Category: ABC Laying

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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.

Categories
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.