Question
No. 181
What are
the three major types of reinforcement used in pre-stressing?
Answer:
- Spalling reinforcement Spalling stresses are established behind the loaded area of anchor blocks and this causes breaking away of surface concrete. These stresses are induced by strain incompatibility with Poisson’s effects or by the shape of stress trajectories.
- Equilibrium reinforcement Equilibrium reinforcement is required where there are several anchorages in which pre-stressing loads are applied sequentially.
- Bursting Reinforcement Tensile stresses are induced during pre-stressing operation and the maximum bursting stress occurs where the stress trajectories are concave towards the line of action of the load. Reinforcement is needed to resist these lateral tensile forces.
Question
No. 182
How
many Lbs are there in a yard?
Answer: A pound (Lb) is a unit of measurement for weight while a yard is a
unit of measurement for distance.
If you are referring to common measurements
used on a construction site, a "yard" is a common abbreviation for a
"cubic yard", which is a unit of measurement of volume. (A cubic yard
equals 27 cubic feet.) Since dirt weighs about 110 pounds per cubic feet, a
cubic yard of dirt weighs about 2970 Lbs. Since concrete is heavier (150 PCF),
a cubic yard of concrete weighs about 4050 Lbs.
Question
No. 183
Sometimes
the side of concrete bridges is observed to turn black in colour. What is the
reason for this phenomenon?
Answer:
In some cases, it may be due to the accumulation of dust and dirt. However,
for the majority of such phenomenon, it is due to fungus or algae growth on
concrete bridges. After rainfall, the bridge surface absorbs water and retains
it for a certain period of time. Hence, this provides a good habitat for fungus
or algae to grow. Moreover, atmospheric pollution and proximity of plants
provide nutrients for their growth. Improvement in drainage details and
application of painting and coating to bridges help to solve this problem.
Question
No. 184
What are
the components of a waterproofing system in the roof of a typical pumping
station?
Answer: In the design of a waterproofing
system at the roof of a pumping station, normally the following components are:
- Above the structural finish level of the concrete roof, a screed of uniform thickness is applied to provide a smooth surface for the application of waterproofing membrane. (Screed of varying thickness can also be designed on the roof to create a slope for drainage.) The screed used for providing a surface for membrane should be thin and possess good adhesion to the substrate. Moreover, the screed aids in the thermal insulation of the roof.
- Above the screed, waterproofing membrane is provided to ensure water-tightness of the roof.
- An insulation board may be placed on top of waterproof membrane for thermal insulation. In cold weather condition where the loss of heat at the roof is significant, the insulation board helps to reduce these losses. On the contrary, in summer the roof is heated up by direct sunlight and the insulation layer reduces the temperature rise inside the pumping station.
Question
No. 185
If the
contractor is liable for defective works for 12 years with contract under seal
(6 years with contract not under seal), then what is the significance of
Maintenance Period?
Answer: Defective works constitute a breach
of contract in accordance with Limitation Ordinance An action founded on simple
contract (not under seal) shall not be brought after expiration of 6 years
while an action founded with contract under seal shall not be brought after
expiration of 12 years. For construction works, the date of counting these
actions should be the date of substantial completion.
To answer
the above question, one should note that under the contractual requirement, the
contractor during Maintenance Period has the right to rectify the defects and
the employer has also the right to request the contractor to make good
defective work. However, after the expiry of Maintenance Period, in case of any
arising of defects, the employer has to employ others to rectify these works
and bring the action to court to claim the contractor for the costs associated.
Question
No. 186
What
is the biggest dam in America?
Answer: The Grand Coulee Dam Grand - Coulee, Washington
- Length 5,223 ft
- Height 550 ft
Question
No. 187
In the
design of elastomeric bearings, why are steel plates inserted inside the bearings?
Answer:
For elastomeric bearing to function as a soft spring, the bearing should be
allowed for bulging laterally and the compression stiffness can be increased by
limiting the amount of lateral bulging. To increase the compression stiffness
of elastomeric bearings, metal plates are inserted. After the addition of steel
plates, the freedom to bulge is restricted and the deflection is reduced when
compared with bearings without any steel plates under the same load. Tensile
stresses are induced in these steel plates during their action in limiting the bulging
of the elastomer. This in turn would limit the thickness of the steel plates.
However, the
presence of metal plates does not affect the shear stiffness of the elastomeric
bearings.
Question
No. 188
What is
the indication of shear slump and collapse slump in slump tests?
