B.B. Pandey

SELECTION OF GENETIC ALGORITHM PARAMETERS FOR BACKCALCULATION OF PAVEMENT MODULI

In the context of pavement evaluation, backcalculation is the process of estimation of elastic properties of pavement layers using measured structural responses. A number of backcalculation programs are available for estimating effective pavement layer moduli from surface deflections. Different optimization techniques have been used in the development of these backcalculation models. Genetic algorithm (GA) has been used successfully in the recent past for backcalculation of pavement layer moduli. Selection of appropriate GA parameters is important for the efficient performance of the GA-based algorithm. However, there are no general guidelines available at present for the selection of GA parameters. This paper presents a study conducted for the selection of optimal GA parameters to be adopted for backcalculation of pavement layer moduli. The parameters have been selected on the basis of the level of accuracy desired and the corresponding computational effort (CE). The performance of the GA-based program with the selected parameters was evaluated using some hypothetical and field problems.

FLEXURAL FATIGUE CHARACTERISTICS OF ASPHALT CONCRETE WITH CRUMB RUBBER

The paper describes an investigation on fatigue of Asphalt Concrete modified by addition of crumb rubber as a pan of aggregates. Flexural fatigue tests on Asphalt Concrete and Rubber Modified Asphalt Concrete conducted at 20. 25 and 30°C under constant strain mode indicated that the fatigue life of Rubber Modified Asphalt Concrete is significantly higher than that of the plain Asphalt Concrete. Design charts are presented to show that the pavement with Rubber Modified Asphalt Concrete requires a lower design thickness.

Evolution of Non-standard Bituminous Mix—A Study on Indian Specification

In India, the aggregate gradation of bituminous mixes and acceptable limits of mix design parameters have evolved through experience in construction and performance. Emphasis, generally, is on the maximum attainable density and strength parameters. However, in view of the fact that pavement failure due to fatigue cracking is predominantly observed in bituminous roads in India, it is necessary to develop or revise suitable specifications for bituminous mixes so that the mixes have high fatigue strength while satisfying the Marshall stability requirement. The present work reports a comparative study of the engineering parameters of various bituminous mixes with aggregate gradations that are different from those recommended in the Ministry of Surface Transport (MOST) specifications for bituminous concrete (BC). New mix specifications for BC have been proposed in this paper, which showed better performance than the conventional gradation without compromising with the Marshall stability and other mix volumetric requirements. A model table is presented to show the economy in terms of reduction of design thickness of pavement compared to the conventional BC mix.

An investigation on cell-filled pavements

This paper describes the findings of a study carried out for investigating the structural behaviour of different types of cell-filled pavements. The main objective of the present study is to investigate the behaviour of pavements constructed by filling the cells with (a) cement concrete (b) soil cement and (c) sand cement laid over two different types of sub-bases (moorum and soil cement). A formwork of cells of thin recycled plastic sheets was used to construct cell-filled pavements, which function as cast-in situ interlocked block pavements. A loaded truck was used to apply about 1500 load passes on test sections for the purpose of conditioning the pavement sections before structural evaluation. Surface deflections were measured using a falling weight deflectometer and resilient moduli of pavement layers were estimated from the measured deflections. A comparison of costs of different types of cell-filled pavements with those of traditional flexible and rigid pavements designed for low traffic volumes indicates that cell-filled pavements are cost-effective compared with conventional pavements, particularly in locations with scarcity of aggregates.

Evaluation of rehabilitated urban recycled asphalt pavement

Recycling of pavements is a relatively new technique for India and is gaining popularity in recent times due to several merits the technique has over conventional pavement rehabilitation techniques. The first recycling work of flexible pavements in India was undertaken a decade ago and since then the option of milling and recycling of bituminous layers has been adopted in some parts of urban and high-volume roads in India. However, no research studies were conducted on these works. Foamed bitumen recycled pavement work, which was undertaken on some urban roads of Kolkata city in India, has been reported in this paper. Detailed investigations conducted on the milling and foamed bitumen recycling work have been presented in this paper. Laboratory investigation was carried out on the milled and recycled material. Field evaluation of the pavements was done before and after rehabilitation using falling weight deflectometer. Results indicate that foamed bitumen recycling is a very promising alternative to rehabilitate bituminous pavements and to address the concern of conservation of energy and natural resources.

ANALYTICAL DESIGN CRITERIA FOR VILLAGE ROADS IN INDIA

Pavement condition data collected from several sections of village roads were correlated with analytical structural response of pavements for developing a performance-based rutting criterion. Laboratory tests were carried out to obtain the design parameters, and a computer program was used for layered elastic analysis of pavement structure. Charts were prepared for design of village road pavements with a reliability level of 50 percent.