Investigations on the interfacial zone between aggregate and portland slag cement paste

The composition and structure of the interfacial zone between aggregate and portland slag cement paste as well as the orientation coefficient of portlandite (ICH) have been studied by means of XRD and SEM. The results show that the main components in the interfacial zone are C-S-H gel, portlandite and AFt as well as unhydrated clinder particles. Compared with portland cement, there are more C-S-H gel and less portlandite in the zone and the portlandite crystallizes badly with lower ICH in a narrower region. After adding 5.0% silica fume to the cement, the orientation of portlandite in the zone disappears; after 90d, the bond strength between #425 portland slag cement paste and aggregate approximately attains that between #525 portland ciment paste and aggregate.