Assessing the aptitude of vesicular volcanic rocks as pozzolanic sources for supplementary cementitious materials

摘要

The research was conducted to verify two vesicular basalt deposits identified for pozzolanic sources. These are Wejerat site, in southern Tigray, which has been the major source of vesicular basalt for cement production, and Adisherafo site found near Hagerselam, central Tigray. Rock samples were collected from both sites to undergo major oxides analysis, possolanacity tests and compressive strength measurements of 2 and 28days, as well as mineralogical examinations on polished surfaces and thin sections. Field surveys and sample observations revealed the presence of varieties of vesicular, scoriaceous, doleritic, porphyritic and Aphanitic basalts, in decreasing order of vesicularity. The Adisherafo site has dominantly vesicular basalt intermingled with intravolcanic diatomite units. The Wejerat vesicular basalts are best fit for pozzolan source with mean 2 and 28days compressive strength of 14.9 and 34.0MPa, exceeding the minimum limits of 10.0 and 32.5MPa, respectively. Their mean [OH-] and [CaO] values in the pozzolanicity test are 43.0 and 11.4mmol/l, respectively, falling on the pozzolanic area of the Frattini curve. Dolerite samples turned out to be promising sources in all tests. The scoriaceous as well as Adisherafo's vesicular basalt and diatomite units show marginal pozzolanic characteristics. The total sum of oxides (SiO2+Al2O3+Fe2O3) minimum 70%, is met with samples from all but the weathered basalt unit. The research has indicated the effect of the texture and mineral constituents on the pozzolanic charactertics of volcanic rocks as well as the importance of relying on more methods than conventional ones to characterize pozzolanic materials.