Rice husk ash (RHA) is produced when rice husks are burned in boilers. Approximately 25% of rice husk mass becomes RHA. RHA has a high silica content and fineness similar to or finer than cement. Concrete containing 10-20% RHA as a partial cement substitute has superior performance characteristics compared to normal concrete. RHA is estimated to be produced at 70 million tons annually worldwide and has applications in high performance concrete, insulation, and construction due to its pozzolanic properties.

1. RICE HUSK ASH

2. Rice husk
• They are the hard protecting coverings of grains of rice.
• It is used as fuel in the boilers for processing of paddy producing energy
through direct combustion and / or by gasification .
• for every 1000 kgs of paddy milled , about 220 kgs ( 22 %) of husk is
produced.

4. Rice hull ash/Rice husk ash
• Combustion of rice hulls affords rice husk ash (RHA).
• Concrete made with RHA as a partial cement substitute to levels of 10% to
20% by weight of cement has superior performance characteristics
compared to normal concrete.
• The fineness of the ash also makes it a very good candidate for sealing fine
cracks in civil structures, where it can penetrate deeper than the
conventional cement sand mixture.

5. • When burnt completely, the ash can have a Blaine no. of as much as 3,600
compared to the Blaine no. of cement between 2,800 to 3,000, meaning it is finer
than cement.
• RHA is about 25% by weight of rice husk when burnt in boilers. It is estimated
that about 70 million tones of RHA is produced annually worldwide.
• So for every 1000 kgs of paddy milled , about 220 kgs ( 22 % ) of husk is produced
, and when this husk is burnt in the boilers , about 55 kgs ( 25 % ) of RHA is
generated.

6. X-rayspectrumof RHA

7. Chemical composition
The rice husk ash possesses a chemical composition similar to many of the
organic fibre.
 Cellulose
 Lignin
 Hemi cellulose
 SiO2
 holocellulose

9. Production
 Winnowing
It used to separate the rice from hulls, is to put the whole rice into a pan and
throw it into the air while the wind blows. The light hulls are blown away
while the heavy rice fall back into the pan.
 Burning
Rice husk is produced by burning rice husk between 600-700 0c
temperatures for 2 hours.

10. Winnowing Procedure

12. Types of burning process
 On field burning
Produce poor quality of rice hush ash and also it has low reactivity.
 Fluidized -bed furnace burning
 This is a controlled method of burning the rice husk.
 The combustion heat of rice husk is used for the generation of electricity.

13.  Industrial furnace
 This is more environmental and economical method of burning
 The efficient combustion will give a silica content of 90-95%.

14. When Mixed with concrete…
 The heat of hydration is reduced this results in drying shrinkage and durability of
concrete.
 Reduction in permeability of concrete results in the disintegration of concrete
structure.
 Resistance against chloride and sulphate attack.
 Reduce the failure of RCC beam.

15. Applications
 High performance concrete
 Insulator
 Green concrete
 Bathroom floors
 Industrial factory flooring
 Concreting the foundation
 Swimming pools
 Water proofing and rehabilitation

16. TECHNICAL SPECIFICATIONS :
SiO2 – Silica 85 % minimum
Humidity 2 % maximum
Particle size 25 microns
Color Grey
Loss on ignition at 800°C 4 % maximum
pH value 8
Properties

17. Advantages
 Improves compressive strength ,flexural strength and split tensile strength
of concrete when mixed with RHA.
 RHA mixed with concrete shows better bond strength as compared to
OPC concrete.
• RHA makes a role to increase resistance to chemical reactions.
• RHA would result in a reduction of the cost of concrete construction,
• Reduction of the environmental greenhouse effects.

18. Disadvantages
• Suitable incinerator /Furner as well as grinding method is required for burning
and grding rice husk in order to obtain good quality ash
• Transportation problem
• Unburnt RHA is not suitable for concrete production.

19. THANK YOU