Tests for Bricks

v  Absorption of Water Test

v  Crushing Strength Test

v  Hardness Test

v  Shape and Size Test

v  Soundness Test

v  Test for Presence of Soluble Salts 

Coloring of Bricks

v  The color of the bricks depends upon the following factors

ü  Burning temperature of bricks

ü  Type of fuel used during burning

ü  Chemical composition of the brick earth

ü  Nature of sand used during moulding

ü  Degree of dryness achieved before burning

ü  Amount of air admitted to the kiln during burning

v  The color attained by any of the above causes is known as the natural color of the brick

v  Bricks can be colored artificially also

ü  By dipping (immersing in coloring mixture)

ü  By mixing appropriate coloring material during preparation of brick earth/clay

Fire Bricks or Refractory Bricks

v  These bricks are manufactured from specially designed earth, so that after burning, they can withstand very high temperatures without affecting its shape, size and strength

v  They are used for lining of chimneys, furnaces etc., where usual temperatures are expected to be very high

CEMENT

v  Cement is a very important building material, which is extensively used in the construction industry

v  Cement is always used in the form of mortar and concrete in construction works and never alone

Natural Cement

v  Natural cement is manufactured by burning and then crushing the natural cement stones

v  Natural cement stones are such stones which contain 20 to 40 % of argillaceous matter and remaining content mainly calcareous matter

v  Since chemical composition of natural cement stones vary considerably from place to place, the properties of natural cement also vary

v  Even cement being manufactured in one factory may be varying in properties

v  For example, hydraulic properties of cement are entirely dependent on the percentage of clayey materials present. If  % of clay is high, quick setting cement is produced with low ultimate strength

v  Examples: Roman cement, Pozzolana cement and Medina cement

Artificial Cement

v  Artificial cement is manufactured by burning appropriately proportioned mixture of calcareous and argillaceous matters at a very high temperature and then grinding the resulting burnt mixture to a fine powder

v  The burnt mixture of calcareous and argillaceous matters is known as clinker

v  A little percentage of gypsum is also added in the clinkers before grinding them to fine powder

v  Gypsum is added to delay the setting action of the cement for some time so that, it can be properly mixed, applied and finished

v  The setting time can be varied by suitably varying the percentage of gypsum

Advantages of Artificial Cements

v  Can be manufactured in any desired color 

v Initial setting time can be easily regulated

v  Rate of hardening can be regulated

v  Rate of evolution of heat can be regulated

v  Properties can be maintained always same by maintaining same composition of raw material

v  Can be manufactured in very large quantities 

Ordinary Portland Cement

v  Common variety of artificial cement is known as normal setting cement or ordinary cement

v  This cement was first invented by Joseph Aspdin of England in 1824

v  This cement resembles very closely to a sandstone, which is found in large amount at a place Portland in England and thus this cement is also referred to as Portland cement

Composition of Ordinary Portland Cement

Functions of Ingredients of Cement

Alumina or Clay

v  Alumina is responsible for setting action of cement

v  Larger the amount of alumina present in the cement, quicker it will start setting

v  Excess quantity of alumina weakens the cement

v  Alumina forms complex aluminates with silica and calcium and imparts the setting property to the cement

Silica 

v  It also goes in to chemical combination with calcium and forms hard silicates which are responsible for imparting strength to the cement

Lime

v  It is the most important ingredient of the cement and its amount in cement is above 60 % of the total contents

v  Its proportion should be carefully decided

v  If lime is added in excess quantity, some part of it is left in forms of free lime which causes expansion and disintegration of cement at the time of setting and hardening

v  Lesser than the required quantity will cause decrease in the strength of the cement, as then sufficient calcium silicates will not be formed, which are mainly responsible for the strength characteristics of the cement

Iron Oxide

v  Iron oxide mainly imparts color to the cement

v  Besides this, it also goes into chemical combination and helps to increase strength and hardness of cement

Magnesium Oxide

v  It also imparts strength and hardness to cement, but only when present in small amount

Sulphur Trioxide

v  Small percentage of sulphur renders cement sound

v  Excess amount of it may make it unsound

Alkalies

v  Alkalies, present in the raw materials used for the manufacture of cement are mostly drive out by the flue gases during burning

v  Still it may be present in the cement in very small amount

v  Excess amount of alkalies cause efflorescence in the cement

Calcium Sulphate/Gypsum

v  Gypsum is used to retard or prolong the initial setting action of the cement

Harmful Constituents of Cement

Alkalies

v  Alkalies are oxides of potassium and sodium

v  If amount of alkalies exceeds 1 % it causes unsoundness of cement

Magnesium Oxide

v  If amount of MgO exceeds 5 % it causes cracks in hardened mortar or concrete as it burns at about 1500° C and slakes very slowly when mixed with water

Proportioning of Cement Ingredients

Acidic Constituents

• Ø  SiO2, Al2O3, Fe2O3

• Ø  Argillaceous Materials

Alkaline Constituents

• Ø  CaO & MgO

• Ø  Calcareous Materials 

Neglecting the rest (i.e., CaSO₄ & other compounds ≈ 8% of total mass), the % of acidic and alkaline constituents are 32 and 63.5 respectively. The ratio of these constituents is given by:

Sometimes, the index of cementation value (or cement moduli) is used for proportioning raw materials of cement, which is given by:

In the above index, % molecular weight of the individual ingredients is used. Thus,

v  Either index can be used for proper proportioning of cement constituents

v  It is clearly understandable that, the calcareous and argillaceous materials should be carefully selected and proportioned

v  On the other hand, Clinkering helps in a through and intimate mixing of raw materials

v  It ensures a thorough and complete chemical reaction between the ingredients to form the following mineral constituents: 

 

Name of Compound	Oxide Composition	Abbreviation	Range of Percent Composition
Tri-Calcium Silicate	3 CaO.SiO2	C3S	45-55
Di-Calcium Silicate	2 CaO.SiO2	C2S	20-30
Tri-Calcium Aluminate	3 CaO.Al2O3	C3A	9-13
Tetra-Calcium Aluminoferrite	4 CaO.Al2O3.Fe2O3	C4AF	8-20
Calcium Sulphate (Gypsum)	CaSO4	----	2-6
Other Compounds	----	----	2-8

