Many countries in all over the world
Many countries in all over the world generate a large amount of RHA from uncontrolled and controlled burning. RHA is a pozzolanic material due to this high percentage of SiO2 in RHA. Rice husk ash, as a mineral additive, is produced by burning rice husks, which are obtained in the rice milling industry as agricultural organic wastes during the processing of paddy rice. In the countries, where rice is growth up, about 120million metric tons of RHA are generated annually for removal . China, India, Indonesia and Bangladesh are the major countries where rice is producing in large amounts. When this agricultural organic waste is burned, crystalline or amorphous (non-crystalline) rice husk ash can be produced with respect to temperature and the time of burning. Crystalline RHA is generated at the after burning processes if temperature is higher than 800°C. Therefore at this situation RHA shows poor pozzolanic properties . On the other hand, non-crystalline RHA can be generated with respect to controlled burning of rice husks at the temperature ranged between 500°C and 800°C. A huge amount of amorphous silica content is obtained from non-crystalline RHA , . Because of high SiO2 content, higly pozzolanic reaction is observed with respect to the amorphous RHA. As a result, amorphous RHA is more convenient than crystalline RHA for use in cement Dexamethasone grout. In order to obtain high performance and strength concretes with a suitable fluidity, amorphous RHA has been successfully used , .
RHA is used as a supplementary cementitious material in concrete , , . Previous studies have indicated that up to 20% RHA may be advantageously blended into the mixture without adversely affecting the strength and durability of the resulting concrete . The other studies examining the utilization of rice husk ash (RHA) as a cement replacement have demonstrated that incorporation of RHA in self compacting concrete (SCC) decrease the unit weight, flowability, water absorption, total porosity, compressive strength, ultrasonic pulse velocity, and cost , , , . In addition, some of the researchers investigated the flowing behavior of mortar, paste, and grout with respect to the flow time and flow spread to facilitate the design process of SCC , , , .
Results and discussions Lombardi plate cohesion, mini slump flow diameter and marsh cone flow time of grout samples are shown in Table 2. Moreover the rheological properties including plastic viscosity and yield stress of grout samples are listed in Table 3. The correlation coefficients (R2) obtained from the modified Bingham model are also given in Table 3.
Conclusion The important points of the study was concluded as following;
Introduction Cement concrete is the most widely used material for constructing the various types of structures since it has higher structural stability. Recently, cement replacement of agricultural waste in concrete making process is gained more attention to reduce the CO2 emission during cement manufacturing process as well as solid waste disposal problems . Agriculture waste namely palm oil fuel ash, bagasse ash, wood waste ash, corn cob ash and rice husk ash, etc. The most widely available agricultural waste throughout the world is rice husk and it is burned to produce rice husk ash, which contains high silica in amorphous form. Thus, it is usually referred as pozzolanic material and can be used as supplementary cementitious material for concrete making process , , . India alone produces 31 million tones per annum of rice husk that yields 22 wt% rice husk ash (RHA) while burning. The effective usage of RHA is limited. Recent research reported that the partial replacement of cement reduces the cost and energy requirement of cement manufacturing process , . Ordinary concrete may fail to exhibit the required strength and durability. In such cases, concrete porosity and permeability must be reduced to decrease the rate of penetration of aggressive agents and mitigate the acid and alkali effects of the concrete hence; mineral admixture is used to modify the properties of concrete which can withstand for any situation . It is recognized that addition of pozzolan (RHA) generally improves the durability of concrete especially for sulfate resistance and chloride penetration .