Types of Machinery and Equipment for Road (Pavement) Construction

Uses of Road Machinery

For constructing (paving) major roads of large magnitude, plants, and machinery of various types will be required. The world cruise and slow methods of highway construction and maintenance are been replaced rapidly by the use of modern sophisticated machinery so as to grant the flowing advantages.

• The cost of highway maintenance is reduced
• The time of highway construction is considerably reduced.
• The ensure better and standardise quality of work.
• The useful life of a structure is increased to a great extent.

The highway construction in modern days has received considerable attention and depending upon the several factors affecting the choice of highway making (paver) machinery, suitable plant and equipment for a particular project will have to be recommended.

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Here we briefly discuss the common types of highway making machineries (road construction machines) i.e. road paver required for various operations involved in highway construction.

Road Excavating equipment

The process of cutting or loosing and removing earth from its original position, transport and improve it as a fill or spoil bank is known as excavation. For any type of soil such as soil, soft rock or even hard rock before preparing the subgrade excavation is needed. The reservation will also be required for the construction of side drains. Choice of suitable equipment will only depend on the nature of soil to be excavated.

These are intermittent types of equipments. Tractors, power shovels, draglines, Clam shells, bulldozer, angle dozer, scrapers, back hoes, dredger, ripper, motor grader, etc are the earth excavating equipments.

Tractor:

This equipment is a self propelled machine which is used mainly to exert a powerful attractive force for pulling other machines. When the tractor is not required for hauling other machines, it can be easily converted to serve as bulldozer, angle dozer, etc.  The tractors are used to for agricultural operations such as hoeing, tilling, harvesting, etc. When tractors are equipped with shovels, they can even be used for the mining operations.

Tractor may be crawler mounted or wheel mounted. In the farmer type the tractor is supported on endless chain of plates and it is used for rough and uneven ground. In the latter type tractor is supported on wheels and it is use the bulldozers are classified as follow for or even ground .

Bulldozer and angle dozers:

PURPOSE OF BULLDOZER

BULLDOZER IS VERY USEFUL EQUIPMENT AND IT CAN BE  USED ON THE THE CONSTRUCTION WORK FOR THE  FOLLOWING PURPOSES:

• To clear the site of work,
• To make the land level,
• To prepare for pilot roads through mountains and hard ground and,
• To excavate material and howl for distance of about 100 metres.

classification of  bulldozer

The bulldozer are classified as follows:

• Bulldozer maybe cable controlled or hydraulic controlled.
• Depending upon the mountings bulldozer maybe a crawler tractor mountain bulldozer or wheel tractors mounted bulldozer. The latter can attain higher travel speed on the job and can be moved on paper floors without causing damage to the Floors.
• Depending on the nature of the blade the bulldozer may be a front casting dozer or angle dozer. In the former case, the blade is fixed perpendicular to the direction of travel. The front casting 2000 I will move the earth in the forward direction. The angle 2000 will push the earth on one side in the forward direction.

Bulldozer may be provided with blades of such arrangement that it can be converted into either of the two types.

  Size and output of a bulldozer:

The size of a bulldozer indicated by the dimensions of the blade and its output depends upon the conditions under which it operates. Each blade has a Provided capacity of hauling a particular type of earth and knowing the number of turns a bulldozer will do in a given time, the approximate output of a bulldozer can be estimated. In general, it can be stated that the output of all the earthmoving machinery will depend on the following factors:

(a) efficiency of the operator,

(b) nature of soil,

(c) topography of the area,

(d) type of equipment, and

(e) weather

(iv) Utility of a bulldozer:    

 By suitable attachments to the bulldozer, it is often utilized to get rid of trees, rocks, boulders, etc. so as to extend the output, two bulldozers working side by side with their blades in touch, are often used. A bulldozer is often used on wet ground and altogether conditions of weather.

Grader:

it is self-propelled or towed by a tractor. It consists of a 3 to 4 m long angled blade supported on a framework mounted on wheels, The self-propelled grader is understood as a motor grader and a grader which is towed by a tractor is understood as elevating grader.

The various attachments of the grader are: the blade, bulldozer, snow plough, the scarifier, elevator attachment and rollers. For grading the machine moves forward and steering is controlled by the wheel. It performs various operations like grading, spreading, side cutting, road crowning, bank dressing and mixing of materials.

