Acoustic microscopy of portland cement mortar aggregate/paste interfaces

We have demonstrated the use of acoustic microscopy to characterize hydrate d Portland cement microstructure. High frequency (1 GHz) studies identified reaction zones around bubbles, ettringite formation, and effects of aggreg ate composition. Lower frequency images (200-400 MHz) have been used to cha racterize effects of aggregate composition on cement/grain interface. The i nformation obtained from acoustic microscopy complements optical and scanni ng electron microscopy. We demonstrate the importance of acoustic microscop y as an important nondestructive in situ technique for characterization of concrete. A major, unique advantage of the scanning acoustic microscope tec hnique is its capability of penetrating into the material, which allows us to study cracks, defects and other zones of weakness that might be hidden b elow the surface. (C) 2000 Kluwer Academic Publishers.