UNIT III

III. Limes, Cements & Mortar:

Lime – Types, properties and uses.

Cement – Composition, Varieties, Properties, Methods of

manufacture; Tests on cement.

Mortar- Lime mortar, Cement mortar, Surkhi mortar, Mud mortar,

Stabilized mud mortar, Gypsum and plaster of paris, Hydraulic mortar,

Puzzolona mortar.

INTRODUCTION:-

• Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, concrete blocks, cinder blocks, etc.

• Mortar is mixture of binding material, water and sand. It is similar to concrete but it do not contains coarse aggregates.

• Mortar becomes hard when it sets, resulting in a rigid aggregate structure.

MORTAR

• Mortars are usually named according to the

binding material used in their preparation.

• They are essentially required for masonry work,

plastering and pointing etc.

FUNCTIONS OF MORTAR:

• To bind together the bricks or stones properly so

as to provide strength to the structure.

• To form a homogenous mass of the structure so

as to resist all the loads coming over it without

disintegration.

An ideal mortar: Adheres completely and durably to all the masonry

unit to provide stability.

Remains workable long enough to enable theoperative to set the masonry unit right to line andlevel; this implies good water retentivity.

Stiffens sufficiently and quickly to permit the laying ofthe units to proceed smoothly, and provides rapiddevelopment of strength and adequate strengthwhen hardened.

Is resistant to the action of environmental factors suchas frost and/or abrasion and the destructive effects ofchemical salts such as sulfate attack.

Resists the penetration of rain.

Accommodates movement of the structure.

Accommodates irregularities in size of masonry units.

Contributes to the overall aesthetic appearance.

Is cost effective

Mortar as Binding Material Plastering

Pointing Masonry joint Cement Slurry

Nature of application

• Brick Laying MortarsFinishing Mortars

Workability

• Workability may be defined as the behavior of a

mix in respect of all the properties required, during

application, subsequent working and finishing.

• Ease of use, i.e. the way it adheres or slides on the

trowel.

• Ease of spread on the masonry unit.

• Ease of extrusion between courses without

excessive dropping or smearing.

• Ease of positioning of the masonry unit without

movement due to its own weight and the weight of

additional courses

Water Retentivity & Air content

• This is the property of mortar that resists water loss

by absorption into the masonry units (suction)

and to the air, in conditions of varying

temperature, wind and humidity. Water

retentivity is related to workability.

• The air content of the mortar in its plastic state is

also important. In order to achieve good

durability it is necessary that there is sufficient air

content (entrained air) to enable freeze-thaw

cycles to be resisted without disrupting the matrix

of the material.

Stiffening and hardening

• The progression of stiffening, defined in the

European Standard as workable life, refers to the

gradual change from fresh or plastic mortar to

setting or set mortar.

• Hardening refers to the subsequent process

whereby the set mortar progressively develops

strength.

Properties of hardened mortar

Durability of mortar maybe defined as its ability toendure aggressiveconditions during itsdesign life. A number ofpotentially destructiveinfluences may interactwith the mortar: theseinclude water, frost,soluble salts andtemperature change. Ingeneral, as the cementcontent increases so willdurability. Airentrainment of mortarsimproves resistance tofreeze-thaw damage.

Compressive strength

• The use of too much cement will

produce a more rigid mortar,

which may result in vertical

cracking passing through units

and mortar joints as stresses are

imposed

• Use of the appropriate mortar

should not result in cracking, but

any that does occur, (e.g. due to

movement), will tend to follow

the joints, which will be much

easier to repair

Flexural strength

Traditional masonryconstruction tended to bemassive relative to modernstructures, typically withvery thick walls. This meantthat the mass or bulkgenerally resisted thevarious forces applied to it.

The development ofmodern masonry units andadvances in mortartechnology have led tomore slender structureswhich are more vulnerableto lateral forces e.g. windloads.

MIXING THE MORTAR:

•The sand and the cement

have to be thoroughly mixed

by hand or in a mechanical

mixer before adding any water

- do not use dirty water, or

water from puddles or ponds,

as this could impair the final

strength of the mortar.

