Chapter III
JOB Planning & Operation
3.1 Planning the Job
It is very important to plan the job properly both for the good quality & for the efficiency of the work. The following matters should be taken in consideration for planning the job
1. Weather: Suitable weather conditions are extremely important to obtain the satisfactory surface treatment. It should be dry, hot & the road surface temperature should be above 60oF before spraying. Early summer weather is ideal for the surface treatment work. No work can be started when the surface is wet and work should never continue during rain.
2. Cleaning the surface: The surface to be treated must be cleaned immediately before the asphalt is applied. All the mud & the foreign material must be thoroughly swept & cleaned by means of cleaning equipment.
3. Material on the Job: The delivery of material should be coordinate for the smooth operation of the work. Sufficient number of trucks should carry the aggregate to assure a continuous supply. Enough aggregate should be stock piled near the job site to finish the planed work. Enough asphalt delivery should be arranged to complete each day work without any delay.
3.2 Checking the Equipment
All the equipment should be checked properly before the work in order to be sure whether they are in good condition or not. The supervisor of the work should check the height of spray bar & all nozzles are spraying properly even they have been checked the night before. The aggregate spreaders should be checked whether they are working properly or not.
After each day's operation all the equipments should be checked & cleaned. All the necessary preventive maintenance should be done at this time. Clean equipment that seldom breakdown on the job not only saves the money but also promotes the pride of the workmanship.
3.3 The surface dressing operation
Spraying the Asphalt: Before the surface dressing operation, a line should be marked on the edge of the road as a guide line for the driver of the distributor truck. On rural road, a string line or a series of small rocks can do this. On city road the curb and the gutter line can be used as a guideline. These curb and gutter should be covered by the paper or, empty jute bags to protect from Bitumen while spraying.
Before the asphalt application each length spread should be determined. It is based mainly on the number of loaded aggregate trucks when operation begins. Another important factor is the time between the spraying of asphalt & the spreading the aggregate. The sprayed bitumen should be covered within a minute by the aggregate. So no more asphalt should be sprayed which cannot be covered within this time. Application of binder should not be permitted until the loaded aggregate trucks are ready to cover the binder.
After all the adjustment & checks including the heating of the asphalt to proper spraying viscosity, the distributor driver has to maintain the fixed pre-determined speed for the rate of application to be sprayed. (See the chart for spraying temperature)
Spraying temperatures for binders
Cutback grades (US Asphalt Institute)
|
Whirling spray jets
|
Slot jets
| ||
Min o C
|
Max o C
|
Min o C
|
Max o C
| |
MC 30
|
50
|
60
|
40
|
50
|
RC/MC 70
|
65
|
80
|
55
|
70
|
RC/MC 250
|
95
|
115
|
80
|
90
|
RC/MC 800
|
115
|
135
|
105
|
115
|
RC/MC 3000
|
135
|
150
|
120
|
130
|
Penetration Grades
| ||||
400/500
|
160
|
170
|
140
|
150
|
280/320
|
165
|
175
|
150
|
160
|
180/200
|
170
|
190
|
155
|
165
|
80/100
|
180
|
200
|
165
|
175
|
Asphalt-Emulsion
| ||
Anionic
|
Degree C.
|
Degree F.
|
RS-1
|
21-60
|
70-140
|
RS-2
|
52-85
|
125-185
|
MS-2
|
21-71
|
70-160
|
SS-1
|
21-71
|
70-160
|
SS-1h
|
21-71
|
70-160
|
Cationic
| ||
CRS-1
|
52-85
|
125-185
|
CRS-2
|
52-85
|
125-185
|
CNS-2h
|
21-71
|
70-160
|
CMS-2
|
21-71
|
70-160
|
CSS-1
|
21-71
|
70-160
|
CSS1h
|
21-71
|
70-160
|
It is very important to check the amount of asphalt sprayed after each run with the distributor. Calculating the liters per M2 can do this quickly and easily by using the formula given below:
R = T x m
WL
Where:-
R = rate of application in liter per square meter.
T = total liters spread from the distributor at spraying temperature = (Gauge stick reading before spread) – (Gauge stick reading after spread)
W = width of spray in Meter
L = length of spray in Meter
M = multiplier for correcting asphalt volume to basis of 60oF
(See the table for temperature volume: correction factor for asphaltic material in Appendix Page 9)
Example: -
Gauge stick reading before spread = 4000 liter
Gauge stick reading after spread = 3625 liter
Total sprayed = 375 liter
W = 3.5 meter
L = 100 meter
M = 0.9305 (From table for asphaltic materials and temperature of 240o F)
Therefore R = T X M or R = 375.00 X 0.9305
WL 3.50 X 100
= 0.9905 or say 1.00 Liter per M2
Determining Distributor speed:
S= GT
WR
Where S = Road speed in meter per minute
GT = spray bar out put in liter per minute.
W= spray width on road in meter.
