Types of Formwork (Shuttering) for Concrete Construction:

Types of Formwork (Shuttering) for Concrete Construction:

Timber Formwork:

Timber for formwork should satisfy the following requirement:

It should be

1. well seasoned
2. light in weight
3. easily workable with nails without splitting
4. free from loose knots

Timber used for shuttering for exposed concrete work should have smooth and even surface on all faces which come in contact with concrete.

Compressive Strength Definition

Compressive Strength Definition

Compressive strength is the ability of material or structure to carry the loads on its surface without any crack or deflection. A material under compression tends to reduce the size, while in tension, size elongates.

Cement and History of cement

Cement

• A cement is a binder, a substance used in construction that sets and hardens and can bind other materials together.

• The most important types of cement are used as a component in the production of mortar in masonry, and of concrete, which is a combination of cement and an aggregate to form a strong building material.

Cement History

• Joseph Aspedin of Yorkshire (U.K.) was the first to introduce Portland cement in 1824 formed by heating a mixture of limestone and finely divided clay in a furnace to a temperature high enough to drive off the carbonic acid gas.
• In 1845, Issac C. Johnson invented the cement by increasing the temperature at which the mixture of limestone and clay were burned to form clinker. This cement was the prototype of the modern Portland cement.
• From then onward, a gradual improvement in the properties and qualities of cement has been made possible by researchers in U.S.A., U.K., France and Germany

Cement Clinker

In the manufacture of Portland cement, clinker occurs as lumps or nodules, usually 3 millimeters (0.12 in) to 25 millimeters (0.98 in) in diameter, produced by sintering (fused together without melting to the point of liquefaction) limestone and alumino silicate materials such as clay during the cement kiln stage.

Today cement finds extensive use in all types of construction works; in structures where high strength is required e.g. bridge piers, light houses, lofty towers, and large structures such as bridges, silos, chimneys. And also in structures exposed to the action of water, e.g. reservoirs, dams, dock yards etc. Cement mortar, concrete, reinforced brick work, artificial stones, plastering, pointing and partition walls are routinely used in buildings.

Lime Production

Lime Production

When limestone (calcium carbonate) is heated, at about 1000 °C it undergoes thermal decomposition. It loses carbon dioxide and turns into quicklime (calcium oxide).

The reaction is carried out in specially constructed lime kilns(a kiln is a high temperature oven). Limestone is added at the top and quicklime is removed from the bottom in a continuous process.

Lime Cycle

Lime Production

FACTORS AFFECTING CONCRETE ADMIXTURES PERFORMANCE

The various factors which affect the performance of concrete admixtures are:

1. Type of super-plasticizer:

The admixture will be more effective if molecular weight of the super-plasticizer is high.

2. Dosage:

The quantity of admixture should be optimum. Excess of admixture may cause segregation or bleeding. It may also cause excessive retardation. The optimum does should be estimated by trials.

3. Compatibility with Cement:

All admixtures may not produce same results with different cements. Therefore before using any admixture, its compatibility with cement has to be established. Properties of cement like fineness, chemical-composition, C3A content etc. affect the performance of admixture. Therefore, trials have to be made before finalizing an optimum does of admixture.

4. Mix Design:

All constituents of mix affect the performance of the super-plasticizer as given below:

• Water: more water in the mix improves the physical interaction and dispersion of admixtures.
• Coarse aggregate: proportioning and grading of coarse aggregates influence the performance of concrete admixture.
• Fine aggregate: proportioning, grading and silt content also influence the performance of concrete admixture.
• Cement: its fineness, C3A content influence the performance of admixture. Higher C3A reduces efficiency of admixture.
• Other admixture: presence of other admixtures also influences the performance of concrete admixtures.

Therefore, proper trials before actual use are very vital for effectiveness of admixture.

Other factors admixture performance:

Certain other factors like temperature and humidity at the time of concreting also affect the performance of the concrete admixtures.

Drum mixtures are considered ideal for mixing admixtures, instead we should use pan or compulsive shaft mixes.