Scraper:

This equipment consists of a large bucket called the scraper and it is attached to a tractor. Its capacity varies rom 3 m3 to 9 m3, The scraper has a cutting edge or blade at the tom and it is possible to dig earth to a depth of about 250 mm.

During its forward movement, the blade cuts the ground and he loosened earth is collected in the body of scraper. When the paper is fully loaded, it is raised above ground and taken to the of dumping, The earth from the scraper is then taken out by hing the bottom of it and the earth is laid in layer of required mickness, The scraper thus combines three operations, namely, those of digging, conveying and dumping.

Scrapers are usually mounted on two or four pneumatic tyred wheels. An apron is provided ahead of the container which opens and closes so as to manage the flow of earth in and out of the container. Scrapers are capable of manufacturing a really smooth and accurate formation level. Below are the list of  the basic three types of scrapers available:

(i) Crawler-drawn scraper

(ii) Two-axle scraper

(iii) Three-axle scraper.

• Crawler-drawn scraper:

The crawler-drawn scraper consists of a four-wheeled scraper bowl towed behind a crawler power unit. Capacities of a scraper bowl range from 3 m3 to 50 m3. The speed of operation is governed by the speed of towing which is 8 km/h when hauling, and 3 km/h, when scraping. This type of scraper is used on small hauls of up to 300 m.

• Two axle scraper:    

Two-axle scraper is more maneuverable, offers less rolling resistance and has better traction, as the engine is mounted closer to the driving wheels.

• Three axle scraper:

Three-axle scraper is able to use its top speed more frequently and is easier to control.

Excavators:

Excavator is the most used oldest type of machine used for the movement of the earth for road paver by doing its work of moving the earth while the main unit is stationary. Little effort is required to move the dead weight of the earth in a vertical plane. The lateral motion is in the horizontal plane and the effort required is primarily limited to acceleration and deceleration of the bucket in the plane. The range of an excavator is limited to the reach of the boom carrying the dead weight. The excavators may be mounted on crawlers, wheels or trucks and they may be provided with buckets of suitable sizes and capacities.

The excavators in common use are of the following five types:

• Back trench hoe excavators
  • Clamshell excavators
  •  Power shovel excavators
•  Dragline excavators
• Skimmer excavators.

Each of the above type of excavator will now be briefly described.

Back trench hoe excavators (Backactor):

This type of excavator is used for digging the foundation trenches below the normal surface  level at working time. This is also useful tool for the excavation of smaller areas such as basements, footings and trenches. The material caught is suitably discharged. The boom of the hoe is not interchangeable with the other attachments. The hoe is an instrument for scraping or digging and loosening the earth. Fig. 1 shows the back trench excavator. It is useful under the following conditions:

(a) The bottom and sides require trimming closely. (b) The excavation is to be done infirm to hard ground. (c) The material is to be deposited at a fairly close range.

Clamshell excavators:

This type of excavator is used for digging below, at or above operating level in a vertical range.

The material removed is suitably dumped. The material to be handled should be relatively loose or soft up to medium-hard. The clamshell excavators are widely used for rehandling of fabric and for working in limited space as just in case of foundation trenches for pipelines, etc. it’s also used for jobs that require fairly accurate dumping and disposal of materials.

It consists of a bucket of two halves, which are hinged together at the top. The bucket halves are often attached to the shovel crane or to the boom of the dragline. The bucket is allowed to succeed in on the highest of the loose material to be dug As the bucket is lifted, the 2 halves close entrapping the fabric into the bucket. Refer fig. 2 

• Power shovel excavator:  

This type of excavator is made with a shovel at its lower end. The shovel is provided with a sharp cutting edge. This type of excavator is used to dig at or above the operating level. It can handle loose rock and the material caught in the shovel may be suitably disposed off. The boom of the shovel excavators is not interchangeable with other attachments. It is suitable for a firm and hard grounds and at places where sufficiently wide areas are available for the working space of the shovel and for the hauling equipment to gain access to the shovel.

It consists of six basic parts: Boom, cabin, dipper with stick, hoist line, mounting and power system and controls as shown in fig. 3.

There are two types of power shovel:

• Crawler mounted:

It is mounted on crawler and it posses low travel speed. It can be operated on soft ground only

• Wheel mounted:

It may be self-propelled or truck mounted. It possesses high speed and is suitable for hard ground.