R= Rate of application in litre/m2
Example: -
R= 1 Lit. Per M2, W= 3.5 Meter. GT = 269.5 Lit/minute
Then: - S= 269.50 = 77 Meter/ Minute
3.5x1
Determining the Length of spray for a distributor load:
L = T__
WR
Where L= Length of spread in meter; T= Total liter to be spread from the distributor; W= sprayed width; R= Rate of application in Lit/m2
Example
T=4000 Lits., W= 3.5 meter, R= 1 Lit./m2
L= 4000 = 1142.85 meter.
3.5x1
Note: IF the distributor does not have a sump, about 200 liters should be left in the tank to prevent the pump from pulling air & causing insufficient application of asphalt in end area of the spread.
Transverse Joints: An important point to be watched in application of binder is to get a clean transverse joint. This can be obtained by using a strip of empty bitumen sheet or a thin sheet on which the spraying is to be started & stopped. The distributor travelling at the correct speed for the desired rate of application should spray the bitumen on the drum sheet so that when it reaches to exposed surface, the spray bar should make uniform spray.
Longitudinal Joints: When the longitudinal joints are necessary, the width of the spray bar should be adjusted so that the minimum such joins are required. The number of passes of the distributor should be the same as the number of traffic lanes i.e. two lane road 7 meter should cover in two passes. The spray pattern leaves a 10-15 inch wide on the edge with less binder on the first lane (see fig in chart II for the spray patterns of binder). It is important to prevent aggregate on it. This allows a width that can be overlapped, when the binder is applied in the adjacent lane. When the aggregate is spread on full width, a neat & tidy joint can be achieved. It depends on the distributor driver in making the proper overlap.
Spreading the aggregate: It is very important to spread the aggregate immediately after binder application. All the loaded truck with aggregate should be on site before applying the binder. The aggregate spreader should follow right behind the bitumen distributor. It is desirable to spread the aggregate within one minute of spraying. A maximum of five minute will however be allowed. Anyhow the job should be well organized to cover the aggregate on the binder as quickly as possible because the increase in viscosity in the binder may prevent good wetting & binding the aggregate.
It is important to spray the aggregate uniformly on the surface at the proper rate. It should cover the full width of spray in a single pass. Aggregate normally will not stick more than one particle thick to the binder. Therefore it is useless & wasteful to apply the aggregate more than the desired rate. A small excess over the theoretical cover rate is however needed to give an even application to allow the whip off under traffic, but maximum 10 percent can be allowed for it.
Hand brooming & hand spotting can be carried out immediately in that area where there are deficiency in aggregate & excess heaps & rills should be removed before rolling. A light spray with some hand spotting is preferable than to a heavy spread. However the hand spreading will not be necessary, if the spreader is operated in a controlled way with proper adjustment.
Rolling: Rolling should begin immediately after laying the aggregate & continue until the aggregate is well embedded in the binder. When the asphalt has a definite set or hardening, the rolling should be stopped, because the roller can break the bond between the asphalt & aggregate. The rolling should begin in a longitudinal direction from the outer edge & proceed to wards the center of the road. Each pass of the rolling should overlap the previous pass by about half the width of the front wheels. If the aggregate contains moisture, the rolling should continue until it evaporates. If satisfactory embedment does not occur, rolling shall be continued on the following afternoon or as per the weather condition of the place when the binder viscosities are in the higher stage.
The asphalt institute recommends the Pneumatic tyred roller for all the surface treatment work with a wheel load of 1000 to 1500 kg & the tyrse pressure should not be more than 80 PSI. The work should begin with two pneumatic rollers.
Removing excess aggregate:-After the rolling operation is completed, the loose aggregate on the road surface should be swept & should be deposited in one place, so that it can be reused.
An aggregate, which does not stick up, creates a problem. The fast moving vehicles will pick up the particles & throw them against the following vehicle damaging headlights, windshields etc. These loose aggregates may be removed by lightly brooming with a rotary power broom during early morning time.
Traffic Control: - Adequate measures should be taken to control the traffic. Fast moving uncontrolled traffic over a fresh surface dressing does serious harm & displaces the aggregate. Traffic must be strictly controlled in the early stage with a speed limit of 30 K.M./ Hour. Slow moving traffic in fact will act as a form of pneumatic tyred roller. The best way to control the traffic is with warning signboard & flagmen on both side of the working area.
In H.N.H.P the surface treatment is designed for double coat. It is known as "D.B.S.T. " (Double Bitumen surface treatment) in this project. The following work procedure is adopted in this project. The operation of D.B.S.T. takes place on the half road width due to the traffic.
a) Cleaning the base surface: - The rotary power broom cleans the base surface followed by air blower. The remaining dust is removed by means of hand brushes (Jute brushes).
b) Priming - After clearing the base, a series of rocks are placed on the edge of the road as a guideline of the asphalt distributor driver. Then the driver starts the distributor about 20 meter away from the line of priming, so that he can maintain the correct speed when he reaches at the starting line of priming. The man who stays at backside of the distributor controls the valve. Some signs are given to open & close the valve at the beginning & ending of the work. Then the primed portions are left for 48 hours to soak the bitumen on the base. The remaining excess bitumen after 48 hours is blotted by sand to open the traffic on the primed area. The same procedure is adopted to prime the next lane.
