CONTENT
| SL NO | DESCRIPTION OF TESTS | |
| 1 | PENETRATION TEST | |
| 2 | SPECIFIC GRAVITY TEST. | |
| 3 | SOFTENING POIN TEST ( RING AND BALL TEST ) | |
| 4 | VISCOSITY TEST | |
| 5 | FLASH AND FIRE POINT TEST. | |
| 6 | DUCTILITY TEST. | |
| 7 | LOSS ON HEATING OF BITUMINOUS MATERIALS | |
| 8 | STRIPPING VALUE OF AGGREGATES. | |
| 9 | BINDER CONTENT OF PAVING MIXTURES | |
| 10 | TEST FOR CONTROL OF RATE OF SPREAD OF BINDER | |
| 11 | TEST FOR RATE OF SPREAD OF GRIT IN SURFACE DRESSING. | |
| 12 | MARSHALL STABILITY TEST. | |
INTRODUCTION
Bitumen:
Bitumen is a petroleum product obtained by the distillation of petroleum crude.
Tar:
Tar is obtained by the destructive distillation of coal or wood.
Both bitumen and tar have similar appearance, as both are black in color, both these materials can be used for pavement works, but they have different characteristics.
The bitumen is brought to sufficient fluidity or viscosity before use in pavement construction by any one of the following three methods:
a) by heating, in the form of hot bitumen binder.
b) by dissolving in light oils, in the form of cutback bitumen.
c) by dispersing bitumen in water, in the form of bituminous emulsion.
The paving bitumen available in India is classified into two categories:
i) paving bitumen from Assam petroleum denoted as A-type and designated as A35, A45, A55, A65, A90 & A200.
ii) paving bitumen from other sources denoted as S-type and designated as S35, S45, S55, S65, S90 & S200.
Cutback bitumen: is defined as the bitumen, the viscosity of which has been reduced by a volatile diluents. For use in surface dressings, some types of bituminous macadam.
Cutback bitumens are available in three types, namely (i) Rapid curing (RC), (ii) Medium curing (MC) and (iii) Slow curing(SC).
Bitumen Emulsion: is a liquid product in which a substantial amount of bitumen is suspended in a finely divided condition in an aqueous medium and stabilized by means of one or more suitable materials. The main advantages of emulsions are that (i) they can be used, without heating for preparing mixes, (ii) they are particularly useful for patch repair works and can be used even when the surface is wet or it is raining. Three types of emulsified bitumen can be prepared (i) Rapid Setting (RS)- is a setting emulsified bitumen used for penetration and surface treatment, (ii) Medium Setting (MS)- is used for plant mixes with coarse aggregate, (iii) Slow Setting (SS)- is used for fine aggregate
mixes.
1.
PENETRATION TEST
(
IS : 1203 – 1978 )
INTRODUCTION:
Penetration test is the test on bitumen to grade the material in term of its hardness.
Object:
To determine the penetration of bitumen by penetration test.
Apparatus:
a) Container: A flat-bottomed cylindrical metallic container 55mm in diameter and 35mm or 57mm in height.
b) Needle: A straight, highly polished hard steel needle.
c) Water bath: A water bath is maintained at 25 +/- 1 deg.C containing not less than 10 liters of water, the sample is immersed to depth not less than 100mm from the top and supported on a perforated shelf not less than 50mm from the bottom of the bath.
d) Penetrometer: Electrically operated automatic penetrometer / Manually operated penetrometer. It is an apparatus, which allows the needle assembly of gross weight 100gm to penetrate without appreciable friction for the desired duration of time 5 sec.
The dial is accurately calibrated to give penetration value in units of one tenth of an mm.
e) Transfer tray: A small tray, which can keep the container fully immersed in water during the test.
f) Stop Watch.
Procedure:
The bitumen is softened to a pouring consistency between 75 deg.C and 100 deg.C above the approximate temperature at which bitumen softens. The sample material is thoroughly stirred to make it homogenous and free from air bubbles and water. The sample material is then poured into the containers to a depth at least 15 mm more than the expected penetration. The sample containers are cooled in atmosphere temperature not lower than 13 deg.C for one hour. Then they are placed in temperature controlled water bath at a temperature of 25 deg.C for a period of one hour.
The sample container is placed in the transfer tray with water from the water bath and placed under the needle of the penetrometer. The weight of needle, shaft and additional weight are checked. The total weight of this assembly should be 100gm.