The power shovel is first moved to the required position within the reach of the earth face to be excavated. Then the dipper is lowered to the bottom of the pit, with teeth pointing into the face.

Now, force is applied through the dipper stick and at the same time tension is applied to the hoisting line to pull the dipper up the face of the pit. Then the whole revolving unit with front attachment is revolved to dump the excavated materials into truck. Again the unit is brought back by swinging to the face of excavation operation.

The size of the power shovel is indicated by the size of the dipper in cubic metres. It is available in size like 3/8, ½, %, 1, 1 4, 1 %, 2 and 2 2 cubic meter. The output depends upon the types of materials to be excavated, depth of cut, angle of swing, site condition, size of hauling units, skill of the operator and physical conditions of the shovel. The output is measured in cubic meter per hour.

Output of power shovel =  (Volume of excavated material) / (TXN)

where,

T = Time in Hour,  to complete one cycle of excavation

N = Number of such cycles in one hour.

Following conditions must be satisfied by power shovel while being operated.

(a) There should be large open pit.

(b) The floor must be well drained. (c) Haul road must not be affected by climatic condition.

(d) The trucks must be standing on both the sides of power shovel.

(e) Angle of swing should be 900

Required boom angle must be maintained for specific soils. (g) The depth of cut in an operation must be optimum, i.e., the dipper should be completely filled up when it reaches the face. If the dipper is partially filled then the depth of cut is less and it will result in lesser output. If the dipper is overfilled then depth is more than optimum and it will result in excessive strain on the machine. Hence, the dipper should strike the face at optimum depth for given soil to have a maximum output of power shovel.

Dragline excavators:  

This type of excavator is used for excavation and digging for both at below the operating level. Fig. 4 shows the basic parts of a dragline excavator. The various types of dragline excavators are available and the factors affecting the output of a dragline excavator are:

(a) size and type of bucket,

(b) depth of cutting,

(c) length of boom,

(d) angle of swing

(e) material to be cut or handled,

(f)  conditions under which work is to be carried out,

(g) skill of the operator,

(h) method adopted for removal of material, and (i) physical conditions of the machine.

It is useful under the following conditions:

(i) The bottom conditions are wet i.e. dredging in river beds and clearing of ditches.

(ii) The digging is to be done well below the ground level. The dragline bucket is better filled by jerking means it is done by intermittent pulling

(iii) The ground to be excavated is soft or medium hard. The thickness of the soil layer caught and removed by the bucket depends on the density of the soil.

(iv) The stuff is to be dumped as far from the unit as possible.

There are three types of dragline excavators. (a) Crawler mounted: It has a low travel speed and is suitable for soft ground and for large projects.

(b) Wheel mounted: It has a high travel speed and suitable for firm ground and for scattered jobs.

(c) Truck mounted: It has a high travel speed and suitable for firm ground and scattered jobs.

The output of the dragline is only 75% to 80 % of that of a shovel of the same capacity. The output of the dragline is measured in cubic metre per hour. The factors affecting the output of power shovel holds true for dragline also. But over and above those factors, size and type of bucket and length of the crane also play an important role in output of dragline. The type and size of the bucket and length of the boom crane should be ma ched properly with a dragline to get the best effecting and maximum output.

The dragline is operated as follows:

(i) The empty bucket is thrown out on the top of the earth to be excavated by releasing the drag cable and hoist cable.

(ii) The bucket is pulled towards the base of machine for excavation. (iii) The hoist line is taken in and the drag cable is played out.

(iv) The loaded bucket is hoisted, swung and dumped. It is so arranged that unless desired by the operator, the contents of the bucket will not be released.

(v) The cycle is repeated.

Following are the advantages of a dragline over a power shovel. (a) A dragline can work on a natural ground while a power shovel will have to be taken into the pit or trench.

(b) Hauling units like trucks or tractors do not have to go into trench or pit while using dragline.

(c) The excavated material can be disposed off in one operation. 

Skimmer excavators:

This type of excavator carries the skimmer at its lower end as shown in fig. 5. It is used for surface excavation and leveling and it cuts the surface of the earth to a depth of about 200 mm to 300 mm. The skimmer excavator can also be used for loading the loose excavated material.

(6) Dredgers:

In order to provide the necessary depth of water near the ports, is becomes essential to do the process of dredging which is a typical type of  form of excavation. The various types of dredgers are employed for this purpose. For the construction of marine works below are the dredgers used:

(i) Bucket-ladder dredgers (iii) Grab dredgers

(ii) Dipper dredgers (iv) Hydraulic dredgers.

