👉CONSTRUCTION ENGINEERING TIPS @engineer03
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*ASTM Abbrevation : American Society for Testing Materials
*Grade of Concrete is denoted as Cement: Sand: Aggregate (Ex C-20 Grade : 1:2:3)
*C/C means Center to Center Distance
*DL means Development Length
*Lapping of bars not allowed if the dia of bar is more than 36mm.
*For circular column minimum of 6 longitudinal bars are used and 4 for Rectangular.
*The minimum thickness of slab is 0.125m
*Water pH value less than 6 should not be used for construction purpose.
*The concrete Should not be thrown from a height more than 1.5m.
*The Compressive strength of Bricks is 3.5 N /mm
*The initial setting time shall not be less than 30 minutes and the final setting time of cement is 10hours.
*Dead Load means Self weight of Structure
*Sand having moisture content more than 5% should not be used for Concrete mix.
*DPC means Damp Proof Course. The thickness of DPC should not be less than 2.5cm.
*Cube test is carried out for each 30m usage of concrete.
*RMC : Ready Mix concrete, The concrete is made at factory and transported to the site, This type of concrete is used where there is a lack of space for mixing the concrete and used where a huge amount of concrete is required for construction.
*The height of floor is usually 3m or 10ft (If a person asks you whats the height of 12 storied building?
Ans: 3m x 12floors = 36m)
*A head mason can work 25-30m in a day.
*In construction, the rate analysis for the work of workers is calculated in Man Hours. (Ex: 10 Birr for 1 Man hour)
*Cantilever Beam has One fixed support and the other end is free.
*Simple supported beam has a minimum of two supports.
*PCC (Plain Cement Concrete) this type of concrete is used on members only when the tensile forces are not acting on it.
*The weight of first class clay brick should be 3.85 Kg. and it has a crushing
strength of 10.5MN/m
*Adding more water in the concrete mix to increase setting time leads to form
the Cracks or honeycomb in hardened concrete.
*Vibration in freshly made concrete is done to remove the air bubbles in concrete mix.
*Impermeability of concrete: The concrete which resists the the entry of water or moisture into it.
*The concrete can be lifted to a maximum height of 50m using Concrete
Pumps.
*The curing Period of RCC is 28days .
*The minimum sill level height should be
44 inches.
✔️The transverse reinforcement provided in columns are called Ties .
✔️The transverse reinforcement provided in
Beams is called as Stirrups .
✔️Stirrups in Beams and Ties in Column are provided to handle the shear force and to keep longitudinal bars in position.
✔️The Prime reason for using steel as reinforcement is due to thermal expansion.
The thermal expansion
coefficient of concrete and steel is (approximately) same having value
✔️C-25 grade of concrete is generally used in the construction of slab.
✔️Weight of Bar is calculated using formula D /162 (D = Dia of bar in mm)
✔️The No. of HCB required for 1 metr square of masonary wall are 13 HCB blocks.
✔️Specific gravity of Cement is 3.16g/ cm ; Bricks is 2g/cm ; Sand is 2.65g/cm ,
✔️Standard Size of Brick is 19cm x 9cm x 4 cm or 19cm or 9cm x 9 cm
✔️Floor area occupied by 50kg of Cement bag is 0.3m and height of 0.18m.
✔️As per EBCS Maximum dia of bar used in the slab should not exceed 1/8th of the total thickness of the slab.
✔️The slope or Pitch of the stair should be in between 25 degrees to 40 degrees.
✔️The rise in stairs is in between 150mm to 200mm.
✔️Tread in staircase is in between 250mm to 300mm.
✔️Hook length should not be less than 9D (Dia of Bar)
✔️Unit weight of PCC is 24KN/m , RCC is 25 KN/m , Steel is 7850Kg/m
✔️The volume of 50kg cement bag is
1.3CFT.
✔️Theodolite least count is 20Secs whereas Compass Least count is 30mins .
✔️TMT bars : TMT means Thermo Mechanically treated bars
✔️Cement more than 3 months old cannot be used for construction
✔️The length of each bar from factory is 12m.
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♻️Slab directly supported on columns( without beams or beams only at the perimeter of the building) are called Flat slabs or flat plates.

❓What is the Difference between flat slab and flat plate?

♻️Flat slab is one with either drop panel or column capital(or both at the same time) that helps reduce shear stress on the column slab junction. On the other hand flat plates are slabs systems with the slab connected to the column directly.

