ABC Laying Road Construction

Motor Grader Operation for Road Finish Level

There are a number of methods to control the final finish of a  road surface  by using motor grader. No matter which method issued the motor grader will set the Moldboard to the trimming tilt and at 45°. With this tilt the cutting edge is almost vertical to the road surface and only scrapes the surface. It is also advisable to use new cutting edges or reasonably flat surfaced edges. By lightly moving over the surface the material is trimmed from the high sections and deposited into the lower sections. The  motor grader  should start at one edge and move to the other side of the road using several passes. A roller should follow the motor grader to compact the surface and care should be taken not to let the surface become dry.

Methods of Control.

Straight edges.

If the final road surface level is not required to be accurate but the finish surface is to be smooth, as in maintenance work, then this straight edges method is suitable.A profile board can be constructed for this purpose. This board is constructed to have a 3 percent difference from one end to another and is generally about 2 meters in length. The board is used with a spirit level to find the cross fall and without a spirit level to see any variations in flatness along the length off the road. This board can be easily carried in a Site Engineer’s vehicle for spot-checking.

String Line.

This method is acceptable for most classes of roads and has the advantage of being very quick when working with the motor grader. It however requires a surveyor or technician to do the initial setting out. Once the setting out has been done it should not have to be done again other than to replace damaged pegs. Two wooden pegs of say 1 to 1.5 meters are securely placed outside the shoulder edge on both sides of the road. A nail is then driven into the side of each peg at reduced level that has been calculated to give a height 300mm above and parallel to the designed finish road surface. A string line is strung between the upper and lower nails, for straights and between the two nails for curves. The Site Engineer/Site Supervisor then reads a tape measure vertically down from the string line and informs the  motor grader operator  as to the depths of cut or fill required.


Box Pegs.

This is a very accurate method of control but is very time consuming. So it is not used extensively any more. After the material has been placed and compacted, the surveyor or technician hammers small wooden pegs into the surface at the correct reduced level. The  motor grader operator  then trims to the tops of the pegs. This method requires a laborer to clean the top of the peg after every pass of the motor grader in order that the operator can see the peg. Pegs can also be knocked out and have to be replaced. As the material is already compacted the pegs are very difficult to hammer in to place.


High Tech

This is only used in highly specialized areas such as Freeways leveling and not in general use. This method would include Laser leveling etc. The manufacturer’s methods would have to be followed and the Motor Grader fitted with the special controls.

ABC Laying Road Construction

Optimum water of Material by using motor grader

 In order manage optimum water of road pavement, we have to add some water or have to dry the material to achieve optimum water of material by using motor grader 

Adding Water.

The above method of moving a windrow from one side to another can be used to add water to a premixed or single type material. As each layer is exposed the water tanker will place water on
until the mixed material is to the required water content.

Dry over wet material.

If the material is worked in the layers from side to side the wind and the sun will dry the surface of the layer. Over one day quite an amount of water can be removed.

A simple test for optimum water content.

1. Take a handful of the mixed material and squeeze hard in the palm of the hand.
2. Using both hands gently break the roll of material in half.
3. If the material falls apart then it is too dry.
If it is muddy on the hands and sticky it is too wet.
If it breaks clean with no ‘crumbs’ then the material is close to optimum.


Spreading Materials and Shaping of Surface.

1. The surveyors should place the pavement edge pegs on both sides of the formation. The windrow to be spread should be placed just to the centre of the edge of pavement peg on one side.

2. The mouldboard is set to the approx height (thickness) of the layer required with the tilt being in the general position and angle of 45°. A sufficient cut is made into the windrow for the material to flow along the mouldboard and form the layer at the required depth.

3. Using this as a base more material is cut and moved across this surface to spill over the edge and extend the base. On wide  roads  this may take a few passes to get all the material to the far edge and spread.

4. After the far edge pegs have been reached the surface is lightly motor graded to the other side to bring the material to edge pegs.

Mouldboard and the wheels of the motor grader.

Only when the final shape of the finish surface has been approximated should a roller be used. Rolling should start from the outside and move towards the centre, and on curves should start at the inside and move to the outside of the curve.

If ‘Box’ type construction is not being used then the roller should leave the edge 150mm until the rest of the pavement has become firm enough to support the roller.

Motor Grader Road Construction

Techniques on Using a Motor Grader.

There can be variations on the exact techniques of motor grader that are described here, but generally similar type methods will be used with only operator preferences and site conditions changing.

Mixing Materials and Adding Water by using motor grader.

Some times two types of material may have to be blended in order to get the specified base or sub-base material. For example, Natural hillside gravel may have a high clay content, which can be reduced with the addition of sand.

A method of combining these two materials is as follows;

1. Stockpile the gravel material along the road at the correct rate. Use the motor grader to level out this material into a pad just wide enough to drive the tipping trucks on. The blade can be set at the general tilt and say 30° and the motor grader drives over the stockpiles flattening and shaping them. If a square blade is used then there is no control over the material flow and segregation of the material can occur.

