Geochemical and Engineering Properties of Selected Lateritic Deposits in Akure Metropolis as Highway Subgrade Foundation Material

Abstract

Laterite occurrences at three locations in Akure metropolis, Ondo State, southwestern Nigeria were characterized geochemically and geotechnically in order to evaluate their potentials as subgrade and subbase/base civil engineering foundation material. The geochemical analysis employed X-ray fluorescence and Atomic Absorption Spectrophotometer (AAS) to determine the major and minor oxide geochemistry while particle size analysis, Atterberg limit test, compaction test, specific gravity, triaxial compression test and California bearing ratio were determined following the British Standard (BS-1337). Abundances of major elements show that SiO2 (50.44 - 58.82%), Fe2O3 (18.34 – 24.41%), Al2O3 (16.30 – 53.82%) constitute over 95% of the bulk chemical compositions. Other constituents include Na2O3, k2O and TiO2. Although notable disparities exist in the SiO2  and Fe2O3  contents of the samples, as the LC2 samples are more siliceous and ferrous than others. The silica: sesquioxide ratio (Se) of the samples are generally less than 1.33 indicating true laterite. Geotechnically, the in-situ derived LC 2 samples have distinctive characteristics in terms of compaction, consistencies, and CBR as they satisfied the Federal Ministry of Works and Housing recommended liquid limits of 50% maximum, plastic limits of 30%, plasticity index of 20% for subbase and base materials; while LC 1 and LC 3 are characterized by values higher than FMWH specification This also corroborates AASHTO classification which rates samples in LC 1 and 3 as fair to poor (i.e. A-7), and LC 2 as excellent to good subgrade (A-2-4/A-2-4). Thus LC 2 samples are suitable for subbase and base foundation materials, while LC 1 and LC 3 for them to be suitable as foundation material would require stabilization, to improve their density and compaction characteristics using conventional lime, cement, and asphaltic stabilization.