ANALYSIS AND DESIGN OF PAVEMENTS FOR HEAVY VEHICLES

Abstract

The transportation by roads is most preferred mode of transportation by the people and industries due to maximum flexibility in speed of travel, direction, route and time. India, having roads network of over 4.2 million km of roads, is at second position after the U.S.A. in the world. To achieve higher economic growth there is need of efficient roads infrastructure. India having only 2% length of national highways of the total roads network carrying about 40% traffic. Because of lack of roads infrastructure, the goods and people do not reach the destination in time. To reach the destination in time is possible through efficient roads infrastructure network. Realizing the need for efficient road infrastructure networks, the Govt. of India has launched most ambitious National Highway Development Plan (NHDP). NHDP consist of major projects like Golden Quadrilateral (GQ) (6000 km, phase-I), North-South and East-West Corridors (7300 km, phase-II), High Density Corridors of NH to give connection to ports and State capitals, (10,000 km, phase-III), All remaining NH to be made 2 lanes (Phase-IV), Expressways (1000 km, Phase-V), widening of G.Q roads project from 4 lane to 6 lane (Phase-VI), constructing by passes and bridges up to 2012 (Phase-VII). Therefore, it is quite clear from above discussion that we still need of large length of roads network. Generally pavements are of two types on the basis of structural behavior. These are flexible pavements and rigid pavements. Construction of pavements cost about approximately 50% of the project cost. Therefore, careful right choice of pavement is necessary on some national basis. This will result in saving of enormous amount of money. From the recent studies by various researchers, it has been proved that rigid pavements are economical to flexible pavement. The initial construction cost of cement concrete roads are higher by 10 to 20% over flexible pavements but life cycle cost of cement concrete are lower than for the flexible pavements. Realizing the advantages of rigid pavements like smooth riding, saving in fuel, longer design life and less maintenance compared to flexible pavements etc., many developed countries have already constructed long stretches of concrete roads. Seeing the advantages of concrete pavements, about 30% length of new pavements of Golden ii Quadrilateral under NHDP has been constructed with concrete pavements and about 15% in NSEW corridors. Delhi – Matura road, Mumbai Pune expressway, Indore bypass and Yamuna expressways have been constructed with cement concrete. Generally, in construction of all rigid pavements, the concrete of grades M30 or M40 have been used on a sub base of dry lean concrete. The pavements thickness range from 30 to 35 cm or oven more. With the invention of plasticizer and super plasticizer, the concretes of much higher strength are being developed. According to IS:456, the concrete strength equal to or greater than 60 MPa are known as high strength concrete. The interest in using high strength high performance concrete is continuously increasing. It is being used in the areas of buildings and bridges most frequently. Generally, HSHPC is being used for patch repair and damaged sections of rigid pavements. In India, HSHPC has not been used as full depth of pavements. According to Henry Russel, ACI defines high performance concrete as concrete that meets special performance and uniformity requirements that cannot always be achieved routinely by using only conventional materials and normal mixing, placing and curing practices. The requirements may involve enhancement of placement and compaction without segregation, long term mechanical properties, early age strength, toughness, volume stability or service life in severe environments. India comes under developing nation. Being developing nation, many infrastructure projects are under implementation and more infrastructure projects to be implemented in future. These infrastructure projects require the movement of people and goods from one place to another place as early as possible. Because of these infrastructure projects, to reach the goods and people to their destination with safety and economically, there is continuously growing number of heavy vehicles and also the size and weight of heavy vehicles. These heavy vehicles cause consumption of fatigue life of normal pavements and lead to early rehabilitation. A heavy vehicle is a vehicle that has a gross vehicle mass (GVM) or aggregate trailer mass (ATM) of more than 45 kN and a combination that includes a vehicle with a GVM or ATM of more than 45 kN, as per Heavy Vehicle National law of Australia. As per Societe de i’ Assurance Automobile du Quebec (SAAQ), Canada, any road vehicle or combination of road vehicles with a gross vehicle weight rating (GVWR) of 45 kN or more is considered a iii heavy vehicles. The GVWR of vehicle include its maximum load capacity and net mass of vehicle as per manufacturer specifications. GVWR = Net Mass of Vehicle + Maximum Load Capacity By using HSHPC, it will not only reduce the design thickness of pavements compared to normal strength concrete but could also design the pavements for longer design period due to higher durability and impermeability. This will result in lower life cycle cost compared to flexible pavements. Today’s need is concrete pavements of longer design life more than 40 years and should be durable. All the above goals could be achieved by using HSHPC in concrete pavements. The cost of HSHPC per m3 is higher than the normal strength concrete. But due to thinning of the pavements and longer design life will offset the increase in cost. During the investigations, HSHPC of grade M60 with fly ash has been used. Due to much higher load carrying capacity and high durability of HSHPC, the HSHPC pavement could be recommended for heavy duty pavement and longer design period. The flexural strength and fatigue properties of HSHPC are quite high, which are essential