COMPARATIVE ANALYSIS OF CRUSHABILITY OF SELECTED ROCKS FOR PREDICTING AGGREGATES QUALITY IN EKITI AND ONDO STATES NIGERIA

Abstract

In this research, Bond work index also known as crushability work index was used in predicting aggregate quality of selected rock samples. Samples of granite gneiss, porphyritic granite (L1), charnockitic rock and porphyritic granite (L2) from Itaji-Ekiti State, Ikere-Ekiti State, Akure-Ondo State and Itaogbolu-Ondo State respectively; all in south western Nigeria were tested for hardness (aggregate crushing value, ACV and aggregate impact value, AIV), soundness and water absorption. The crushability work index of these samples was also determined. The crushability work index of the granite gneiss was found to be 13.72kWh/t, that of the porphyritic granite (L2) 12.76kWh/t and that of the porphyritic granite (L1) and charnockite rock were found to be 13.64kWh/t and 17.12kWh/t respectively. In order to predict aggregate quality, crushability work index (Wi) of samples were correlated with aggregate crushing value (Xacv) and aggregate impact value (Xaiv), soundness (Xs) and water absorption (Xwa). The best correlation was found between crushability work index (Wi) and aggregate crushing value (Xacv) according to equation Wi= -71.7ln(Xacv) + 251.4 with correlation coefficient (Racv) of 0.98. Hence, the crushability work index values ranging between 0-7kWh/t, 7-10kWh/t, 10-14kWh/t, 14-18kWh/t and >18kWh/t were acknowledged as ‘very easy’, ‘easy’, ‘medium’, ‘difficult’ and ‘very difficult’ respectively, in ability to resist crushing. From these results, the resistances of the selected samples to crushing were observed to range between “medium” for granite gneiss, porphyritic granite (L2) and porphyritic granite (L1) to “difficult” for charnockite rock which has the best strength properties for aggregate production. In essence, aggregates falling within the ‘medium’, ‘difficult’ and ‘very difficult’ classification in ability to resist crushing are qualified for use in flexible road pavement