MARSHALL STABILITY AND FLOW VALUES OF BITUMINOUS MIX SPECIMEN

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 specimens 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 0.01 mm units) are noted. The corrected Marshall stability value of each specimen is determined by applying the appropriate correction factor, if the average height of the specimen is not exactly 63.5 mm. The correction factors are given in Table.

Correction Factors for Stability and Flow Value

Volume of Specimen  in Cubic Centimeters	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

DESIGN PROCEDURE OF BITUMINOUS MIXES

In the design procedure of a bituminous mix, following steps are involved.

i) Selection of aggregate to be employed in the mix.

ii) Selection of aggregate grading.

iii) Determination of the proportion of each aggregate required to develop the design grading.

iv) Determination of the specific-gravity of the aggregate blend.

v) Determination S.G. of the bitumen.

vi) Make up trial specimens with varying bitumen contents.

vii) Determination of the specific-gravity (S.G) of each compacted specimen.

viii) Make stability test on the specimen.

ix) Determine the percentage of voids in each paving specimen and if the design method in use requires it, calculate the VMA and percent voids filled with bitumen.

x) Selection of the optimum bitumen content from the obtained data.

PREPARATION OF TEST SPECIMEN FOR MARSHALL METHOD

The coarse aggregates, fine aggregates and the filter materials should be proportioned and mixed specified gradation of mineral aggregates and bitumen binder as per IRG: 29–1968 are given in Table. The aggregates and filler are mix 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.

Approximately 1200g of aggregates and filler are taken and heated to a temperature of 175⁰ to 190⁰C. The compaction mould assembly and rammer are cleaned and kept pre-heated to a temperature of 100⁰C to 145⁰C. The bitumen is heated to temperature of 121⁰C 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 for 80/100grade bitumen may be around 154⁰C and that for 60/70grade, about 160⁰C.The mix is placed in a mould and compacted by rammer, with 50 blows on either side. The compacting temperatures may be about 138⁰C for 80/100grade bitumen and 149⁰C for 60/70grade. The compacted specimen should have thickness of 63.5mm. The weight of the aggregate taken may be may be suitably altered to obtain a thickness of 63.5±3.0 mm.  At least two specimens, but preferably three or four 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.

 

Specified Grading of Aggregates for Bituminous Concrete

Passing Sieve size	Retained Sieve size	Weight of Aggregate (gm)
20 mm	12.5 mm	120
12.5 mm	9.5 mm	120
9.5 mm	4.75 mm	240
4.75 mm	2.36 mm	216
2.36 mm	600 micron	216
600 micron	300 micron	72
300 micron	150 micron	72
150 micron	75 micron	84
75 micron	Filler	60
Total =		1200 gm

EFFECTS OF POLYETHYLENE AND KEROSENE ON THE PROPERTIES OF BITUMEN

TEST PROCEDURE & GRAPHICAL PRESENTATION

Specific Gravity Test

           (a)        Wt. of bottle at clean and dry condition = A gm

           (b)        Wt. of (bottle+ water full) at 25⁰ C after 30 min = B gm

           (c)        Wt. of (bottle+ bitumen) at 25⁰ C after 60 min = C gm

           (d)        Wt. of (bottle+ bitumen +water full) at 25⁰ C after 30 min = D gm

                                                    Sp. Gr. = (C-A) / ((B-A)-(D-C))

Penetration Test

(a) Bitumen at 100-1100 C was poured into the container and then cooled to room temperature for one hour.
(b) Container with bitumen was submersed in water at 250 C for one hour.

(c) At constant temp. of 250C, the sample was placed in penetrometer and then readings were recorded for a period of 5 seconds.

Ductility Test

(a) Bitumen was strained through 0.6 mm sieves and then poured into the briquette and was cooled to room temperature for 30 min.
(b) Then sample was placed in water at 25 0C for 30 min.
(c) Excess bitumen was cut off and the briquette was placed in water at 250 C for 1.5 hour. 

(d) Briquette was placed in ductility machine and recorded the reading in cm at which the bitumen threads were broken.