parameters from the point of pavement performance. Therefore, it is essential to examine the structural behavior of high strength high performance concrete pavement. Also the load at first crack, crack patterns, formation of cracks, crack propagation and crack width and ultimate load carrying capacity of HSHPC pavements under varying loads and loading positions needs to be studied. Therefore, the present experimental study on high strength high performance concrete (HSHPC) pavement has been carried out with the objective whether the existing theoretical methods of analysis could be used or there is need to develop a suitable design approach for the analysis of stresses and deflections in HSHPC pavements. The local materials, which were used in development of mix design, were tested. Fine aggregate having F.M. 2.89, coarse aggregate having F.M. 6.7, 11% fly ash having fineness 3500 cm2/gm and specific gravity 2.24, by weight of cement and 1.6% super plasticizer Sikament-N (modified naphthalene formaldehyde sulphonate) by weight of cement were used in development of design mix of grade M60 on trial basis. Then the design mix of grade M60 was developed using fly ash on trial basis. Finally the design mix ratio came out as 1:1.1:1.9 (cement: F.A.: CA). The water cement ratio was 0.29. To assess suitability of HSHPC mixes for laying highway pavements, different tests were iv carried out. For this purpose, cubes of dimensions 150 mm were prepared for finding out compressive strength, 150 mm diameter and 300 mm height cylindrical specimens for determination of modulus of elasticity and beams of dimensions 100 mm x 100 mm x 500 mm were prepared for determining flexural strength. All these specimens were prepared as per Indian Standard Code of practice and tested according to IS: 516 – 1959. 7 days and 28 days compressive strength were found to be 46.14 MPa and 70.4 MPa respectively. 7 days and 28 days flexural strength were found to be 4.82 and 6.4 MPa. Modulus of elasticity was found to be 41.7 GPa and slump was found to be 31.67 mm. Poisson’s ratio 0.2 was used in the analysis for finding out stresses, strains and deflections. The subgrade was prepared according to IRC: 15. The soil was compacted at optimum moisture content and dry density. Roorkee soil was classified as A-3 as per U.S.P.R.A. The optimum moisture content was found to be 11% and dry density was found to be 1.92 gm/cm3. The modulus of subgrade reaction was found to be 0.0463 N/mm3 (4.63kg/cm3) and four days soaked CBR value of Roorkee soil was found to be 6%. The poisons ratio and modulus of elasticity of Roorkee soil had been taken for the analysis as 0.305 and 20.96 MPa respectively. By using high strength high performance concrete mix developed in the lab of grade M60 having fly ash 11% and super plasticizer 1.6%, three concrete pavements of size 1800 mm x 1800 mm had been cast with varying thicknesses viz. 160 mm, 200 mm and 240 mm. All the pavements with different thicknesses were cast directly over the compacted subgrade having modulus of subgrade reaction 0.0463 N/mm3 (4.63kg/cm3). To measure the deflections of pavement surface due to loading, mechanical dial gauges with least count 0.01 mm were used. Studs have been fixed with araldite on the surface of the pavement to measure the surface strain with Huggenberger mechanical deformometer. The loading arrangement for applying a static load to the pavement consisted of a 250 kN capacity reaction frame fabricated with steel portal frame and steel girders. The reaction loading frame was mobile for carrying out the plate load test at any position along or across the test pit 2000 mm x 8000 mm in size. The testing was done in test hall of transportation engineering group. All concrete pavements slab were tested for corner, edge and central loading positions. v Wheel load stresses were calculated by Westergaard, Mayerhof’s, Ghosh’s and IRC- 58 methods. For different thicknesses 160 mm, 200 mm and 240 mm pavements of dimensions 1800 mm x 1800 mm. the stresses, strains and deflections were also calculated by analytical technique i.e. Finite Element Method. Stresses calculated through different theories had been compared with the experimentally observed values and stresses obtained through analytical method i.e. FEM. It has been found that stresses obtained through existing theories and through analytical method i.e. FEM are in good agreement with the observed values and can be used successfully in designing of HSHPC pavements. The strains and deflections obtained through FEM are in good agreement with the observed values. Mayerhof’s method can be used in designing of HSHPC pavements with factor of safety 2 to 3. The load carrying capacities of HSHPC pavements at each position are sufficiently high at flexural strength when pavement was laid on compacted subgrade having modulus of subgrade reaction 4.63 kg/cm3. With the increase in thickness, the load carrying capacity at each position increase. 200 mm thick pavement carry sufficiently high load of the order 230 kN at each positions. The existing IRC-37 code could be used for design of flexible pavements for heavy vehicles. But design period should be reduced to corresponding to150 msa. Economic analysis has been carried out and found that life cycle cost analyses of HSHPC pavements are lower than the flexible pavements. From the above discussion, it is quite clear that the existing methods for designing of rigid pavements and analytical method i.e. FEM can be used in designing of thickness of HSHPC pavements. By using HSHPC, the thinner pavement can be designed for the same traffic. Thus there is lots of saving of natural aggregate that will result in less quarrying putting least impact on environment. Hoped that the methodology for the design of HSHPC Pavements and flexible pavements for heavy vehicles will cater the need of pavements where heavy vehicle movements is high, in industrial as well as for construction sites of irrigation structures like dams, power houses etc. and other sites too.