•Similarly, keep any sugar-

containing liquids, such as soft

drinks, well away from the mix -

sugar, even in small amounts,

seriously impairs the setting

ability of the cement.

TYPES OF MORTAR

• Lime Mortar

• Lime – Surkhi Mortar

• Mud Mortar

• Cement Mortar

• Puzzolana mortar

FUNCTION OF SAND AND SURKHI IN MORTARS:

Functions of sand:•It reduces shrinkage of the building material.•It prevents development of cracks in the mortaron drying.•It helps in making mortars and concretes ofdesired strength by varying its proportions with thebinding material.•A well graded sand adds to the density ofmortars and concretes.

Functions of surkhi:•It provides brick color and make the mortareconomical

LIME MORTAR:

• Lime mortar is a type of mortar composed of lime and

an aggregate such as sand, mixed with water.

• Lime mortar is primarily used in the conservation of buildings

originally built using lime mortar, but may be used as an

alternative to ordinary portland cement.

Slaking of Lime

When water is added to quick lime in sufficient quantity, lime cracks, swells and falls into

powder form due to the chemical reaction thus forming calcium hydrate Ca(OH)2.

Quick Lime: Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a

widely used chemical compound. It is a white, caustic, alkaline crystalline solid at

room temperature usually obtained from limestone.

A lime kiln is used to produce quicklime through the calcination of

limestone (calcium carbonate).

CaCO3 + heat → CaO + CO2

Types of lime

Hydrated lime: It is created by adding water to quicklime in order to turn oxides into

hydroxides. Combined with water and sand or cement, hydrated lime is

most often used to make mortars and plasters. Its chemical name is

calcium hydroxide, or Ca(OH)2.

This is sold in most builders’ merchants as bags of dry powder.

After Soaked in just enough clean water, for at least twenty-four hours,

it makes a lime putty. This putty may be of a poor quality due to

carbonation of the powder occurring in the bag before use

Hydraulic lime:• A specialized form of limestone is used to make hydraulic lime. The

limestone is mixed with clay then fired in a kiln to high temperatures. This

process removes much of the moisture from the lime and also produces

mineral by-products known as silicates. The remaining limestone and

silicates are combined to form hydraulic lime.

• Hydraulic lime offers a number of benefits over traditional lime mortar

blends. The most important is its ability to cure and harden when wet,

which means it can be used in many applications where other mortar

products would fail.

Lime mortar:

•The paste is prepared by mixing lime and sand or surkhi in

suitable proportions in addition to water.

•If surkhi is to be added in lime mortar the equal proportions of

sand and surkhi should be mixed with lime.

•These mortars are inferior to cement mortars in strength as well

as water tightness.

•These mortars should not be used for underground works as they

set in the presence of carbon dioxide and break up in damp

conditions.

•This type is used for construction work above ground level i.e.

exposed positions.

Mud mortar:

•The paste is prepared by mixing suitable clay, soil with

water.

•The soil which is used for preparing mud mortar

should be free from grass, pebbles etc.

•These are the cheapest mortars but weakest in

strength.

•These mortars are used for brickwork of ordinary

buildings and for plastering walls in rural areas.

PREPARATION OF CLAY

Mixing With Hand Ramming Homogenous Mixture Clay Mortar

MUD wall

Applications of MUD MORTAR

Walls

Mud Plaster

Mud being Plastered to wooden Framework

Mud wall

Wall with Mud Blocks

Binding Material

MUD / CLAY BLOCKS

MOULD

Cement

Cement is the mixture of calcareous, siliceous,argillaceous and other substances. Cement is used as abinding material in mortar, concrete, etc.

Cement is a fine powder which sets after a few hourswhen mixed with water, and then hardens in a few daysinto a solid, strong material. Cement is mainly used tobind fine sand and coarse aggregates together inconcrete. Cement is a hydraulic binder, i.e. it hardenswhen water is added.

