Microstructure and reactivity of rich husk ash

Rice husk ash (RHA) is bio-organic nano SiO₂ produced by controlled burning of rice husk and has high pozzolanic activity. The present paper is aimed at revealing the origin of high specific surface area and high pozzolanic activity of RHA by exploring its structure at micro and nano level. Rice husk calcined at 500, 600, 700 and 800 °C, was tested for compressive strength and X-ray diffraction (XRD) analysis while Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM) analysis were carried out on selected samples of RHA. From the XRD analysis and compressive strength test results, it can be concluded that the optimum combustion temperature for obtaining highly reactive RHA is 600 °C. SEM and TEM images showed that RHA has three layered structure i.e. inner, outer and interfacial with honeycombed and interstitial pores. These pores are actually the main reason for very large specific surface area and very high chemical activity of RHA.