Life Cycle Cost Analysis of Overlay for an Urban Road In

IJRET : International Journal of Research in Engineering and Technology
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  IJRET: International Journal of Research in Engineering and Technology   eISSN: 2319-1163 | pISSN: 2321-7308   __________________________________________________________________________________________ IC-RICE Conference Issue | Nov-2013, Available @  167 LIFE CYCLE COST ANALYSIS OF OVERLAY FOR AN URBAN ROAD IN BANGALORE   Preethi.S 1 , Radhakrishna 2 , Raghavendra Prasad 3   1 PG Student, 2  Associate Professor, 3  Research Scholar, Department of Civil Engineering, R. V. College of Engineering,  R. V. Vidyaniketan Post, Mysore Road, Bangalore 560059, India Abstract Pavements are subjected to severe condition of stresses and weathering effects from the day they are constructed and opened to traffic mainly due to its fatigue behavior and environmental effects. Therefore, pavement rehabilitation is one of the most important components of entire road systems. This paper highlights the design of concrete pavement with added mono fibers like polypropylene, steel and hybrid fibres for a widened portion of existing concrete pavement and various overlay alternatives for an existing bituminous pavement in an urban road in Bangalore. Along with this, Life cycle cost analyses at these sections are done by Net Present Value (NPV) method to identify the most feasible option. The results show that though the initial cost of construction of concrete overlay is high, over a period of time it prove to be better than the bituminous overlay considering the whole life cycle cost. The economic analysis also indicates that, out of the three fibre options, hybrid reinforced concrete would be economical without compromising the performance of the pavement.  Keywords: -  Fatigue, Life cycle cost analysis, Net Present Value method, Overlay, Rehabilitation --------------------------------------------------------------------***---------------------------------------------------------------------- 1. INTRODUCTION Road network in India has grown exponentially from 0.4 million km in 1951 to 3.32 million km presently with increase in motor vehicles from 0.3 million in 1951 to 108 million in 2008 [1]. Due to this gigantic increase in traffic load, its intensity, tire pressure, inadequate design of pavement thickness and ill-drained effects, highway engineers are finding themselves at a great disadvantage in keeping pavements in a traffic- worthy state. The scarcity of resources for the road sector in the past has lead to the adoption of stage wise construction strategies with a short design period [2]. Therefore road construction in our country will be a never ending process, with pavement strengthening to be a major activity for many years to come. An overlay is a layer of suitable thickness provided on top of an existing pavement to improve its structural adequacy and riding quality. The two principal options for overlay in terms of specification of binder are [3]: ã   Flexible overlay, consisting of granular layers and bituminous layers ã   Cement concrete overlay Cement concrete overlay on top of an existing bituminous surface is commonly known as white-topping. White-topping based on thickness and bonding conditions are again classified as: Conventional white-topping : thickness range : 200-300 mm, Thin white-topping : thickness range : 100-200 mm and Ultra thin white-topping : thickness range : 50-100 mm. Overlay practice in India:  In India, the most common strategy for pavement maintenance and rehabilitation was to provide bituminous overlays on existing black topped surface. This was mainly due to abundant supply of bitumen, in addition to the comfort levels of construction methods among engineers. In recent times all these advantages are reversed and petroleum industry is using refined processing technology leading to reduction in the production of bitumen thereby increasing imports [4, 5]. The rapid developments in concrete material technology and mechanization are favoring concrete overlays as a sustainable option. A typical mix proportion of concrete overlays by taking into consideration polypropylene fiber, mineral admixtures like fly-ash, granulated blast furnace slag, silica fume have shown increase in density of concrete due to particle packing theory [6]. 2. OBJECTIVES & SCOPE OF THE STUDY The main objective of the research is to study the structural adequacy of existing pavement and to design the overlay alternatives along with cost evaluation of each alternative. 3. DATA ACQUISITION   3.1 Stretch Selected The stretch selected is located in eastern part of Bangalore city and acts as a link between NH-4 (Old Madras road) on north western side and Old Airport road on south western side as shown in Figure 1. This is one of the busiest stretches in the city. The traffic in the area chosen was moderately dispersed  IJRET: International Journal of Research in Engineering and Technology   eISSN: 2319-1163 | pISSN: 2321-7308   __________________________________________________________________________________________ IC-RICE Conference Issue | Nov-2013, Available @  168 at all times of the day, since the either side of corridor is populated with establishments like HAL, BEML limited, Bagmane Tech park, HAL engine division etc. The road is 2 lane with a total length of about 3.8 km in which 2.7 km is rigid pavement and the remaining 1.1 km is flexible pavement as shown in Figure 2. 3.2 Benkelman Beam Deflection Study Surface deflections of existing flexible pavements are usually measured by Falling Weight Deflectometer (FWD) and Benkelman Beam Deflection test (BBD). A good correlation strength was obtained between FWD and BBD values in a study done by Jundhare.D.R [9] on conventional white-topping of 320 mm thickness. Benkelman beam deflection study was done on the stretch, and the characteristic deflection obtained was 1.67 mm. 3.3 Traffic Data For the design purpose, analysis is being made on the number of commercial vehicles of laden weight having 3 Tons or more. From traffic analysis, the commercial vehicles per day obtained for section 1 and section 2 was 1146 cvpd and 982 cpvd respectively. Fig 1:  Map showing the selected stretch Fig2:  Different pavement sections in the selected stretch 4. DESIGN OF SECTIONS Design of flexible overlay has been done as per IRC:81-1997 using Benkelman Beam Deflection value and traffic in msa [6]. Rigid overlay design has been done as the same procedure for new pavement given in IRC: 58-2002 [7]. White-topping design is done as per IRC: SP: 76-2008 [8]. 