2. Place sand on the previous layer using the same technique as above.

3. In order to give the motor Grader as much room to work, no pavement edge pegs are placed until the material has been completely mixed.

With the mouldboard being set at the mixing tilt and placed at approx 45° and raised on the side away from the windrow, a cut is taken from the side so that both layers are cut. The material as it
moves along the blade is rolled by the shape of the mouldboard and so mixed.

If water is to be added then it is placed on the new pad that has been formed using a Water Bowser with spraybar fitted. This is repeated on each layer.

This is repeated with new layer being placed on the top of the previous using the above method. When all the material has been moved they the motor grader will then form a new windrow on the other side of the roadway.

4. Using the above techniques of motor grader , the material is moved to the opposite side of the roadway. This is repeated, moving the material from side to side, for 4 to 6 times by which time the material should be thoroughly blended and the correct percentage of water has been added. The operator will then tell the surveyors to place edge pegs on one side of the road formation and place the windrow approx 100 to 200 mm from these pegs.

Motor Grader Road Construction

Maintenance of motor grader – 1


A Motor grader is a high performance machine and should be treated as such. The manufacturer’s guide to maintenance of motor grader should be followed using only the approved lubricants and service schedules. If incorrect or substandard servicing is done then the life of the machine will be shortened and the running costs increased.


The rubber tyres of a motor grader are expensive, so every care should be used to stop undue damage.

  •  Direction of rotation.

Care must be taken in fitting of tyres of motor grader to follow the manufacture’s instructions. If a drive tyre is not installed to the correct direction of rotation then the ‘lugs’ will quickly be damaged.

RULE: Looking down on the rear drive tyres the drive lugs will form a ‘V’ pointing to the front. The front wheels will form the ‘V’ facing the rear.

  •  Size of tyres.

As the driving tyres of motor grader are all rotating at exactly the same speed of rotation, if tyres of different diameters are used (Old with New) then the larger diameter tyres wear quickly to become the same size as the old tyres.

  •  Wheel slip.

Wheel slip of motor grader causes excessive wear and cutting. The motor grader operator with experience and training should know the correct amount of material to move.

Maintenace of motor grader’s cutting edge .

It is essential that the cutting edges be replaced or turned when they reach the limit of wear. This is about 2 cm from the mouldboard. A cutting edge of motor grader is double edged so when one edge wears out it can be turned to use the new edge. If this is not done then damage to the mouldboard could be such that a new backing surface has to be welded on to the mouldboard causing down time and losses.

There are may be additional maintenance of motor grader which can be arise when it is working during the night.

Motor Grader Road Construction

Mouldboard of motor grader

Blade Tilt of motor grader.

The tilt or vertical angle of the mouldboard of motor grader  is variable. It can be tilted from an almost vertical position to an angle of approx 10 to 20 degrees.
The Three basic positions are:

  •  Mixing or Cutting.

The mouldboard is tilted back close to the extent of full tilt. The cutting edge of motor grader will be at an angle such that material can easily be cut and drawn onto the blade. Because of the curved shape of the mouldboard the material will rise to the top of the blade then fall back to the bottom, thus mixing the material.

The mouldboard of  motor grader  is tilted near to the extreme of forward tilt causing the cutting edge to be nearly vertical. The edge will not cut in this position but only slid over the surface. This can be used to take very small amounts of material from the surface.

  • General.

The mouldboard of  motor grader  is placed near the centre of tilt angle. This is a compromise position and is handy for ordinary work. This position should not be used for specialised cases as above.

Motor Grader Road Construction

How to maintain Motor Grader – 3

Front Wheel Lean of Motor Grader.

If a motor grader is working and the mouldboard either takes too much material or strike an immovable object the motor grader will slip sideways at the front to the direction of cut. To overcome this a motor grader has been fitted with ‘Wheel Lean of motor grader’. The front wheels should lean to the side of the flow of material, or that is away from the cutting side.

Articulation of the Frame.

Most modern motor graders have ‘Articulated Frames’. The main reasons for articulation is;

This extra reach can be used to keep the driving wheels of motor grader on firm ground while the front wheels and the end of the mouldboard could be on unstable or steep ground.

  • Small Radius Turning.

This extra sharp turning is used in construction of small radius curves such as found in  rural roads  or cul-de-sac The operator can also use this to turn the motor grader about in a small area.

WARNING! When turning with the motor grader articulation, care must be taken to avoid the corner of the blade coming into contact with the rear tyres.

Motor Grader Road Construction

Motor Grader – Windrows

Material that is stockpiled in a continuous row is called a windrow. Motor Graders work with windrows, either moving them from side to side or spreading material from them. The new windrow that is formed from the material coming off the mouldboard should fall between the wheels of the motor grader or sometimes past the wheels of the motor grader. The motor grader should never run on the new windrow, as that will compact the windrow.

CAUTION: A motor grader tends to move the material in the direction of travel. It is recommended that the direction of working be reversed periodically to bring the material back to the original positions.



Motor Grader Road Construction

Effective Usage of Motor Grader

An idle motor grader is costing money. A small time spent in producing a program for the working of a motor grader will save much expense. For example in laying of Overlay material a small program would be as follows.

