PRP f2w
Rice husk ash when mixed with lime, gives a black cement. It can also be mixed with
Portland cement and 28 day strength upto 55 MPa can be obtained. Rice husk ash cements
containing not more than 20 per cent of lime are acid-resisting. To improve its reactive properties
the rice husk ash should be ground in ball mills for about one hour. Concrete produced with
rice husk ash display low permeability and no bleeding at all. The major drawback of rice husk
ash is that it is very strong absorbent of sodium, potassium and other ions which are good
conductors of electricity. It can replace cement in mortars by 30 per cent.
The rice husk mixed with 20-50% hydrated lime is ground in a ball mill to produce ASHMOH,
a hydrated binder suitable for masonry, foundation and general concerting. When rice husk is
mixed with cement instead of lime, the hydraulic binder is termed as ASHMENT.
Rice husk ash can also be used with lime sludge obtained from sugar refineries. The dried
lime sludge is mixed with an equal amount of crushed rice husk. It is then mixed with water
and tennis ball size cakes are prepared and sun-dried. The cakes so prepared are fired to
produce powder which can be used as a hydraulic binder.
Rice husk ash when mixed with soil (20 per cent), instead of lime sludge, produces excellent
binding properties. This binder when used as 30 per cent in mixture with Portland cement
gives the properties of Portland puzzolana cement.
iigsi
- What is puzzolana? How is it classified?
- Name different artificial puzzolanas. What are the properties of puzzolana?
State the uses for which different puzzolanas can be considered. - Write short notes on
(a) Fly ash (b) Surkhi
(c) Blast furnance slag (d) Rice husk ash - Discuss briefly the various effects of adding puzzolanas to cement concrete.
- What are the conditions mainly accentuating the puzzolanas to become active?
- Write short notes on
(a) Puzzolanic activity (b) Silica fume
(c) Calcinid clay puzzolana.
yftigsi2i2 isyx
- Which of the following is not true with regards to replacement of cement partly by
puzzolana in making concrete?
(a) Impermeable concrete at later ages
(b) More resistance to sulphate attack
(c) Reduction in bleeding and segregation
(d) Reduction in setting time. - Which of the following is not natural puzzolana?
(a) Volcanic tuff (b) Diatomaceous earth
(c) Surkhi (d) Rhenish