Bitumen Concrete Mix Design Using Cement and Phosphogypsum as Filler Materials

— Fillers play an important role in engineering properties of bituminous paving mixes. Conventionally stone dust, cement and lime are used as fillers. An attempt has been made in this investigation to assess the influence of non-conventional and cheap fillers such as phosphogypsum (which is a waste product generated for phosphoric acid industries in large quantities discussed later) in combination with cement in asphalt paving mixes. It has been observed as a result of this study that asphalt mixes with these non-conventional fillers result in satisfactory Marshall Properties though requiring a bit higher bitumen content, thus substantiating the need for its use. The fillers used in this investigation are likely to solve the problem of solid waste disposal of the environment to a very large extent. In this study we have worked out the optimum percentage of cement and phosphogypsum to be mixed in bitumen which gives best results in Marshall Stability Test. The combination of both optimum values are then taken to prepare the Asphalt mix for paving flexible pavements. The various results obtained live upto the expectations and are tabulated later on.


INTRODUCTION
Construction of highway involves huge outlay of investment. A precise engineering design may save considerable investment; as well as reliable performance of the in-service highway can be achieved. Two things are of major considerations in this regardpavement design and the mix design. The study emphasizes on the mix design considerations. A good design of bituminous mix is expected to result in a mix which is adequately strong, durable and resistive to fatigue and permanent deformation and at the same time environment friendly and economical. A mix designer tries to achieve these requirements through a number of tests on the mix with varied proportions of material combinations and finalizes the best one. This often involves a balance between mutually conflicting parameters. Bitumen mix design is a delicate balancing act among the proportions of various aggregate sizes and bitumen content. For a given aggregate gradation, the optimum filler content (Phosphogypsum and cement) content is estimated by satisfying a number of mix design parameters.

II. NEED OF STUDY
The need of study lies in the fact that millions of tones of Phosphogypsum is generated every year as a waste in phosphoric acid industries, the disposal of which is a major problem. Blending phosphogypsum with bitumen to be used in asphalt brings the solution to this problem of waste disposal.

III. METHOD AND MATERIALS
The materials used in this study work along with their desired characteristics are stated under. The gradation aggregates used in this project are as per IRC grading 2 as given in the following:

Penetration Test:
The consistency of bitumen cement is measured by the penetration test.A weighted needle (100 g) is allowed to bear on the surface of a dish of bitumen of standard test temperature (770 F) for a given length of time (5 sec). The depth of penetration of needle into the bitumen is termed as the penetration of the bitumen and is measured in units of 0.1mm.The needle penetrates farther into soft bitumen than into the harder grades, and thus the lower the penetration, the harder the bitumen. The test performed to check the penetration value of bitumen is tabulated as under:

2.Specific Gravity
Specific gravity is used to calculate voids in the compacted bituminous mix and to adjust quantities in mixture. Specific gravity of bitumen is found to be 1.05 by balance method.

Specific gravity of Filler
Two fillers are being used in this study namely cement (Gr.-43) and Phosphogypsum. The specific gravity of cement is found to be 3.15 and that of phosphogypsum is found to be 2.4 by pycnometer method.

Specific Gravity of Aggregate
The specific gravity of aggregates was found to be 2.67.
The results of various tests performed on the materials are tabulated as under:

Marshall Stability Test:
The objective of bituminous paving mix design is to develop an economical blend of aggregates and bitumen. In the developing of this blend the designer needs to consider both the first cost and the life cycle cost of the project.
Considering only the first cost may result in a higher life cycle cost. Marshall Method of mix design has been adopted in this study. Accordingly aggregates with the grading 2 of IRC and bitumen 60/70 having properties as described in the preceding paragraphs have been used.
In this method, the resistance to plastic deformation of a compacted cylindrical specimen of a bituminous mixture is measured when the specimen is loaded diametrically at a deformation rate of 50mm/minute. The two major features of Marshall Method are Density Void Analysis and Stability Flow Test.
The marshall stability of mix is defined as the maximum load carried by the specimen at a standard test temperature of 60ºC. The flow value is the deformation that the test specimen undergoes during loading upto maximum load. Flow is measured in 0.25 mm units. In this test, an attempt is made to obtain optimum binder content for the type of aggregate mix used.

Marshall Test Data Compilation:
Type of Grading aggregate = B Mixing Temperature = 60ºC Number of blows = 75 Grade of Bitumen VG 30 Compaction temperature 27ºC  /dx.doi.org/10.22161/ijaers.76.36  ISSN: 2349-6495(P) | 2456-1908(O) Bituminous mixes containing marble dust as filler displayed maximum stability at 6% content of bitumen, having an increasing trend upto 6% and then gradually decreasing. The unit weight/bulk density also displayed a similar trend with flow value being satisfactory at 6% content of bitumen. 2. Bituminous mixes containing OPC as filler displayed maximum stability at 1.5% content of bitumen having an increasing trend upto 1.5% and then gradually 3. Bituminous mixes containing phosphogypsum as filler showed maximum stability at 8% bitumen content displaying an ascending trend up till 8% and then decreasing, the flow value showed an increasing trend and similar was the trend shown by unit weight or bulk density, the percentage of air voids obtained were seen to be decreasing with increase in bitumen content thus from here we can say that 8% bitumen content, satisfactory results are obtained.

Results of Marshall
4. The combination of these above two results is considered and results are summarized in Table 5. These results are clearly better.
5. From the above discussion it is evident that phosphogypsum generated as waste material can be utilized effectively in making of bitumen concrete mixes for paving purposes.
6. Further modification in design mixes can result in utilization of phosphogypsum as filler in bituminous pavement thus solving the waste material disposal substantially resulting in utilization of industrial space being consumed in disposal of industrial wastes.
7. Though stone dust being conventional filler however marble dust can be utilized in its place effectively thus solving the waste material disposal substantially resulting in utilizing of industrial space being consumed in disposal of industrial wastes.
8. The cost effectiveness of these non conventional filler specimens can be realized after performing a cost analysis of these non-conventional materials against the conventional specimens resulting in reduction of the construction cost considerably.
9. It is evident that with further tests phosphogypsum generated as waste material can be utilized effectively in making of bitumen concrete mixes for paving purpose.