INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 6308 ISSN 0976 6308 (Print) ISSN 0976 6316(Online) Volume 4, Issue 2, March - April (2013), pp. 208-214 IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2013): 5.3277 (Calculated by GISI) www.jifactor.com IJCIET IAEME GRADING SYSTEM IN PAVING BITUMEN AN INDIAN SCENARIO Apparao G 1*, Rajesh G 2, Gopala Raju S.S.S.V 1 1 Civil Engineering Department, GITAM University, Hyderabad-502329 2 Assistant Manager, AARVEE Associates, Hyderabad. - 500072 ABSTRACT In India almost 90 per cent road network is occupied by bituminous pavements only. Because bitumen is extensively used as the binding material and it prevents water penetrating in to the structures. That to a rapid rate of development in every aspect of life and it was dominated by construction boom, it resulted in increased traffic volumes, pavement temperatures and higher than the design load magnitude; leads to the failure of bituminous pavements. In fact, there is a huge gap in India between proper characterization of bitumen and its execution in the industries true to the specifications and the aspirational planning of creation of important public assets in the road sector whose durability and serviceability is very important socioeconomic improvement of the country. This paper gives an overview of paving bitumen grading system, characterization and the new viscosity graded (VG) bitumen specifications has been compared with the old penetration graded bitumen specification. KEY WORDS: Bitumen, Flexible Pavements, Viscosity gardening, and Penetration. 1.0 INTRODUCTION In India Viscosity Grading (VG) system has b e e n adopted for paving bitumen since 2006. And at the same time, the Bureau of Indian Standards has issued IS 73:2006 paving bitumen specification (Third Revision), which specifies paving bitumen by viscosity at 60 C and 135 C rather than the old system of grading paving bitumen by penetration at 25 C. But still in the specifications given in the Ministry of Road Transport and Highways (MoRTH), so called orange book, does not revise its highway specifications related to base and surface of bituminous grading. This paper gives an idea of characterization of bitumen, merits and demerits of penetration and viscosity grading systems, and need to be changes incorporated in the Ministry of Road Transport and Highways (MoRTH) specifications. 208
2.0 CHARACTERIZATION OF BITUMEN Bitumen is available in variety of types and grades. To judge the suitability of bitumen binders are most commonly characterized by their physical properties rather than its chemical properties. For engineering and construction purposes, normally three physical properties of bitumen are important; 2.1 Consistency Consistency is the term used to measure its degree of stiffness a b i l i t y t o f l o w. Bitumen is thermoplastic material which means it liquefy when heated and solidify when cooled and its state of solidness (stiffness) or liquidness (i.e., ability to flow) is very much temperature sensitive. Consistency of bitumen can be judged by some empirical tests such as penetration, softening point, ductility etc. and also by testing the fundamental property of bitumen such as viscosity. 2.2 Purity Pure bitumen is completely soluble in solvents like carbon disulphide and carbon tetrachloride. Hence any impurity in bitumen in the form of inert minerals, carbon etc. could be quantitatively analysed by dissolving the samples of bitumen in any of the above mentioned solvent. 2.3 Safety Bitumen materials leave out volatiles at temperatures depending upon their grade. These volatiles catch fire causing a flash. The definition of flash and fire points as given by the Indian standards are as follows: The flash point of a material is the lowest temperature at which the vapour of a substance momentarily takes fire in the form of a flash under specified condition of test. The fire point is the lowest temperature at which the material gets ignited and burns under specified conditions of test. Thus, it can be concluded that there is no point to grade bitumen on purity and safety aspect. It is the consistency property of bitumen by which it can be graded. 