(i) Bucket-ladder dredgers:

A bucket-ladder dredger consists of an endless chain of buckets mounted on a ladder as shown in fig. 6. The buckets are provided with a suitable cutting edge to do the digging operation. The material brought up by the buckets is either dropped directly into the hoppers provided on the vessel or conveyed to the barges standing towards the vessel. The bucket-ladder dredger has the capacity to lift large quantities of heavy fluid in a short time and to form a level bottom.

(ii)Dipper dredgers:

A dipper dredger consists of a pontoon carrying a frame in which a revolving boom is fixed as shown

The dipper stick connects the bucket and boom. The bucket is arranged by releasing and pulling the hoist cable. The dipper dredger is ideal for working in heavy grounds. It can excavate boulders and stiff clay. It can also lift any obstruction that is not beyond its power, provided it gets a hold of the obstruction. The dipper dredger does not require anchor mooring and hence, it does not obstruct traffic during its working. It can also be used as a rock breaker.

(iii) Grab dredgers: A grab dredger essentially consists of a grab suspended from a cable. A grab is in the shape of a scooper looks like a quadrant of a circle as shown in fig. 8.

The grab is open in its normal position. On being attached to the bottom, the grab digs into the mud and by suitable arrangement, the grab is closed. The material thus caught in the grab is lifted up and suitably disposed off. The grabs arranged to operated from cranes and there may be more than one grab on the dredger. This type of dredger is useful for dredging materials like sand, clay, mud, etc.

(iii) Hydraulic dredgers:

A hydraulic dredger essentially consists of a sand pump that excavates and transports the bed material in one operation. The suction pipe is provided at the heart with a cutter for hard material. this sort of dredger is additionally referred to as the suction dredger. A hydraulic dredger is unsuitable for the open sea where the height of sea-waves exceeds 1200 mm. In such cases, the suction pipe is likely to be damaged. This type of dredger has proved very successful and economical in dredging sand and light silt. The modern suction dredgers with a suitable cutter at the bottom can be used for dredging soft rock.

(7) Ripper or rooter or scarifier:

This is an equipment which is sometimes attached to a tractor. It is mounted on the wheels and carries two to four teeth, the standard number being three. The ripper is employed to interrupt up the bottom and to tug up the roots. This loosened material can then be removed by the scraper.

With the aid of ripper, the scraper can be used for stiff clay, soft rock and such other material as can be ploughed. The rippers are drawn by tractor and that they function auxiliary instruments or appliances for dozers and scrapers. When rippers are used, there’s considerable increase within the output of labor and that they also reduce the strain and decline tractors.

The cost of fuel is also reduced, when rippers are adopted. Depending upon the nature of soil, size of the tractor and number of twines or twisted cords, the depth of rooting varies from 300 mm to 750 mm.

(8) Trencher or ditcher: To excavate the trenches of width from 250 mm to 450 mm and depth upto 4 m with accuracy and speed, this type of equipment is used. It is mainly used to excavate trenches for mains, gas lines, oil pipelines, telephone cables, drainage lines, sewers, etc. These machines are generally crawler mounted. That may also be wheel type or ladder type.

Wheel type trencher can dig a trench pre 2.5 m depth and Ó mm to 1500 mm in width, The excavator parts of the chine include power driven wheel with cutting teeth to which Venable buckets are attached.

Ladder type trencher can dig a trench upto 10 m in depth and 4 m in width. It consists of two endless chains which travel along the boom, to which teethed cutter buckets are attached By setalling shaft-mounted side cutter on each side of the boom, the width of the trench can be increased.

Thus, in a trencher, a series of small cutting buckets attached to two endless chains which are supported by a boom, which is lowered into the ground upto the required depth. A single machine can be used for digging trenches of various sizes by varying the lengths of the boom. Some trenchers have an angle mould blade, which helps to carry out the back-filling operation

ROAD COMPACTING EQUIPMENTS

The compaction of soil in the field is to be achieved by the use of some road construction equipment, the most common being road rollers. For compacting relatively small areas and at places where the rollers cannot be operated such as foundation trenches, slopes. etc., the use of rammers is made.

