Rice Husk Ash

Abstract

IntroductionRice-husk (RH) is an agricultural by-product material. It constitutes about 20 % of the weight of rice. It contains about 50 % cellulose, 25-30 % lignin, and 15-20 % of silica. When rice-husk is burnt rice-husk ash (RHA) is generated. On burning, cellulose and lignin are removed leaving behind silica ash. The controlled temperature and environment of burning yields better quality of rice-husk ash as its particle size and specific surface area are dependent on burning condition. For every 1000 kg of paddy milled, about 200 kg (20 %) of husk is produced, and when this husk is burnt in the boilers, about 50 kg (25 %) of RHA is generated. Completely burnt rice-husk is grey to white in color, while partially burnt ricehusk ash is blackish [1][2][3].Rice-husk ash (RHA) is a very fine pozzolanic material. The utilization of rice husk ash as a pozzolanic material in cement and concrete provides several advantages, such as improved strength and durability properties, reduced materials costs due to cement savings, and environmental benefits related to the disposal of waste materials and to reduced carbon dioxide emissions. Reactivity of RHA is attributed to its high content of amorphous silica, and to its very large surface area governed by the porous structure of the particles [1,2]. Generally, reactivity is favored also by increasing fineness of the pozzolanic material. However, Mehta [1] has argued that grinding of RHA to a high degree of fineness should be avoided, since it derives its pozzolanic activity mainly from the internal surface area of the particles. ProductionRice is the seed of the monocot plants Oryza sativa or Oryzaglaberrima. As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East and South Asia, the Middle East, Latin America, and the West Indies. It is the grain with the second-highest worldwide production, after corn.

Rice Husk Ash in Concrete

“…The mills are typically larger, and disposal of the husks is a big problem. Rice husks are the coating of the seeds or grains of the rice plant to protect the seeds from physical damage and attacks by pathogens, insects, and pests during the growing season, and are separated from the grains during milling process [12]. During the milling process, the husk is removed from the grain to make brown rice; the brown rice is then further milled to remove the brown layer and become white rice [12].…”

“…Well-burned and well-ground RHA is very active and greatly improves the strength and durability of cement and concrete. This pozzolanic material with good and consistent properties can only be obtained by burning the rice husks under precisely defined conditions [12].…”

“…Therefore, the type of silica formed after rice husk combustion is determined by the temperature and duration of the process. According to the literature, burning rice husks at temperatures ranging from 400 • C to 1100 • C produces RHA with high pozzolanic activity that remains in the amorphous or crystalline silica form [12,23,[26][27][28].…”

“…According to the Food and Agricultural Organization's rice market monitor, the global rice paddy field forecast for 2021/22 is 714.2 million tons, which equates to approximately 142.84 million tons of rice husks [11]. When burned, each ton of paddy field yields about 0.2 tons of rice husks, which yields about 0.05 tons of rice hull ash (RHA), which contains a significant amount of silica and thus contributes to pozzolanic activity [12]. For this reason, RHA can be used as a supplementary cementitious material with a color range of white, grey, and black depending on the raw material source, mode of incineration, and duration and temperature of burning [13,14].…”

Development of a High Strength Geopolymer Incorporating Quarry Waste Diabase Mud (DM) and Ground Granulated Blast-Furnace Slag (GGBS)

“…Geopolymers are alkali-activated aluminosilicates, integrating silica-rich industrial byproducts and wastes that are activated using alkaline solutions such as NaOH, potassium hydroxide and calcium hydroxide among others [ 1 , 11 ]. In addition to industrial byproducts such as fly ash (FA), metakaolin (MK), silica fume (SF) and ground granulated blast-furnace slag (GGBS), which have been most commonly used as partial cement replacement in concrete technology, geopolymer mixtures can incorporate additional types of wastes such as waste clay brick powder [ 1 , 12 ], glass polishing waste [ 1 , 13 ], palm oil fuel ash (POFA) [ 14 ] and even rice husk [ 1 ], a silica-rich waste material, abundantly available in all rice producing countries [ 15 , 16 ]. Previous research studies have denoted the potential of geopolymer mixtures to reach higher compressive strengths than conventional concrete [ 17 ] and possess fracture energy comparable to cement concrete [ 14 , 18 ] as well as superior durability [ 19 ].…”