MARSHALL STABILITY TEST.(ASTM – D – 1559 & MS-2)

                                    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. The aggregate size more than 25mm use the Modified Marshall method.  

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 – 360⁰C with 1⁰C 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 175⁰ to 190⁰C. The compaction mould assembly and hammer are cleaned and kept pre-heated to a temperature of 100⁰C to 145⁰C. The bitumen is heated to temperature of 121⁰ to 138⁰C 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 153⁰ to 160⁰C. 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 138⁰ to 149⁰C. 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 0.5 percent 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:

                             P1 + P2 +. ……+ Pn

Gsb   =      

                     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:

                    100 - Pb

Gse   =

               Pmm/Gmm – Pb/Gb

Where, Gse          = Effective sp.gravity of aggregate, constant for all at 5% bitumen content.

             Gmm       = Maximum sp.gravity of paving mixture 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:

                                   100

Gmm          =

                         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:

                           Gse - Gsb   

Pba   =       100                   Gb

                            Gse Gsb

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:

                            Pba

Pbe   =     Pb -              Ps

                            100            

vi) Voids in mineral aggregate in compacted paving mixture ‘VMA’ is given by: 

                              Gmb Ps

VMA     =  100  -

                                 Gsb

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:

                           Gmm  -  Gmb

Va     =  100 X

                                  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:

                 100(VMA – Va)            

VFB =

                               VMA

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.

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 for Std. Marshall

Correction Factors for Modified Marshall

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 limits

for base course = 350

for wearing surfaces = 400.

Marshall Curves:

             Bitumen(%) ’vs’ Stability(kg)                                                    Bitumen(%) ‘vs’ Density (g/cc)

                            

              Bitumen(%) ‘vs’ Flow(mm)                                                      Bitumen (%) ‘vs’ Voids(%)

                            

              Bitumen(%) ‘vs’ VFB(%)                                                          Bitumen(%) ‘vs’ VMA(%)

                            

LOSS ON HEATING OF BITUMINOUS MATERIALS.( IS : 1205 – 1978 )

                             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 180⁰C 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 360⁰C – sensitivity 0.1⁰C.

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 163⁰C 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.

  

 

Hydrometer method.

Hydrometer method.

Apparatus:

a) Density hydrometer confirming to IS: 3104-1965 – (Range 0.995 – 1.030).

b) Two glass-measuring cylinders of 1000ml capacity with ground glass or rubber stoppers about 7cm diameter and 33cm high marked at 1000ml volume.

c) Thermometer to cover the range 0 to 50⁰C, accurate to 0.50⁰C.

d) Water bath or constant temperature room

e) Stirring apparatus

f) 75 micron sieve.

g) Balance accurate to 0.01g

h) Stop watch

i) Wash bottles containing distilled water

j) Glass rod, about 15 to 20 cm long and 4 to 5 mm in diameter

k) Reagents: Hydrogen peroxide, Hydrochloric acid N solution and Sodium hexametaphosphate.

l) Conical flask of 1000ml capacity

m) Funnel, filter paper, measuring cylinder of 100ml capacity and blue litmus papers.

Procedure:

(A) Calibration of Hydrometer:

1. Determination of volume of the hydrometer bulb (V_h): Pour about 800ml of distilled water in the 1000ml-measuring cylinder and note the reading at the water level. Immerse the hydrometer in water and note the water reading. The difference between the two readings is recorded as the volume of the hydrometer bulb plus the volume of that part of the stem, which is submerged. For practical purposes, the error due to the inclusion of this stem volume may be neglected. Alternatively, weigh the hydrometer to the nearest 0.2g. This weight in grams is recorded as the volume of the hydrometer in ml. This includes the volume of the bulb plus the volume of the stem. For practical purposes the error due to the inclusion of the stem may be neglected.

2. In order to find the area of cross-section (A) of the measuring cylinder in which the hydrometer is to be used, measure the distance, in cm, between two graduations of the cylinder. The cross-section area (A) is then equal to the volume included between the two graduations divided by the distance between them.

3. Measure the distance (h) from the neck to the bottom of the bulb, and record it as the height of the bulb.

4. With the help of an accurate scale, measure the height (H) between the necks of the hydrometer to each of the other major calibration marks (R_h).

5. Calculate the effective depth (H_e) corresponding to each of the major calibration marks (or hydrometer readings, R_h) by the following expression:

                                                 1              V_h

                   He     =         H +        (h -           ) 

                                                 2                A

6. Draw a calibration curve between H_e and R_h, which may be used for finding the effective depth (H_e) corresponding to hydrometer readings (R_h) obtained during the test.

7. Meniscus correction (C_m) : Insert the hydrometer in the measuring cylinder containing about 700ml of water. Take the readings of the hydrometer at the top and bottom of the meniscus. The difference between two readings is taken as the meniscus correction (C_m), which is a constant for hydrometer. During the actual sedimentation test, the readings should be taken at the bottom of the meniscus but since the soil suspension is opaque, readings are taken at the top of meniscus. The meniscus correction is always positive.

(B) Pre- treatment of soil: 

1. Weigh accurately (to 0.01g) 50 to 100 g of oven dried soil sample (W_d) passing the 0.075mm IS sieve. If the percentage of soluble salts is more than one percent, the soil should be washed with water before further treatment, taking care to see that the soil particles are not lost.