For compacting dry cohesionless granular material, the vibrators are employed and on being vibrated, the smaller particles get into the voids larger particles and form a dense mass. For this purpose, separate engines are mounted on the rollers to produce vibrations from 1000 to 5000 per minute. For getting maximum effect, the actual number of vibrations should correspond to the natural resonant frequency of the soil.

 Followings are the type of Compacting equipment for road :

• Road rollers,

• Rubber-tyred or pneumatic rollers,

•  Sheep’s foot rollers,

• Smooth wheeled rollers

• Vibratory Compactors
• Earth Rammers
• Jetting and pounding

Road rollers:

The principle on which a road roller is working is the application of pressure which is slowly increased and is then gradually decreased. Following are the three types of Vot rollers that are in common use:

•  Rubber-tyred or pneumatic rollers:

A pneumatic roller consists of a flat platform below which number of smooth rubber-tyred wheels are mounted on two or more axles. The platform is then loaded with sand bags or some other weight and the roller is moved by tractor.

The rubber-tyred rollers are found to be very efficient in the compaction of earth subgrades, granular soils in base course, final operations for bituminous surface dressings, etc.These rollers provide a slight kneading action with the direct pressure due to rolling.

(iii) Sheep’s foot rollers:

These are also known as tamping rollers. This type of roller consists of hollow steel cylinder or cylinders, each about 1.20 m long and 1.20 m in diameter with 180 mm to 230 mm projections extending out from the curved surface of the cylinder. These projections are made of steel and they resemble sheep’s feet and are arranged in rows round the cylinders, the projections in successive rows being staggered. The weight of the roller can be increased by filling the drum with water or wet soil. The weight, diameter and width of roller may be varied and so also the shape and size of the feet can also be varied.

The roller is made in sections that can be connected together one behind another or in series and the unit is then pulled by tractor. As the roller is pulled forward over a layer of loose material, the projections penetrate the layer and compact the soil from top to bottom by kneading it. After a few rollings, the layer becomes more and more compact and the projections penetrate less and less in the rolled material. The roller is continued over the surface till the feet do not penetrate the soil.

The sheep’s foot rollers are considered most suitable for compacting clayey soil or soil containing mixture of sand and clay. In the modified form, the projections are replaced by segments or pads or grids and such modified form of sheep’s foot roller can be used satisfactorily for compacting granular material also.

(iv) Smooth wheeled rollers:

 A smooth wheeled roller is a multi-purpose road machinery (roller ) which is used for various purposes and for practically all types of roads . These rollers are suitable for compaction of  more ranges of soils, preferably granular soils and pavement  different layers materials. These rollers are particularly helpful in compacting soils and other materials where a crushing action is advantageous.

The smooth wheeled roller consists of one, two or three smooth wheels. The single wheel roller has diameter of about 900 mm and length of about 1.20 m to 1.50 m.

It is driven by hand or animal The weight of such roller is about 2 1 and effective compaction is not achieved by such roller.  The smooth-wheeled rollers with two or three wheels are power-driven. The front wheel is known as the steering wheel and the rear wheels are known as driving wheels. The roller with two wheels is known as a Tandem roller and its weight is about 6 t to B 1. The roller with three wheels is known as a three-wheeled roller and its weight is about 10 t to 15 t. The performance of a three-wheeled roller is better as compared to a two-wheel unit because of the concentration of pressure on the middle wheel when the roller passes over high spots in the surface that is being compacted.

• Vibratory compactors:

It consists of a vibrating unit provided on a screed, plate or roller. The vibrating unit may be the out-of-balance weight type or a pulsating hydraulic type. This type of compactors is the most suitable for coarse-grained soils.

• Earth rammers:

The earth rammers may be static or vibrating. The static earth rammers compact soil near to the surface only. Hence, the vibrating earth rammers are generally used to achieve better compaction of soil. The vibration also suitble to adopt small and light equipment and to lay soil in thick layers.

The earth rammers may be operated by fuel like petrol or diesel engines. These rammers can be designed to impart vertical blows in sequence with forwarding movement at the same time. Usually, 2000 blows are imparted per minute which may give an impact force of about 10 kN to 30 kN. The horizontal movement is about 300 mm per second. Depending upon soil conditions, the compaction depth of 450 mm to 500 mm may be achieved and an area of about 10 m2 per minute may be compacted by such rammers.

• Jetting and pounding:

This technique is best suited for the compaction of cohesion less soil.

You can read here: Equipment used for Bituminous Road construction

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