Using the adjusting screw, the needle assembly is lowered and the tip of the needle is made to just touch the top surface of the sample, the needle assembly is clamped in this position. The contact of the tip of the needle is checked using the mirror placed on the rear of the needle. The initial reading of the penetrometer dial is either adjusted to zero or the initial reading is taken before releasing the needle. The needle is released exactly for a period of 5 secs. by pressing the knob and the final reading is taken on the dial. At least three measurements are made on this sample by testing at distance of not less than 10mm apart. After each test the needle is disengaged and cleaned with benzene and carefully dried. The sample container is also transferred in the water bath before next testing is done so as to maintain a constant temperature of 25 deg.C. The test is repeated with sample in the other containers.
Results:
The difference between the initial and final penetration readings is taken as the penetration value.
|
Bitumen grade |
A35 & S35 |
A45
& S45 |
A55
& S55 |
A65
& S65 |
A90
& S90 |
A200
& S200 |
|
Penetration value |
30 to 40 |
40
to 50 |
50
to 60 |
60
to 70 |
80
to 100 |
175
to 225 |
2.SPECIFIC
GRAVITY TEST.
(
IS : 1202 – 1978 )
Object:
To determine the
specific gravity of the bitumen by specific gravity bottle.
Apparatus:
a) Pycnometer /
specific gravity bottle – 50 ml capacity.
b) Balance –
sensitivity 0.1mg.
Procedure:
The specific gravity bottle is cleaned, dried and weighed along with the stopper. It is filled with fresh distilled water, stopper placed and the same is kept in water container for at least half an hour at temperature 27 +/- 1 deg.C. The bottle is then removed and cleaned from outside. The specific gravity bottle containing distilled water is now weighed.
The bituminous material is heated to a pouring temperature and is poured in the above empty bottle taking all the precautions that it is clean and dry before filling sample materials. The material is filled up to the half taking care to prevent entry of air bubbles.
To permit an escape of air bubbles, the sample bottle is allowed to stand for half an hour at suitable temperature cooled to 27 deg.C and then weighed. The remaining space in the specific gravity bottle is filled with distilled water at 27 deg.C, stopper placed and is placed in water container at 27 deg.C. The bottle containing bituminous material and remaining water is removed, cleaned from outside and is again weighed.
Calculations:
The specific gravity of the bituminous material is calculated as follows:
Weight of bituminous
material ( c
– a )
Specific gravity = ---------------------------------------------------------- = ------------
Weight of equal volume of water at 27 deg.C (b – a) – (d – c)
Where a = weight of the specific gravity
bottle
b = weight of the
sp.gravity bottle filled with distilled water.
c = weight of the
sp.gravity bottle about half filled with bitumen.
d = weight of the
sp.gravity bottle about half filled with bitumen and the distilled water.
Limits: Specific gravity of Bitumen at 27 deg.C is Minimum 0.99.
3.SOFTENING
POIN TEST ( RING AND BALL TEST ).
(
IS : 1205 – 1978 )
INTRODUCTION:
Bitumen does not suddenly change from solid to liquid state, but as the temperature increases, it gradually becomes softer until it flows readily. All semi-solid state bitumen grades need sufficient fluidity before they are used for application with the aggregate mix. For this purpose bitumen is sometimes cutback with a solvent like kerosene. The common procedure however is to liquefy the bitumen by heating. The softening point is the temperature at which the substance attains particular degree of softening under specified condition of test. For bitumen, it is usually determined by ‘Ring and Ball’ test.
Object:
To determine the
softening point of the bitumen by ‘Ring and Ball’ apparatus.
Apparatus:
a) Ring and Ball
apparatus – It consists
(i) Steel Balls – 2 nos.each has a diameter of 9.5mm and weight is 2.5+/-0.05gm.
(ii) Brass Rings – 2 nos. each 6.4mm depth, inside diameter at top 17.5mm, inside diameter at bottom 15.9mm and outside diameter 20.6mm and three equally spaced ball guides.
(iii) Support - The metallic support is used for placing pair of rings. The upper surface of the rings is adjusted to be 50mm below the surface of water or liquid contained in the bath. A distance of 25mm between the bottom of the rings and top surface of the bottom plate of support is provided. It has a housing for a suitable thermometer.
b) Thermometer – 0 deg.C to 350 deg.C – sensitivity 0.1 deg.C.
c) Bath and stirrer – A heat resistant glass container of 85mm diameter and 120mm depth is used.