 

 

Functions/Hydration of Mineral Constituents

v  All the cement constituents are in dry state

v  As soon as water is added to cement, chemical reactions start simultaneously between them

v  The term hydration is applied to all reactions of cement with water

v  The process of hydration is essentially the formation of minute crystals of calcium and gels from the solution of cement and water. It continues for a long time. The hydration rate of different mineral compounds is different as mentioned below

v  As the crystals adhere to one another and to the surface of sand or inert particles of aggregate (with which cement is mixed), the entire mixture gets set and hardened resulting in gaining strength

v  The strength developed depends on the amount of gel formed and the degree of crystallization

v  After setting is initiated, hardening of cement follows and in the course of time, hydration process advances further into the interior 

Tri-Calcium Aluminate (C₃A)

v  C₃A is one of the first compounds to start hydrating after addition of water

v  Hydration leads to immediate stiffening of the paste, known as flash setting

v  The hydration completes in a day

v  It is responsible for early setting of cement and hampers the workability

v  Gypsum is added to retard the setting action

v  C₃A does not contribute any strength to concrete and only contributes to the setting action of cement

Trii-Calcium Silicate (C₃S)

v  Hydration of C₃S starts after that of C₃A

v  Its hydration is responsible for the initial strength of cement

v  The strength acquired during first 7 days is mostly due to hydration of C₃S

Di-Calcium Silicate (C₂S)

v  C₂S reacts with water at a very slow rate

v  Hydration of C₂S continues for several weeks

v  It is responsible for the progressive strength of cement, especially strength gaining after a week of mixing

Tetra-Calcium Aluminoferrite (C₄AF)

v  It reacts with water instantly after mixing and hydrates simultaneously with C₃A

v C₄AF has no influence on setting action of cement and hardening

Heat of Hydration

v  The setting action of cement is a process of hydration and is accompanied by generation of heat called ‘Heat of hydration’

v  The C₃A generates much of the heat. Similarly, C₃S also generates considerable heat during hydration

v  The process of heat generation is quite rapid in the initial phase of the setting, but its rate diminishes with the passage of time

v  1 gram of OPC generates about 120 calories on setting, out of which, 80 calories are generated in first 7 days

v  Special care has to be taken to dissipate this heat, otherwise mass concrete works (dams, rafts etc.) are likely to develop cracks resulting in weakening the concrete

v  A rise in temperature to the extent of 15° to 25°C is observed in many cases. The rise in temperature is the largest during the first few days. But in the large masses of concrete, the maximum temperature is generally reached as late as after 2 to 3 months

v  Therefore, in such cases, the devices for cooling down the interior have to be adopted

 

False Setting of Cement

v  False setting is the name given to the abnormal premature stiffening of cement within a few minutes of mixing with water

v  It differs from flash setting by following

ü  No appreciable heat is evolved in this case

ü  Re-mixing the cement paste without further addition of water restores plasticity of the paste

ü  The restoration will not cause strength loss as long as it does not set in the normal manner

Some Causes of False Setting

v  Dehydration of gypsum while grinding to powder with too hot clinker

v  Semi-hydrate (CaSO₄.½H₂O) or anhydrite (CaSO₄) are formed and if cement is mixed with water, this CaSO₄ hydrates to form gypsum again (CaSO₄.2H₂O). thus setting takes place with resulting stiffening of the paste

v  Excess alkalies present in cement may cause false setting. During storage, the carbonates of alkalies reacts with Ca(OH)₂ liberated by hydrolysis of C₃S to form CaCO₃. This precipitates and induces a rigidity of the paste

Manufacturing of Cement

Considerations for the Location of Factory Site

v  Climatic conditions at site should be favorable for the manufacture of cement

v  Required labor should be available abundantly and economically

v  Local and nearby area should provide adequate market for sale

v  Supply of electricity should be available abundantly, economically and continuously

v  Raw materials should be available locally

v  Transportation facilities should be available adequately

v  Gardens, parks etc. and other recreation centers should be available

Process of Manufacturing

Cement can be manufactured by following two methods-

1)     Dry process (Modern technology)

2)     Wet process (Old technology)

The following three distinct operations have to be performed in manufacturing of cement by either dry process or wet process.

1)     Mixing of raw materials

2)     Burning

3)     Grinding

Cement Storage

Cement Silos

v  In factory, cement is stored in a large sized, reinforced concrete vertical cylinder, called silos

v  Their diameter varies from 7m to 10m and height from 15m to 24m

v  Cement is drawn from them at the bottom

Cement Packing

v  Cement is packed in gunny bags or in bags of cloth or paper

v  Packing is done with the aid of automatic weighing and packing machines

v  A special rotary type screw feeding device armed with a trigger is provided for filling the bags

v  When a specific quantity of cement is admitted in each bag, the trigger is operated by the weight of the filled bag and the feed is automatically closed

v  OPC weighs 50 kg per bag, which is equivalent to 1.25 cft in volume

Cement Storage by User

The precautions for the storage of cement during works

v  Cement should be stored in a dry place and on a raised platform, which is covered and guarded from sun, wind and rain. A maximum of 15 bags is placed vertically

v  Long periods of storage should be avoided as far as possible

v  Storage of cement in rainy season is not recommended

 

Types of Portland Cement

 

No.	English Description (BS)	American Description (ASTM)
1	Ordinary Portland	Type I
2	Modified Portland i. Air Entraining ii. Expanding	Type II
3	Rapid Hardening Portland	Type III
4	Quick Setting Portland	----
5	Low Heat Portland	Type IV
6	Sulphate Resisting Portland	Type V
7	Blast Furnace	Type IS
8	Pozzolana Portland	Type IP
9	White Portland	----

 

 

Air Entraining Cement

v  0.01 to 0.05 % by weight air entraining foaming agents are used. Agents are resinous materials such as vinsol, resin, darex etc. They are added during the grinding of clinker

v  Concrete made with such cement contains minute, well-distributed air bubbles throughout the mass. Air bubble reduces strength by 10 to 15 % and hence, the bubbles should not be more than 3 to 4 % of the volume of concrete

v  Air entrainment improves the workability and durability of cement

v  Such cement is resistant to severe frost action, fire, surface scaling and other similar effects

