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This paper presents experience gained in the evaluation of pavement structures in the sub-Saharan region of Africa for the design of rehabilitation and maintenance alternatives. Most of the pavement structures in this region are very light with thin layers of subbase and base materials. The surfaces are sometimes single surface treatments or thin layers of asphaltic concrete. The evaluation of these pavement structures was made using state-of-the art equipment such us FWD equipment and laboratory resilient modulus equipment to test soils and asphalt samples. Backcalculation software such as ELMOD and Modulus 5 was used to characterize the pavement materials. This characterization was supplemented with laboratory tests of resilient modulus characteristics of soil and asphalt concrete samples.
This paper discusses the limitations and advantages of backcalculation software and how the backcalculated moduli compared with a laboratory measured resilient moduli of undisturbed samples. This comparison is also used to evaluate the correction factor (C=0.33) included in the AASHTO DARWin software. This correction factor reduces the backcalculated subgrade MRin the determination of the required structural number for the design.
Comparison of test procedures AASHTO T294-94, SHRP P46 and a variation of the P46 protocol, which uses grouting to secure the loading plates to the sample, is also included in the paper. Based on the above comparison, a practical procedure for routine testing of resilient modulus of soil samples is proposed. Design of the rehabilitations was done using the AASHTO DARWin software and mechanistic analysis. Comparison of these two methods of design is presented in the paper with practical recommendations for their use.
resilient modulus, back calculation, dynamic cone penetrometer mechanistic analysis
Senior Pavement Specialist, Wilbur Smith Associates, Columbia, S.C.
Ghana Highway Authority, Accra,