The characterization of Rice Husk Ash (RHA) was carried out using conventional chemical analysis and instrumental techniques. Chemical analysis reveals that RHA contains mainly silica along with minor inorganic oxides. Phase analysis by X-ray diffraction (XRD) indicates the presence of quartz, crystobalite and anorthite, while micro structural features obtained from Scanning Electron Microscopy (SEM) shows that RHA particles are highly porous and honeycombed structure. Thermal analysis indicates the presence of surface moisture. A wide range of particles (0.001-0.100 mm) are present in the sample with 59% below the size of 0.05 mm. However after characterization, utilization of RHA as a potential cost effective ingredient in developing a variety of construction materials (e.g. building brick, insulating brick and pozzolana cement) have been examined. The results obtained are very promising.

Organic Polymer carboxymethyl cellulose (CMC) (0.25, 0.50 and 1.5% solution) was incorporated in Ordinary Portland Cement (OPC) and its effect on compressive strength, setting time, porosity, corrosive resistance, density and water absorbance have been studied. Organic polymer retards the setting time and a small increase in compressive strength was observed after 90 days for 0.5% CMC. Addition of polymer has been found to be effective in improving the acid resistance of OPC. Interaction of CMC with OPC causes decrease in water absorption, porosity and chemically bound water. X-ray diffraction of OPC-CMC pastes after 4 months and 1 year display some new peaks as well as disappearance of few peaks showing interaction of CMC with hydrated cementitious pastes. Examination of microstructure reveals that fibre types of matters were formed in hardened cement paste.

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Various physico-chemical properties such as particle size distribution, specific gravity, specific surface area, chemical composition, solubility of Fly Ash (FA) in NaOH and pozzolanic activity of fly ash towards lime have been investigated. Chemical analysis of FAreveals that the FA used in this present investigation belongs to class F type of fly ash. XRD investigation of FA depicts the presence of crystalline mullite and quartz phases. Pozzolanic activity of fly ash was investigated by pH and electrical conductivity measurement, by determining the amount of calcium reacted with fly ash and by the amount of Insoluble Residue (IR) observed in FA-lime paste. XRD investigation of ash-lime paste identified the Calcium Silicate Hydrate (C-S-H) phase. The results obtained from these studies suggested that fly ash possesses pozzolanic activity. Key words: Pozzolanic activity; Fly ash (FA); Rice husk ash; Ordinary Portland Cement (OPC); Insoluble residue (IR); Calcium hydroxide (CH); Calcium silicate hydrate (C-S-H); Kinetics; XRD. DOI: 10.3329/bjsir.v45i4.7326 Bangladesh J. Sci. Ind. Res. 45(4), 303-308, 2010