♻️Flat slabs can bridge larger spans when compared to flat plates. Due to shear demand and deflection requirement the span flat plates can bridge is very small. According to macgregor and whites book, mechanics and design of reinforced concrete Structures, flat plates are most economical for spans from 15 to 20ft [4.5 to 6 m] and flat slabs are used for spans of 20 to 30 ft[6 to 9 m].

♻️Flat slab or plates can be analyzed using several methods of structural analysis. Some of these methods are:

✅DDM(direct design method),

✅EFM(equivalent frame method),

✅FEM(finite element method),

✅Grillage method,

✅Yeild line method and

✅Strip method of analysis.

discussed on
@engineersWorks

Flat slab( notice the column head and drop panel at the column slab junction).

@engineersWorks

Flat plate(notice the direct connection between the slab and the column).

@engineersWoks
@engineer03
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👉PROPERTIES OF AGGREGATES FOR CONCRETE @engineersWorks
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▶Approximately 75% of the volume of concrete is occupied by aggregates,so
quality of aggregates plays an important role in determining properties of concrete.
*Aggregates come in various shapes, sizes, and materials ranging from fine particles of sand to large, coarse rocks. *Natural aggregates are formed by process of weathering and abrasion or by artificially crushing large parent mass.
Because cement is the most expensive ingredient in making concrete, it is
desirable to minimize the amount of cement used. 70 to 80% of the volume of
concrete is aggregate in order to keep the cost of the concrete low.
*Soft, porous aggregates can result in weak concrete with low wear resistance, while using hard aggregates can make strong concrete with a high resistance to abrasion.
*Aggregates are of two basic types: Coarse: crushed rock, gravel or screenings.
*Fine: fine and coarse sands and crusher fines Aggregates should be clean, hard, and strong.
*The aggregate is usually washed to remove any dust, silt, clay, organic matter, or other impurities that would interfere with
the bonding reaction with the cement paste.
*The choice of aggregate is determined by the proposed use of the concrete.
*Normally sand, gravel, and crushed stone are used as aggregates to make concrete.
*The aggregate should be well-graded to improve packing efficiency and minimize the amount of cement paste needed. Also, this makes the concrete more workable.
Some of the important properties of aggregates are discussed below.
▶PROPERTIES OF AGGREGATES
1. SOUNDNESS:Rocks that undergo volume changes due to wetting and drying are rare. However, aggregate is susceptible to volume change during freezing and thawing cycles.
*Freezing can cause internal stresses to build up as water inside the aggregate freezes and expands.
2. WEAR RESISTANCE
A good aggregate will be hard, dense, strong, and
free of porous material. The abrasion resistance of
aggregate can be tested by the Los Angeles abrasion test; however, this test does not match
well with concrete wear in the field.
3. ALKALI-AGGREGATE
REACTION: An expansive reaction between some reactive forms of silica with the aggregate and alkalis in the cement paste.
*The result is overall cracking in the
structure, manifesting itself in map or pattern cracking at the surface. *This reaction can be
controlled most easily by using low-alkali cements.
However, due to changes in manufacturing, low-
alkali cements may not be feasible.
*A better approach is to avoid aggregate with the potential or proven record of reactivity. A low w/c ratio is very impermeable and will slow down the reaction but not stop it. No adverse reactions will occur without external water.
4. OTHER ALKALI-SILICA
REACTIONS: Sand-gravels found in river systems of Kansas and Nebraska are highly reactive and cause map cracking. *Replacement of 30% of the aggregate with
crushed limestone is effective in reducing the damage. Basically, it results in the separation of flat clay minerals causing very slow expansion.
5. ALKALI-CARBONATE REACTIONS: An expansive reaction involving clayey
carbonate rock. Reaction can be controlled by using low-alkali cements or blending aggregate with other less reactive material.
*ASTM has set standards for deleterious substances in aggregates, which depend on application.
6. IMPURITIES: Solid materials – particles passing a 200- mesh sieve.
*These fine particles may increase water requirements and interfere with surface bonding
between cement and coarse aggregates.
Soluble substances –organic matter may interfere chemically with alkaline cement pastes affecting setting time. *Aggregates obtained from the sea should be thoroughly cleaned
to avoid problems from salt contamination.
7. UNSOUND PARTICLES
Soft particles such as clay lumps, wood, and coal
will cause pitting and scaling at the surface. Organic compounds can be released which interferewith setting and hardening. Weak material of low density which have low wear resistance should also be avoided.

