Reliability Estimate of Strength Characteristics of Black Cotton Soil Pavement Sub-Base stabilized with Bagasse Ash and Cement Kiln Dust

Abstract

Reliability of estimates of strength characteristic values from laboratory results for specimens compacted at the energy levels of British Standard Light (BSL), WestAfrican Standard (WAS) and British Standard Heavy (BSH)for compacted bagasse ash treated black cotton soil using cement kiln dust (CKD) as an activator was developed by incorporating data obtained fromUnconfined compressive strength(UCS) test gotten from the laboratory test to produce a predictive model. Data obtained were incorporated into a FORTRAN-basedfirst-order reliability program to obtain reliability index values. variable factors such as water content relative tooptimum (WRO), hydraulic modulus (HM), bagasse ash (BA), cement kiln dust (CKD), Tri-calcium silicate (C₃S), Di-calcium silicate(C₂S), and maximum dry density (MDD)do not produced acceptable safety index value of1.0 at the three energy levels namely BSL, WAS and BSH compactive effort at coefficient of variation (COV) ranges of 10-100% for the Unconfined compressive strength but they produces acceptable safety index value at the three energy level at coefficient of variation (COV) ranges of 10-100% for both California bearing ratio and resistance to loss in strength. Observed trends indicate that for unconfined compressive strength WRO, HM, CKD and MDD is greatly influenced by the COV and therefore must be strictly controlled in CKD/BA treated black cotton and California bearing ratio indicate that theCKD, C3S, C2S and MDD is greatly influenced by the COV and therefore must be strictly controlled in CKD/BA treated black cotton while for resistance to loss in strength indicate that theWRO, CKD, C3S, C2S and MDD is greatly influenced by the COV and therefore must be strictly controlled in CKD/BA treated black cotton. Stochastically, none ofthe compactive efforts can be used to model the 7 days unconfined compressive strength of compacted CKD/BA treated black cotton soil as a sub-base material for road pavement at all COV range because the safety index are lower than the acceptable 1.0 value. All the compactive effort, BSL, WAS and BSH compactive efforts can be used to model both California bearing ratio and resistance to loss in strength of compacted CKD/LBWA treated black cotton soil as sub-base material for road pavement at the variable ranges of COV between 10-100% at BSL, WAS and BSH compactive efforts respectively. Finally, care must be taken in ensuring that the compactive efforts required to produce successful safety index are carefully monitored during the construction.

Keywords: Compaction, Compactor weight, Hydraulic Modulus, BagasseAsh, Black Cotton Soil, Cement Kiln Dust, ReliabilityAnalysis, Reliability Index, Unconfined Compressive Strength.