Rapid Hardening Cement

v This type of cement can be produced by

i) Increasing the fineness of cement (i.e., by increasing their specific surface) ii) Allowing a low percentage of alumina since Al₂O₃ sets early and offers a covering layer over Calcium and Silica compounds and retards their hydration and hence hardening

iii) Increasing the C₃S content to impart rapid hardening. This requires an increase in lime contents and the consequent careful clinkering at a higher temperature. With the increase in lime content in raw materials, however, there is always a danger of the presence of free lime in cement

v  Used for highway slabs, which is to be open to the traffic at the earliest possible moment

v  Used in cold weather concreting because its rapid hardening and high rate of heat evolution protects concrete against freezing

v  Also used for manufacturing of precast elements

Quick Setting Cement

v  Cement possessing initial setting time of 5 minutes and final setting time of 30 minutes

v  It is difficult to work with this cement, as little time is allowed for mixing and laying of concrete; i.e., these works have to be completed in 5 minutes

v  Quick setting property is achieved by

i) Increasing fineness ii) Adding small percentage of Al₂(SO₄)₃

iii) Adding very little or no percentage of gypsum to the clinker during grinding

v  Al₂(SO₄)₃ together with Al₂O₃ (as an ingredient of cement) hydrates quickly to form C₃A and C₄AF more in quantity than OPC

v  Used for concreting under running water as quick setting action prevents cementing material from being washed out by running water

 

Low Heat Cement

v  In mass concrete structures such as dams, retaining walls, bridge abutment, raft etc., the rate of dissipation of heat due to hydration from the surface is much lower than that generated

v  It causes rise in temperature inside the concrete mass and may develop thermal and shrinkage cracks if proper precautions for dissipating the thermal gradient are not taken

v  Under this circumstance, the low heat cement can be effectively used

v  Cement ingredients are proportioned in such a way that C₃A and C₂S are formed in less amount, but C₂S is formed in increased amount so that C₂S and C₃S collectively impart the same strength as OPC

v  The rate of heat generation is slow initially (as the hydration rate is slow), so both setting and hardening rates are slow initially. But in the later stage both rates are faster than the OPC

Typical composition of Low Heat Cement

Type	C3S (%)	C2S (%)	C3A (%)	C4AF (%)
OPC	48	24	10	9
LHC	24	48	5	14

 

Pozzolana Cement

v  Pozzolanic materials are mainly burnt clay like surkhi, fly ash or shale. They can be added to cement to react with free lime present in OPC. These materials, though inert, are capable of combining with lime when wet and form cementitious products. Volcanic ash is also used as pozzolana

v  These materials are pulverized and then mixed with cement. Or, they can be mixed with clinker and ground with it

v  The percentage usually varies from 10 to 25 % by weight of the finished cement

v  Pozzolana cements impart plasticity and workability to mortars and cement

v  The free lime present in OPC is liable to leaching action by percolating waters in dams and other hydraulic structures, which are thereby rendered permeable. 

v  Pozzolanic cements, on the other hand, will impart impermeability to hydraulic structures

v  An excess of pozzolanic materials makes mortars and concrete shrink more. Their strength also is proportionately reduced

 

 

Tests of Cement

• Fineness Test
• Consistency Test
• Test for Strength

            • Tensile
            • Compressive

• Test for Setting Time

            • Initial Setting

           • Final Setting

• Test for Soundness/Expansion Test

• Test for Chemical Composition               

 

  

SAND

 

v  Sand is a form of silica of small grains

v  Formed by decomposition of sandstone due to various weathering effects v Mostly obtained from pits, shores, river beds and sea beds

 

Sources of Sand

Pit Sand

v  Obtained by forming pits into the soil

v  It is sharp, angular, porous and free from harmful salts

v  Clay and other impurities should be washed and screened before using in engineering purposes

v  Fine pit sand, when rubbed between fingers, should not leave any stain on it. It indicates the presence of clay

v  Used for the mortars

River Sand

v  Found at river beds and banks

v  Fine, round and polished due to rubbing action of water currents

v  Having less frictional strength because of roundness

v  Almost white in color

v  Grains are smaller than pit sand, and hence more suitable for plastering work

v  Normally available in pure condition and hence can be used for all kinds of civil engineering works

Sea-Sand

v  Obtained from sea-shores

v  Fine, rounded and polished due to rubbing action of water

v  Light brown in color

v  Worst of the three kinds of sand because of containing lot of salts

v  Salts absorb moisture from atmosphere and cause permanent dampness and efflorescence in the structure

v  Sea salts also retards the setting action of cement

v  Besides, it contains shells and organic matter which decompose in the body of mortar and concrete and hence reduce their life and strength

v  Sea sand should be discarded as far as possible

Desirable Properties of Sand

v  Inert completely (i.e. should not have any chemical activity)

v  Grains should be sharp, strong and angular

v  Should not contain hygroscopic salt

v  Should not contain clay & silt, which are harmful ingredients (usually 3-4 % clay

& silt is ordinarily permitted for practical reasons)

v  Should not contain any organic matter

 

Functions of Sand in Mortar/Concrete

v  Offers requisite surface area for the film of finding material to adhere and spread

v  Increases the volume of mortar and consequently makes mortar more economical

v  A well-graded sand adds to the density of mortars and concrete

v  Prevents excessive shrinkage of mortar

v  Since inert material, it renders structure more resistant against atmospheric actions

 

Classification of Sand

v Classification is based on ASTM Standards

 

 

Fine Sand

ü  FM = 2.20~2.60

Medium Sand

ü  FM = 2.60~2.90

Coarse Sand

ü  FM = 2.90~3.20

 

Fineness Modulus (FM) of Sand

 

Example of FM of Sand

Tests for Sand

Tests for Presence of Silt and Clay

1)     If silt & clay are present in sand, then could be found out by determining the percentage loss in weight of a sample of sand after washing the same with the aid of clean water.