@engineer03

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👉Morning Lecture @engineers Works
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*Different Ingredients of Cement-Their Proportion,
Functions and Limitations
The Ordinary Portland cement contains different
ingredients with varied proportions. Each ingredients
imparts different property to the cement. To
produce good quality of cement, we must know the
proportions, functions and limitations of different
ingredients of cement.
Proportion of Ingredients of Cement
Different ingredients of cement and their proportions
are as follows:
1. Lime (CaO)
2. Silica (SiO )
3. Alumina(Al O )
4. Iron (Fe O )
5. Magnesia (MgO)
6. Calcium sulfate (CaSO )
7. Sulfur (SO )
8. Alkalis
Functions and Limitations of Cement Ingredients
1.Lime (CaO)
Lime or calcium oxide is the most important
ingredient of cement. The cement contains 60 to
67% of lime in it. It is obtained from limestone,
chalk, shale etc. Adequate quantity of lime in
cement is helpful to form the silicates and
aluminates of calcium.
If lime is added in excess quantity the cement
becomes unsound as well as expansion and
disintegration of cement will occur.
If lime content is lower than the minimum
requirement strength of cement will reduce and also
setting time of cement will decrease.
2.Silica
Silica or silicon dioxide is the second largest
quantity of cement ingredients which is about 17 to
25%. Silica can be obtained from sand, argillaceous
rock etc. Sufficient quantity of silica helps for the
formation of di-calcium and tri-calcium silicates
which imparts strength to the cement.
Excess silica in cement will increase the strength of
cement but at the same time setting time of
cement also increased.
3.Alumina (Al O )
Alumina in cement is present in the form of
aluminum oxide. The range of alumina in cement
should be 3 to 8%. It is obtained from bauxite,
alumina contain clay etc. Alumina imparts quick
setting property to the cement.
In general, high temperature is required to produce
required quality of cement. But alumina when added
with cement ingredients it behaves as a flux and
reduces the clinkering temperature which finally
weakens the cement. So, to maintain the high
temperature alumina should not be used in excess
quantity.
4.Iron oxide (Fe O )
Iron oxide quantity in cement is ranges from 0.5 to
6%.It can be obtained from fly ash, iron ore, scrap
iron etc. The main function of iron oxide is to
impart color to the cement.
At high temperatures, Iron oxide forms tricalcium
aluminoferrite by reacting with aluminum and
calcium. The resultant product imparts the strength
and hardness properties to the cement.
5.Magnesia (MgO)
Cement contains Magnesia or Magnesium oxide in
the range of 0.1 to 3%. Magnesia in cement in
small quantities imparts hardness and color to the
cement.
If it is more than 3%, the cement becomes unsound
and also strength of the cement reduces.
6.Calcium sulfate (CaSO )
Calcium sulfate is present in the form of gypsum in
the cement. It is found together with limestone. It
ranges between 1 to 3%.
The function of calcium sulfate in cement is to
increase the initial setting time of cement.
7.Sulfur (SO )
Sulfur or sulfur trioxide in the cement is about 1 to
3%. Its function is to make the cement sound. If it
is in excess quantity the cement becomes unsound.
8. Alkalis
Alkalis like soda and potash are present in the
cement which normally ranges from 0.1 to 1%.
During manufacturing process of cement most of
the alkalis are carried away by the flue gases at the
time of heating. Hence cement contains very small
quantities of alkalis in it.
If alkalis content is more than 1% then it will cause
several problems like alkali aggregate reaction,
efflorescence, staining etc.
.
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👉BASICS OF CRACKING PROBLEMS: @engineer03
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▶The subject “ CRACKS “ or “ CRACKING “ in
concrete is indeed much debated. However, there is
inadequate clarity as to the reason for cracking and what may be done to limit its occurrence or
eliminate it altogether.
The phenomenon of the appearance of cracks in
concrete is often a subject that raises several
questions. Either at the initial stage or with time,
cracks may appear in a concrete structure. It should first of all be accepted that cracks of some type or other are inevitable in any concrete. They can be minimized to a large extent by proper practices.
*Cracks may be big or small, structural or non-
structural. All of them can be a nuisance by way of
either marring the appearance or function as a passage for atmospheric polluting gases and
moisture to either the body of concrete and causes
distress.
*Cracks in the concrete structure do not always
mean that the structure is not usable. As cracking
of concrete is inherent, what really matters is the
type of structure and the nature of cracking. Cracks
that are acceptable for building structures may not be acceptable for water relating structures.
Considering that cracking can never be completely