Result of Specific gravity, Penetration and Ductility Test.
(Modified Bitumen Sample made with mixing of Pure Bitumen,
Polyethylene and Kerosene)

Type of Sample	% of Polyethylene content	% of Kerosene content	Specific Gravity	Penetration value	Ductility value
Pure bitumen	0	0	1.020	85	100+
Sample-1	1	1	1.016	41	74
Sample-2	2	2	1.013	53	60
Sample-3	3	3	1.009	50	44
Sample-4	4	4	1.006	41	26
Sample-5	5	5	1.003	38	18

 

Result of Penetration Test (only for % of kerosene content)

Type of Sample	% of Kerosene content	Penetration value
Pure bitumen	0	85
Sample-1	1	80
Sample-2	2	60
Sample-3	3	55
Sample-4	4	54
Sample-5	5	82

 

Solubility Test

(a) 0.50 gm asbestos fiber was thoroughly shaked in 150 cc water.

(b) The crucible was filled with some of the suspension of asbestos in water and applied a light suction to draw off the water, leaving a firm mat of asbestos in the crucible.

(c) The crucible was heated for 10 to 15 min. for the constant weight of A.
(d) 2 gm bitumen was stirred in 100 cc CS2 until all lumps were disappeared and no undissolved sample was adhered to the container. (e) The prepared weighed Gooch crucible was placed in the filter flask. Decanted the solution through the asbestos mat of the crucible with light suction. Removing the crucible from the flask and then heating for 10 to 15 min. for constant weight of B gm.

 

Softening Point Test

(a) Completely fluid bitumen was poured in heated rings placed on metal plate.
(b) After cooling the rings in air for 30 min. the excess bitumen was trimmed.
(c) At this time the temperature of water was kept at 50C for 15 min. and then the balls were placed in position. 

(d) The temperature of water was raised at uniform rate of 50C/min. until the bitumen was softened and touched the bottom plate by sinking of balls.

  

Flash and Fire Point Test

(a) Bitumen was poured into the clean and dried cup up to a filling mark.
(b) Sample was then heated at the rate of 5 to 60C/ min.

(c) Test flame was applied at intervals depending upon the expected flash and fire points.

Result of Solubility, Softening, Flash and Fire Point Test.
(Modified Bitumen Sample made with mixing of Pure Bitumen,
Polyethylene and Kerosene)

Type Of Sample	% of Polyethylene content	% of Kerosene content	Solubility (%)	Softening Point (0C)	Flash Point (0C)	Fire Point (0C)
Pure bitumen	0	0	95.70	43	290	300
Sample-1	1	1	90.05	55	280	295
Sample-2	2	2	85.70	56	270	285
Sample-3	3	3	82.13	57	260	275
Sample-4	4	4	84.30	58	255	270
Sample-5	5	5	87.50	59	250	265

MARSHALL METHOD OF BITUMINOUS MIXES

Bruce Marshall, formerly Bituminous Engineer with Mississippi State Highway Department, USA formulated Marshall Method for designing bituminous mixes. Marshall’s test procedure was later modified and improved upon by U.S. Corps of Engineer through their extensive research and correlation studies. ASTM and other agencies have standardized the test procedure. Generally, this stability test is applicable to hot-mix design of bitumen and aggregates with maximum size 2.5 cm. In Bangladesh, bituminous concrete mix is commonly designed by Marshall Method.

In this method, the resistance to plastic deformation of cylindrical specimen of bituminous mixer is measured when the same is loaded at the periphery at a rate of 5 cm per minute. The test procedure is used in the design and evaluation of bituminous paving mixes. The test is extensively used in routine test programmers for the paving jobs. There are two major features of the Marshall method of designing mixes namely,

i) Density-voids analysis
ii) Stability-flow test.

The stability of the mix is defined as a maximum load carried by a compacted specimen at a standard test temperature of 60⁰C. The flow is measured as the deformation in units of 0.25mm between no load and maximum load carried by the specimen during stability test. In this test an attempt is made to obtain optimum binder content for the aggregate mix type and traffic intensity.