CHAPTER II
2.1 Materials
2.1.1 Binder
The binder is used for surface dressing may be penetration bitumen, cut back bitumen or a bitumen emulsion. (Refer the chart for the types of asphalt for surface treatments recommended by the asphalt institute in M.S.13). In our country, we are using mostly 80/100 Penetration Bitumen.
TYPES OF ASPHALT FOR SURFACE TREATMENTS
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Types of Construction
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Asphalt Cements
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Emulsified and Cutback Asphalt
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120\150
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200\300
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Rapid
Curing
(RC)
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Medium
Curing
(MC)
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Slow
Curing
(SC)
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Emulsified
(Anionic)
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Emulsified
(Cationic)
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70
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250
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800
|
3000
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30
|
70
|
250
|
800
|
3000
|
70
|
250
|
800
|
3000
|
RS-1
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RS-2
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MS-2
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SS-1
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SS-1H
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CRS-1
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CRS-2
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CMS-29
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CMS-2
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CSS-1
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CSS-1H
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Surface Treatments With Cover Aggregate
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
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Seal Coats…………
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
|
x
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Prime……………...
|
x
|
x
|
x
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x
|
X
|
x
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x
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SS grades can be used when sand is used for cover
Water diluted
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Factors, which will affect the choice of binder to be used, are as follows.
1) Climatic condition
2) Type & condition of the aggregate to be applied.
3) Equipment to be used.
Climate Condition: This will affect the rate of setting of the binder. Cold damp conditions required either an emulsion or cut back of a lower viscosity & slower rate of cure than would normally be used in order to give time for it to wet the chippings. In hot weather on the other hand, high viscosity binders may be used as they will remain soft long enough to allow the chippings to stick. Medium curing cutback asphalt can be used successfully provided sufficient curing time is permitted before traffic is allowed on the surface treatment.
Types & Condition of Aggregate to be Applied: This is one of the main factors governing the choice of grade, the larger the size of chipping the more viscous the binder required to hold it. For this reason low viscosity binders can only be accepted to hold small chippings.
Equipment to be Used: If the boilers & the sprayers capable of high temperature are not available. It is obvious that either a low viscosity cut-back that requires little heating or a bitumen emulsion will have to be used.
In deciding on the grade of binder to be used due consideration must be given to each of the above factors. However it may well be that each factor does not indicate the same choice, so that it may frequently be necessary to make the best possible compromise based on practical experience.
In H.N.H.P., N.D>LEA. & Associates has recommended the binder for surface dressing 80/100 bitumen cut-back with power kerosene (generally about 20%) to form Mc4. But we are using directly Mc4 for this project (see the chart of specification & test result for Mc.0 & Mc 4 bitumen)
Asphalt quantities required: The quantity of binder required will depend on the following main factors.
a) The shape & size of chippings used as cover material.
b) The volume of traffic.
c) The nature of the existing surface.
d) The climate conditions.
Specification and Result
MC-0 & MC-4 Bitumen
Description
|
Summary of Results
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Specification
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Sample Mc-0
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Sample Mc-4
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Mc-0
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Mc-4
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1. Distillate (% of Total Distillate to 680o F
To 437. F
To 500. F
To 600. F
|
4.35
67.39
92.39
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0
16.67
73.33
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25-
30-60
75-93
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0-
30-
40-80
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2. Residue from Distillation to 680. F
Volume Percent by difference
|
54.00
|
85.0
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50
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78
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3. Kinematics Viscosity at 140 Pcs
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46.7
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2380.5
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30-60
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800-1600
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4. Flash point (opentag).F
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165
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206
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100 min
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150 min
|
5. Penetration 77.F (100 Gm. SSEC)
|
143.6
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190.0
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120-300
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120-300
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6. Ductility 77.F Cm
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Over 100
|
Over 100
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100 min
|
100 min
|
7. Solubility in cc14'%
|
100
|
99.93
|
99.5 min
|
99.5 min
|
Tested At
Materials and Research Division Department of Highway Phyathai Bangkok, Thailand
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After a surface treatment when the road is opened to traffic, the aggregate particles will have oriented into their densest position. The particles will be lying on their flattest position & their voids between them will be about 20% of the total volume. The application rate fixed for the surface treatment should fill 70% of this void. (See chapter IV for the detail calculation of design application
rate)
rate)
2.1.2 Aggregates
Many kinds of aggregates can be used for the chippings of surface dressings, such as crushed stone, gravel & even coarse sand under certain condition. It should be hard, tough & should have following requirements.
Size of the Aggregate: It should be as close to uniform in size so that the surface treatment will have the only one layer of aggregate. If there is a vast difference between the largest & the smallest size of aggregate, the asphalt film may completely cover the smallest size & prevent proper embedding of the larger particles. If it happens the larger particles may be whipped off easily by high-speed traffic.
Therefore the larger size of the aggregate used should not be twice than the smaller size. Some agencies has given the gradation chart for it (see the gradation of surface dressing aggregate)
Shape of the Aggregate: It is one of the important factors for the surface treatment. The shape of the aggregate should be cubical & pyramidal. A large amount of flat & elongated particles is undesirable, because they may get completely covered by bitumen if enough asphalt is used to hold the cubical particles. (See Fig)
Cleanliness of Aggregates: It is extremely important to clean the aggregate for surface treatment work. If the particles are dusty, coated with dust silt, the bitumen may not stick on it. Good result can not be assured with the dusty aggregate. There is some evidence that dusty aggregates give better result when damp. For this reason dusty aggregates often are moistened when they must be use. This Type of work is suggested during hot weather.