2)     However, field test can be performed by rubbing a small amount of sand between finger tips. If clay spots are left on finger tips, it indicates the existence of clay in the considerable amount.

Test for Presence of Salt

v  Can be tested by putting some amount in mouth. The test will reflect the presence of any salt.

Test for Organic Matter

v  Make 3 % solution of NaOH & put some sand into the solution. 

v  Close the bottle for 24 hours and meanwhile shake the solution vigorously. 

v  The color of the liquid turns brown if any organic matter is present in sand. 

v  The darkness of color gives the estimation of the amount of organic matter exists in the salt. 

Substitute for Sand

If good sand is not available in the nearby of the site, the substitutes may be used

Stone Screenings

v  Fine particles obtained by screening crushed stones

v  The grains are sharp and strong and impart better strength to the concrete if used

Surkhi

v  Obtained from finely powered burnt clay (brick)

v  Also obtained by grinding slightly underburnt bricks

v  It distinguishes under the action of air and humididty

v  Not used for external mortar

Bulking of Sand

v  Bulking of sand means increase in volume. Fine aggregates (i.e. sand) increase in volume when they posses some moisture

v  It is due to the formation of a thin film of water around the aggregate or sand particles

v  The thickness of this film goes on increasing with more and more moisture. Therefore, the increase in volume of sand mass continues. This increase in volume varies 20~30 % (volume basis) depending upon the fineness of sand. The finer will undergo with greater increase in volume

v  After certain % of water (5~8 %, also depends on the fineness of sand), the volume of sand starts decreasing with the further increase in water and eventually the increased volume completely vanishes, and at this moment, the volume occupied by sand becomes equal to the volume of dry sand

Importance

Bulking of sand effects water cement (w/c) ratio and the proportioning of aggregate

MORTAR

v Intimate mixtures having the consistency of a paste and prepared by mixing a binding material (e.g., cement, lime, surkhi etc.) and inert matter (e.g., sand, stone, screenings etc.) and water in various proportions

Types of Mortar

Cement Mortar

v  Consists of mixture of cement, sand & water in suitable proportion

v  Stronger than any other mortar

v  Commonly used in the construction of load bearing wall, columns etc.

v  The proportion of cement to sand (volume basis) varies from 1:2 to 1:6 or even more, such as

•      Masonry wall             1:6 to 1:8

•      Foundation concrete 1:3 to 1:4

Lime Mortar

v  Mixture of lime (fat, normal or hydraulic lime), sand & water

v  If fat lime is used, it should be slaked before using

v  Fat lime mortar proportion                          1:1 v Ordinary lime mortar proportion   1:2 v Hydraulic lime mortar proportion   1:4

v  Hydraulic lime has greater cementing power than others

Mud Mortar

v  Mixture of puddle mud and water at the required consistency

Gauged Mortar

v  Lime mortar with having some cement to increase cementing properties

v  Usually used with fat lime mortar, as this kind of lime possesses very weak cementing property

v  Cement in lime mortar increases its strength, hydraulicity and the rate of setting v Used for brick or stone masonry in foundation

Preparation of Cement Mortar

v  Sand and cement are measured in a dry state and spread to a uniform thickness on a non-porous platform. Cement is spread over sand. As usual, sand is measured in ft³, but cement is measured by weight, 40 kg/ft³

v  For a given batch, the quantity of water to be added is calculated. One half of that quantity is sprinkled on the above dry mix. The mixture is again turned over twice or thrice to prepare a semi-wet mix

v  The remaining quantity of water is added to the semi-wet mix and again the whole mixture is turned twice or thrice to form cement mortar of the required consistency

v  Now the mortar is ready for use. All the work done in cement mortar should be kept wet for about 15 to 21 days for curing by occasional sprinkling with water

Precautions in Using Mortar

v  Bricks or stones to be jointed by mortar should be used by soaking them in water for at least 12 hours

v  After preparation of mortar, it should be used at its destined place as early as possible; cement mortar within 30 minutes of adding water to it and lime mortar within 36 hours

v  Mortar should be stiff but workable; i.e., it should be as stiff as possible without affecting its convenience in use

v  Works made from mortar should be kept wet for two weeks to three

Tests for Mortar

Tensile Strength Test

Using briquette apparatus with minimum cross-section of 1.5”x1.5”

Compressive Strength Test

By using cube (2”x2”x2”) made from cement mortar

Adhesive Strength Test

v  Arrange two bricks in T-shape and use mortar at the intersection line.

v  When they gain sufficient strength after curing of 7, 14 or 28 days, the T is suspended invertedly from the upper brick and weights are attached to the lower brick

v  Weights are gradually increased till both bricks split from each other

Special Mortars

Light weight Mortar

v  Ordinary cement or lime mortar including asbestos. Fibres, jute fibre, wood powder, saw dust etc.

v  For developing adhesion under special conditions, small quantities of glue can be added to mortars

v  Potable water should be used

v  Used for heat or soundproof structures

Fire Resistant Mortar

v  Obtained by mixing firebricks or fire clays with aluminous cement

v  Usual proportion is one part aluminous cement and two parts powdered fire cay

v  Withstand the effects of very high temperature v Used for lining of furnaces, fire places and ovens etc.

