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INTRODUCTION:-The Softening Point of bitumen or tar is the temperature at which the substance attains particular degree of softening. As per IS: 334-1982, it is the temperature in ºC at which a standard ball passes through a sample of bitumen in a mould and falls through a height of 2.5 cm, when heated under water or glycerine at specified conditions of test. The binder should have sufficient fluidity before its applications in road uses. The determination of softening point helps to know the temperature up to which a bituminous binder should be heated for various road use applications. Softening point is determined by ring and ball apparatus.
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APPARATUS:-(i) The ring and ball apparatus consisting of
(a) Steel balls-two numbers each of 9.5 mm diameter weighing 3.5 ± 0.05 g.
(b) Brass rings-two numbers each having depth of 6.4 mm. The inside diameter at bottom and top is 15.9mm and 17.5 mm respectively.
(c) Ball guides to guide the movement of steel balls centrally.
(d) Support -that can hold rings in position and also allows for suspension of a thermometer.
The distance between the bottom of the rings and the top surface of the bottom plate of the support is 25mm.
(i) Thermometer that can read up to 100° C with an accuracy of 0.2° C.
(ii) Bath–heat resistant glass beaker not less than 85 mm in diameter &1220mm deep.
(iii) Stirrer
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PROCEDURE:-(i) Preparation of test sample: Heat the material to a temperature between 75-100° C above its softening point; stir until, it is completely fluid and free from air bubbles and water. If
necessary, filter it through IS sieve 30. Place the rings previously heated to a temperature approximating to that of the molten material, on a metal plate which has been coated with a mixture of equal parts of glycerine and dextrin. After cooling for 30 minutes in air, level the material in the ring by removing the excess material with a warmed, sharp knife.
(ii) Assemble the apparatus with the rings; thermometer and ball guides in position
(iii) Fill the bath with distilled water to a height of 50mm above the upper surface of the rings.
The starting temperature should be 5° C.
Note: Use glycerine in place of water if the softening point is expected to be above 80° C; the starting temperature may be kept 35° C.
(iv) Apply heat to the bath and stir the liquid so that the temperature rises at a uniform rate of 5
± 0.5 °C per minute.
(v) As the temperature increases the bituminous material softens and the balls sink through the rings carrying a portion of the material with it.
(vi) Note the temperature when any of the steel balls with bituminous coating touches the bottom plate.
(vii) Record the temperature when the second ball touches the bottom plate.
The average of the two readings to the nearest 0.5°C is reported as softening point.
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PRECAUTIONS:-(i) Distilled water should be used as the heating medium.
(ii) During the conduct of test the apparatus should not be subjected to vibrations. (iii)The bulb
of the thermometer should be at about the same level as the rings.
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OBSERVATIONS:-•
RESULT:-Softening point of bitumen / tar = 46.4+45.8 /2 =46.1 °C.
Temperature when the ball touches bottom,
°C
1 2
46.4 °C 45.8 °C
5. COMPARISON BETWEEN FLEXIBLE AND RIGID PAVEMENT
Difference between flexible and rigid pavement
6. ROLE OF STABILISATION
Pavement materials include a combination of coarse and fine aggregate with a proportion of a smaller clay/silt -sized particles. The objective is to ensure a final grading matrix that will allow maximum compaction of the product with the least void present. This is to achieve a solid layer that is in part impervious to water infiltration. Pavement materials can be used in different layers of the pavement and requirement of such a layers will be determined by applied load and payment compaction selected by designer.
