PREPARATION OF SAMPLE FOR MODIFIED BITUMINOUS MIXES

The samples are prepared by adding polyethylene and kerosene with pure bitumen. The amounts of polyethylene and kerosene are added by weight of percentage of pure bitumen separately.

First of all fresh bitumen, without debris and adulterants was collected. The properties of the bitumen were justified. Five bowls for preparing samples was weighed. Hot bitumen was poured in those bowls. The weight of the bitumen was taken. Then polyethylene was weighed with respect to 1%, 2%, 3%, 4%, and 5% weight of the bitumen. The kerosene was also weighed with respect to 1%, 2%, 3%, 4%, and 5% weight of the bitumen. The samples were prepared one after another. At first the bitumen for 1% polyethylene and 1% kerosene content was heated till it fully liquefied and was in a state to dissolve polyethylene and kerosene. The polyethylene bags were gradually left in the bitumen. The softened form of the polyethylene bags was floating on the hot bitumen. But after continuous stirring by steel spoon it was thoroughly mixed with the bitumen. Though the final mixing temperature was not observed but it is assumed that it was near the flash point of the bitumen. There was a little change in the color. This mother sample is kept for further experiments. Thus five samples were prepared with variable polyethylene and kerosene contents. When a test was to be performed the sample was thoroughly heated so that a homogeneous liquid state could be gained and neither precipitation nor floatation nor suspension was observed.

Sample-1. Weight of pure bitumen + 1% polyethylene of pure bitumen + 1% kerosene of pure bitumen (by weight)

Sample-2. Weight of pure bitumen + 2% polyethylene of pure bitumen + 2% kerosene of pure bitumen (by weight)

Sample-3. Weight of pure bitumen + 3% polyethylene of pure bitumen + 3% kerosene of pure bitumen (by weight)

Sample-4. Weight of pure bitumen + 4% polyethylene of pure bitumen + 4% kerosene of pure bitumen (by weight)

Sample-5. Weight of pure bitumen + 5% polyethylene of pure bitumen + 5% kerosene of pure bitumen (by weight).

CHARACTER OF MATERIALS ARE USED IN MODIFIED BITUMINOUS MIXES

Characteristics of Materials used in modified bitumen:

i)          Bitumen

ii)         Polyethylene

i)                    Kerosene

ii)                   Ice

iii)                 Greece

iv)                 Stone aggregate

v)                  Fine aggregate

vi)        Filler materials.

 

Pure Bitumen

i)        Penetration grade: 80/100

ii)       Specific gravity: 1.02

iii)     Ductility value: 100⁺

iv)     Flash point: 290 ⁰C

v)      Fire point: 300 ⁰C

vi)     Softening point: 43 ⁰C

vii)  Solubility: 95.7%

 

Polyethylene

A particular type of polythene bags, transparent in color, mostly representing the low-density polyethylene purchased from the local market is used. Specific gravity of this specimen varies from 0.95 to 0.93.
 

Coarse Aggregate

It was collected from the hump beside Strength of Materials Lab, Transportation Lab, and from site of under construction Computer Science and Engineering building. The white stone aggregate was used with rather mix of black stone. The aggregate was to pass through 20 mm sieve. Other sieves where retained aggregates were collected are   12.5mm, 9.5mm, 4.75mm and 2.36mm.

Fine Aggregate

Fine aggregate of grade 2.36mm passing and retained at 600mm, 300mm, 150mm, and 75 mm. It was collected from the construction site of new student hostel.

Mineral Filler

It was the residuals received after sieving the fine aggregate in the soil lab by mechanical shaker. It was passed through 75mm sieve. 

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.

MIX DESIGN METHOD OF BITUMINOUS MIXES

Various methods of designing the mix proportions of dense bitumen concrete have been evolved. The most widely used methods are the following:

i) The Marshall method.
ii) The Hubbard-field method.
iii) The Hveem method.
iv) The Smith triaxial method

SOLUBILITY TEST OF BITUMINOUS MATERIAL

Pure bitumen is fully soluble in carbon disulphide and carbon tetrachloride. If some quantity remains undissolved it exhibits the quantity of inert mineral present in the bitumen. Bitumen should be soluble in carbon disulphide at least 99%.

FLASH AND FIRE POINT TEST OF BITUMINOUS MATERIAL

Bituminous materials leave out volatiles at high temperatures depending upon their grade. These volatile vapors catch fire causing a flash. This condition is very hazardous and it is therefore essential to determine this temperature for each bitumen grade, so that the paving engineers may restrict the mixing or application temperatures well within the limits. The flash point is the lowest temperatures at which flash occurs due to the ignition of the volatile vapors when a small flame is brought in con tact with the vapors a bituminous product, gradually heated under standardized conditions. As mentioned above, this test is an indication of the critical temperature at and above which suitable precautions should be taken to prevent fire hazards during application. When the bituminous material is further heated to a higher temperature, the material itself catches fire and continues to burn; the lowest temperature causing this condition is the fire point. The fire point is always higher than the flash point of a material. ISI vide specifications I.S: 1209-1258 gives the following definitions.

Flash point-“The flash point of a material is the lowest temperature at which the vapor 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.”

SPECIFIC GRAVITY TEST OF BITUMINOUS MATERIAL

The density of a bituminous binder is a fundamental property frequently used as an aid in classifying the binders for use in paving jobs. In most applications, the bitumen is weighted, but finally in use with aggregate system, the bitumen content is converted in volume basis. Thus an accurate density value is required for conversion of weight to volume. The specific gravity is greatly influenced by the chemical composition of the binder. Increased amounts of aromatic type compounds cause an increase in the specific gravity. The test procedure has been standardized by the ISI.