PETROGRAPHIC AND AGGREGATE-QUALITY STUDIES OF AFIKPO SANDSTONE AND AMASIRI SANDSTONE OUTCROPS IN AFIKPO AREA, SOUTHEASTERN NIGERIA,IN RELATION TO SUITABILITY OF CRUSHED-SANDSTONE AGGREGATES AS HIGHWAY PAVEMENT MATERIALS

Over the years, there is a continued used of sandstone from Afikpo and Amasiri area South-eastern Nigeria for construction purpose even though their mineralogy and strength and durability characteristics were unknown. This research was carried out to properly identify the mineralogical composition of the sandstone samples (petrography) and ascertain their suitability to serve as highway pavement aggregate materials through the physico-mechanical study. Samples used are collected from the AfikpoSandstone (Nkporo Formation) and AmasiriSandstone(Ezeaku Formations) outcrops in South-eastern Nigeria. The collected samples were crushed and thin sections were prepared and viewed under cross polarized and plain polarized microscope to determine their mineralogical composition. Physico-mechanical analysis were also carried out to study their parameters like “Aggregate Crushing Value (ACV), Aggregate Impact Value (AIV), Los Angeles Abrasion Value (LAAV), Water Absorption and Specific Gravity, so as to determine their strength and durability characteristics”. AfikpoSandstone contains monocrystalline quartz, microcline, opaque minerals and Silica minerals (opal/chalcedony). The presence of opal/chalcedony as the silica cementing minerals informed the naming of this sample as siliceous sandstone. However, AmasiriSandstone, observed in the field to have milk-whitish colour, contains angular-“sub rounded monocrystalline and polycrystallinequartzgrains” (Oladejiet al.,) calcite and plagioclase mineral, it is a calcareous sandstone. AmasiriSandstone (Ezeaku Formation) and AfikpoSandstone (Nkporo Formation) have ACV values of 80.95% and 76.95% respectively. Aggregate Impact Value (AIV) are; Afikpo 80.60%, and Amasiri 88.90%, Los Angeles Abrasion Values (LAAV) for AfikpoSandstone is 83.86% and AmasiriSandstoneis 96.94%, water absorption values for AfikpoSandstone is 5.4% while AmasiriSandstone is 5.52%. The specific gravity of AfikpoSandstone 2.78 whereas that of AmasiriSandstone is 2.94. Also, the AfikpoSandstone has bulk density of 2.60Mg/m³ and AmasiriSandstone has its bulk density as 2.75Mg/m³ which is below the acceptable limit. The samples are not suitable to be used as road aggregate because they have poor/weak strength and durability characteristics which is evident in their failure to meet the acceptable standard limits for highway pavement aggregates.