Reaction of rice husk ash with OPC and portlandite

Abstract

Sandwiches made of pelleted rice husk ash (RHA) and an OPC/hydrated lime mixture were immersed in distilled water for 7 and 28 days at 25° and 40 ± 1°C to study interdiffusion occurring during pozzolanic reaction. For this purpose BSE microphotographs and chemical image maps for Si, Ca, K, Na, Fe, Al and S were made across the reaction interface of pellets. Furthermore, porosities of RHA pellets were determined. BSE and Ca maps show the formation of a reaction product layer within the space formerly occupied by RHA. This layer is composed of C-S-H and is thicker in RHA/hydrated lime (125–150 μm) than in RHA/OPC (20–40 μm) pellets after 7 days. Its thickness does not much increase after 7 days. In a fixed time, reaction extends to greater depth at 20°C than 40°C, indicating that the pozzolanic reaction rate is not accelerated by temperature in this range.