Comparative Evaluation of Dolerite and Syenite as Crushed Stone Aggregate

Abstract

Dolerite and syenite were comparatively studied and evaluated for their potential as crushed stone for civil engineering construction. Properties of the rocks tested included specific gravity, moisture absorption, Schmidt hammer rebound, point-load strength, unconfined compressive strength, Los Angeles abrasion, aggregate crushing value, sodium sulphate soundness, and ultrasound velocity. The thermal heat capacity and coefficient of expansion of the stones were also determined. The rocks had high specific gravity of over 2.75, high compressive strength of 196-256 MPa, high point load index (Is50) of 17-23 MPa and low porosity of 0.27-0.29 % required of good aggregates. However, the rather high moisture absorption and high magnesium sulphate loss of the rocks exceeded the 3 and 18 % considered as the upper limits for good aggregates. This raised concern as to the durability of the rocks under aggressive environment. Also, the ferromagnesian minerals of the dolerite are prone to deteriorate badly under harsh environment. The typically elongate and angular aggregate shape of dolerite aggregate meant poor mix workability and more cement requirement for a given strength than the less angular syenite aggregate.