Procedure:
Sample material is heated to a temperature between 75 and 100 deg.C above the approximate softening point until it is completely fluid and is poured in heated rings placed on metal plate.
To avoid sticking of the bitumen to metal plate, coating is done to this with a solution of glycerin and dextrin. After cooling the rings in air for 30 minutes, the excess bitumen is trimmed and rings are placed in the support as mentioned in item(iii) above.
At this time the temperature of distilled water is kept at 5 deg.C. This temperature is maintained for 15 minutes after which the balls are placed in position. The temperature of water is raised at uniform rate of 5 deg.C per minute with a controlled heating unit, until the bitumen softens and touches the bottom plate by sinking of balls. At least two observations are made.
Results:
The temperature at the instant when each of the ball and sample touches the bottom plate of support is recorded as softening value.
Limits:
|
Bitumen grade |
A35
& S35 |
A45
& S45 |
A55
& S55 |
A65
& S65 |
A90
& S90 |
A200
& S200 |
|
Softening point |
50
to 65 deg.C |
45
to 60 degC |
45
to 60 degC |
40
to 55 degC |
35
to 50 degC |
30
to 45 degC |
4.VISCOSITY TEST.
(
IS : 1206 – 1978 )
INTRODUCTION:
Viscosity is defined
as inverse of fluidity. Viscosity thus defines the fluid property of bituminous
material. The degree of fluidity at the application temperature greatly influences
the ability of bituminous material to spread, penetrate into the voids and also
coat the aggregates and hence affects the strength characteristics of the
resulting paving mixes.
Object:
To determine the viscosity of bitumen by Tar Viscometer.
Apparatus:
Tar Viscometer with 4mm and 10mm orifices – The apparatus consists of main parts like cup, valve, water bath, sleeves, stirrer, receiver and thermometers etc.
Procedure:
The tar cup is properly leveled and water in the bath is heated to the temperature specified for the test and is maintained throughout the test. Stirring is also continued. The sample material is heated at the temperature 20 deg.C above the specified test temperature, and the material is allowed to cool. During this the material is continuously, stirred.
When material reaches slightly above test temperature, the same is poured in the tar cup, until the leveling peg on the valve rod is just immersed. In the graduated receiver (cylinder), 25ml of mineral oil or one percent by weight solution of soft soap is poured.
The receiver is placed under the orifice. When the sample material reaches the specified testing temperature within +/- 0.1 deg.C and is maintained for 5 minutes, the valve is opened.
The stopwatch is started, when cylinder records 25ml. The time is recorded for flow up to a mark of 75ml.(i.e., 50ml of test sample to flow through the orifice).
Results:
The time in seconds
for 50ml of the test sample to flow through the orifice is defined as the
viscosity at a given test temperature.
Limits:
|
Type of material |
Orifice size, mm |
Test temp, |
Viscosity range, sec. |
|
A35
& S35 |
10mm |
60
deg.C |
90
- 100 |
|
A45
& S55 |
10mm |
60
deg.C |
80
- 90 |
|
A55
& S55 |
10mm |
60
deg.C |
70
- 80 |
|
A65
& S65 |
10mm |
60
deg.C |
60
- 70 |
|
A90
& S90 |
10mm |
60
deg.C |
50
- 60 |
|
A200
& S200 |
10mm |
|
40
- 50 |
|
Cutback
- RC,MC&SC
- Grade -
0 |
4mm |
25
deg.C |
25
- 75 |
|
Grade
- 1 |
4mm |
25
deg.C |
50
- 150 |
|
Grade
- 2 |
10mm |
25
deg.C |
10
- 20 |
|
Grade
- 3 |
10mm |
25
deg.C |
25
- 75 |
|
Grade
- 4 |
10mm |
40
deg.C |
14
- 45 |
|
Grade
- 5 |
10mm |
40
deg.C |
60
- 140 |
Viscosity conversion
chart:
5.
FLASH AND FIRE POINT TEST.
(
IS : 1209 – 1978 )
INTRODUCTION:
Bituminous materials
leave out volatiles at high temperatures depending upon their grade.
These volatile catch
fire causing a flash. This condition is very hazardous and it is therefore
essential to qualify this temperature for each bitumen grade.
Flash point: The flash point of
a material is the lowest temperature at which the vapour of substance
momentarily takes fire in the form of a flash under specified condition of test.
Fire point: The fire point is
the lowest temperature at which the material gets ignited and burns under
specified condition of test.
Object:
To determine the
flash and fire point of bitumen by Pensky-Martens closed tester.