What are the reasons of establishing minimum area of reinforcement and maximum area of reinforcement?

Beams may be designed to be larger than required for strength consideration owing to aesthetics or other reasons. As such, the corresponding steel ratio is very low and the moment capacity of pure concrete section based on the modulus of rupture is higher than its ultimate moment of resistance. As a result, reinforcement yields first and extremely wide cracks will be formed. A minimum area of reinforcement is specified to avoid the formation of wide cracks.

On the other hand, a maximum area of reinforcement is specified to enable the placing and compaction of fresh concrete to take place easily.

Units of Measurement

Units of measurement used in past and present surveys are

For construction work: feet, inches, fractions of inches (m, mm)
For most surveys: feet, tenths, hundredths, thousandths (m, mm)
For National Geodetic Survey (NGS) control surveys: meters, 0.1, 0.01, 0.001 m

The most-used equivalents are
1 meter=39.37 in =3.2808 ft
1 rod =1 pole=1 perch=16.5ft(5.029 m)
1 engineer’s chain =100 ft =100 links (30.48 m)
1 Gunter’s chain= 66 ft (20.11 m) =100
Gunter’s links(lk)=4 rods=0.020 km

1 acre=100,000 sq (Gunter’s) links=43,560ft²= 160 rods²=10 sq (Gunter’s) chains=4046.87m²=0.4047 ha

1 rood=1011.5 m²=40 rods²

1 ha= 10,000 m²=107,639.10 ft²=2.471 acres

1 arpent=about 0.85 acre, or length of side of 1 square arpent (varies) (about 3439.1 m²)

1 statute mi=5280 ft=1609.35 m

1 mi²=640 acres (258.94 ha)
1 nautical mi (U.S.)= 6080.27 ft= 1853.248 m

1 fathom=6 ft (1.829 m)

1 cubit=18 in (0.457 m)

1 degree=0.01745 rad=60 min =3600 s
sin 1 =0.01745241
1 rad = 57.30 degree

Design of foundations for building

Depth of Foundation :
                       Minimum depth of foundation is given by: H=P/W(1-Sinᶲ/1+Sinᶲ)
Ranking formula applicable to loose soils.
Where H= Depth of foundation in m Below ground level.
            P= Safe permissible pressure on base in kg/sq.m
            W= Weight of soil in kg/cu.m
            ᶲ  = Angle of response of soil material.

for tall structure such as chimneys and towers  3/4th of safe load om the soil should be taken and the depth  h increased by 1/3 .
foundations are generally taken down to about  90 to 120  Cm for main walls 45 to 60 Cm for partition walls and 30 cm for boundary walls in ordinary soil  2 to 3 story building weight . But foundation must be taken down to a firm soil and below weathering effects . when part of a footing is in weaker soil , that part should be take down deeper and separated , or measures adopted for equal distribution  of pressures according to the bearing capacity if the respective soils.

ESTIMATION METHODS OF BUILDING WORKS

The estimation of building quantities like earth work, foundation concrete, brickwork in plinth and super structure etc., can be workout by any of following two methods:

a) Long wall – short wall method

b) Centre line method.

c) Partly centre line and short wall method.

a) Long wall-short wall method:

In this method, the wall along the length of room is considered to be long wall while the wall perpendicular to long wall is said to be short wall. To get the length of long wall or short wall, calculate first the centre line lengths of individual walls. Then the length of long wall, (out to out) may be calculated after adding half breadth at each end to its centre line length. Thus the length of short wall measured into in and may be found by deducting half breadth from its centre line length at each end. The length of long wall usually decreases from earth work to brick work in super structure while the short wall increases. These lengths are multiplied by breadth and depth to get quantities.

b) Centre line method:

This method is suitable for walls of similar cross sections. Here the total centre line length is multiplied by breadth and depth of respective item to get the total quantity at a time. When cross walls or partitions or verandah walls join with main wall, the centre line length gets reduced by half of breadth for each junction. Such junction or joints are studied carefully while calculating total centre line length. The estimates prepared by this method are most accurate and quick.

c) Partly centre line and partly cross wall method:

This method is adopted when external (i.e., around the building) wall is of one thickness and the internal walls having different thicknesses. In such cases, centre line method is applied to external walls and long wall-short wall method is used to internal walls. This method suits for different thicknesses walls and different level of foundations. Because of this reason, all Engineering departments are practicing this method.

