STANDARD
- MS-4 1989, ASTM D 1559 and AASHTO Designation: T 166 —78.
OBJECTIVE
- To determine the properties of asphalt mix such as density, voids, stability, and flow.
APPARATUS
- Marshal Testing Machine
- Compaction pedestal consisting of a 200x460x460mm wooden post capped with a 305x305x25mm steel plate.
- Compaction mould consisting of a base plate, forming mould and color extension. The internal diameter of forming mould should be 101.60mm and a height of approximately 75mm.
- Compaction hammer consisting of flat circular tamping face 98.40mm diameter and equipped with 4.50 Kilogram weight constructed to obtain a specified 457mm height of the drop.
- Mould holder consisting of a spring tension device designed to hold compaction mould in place on compaction pedestal.
- Pans, metal, round, approximately 4 liters capacity for mixing of asphalt and aggregates.
- Thermostatically controlled oven and electrical hot plate.
- Scoop, mixing spoon, trowel, and spatula.
- Mechanical mixer (optional) of 4lits capacity equipped with two metal mixing bowls and two-wire stirrers.
- Thermostatically controlled water bath.
- Gloves and welders for handling hot equipment.
- Marking crayons.
- Extrusion jack for extruding compacted specimens from mould.
- Balance of capacity 10 kg’s and sensitivity 0.5 gms and of such a type and shape so as to pennit the basket containing the sample to be suspended from the beam and weighed in water.
- A wire basket of not more than 6.3nnn mesh or a perforated container of convenient size preferably chromium plated and polished, with wire hangers thickness not less than 1mm.
- A stout watertight container in which the basket may be freely suspended Two dry soft absorbent clothes each not less than 650 cm2
PROCEDURE
- Prepare test specimens either from Laboratory mix or from plant mix or from the paved surface.
Preparation of Mix in the Laboratory. - Take a representative sample of aggregates and dry to constant weight at 1050 to 110°C.
- Separate the aggregates by dry sieving into the desired size of the fraction.
- Weigh in to separate pans for each test specimen the amount of each size of fraction required to produce a batch that will result in a compacted specimen of height 63.5 ± 1.3 mm which is generally of 1.20kg including asphalt percentage.
- It is generally desirable to prepare a trial specimen prior to preparing aggregate batches.
- If the trial specimen height falls outside the limits, the amount of aggregate used for the specimen may be adjusted as follows
Adjusted mass of aggregate = 63.50 (Mass of aggregate used) / Specimen height (mm) obtained
- Place the pans in the oven or on the hot plate and heat the aggregates to a temperature of approximately 28°C above the mixing temperature
- Heat the asphalt cement to a temperature of not more than 160°C.
- Charge the mixing bowl with heated aggregates and dry nix thoroughly.
- From a carter in the dry blended aggregates and weigh the required amount of asphalt cement into the mixture in accordance with the accumulative batch weights.
- The temperature to which the asphalt must be heated to produce viscosity of 170 ± 20 centistokes shall be taken as the mixing temperature.
- Care shall be taken to maintain the temperature of aggregates and asphalt cement be within the limits of the mixing temperature.
- Mix aggregates and asphalt cement, preferably with a mechanical mixer or by hand with a trowel as quickly and thoroughly as possible to yield a mixture having a uniform distribution of asphalt throughout.
Determination of Compacting Temperature
- The temperature to which the asphalt must be heated to produce viscosity of 280 ± 30 centistokes shall be taken as the compacting temperature.
Preparation of Mould and Hammer –
- Thoroughly clean the mould assembly and heat the face of the compaction hammer in a boiling water bath or on the hot plate to a temperature between 93°C and 149°C.
Compaction of Specimens –
- Place a piece of waxed paper cut to size in the bottom of the mould before the mix is placed in the mould.
- Place the entire batch in the mould.
- Spade then mix vigorously with a heated spatula or trowel 5 times round the perimeter and 10 times over the interior.
- Remove the collar and smoothen the surface to a slightly rounded shape.
- The temperature of the mix immediately prior to compaction shall be with in the limits of the compaction temperature.
- Replace the collar, place the mould assembly on the compaction pedestal in the mould holder.
- Apply either 35,50 or 75 blows as specified according to the design traffic category with the compaction hammer using a free fall of 457mm. Hold the axis of the compaction hammer as nearly perpendicular to the base of the mould assembly during compaction.
- Remove the base plate and collar, reverse and reassemble the mould.
- Apply the same number of compaction blows to the face of the reversed specimen.
- After compaction, remove the base plate and allow the specimen to cool in the air until no deformation will result while removing it from the mould.
- Remove the specimen from the mould by means of extrusion jack and then place on a smooth level surface until ready for testing.
- Marking shall be done on the specimens for identification.
- Leave the specimens to cool overnight.
- In the Marshall Method, each compacted specimen is tested to determine the following properties
i. Density and Voids Analysis
ii. Stability and Flow
Density and Voids Analysis
- The bulk density test be may be performed as soon as the freshly compacted specimens are cooled to room temperature (AASHTO Designation: T 166 – 78)
- There are two methods for the determinatiofl of bullc density
- Bulk density of compacted specimens with Paraffm coating
- Bulk density of compacted specimens on a saturated surface dry basis
Bulk density of Paraffin coated Specimen
- Record the mass of the uncoated specimen to an accuracy of 0.5 grams (A).