Answer:
There are three types of slump that
may occur in slumps test, namely, true slump, shear slump and collapse slump.
- True slump refers to general drop of the concrete mass evenly all around without disintegration.
- Shear slump implies that the concrete mix is deficient in cohesion. Consequently, it may undergo segregation and bleeding and thus is undesirable for durability of concrete.
- Collapse slump indicates that concrete mix is too wet and the mix is deemed to be harsh and lean.
Question
No. 189
Is the
material of formwork (timber or steel) helps to reduce thermal cracks in concreting
operation?
Answer: To answer this question, one must
fully understand the effect of formwork on the temperature of concreting
structure. Without doubt, with better insulation of structure by timber
formwork, the overall rise of temperature and hence the peak hydration
temperature is also increased. However, for a well-insulated structure, the
temperature gradient across concrete element is reduced. Therefore, the use of
well-insulated formwork (like timber) increases the maximum temperature and
reduces the temperature gradient across the structure at the same time. Hence,
whether steel or timber formwork should be used to control thermal cracking is
dependent on the restraints and the size of section. If the section under
consideration is thick and internal restraint is the likely cause to thermal
cracking, then timber formwork should be used. On the other hand, if external restraint
is the main concern for thermal cracking, then steel formwork should be used instead.
Question
No. 190
What is
the importance of critical steel ratio in calculating thermal reinforcement?
Answer: The fulfilment of critical steel
ratio means that in construction joints or planes of weakness of concrete
structure, steel reinforcement will not yield and concrete fails in tension
first. This is important in ensuring formation of more cracks by failure of
concrete in tension; otherwise failure in steel reinforcement would produce a
few wide cracks which are undesirable.
Question
No. 191
What is the
purpose of skin reinforcement for deep beams?
Answer:
In BS8110, it states that secondary
reinforcement should be provided for beams exceeding 750 mm deep at a distance
measured 2/3 depth from the tension face. Experimental works revealed that at
or close to mid-depth of deep beams, the maximum width of cracks arising from
flexure may be about two to three times larger than the width of the same crack
at the level of surface where the crack originally forms.
The presence of crack is undesirable from aesthetic
point of view. Moreover, it poses potential corrosion problems to reinforcement
of deep beams. To safeguard against these crack formation, skin reinforcement
is designed on the sides of deep beams to limit the formation of flexural crack
widths. Though the principal function of skin reinforcement is to control crack
width, it may be employed for providing bending resistance of the section.
Question
No. 192
What
is the average density of soil?
Answer: For purposes of civil engineering, an average soil will have a density
of about 100 to 110 pounds per cubic foot. (This can vary a little depending
upon how well compacted the soil is.)
Question
No. 193
What is
the difference between normal bolts and high friction grip bolts?
Answer: High friction grip bolts are commonly
used in structural steelwork. They normally consist of high tensile strength
bolts and nuts with washers. The bolts are tightened to a shank tension so that
the transverse load across the joint is resisted by the friction between the
plated rather than the bolt shank’s shear strength.
Question
No. 194
In the
design of watermain, the normal practice is to use ductile iron for pipe size less
than 600 mm and to use steel for pipe size more than 600 mm. Why?
Answer: For watermain pipe size less than 600
mm, ductile iron is normally used because internal welding for steel pipes
below 600 mm is difficult to be carried out. Moreover, it requires only simple
jointing details which allow for faster rate of construction. For watermain
pipe size above 600 mm, steel pipes are recommended because steel pipes are
lighter than ductile iron pipes for the same material strength and therefore
the cost of steel pipes is less than that of ductile iron pipes. In addition,
in areas of difficult access the lighter mild steel pipes pose an advantage
over ductile iron pipes for easy handling.
Question
No. 195
In
carrying out compression test for concrete, should test cubes or test cylinders
be adopted?
Answer:
Basically, the results of
compression test carried out by using cubes are higher than that by cylinders.
In compression test, the failure mode is in the form of tensile splitting
induced by uniaxial compression. However, since the concrete samples tend to
expand laterally under compression, the friction developed at the
concrete-machine interface generates forces which apparently increase the
compressive strength of concrete. However, when the ratio of height to width of
sample increases, the effect of shear on compressive strength becomes smaller. This
explains why the results of compression test by cylinders are lower than that of
cubes. Reference is made to Longman Scientific and Technical (1987).
Question
No. 196
Should
design life be the same as return period for design conditions?