X-Ray Shielding Mortar

v  Special heavy mortars (2.7 gm/cm³) are used to cover walls and ceiling of X-ray cabinets

Lean Mortar

v  Cement/lime mortar with very small proportion of cementing material

v  Used to fill the cracks, faults or narrow joints. The process is known as ‘Grouting’

CONCRETE

v  Concrete is an artificial material, obtained by mixing together cementing material, coarse aggregate, fine aggregate and water

v  If cement is used as cementing material in the mix, it is known as plain cement concrete

v  If steel rods are embedded in the plain concrete, it is then called reinforced cement concrete, abbreviated as RCC. 

v  If instead of cement, lime is used as cementing material in the mix, the resulting mass is termed as lime concrete

Classification of Concrete

Concrete Classification

Ø  Mud Concrete

Ø  Lime Concrete

Ø  Cement Concrete

Mud Concrete

v  This concrete does not carry any importance

v  It is prepared by mixing brick bats in mud mortar

v  Sometimes crushed stone may be mixed with mud mortar to form mud concrete

v  Mud concrete is used for preparing hard base, over which lime concrete may be laid and then permanent flooring may be spread

Lime Concrete

v  This concrete carries lot of importance

v  Hydraulic lime is always used in this concrete

v  Fine sand or finely ground surkhi is used as fine aggregate and brick chips or crushed stone is used as coarse aggregate

v  Firstly, lime and sand/surkhi are mixed together by adding suitable amount of water resulting lime mortar

v  Prepared lime mortar is spread over coarse aggregate stacked in uniform layer and mixed by manual labor

v  It is used

ü  Extensively in foundations of two or three storied buildings

ü  In preparation of hard base for floors

ü  Over roof slabs 

Cement Concrete

v  Cement concrete is very important structural material & there is no structural element that cannot be made from cement concrete or RCC

v  It should be carefully designed, mixed, placed and cured

v  Cement concrete is prepared by mixing together cement, sand, crushed stone/brick chips and water

v  All the ingredients of the cement concrete when freshly mixed, produce a plastic mass which can be poured into suitable forms or moulds to give desired shape to the resulting solid mass

v  RCC is used in all kinds of civil engineering structures

Ingredients of Cement Concrete

Desirable Properties of Cement Concrete Ingredients

Water Cement Ratio (W/C Ratio)

v  It is the ratio of water to cement in a concrete mixture

v  Strength and workability of the concrete greatly depend on the amount of water

v  For a particular proportion of materials, there is a specific amount of water that gives the optimum strength to the concrete

v  Amount of water more or less than the specified amount, causes decrease in the strength of the concrete

Water

ü  Potable or Drinking Water

ü  Free from acids, alkalies & decayed vegetable matter

Coarse Aggregate

• ü  angular shape & Rough surface

• ü  having smaller porosity & absorption capacity

• ü  free from deleterious materials (coal, mica, alkali etc.)

Fine Aggregate

• ü  Properly Graded

• ü  free from salt & other impurities

Properties of Cement Concrete

ü  Properties of Concrete in Plastic Range

ü  Properties of Hardened Concrete

Properties of Concrete in Plastic Range

Workability

v  It is a measure of ease with which concrete can be handled from the mixer stage to its final fully compacted stage

v  The proportion and properties of water, cement and aggregates influence the workability of concrete

Elements that Effects Workability

Segregation

v  Tendency of separation of CA particles from the concrete mass is called segregation

v  Harmful for concrete strength

Causes of Segregation

v  When concrete mixture is lean and too wet

v  When larger and rough textured aggregate is used

Avoidance of Segregation

v  Addition of little air entraining agents in the mix

v  Restricting the amount of water to smallest possible amount

v  All the operations like handling, placing & compaction are carefully conducted v Concrete should not be allowed to fall from larger heights

Bleeding

v The tendency of water to rise to the surface of freshly laid concrete is known as bleeding

Problems due to Bleeding

v  Delays in finishing

v  Loss of particles of sand & cement

Causes of Bleeding

v  Lack of fines

v  Too much amount of water

Remedies of Bleeding

v  By adding more cement

v  By properly designing the mix and using minimum quantity of water

v  By using little air entraining agent

v  By increasing finer part of fine aggregate 

Properties of Hardened Concrete

Factors Affecting Proportions of Concrete

W/C Ratio

v  Strength, elasticity, durability and impermeability of concrete is ncreased with decreas in W/C ratio, provided the concrete is workable

v  Shrinkage increases with larger W/C ratio

Cement Content

v  With increase in cement content, W/C ratio is decreased and consequently strength, elasticity, durability and impermeability is increased

v  More cement, improved workability increase shrinkage

Temperature

v  Rate of setting and hardening of concrete is high at higher temperature

Age of Concrete

v  Strength of concrete goes on increasing with age, though the rate of increase becomes very slow as time passes

Aggregate

v  Size, shape & grading of aggregate control the concrete properties to a large extent

v  Larger the size of the aggregate, greater will be the strength, provided mix is workable

v  Properly graded aggregates give better workability and strength than poorly graded mixes

Curing

v  Curing is the process of keeping the setting concrete damp, so that complete hydration of cement is brought

v  Curing improves strength, resistance to wear & weather

v  It reduces shrinkage

v  It increases impermeability and durability of concrete

Frost

v  Causes disintegration of concrete

Entrained Air

v  The entrained air in concrete is due to incomplete compaction

v  It reduces the strength of concrete

v  It also increases permeability

Mixing of Concrete

v  The process of mixing cement, water, FA & CA in suitable proportion is known as mixing of concrete

v  This process should ensure uniform color, consistency and homogeneity of the concrete

v  Segregation should not take place during process of mixing

Hand Mixing

v  Hand mixing is used, where quantity of concrete is very small

v  Firstly, cement and sand are mixed dry on a clean, dry & hard platform

v  Dry mixing is continued until the mix attains uniform color

v  The mix is spread over the measured stock of coarse aggregate in required amount and they are mixed dry again to have uniform color

v  A hollow is made in the middle of the mix and about 75 % of the required amount of water is added

v  Mixing is done and remaining water is added to acquire uniform workability

Machine Mixing

v  On large works, machine mixing proves economical and convenient

v  Concrete produced by machine mixing is more homogeneous and can be prepared with comparatively lesser W/C ratio

v  The concrete mixers may be of two types

ü  Batch Mixers 

ü  Continuous Mixers

v  Batch mixers mix and discharge each load of materials separately

v  Continuous mixers produce steady stream of concrete as long as it is in operation

v  Batch type mixers are mostly adopted

Transporting the Concrete

v  Concrete prepared, either by hand mixing or machine mixing has to be transported to its place of use, before hydration of cement starts

v  During transportation, efforts should be made to prevent segregation or less of any of the ingredients

v  The method of transportation of concrete depends on the quantity of concrete and situation of work site