  •  Motor Grader  scarifies and shapes 1st and 2nd sections for overlay.
  • Motor Grader cleans drains and does shoulder work while material is placed on the scarified 1st section.
  •  Motor Grader  scarifies 3rd section then spreads and trims 1st section while material is placed on 2nd section.

This process would be repeated with maybe minor changes due to unexpected conditions.

Tipping of Material

The motor grader should not be waiting for the material to be delivered to site. One method is to have the trucks tip the material at pre-marked positions.


The 4.5 metre wide road requires 150 mm of overlay. The Trucks/Trailers have a capacity of 3m3. The  compaction factor  of the material is assumed to be 25%. To find the length that each load has to be placed in the following calculations can be done.

1   Find out how much material is required for every 1 metre in length of the road.

Cross-section is 4m x 0.15m = 0.6m2
Therefore for every 1 metre in length 0.4 x 1 = 0.6m3
Using the compaction factor to find additional material. 0.6m3 x 1.25 = 0.84m3.
To find the length of each load, divide the load by the  material  required for one lineal metre. 3.0 ÷ 0.84 = 3.6m

2   Place two rocks one on top of the other at every 3.6 lineal metres and then the trucks can tip between each section of rocks.

3   The Motor Grader may have to come back to the tipping site periodically to move the tipped material into a windrow to allow a free lane for the traffic.

The above method requires only one laborer to help the trucks after the supervisor has marked out the positions.

Motor Grader Road Construction

What are the uses of Motor Grader?

Uses of motor grader can be classified to followings. 

  •     Mix two or more materials to form base or sub-base materials.
  •     Mix the water into a material ready for compaction.
  •     Dry material  with to much water content.
  •     Spread the material to the required depth.
  •     Shape the cross-fall of the road surface.
  •     Level or trim the finish of a road surface to better than ± 5mm.
  •     Trim and grade shoulders.
  •     Cut or clean side drains.
  •     Scarify existing surfaces (Scarifying attachment fitted).
  •     Trim batters .

Tips on Productivity of Motor Grader.

  • No Idle time
  • As a Motor grader is an expensive machine to hire or own, every attempt should be made to keep it 100% utilized.

Motor Grader Operator Training.

A well-trained and experienced operator will use the machine to the greatest efficiency. Time spent in training is never wasted. All of the manufacturers and most of suppliers of  motor graders  have trained personnel for this purpose and also have literature and videos for hire or purchase. If the motor grader is being hired then some time in observing the operator should be carried out. If the operator does not seem experienced enough then talk to the hire firm to see if the operator could be replaced or under go further training.

Program work of Motor Grader.

An idle Motor grader is costing money. A small time spent in producing a program for the working of a grader will save much expense. For example in laying of Overlay material a small program would be as follows.

  •     Motor Grader  scarifies and shapes 1st and 2nd sections for overlay.
  •     Motor Grader  cleans drains and does shoulder work while material is placed on the scarified 1st section.
  •     Motor Grader  scarifies 3rd section then spreads and trims 1st section while material is placed on 2nd section.

This process would be repeated with maybe minor changes due to unexpected conditions.

Motor Grader Road Construction

General description of Motor Grader

A motor grader has a chassis or frame made of steel that supports the engine, drive mechanisms, control compartment, the motor grader mouldboard, steering mechanism and any extra attachments. In many modern motor graders the chassis is hinged between the Cabin and the engine and is able to be articulated at this point by hydraulic rams.

The engine drives the rear wheels through an automatic preselecting gearbox. The drive is via a limited slip differential and or a locking differential. The two (tandem) wheels at each side are driven by chains in such a way that both wheels are linked and revolve at the exact same revolutions. This method gives maximum traction and driving forces.

The steering wheels are not only capable of turning left and right, but they can also be tilted vertically. This tilting is done to reduce the sideways forces causing slippage in the direction of travel. All modern motor graders use hydraulics to control the mouldboard and other equipment. Most also use constant flow hydraulics which mean that the speed of operation of the hydraulic rams is constant no matter at what speed the engine is running.

The ‘Mouldboard’ of a motor grader is from 6ft to 14ft in length (typically 12ft) and is of a curved cross section. It has a ‘skin’ of special high wearing steel on the surface with disposable ‘cutting edges’ on the base and disposable ‘end bits’ and ‘overlays’ at each end of the mouldboard.

The mouldboard is attached to ‘Circle’. The attachment to the circle allows the mouldboard to be tilted in the vertical direction and moved horizontally sideways. The Circle is able to rotate a full 360°.  The Circle is attached to the frame of the grader by an ‘A’ frame. This frame is attached to the frame of the motor grader near the front wheels by a ball joint. The frame is suspended from the ‘saddle’ of the frame by two hydraulic rams that allow both sides the be moved in a vertical direction independently of each other. A third ram allows the frame to be moved sideways horizontally. The saddle is also movable which allows for further  sideways movements .

All of this means that the mouldboard of  motor grader  can be positioned very precisely in many different positions and angles giving a grader many uses.