Answer: Design life means the minimum
duration a structure is expected to last. The longer is the design life; the
higher is the cost of a project. Therefore, in choosing the design life for a
structure, engineers should consider the design life which generates a economical
project without sacrificing the required function.
In selection
of return period of certain design conditions, winds, waves, etc., one should
consider the consequences of exceedance. In fact, there are normally no extreme
maximum values of these design conditions and its selection is based on the
probability of exceedance which is related to return period.
Therefore,
design life may not be equal to return period of design conditions because
their selections are based on different considerations.
Question
No. 197
How
are freeway bridges built?
Answer: After calculating the anticipated traffic for the bridge,
cement/reinforced-with-rebar stanchions are spaced over the freeway to
accommodate the bridge. An 'off-ramp' from the freeway to the bridge is
constructed, as is an 'on-ramp' to the subsequent road. Cement/rebar slabs are
built and lifted with cranes to form the platform, and voila! Drive carefully.
Although the bridge deck/roadway is almost
always a concrete slab, the structure that holds up the bridge deck can be reinforced
concrete, structural steel, or a combination of steel and concrete.
Question
No. 198
What is
the difference between sureties and security?
Answer: In construction contracts, if a
contractor fails to perform the works, the employer would suffer from severe
financial loss and therefore some forms of protection has to be established in
the contract.
For surety
bond, the contractor obtains a guarantee from a third party i.e. a bank or an
insurance company, which in return for a fee, agrees to undertake the financial
responsibility for the performance of contractor’s obligations. This third
party will pay to the employer in case there is a contractor’s default.
For
security, a sum of money is deposited in the employer’s account and upon
satisfactory fulfilment of contractor’s obligations; the sum will be repaid to
the contractor.
Question
No. 199
What is
the difference between air chamber and surge tank?
Answer: Air chambers and surge tanks are
normally installed in watermain to ease the stress on the system when valves or
pumps suddenly start up and shut down. A surge tank is a chamber containing
fluid which is in direct contact with the atmosphere. For positive surge, the
tank can store excess water, thus preventing the water pipes from expansion and
water from compression. In case of down-surge, the surge tank could supply
fluid to prevent the formation of vapour column separation. However, if the
surge pressure to be relieved is very large, the height of surge tank has to be
designed to be excessively large and sometimes it is not cost-effective to
build such a chamber. On the contrary, an air chamber can be adopted in this
case because air chamber is a enclosed chamber with pressurized gases inside.
The pressure head of gas inside the air chamber is the component to combat the
hydraulic transient. However, air chamber has the demerits that regular
maintenance has to be carried out and proper design of pressure level of gas
has to be conducted.
Question
No. 200
What
is Gravity flow?
Answer: Gravity flow is fluid flowing due to the forces of gravity alone and
not to an applied pressure head. In the Bernoulli equation, the pressure term
is omitted, and the height and velocity terms are the only ones included.
Question
No. 201
How do
rock sockets take up loads?
Answer: The load transfer mechanism is
summarized as follows:
When a
socketed foundation is loaded, the resistance is provided by both rock socket
wall and the socket base and the load distribution is a function of relative
stiffness of foundation concrete and rock mass, socket geometry, socket
roughness and strength. At small displacements the rock-socket system behaves
in an elastic manner and the load distribution between socket wall and socket
end can be obtained from elastic analysis. At displacements beyond 10-15 mm,
relative displacement occurs between rock and foundation and the socket bond
begins to fail. This result in reduction of loads in rock-socket interface and
more loads are transferred to the socket end. At further displacements, the
interface strength drops to a residual value with total rupture of bond and
more loads are then distributed to the socket end.
Question
No. 202
What
is made from large rocks, which protects the base of cliffs?
Answer: Stacks
Question
No. 203
In
designing the lateral resistance of piles, should engineers only use the earth
pressure against pile caps only?
Answer: In some design lateral loads are
assumed to be resisted by earth pressure exerted against the side of pile caps
only. However, it is demonstrated that the soil resistance of pile lengths do
contribute a substantial part of lateral resistance. Therefore, in designing
lateral resistance of piles, earth pressure exerted on piles should also be
taken into consideration.
In analysis
of lateral resistance provided by soils, a series of soil springs are adopted
with modulus of reaction kept constant or varying with depth. The normal
practice of using a constant modulus of reaction for soils is incorrect because
it overestimates the maximum reaction force and underestimates the maximum
bending moment. To obtain the profile of modulus of sub-grade reaction,
pressure-meter tests shall be conducted in boreholes in site investigation.
