distance less than 200ft
Channels
Transfer concrete from a higher elevation to a lower elevation
They should have a round bottom and the slope should be steep enough for the concrete to flow continously.
Belt conveyers
1.Portable or self containers 2.Feeders or series conveyers
Side discharge or spreader conveyer
All types must have proper belt size and speed to achieve the desired rate of transportation Concrete pumps
The pump must be fed with concrete of uniform workability and consistency Pumps can be mounted on trucks and trailers.
The truck mounted pump and boom combination is efficient and cost effective The following rules must be followed
1. Min pipe dia 5 inch
2. Always lubricate the line with cement paste 3. Ensure a steady uniform supply of concrete 4. Always presoak the aggregates before mixing 5. Avoid the use of reducers in the conduit line
6. Never use aluminum lines. Aluminum and Portland cement react ,librating hydrogen gas that can cause rupture of concrete
Generally small diameter pipes of 75 and 100mm are used for vertical pumping whereas large diameter up to 150mm are used for horizontal pumping
The time required on site to set up a pump is approximately 30 to 45 min.
The output of the concrete pump will be affected by the distance the concrete is to be pumped.
Therefore the pump should be positioned so that it is too close to the discharge point as it is practicable.
Pours should be planned so that they progress backwards towards the pump removing the redundant pipe lengths as the work proceeds.
As compared to the conventional placing of concrete where the output is 15 to 20cum/hr.These typical output of the pumps are 60 to 100cum/hr but certain amount of skill and experience is required