Apparatus:
a) Pensky-Martens closed tester consist of cup, lid, stirrer device, shutter, flame exposure device.
b) Thermometer ( 0 – 350 deg.C) – sensitivity – 0.1 deg.C.
Procedure:
The material is filled in the cup up to a filling mark. The lid is placed to close the cup in a closed system. All accessories including thermometer of the specified range are suitably fixed. The bitumen sample is then heated. The test flame is lit and adjusted in such a way that the size of a bleed is of 4mm diameter. The heating is done at the rate of 5 to 6 deg.C per minute. The stirring is done at a rate of approximately 60 revolutions per minute. The test flame is applied at intervals depending upon the expected flash and fire points. First application is made at least 17 deg.C below the actual flash point and then at every 1 deg.C to 3 deg.C. The stirring is discontinued during the application of the test flame.
Results:
The flash point is taken as the temperature read on the thermometer at the time of the flame application that causes a bright flash in the interior of the cup in closed system. For open cup it is the instance when flash appears first at any point on the surface of the material. The heating is continued until the volatiles ignite and the material continues to burn for 5 seconds. The temperature of the sample material when this occurs is recorded as the fire point.
Limits: The flash point for all grades of bitumen materials is 175 deg.C, minimum.
6.DUCTILITY
TEST.
(
IS : 1208 – 1978 )
INTRODUCTION:
In the flexible pavement construction where bitumen binders are used, it is of significant importance that the binders form ductile thin films around the aggregates. This serves as a satisfactory binder in improving the physical interlocking of the aggregates.
Object:
To determine the ductility of the bituminous material.
Apparatus:
a) Ductility machine.
b) Briquette moulds.
c) Knife.
Procedure:
The bitumen sample is melted to a temperature of 75 to 100 deg.C above the approximate softening point until it is fluid. It is strained through 90 micron sieve, poured in the mould assembly and placed on a brass plate, after a solution of glycerin and dextrin is applied at all surfaces of the mould exposed to bitumen. After 30 to 40 minutes, the plate assembly along with the sample is placed in water bath maintained at 27 deg.C for 30 minutes. The sample and mould assembly are removed from water bath and leveling the surface using hot knife cuts off excess bitumen material. After trimming the specimen, the mould assembly-containing sample is replaced in water bath maintained at 27deg.C for 85 to 95 minutes. The sides of the mould are now removed and the clips are carefully hooked on
the machine with out
causing any initial strain.
The pointer is set to zero, the machine is started and the two clips are pulled apart horizontally at a uniform speed of 50 +/- 2.5mm per minute. While the test is in operation, it is checked whether the sample is immersed in water at depth of at least 10mm. The distance, at which the bitumen thread of each specimen breaks, is recorded (in cm) to report as ductility value.
Results:
The distance stretched by the moving end of the specimen up to the point of breaking of thread measured in centimeters is recorded as ductility value.
Limits: The minimum ductility value of A35 & S35 grade bitumen is 50 cm at 27deg.C.
All other grades, the ductility value is 75 cm at 27 deg.C.
7.LOSS
ON HEATING OF BITUMINOUS MATERIALS.
(
IS : 1205 – 1978 )
INTRODUCTION:
The loss in weight (exclusive of water) of bituminous materials when heated is called loss on heating of bituminous materials.
Object:
To determine the loss on heating of bituminous materials.
Apparatus:
a) Oven – heating capacity is minimum 180 deg.C and interior dimensions min.330X330mm.
b) Aluminum Rotating shelf - the self shall be suspended by vertical shaft and centered with respect to the horizontal interior dimensions minimum diameter of 250mm, and shall be provided with a mechanical means of rotating it at the rate of 5 to 6 rpm.
c) Thermometer – 0 to 360 deg.C – sensitivity 0.1 deg.C.
d) Containers- Metal or glass cylindrical containers shall have a flat bottom and diameter 55mm, 35mm depth minimum.
e) Balance – sensitivity 0.01gm.
Procedure:
Heat the sample with care, stirring constantly to prevent local overheating, until the sample has become sufficiently fluid to pour. Place the sample in container and cool the sample to room temperature and then weigh to the nearest 0.01gm. Bring the oven to a temperature of 163 deg.C and place the container in oven for period of 5 hr. Remove the sample from the oven, cool to room temperature, and weigh to the nearest 0.01gm. And calculate the loss due to heating.