Reference is made to Bryan Leach (1980).
Question
No. 204
What
is the density of most of construction materials?
Answer: If it floats it is less dense than water, 62.4 lbs/cubic ft. Wood is
about 40 lbs/ cu.ft.it floats. Concrete is 150 lbs. / cu.ft. It does not float.
Question
No. 205
What are
the differences in function between rock anchors and rock sockets?
Answer: Rock anchors are used primarily for
resisting uplift forces. On the contrary, rock sockets serve three main
purposes:
- Rock socket friction and end bearing to resist vertical load;
- Passive resistance of rock sockets contribute to resistance of lateral load; and
- Socket shaft friction is also used for resisting uplifting forces. But only 70% of this capacity should be used because of the effect of negative Poisson ratio.
Note: Rock
anchors, which may consist of a high tensile bar or a stranded cable, are
provided for tension piles when there are insufficient soil covers to develop
the required uplifting resistance.
Question
No. 206
In
designing concrete structures, normally maximum aggregate sizes are adopted with
ranges from 10 mm to 20 mm. Does an increase of maximum aggregate size benefit
the structures?
Answer:
To answer this question, let’s
consider an example of a cube. The surface area to volume ratio of a cube is
6/b where b is the length of the cube. This implies that the surface area to volume
ratio decreases with an increase in volume. Therefore, when the size of maximum
aggregate is increased, the surface area to be wetted by water per unit volume
is reduced. Consequently, the water requirement of the concrete mixes is
reduced accordingly so that the water/cement ratio can be lowered, resulting in
a rise in concrete strength.
However, an increase of aggregate size is
also accompanied by the effect of reduced contact areas and discontinuities
created by these larger sized particles. In general, for maximum aggregate
sizes below 40 mm, the effect of lower water requirement can offset the
disadvantages brought about by discontinuities as suggested by Longman
Scientific and Technical (1987).
Question
No. 207
Why
nautical mile is different from statute mile?
Answer: One nautical mile is defined by one latitude minute of arc (there are
60 such minutes to a degree). This equals 1852 meters, and roughly (but
coincidentally) 2000 yards or 6000 feet. (Edit: actually, a standard nautical
mile is 6076 feet, 6000 feet and 2000 yards are commonly used approximations,
but produce an error of about 1%).
The statute mile had a little fuzzier
definition to start with, as one mile was the same as 1000 roman Paces/steps.
The definition has since changed, but one statute mile equals about 1609
meters.
Question
No. 208
What is
the function of followers in driven H-piles?
Answer: A follower is an extension between
the pile head and the hammer that transfers the blow to the pile in which the
pile head cannot be reached by the hammer or is under water .For construction
of driven piles, the piling frame and hammer are normally erected on existing
ground level but not at the base of pile caps. However, H-piles are designed to
be terminated near the base of pile caps. If piles are driven at ground level,
a certain length of H-piles is wasted and cut when constructing pile caps. In
this connection, pile followers are used so as to save the wasted section of H-piles
because followers can be removed during subsequent construction of pile caps.
Question
No. 209
In deep
excavation, adjacent ground water table is drawn down which may affect the
settlement of nearby buildings. What is the remedial proposal to rectify the
situation?
Answer: One of the methods to control
settlement of nearby buildings due to excavation work is by recharging. Water
collected in wells in deep excavation is put back to the top of excavation in
order to raise the drawn-down water table. The location of recharge should be
properly selected to ensure the soil is sufficiently permeable to transfer the
pumped water back near the affected buildings.
Question
No. 210
Why are
vibrators not used in concrete compaction in piling works?
Answer: Concrete for piles should be a
high-slump self-compacting mix which is capable of flowing between
reinforcement cage with ease. Since concrete is designed to be self-compacting,
vibrators are not used for providing further compaction. Moreover, the concrete
in piles is compacted by energy derived from free falling. However, if
vibrators are used, the vibrated concrete may be compacted to the sides of the
concrete casings and hinders the lifting up of casings. Reference is made to
GEO (1996).
Question
No. 211
Why
are the bolts that hold steel rails together in oval holes?
Answer: It has to do with the design of the bolts. The reason that head of the
bolt is oval. The head of a bolt fit flush into the bar and set in opposing
sets is so that a piece of dragging equipment will not shear off all the bolts
in a joint but rather the just the nuts one side. As a result, if the hole were
not oval on one side there would be no way to tighten or loose the bolts in a
joint.
