CONTENTS Lime – Preparation of lime mortar – Cement –
Ingredients – Manufacturing process – Types and Grades – Properties of cement and Cement mortar – Hydration – Compressive strength – Tensile strength – Fineness– Soundness and consistency – Setting time – Industrial byproducts – Fly ash – Aggregates – Natural stone aggregates – Crushing strength – Impact strength – Flakiness Index – Elongation Index – Abrasion Resistance – Grading – Sand Bulking.
LIME Lime used in construction is produced from calcium
carbonates in the form of limestone, seashells, coral, kankar, etc
While heating calcium carbonate, (calcination process) carbon dioxide is given off as gas, and the resulting product is calcium oxide or quicklime
CaCO3 + heat → CaO + CO2
SLAKING OF LIME Quicklime is not a stable product. If it is left
exposed to air, it absorbs carbon dioxide from air and reverts back to carbonate
Hence quicklime should be slaked to calcium hydroxide (hydrated lime or slaked lime) as early as possible to make the material stable.
This is done by pouring water over quicklime.
SLAKED LIME /HYDRATE OF LIME It is formed by the absorption of water by quick lime
and is the hydrated oxide of calcium, Ca(OH)2
CaO + H2O → Ca(OH)2
(quick lime) (slaked lime)
A dry powder obtained by treating quick lime with water, just sufficient to convert lime into calcium hydroxide is called hydrated lime
SLAKING OF LIME It is the process of chemical combination of quick
lime with required quantity of water for killing the heat and getting into powder form for use
SOURCES OF LIME Limestone found in hills, in the beds of old rivers Kankar found below ground Shells of sea animals
PROPERTIES OF LIME Easily workable Offers good resistance to moisture Stiffens early An excellent cement and adheres to the masonry units
perfectly
USES OF LIME It is used as a matrix for concrete. It is used as a binding material in mortars for
stoneware. It is used for plastering walls, ceilings, etc. It is employed for white washing and as a base coat
for distempers.
LIME MORTARSTypes Non-hydraulic lime mortars Hydraulic lime mortars Black mortars
Non-hydraulic lime mortars These mortars are prepared by mixing fat lime (well
slaked before use) with sand. The usual proportions of lime and sand are 1:2 or 1:3 by volume
They are suitable only for thin joints
Hydraulic lime mortars These mortars for made from class A and class B
limes Mortar made with 1 part of fat lime and 2 parts of
surkhi or 1 part of the lime plus 1 part of surkhi and 1 part of sand is mostly used in the foundations and superstructures of ordinary buildings
Black mortars In these mortars, the usual proportions are 1 part lime
to 3 parts of ash or cinder (1:3)
PREPARATION OF LIME MORTARS Ordinary lime mortars are made by grinding lime with
sand. They have good working qualities, high water
retention and freedom from shrinkage and cracking as compared to cement mortar. But they give only low strengths
PREPARATION METHODSMethod 1
Dry-mix the lime and sand in the specified proportion on a platform or more often in a trough. The necessary quantity of water is sprinkled in stages and the mixture is ground to a plastic mix by pounding with heavy wooden hammers
Method 2 (Bullock-driven mortar mill)
It is adopted when a large quantity of mortar is needed, is to use a bullock-driven mortar mill. The mixture is ground at least for 180 revolutions to get a suitable mortar
Method 3 (power-driven mortar mill) It is the modern method for preparing large quantities
of lime mortar, is to use a machine-driven pug or mortar mill for making lime mortar.
Mixing (or rather grinding) is done for at least three minutes for brickwork and longer for plaster for plasterwork and pointing and terrace works.
Note: The grinding thus depends on the need for fineness of work