Rice Husk Testing
Rice husk ash as a partial replacement of cement in high strength concrete containing micro silica: Evaluating durability and mechanical properties.
Rice husk is an agricultural residue which accounts for 20% of the 649.7 million tons of rice produced annually worldwide1. The produced partially burnt husk from the milling plants when used as a fuel also contributes to pollution and efforts are being made to overcome this environmental issue by utilizing this material as a supplementary cementing material2. The chemical composition of rice husk is found to vary from one sample to another due to the differences in the type of paddy, crop year, climate and geographical conditions3.
Burning the husk under controlled temperature below 800 °C can produce ash with silica mainly in amorphous form3-5. Recently, Nair et al.6 reported an investigation on the pozzolanic activity of RHA by using various techniques in order to verify the effect of incineration temperature and burning duration. He stated that the samples burnt at 500 or 700 °C and burned for more than 12 hours produced ashes with high reactivity with no significant amount of crystalline material. The short burning durations (15 - 360 minutes) resulted in high carbon content for the produced RHA even with high incinerating temperatures of 500 to 700 °C. A state-of-the-art report on rice husk ash (RHA) was published by Mehta7 in 1992, and contains a review of physical and chemical properties of RHA, the effect of incineration conditions on the pozzolanic characteristics of the ash, and a summary of the research findings from several countries on the use of RHA as a supplementary cementing pozzolanic material.
- Concrete materials
Concrete mixtures to be examined were made in the laboratory using the following materials: cement, gravel, plasticizer, rice husk ash, sand, and MS powder.
The shahrekord type II cement was used as the main binding material in this reaserach work, which is sulphate resistance with average heat of hydration; its specifications are tabulated in Table 1 . The grading and physical properties are in conformity with the requirements necessitated by standard specifications of ASTM C 150 (Standard Specification for Portland cement).
- Micro silica (MS)
Amorphous silica is beneficial as filler to improve the interface transition zone and to produce more dense concrete , , . Merits of micro-silica addition can be categorized by production of high strength concretes, exothermic rate reduction, more corrosion resistance, increase sustained strength of concrete permeated with chloride ions and sulphates in the range of 2–4 times, less permeability, more durability, and less interaction between alkali cement with aggregates. Micro-silica tends to more strength. The amount of micro-silica offer more quality and strength by about 10–15% replacement percentage instead of cement.
- Rice husk ash (RHA)
RHA generally referred to an agricultural by-product of burning husk under controlled temperature of below 800 °C. The process produces about 25% ash containing 85% to 90% amorphous silica plus about 5% alumina, which makes it highly pozzolanic. “Study conducted by Mehta  indicated that concrete with RHA required more water for a given consistency due to its absorptive character of the cellular RHA particles.
Rice dust is formed during the processing of rice grain at a rice-processing plant as a result of the discharge upon the receipt of raw rice from vehicles, removal of impurities, sorting by size, during separation of membranes, crushing, grinding, polishing, moving grain along the elevators and conveyors, etc., i.e. during all technological operations of the rice groats production.