Question
No. 212
What is
the difference between capping beams and ground beams for piles?
Answer: Capping beams for piles aim at
transferring loads from closely spaced columns or walls into a row of piles. On
the other hand, ground beams are beams provided between adjacent pile caps and
they perform as compression struts or ties in an attempt to prevent lateral
displacement or buckling of piles under uneven distribution of loads on pile
caps. Both of them have to be specially designed to cater for differential
settlement of piles. Capping beam performs the same functions as pile caps.
However, ground beams are structural elements to connect adjacent pile caps to
improve the stability of foundation.
Question
No. 213
It is not
necessary to design nominal reinforcement to piles. Is it true?
Answer: In BS8110 and BS5400 Pt.4, they
require the provision of nominal reinforcement for columns. However, for pile
design the requirement of nominal reinforcement may not be necessary. Firstly,
as piles are located underground, the occurrence of unexpected loads to piles
is seldom. Secondly, shear failure of piles is considered not critical to the
structure due to severe collision. Moreover, the failure of piles by buckling
due to fire is unlikely because fire is rarely ignited underground.
However, the
suggestion of provision of nominal reinforcement to cater for seismic effect
may be justified. Reference is made to J P Tyson (1995).
Question
No. 214
What are
the head details of H-piles under compression and subject to bending moment?
Answer: For steel sections referred to in
BS5950, universal bearing pile is characterized by having equal flange and web
thickness while universal column has different flange and web thickness.
Universal columns can also be used as bearing piles.
In the
design of the head details of H-piles, there are three typical cases to be
considered, namely compression piles, tension piles and piles with bending
moment at the head in addition to tension or compression. The design of these
piles recommended by G. M. Cornfield (1968) is listed below:
- Compression piles: For this type of piles, H-piles should be embedded 150 mm in concrete pile caps and it is not necessary to use any dowels and capping plates in their connection.
- Tension piles: A number of hook-ended bars are welded to the top of H-piles.
- Piles with bending moment at their head (tension or compression): The depth of embedment of piles into pile caps is substantially increased and loads are transferred by horizontal bars welded to piles’ flanges.
Question
No. 215
What
are some facts about concrete?
Answer: Actually, drying is not directly linked to hardness in concrete. After
concrete is poured, putting it in a wet environment by spraying it constantly
with water will hasten its hardening and its curing. After concrete cures, it
is hard.
Question
No. 216
What are
the problems associated with pre-stressed concrete piles (Daido)?
Answer: The origin of Daido piles comes from
Japan where these pre-stressed concrete piles are used as replacement plies.
Holes are pre-formed in the ground and Daido piles are placed inside these
pre-formed holes with subsequent grouting of void space between the piles and
adjacent ground. However, in Hong Kong Daido piles are constructed by driving
into ground by hammers instead of the originally designed replacement method.
Since the installation method of Daido piles is changed, construction problems
like deformation of pile tip shoes, crushing of concrete at pile tip etc.
occur. Reference is made to B. W. Choy (1993).
Question
No. 217
Which one
is a better choice, a large diameter piles or a system of several smaller piles
with the same load capacity?
Answer: The choice of a large diameter pile
suffers from the disadvantage that serious consequences would occur in case
there is setting out error of the pile. Moreover, in terms of cost
consideration, for the same load capacity the cost of a group of small diameter
piles is generally lower than that of a large diameter pile. On the other hand,
for small diameter piles i.e. mini-piles, they are advantageous in site
locations with limited headroom and space. In addition, in some structures with
only a few piles, it is uneconomic because of its high mobilization cost.
Reference is made to Dr. Edmund C Hambly (1979).
Question
No. 218
In some
codes, they limit the ratio of weight of hammer to weight of pile for pile
driving. What is the reason behind this?
Answer: When a hammer with initial motion
collides with a stationary pile, the transfer of energy is most efficient when
the two masses are comparable. That is the reason why some codes limit the
ratio of weight of hammer to the weight of pile to be more than 0.5. If the
weight of hammer is too low, most of energy during hammer driving is
distributed to the hammer and this causes tension induced in hammer and results
in inefficient transfer of energy.
Question
No. 219
What is
the significance of driving sequence of driven piles?