MATERIALS FOR DAMP PROOF COURSE

Damp proof course (DPC) is a barrier of impervious material built into a wall or pier to prevent moisture from moving to any part of the building.

Following are the materials generally used for damp proofing of structures:

1) Flexible Materials:

The materials, which do not crack and deform their shape when subjected to loading, are called Flexible Materials

a) Bitumen Mastic (Mastic Asphalt)

• It consists of asphalt or bitumen mixed with fine sand in hot state to form an impervious mass.
• Due to this consistency it can be spread (when hot) to a depth of 2.5cm to 5cm, which sets on cooling.
• It provides good impervious layer but special care is needed in its laying.
• b) Bitumen Felts (Sheets):
  • It consists of 6mm thick sheet of bitumen prepared in rolls having width equal to that of brick wall.
  c) Hot laid Bitumen:
  This material is used on a bedding of cement concrete or mortar.
  • This should be applied in two layers at the rate of 1.75kg/m2 of the area.
  d) Metal Sheets:
  
  • Metal sheets of Copper, Aluminium, or Lead are used to prevent dampness, but they are costly.
  • Sheets of these materials are used throughout the thickness of the wall.
  • The sheets of Lead are laid over Lime Mortar and not with Cement.
  • Mortar due to the chemical reaction of Cement over the Lead.
  • The sheets of metal should be coated with asphalt.
  • The thickness of the sheets should not be less than 3mm.
  • 
    

  2) Rigid Materials:

  • The materials, which do not resist transverse stresses and cracks when subjected to sever loading, are known as Rigid Materials.
  a) Rich Concrete
  • 1.2cm to 4cm thick layer of Rich Concrete (1:2:4) painted with two coats of hot bitumen is used as horizontal D.P.C.
  • It also prevents the moisture penetration by capillary action.
  • These layers are laid where the damp is not excessive.
  b) Mortar:
  • 2cm thick layer of Rich Cement and Sand Mortar (1:3) is applied on the inner face of external wall.
  • This is a vertical D.P.C.
  • The surface is than painted with two coats of hot bitumen.
  c) Bricks:
  • Over burnt or dense bricks in one or two layers can be used as cheap and effective DPC.
  • They are laid in Rich Cement and Sand Mortar (1:3).
  • Bricks are rarely used as DPC except in cheap houses.
  d) Stones or Slates:
  • Two layers of stone slabs or slates laid in Lime, Cement and Sand Mortar (1:1:6) make a best DPC.
  • They can also be laid in Cement Sand Mortar.
  • It is used where a good quality of stone is easily and cheaply available.
  
  

FACTORS AFFECTING CONCRETE MIX DESIGN STRENGTH

Factors that affects the concrete mix design strengths are:

Variables in Mix Design

A. Water/cement ratio

B. Cement content

C. Relative proportion of fine & coarse aggregates

D. Use of admixtures

A. Water/cement ratio

Water to cement ratio (W/C ratio) is the single most important factor governing the strength and durability of concrete. Strength of concrete depends upon W/C ratio rather than the cement content. Abram’s law states that higher the water/cement ratio, lower is the strength of concrete. As a thumb rule every 1% increase in quantity of water added, reduces the strength of concrete by 5%. A water/cement ratio of only 0.38 is required for complete hydration of cement. (Although this is the theoretical limit, water cement ratio lower than 0.38 will also increase the strength, since all the cement that is added, does not hydrate) Water added for workability over and above this water/cement ratio of 0.38, evaporates leaving cavities in the concrete. These cavities are in the form of thin capillaries. They reduce the strength and durability of concrete. Hence, it is very important to control the water/cement ratio on site. Every extra liter of water will approx. reduce the strength of concrete by 2 to 3 N/mm2and increase the workability by 25 mm. As stated earlier, the water/cement ratio strongly influences the permeability of concrete and durability of concrete. Revised IS 456-2000 has restricted the maximum water/cement ratios for durability considerations by clause 8.2.4.1, table 5.