Limits: Loss on heating of all grades, except A200 & S200 of bitumen is maximum 1% by mass. Loss on heating of grade A200 & S200 is maximum 2% by mass.
8.STRIPPING
VALUE OF AGGREGATES.
(
IS : 6241 – 1959 )
INTRODUCTION:
Bitumen and tar
adhere well to all normal types of aggregates provided they are dry and are not
exceptionally dusty. Largely the viscosity of the binder controls the process
of binding. When the viscosity of the binder is high, coating of aggregates by
the binder is slower. In the absence of water there is practically no adhesion
problem in bituminous road construction. Two problems are observed due to the
presence of water. First, if aggregate is wet and cool it is normally not
possible to coat with a bituminous binder.
This problem can be dealt with by removing the water film on aggregate by drying, and by increasing the mixing temperature. Second problem is stripping of coated binder from the aggregate due to the presence of water. This problem of stripping is experienced only with bituminous mixtures, which are permeable to water.
Object:
To determine the stripping value of aggregates by static immersion method.
Apparatus:
Thermostatically controlled water bath, beaker.
Procedure:
This method covers the procedure for determining the stripping value of aggregates by static immersion method, when bitumen and tar binder are used. 200gm of dry and clean aggregates passing 20mm IS sieve and retained on 12.5mm sieve are heated up to 150 deg.C when these are to be mixed with bitumen and the aggregates are heated up to 100 deg.C when these are to be mixed with tar. 5% by weight of bitumen / tar binder is heated to 160 deg.C (110 deg.C in the case of tar binder). The aggregate and binder are mixed thoroughly till they are completely coated and the mixture is transferred to a 500ml beaker and allowed to cool at room temperature for about two hours. Distilled water is then added to immerse the coated aggregates. The beaker is covered and kept in a water bath maintained at 40 deg.C, taking care that the level of water in the water bath is at least half the height of the beaker. After 24 hours the beaker is taken out, cooled at room temperature and the extent of stripping is estimated visually while the specimen is still under water.
The stripping value is the ratio of the uncovered area observed visually to the total area of aggregates in each test, expressed as a percentage.
Limits: The maximum stripping value is 5%( i.e., minimum retained coating is 95%).
9.BINDER
CONTENT OF PAVING MIXTURES.
(
SP : 11 – 1976 )
Object:
To determine the binder content in the mix by cold solvent extraction.
Apparatus:
a) Centrifugal extraction machine electrically operated.
b) Balance – 15 kg
capacity – sensitivity 0.1gm.
c) Cold solvent –
Commercial grade of Benzene.
d) Filter paper – Wat
60.
e) Oven.
Procedure:
A representative sample about 1000gm is exactly weighed and placed in the bowl of the extraction apparatus and covered with commercial grade of benzene. Sufficient time (not more than 1 hour) is allowed for the solvent to disintegrate the sample before running the centrifuge.
The filter paper of the extractor is dried, weighed and then fitted around the edge of the bowl. The cover of the bowl is clamped tightly. A beaker placed under to collect the extract.
The machine is revolved slowly and then gradually increases the speed, maximum of 3600 rpm. This speed is maintained till the solvent ceases to flow from the drain. The machine is allowed to stop and 200ml of benzene is added and the above procedure is repeated. A number of 200ml solvent additions (not less than three) are used till the extract is clear and not darker than a light straw colour.
The filter paper removed from the bowl, dried in air then in oven to constant weight at 1150C and weighted the fine materials that might have passed through the filter paper are collected back from the extract preferably by centrifuging. The material is washed and dried to constant weight as before. The percentage of binder in the sample is calculated as below.
W1 – ( W2 + W3 ) + W4
Percentage of binder
= -----------------------------------
X 100
W1
Where W1 = Weight of sample.
W2 = Weight of the
sample after extraction.
W3 = Weight of Fine
material recovered from the extract.
W4 = Increase in
weight of the filter paper.
10.TEST
FOR CONTROL OF RATE OF SPREAD OF BINDER.
(
SP : 11 – 1976 )
Object:
To determine the rate of spread of binder by tray test.
Apparatus:
a) 20cmX20cm and 3cm deep metal trays – 5 nos.
b) Balance – 0.1gm
sensitivity.
Procedure:
Light metal trays of about 20cmX20cm and 3cm deep previously weighed and numbered, are placed at intervals along the road in the path of the binder distributor between the wheel tracks. After the distributor has passed, the trays are removed and wrapped in weighed sheets of paper so that they can be handled stocked and weighed as soon as convenient. The spacing and the number of trays can be varied to suit the circumstances of the particular site, but at least five trays shall normally be used. The tray test gives a measure of the variation in rate of spread along the road and a good approximation to the average rate of 0 spread.