v  Transportation of concrete is done by

ü  Pans

ü  Wheel barrows

ü  Truck mixers

ü  Belt conveyors

ü  Pumps

Placing of Concrete

v  The concrete should be placed and compacted before its setting starts

Precautions while Placing Concrete

v  Concrete should be laid continuously to avoid irregular and unsightly lines

v  To avoid sticking of concrete, form work should be oiled before concreting

v  While placing concrete, the position of form-work and reinforcement should not be disturbed

v  To avoid segregation, concrete should not be dropped from height more than 1m

v  Concrete should not be placed in rains

v  Walking on freshly laid concrete should be avoided

Compaction of Concrete

v  Consolidation of plastic concrete is termed as compaction of concrete

v  In this process, efforts are only directed to reduce the voids in the concrete

v  Compaction of concrete can be done either manually or mechanically

Manual/Hand Compaction

v  It is done with the help of steel tamping rods or timber screeds

v  Narrow & deep members are compacted with tamping rods

v  Thin slabs and floors are tamped with the help of screeds

Mechanical Compaction

v  It is done with the help of vibrators

v  Vibrators produce vibrations, which, when transmitted to plastic concrete, make it flow and affect compaction

Finishing of Concrete

v Finishing means, giving desired smoothness to the surface of compacted concrete v Finishing can be done by Screeding, floating or trowelling

Curing of Concrete

Curing is the operation by which moist conditions are maintained on finished concrete surface, to promote continued hydration of cement

Importance of Curing 

v  If proper curing is not done, complete hydration of cement will not take place and concrete will not acquire its full intended strength

v  Shrinkage will develop in the concrete without proper curing

v    Curing also improves durability, permeability and wear & weather resisting qualities

Methods of Curing

Shading Surface

ü  To prevent evaporation of water from the surface

ü  To protect concrete surface from heat, direct sun & wind

Covering

ü  With hessian or gunny bags

Sprinkling Water

ü  Water is sprinkled on the surface from time to time

Ponding of Water

ü  Water is filled in kiaries formed on surface by sand or mud

ü  Used for curing horizontal surface

Membrane Curing

ü  Concrete surface is covered by water proof membrane that prevents
evaporation of water from concrete

ü  Wax, bitumen emulsion, plastic films etc. are common membrane materials

Steam Curing

ü  Adopted in the case of precast members

ü  Hydration of cement is brought within very short time

TIMBER

Ø  Denotes structural wood obtained from tree

Ø  A standing tree is called standing timber

Ø  When a tree has been cut and its stems and branches are roughly converted into pieces of suitable lengths, it is known as rough timber 

Ø  When a roughly converted timber is further sawn and converted into commercial size, such as: plank, logs, batten, post, beam, etc., it is called converted timber

 Difference between wood and timber 

Ø  Wood includes all types of wood which may be burning wood, structural wood, furniture wood, etc. 

Ø  However, wood used as a structural material is called timber

Advantages of using timber

Ø  Easily available everywhere

Ø  High salvage value

Ø  Can be transported easily by converting into small commercial sizes

Ø  Working with timber (i.e., repairing, alteration, addition, etc.) is easy

Ø  Can be easily jointed

Ø  Not corroded (so, it can be used in marine works)

Ø  Light weight

Ø  Withstands shocks better than iron and concrete

Ø  Good insulator of heat and electricity

Ø  Good sound absorbing material

Classification of trees

Exogenous trees

Ø  These trees increase in bulk by the formation of successive annual rings radially on the outside under the bark 

Ø  Every year a new ring is added to the tree section

Ø  Age of tree can be determined from the number of annual rings

Ø  Used for engineering purposes

Two types

i) Evergreen trees or conifers

ü  Having pointed needle-like or scale-like leaves bearing cone-shaped fruits

ü  Yield softwood

ü  Examples: The Pines, Fur, Kail, Ceder, Chir, Deodar and Cypress Trees

ii) Deciduous trees 

ü  Having flat broad leaves, which fall in autumn and new leaves appear in spring

ü  Yield hardwood

ü  Examples: Oak, Mehogany, Teak, Sal, Gorjon, Chambal, Telsu, Nageshwar, etc.

Endogenous trees

Ø  These trees grow inward by depositing each fresh layer internally. 

Ø  Thus, the older formations/layers of wood material are on the outside

Ø  They grow vertically in a fashion that the links (approx. annual growth) placed end-to-end with knot connecting two adjacent links Ø Example: Bamboo, Palm, etc. 

 Hardwood/Softwood

Ø  Characteristically, broad-leaved trees yield hardwood while conifers (needleleafed trees) yield softwood

Ø  Hardwoods are dense with having narrow and well-defined annual rings.

Softwoods are comparatively less dense, lighter in color

Ø  They are not very strong but are soft with straight grains

Ø  Softwoods have more uniformity of structure than hardwoods

Timber Section

Ø Consists of pith, heartwood, sapwood, cambium layer, inner bark, outer bark and medullar ray (Fig. 15.1, page no. 287, Aziz)

Pith 

Central part, dark colored, consists of cellular tissues and nourishes the plant in its young age; in old age, the pith dries up and decays; Sap is transmitted by fibers deposited round the pith.

Cambium Layer 

A thin layer of sap lying between sapwood and the inner bark; it is full of sap which is yet to convert into sapwood; this is very sensitive layer; if it is exposed by removing the bark, cell stopped transmitting sap into the inner part and the tree dies. 

Medullar Ray

These are thin radial fibers, extending from cambium layer right up to pith. These rays help in holding together annual rings of both heartwood and sapwood. They may be continuous but mostly they are broken. 

Heartwood

Dark colored portion of the tree surrounding the pith. Almost dead portion of tree and does not take active part in its growth. It provides strongest and durable timber for various engineering purposes. 

Sapwood

Light colored wood lying between heartwood and cambium layer. Light in weight and is of recent growth containing a lot of sap. This is the active part of the wood and thus helps in growth in the tree. 

Felling of Trees  

Cutting of trees in order to get timber from them is called felling of timber. The following facts should be carefully considered while felling trees

Season of Felling

Trees should be cut only when sap is not active, i.e., in mid-summer and mid-winter. In autumn and spring sap is in vigorous motion, hence felling should be avoided. For hilly region, mid-summer and for plain areas, mid-winter are proper seasons for felling trees. 

