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.