2. Add 150ml of hydrogen peroxide to the soil sample placed in a wide mouth conical flask and stir it gently for few minutes with a glass rod. Cover the flask with glass and leave it to stand overnight.

3. Next morning, the mixture in the conical flask is gently heated in an evaporating dish, stirring the contents periodically. Reduce the volume to about 50ml by boiling. With very organic soils additional peroxide may be required to complete the oxidation.

4. If the soil contains insoluble calcium compounds, add about 50ml of hydrochloric acid to the cooled mixture of soil obtained in step 3. The solution is stirred with a glass rod for a few minutes and allowed to stand for one hour or for longer periods, if necessary. The solution will have an acid reaction to litmus.

5. Filter the mixture and wash it with warm water until the filtrate shows no acid reaction to litmus. Transfer the damp soil on the filter paper and funnel to the evaporating dish using a jet of distilled water. Place the dish and its contents to the oven. Take the weight (W_b) of the oven-dried soil remaining after pre-treatment and find the loss of weight due to pre-treatment.

(C) Dispersion of soil:

1. To the oven-dried soil, add 100ml of sodium hexametaphosphate solution and warm the mixture gently for about 10 minutes. Transfer the mixture to the cup of the mechanical mixer using a jet of distilled water, and stir it well for about 15 minutes. The sodium hexametaphosphate solution is prepared by dissolving 33 g of sodium hexametaphosphate and 7 grams of sodium carbonate in distilled water to make one liter of solution. This solution is unsuitable and should be freshly prepared approximately once in a month.

2. Transfer the soil suspension to the 75 micron IS sieve placed on a receiver and washes the soil on this sieve using jet of distilled water from a wash bottle. The amount of distilled water used during this operation may be about 500ml.

3. Transfer the soil suspension passing the 75-micron IS sieve to the 1000ml-measuring cylinder, and adds more water to make the volume to exactly 1000ml in the cylinder.

4. Collect he material retained on 75-micron sieve and put it in the oven for drying. Determination the dry weight of soil retained on 75-micron sieve.

(D) Sedimentation test with hydrometer:

1. Insert a rubber bung or any other suitable cover on the top of the 1000ml-measuring cylinder containing the soil suspension and shake it vigorously end over end. Stop shaking and allow it to stand. Immediately, start the stopwatch, and remove the top cover from the cylinder.

2. Immerse the hydrometer gently to a depth slightly below its floating position and then allow it to float freely. Take the hydrometer readings after periods of 0.5, 1, 2 and 4 minutes. Take out the hydrometer, rinse it with distilled water and allow it to stand in a jar containing distilled water at the same temperature as that of the test cylinder.

3. The hydrometer is re-inserted in the suspension and readings are taken after periods of 8, 15 and 30 minutes; 1, 2 and 4 hours after shaking. The hydrometer should be removed, rinsed and placed in the distilled water after each reading. After the end of 4 hours, readings should be taken once or twice within 24 hours.

4. Composite correction (C): In order to determine the composite correction, put 100ml of dispersing agent solution in another 1000ml measuring cylinder and make it to 1000ml by adding distilled water. The cylinder should be maintained at the same temperature as that of the test cylinder containing soil specimen. Insert the hydrometer in this comparison cylinder containing distilled water and the dispersing agent and take the reading corresponding to the top of the meniscus. The negative of the hydrometer reading so obtained gives the composite correction (C). The composite correction is found before the start of the test, and also at every time intervals of 30 minutes, 1 hour, 2 hours and 4 hours after the beginning of the test, and afterwards, just after each hydrometer reading is taken in test cylinder.

5. The temperature of the suspension should be observed and recorded once during the first 15 minutes and then after every subsequent reading.

Calculations:

(1) The loss in weight in pre-treatment of the soil in percentage is calculated from the following expression:

                                                       

                              W_b                                 Where,  P    = loss in weight in percentage

P       =       1 -   -------   X 100                     W_d = weight of dry soil sample taken from the soil passing 2mm Sieve

                              W_d                                                      W_b = weight of the soil after pre-treatment

(2) The diameter of the particle in suspension at any sampling time t is calculated from:

D       =   10^-5 M ( H_e / t ) ^0.5              Where, M = poise constant factor

                                                                  H_e = effective depth of the hydrometer

                                                                    t  = elapsed time, minutes

(3)  The percentage finer N^/ based on the weight W_d is calculated from:

                 100 G                     Where, N^/ = percentage finer, based on the weight of dry soil sample W_d

N^/      =                    X R                     W_d = weight of dry soil sample taken from the soil sample passing 2mm sieve.

               W_d ( G – 1 )                          G = specific gravity of the soil passing 75 micron sieve.

                                                            R = corrected hydrometer reading

                                                             R = R_h^/ + C

                                                             R_h = R_h^/ + C_m

                                               Where, R_h^/ =  observed hydrometer reading

                                                            R_h = hydrometer reading, corrected for meniscus correction 

(4) The percentage finer (N) based on the total weight of dry soil sample (W) is obtained from the relation:

N       =  N^/  X (W^/ / W)           Where,   W^/ = cumulative weight passing 2mm sieve.

Values of Factor ‘M’