Age of Trees

Trees should be felled only when it has just attained maturity. Under-aged trees would yield more of sapwood, while over-aged trees develop certain defects in heartwood.

Method of Felling Trees

Felling should be entrusted to an experienced person. Before felling, slope of the tree is assessed and cut is given to  the stem on the side of the slope of the tree, as near to the ground as possible. Then cut is made on the opposite side of the slope to fell the tree. 

If tree is to be felled against the direction of the slope, ropes are tied to the tree and pulled to the direction of felling by giving suitable cut to the stem. 

Conversion of Timbers

The process by which timber is cut and sawn into suitable marketable sizes is known as conversion of timber. After felling, stems and branches of trees are cut into logs of suitable lengths. The logs are then transported to the saw-mill and converted into marketable sections (i.e., planks, battens, beams, etc.). 

Sawing of Timbers

ü  Ordinary sawing or cross sawing 

ü  Radial or Rift sawing 

ü  Tangential or slash sawing 

ü  Quarter sawing 

ü  Combination sawing 

Seasoning of Timbers

The process of removing surplus moisture (in excess of equilibrium moisture content) from freshly converted timber is seasoning.

Advantage of Seasoning

v  Seasoned timber is light

v  Improves strength properties

v  Easy to transport and handle

v  Timber less liable to be attacked by fungus and insects

v  Reduces the tendency to shrink and warp

v  Can easily be worked with

v  A seasoned timber maintains the shape of timber article unchanged

Methods of Seasoning

v  Natural seasoning 

v  Artificial seasoning 

v  Water seasoning 

 Natural Seasoning

v  After felling, timbers are sawn into commercial sizes; 

v  They are stacked under covered shed; 

v  Sufficient space is left around each sawn piece for free air-circulation; 

v  Also known as air seasoning;  natural air remains circulating around each piece of the stack  and in due course of time, seasoning is brought about. 

 Advantages  

v  No skilled supervision is required; 

v  Simple and cheap method of seasoning; 

v  Thick section can be successfully seasoned. 

 Disadvantages  

v  Since depends on natural air, no control can be exercised over it; 

v  Slow method; depends  on climatic conditions, size and shape of the timber; 

v  Seasoning non uniform and uneven; 

v  Requires large space; 

v  Moisture cannot be brought to the desired level; 

v  Seasoned timber may have end split; 

v  Liable to be attacked by fungus and insects. 

Artificial Seasoning

The drying of timber by exposure to high temperatures in a closed chamber or by applying chemicals, steam and smoke is termed as artificial seasoning. 

Advantages of Artificial Seasoning

v  Rate of drying can be regulated; 

v  No chance of timber being attacked by fungus and insects; 

v  Takes short time; 

v  Desired moisture content can be attained during seasoning; 

v  Better control of air, temperature and humidity; 

v  Seasoning more uniform; 

v  No end splits. 

 Methods of Artificial Seasoning

1)     Smoking;  

2)     Boiling;  

3)     Steaming; 

4)     Kiln seasoning; 

5)     Chemical seasoning; 

6)     Electrical seasoning; 

Water Seasoning

Timbers and logs are immersed and allowed to remain in water for a couple of days, then dried in natural air. In this process, the sap is diluted and is partly removed. 

Decay or Disease of Timber 

Occurs due to fungal action; the fungi feeds on softwood and converts it into powder; however, decay does not occur either due to any chemical action or due to fermentation of sap. 

The Main Causes of Timber Decay are

v  Alternate dry and wet conditions; 

v  Defective seasoning of timber; 

v  Presence of fungi and insects such as marine borer, beetles, termite, etc. 

v  Lack of ventilation; 

v  Dark and damp condition; 

Timber Rots

v  It is a sort of timber decay. During rot disintegration of timber takes place and gases like H2S and CO2 are generated. 

v  Two types

ü  Dry rot 

ü  Wet rot

 Dry Rot

v  Disintegration of converted timber by the harmful effects of certain fungi, which feeds on timber and converts it into dry powder. 

v  Factors responsible are the same as those responsible for decay; 

v  If some timbers are affected by dry rot, the best way is to cut the affected portion; 

v  Dry rot may be preserved by using well-seasoned timber free from sap, and the timber should be adequately ventilated by fresh air; 

v  Detection: by tapping or scratching at one end and placing the ear at the other end of log. 

Wet Rot 

v  It is the decomposition of timber caused by moisture 

v  It is caused if alternate dry and wet conditions prevail around the timber

v  Not caused by fungal attack

v  When unseasoned timbers are exposed to rain and wind, they are liable to be attacked by wet rot

v  In wet rot, the timbers get converted into grayish brown powder

v  Can be prevented by using well-seasoned timber; also using tarred or painted timbers exposing to rain or water

Preservation of Timber

v  Preservation indicates an increase in life by developing resistance to insect attack, fungal infection and disease of timbers

v  A preservative acts like a disinfectant

v  A seasoned timber, since dried, is hygroscope and  to prevent re-absorption of moisture and to impart immunity, the tissues of dry/seasoned wood have to be soaked with some type of a preservative

v  Seasoning, therefore, prepares a timber for preservative treatment by driving away moisture and sap

Choice of Preservative is governed by 

v  Their toxicity and poisonous effects

v  Permanency in their effect in treated wood

v  Should not be injurious to wood tissues

v  Cheaply available and safe to handle v Should allow a decorative treatment

v  Should not disfigure exposed surface of timber

v  Non-inflammable

v  Should have a good covering quality

Methods of Preservatives

Charring  

v  Crude method; No special preservative is used

v  Timber kept wet for 0.5~1.0 hour and then burnt to a depth of 15-mm and cooled with water

v  A coal layer is formed on the surface which performs preservative functions

v  Layer is not affected by fungi, moisture or white ant

v  Used at lower ends of posts of timber

Tarring  

v  Application of a layer of hot tar on the surface

v  Generally applied to an embedded ends of posts

Painting

v  Performs both aesthetic and preservative purposes

Creosoting  

v  Creosotes are obtained by the distillation of coal, petroleum or wood substances 

v  Three types: Coal-tar creosote, water gas-tar and wood tar creosote 

v  Creosote oil is applied under pressure on wood surface 

v  Used on piles, poles and railway sleepers, etc. 