- Coat the test specimen on all surfaces with melted paraffm sufficiently thick to seal all surface voids.
- Application of the paraffin may be accomplished by chilling the specimen in a refrigerating unit to a temperature of approximately 4.5°C for 30mm at then dipping the specimen in warm paraffin (5.5°C above matching).
- It may be necessary to brush the surface of the paraffin with added hot paraffm in order to fill any pinpoint holes.
- Allow the coating to cool in the air at room temperature for 30mm and then weigh (D) the specimen.
- Weigh the paraffin coated specimen (E) in a water bath at 25± 1°C.
- Determine the Specific Gravity of Paraffin at 25 ± 1°C if unknown and designate this as F.
Bulk Density = A /( D-E ) – { ( D-A ) / F }
A = Mass of dry specimen in air
D = Mass of paraffin coated specimen in air
E = Mass of paraffin coated specimen in water
F = Specific gravity of paraffin
Bulk Density of Compacted Specimens on Saturated Surface Dry Basis
- Record the mass of the specimen (A) to an accuracy of 0.5 grams.
- Record the mass of the specimen (C) in water at 25 ± 1°C
- Remove the specimen from the water, surface dry by blotting with a damp towel and determine the surface dry mass (B).
A
Bulk Density = ——-
C-B
A = Mass of specimen in air
B = Mass of specimen in water
C = Mass of surface dry specimen in air
Voids Analysis
- For the calculation of voids initially calculate the theoretical specific gravity of the aggregates (Gt1) and the theoretical specific gravity of the mix (Gt).
Theoretical specific gravity of the aggregates (Gt1) = 100/Wl+ W2 + W3 +W4
G1 G2 G3 G4
Wi, W2 , W3 and W4 = Percentages of the aggregate.
GI, G2, G3andG4 = Specific gravity of the aggregate.
100
Theoretical specific gravity of the mix (Gt) = ——————————————-
100- % of bitumen – % of bitumen
Gt1 spgr of bitumen
• Calculate the Voids from the equations given below
% of bitumen
Volume of bitumen (Vb) = Gb x ————————————
Specific gravity of bitumen
Gt – Gb
Air voids (Vv) = ———–x100
Gt
Voids in nteral aggregate (YMA) = Vv + Vb
100 Vb
Voids filled with bitumen (VFB) = ———
VMA
Gb= Bulk density of the specimen.
Stability and Flow
- Immerse the test specimens in a water bath maintained at 60°C ± 1°C for 30 to 40 minutes before commencing the test.
- Thoroughly clean the inside surface of the testing head.
- The temperature of the testing head shall be maintained within 21°C to 37.80°C using a water bath whenever required.
- Lubricate guide rods with a thin film of oil so that upper test head will slide freely without binding.
- Check the dial indicator of the dial gauge to be firmly fixed and set to zero load position.
- With testing apparatus ready, remove test specimen from the water bath and carefully wipe the surface.
- Place the specimen in the lower testing head and center, and then fit the upper testing head into position and center complete loading device.
- Place flow meter over marked guide rod and set the needle to zero.
- Apply load on the specimen at the constant rate of deformation 51mm per minute.
- The point of failure is defined by the maximum load reading obtained.
- Maximum load taken by the specimen at 60°C shall be recorded as its Stability value.
- Note the flow meter reading immediately when the load begins to decrease in load meter.
- This reading is the flow value of the specimen, expressed in units of 0.25mm.
- The entire procedure, both Stability, and Flow tests, starting with the removal of specimen from the water bath and testing shall be completed within a period of 30 seconds.
- Measured Stability values for specimens that depart from the standard 63.50mm thickness shall be converted to an equivalent 63.50mm value by means of conversion factor from the Table: 7.3.1.
- Average the flow values and the converted Stability values for all specimens.
Table: 7.3.1 Stability Correlation Ratios
| Thickness of specimen, in mm | Correlation Ratio |
| 58.70 | 1.14 |
| 60.30 | 1.09 |
| 61.90 | 1.04 |
| 63.50 | 1.00 |
| 64.00 | 0.96 |
| 65.10 | 0.93 |
| 66.70 | 0.89 |
| 68.30 | 0.86 |
Note*
The measured stability of a specimen multiplied by the correlation ratio for the specimen thickness equals the corrected stability for a 63.50 mm specimen.
REPORT
- Report all the test results density, voids, stability and flow in a typical format.
PRECAUTIONS
- In no case shall the mix be reheated if the temperature falls down the specified limits of compacting temperature.
- When more rapid cooling of moulds is desired table fans might be used but not water unless the specimen is in water bags.
- Asphalt should not be at mixing temperature for more than one hour before using.
DETERMINATION OF ASPHALT MIX PROPERTIES
| Theoretical specific gravity of mineral mix Gt1 | Sp.gr of Paraffin :0.88 | Sp.gr of Bitumen | |||||||||||
| Sample No |
Gt (Mix) | Bitumen content % |
Height of sample in air |
Weight after Paraffin |
Bulk Weight Density in water Gb |
Vv | Vb | VMA | VFB | Reading | . Stability (Kgs) |
Flow (mm) |
|
| 1 | |||||||||||||
| 2 | |||||||||||||
| 3 | |||||||||||||
| Average | |||||||||||||