In H.N.H.P. the aggregates used are screened from the various source of the river (uncrushed gravel). The shape of the aggregates are round. However the adjustment in rate of application of bitumen has been done to get the better result as per the trial in the field.
2.2 Equipment
2.2.1 Asphalt Distributor
The asphalt distributor is the most important piece of equipment on a surface treatment project to apply the asphalt uniformly to the surface at a specified rate. It should be equipped with a calibrated dipstick marked in liter /cm, gallon/inch to check the quantity in each load (see the calibration chart of Isuzu bitumen tank). It should also be equipped with thermometer to measure the accurate temperature before spraying the bitumen. The accurate rate of application depends on the speed of travel of the distributor; hence the accurate tachometer is necessary. The most common problem of the streaking is due to the improper distribution of asphalt. Variation can occur both along & across the road. It is caused due to the clogged nozzles of distributor, improper pump pressure, interference of sprayed asphalt from the adjacent nozzles & improper spray bar height.
All nozzles should be inspected for nicked or damaged edges. Improper nozzles opening result an uneven distribution of the spray fan.
To have a uniform spray of bitumen, proper pump pressure must be maintained.
Although several methods may be used to maintain pressure, all distributors use gear type pump to deliver asphalt to the spray bar. In some distributor pressure is governed by variable pump speed, measured with a tachometer, in other by constant pump speed & a pressure relief valve.
When a variable speed pump & metering system is used, the manufacturer will furnish the charts with the distributor for selecting the proper pump speed for each application rate.
When a pressure relief valve is used the pump runs at a constant speed & the pressure is automatically held in the spray bar. The manufacturer will furnish the charts with the distributor for selecting the proper pump speed for each application rates.
Improper angle setting of the spray nozzles causes the poor asphalt distribution. The angle of the nozzles should be properly adjusted in respect with the spray bar so that the spray fans will not interfere with each other. The angle varies with one manufacturer to another but it must give uniform spray. The angle recommended by the Asphalt Institute measured from the spray bar axis is 15 degrees to 30 degrees. (See the sketch)
Another cause of uneven distribution of asphalt is due to the variation of spray bar. As the asphalt leaves the spray bar the load lightens & the spring raise the distributor as much as 4 inches resulting to an uneven application. The height of the spray bar should not vary more than ½ inch from the pavement surface. Therefore it should be checked from time to time after each successive stretch of spray. The best result with four-inch nozzle spacing will come an exact triple coverage of the spray fans. But six-inch nozzle spacing cause the wind distortion of spray fans for triple coverage, resulting non-uniform application of asphalt. Therefore six inches nozzle is recommended for double coverage (See the Sketches).
A simple test procedure has been devised which will give the setting of the proper height of the spray bar with four inches nozzle spacing. It is based on the fact that, by visual inspection, one can see whether or not the single coverage of asphalt is being applied.
Procedure: Take the center section of the bar. The second & third, fifth & six, eight & nine bars are closed. Operate the distributor in correct pump pressure with the spray bar height changed not more than ½ inch at a time. When an even single coverage of asphalt is applied on the surface, it will give the exact triple coverage of asphalt with all nozzles opening.
Double coverage involving the same procedure except that every alternative nozzles are open & the remaining one are closed. When an even double coverage is applied on the surface by increasing 50 percent of the bar height will give the triple coverage.
2.2.2 Aggregate Spreader
A uniform spray of asphalt is of little value if the aggregate is not sprayed timely & properly on it. An aggregate spreader if operated properly will give the uniform spread of aggregate on the surface. Aggregate spreaders range form simple van type attached to truck tailgate to the highly self-propelled type.
2.2.3 Rollers
Proper embedment of aggregate is very important part of the surface treatment operation. Only proper Roller applied on it can achieve this. Generally there are two kinds of rollers, which can be used in surface dressing work. (Pneumatic tyred & steel wheels roller).
The asphalt institute recommended the self propelled smooth pneumatic tyred roller for the surface treatment work. This type of roller forces the aggregate firmly into the asphalt binder without crushing the particles. Generally the steel wheel roller should not be used. It can crush the softer part of the particles. If it is to be used the weight should not be more than five ton.
2.2.4 Cleaning equipment
Just before applying the asphalt the surface must be thoroughly cleaned. Generally the rotary power brooms towed by tractor are used to clean the surface. The remaining dust particles after brooming by power brooms should be blown out by air blower. After the surface treatment is completed it is necessary to sweep out the loose & excess aggregates by the power broom.
In H.N.H.P. the following types of equipment are used.
Asphalt distributor: - There are two numbers of asphalt distributors manufactured by Isuzu of Japan fitted with gear type pump.
Capacity of tank
|
4500 Liters
|
Nozzle size
|
1/8”
|
Nozzle slot & angle
|
15.to 30. with spray bar
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Nozzle height above ground
|
10 to 15 inch
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Pump discharge
|
Not known
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Pump pressure
|
2Kg/m2
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Nozzle spray bar
|
6” center to center
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Length of spray bar
|
6 & 4 meter
|
The width of spray in H.N.H.P. is 5 meter for priming & 3.5 meter for surface dressing (Total width of road is 7 meter)
Aggregate spreader: - There are two aggregate spreaders (Mechanical type) with adjustable locks in this project manufactured by Isuzu of Japan.
Total spray width: 3.5 Meter.
Capacity: 10-ton (6m3)
It can spray 100-125 meter for bottom layer (20mm aggregate) & 200 to 250 meters for top layer (10mm aggregate).
Cleaning Equipment: Two rotary power brooms towed by tractor & two air blowers are used in this project.
Roller: Two self propelled pneumatic tyred rollers manufactured by Sakai of Japan.
Heating equipment: There is one Preheater in this project. The capacity is 4500 liters.
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