Water-Soluble Chemical Salts

v  Used some chemical salts which are not toxic in nature and are also soluble in water

v  They are odorless and can be painted on drying

v  When appearance is important in wood, this type is most suitable

v  Wood treated with water soluble salts requires to be re-dried

v  The effects of these chemicals are lost gradually and so wood requires be painting or varnishing for surface treatment

v  Cheaper than creosote treatment

v  Example: Zinc chloride treatment; Creosote oil + NaF→ known as Wolman’s salt

 Artificial Wood

 Veneer  

v  Thin sheets of timber of superior quality 

v  Obtained by rotating wooden logs of the timber against a sharp knife of rotary cutter

v  Thickness 0.4 to 6.0 mm or even more

v  After removing from parent logs,  they are dried in kiln to remove moisture

v  Used for manufacturing of plywood

 Plywood

v  Made from multiple veneers

v  Veneers are taken in odd numbers and are placed one above the other at right angles in successive veneers 

v  All veneers held together with the help of adhesives

v  3-ply, 5-ply, 7-ply, etc. are available; that is, veneers are used in odd numbers in a plywood

Advantages of plywood

v  Suffers little expansion or shrinkage due to change in moisture content 

v  Light and available in large sizes 

v  Available in decorative designs 

v  Not liable to split and cracks

v  Easy to work with

v  Make use of costly timber in most economical manner

 Impreg Timber  

v  Sunmica, formica, sungloss, etc. 

v  Veneers are partly or fully covered with resin; 

v  For this purpose, veneers are taken and immersed in resin. The resin fills in the wood cells and a consolidated mass is developed. The mass is then cured at a temperature of about 150 to 1600° C

 Characteristics of Impreg Timber

v  Strong, durable, good looking, weather resistant, electrically insulated and resists acidic effects

 Compreg Timber

v  Same as impreg timber; except, they are cured under pressure 

v  More durable and stronger than impreg timber

Fiber-Board 

v  Manufactured from wood or other  vegetable fibers; they are rigid boards of thickness varying from 6 mm to 25 mm; width 1.2m and length 3.5 m; 

v  The pieces of woods, cane or other vegetable fibers are heated in a hot water boiler; Due to boiling, the fibers get separated; 

v  These fibers are put in a vessel and steam is admitted in it under a pressure;

v  The steam pressure is then suddenly increased to 70 kg/cm2and this pressure is maintained for a few seconds; 

v  The steam pressure is  suddenly dropped down; in doing so, the natural adhesive contained in fibers is completely separated; 

v  Fibers are taken out of vessel and cleaned off all superfluous gums; 

v  They are spread on wire screen in form of loose sheets and pressed; the resulting material is called fiberboard; 

v  Depending on their form and composition, they are classified as insulating boards, medium hardboards, hardboards, super hardboards and laminated boards. 

v They may be used for following purposes 

ü  For the construction of walls panels and suspended ceilings

ü  Construct partitions

ü  Form-works

ü  As insulating materials against heat and sound ü As tabletops and for flush doors.

SOIL

v  The term soil is defined as an unconsolidated material, composed of solid particles, produced by the disintegration of rocks

v  The void space between the particles may contain air, water

v  The solid particles may contain organic matter

Classification of Soil

Based on Grain Size

Some Soil Classification Systems

1)     Unified Soil Classification System (USCS)

2)     American Association of State Highways & Transportation Officials (AASHTO) classification

3)     United States Department of Agriculture (USDA) classification

USCS

Importance of Soil in Civil Engineering

v  Any Civil Engineering Structure needs a stable foundation and all foundations constructed ultimately derive their support from the underlying soil

v  Soil is used in 

ü  Construction of embankments, dams

ü  As a stabilized sub-grade for roads, airports & runways

ü  Manufacturing of bricks, tiles, mortar etc.

v  Soil is, therefore, of great importance to engineers as a material of foundation and also as a material of construction

Basic Properties of Soil

v  Moisture Content

v  Specific Gravity

v  Unit Weight/Density

v  Void Ratio

v  Porosity

v  Relative Density

v  Permeability

v  Capillarity

v  Shrinkage & Expansion

v  Compressibility

v  Shearing Resistance

Shearing Resistance

v  Internal Friction

v  Cohesion

𝝉 = 𝒄 + 𝝈 𝒕𝒂𝒏𝝋

Where,

𝜏 = 𝑆ℎ𝑒𝑎𝑟𝑖𝑛𝑔 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑟 𝑠ℎ𝑒𝑎𝑟 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑠𝑜𝑖𝑙

𝑐 = 𝐶𝑜ℎ𝑒𝑠𝑖𝑜𝑛 𝑜𝑓 𝑠𝑜𝑖𝑙

𝜎 = 𝑁𝑜𝑟𝑚𝑎𝑙 𝑠𝑡𝑟𝑒𝑠𝑠 (𝑓𝑜𝑟𝑐𝑒) 𝑜𝑛 𝑡ℎ𝑒 𝑠𝑜𝑖𝑙 𝑏𝑒𝑖𝑛𝑔 𝑐𝑜𝑛𝑠𝑖𝑑𝑒𝑟𝑒𝑑

𝜑 = 𝐴𝑛𝑔𝑙𝑒 𝑜𝑓 𝑖𝑛𝑡𝑒𝑟𝑛𝑎𝑙 𝑓𝑟𝑖𝑐𝑡𝑖𝑜𝑛

Phase Diagram

Soil is a three-phase material which consists of solid particles which make up the soil skeleton and voids which may be full of water if the soil is saturated, may be full of air if the soil is dry, or may be partially saturated as shown in Figure

Figure: Air, Water and Solid phases in a typical soil

It is useful to consider each phase individually as shown in following Table

Index Properties/Consistency of Soil

v  Liquid Limit (LL)

v  Plastic Limit (PL)