Chemical Composition of cement

Lime 63%

Silica 22%

Alumina 06%

Iron oxide 03%

Gypsum 02 to 05%

Function of composition of cement

(i) Lime(CaO):

Lime forms nearly two-third (2/3) of the cement. Therefore

sufficient quantity of the lime must be in the raw materials

for the manufacturing of cement. Its proportion has an

important effect on the cement. Sufficient quantity of lime

forms di-calcium silicate and tri-calcium silicate in the

manufacturing of cement.

Lime in excess, causes the cement to expand and

disintegrate.

(ii) Silica (SiO2):

The quantity of silica should be enough to form di-calcium silicateand tri-calcium silicate in the manufacturing of cement. Silica givesstrength to the cement. Silica in excess causes the cement to setslowly.

(iii) Alumina (Al2O3):

Alumina supports to set quickly to the cement. It also lowers theclinkering temperature. Alumina in excess, reduces the strength ofthe cement.

(iv) Iron Oxide (Fe2O3):Iron oxide gives colour to the cement.

(v) Calcium Sulphate (or) Gypsum (Ca SO4) :At the final stage of manufacturing, gypsum is added to increase the setting of cement.

MANUFACTURING OF CEMENT

(1) Mixing and crushing of raw materials

a.Dry process

b.Wet process

(2) Burning

(3) Grinding

(a) Dry process:

In this process, the raw materials are changed to

powdered form in the absence of water.

In this process calcareous material such as lime stone

(calcium carbonate) and argillaceous material such

as clay are ground separately to fine powder in the

absence of water and then are mixed together in the

desired proportions.

Water is then added to it for getting thick paste and

then its cakes are formed, dried and burnt in kilns.

This process is usually used when raw materials are

very strong and hard.

(b)Wet process:

In this process, the raw materials are changed topowdered form in the presence of water.

In this process, raw materials are pulverized by using aBall mill, which is a rotary steel cylinder with hardenedsteel balls. When the mill rotates, steel balls pulverizethe raw materials which form slurry (liquid mixture).

The slurry is then passed into storage tanks, wherecorrect proportioning is done. Proper composition ofraw materials can be ensured by using wet process thandry process. Corrected slurry is then fed into rotarykiln for burning.

This process is generally used when raw materials are softbecause complete mixing is not possible unless water is added.

Among wet process and dry process,

which is economical?

(2) Burning: The raw slurry (wet Process) or raw meal (dry process), obtained by

one of wet or dry process is called charge.

Charge is introduced into a rotary Kiln. The rotary kiln consists of asteel cylinder about 150meters long and 4meter diameter and rotates30 to 60 turns per hour.

At one end of the cylinder a screw conveyer is arranged which slowlyallows the charge into the cylinder.

In the other end of the cylinder, a burner is arranged. Coal orburning oil is burnt at this end.

The charge entering the cylinder slowly moves towards the hot end.At the burning end of the kiln, the temperature is around 1600 to1900 degrees centigrade.

At this end some chemical reactions takes place between oxides ofcalcium , aluminium and silica.

Mixture of calcium silicates and calcium aluminates is formed.

The resultant product consists of grey hard balls called clinkercement.

The percentage of important compound formed in cement

is given below:

(bogue's compound of cement)

(3) Grinding:

• Clinker cement is cooled, ground to fine

powder and mixed with 2 to 5 percent of

gypsum (Calcium sulphate Ca SO4) .

(added for controlling the setting time of

cement)

• Finally, fine ground cement is stored in

storage tanks from where it is drawn for

packing.

Hydration of cement

The chemical reactions that take place between cement and

water is referred as hydration of cement.

On account of hydration certain products are formed. These

products are important because they have cementing or

adhesive value.

Out of all cement compounds (bogue's compound of cement),

the strength of cement is contributed mainly by silicates.

Silicates react with water and produce a gel called Calcium

Silicate Hydrate or ‘C-S-H’ gel.

This gel is initially weak and porous, but with the passage of

time it becomes stronger and less porous.

Q? Is it desirable to put in as much cement as possible in

a concrete mix provided cost is not a constraint.

