Surkhi,Powdered broken brick (burnt brick) locally called surkhi is used as fine aggregate in lime mortar. Surkhi,Powdered broken brick shall be prepared by finely grinding well burnt good quality bricks free from under burnt particles of soluble salts, pyrites and adherent coatings of soil or silt. The maximum quantity of clay, fine silt and fine dust present shall not exceed five per cent by weight.
Requirements for Broken Brick (surkhi) fine Aggregate for use in Lime Mortar
|The particle size grading of surkhi for use as aggregate in lime mortar in masonry works shall be within the limits specified in table below as per IS: 3182-1975.|
|IS Sieve designation||Percentage passing(By mass)|
|2.36 mm||90 to 100|
|1.18 mm||70 to 100|
|600 micron||40 to 100|
|300 micron||5 to 70|
|150 micron||0 to 15|
FUNCTIONS OF SURKHI IN MORTAR
Surkhi,Powdered broken brick is used as an adulterant but it imparts strength and hydraulic properties to the mortar. To develop more strength is should be ground very finely with lime in the mortar grinding mill.
Surkhi mortar is a mixture of lime,surkhi and water. It is lime morta in which sand has been substituted by surkhi for economy and strength.
Note:- surkhi is finely powdered burnt clay and genarally made from slightly under burnt bricks. Good surkhi should be perfectly clean and free from any admixture of foreign substances and should not contain particles retained on IS sieve No.9 more than 10% by weight surkhi like sand is largely used in preparation mortar,concrete,plaster etc.. For economic considerations
This type of mortar is prepared by using fully surkhi instead of sand or by replacing half of sand in case of fat lime mortar. The powder of surkhi should be fine enough to pass BIS No. 9 sieve and the residue should not be more than 10% by weight. The surkhi mortar is used for ordinary masonry work of all kinds in foundation and superstructure. But it cannot be used for plastering or pointing since surkhi is likely to disintegrate after some time”