BITUMEN STABILIZATION OF LATERITE PRETREATED WITH HEAT AS A FLEXIBLE PAVEMENT MATERIAL

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Author

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Department of Engineering

ABSTRACT
The search for an alternative to the conventional way of treating soil for use in road work, informed laterite soil sample classified as A-7-5(11) on AASHTO soil classification system, collected from a borrow pit at Shika, along Zaria-Funtua road in Kaduna State of Nigeria was pretreated with heat and stabilized with bitumen. Sample of the laterite soil subjected to heat treatment at temperatures of 37oC (room temperature), 200oC 400oC and 600oC for one hour each and stabilized with 0, 3, 6 and 9% cutback bitumen, were subjected to Atterberg?s limits test, particle size analysis, California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) tests. Optimum CBR value of 28.52 % corresponding to 44.8 % increase in strength above the value obtained for natural laterite, was obtained when laterite was subjected to heat at a temperature of 400°C for a period of one hour and stabilized with 6 % bitumen. Maximum 7 day UCS value of 417.23 kN/m2 corresponding to 56.6 % increase in strength above value obtained for the natural laterite was obtained when the laterite was subjected to heat at a temperature of 200oC at a period of one hour and stabilized with 3 % bitumen. The highest resistance to loss in strength after 7 days soaking of 24.58% for West Africa Standard Compaction (WASC) energy was obtained when laterite was subjected to heat at a temperature of 200°C for one hour with 3 % bitumen stabilization. This falls below recommended 80% resistance to loss in strength, though, after 4 days soaking. Based on the results obtained, A-7-5(11) laterite soil, pretreated with heat at a temperature of 200°C for a duration of one hour, and stabilized with 3 % bitumen content can be used as subgrade/fill material. Its usage as sub-base or base material will require some further treatment. The results of tests from the study will serve as a guide in the selection of pretreatment temperature for effective and economic stabilization of laterite as flexible pavement materials.