Geo-engineering evaluation of Termaber basalt rock mass for crushed stone aggregate and building stone from Central Ethiopia

Abstract

The geology of the central part of Ethiopia exhibits a variety of rock types that can potentially be developed for construction stone production, of which the most wide spread and important one is the Termaber basalt. Even though some preliminary work is done on these rocks towards construction material application, it remains largely that this resource is untouched and needs further scientific characterization for the use in large scale industrial application. Basaltic rocks have been widely used in many parts of the world as concrete aggregate and dimension stone for various civil structures. The present research study was carried out for Geo-engineering evaluation of Termaber basalt rock mass for crushed stone aggregate and building stone from Central Ethiopia (around Debre Birhan).The main objective of the present research study was to assess the general suitability of the Termaber basalt to be used as coarse aggregate for concrete mix and/or to utilize it as cut stone at industrial level. Only choice made with full knowledge of the basic characteristics of the material, of its performance and durability against the foreseen solicitations will ensure the necessary quality of the stone work and thereby a possibility to reach its intended service life.In order to meet out the objective of the present study, data from both field and laboratory were collected and analyzed. The field data included geological investigations based on different methods and sample collection while the laboratory work included, uniaxial compressive strength, ultrasonic pulse velocity, dynamic elasticity modulus, bulk density, water absorption, specific gravity, open porosity, aggregate impact value, petrographic examination and XRF, aggregate crushing value, Los Angeles abrasion value, sodium sulfate soundness, X-ray diffraction and alkali silica reactivity tests. The field and laboratory data were compiled and compared together to reveal the engineering performance of the rock mass in terms of cut stone and coarse aggregates. The basaltic rock shows a variety of textural and mineralogical characteristics which could affect their physical and mechanical properties as well as their use as construction material. The compressive strength of the basaltic rock ranges from 130MPa to 350MPa, ultrasonic pulse velocity from 4000m/s to 7000m/s, open porosity from 0.33% to 3.08%, bulk density from 2.6g/cm3 to 3.1g/cm3, dynamic elasticity modulus from 64GPa to 129GPa, etc. The petrographic examination also indicated some deleterious constituents within the middle basaltic flow layers however; there are distinct flow layers which could be used as dimension stone and coarse aggregate for concrete and asphalt mix. The field investigation as well as the laboratory tests conducted indicated the high potential of the Termaber basalt formation to be used as construction material with further refining works. The study presented in this paper was carried out on basalts that are widespread in the central highland of Ethiopia and that comprise the major source of local crushed rock aggregates and building stone.