Excerpt from the Study
In an effort to improve the suitability of lateritic soil as a pavement material, the air dried samples were treated with Lime/Bitumen in stepped concentration of 0, 2, 4, 6, 8, 10 % by dry weight of the soil. The preliminary investigation conducted on the natural lateritic soil showed that the soil belongs to the CH group using the Unified Soil Classification System (ASTM, 1992) or A-7-6(14) soil group using the AASHTO soil classification system (AASHTO, 1986). The MDD decreased with higher additive blend as it decreased from 1.67 to 1.49 mg/m3 at 6 % Lime with 6 % Bitumen treatment. The OMC, on the other hand, decreased with higher bitumen content but increases with higher lime content. The decreases may be due to the effect of breakdown of the flocculated aggregates and elimination of large pores. The increase in OMC is as a result of increase in lime content is as a result more water needed to dissociate Ca2+ and OHions to supply Ca2+ for the cation exchange reaction. The OMC value decreases from 13.2 % for the natural soil to a value of 12.3 % at 0% lime with 8% bitumen emulsion. This is in comformity with same trend reported by Hausmann (1990), Stephen (2006), Osinubi et al.(2007a) and Sani (2012). The UCS values showed a sharp increase from 235 to 985, 999 and 1078 kN/m2 at 6 % bitumen emulsion with 6 % lime, 6% bitumen emulsion with 8% lime and 6% bitumen emulsion with 10% lime respectively. The UCS values obtained fell short of 1710 kN/m2 specified by TRRL (1977) as a criterion for adequate stabilization using OPC. The values of 985, 999 and 1078 kN/m2 at 6 % bitumen emulsion plus 6 % lime, 6 % bitumen emulsion plus 8 % lime and 6 % bitumen emulsion plus 10 % lime 66 respectively on the other hand meet the requirement of 687–1373 kN/m2 for sub-base as specified byIngles and Metcalf (1972). The 28 days curing period UCS values obtained showed that the Lime/Bitumen blend had a long time advantage in terms of strength gain. There were tremendous increases in the values of UCS from their natural states. A peak value of 1839 kN/m2 was recorded at 6 % bitumen emulsion with 10 % lime from a natural value of 305 kN/m2 . The CBR value increased with higher additive content to a peak value of 47 % at 8 % bitumen emulsion with 10 % lime. The low value of CBR recorded is as a result of the ingress of water into the specimen which weakened it and reduced its strength. The CBR value obtained did not meet the 80 % value for Base material as recorded by the Nigeria General Specification (1997), but meets the 30 % requirement for sub-base materials specified by the Nigeria General Specification (1997). The resistance to loss in strength increased from 14.5 for the natural to a peak value of 61.25 % at 6 % bitumen emulsion with 2 % lime content. The peak resistance to loss in strength value of 61.25 % fell short of the acceptable 80 % specified by Ola (1974) and Osinubi(1998, 1999). Based on the test results presented, the stabilized soil using bitumen emulsion (MS2) and hydrated lime, meet the specification for mainly sub-base. Therefore, bitumen emulsion stabilization and lime modifications may be employed to improve A7-6 laterite as only fill or sub-base material on very lightly trafficked roads with restriction on the wheel loads.
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