Abstract In this study, the effect of chemical and thermal treatment on the pozzolanic properties of rice husk ash (RHA) was investigated. The rice husks were subjected to chemical and thermal treatments. After the chemical treatment, the husks were burned under controlled conditions in order to obtain amorphous silica to be used as a pozzolanic material. Finally the ash obtained was milled in a ball mill to reduce the size of the particles. All the products obtained were characterized in terms of silica content, amorphous character, particle size distribution, and pozzolanic activity. The ash produced after an acid treatment with HCl to the husks produced a high percentage of ash with amorphous silica; high fineness, purity, and pozzolanic activity. The silica obtained was incorporated to cement pastes and concretes to evaluate the mechanical, rheological and durability properties. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)