B. Cement content

Cement is the core material in concrete, which acts as a binding agent and imparts strength to the concrete. From durability considerations cement content should not be reduced below 300Kg/m3 for RCC. IS 456 –2000 recommends higher cement contents for more severe conditions of exposure of weathering agents to the concrete. It is not necessary that higher cement content would result in higher strength. In fact latest findings show that for the same water/cement ratio, a leaner mix will give better strength. However, this does not mean that we can achieve higher grades of concrete by just lowering the water/cement ratio. This is because lower water/cement ratios will mean lower water contents and result in lower workability. In fact for achieving a given workability, a certain quantity of water will be required. If lower water/cement ratio is to be achieved without disturbing the workability,cement content will have to be increased. Higher cement content helps us in getting the desired workability at a lower water/cement ratio. In most of the mix design methods, the water contents to achieve different workability levels are given in form of empirical relations.

Water/cement ratios required to achieve target mean strengths are interpolated from graphs given in IS 10262 Clause 3.1 and 3.2 fig 2. The cement content is found as follows: –

Thus, we see that higher the workability of concrete, greater is cement content required and vice versa. Also, greater the water/cement ratio, lower is the cement content required and vice versa.

C. Relative proportion of fine, coarse aggregates gradation of aggregates

Aggregates are of two types as below:

a. Coarse aggregate (Metal): These are particles retained on standard IS 4.75mm sieve.

b. Fine aggregate(Sand): These are particles passing standard IS 4.75mm sieve.

Proportion of fine aggregates to coarse aggregate depends on following:

i. Fineness of sand: Generally, when the sand is fine, smaller proportion of it is enough to get a cohesive mix; while coarser the sand, greater has to be its proportion with respect to coarse aggregate.

ii. Size& shape of coarse aggregates: Greater the size of coarse aggregate lesser is the surface area and lesser is the proportion of fine aggregate required and vice versa. Flaky aggregates have more surface area and require greater proportion of fine aggregates to get cohesive mix. Similarly, rounded aggregate have lesser surface area and require lesser proportion of fine aggregate to get a cohesive mix.

iii. Cement content: Leaner mixes require more proportion of fine aggregates than richer mixes. This is because cement particles also contribute to the fines in concrete.

TYPES OF DEEP FOUNDATION

Deep foundations are required to carry loads from a structure through weak compressible soils or fills on to stronger and less compressible soils or rocks at depth, or for functional reasons. These foundations are those founding too deeply below the finished ground surface for their base bearing capacity to be affected by surface conditions, this is usually at depths >3 m below finished ground level. Deep foundations can be used to transfer the loading to a deeper, more competent strata at depth if unsuitable soils are present near the surface.

The types of deep foundations in general use are as follows:

1) Basements

2) Buoyancy rafts (hollow box foundations)

3) Caissons

4) Cylinders

5) Shaft foundations

6) Piles

Basement foundations:

These are hollow substructures designed to provide working or storage space below ground level. The structural design is governed by their functional requirements rather than from considerations of the most efficient method of resisting external earth and hydrostatic pressures. They are constructed in place in open excavations.

Buoyancy rafts (hollow box foundations)

Buoyancy rafts are hollow substructures designed to provide a buoyant or semi-buoyant substructure beneath which the net loading on the soil is reduced to the desired low intensity. Buoyancy rafts can be designed to be sunk as caissons, they can also be constructed in place in open excavations.

Caissons foundations:

Caissons are hollow substructures designed to be constructed on or near the surface and then sunk as a single unit to their required level.