Precautions:
The trays shall be weighed correct to first place of decimal in gram. The maximum longitudinal distribution error shall be within 10% of the specification.
Transverse
distribution by the machine can be checked by placing a number of trays to collect
the binder sprayer over each 5cm of the width of the spray bar. The variation
in transverse distribution shall not be more than 20% from the man (not
counting the extreme 15cm at either side of sprayed area).
11.TEST
FOR RATE OF SPREAD OF GRIT IN SURFACE DRESSING.
(
SP : 11 – 1976 )
Object:
To determine the rate of spread of grit by measuring the area covered by each lorry load of known capacity.
Procedure:
Measuring the area covered by each lorry load of known capacity can check the rate of spread of grit by gritters.
Removing the chippings from small areas of the road and weighing them can also check this. A small square metal frame is laid on the new dressing and all the chippings within the enclosed area which is 10cm square are collected and washed in solvent to remove the binder, weighed and the rate of spread is measured at points along the road at intervals of between 1 meter to 4 meters.
The transverse variation shall be less than +/- 20 percent of the mean.
12.MARSHALL
STABILITY TEST.
(
ASTM – D – 1559 & MS-2)
INTRODUCTION:
Bruce Marshall, a former Bituminous Engineer with the Mississippi State Highway Department, formulated the concepts of the Marshall method of designing paving mixtures. The U.S.Army Crops of Engineers, through extensive research and correlation studies, improved and added certain features to Marshall’s test procedure, and ultimately developed mix design criteria.
The original Marshall method is applicable only to hot-mix asphalt paving mixtures containing aggregates with maximum sizes of 25mm or less.
This method covers the measurement of the resistance to plastic flow of cylindrical specimens of bituminous paving mixture loaded on the lateral surface by means of the Marshall apparatus.
Object:
To determine the
stability, flow, voids, voids in mineral aggregates, voids filled with asphalt
and density of the asphalt mixture by Marshall stability test.
Apparatus:
a) Specimen Mould Assembly – Mould cylinders 101.6mm(4 in.) in diameter by 75mm(3 in.) in height, base plates, and extension collars.
b) Specimen Extractor – Steel disk with a diameter 100mm, and 12.7mm thick for extracting the compacting specimen from the specimen mould with the use of the mould collar. A suitable bar is required to transfer the load from the proving ring adapter to the extension collar while extracting the specimen.
c) Compaction Hammer – The compaction hammer shall have a flat, circular tamping face and a 4.5kg(10 lb) sliding weight with a free fall of 457mm (18 in.). Two compaction hammers are recommended.
d) Compaction Pedestal – The compaction pedestal shall consist of 200X200X460mm(8X8X18 in.) wooden post capped with a 305X305X25mm(12X12X1 in.) steel plate. The pedestal should be installed on concrete slab so that the post is plumb and the cap is level. Mould holder provided consisting of spring tension device designed to hold compaction mould centered in place on compaction pedestal.
e) Breaking Head – It consists of upper and lower cylindrical segments or test heads having an inside radius of curvature of 50 mm. The lower segment is mounted on a base having two vertical guide rods, which facilitate insertion in the holes of upper test head.
f) Loading Machine – The loading machine is provided with a gear system to lift the base in upward direction./ on the upper end of the machine, a calibrated proving ring of 5 tonne capacity is fixed. In between the base and the proving ring, the specimen contained in test head is placed. The loading machine produces a movement at the rate of 50mm per minute. Machine is capable of reversing its movement downward also.
g) Flow meter – One dial gauge fixed to the guide rods of a testing machine can serve the purpose. Least count of 0.25mm(0.01 in.) is adequate.
h) Oven or hot plates
i) Mixing apparatus.
j) Thermostatically control water bath.
k) Thermometers of range 0 – 360 deg.C with 1deg.C sensitivity.
Procedure:
In the Marshall method each compacted test specimen is subjected to the following tests and analysis in the order listed below:
i) Bulk density determination
ii) Stability and flow test
iii) Density and voids analysis
At least three samples are prepared for each binder content.
Preparation of test specimens:
The coarse aggregates, fine aggregates and the filler material should be proportioned and mixed in such a way that final mix after blending has the gradation with in the specified range.