Q? What is the maximum cement content to be used in

concrete? [cl. 8.2.4.2, pg 19, IS456]

In the order of reaction with water, C3A is the first to react with it andimparts setting to the cement paste. Hence C3A is responsible forsetting.

Strength contribution by C3A is negligible and therefore can very wellbe neglected.

Strength of cement is mainly contributed by silicates i.e. C3S and C2S.

In the category of silicates, C3S is quicker in reacting with water ascompared to C2S. Therefore the initial strength up to 7 days is mainlygiven by C3S.

After 7 days when most of C3S has already exhausted, C2S also startreacting with water. The strength between 7 and 28 days is contributedmainly by C2S and a part is contributed by C3S

Which cement to use?

The choice of the cement depends upon the nature of

work, local environment, method of construction etc.

The different type of cement has been achieved by

different methods like :

Types of cement

(a) Ordinary Portland Cement (OPC):

It is the most commonly produced and used cement. It isavailable in three different grades.

(b) Rapid Hardening cement (RHC):

It is also called ‘Early Strength Cement’ because its 3 daysstrength is almost equal to 7 days strength of OPC. One type of thiscement is manufactured by adding calcium chloride (CaCl2) to theO.P.C in small proportions. Calcium chloride (CaCl2) should not bemore than 02%.

In RHC, strength development is very fast. This is because offollowing reasons:

Higher fineness of cement. The specific surface of this cement isincreased to 320 m2/kg as compared to 225 m2/kg for OPC.

Higher quantity of C3S in cement as compared to C2S. C3S ismore reactive in comparison to C2S.

The sulphate present in the soil or surrounding environment reactswith free Ca(OH)2 available in the concrete and CaSO4 is formed.There is no dearth of free Ca(OH)2 as it is available in abundance inthe set cement. The CaSO4 thus produced reacts with hydrate ofcalcium aluminate and form an expansive compound called calciumsulpho-aluminate which causes expansion and cracks in the setcement. Sulphate attack is further accelerated if it is accompanied byalternate wetting and drying also, which normally takes place inmarine structures of the tidal zone.

(d) Sulphate Resistant Cement (SRC):

It is modified form of O.P.C and is specially

manufactured to resist the sulphates. In certain regions/areas

where water and soil may have alkaline contents and O.P.C is

liable to disintegrate, because of un favorable chemical

reaction between cement and water, S.R.C is used. This

cement contains a low %age of C3A not more than 05%.

The quantity of C3A can be controlled simply by blending

OPC with slag cement.

Limitation:

This cement requires longer period of curing (why?). It develops

strength slowly, but ultimately it is as strong as O.P.C.

(e) Portland slag cement:

It is produced by blending OPC clinkers with slag in suitable proportion

(20-25%) and grinding together.

The slag can be separately added to OPC while making concrete.

Limitation of slag cement:

It develops strength slowly, but ultimately it is as strong as O.P.C.

(e) Portland Pozzolana cement:

It is produced by blending OPC clinkers with pozzolana in suitable

proportion (20-25%) and grinding together.

It develops strength slowly, but ultimately it is as strong as O.P.C.

opaline is a man-made

'crystal'

Diatomaceous earth deposit

(f) QUICK SETTING CEMENT:

When concrete is to be laid under water, quick setting

cement is to used. This cement is manufactured by adding small

%age of aluminum sulphate (Al2SO4) which accelerates the

setting action. This cement can also be produced by not adding

gypsum to OPC The setting action of such cement starts with in

05 minutes after addition of water and it becomes stone hard in

less than half an hour.

(h) LOW HEAT CEMENT:

In this cement the heat of hydration is reduced by tri

calcium aluminate (C3A ) content. It contains less %age of lime

than ordinary port land cement. It is used for mass concrete

works such as dams etc.

WHITE CEMENT:

This cement is called snowcrete. As iron oxide gives the grey

colour to cement, it is therefore necessary for white cement

to keep the content of iron oxide as low as possible. Lime

stone and china clay free from iron oxide are suitable for its

manufacturing. This cement is costlier than O.P.C. It is

mainly used for architectural finishing in the buildings.