PROPERTIES FLEXIBLE REGID
DESIGN PRINCIPLE Empirical method based on
load distribution
characteristics of the complements
Designed and analysed by using the elastic theory
MATERIAL Granular material Made of cement concrete either plan, reinforced or prestressed concrete
FLEXURAL STRENGTH Low of negligible flexible strength
NORMAL LOADING Elastic deformation Acts as beam or cantilever EXCESSIVE LOADING Local depression Causes cracks
STRESS Transmits vertical and compressive stresses to the
THE TEMPERATURE No stress is produced Stress is produced FORCE OF FRICTION Less deformation in the
sub-grade is not transferred to the upper layers
Friction force is high
OPENING TO TRAFFIC Road can be used for traffic within 24 hour
For the pavement containing mechan1ically stabilised materials and/or modified materials, the limiting design criteria is the vertical strain at the top of the subgrade. For a stabilised and higher binder content materials, the vertical strain at the top of subgrade is not only design criteria as the fatigue life of cemented material must also be considered. The fatigue life of cemented material is usually the governing criterion.
High-performance quarried materials will likely be obtained from the nearest possible source in order to minimise transport costs. Often, however, imported material may not be sufficiently strong payment design requirements. in such cases, the solution is found in the design of either stronger payment layers or a reduction in the stresses requirement for the layer.one of the most cost effective ways to make the pavement stronger is to modify or a stabilised the pavement material.as an alternative, it is possible to reduce the stress requirement by the stiffening for foundation. Again, this can be done by either modifying are stabilising the foundation
• LIME STABILISATION
Lime stabilisation or modification is used in the road construction to improve the quality of existing material within the construction project. Lime is an effective addictive for plastic soil, improving both workability and a strength. Lime stabilisation can be used to:
modify marginal material to bring it within specification or for performance requirement
increases strength as an alternative to cementetious stabilisation
enhance volumetric stability for various layers of select material
improve surface stability of unsealed road
• CEMENTITIOUS STABILISATION
When stabilising the cement, the working time of the resultant material can be critical. The time available to deliver, incorporate and compact a pavement layer needs to be understood before project commencement. With cement as the only binder, the time for performing placement and compaction process is limited to approximately two-hour from the incorporate of the cement into the moistened payment materials. No rework time is normal provided for. This can be create a demanding schedule with little opportunity for error management on the site.
Cement as the only binder is not often used due to working time restrictions. In addition, higher shrinkage rates can result in an increased cracking tendency. Addition of FA to the binder extends the working life of the stabilised material, allows more time placement in compaction of the material and mitigates risks typically associated with a single cement binder.
7. DESIGN AND COST ANALYSIS OF FLEXIBLE AND RIGID PAVEMENT
The structural capacity of flexible payment is attended by combined action of the different layer of the payment. The load is directly applied on the wearing course and it gets dispread with the depth in base, sub base and subgrade layers and then ultimately to the ground. Since stress induced by traffic load is highest at the top, the quality of top and upper layer of material is better. The subgrade layer is responsible for transferring the load from above layers to the
ground. Flexible payments are design in such a way that the load transmitted to the subgrade does not exceed its bearing capacity. Consequently, the thickness of the layer would vary with CBR of soil and it would affect the cost of pavement.
The thickness design of flexible payment also varies with the amount of traffic. The range of variation in volume at a different highways has direct effect on the repetitions of traffic loads.
The damaging effect of different axle loads is also different. The Indian Road Congress method of flexible pavement design uses the concept of ESAL for the purpose of flexible pavement design and the same has been used in this study also.
DESIGN OF FLEXIBLE PAVEMENT BY GROUP INDEX METHOD
in order to classify the fine grained soil within one group and for judging their suitability as subgrade material, and indexing system has been introduced in HRB classification which is term it as group index. Group index is the function of percentage materials passing through 200 Mesh sieve (0.074 mm), liquid limit and plasticity index of soil and is given by equation:
(0.074 mm). Liquid limit and plasticity index of soil is given by equation:
G.I = 0.2a + 0.005ac + 0.01bd
Here, a = that portion of material passing through0.074 mm sieve, greater than 35 and not exceeding 75%.
b = that portion of material passing through 0.074 mm sieve, greater than 15 and not exceeding 35%.
c = that value of liquid limit in excess of 40 and less than 60
d = that value of plasticity index exceeding 10 and not more than 30 Or, GI = (F-35)0.2 + 0.05(WL-40) + 0.01(F-15) (IP-10) DATA:
F = 66%