2.LIME-CEMENT-AGGREGATES-

MORTAR

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

COMMONLY USED LIME MORTAR PROPORTIONS Mortar for brick or stonework – 1:2 Plaster for first coat – 1:1.5 Plaster for second coat – lime only as putty Mortar for terrace work – 1:1.5 Mortar for flat tiles – 1:1.5