Cylinders:

Cylinders are small single-cell caissons.

Shaft foundations:

Shaft foundations are constructed within deep excavations supported by lining constructed in place and subsequently filled with concrete or other pre-fabricated load-bearing units.

Pile foundations:

Pile foundations are relatively long and slender members constructed by driving preformed units to the desired founding level, or by driving or drilling-in tubes to the required depth – the tubes being filled with concrete before or during withdrawal or by drilling unlined or wholly or partly lined boreholes which are then filled with concrete.

Tests on Bricks

Tests on Bricks
The following laboratory testsmay be conducted on the bricks to find their suitability:
(i) Crushing strength
(ii) Absorption
(iii) Shape and size and
(iv) Efflorescence.
(i)Crushing Strength:The brick specimen are immersed in water for 24 hours. The frog of the
brick is filled flush with 1:3 cement mortar and the specimen is stored in damp jute bag for 24 hours and
then immersed in clean water for 24 hours. The specimen is placed in compression testing machine
with 6 mm plywood on top and bottom of it to get uniform load on the specimen. Then load is applied
axially at a uniform rate of 14 N/mm2
. The crushing load is noted. Then the crushing strength is the
ratio of crushing load to the area of brick loaded. Average of five specimen is taken as the crushing
strength.
(ii)Absorption Test:Brick specimen are weighed dry. Then they are immersed in water for a
period of 24 hours. The specimen are taken out and wiped with cloth. The weight of each specimen in
wet condition is determined. The difference in weight indicate the water absorbed. Then the percentage
absorption is the ratio of water absorbed to dry weight multiplied by 100. The average of five specimen
is taken. This value should not exceed 20 per cent.
(iii)Shape and Size:Bricks should be of standard size and edges should be truely rectangular
with sharp edges. To check it, 20 bricks are selected at random and they are stacked along the length,
along the width and then along the height. For the standard bricks of size 190 mm × 90 mm × 90 mm.
IS code permits the following limits:
Lengthwise: 3680 to 3920 mm
Widthwise: 1740 to 1860 mm
Heightwise: 1740 to 1860 mm.
The following field testshelp in acertaining the good quality bricks:
(i) uniformity in size
(ii) uniformity in colour
(iii) structure
(iv) hardness test
(v) sound test
(vi) strength test.
(i)Uniformity in Size:A good brick should have rectangular plane surface and uniform in size.
This check is made in the field by observation.
(ii)Uniformity in Colour:A good brick will be having uniform colour throughout. This
observation may be made before purchasing the brick.
(iii)Structure:A few bricks may be broken in the field and their cross-section observed. The
section should be homogeneous, compact and free from defects such as holes and lumps.
(iv)Sound Test:If two bricks are struck with each other they should produce clear ringing sound.
The sound should not be dull.
(v)Hardness Test: For this a simple field test is scratch the brick with nail. If no impression is
marked on the surface, the brick is sufficiently hard
(vi)Efflorescense: The presence of alkalies in brick is not desirable because they form patches
of gray powder by absorbing moisture. Hence to determine the presence of alkalies this test is performed
as explained below:
Place the brick specimen in a glass dish containing water to a depth of 25 mm in a well ventilated
room. After all the water is absorbed or evaporated again add water for a depth of 25 mm. After second
evaporation observe the bricks for white/grey patches. The observation is reported as ‘nil’, ‘slight’,
‘moderate’, ‘heavy’ or serious to mean
(a) Nil: No patches
(b) Slight: 10% of area covered with deposits
(c) Moderate: 10 to 50% area covered with deposit but unaccompanied by flaking of the surface.
(d) Heavy: More than 50 per cent area covered with deposits but unaccompanied by flaking of
the surface.
(e) Serious: Heavy deposits of salt accompanied by flaking of the surface.