The aggregates and
filler are mixed together in the desired proportion as per the design requirements
and fulfilling the specified gradation. The required quantity of the mix is taken
so as to produce a compacted bituminous mix specimen of thickness 63.5mm, approximately.
Preparation of Mixtures: Weigh into separate pans for each test specimen the amount of each size fraction required to produce a batch that will result in a compacted specimen 63.5 +/- 1.27mm(2.5 +/-0.05 in.) in height. This will normally be about 1200gm(2.7 lb.).
It is generally to prepare a trial specimen prior to preparing the aggregate batches. If the trial specimen height falls outside the limits, the amount of aggregate used for the specimen may be adjusted using:
63.5 (mass of
aggregate used)
Adjusted mass of aggregate
= -------------------------------------------
Specimen height (mm)
obtained
Take the sample as mentioned above, and heated to a temperature of 175 to 190 deg.C. The compaction mould assembly and hammer are cleaned and kept pre-heated to atemperature of 100 deg.Cto 145 deg.C. The bitumen is heated to temperature of 121 to 138 deg.C and the required quantity of first trial percentage of bitumen (say, 3.5% by weight of mineral aggregates) is added to the heated aggregate and thoroughly mixed using a mechanical mixer or by hand mixing with trowel. The mixing temperature may be 153 to 160 deg.C. The mix is placed in a mould and compacted by hammer, with 75 blows on either side (for light compaction it is 50 blows). The compaction temperature may be 138 to 149 deg.C. The compacted specimen should have a thickness of 63.5 +/- 3.0mm. Three specimens should be prepared at each trial bitumen content, which may be varied at 0.5percent increments up to about 7.5 or 8.0 percent.
Marshall Stability and Flow values:
The specimens to be
tested are kept immersed under water in a thermostatically controlled water
bath maintained at 600
+/- 10C for 30 to 40
minutes. The specimen are taken out one by one, placed in the Marshall test
head and the Marshall Stability value (maximum load carried in kg. before
failure) and the flow value (the deformation the specimen undergoes during
loading up to the maximum load
in 0.25mm units) are
noted. The corrected Marshall stability value of each specimen is determined by
applying the appropriate correction factor.
The following tests are determined first, to find out the density, voids, VMA and VFB.
Tests:
The specific gravity and apparent specific gravity values of the different aggregates, filler and bitumen used are determined first.
i) Bulk specific gravity of aggregate ‘Gsb’ is given by:
Gsb = {(P1 + P2 +. … … + Pn)} / {P1/G1 + P2/G2 +. … … + Pn/Gn}
Where, Gsb = Bulk specific gravity for the
total aggregate.
P1, P2, Pn =
Individual percentages by weight of aggregate.
G1, G2, Gn = Individual bulk specific gravities of aggregate.
ii) Effective
specific gravity of aggregate ‘Gse’ is given by:
Gse = (100 - Pb) / (Pmm/Gmm – Pb/Gb)
Where, Gse = Effective specific gravity of
aggregate, constant for all at 5% bitumen content.
Gmm = Maximum specific gravity of paving
mixture (no air voids), determine by Vacuum pump test (ASTM – D – 2041).
Pb = Bitumen content,
percent by total weight of mixture.
Gb = Specific gravity
of Bitumen.
iii) Maximum specific
gravity of mixture ‘Gmm’ is given by:
Gmm = 100 / (Ps/Gse + Pb/Gb)
Where, Gmm = Maximum specific gravity of paving mixture (no air voids)
Ps = Aggregate
content, percent by total weight of mixture
Pb = Bitumen content,
percent by total weight of mixture
Gse = Effective
specific gravity of aggregate
Gb = Specific gravity
of bitumen
iv) Bitumen absorption ‘Pba’ is given by:
Pba = 100 x {(Gse - Gsb ) / (Gse Gsb)} x Gb
Where, Pba = Absorbed bitumen, percent by weight of aggregate
Gse = Effective
specific gravity of aggregate
Gsb = Bulk specific
gravity of aggregate
Gb = Specific gravity
of bitumen
v) Effective bitumen content of a paving mixture ‘Pbe’ is given by:
Pbe = Pb - (Pba / 100) x Ps
vi) Voids in mineral aggregate in compacted paving mixture ‘VMA’ is given by:
VMA = 100 -
Where, VMA = Voids in mineral aggregate, percent of bulk volume
Gsb = Bulk specific
gravity of total aggregate
Gmb = Bulk specific
gravity of compacted mixture
Ps = Aggregate content, percent by total weight of mixture
vii) Air voids in
compacted mixture ‘Va’ is given by:
Va = 100 X {(Gmm - Gmb) / Gmm}
Where, Va = Air voids in compacted mixture,
percent of total volume
Gmm = Maximum
specific gravity of paving mixture
Gmb = Bulk specific
gravity of compacted mixture
viii) Voids filled with bitumen in compacted mixture ‘VFB’ is given by:
VFB =
Where, VFB = Voids filled with bitumen, percent of VMA
VMA = Voids in
mineral aggregate, percent of bulk volume
Va = Air voids in
compacted mixture, percent of total volume
Determination of
Optimum Bitumen Content:
Six graphs are plotted with values of bitumen content against the values of:
a) Density ‘Gmb’ g/cc.
