Clinker petrography has long been used in the examination of clinker materials. ASTM 1356M [2] provides guidance in phase abundance analysis using a microscopical point-count procedure. The advantages of optical microscopy (OM) over chemical analyses are that it provides direct examination of the clinker, characterization of both phase composition and texture, and a rapid, relatively simple method for estimating the phase volume fraction via point count analysis. Procedures for preparation and examination of clinker may be found in Campbell [3].