1. 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.
2. 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.
3. 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.
4. An ideal mortar:
Adheres completely and durably to all the masonry
unit to provide stability.
Remains workable long enough to enable the
operative to set the masonry unit right to line and
level; this implies good water retentivity.
Stiffens sufficiently and quickly to permit the laying of
the units to proceed smoothly, and provides rapid
development of strength and adequate strength
when hardened.
Is resistant to the action of environmental factors such
as frost and/or abrasion and the destructive effects of
chemical 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
5. Mortar as Binding Material Plastering
Pointing Masonry joint Cement Slurry
7. 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
8. 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.
9. 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.
10. Properties of hardened
mortar
Durability of mortar may
be defined as its ability to
endure aggressive
conditions during its
design life. A number of
potentially destructive
influences may interact
with the mortar: these
include water, frost,
soluble salts and
temperature change. In
general, as the cement
content increases so will
durability. Air
entrainment of mortars
improves resistance to
freeze-thaw damage.
11. 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
12.
13. Flexural strength
Traditional masonry
construction tended to be
massive relative to modern
structures, typically with
very thick walls. This meant
that the mass or bulk
generally resisted the
various forces applied to it.
The development of
modern masonry units and
advances in mortar
technology have led to
more slender structures
which are more vulnerable
to lateral forces e.g. wind
loads.
14. 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.
16. FUNCTION OF SAND AND SURKHI IN MORTARS:
Functions of sand:
•It reduces shrinkage of the building material.
•It prevents development of cracks in the mortar
on drying.
•It helps in making mortars and concretes of
desired strength by varying its proportions with the
binding material.
•A well graded sand adds to the density of
mortars and concretes.
Functions of surkhi:
•It provides brick color and make the mortar
economical
17. 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.
18. 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.
19. 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
20. 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.
21. 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.
22.
23. 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.
31. Cement
Cement is the mixture of calcareous, siliceous,
argillaceous and other substances. Cement is used as a
binding material in mortar, concrete, etc.
Cement is a fine powder which sets after a few hours
when mixed with water, and then hardens in a few days
into a solid, strong material. Cement is mainly used to
bind fine sand and coarse aggregates together in
concrete. Cement is a hydraulic binder, i.e. it hardens
when water is added.
32. Chemical Composition of cement
Lime 63%
Silica 22%
Alumina 06%
Iron oxide 03%
Gypsum 02 to 05%
33. 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.
34. (ii) Silica (SiO2):
The quantity of silica should be enough to form di-calcium silicate
and tri-calcium silicate in the manufacturing of cement. Silica gives
strength to the cement. Silica in excess causes the cement to set
slowly.
(iii) Alumina (Al2O3):
Alumina supports to set quickly to the cement. It also lowers the
clinkering temperature. Alumina in excess, reduces the strength of
the 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.
35.
36. MANUFACTURING OF CEMENT
(1) Mixing and crushing of raw materials
a.Dry process
b.Wet process
(2) Burning
(3) Grinding
37. (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.
38. (b)Wet process:
In this process, the raw materials are changed to
powdered form in the presence of water.
In this process, raw materials are pulverized by using a
Ball mill, which is a rotary steel cylinder with hardened
steel balls. When the mill rotates, steel balls pulverize
the raw materials which form slurry (liquid mixture).
The slurry is then passed into storage tanks, where
correct proportioning is done. Proper composition of
raw materials can be ensured by using wet process than
dry process. Corrected slurry is then fed into rotary
kiln for burning.
This process is generally used when raw materials are soft
because complete mixing is not possible unless water is added.
40. (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 a
steel cylinder about 150meters long and 4meter diameter and rotates
30 to 60 turns per hour.
At one end of the cylinder a screw conveyer is arranged which slowly
allows the charge into the cylinder.
In the other end of the cylinder, a burner is arranged. Coal or
burning 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 to
1900 degrees centigrade.
At this end some chemical reactions takes place between oxides of
calcium , aluminium and silica.
Mixture of calcium silicates and calcium aluminates is formed.
The resultant product consists of grey hard balls called clinker
cement.
41. The percentage of important compound formed in cement
is given below:
(bogue's compound of cement)
42.
43. (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.
44. 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.
45.
46.
47. 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]
48. In the order of reaction with water, C3A is the first to react with it and
imparts setting to the cement paste. Hence C3A is responsible for
setting.
Strength contribution by C3A is negligible and therefore can very well
be 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 as
compared to C2S. Therefore the initial strength up to 7 days is mainly
given by C3S.
After 7 days when most of C3S has already exhausted, C2S also start
reacting with water. The strength between 7 and 28 days is contributed
mainly by C2S and a part is contributed by C3S
49. 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 :
51. (a) Ordinary Portland Cement (OPC):
It is the most commonly produced and used cement. It is
available in three different grades.
(b) Rapid Hardening cement (RHC):
It is also called ‘Early Strength Cement’ because its 3 days
strength is almost equal to 7 days strength of OPC. One type of this
cement is manufactured by adding calcium chloride (CaCl2) to the
O.P.C in small proportions. Calcium chloride (CaCl2) should not be
more than 02%.
In RHC, strength development is very fast. This is because of
following reasons:
Higher fineness of cement. The specific surface of this cement is
increased to 320 m2/kg as compared to 225 m2/kg for OPC.
Higher quantity of C3S in cement as compared to C2S. C3S is
more reactive in comparison to C2S.
52.
53. The sulphate present in the soil or surrounding environment reacts
with 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 in
the set cement. The CaSO4 thus produced reacts with hydrate of
calcium aluminate and form an expansive compound called calcium
sulpho-aluminate which causes expansion and cracks in the set
cement. Sulphate attack is further accelerated if it is accompanied by
alternate wetting and drying also, which normally takes place in
marine structures of the tidal zone.
54.
55. (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.
56. (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.
57. (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.
58.
59.
60. opaline is a man-made
'crystal'
Diatomaceous earth deposit
61. (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.
62. 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.
63. Tests on Cement
FieldTest
Laboratory test
FieldTest
(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.
65. Q? How would you differentiate
between Coarse Aggregate and fine
aggregate.
Aggregate
66. Cement mortar:
•The paste is prepared by mixing cement and
sand in suitable proportions in addition to water.
•The general proportion is 1 part of cement to 2-8
parts 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 where
high strength is desired such as load bearing
walls, deep foundations, flooring etc.
67. •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.
68. 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
69. •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.
70. 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 plus
2 x Grit Sand plus
1 x cement
Mortar for Wide Joints
72. 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.
73. 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.
74. TESTS FOR MORTAR:-
• Test for Adhesiveness to building
units.
• Test for crushing strength of
mortar.
• Test for determining the tensile
strength of mortar.
75. 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.
76. 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.
77. 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.