eliminated, it is necessary to be aware of the
causes, evaluation and the methods of repair
whoever required.
CRACKS Cracks are generally of tow types : Structural and nonstructural
*Cracks can occur in hardened or unhardened concrete.
*STRUCTURAL CRACKS
It is fundamental that hardened reinforced concrete cracks in the tensile zone when subjected to externally imposed structural loads. By means of appropriate design and detailing technique, these cracks can be limited to acceptable levels in terms
of structural integrity and aesthetics.
*NON_STRUCTURAL CRACKS
**Concrete is also liable to crack in both the plastic
and hardened states due to the nature of its
constituent materials. These intrinsic cracks are as inevitable as structural cracks. It is often possible
to predict when intrinsic cracks are likely and to
limit them to acceptable levels by means of good
design and/or proper construction techniques.
*DORMANT AND LIVE CRACKS:
Cracks caused by shrinkage, temperature gradient due to hydration and alkali silica reaction ( ASR ) are less dangerous the cracks caused by thermal expansion and loads. This is because shrinkage and hydration temperature gradient result in dormant cracks ( where the width does not vary with time) and other mechanisms result in live
cracks (where the width increases with time
Dormant cracks, especially narrow ones, are more
likely to undergo auto genius healing and
realkalisation. The crack may heal owing to
following conditions:
• carbon dioxide diffusing into the crack leading to
carbonation of the calcium hydroxide and
precipitation of calcium carbonate.
• Cement hydration due to presence of moisture.
• Hydration diffusing from the bulk concrete into the
heaked zone thereby increasing the pH in that area.
Live cracks are more likely than domant ones. They
result in collection of debris at the base owing to movement of the sides on the cracks. This can
impede temporarily the passage of depassivating
substances to the reinforcements. However,
autodeneous healing is unlikely with live cracks.
▶CAUSES OF CRACKING:
Cracking will occur whenever the applied strain exceeds the tensile strain capacity of the concrete.
*The tensile strain capacity of concrete varies with age and with
Age at which cracks may occur.
*Cracks can appear at any time. The age which
some typical can occur are given in the Table.
▶TABLE – AGE AT WHICH CRACKS MAY APPEAR:
*Sr. no. types of cracks Age
1. plastic shrinkage First few minutes or hours after
concreting .
2. plastic settlement First few minutes or hours
after concreting.
3. due to corrosion After one year or many years.
4. due to loads After loads are imposed and the
time duration of loading.
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5. due to weight Just after formwork support are
removed.6. due to chemical changes in hardened concrete After one or many years depending in
chemical attack from outside (sulphate ) Or
chemical reaction from within (ASR)
*CRITICAL CRACK WIDTH:
The most common reasons for controlling crack width are following:
APPERANCE : Unsightly cracking should be avoid
since it may cause concern to the occupants of the external structure. Ti may also contribute to
unsightly staining on exposed external surfaces,
where salts and rust are washed out from the crack.
*DURABILITY: Excessively wide cracks may lead to
corrosion of the reinforcement which in turn may lead to spalling of concrete due to the expansive nature of the corrosion process.
*WATER-TIGHTNESS: This is of importance in water
retaining structures.
In particular instances there may be other reasons for controlling cracking in addition to the three reasons cited above.
Crack width is, generally, to be taken to mean the
measurable width of a crack at the surface of
concrete. Crack width limitation is important from durability considerations. Most structural codes
prescribe maximum allowed crack widths.
Codes normally consider cracking caused by
external imposed conditions such as live loading and provide formula for calculating the crack width in the design phase. Mainly bending and tension or bending and axial load are considered. The direction of such cracks is perpendicular to the direction of the main reinforcement. Plastic
shrinkage cracks follow the line of reinforcement.
According to IS: 456-2000 the surface of the width
of the cracks should not in general exceeds o.3 mm
in members where cracking is not harmful and does not have any serious effect either on the
preservation of reinforcing steel or on the durability
of the structures.
In members, where cracking of the tensile zone is harmful either because they are moisture or in contact with soil or groundwater, an upper limlt of 0.2 mm is suggested.
*For aggressive conditions the surface width of
cracks should not generally exceed 0.1 mm. The crack width conditions the surface width of cracks should not be generally exceed 0.1 mm. The crack width is measured at the surface for the above purposes. However some other codes specify the
width at points near the reinforcement.
.
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