b) Marshall
Stability, S kg.
c) Voids in total
mix, Va %.
d) Flow value, F
(0.25mm units).
e) Voids filled with
bitumen, VFB %.
f) Voids in mineral
aggregate, VMA %.
Let the bitumen
contents corresponding to maximum density be B1, corresponding to maximum
stability be B2 and that corresponding to the specified voids content Va (4.0% in
the case of dense AC mix) be B3. Then the Optimum Bitumen Content is given by:
Optimum Bitumen Content (OBC) = (B1 + B2 + B3)/3
The values of flow and VFB are found from the graphs, corresponding to bitumen content OBC. All the design values of Marshall stability, flow, voids and VFB are checked at the Optimum Bitumen Content, with the specified design requirements of the mix.
Design Requirements of the mix:
i) Marshall Stability value, kg = 820 kg.(min.)
ii) Flow value, 0.25mm units = 8 – 16
iii) Voids in total mix, Va % = 3 – 5 %
iv) Voids in mineral agg.(VMA), % = 10 – 12 %(min.)
v) Voids filled with bitumen(VFB) %= 65 – 75 %
The highest possible Marshall stability values in the mix should be aimed at consistent with the other four requirements mentioned above. In case the mix designed does not fulfill any one or more of the design requirements, the gradation of the aggregates or filler content or bitumen content or combination of these are altered and the design tests are repeated till all the requirements are simultaneously fulfilled.
Job Mix Formula:
The proportions in which the different aggregates, filler and bitumen are to be mixed are specified by weight or by volume for implementation during construction.
Caution: Mixes with high Marshall stability values and very low Flow values are not desirable as the pavements of such mixes may be brittle and are likely to crack under heavy traffic.
Correction Factors
|
Volume
of Specimen
in cc |
Approximate Thickness
of Specimen
in mm |
Correction
Factors |
|
457 - 470 |
57.1 |
1.19 |
|
471 - 482 |
58.7 |
1.14 |
|
483 - 495 |
60.3 |
1.09 |
|
496 - 508 |
61.9 |
1.04 |
|
509 - 522 |
63.5 |
1.00 |
|
523 - 535 |
65.1 |
0.96 |
|
536 - 546 |
66.7 |
0.93 |
|
547 - 559 |
68.3 |
0.89 |
|
560 - 573 |
69.9 |
0.86 |
Swell
test:
Apparatus:
a) Moulds with internal diameter 101.6mm(4 in.) and length 127mm(5 in.)
b) Perforated, 98.4mm diameter x 3.2mm thick with adjustable stem, for swell measurement.
c) Dial gauge, mounted on tripod, with reading accuracy to 0.025mm.
d) Aluminum pans, 190mm diameter x 64mm deep.
Procedure:
Allow compacted swell test specimen to stand at room temperature for at least one hour. Place the mould and specimen in 190mm diameter x 64mm deep aluminum pan. Place the perforated disk on specimen, position the tripod with dial gauge on mould, and set the adjustable stem to give a reading of 2.54mm on the dial gauge. Introduce 500ml of water into the mould on top of the specimen and the measure distance from the top of the mould to the water surface with the graduated scale. After 24 hours, read the dial gauge to the nearest 0.025mm and record the change as swell. Also, measure the distance from the top of the mould to the water surface with the graduated scale and record the change as permeability or the amount of water in ml that percolates into and/or through the test specimen.
Note:
i) Water Sensitivity: The loss of stability on immersion in water at 600C. The allowable limit is minimum 75% retained strength.
ii) Marshall Quotient (Stiffness): is the ratio of stability and flow.
Allowable limit for base course = 350
for wearing surfaces
= 400.
Marshall Curves:
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