Properties of Bricks

Properties of Bricks
The following are the required properties of good bricks:
(i)Colour: Colour should be uniform and bright.
(ii)Shape: Bricks should have plane faces. They should have sharp and true right angled corners.
(iii)Size:Bricks should be of standard sizes as prescribed by codes.
(iv)Texture:They should possess fine, dense and uniform texture. They should not possess
fissures, cavities, loose grit and unburnt lime.
(v)Soundness:When struck with hammer or with another brick, it should produce metallic
sound.
(vi)Hardness: Finger scratching should not produce any impression on the brick.
(vii)Strength:Crushing strength of brick should not be less than 3.5 N/mm2.
A field test for
strength is that when dropped from a height of 0.9 m to 1.0 mm on a hard ground, the brick should not
break into pieces.
(viii)Water Absorption:After immercing the brick in water for 24 hours, water absorption should
not be more than 20 per cent by weight. For class-I works this limit is 15 per cent.
(ix)Efflorescence:Bricks should not show white patches when soaked in water for 24 hours and
then allowed to dry in shade. White patches are due to the presence of sulphate of calcium, magnesium
and potassium. They keep the masonry permanently in damp and wet conditions.
(x)Thermal Conductivity:Bricks should have low thermal conductivity, so that buildings
built with them are cool in summer and warm in winter.
(xi)Sound Insulation:Heavier bricks are poor insulators of sound while light weight and hollow
bricks provide good sound insulation.
(xii)Fire Resistance:Fire resistance of bricks is usually good. In fact bricks are used to encase
steel columns to protect them from fire.

Types of Bricks

Types of Bricks
Bricks may be broadly classified as:
(i) Building bricks
(ii) Paving bricks
(iii) Fire bricks
(iv) Special bricks.
(i)Building Bricks:

These bricks are used for the construction of walls.
(ii)Paving Bricks: 

These are vitrified bricks and are used as pavers.
(iii)Fire Bricks:

These bricks are specially made to withstand furnace temperature. Silica bricks
belong to this category.
(iv)Special Bricks:

These bricks are different from the commonly used building bricks with
respect to their shape and the purpose for which they are made. Some of such bricks are listed below:
(a) Specially shaped bricks
(b) Facing bricks
(c) Perforated building bricks
(d) Burnt clay hollow bricks
(e) Sewer bricks
(f ) Acid resistant bricks.
(a)Specially Shaped Bricks:Bricks of special shapes are manufactured to meet the
requirements of different situations.

(b)Facing Bricks:

These bricks are used in the outer face of masonry. Once these bricks are

provided, plastering is not required. The standard size of these bricks are 190 × 90 ×

90 mm or 190 × 90 × 40 mm.

(c)Perforated Building Bricks:

These bricks are manufactured with area of perforation of

30 to 45 per cent. The area of each perforation should not exceed 500 mm

2

. The perforation

should be uniformly distributed over the surface. They are manufactured in the size 190

× 190 × 90 mm and 290 × 90 × 90 mm.

(d)Burn’t Clay Hollow Bricks:

Figure  shows a burnt clay hollow brick. They are light

in weight. They are used for the construction of partition walls. They provide good thermal

insulation to buildings. They are manufactured in the sizes 190 × 190 × 90 mm,

290 × 90 × 90 mm and 290 × 140 × 90 mm. The thickness of any shell should not be less

than 11 mm and that of any web not less than 8 mm.

Sewer Bricks:

These bricks are used for the construction of sewage lines. They are

manufactured from surface clay, fire clay shale or with the combination of these. They

are manufactured in the sizes 190 × 90 × 90 mm and 190 × 90 × 40 mm. The average

strength of these bricks should be a minimum of 17.5 N/mm2

. The water absorption

should not be more than 10 per cent.

(f )Acid Resistant Bricks:

These bricks are used for floorings likely to be subjected to acid

attacks, lining of chambers in chemical plants, lining of sewers carrying industrial wastes

etc. These bricks are made of clay or shale of suitable composition with low lime and

iron content, flint or sand and vitrified at high temperature in a ceramic kiln.