4.1. Section 1: Widening of Concrete Road Existing single lane concrete road was to be widened on either side. Concrete pavement combined with fibres where used for this. Fiber reinforced concrete (FRC) is mixtures of cement concrete containing short discrete, uniformly dispersed and randomly oriented suitable fibrous material which increases its structural integrity. The amount of fibers added to concrete mix is measured as percentage of the total volume of composites. Aspect ratio (l/d) is calculated by dividing fiber length (l) by its diameter (d).The types of fibres used for the design along with the flexural strength and obtained thickness is given in Table 1. Table 1:  Thickness of concrete with different fibers Concrete Flexural strength ,MPa Thickness obtained, mm Plain 4.62 290 Polyproplyene 4.762 280 Steel 5.129 270 Hybrid 5.54 250  IJRET: International Journal of Research in Engineering and Technology   eISSN: 2319-1163 | pISSN: 2321-7308   __________________________________________________________________________________________ IC-RICE Conference Issue | Nov-2013, Available @  169 4.2 Section 2: Flexible Pavement The existing flexible pavement has developed distresses like rutting. So overlay has to be provided as a rehabilitation strategy. Flexible or concrete overlay can be provided over the bituminous surface. 4.2.1 Design of Flexible Overlay Based on Benkelman Beam deflection data and commercial vehicles per day using IRC-81, the thickness of flexible overlay has been found out to as 150 mm BM. The thickness deduced is the overlay thickness in terms of BM construction. The equivalent overlay thickness to be provided can b determined using equivalency factors. So the total individual thicknesses obtained are: BC thickness: 40 mm and DBM thickness: 65 mm 4.2.2 Design of Thin White-Topping Thin white-topping design is carried as per IRC; SP: 76-2008 and IRC: 58-2002. The thickness obtained was about 200 mm. The cumulative fatigue life consumed is less than 1. Hence design life is safe from fatigue consideration. Total of temperature warping stress and highest axle load stress = 21.98 kg/cm2, which is less than 45kg/cm2, the flexural strength. 5. ECONOMIC EVALUATION The alternative methods of strengthening or repairing of roads should be based on their durability rather purely by initial cost. The cost comparison for such alternative strengthening/repair methods should be based on the concept of life-cycle cost analysis 5.1 Life Cycle Cost Analysis between Different Types of Fibres in Concrete for Section 1 In Section 1 the existing concrete pavement has to be widened with addition of fibres to enhance its performance. The quantity of work item involved in section 1 per km length is given in Table 2. Table 2:  Quantities of work item involved per km length In the present analysis the rates considered are Rs. 5191/ Cum for control concrete, Rs. 376/kg for polypropylene fibre, Rs. 140/kg for concrete with steel fibre. Inorder to obtain flexural strength of 4.762 MPa for polypropylene fibre reinforced concrete, the percentage of recron 3s fibre used was 0.036% (900g/cum of concrete). Therefore its cost will be Rs. 5529/ Cum. Similarly cost of steel and hybrid fibre concrete was found out to be Rs. 8691/ Cum and Rs. 9029.4/ Cum respectively. Traffic volume survey was conducted at stretch 1 and the volume of commercial vehicles obtained is given in Table 3. Table 3:  Traffic volume obtained from traffic survey A study made by CRRI, New Delhi on Delhi-Agra (NH-2) found that there will be saving of 14% in fuel on concrete road as compared to bituminous road for commercial vehicles [9]. The parameters considered for life cycle cost analysis by Net Present Value method is given in Table 4. Control concrete (cum) Concrete with polypropylene fibre (cum) Concrete with steel fibre (cum) Concrete with hybrid fibre (cum) Heavy traffic 1160 1120 1080 1000 Type Count Bus 166 HCV 570 MAV 44 LCV 332  IJRET: International Journal of Research in Engineering and Technology   eISSN: 2319-1163 | pISSN: 2321-7308   __________________________________________________________________________________________ IC-RICE Conference Issue | Nov-2013, Available @  170 Table 4:  Parameters considered for analysis of section 1 Commercial Vehicles Per Day 1146 Traffic growth rate 7.50% Inflation 5.00% Diesel Cost Rs.54.21/l Fuel Savings 14.00% Mileage 4kmpl Annual Fuel Savings (Rs) CVPD*365*FuelSavings*Mileage*DieselCost 5.2 Economic Comparison between Flexible and Concrete Overlay for Section 2: It will be assumed that bituminous overlays need following interventions during the analysis period: 10th, 20th years : 50 mm BC + 75 mm DBM for heavy traffic , 40 mm BC + 75 mm DBM for medium traffic [10]. Surface renewals are provided as per MORTH as 25 mm BC once in 5 years. The cost of ordinary repairs as per 2011 price is 2,10,000 Rs/ Km. Quantity of work item involved per km length of road is given in Table 5. Road User Cost: The user cost comprises of vehicle operating costs (VOC), time cost of passengers and commodities in transit and accident costs. In present analysis, only VOC is considered, it being assumed that time costs and accident costs on both types of surfaces are the same [11]. The parameters considered for the analysis is given in Table 6. Table 5:  Quantities of work item involved per km length Periodic renewal once in 5 years Heavy traffic 7000 - 175 - - Overlay once in 10 years Heavy traffic 7000 455 280 - - Table 6:  Parameters considered for analysis Parameter Value CVPD 982 Traffic growth rate 7.5% Inflation 5.00% Diesel cost Rs.54.21/liter Fuel savings 14.00% Mileage 4 kmpl Annual fuel savings (Rs) (cvpd x 365 x fuel savings x mileage x diesel cost) Analysis period 30 years Flexible overlay Tack Coat (sqm) DBM (cum) BC (cum) Concrete M-40 (cum) Thin white topping Heavy traffic 7000 455 280 1400
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