Rice Husk Ash (RHA)
Before we talk about ash of rice husk, we must first identify rice plant. One of the plants that absorb silica from the soil and assimilate it into its structure during growth is rice plant. The outer covering of the grain of rice plant has a high concentration of silica and it is called rice husk. Moreover, the husk of rice is produced in millions of tons per year as a waste in agriculture and industrial processes. Furthermore, it contributes about 20% of its weight to rice husk ash (RHA) after incineration. In addition, the threshing of the grain of rice result to what is called rice husk ash.
The controlled burning of rice husk produces a highly pozzolanic material product called rice husk ash. This high Pozzolanic reactivity is attributed to its non-crystalline silica and high specific surface area. According to (Zhang et al., 1996), The use of ash from rice husk in lime Pozzolanic mixes could be suitable for partly replacement for Portland cement.
Chemistry of Rice Husk Ash.
Rice husk ash (RHA) reacts with cement in concrete when mixed to form a binder. This is due to its Pozzolanic properties. When a siliceous or aluminous material gets in touch with calcium hydroxide in the presence of humidity, a Pozzolanic reaction occurs. This occurrence leads to the formation of compounds tha exhibiting cementitious properties. These properties result from cement hydration development. More also, the calcium silicate hydrate and calcium hydroxide (Ca (OH2) are released within the hydration of two main component of cement. Namely, tricalcium silicate. The following are chemical representations of the two components.
- 2(3Cao. Sio2) + 6H2O =3Cao.2Sio23H + 3Ca(OH)2
- 2(2Cao. Sio2) + 4H2O = 3Cao.3H2O + Ca(OH)2
The C-S-H gel generated by the hydration in equation 1 and 2 above is the main strengthen constituent.
Benefits And Effects of Rice Husk Ash(RHA) in Concrete.
The study of rice husk ash (RHA) shows that it has a salient physical and chemical properties. More also, the result got from the controlled burning of rice husk at a controlled temperature has eventually contributed to the quality of concrete. Research shows that the grinding of RHA for high-quality production requires particle size of 5cm – 10cm. Therefore, the incorporation of RHA into concrete production has the following benefits
- Substantial reduction in alkali-silica and sulphate expansion
- Higher compressive strength
- Reduction in the heat of hydration
- Higher abrasion
- Substantial reduction in concrete weight.
Effects of rice husk ash on the properties of concrete.
- It causes a reduction in the weight of concrete
- Addition of it in concrete production reduces strength.
- It increases workability on the bases of the water-cement ratio used.