3.0 OVERVIEW OF BITUMEN GRADING IN INDIA The first Indian standard on the bitumen was first published in 1950 as Specification for asphaltic bitumen and fluxed native asphalt for road making purpose : IS 73 which was revised in 1961 to change the grades of material and incorporate the methods of test as per IS 1201 to IS 1220:1958 Methods for testing tar and bitumen. In the first revision, the grades of fluxed native asphalt were deleted and essentially the paving grades were included. Based on the revised methods of test in IS 1201 to IS 1220:1978 Methods for testing tar and bituminous materials (first revision) and the additional data that had become available, second revision was prepared in 1992. In this third revision (IS: 73-2006) grading of bitumen s is changed from penetration grade to viscosity grade. The variability in performance at high temperatures can be addressed by adopting a viscositygraded bitumen specification (based on viscosity at 60 C) in lieu of the current penetrationgraded specification (based on penetration at 25 C). Since the viscosity-graded bitumen specification has a requirement of minimum viscosity at 135 C, it will also be helpful in minimizing the tender mix problems in the field. 209
Adoption of viscosity-graded paving bitumen specification will also reduce the number of total tests to 7, which will reduce the cost of testing bitumen. This will result from eliminating empirical tests/parameters such as penetration ratio, paraffin wax content, and Fraass breaking point without compromising the quality of bitumen. Since high penetration values are desirable for pavement durability, requirement for a minimum penetration value is adequate and has been retained in the viscosity-graded specification. Specifying a maximum value for penetration is undesirable and will reject some good quality bitumen s unreasonably. 3.1 Grading Systems Bituminous binders are most commonly characterized by their physical properties. The challenge in physical property characterization is to develop physical tests that can satisfactorily characterize key asphalt binder parameters and how these parameters change throughout the life of an HMA pavement. Rather than refer to an extensive list of its physical properties, asphalt binders are typically categorized by one or more shorthand grading systems. These systems range from simple penetration grading to complex Superpave performance grading and represent an evolution in the ability to characterize asphalt binder. 3.1.1 Penetration Grading The penetration grading system was developed in the early 1900s to characterize the consistency of semi-solid asphalts. Grading of bitumen by penetration test at 25 C was adopted by the American Society for Testing and Materials (ASTM) Committee D04 on Road and Paving Materials in 1903. To quantify the Penetration grading the following asphalt concrete characteristics are to be evaluated as per the standard IS: 73-1992; Penetration depth of a 100 g needle; 25 C Flash point, C Softening point C Penetration ratio Ductility at 25 C, cm Paraffin wax content Fraass breaking point Solubility in trichloroethylene Loss on heating (TFOT) Retained penetration after Thin Film Oven Test (TFTO) Viscosity at 60 C and 135 C Water content Specific gravity at 27 C Penetration grading basic assumption is that the less viscous the asphalt, the deeper the needle will penetrate. This penetration depth is empirically correlated with asphalt binder performance. Therefore, asphalt binders with high penetration numbers (called "soft") are used for cold climates while asphalt binders with low penetration numbers (called "hard") are used for warm climates. 210
In figure 1, there are three, bitumen A, B & C whose penetration at 25 o c is same i.e., 65. But these bitumen are having different stiffness values at higher (say 60 o C) temperature and at lower (say 4 o c) temperature The slope of the stiffness Vs. temperature curve is called temperature susceptibility. Steeper is the slope, more will be the temperature susceptibility of the bitumen. In fig 1, bitumen C is most temperature susceptible, in other words more prone to rutting at high temperature and more prone to cracking at low temperatures (sue to higher stiffness) compares to bitumen B and A. Figure 1: Three 60-70 penetration grade bitumen s with different stiffness s at high and low service temperatures 3.1.2 Viscosity grade In the early 1960s an improved asphalt grading system was developed that incorporated a rational scientific viscosity test. This scientific test replaced the empirical penetration test as the key asphalt binder characterization. To quantify the Viscosity grading the following asphalt concrete characteristics are evaluated based on the as per IS: 73-2006; Absolute viscosity at 60 C, poises Kinematic viscosity at 135 C, cst Flash point Solubility in trichloroethylene Penetration depth of a 100 g needle; 25 C Softening point Tests on residue from thin film oven tests/rtfot; viscosity ratio at 60 C and Ductility at 25 C, cm 211
