Overpopulation of infrastructures has resulted in a shortage of resources or raw materials for construction works. So, as alternatives, many artificial raw materials are replacing natural ingredients. Now, we are discussing the alternative of sand. Surkhi is one of the artificial fine aggregate replacing sand.
‘Surkhi’ is a powdered form of over burnt broken brick or clay balls. The name surkhi is derived due to its reddish colour. It shows pozzolanic properties and is composed of about 63 % of silica by weight.
It has various name differing from nation to nation and according to its uses. It can be called surkhi in Hindi, Urdu, Nepali, etc. and brick dust in England or Europe or USA.
Mechanism of manufacturing
In factory; clay containing silica, alumina, lime, oxides of iron, and magnesia is burnt the same as bricks but at a high temperature of about 600° C in a furnace. Then, over burnt product gains reddish like colour. It is after then transferred to mill to grind it into coarsely(like sand) or finely(like cement) powdered form as a requirement. Thus obtained product is surkhi.
( Note: Generally, surkhi is not produced commercially but broken or overburnt bricks from brick factories are used as surkhi after grinding it. So, it is referred to as brick dust in western countries.)
Types of Surkhi
a. Fine Surkhi
This is a finely powered surkhi that is used in place of cement, lime or other binding materials.
Concrete or mortar prepared using fine surkhi as binding material is generally used only for temporary constructions.
b. Coarse Surkhi
This is a coarsely powdered surkhi that is used in place of filling material like sand.
Concrete or mortar prepared using coarse surkhi as filling material is generally used in permanent constructions.
Some of the features are:
a. It contains a high amount of silica.
b. It is a reddish coloured powdery material.
c. It increases its compressive strength, compatibility with time and hydraulicity ( property to set and hardens).
d. It is good binding and filling material having good bond strength, abrasion resistance, durability and thermal resistivity.
a. It can be used as sand in mortar known as Surkhi mortar. It is the mixture of lime/cement, surkhi and water. It is economically accessible too.
b. It can be used as binding material like cement or filling material like sand.
c. As it’s strength increases on more immersion on water, it can be also used for hydro-constructions like constructions in sea, ocean, rivers, blockage, etc.
d. It can be used for plastering of internal walls. External wall plastering is not preferred.
a. Addition of (10- 20) % of quick lime in the clay gives quality surkhi that can give good finishing to the mixture during construction.
b. The alkalis and salt solutions cannot reduce the binding property to some extent.
a. Un-proportion amount of silica-containing clay can cause less cohesion, cracking, shrinking and warping.
b. It cannot resist the long exposure of humidity, weathering, etc.