The prime coat material is Mc 0. It is heated in 100degree to 135o F. (38 degree to 57 degrees Centigrade). No preheating tank is necessary for it. The bitumen can be directly pumped inside the tank from the bitumen drum by the pump fitted on the distributor & can be heated by the heater fitted on the distributor to the specified temperature.
The rate of application in this project is 0.75 lit/m2. The bitumen distributor runs with the speed of 135 meter per minute to spray the primer for this rate of application.
c) Bottom layer of D.B.S.T: The primed area is cleaned & the potholes are repaired by the premix cutting the potholes in rectangular shape with minimum one-centimeter depth. Fine aggregate below 3/8 inch is used to prepare the premix.
After all the necessary repair & cleaning are done two string lines are fixed both on the edge ¢er of road for guidance of the bitumen driver. Then the drum sheets are placed for the transverse joint. When all the arrangements are done, the driver starts the distributor about 20 meters away from the starting line. The man who stays at the backside of the distributor open the valve above the drum sheets carefully to have a good transverse joint. Then the drum sheets are taken away immediately before spreading the aggregate.
Then the driver of the aggregate spreader starts the spreader about 10 meter away from the starting line. Two men stay at the backside of spreader to control & open the locks attached behind the spreader. Hand brooming & hand spotting of areas deficient in aggregate is carried out immediately & excess heaps or rill are removed before rolling. About 20 laborers are needed for this work. 100 to 130 meter length of road is fixed to spray at one time because of the capacity of the spreader truck (10 ton only). After completing the work in this stretch the further work proceeds for the next stretch. In this project maximum 1.2 K.M length of road in half width 3.5m) has been done in one day.
Removing of excess loose aggregates & back rolling continues in the following two days. Back rolling is done generally between 8 to 11 A.M & 2 to 5 P.M or as per the weather condition of the site, when the binder viscosity is higher to bind the particles. Some hand spotting work is carried out in the difficient area of the aggregate during this time.
The excess aggregates are lightly broomed early in the morning & are deposited on the side of the road (It can be re-used). Then the road is opened for the traffic to build the adjacent lane of the road according to same procedure described above.
From our experience in this project, we found a very good result if the traffic is allowed to run about 10 to 15 days on the first coat of D.B.S.T. It embeds the aggregate firmly to the binder and seats the aggregate in the densest position. The binder material is Mc 4. The rate of application of the binder is 1 lit/m2 & 20.4 Kg/m2 is fixed for the aggregate to cover.
The bitumen distributor runs at the rate of 77-meter/ minute to spray 1 lit/m2
d) Top layer of D.B.S.T.: Before starting the top layer, the loose materials of the bottom layer are broomed. All the dust & foreign materials are cleaned by means of air blower & hand brooms. The working procedures are same as described for the bottom layer except that the asphalt distributor is operated in the opposite direction of the first layer when spraying for the second layer & the center joint is off set 15 Cm for the half width construction. The length for one spray is 200-250 meter as one aggregate spreader can spray the aggregate 200-250 meter to cover the binder at one time.
The back rolling continues as per the same procedure of the bottom layer. The excess aggregates are swept after few days of traffic running on it.
The binder is Mc 4. The rate of binder is fixed 1.25 Lit/M2 & the rate of aggregate is fixed 10.2kg/m2. The binder distributor runs at the rate of 61 meter per minute to spray for this rate.
Generally the sequence of operation for this project are given in sketches attached here with (see the sketch for sequence of operation).
1) Sweeping & cleaning: - To remove the dust & cleaning other foreign material.
2) Priming & curing: - Priming the base by the distributor & left for 48 hours for curing.
3) First binder application: - Applied by the distributor.
4) First aggregate applications: - Applied by the mechanical spreaders & brooming the aggregate by means of hand brooms for the uniform layer of aggregate.
5) First rolling & back rolling: - Initial rolling during D.B.S.T. operation & continues for two days.
6) Brooming - to remove excess loose particles by rotary power broom.
7) Second binder application: - Same type of binder as in first coat, applied by distributor.
8) Second aggregate application & hand brooming: - Smaller size of aggregates spread evenly fill surface voids on the first course & same as in number 4.
9) Final rolling & back rolling: - Same as in no.5.
10)Brooming - To remove excess loose particles by rotary power brooms.
Some Important Notes to Remember:
Do: -
1) Take precaution to avoid the segregation of aggregate into large & small size.
2) Provide a fire extinguisher on the distributor truck.
3) Check the spray bar of the distributor frequently for clogged nozzle
4) Check the asphalt application rate frequently especially on the first shots. Apply any needed correction to the application charts.
5) Maintain proper spray bar height while spraying.
6) Clean the strainers on the spray bar each night after use.
Don't: -
1) Try to seal on dusty or wet surface.
2) Excessive asphalt, this cause bleeding.
3) Use insufficient amount of asphalt, loss of cover aggregate result.
4) Allow excessive overlap of asphalt at longitudinal or transverse joint.
5) Allow variations in spray-bar pressure along the length of the bar.
6) Permit travel at speeds greater than 40 km/h for the first 24 hours following construction.
7) Expect to obtain satisfactory result if construction is allowed to proceed under anything but the most favorable weather condition.
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