Viscosity is defined as inverse of fluidity. Viscosity thus defines the fluid property of bituminous material. Viscosity is the general term for consistency and it is measure of resistance to flow. Many researchers believe that grading of bitumen should be by absolute viscosity in it s instead of the conventional penetration units. By measuring consistency at three different penetration, the range (minimum and maximum temperatures (Figure 2) and specifying the ranges, values) for absolute viscosity at 60 o c, and the slope of temperatures Vs. stiffness curve i.e., the temperature susceptibility of bitumen can be bound in a specified range which is the key for better performances. Minimum value for kinematic viscosity at 135 o c have been specified, which are more rotational. As per given the in the table 1 the specifications of the Indian standard which is IS: 73-2006 needs to be modified shortly. Defining the range (minimum and maximum values) for penetration at 25 0 C, minimum value for absolute viscosity at 60 0 C, and minimum value for kinematic viscosity at 135 0 C, the temperature susceptibility of bitumen can be controlled in a better way towards better performance. However, in ASTM D 3381 specification for viscosity graded asphalt binders, the minimum value only for penetration, the range (minimum and maximum values) for absolute viscosity at 60oc, and the minimum value for kinematic viscosity at 135oc have been specified, which are more rotational. As per given the in the table 1 the specifications of the Indian standard which is IS: 73-2006 needs to be modified shortly. Figure 2: Graphical representation of viscosity-graded AC-30 (VG-30) bitumen 212
Table 1: Requirements for Paving Bitumen as per IS: 73-2006 Characteristics VG-10 VG-20 VG-30 VG-40 Absolute viscosity, 60 C, poises, min 800 1600 2400 3200 Kinematic viscosity, 135 C, cst, min 250 300 350 400 Flash point, C, min 220 220 220 220 Solubility in trichloroethylene, %, min 99.0 99.0 99.0 99.0 Penetration at 25 C 80-100 60-80 50-70 40-60 Softening point, C, min 40 45 47 50 Tests on residue from thin film oven test/rtfot: Viscosity ratio at 60 C, max 4.0 4.0 4.0 4.0 Ductility at 25 C, cm, min, after thin film oven test 75 50 40 25 4.0 CONCLUSIONS The existing penetration grading system of bitumen has been replaced by viscosity grading system in India based on improvement in the durability and serviceability condition of the desired extent. For this, issues regarding improvement of the specification and also manufacturing of bitumen true to that specification need to be addressed. In view of modification and improvement of the current specification of IS : 73 (specification for paving grade bitumen), sample of bitumen are being collected from all over the country in Indian Institutes, which are going through rigorous testing. In the specifications for the road and bridge works (fourth revision) addressed by the MoRTH for section 500 which is guidelines for base and surface course of bituminous layers given based on the penetration grading only. Though in the recent revision, these specifications have been revised as per viscosity grading. 5.0 REFERENCES 1. SSSV Gopala Raju (2007), Reuse of polyethylene waste in road construction, Journal of Environmental Science and Engineering, Vol.49, No.1, pp.67-70 2. SSSV Gopala Raju(2010), Utilization of building waste in road construction, Indian Journal of Science and Technology, Vol.3, No.8,pp. 894-896 3. Prithvi Singh Kandhal, P.S (2007), An overview of the viscosity grading system adopted in India for paving bitumen Indian Highways. 4. Rajib Chattaraj (2011) Bitumen Grading system from penetration grading to viscosity grading A step towards better quality control, INDIAN HIGHWAYS 5. MoRTH (Ministry of Road Transport and Highways) (2001). Specification for Road and Bridge Works. Indian Roads Congress, New Delhi, Section 500, Bases and surface courses for bitumen. 6. Kandhal, P. S (2005), Selection of Bitumen for Paving Highways, Indian Roads Congress, Indian Highways 213
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