Answer: For basement construction, if piles
are driven from the centre to the perimeter, there is a tendency of soils to
move outwards. Such lateral movement of soil may cause damage to nearby
structures and utilities.
However, if
piles are driven from the outside perimeter inwards, there are little soil
lateral movements. This results in a well-compacted centre with an excess pore
water pressure built up to resist the loading of piles. Consequently, shorter
pile lengths than the original designed ones may result. However, some time
after the pile driving operation, the excess pore water pressure is dissipated
and the shorter driven piles may not be able to take up the original design
loads. In this situation re-driving is required to drive the piles to deeper
depths after dissipation of excess pore water pressure.
Question
No. 220
During
concreting of diaphragm walls, three tremie pipes are used in one time.
However,
only one concrete truck is available. How should the concreting works be
carried out?
Answer: The most ideal situation is to supply
each tremie pipe with a single concrete truck. However, if only one concrete
truck is available, all the fresh concrete in the truck should not be placed in
one single tremie pipe. With all fresh concrete placed in one single tremie
pipe while the others left void, then due to the huge supply of concrete to the
tremie pipe, a small concrete hump may form at the base of the tremie pipe and
it is likely that it may collapse and trap the slurry inside the diaphragm
walls. Therefore, the fresh concrete should be evenly shared among the tremie
pipes to avoid such occurrence.
Question
No. 221
For a
rigid pile cap with vertical piles at the middle and raking piles at the sides,
what is the pattern of load distribution of piles in such arrangement?
Answer: Due to the effect of interaction of
individual piles, the central piles tend to settle more than the edge piles
when the pile cap is under a uniform load. Therefore, raking piles at the edge
take up a higher fraction of total loads and are subject to higher axial and
bending loads in case the pile cap is stiff. In the extreme case, failure of
these raking edge piles may occur.
Question
No. 222
What is
the difference between direct circulation drilling and reverse circulation
drilling?
Answer: For direct circulation drilling and
reverse circulation drilling, the major difference in drilling method is
related to the direction of movement of drilling fluid. For direct circulation
drilling, the drilling fluid is circulated from the drill stem and then flows
up the annulus between the outside of the drill stem and borehole wall. The
drilling fluid that carries the drill cuttings flows to the surface and the
subsequent settlement pits. Pumps are employed to lift the cuttings free fluid
back to the drill stem.
For reverse
circulation drilling, the direction of flow of drilling flow is opposite to
that of direct circulation drilling. Drilling fluid flows from the annulus
between the drill stem and hole wall to the drill stem. The drilling fluid is
pumped to a nearby sump pits where cuttings are dropped and settled.
Question
No. 223
Should
engineers rely solely on Hiley’s formula in the design of H-piles?
Answer: About 90% of H-piles adopt Hiley’s
formula for design. However, this formula is only applicable to pile lengths
less than 30m and is suitable for course-grained materials (not suitable to
fine-grained soils) as suggested by GEO (1996). In Hiley’s formula, by
observing the penetration of piles after the hammer impact, the pile capacity
could be readily obtained from the response of the impacting force. Therefore,
the individual pile capacity could be obtained by this dynamic method.
However, in
normal foundation, groups of H-piles are present and the soil foundation may
not be able to support these H-piles simultaneously even though individual
piles are proven to have sufficient capacity by using dynamic method. In this
case, static method should be employed to ascertain if the soil foundation
could support these H-piles.
Question
No. 224
What
is the difference between routing maintenance and major maintenance in school
facilities?
Answer: The routine maintenance is the minor and consistent repairs that are
engaged in the school premises. Examples could include Painting, replacement of
fixtures, louver blades, furniture repairs, and patching cracks in the school
buildings.
The major maintenance could also be a total
rehabilitation of the school, either school buildings or any other project
within the school community. It could be total restructuring of the lighting
system in the school or sanitary system.
Question
No. 225
What
are the uses of alloys in daily life and how are alloys made?
Answer: Alloying is not always done to produce a 'superior' material, but to
produce materials having a desired requirement in the industry or elsewhere. A
classic case is of lead solder (containing lead & tin), in which the
melting point of the constituent elements are lowered, not necessarily a
desirable property.
Alloying can be carried out using hot press
method (a sheet of material is sandwiched with alloying material), rolling the heated
base metal in a drum full of alloying metal powder, using hot spraying,
galvanizing (dipping the base in a molten solution of alloying material) etc.
Sometimes the alloying material is added in small proportions to the molten
base metal (e.g., in production of different types of steel).
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