SPECIFIC GRAVITY OF COMPACTED SPECIMEN OF BITUMINOUS MIX

The specific gravity values of the different aggregates, filler and bitumen used are determined first. The theoretical specific gravity G_t of the mix is given by-

 Where,

W₁ = percent by weight of coarse aggregate

                        W₂ = percent by weight of fine aggregate

                        W₃ = percent by weight of mineral filler

                        W₄ = percent by weight of bitumen

                        G₁ = apparent specific gravity of coarse aggregate

                        G₂ = apparent specific gravity of fine aggregate

                        G₃ = apparent specific gravity of mineral filler

            G₄ = apparent specific gravity of bitumen

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 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).