Tests on Cement Field Test

Laboratory test

Field Test

(a) Date of Manufacture

(b) One feels cool by thrusting one’s hand in the cement bag.

(c) It is smooth when rubbed in between fingers.

(d) A handful of cement thrown in a bucket of water should float.

Laboratory test

(Self Study)

(1) Fineness Test. (why?)

(2) Consistency test. (why?)

(3) Setting Time Test. (why?)

(4) Soundness test. (why?)

(4) Compressive strength test. (why?)

Q? How would you differentiatebetween Coarse Aggregate and fineaggregate.

Aggregate

Cement mortar:

•The paste is prepared by mixing cement andsand in suitable proportions in addition to water.•The general proportion is 1 part of cement to 2-8parts clean sand.•These mortars must be use within half an hour,i.e.; before initial setting time of the cement.•This type is used for all engineering works wherehigh strength is desired such as load bearingwalls, deep foundations, flooring etc.

•When mixing by hand, the sands and cement are heaped up on a

mixing board or in a wheel barrow and repeatedly turned over

and over until thoroughly mixed.

•The color of the dry mix will change as the cement is

distributed throughout - there should be no 'streaking' of

cement, and no clumps of pure sand or pure cement.

•Once the dry ingredients are mixed, the water can be added.

Dry sand and cement in

wheelbarrow Begin to mix sand and cement Mix to evenly distribute cement

The dry mix should be all one

colour Add water and plasticiser Mix to required consistency

•When using a mechanical mixer, add half a bucket (2 or 3

liters) of clean cold water to the empty drum before adding the

dry ingredients in sequence.

•Add 4 measures of sand then 1 of cement, followed by 4 sand,

then another cement and so on until the required quantity is in

the mixer.

•This ensures a more thorough mix than adding, say, 20

measures of sand and then 5 measures of cement.

•Again, the water is added to the revolving

drum once the dry ingredients are

thoroughly blended, a bit at a

time until the required consistency

is achieved.

For wide joints in paving or for stonework, either as

paving or as walling, a coarser mortar is often preferred

- replace half of the building/soft sand with grit/sharp

sand. You will probably find that a coarse mortar such as

this requires less gauging water to achieve a working

consistency than does a bricklaying/general purpose

mortar.

2 x Building Sand plus2 x Grit Sand plus1 x cement

Mortar for Wide Joints

SPECIAL MORTARS

Fire – Resistant Mortar

Lightweight Mortar

Packing Mortar

Sound Absorbing Mortar

X-Ray Shielding mortar

Fire resistant mortar:

•The paste is prepared by mixing aluminous cement

and finely crushed fire bricks (1:2) in suitable

proportions in addition to water.

•The usual proportion are 1 part aluminous cement to

2 parts of finely crushed fire bricks.

•These are generally used for lining furnaces, ovens and

fire places with fire bricks.

Light weight mortar:

•The paste is prepared by mixing wood powder, wood

sawing or saw dust with cement or lime mortar.

•In such mortars fibers of jute coir or asbestos fibers can

also be used.

•These are generally used as fiber plasters in sound and

heat proof construction.

TESTS FOR MORTAR:-

• Test for Adhesiveness to building units.

• Test for crushing strength of mortar.

• Test for determining the tensile strength of mortar.

TESTS FOR ADHESIVENESS TO

BUILDING UNITS:- Two bricks are placed at right angles to

each other.

Mortar is placed to join them so as to form

a horizontal joint. If size of the bricks is

19cmx9cmx9cm, a horizontal joint of

9cmx9cm=81cm2 will be formed.

TESTS FOR CRUSHING STRENGTH:-

• Brick masonry or stone masonry laid in mortar to be tested are crushed in compression machine.

• The load applied at which the masonry crushes gives the crushing strength of the mortar present in the masonry.

TESTS FOR TENSILE/Cohesive

STRENGTH :- The mortar mould is prepared in

a briquette as shown

The tensile strength of mortar mould is tested in a tension testing machine.

Cross-sectional area of sample taken for testing is 38mmx38mm or 1444mm2 or 14.44cm2.