FAQ

̊ What is Portland cement?
̊ Is there any shelf life of cement?
̊ Does fineness of cement affect strength gain?
̊ What is initial and final setting time of cement?
̊ What are the reasons for slow or fast setting of
concrete or mortar?
̊ What are the different grades of Ordinary Portland
Cement (OPC)?
̊ What is Portland pozzolana cement?
̊ What are the advantages of using Portland pozzolana
cement over OPC?
̊ Does the shade of cement affect quality?
̊ What is the effect of long storage periods on
cement?
̊ How should cement be stored?
̊ How to identify the time for which the
cement was stored before use?

̊ What is a lap or development length? Where and
how should they be provided?

Q. What is portland cement?
Portland cement is composed of calcium silicates and aluminate and aluminoferrite
It is obtained by blending predetermined proportions limestone clay and other minerals
in small quantities which is pulverized and heated at high temperature – around
1500 deg centigrade to produce ‘clinker’. The clinker is then ground
with small quantities of gypsum to produce a fine powder called Ordinary Portland
Cement (OPC). When mixed with water, sand and stone, it combines slowly with the
water to form a hard mass called concrete.

Q. Is there any shelf life of cement?

Cement is a hygroscopic material meaning that it absorbs moisture In presence of
moisture it undergoes chemical reaction termed as hydration. Therefore cement remains
in good condition as long as it does not come in contact with moisture. If cement
is more than three months old then it should be tested for its strength before being
taken into use.

Q. Does fineness of cement affect strength gain?


Fineness defines the surface area of cement particles present in per unit weight,
which implies that more fineness means more particles in unit weight. This enhances
the reaction rate which in turn will result in faster gain of strength at earlier
stages as well as liberates higher heat, therefore proper curing in initial days
is very essential.

Q. What is initial and final setting time of cement?
Initial set is when the cement paste loses its plasticity and stiffens considerably.
Final set is the point when the paste hardens and can sustain some minor load. Both
are arbitrary points and these are determined by Vicat needle penetration resistance.

Q. What are the reasons for slow or fast setting of concrete
or mortar?
Slow or fast setting normally depends on the nature of cement. It could
also be due to extraneous factors not related to the cement. The ambient conditions
play an important role. In hot weather, the setting is faster, in cold weather,
setting is delayed Some types of salts, chemicals, clay, etc if inadvertently get
mixed with the sand, aggregate and water could accelerate or delay the setting of
concrete.

Q. What are the different grades of Ordinary Portland Cement
(OPC)?
The Bureau of Indian Standards (BIS) has classified OPC in three different grades
The classification is mainly based on the compressive strength of cement-sand mortar
cubes of face area 50 cm2 composed of 1 part of cement to 3 parts of standard sand
by weight with a water-cement ratio arrived at by a specified procedure.

The grades are:
(i)33 grade
(ii)43 grade

(iii)53 grade

The grade number indicates the minimum compressive strength of cement sand mortar
in N/mm2 at 28 days, as tested by above mentioned procedure.

Q. What is Portland Pozzolana Cement?
Portland Pozzolana Cement (PPC) is obtained by either intergrinding a pozzolanic
material with clinker and gypsum, or by blending ground pozzolana with Portland
cement. Nowadays good quality fly ash is available from Thermal Power Plants, which
are processed and used in manufacturing of PPC.

Q. What are the advantages of using Portland Pozzolana
Cement over OPC?
Pozzolana combines with lime and alkali in cement when water is added and forms
compounds which contribute to strength, impermeability and sulphate resistance It
also contributes to workability, reduced bleeding and controls destructive expansion
from alkali-aggregate reaction. It reduces heat of hydration thereby controlling
temperature differentials, which causes thermal strain and resultant cracking n
mass concrete structures like dams.

Q. Does the shade of cement affect quality?
No. The quality of cement depends upon the raw materials used and the quality control
measures adopted during its manufacture, and not on the shade of the cement. The
cement gets its colour from the nature and colour of raw materials used, which will
be different from factory to factory, and may even differ in the different batches
of cement produced in a factory. Further, the colour of the finished concrete is
affected also by the colour of the aggregates, and to a lesser extent by the colour
of the cement. Preference for any cement on the basis of colour alone is technically
misplaced.

Q. What is the effect of long storage periods on cement?
Cement which is in the form of a fine powder has a tendency to absorb moisture present
in the atmosphere. When it absorbs moisture it hydrates, and when subsequently used
does not contribute to the strength development. Jute bags (gunny bags) in which
cement is bagged are neither airtight nor damp-proof and do not prevent absorption
of moisture. Cement deteriorates in quality on long storage.

Cement bagged in woven polythene bags or paper bags are not likely to deteriorate
to the extent mentioned above. The loss of strength also depends on the condition
of the godown. It is advisable to use cement within three months of its bagging,
or to test the cement for its strength if stored for longer periods. Hence cement
bought first should be used first.

Q. How should cement be stored?
Precautions that must be taken in the storage of Portland cement are given below
in a series of DON’Ts.

(i)Do not store bags in a building or a godown in which the walls, roof and floor
are not completely weatherproof.

(ii)Do not store bags in a new warehouse until the interior has thoroughly dried
out.

(iii)Do not be content with badly fitting windowsand doors, make sure they fit properly
and ensure that they are kept shut.

(iv)Do not stack bags against the wall. Similarly, don’t pile them on the
floor unless it is a dry concrete floor. If not, bags should be stacked on

wooden planks or sleepers.

(v)Do not forget to pile the bags close together.

(vi)Do not pile more than 15 bags high and arrange the bags in a header-and-stretcher
fashion.

(vii)Do not disturb the stored cement until it is to be taken out for use.

(viii)Do not take out bags from one tier only. Step back two or three tiers.

(ix)Do not keep dead storage. The principle of first-in first-out should be followed
in removing bags.

(x)Do not stack bags on the ground for temporary storage at work site. Pile them
on a raised, dry platform and cover with tarpaulin or polythene

sheet.

–Back to Questions–

Q. What is concrete?
Concrete is a mixture of cement, sand, stone aggregates and water.

Q. What is RCC?
If a concrete mix is placed in and around a cage of steel rods, it is called
Reinforced Cement Concrete (RCC).

Q. What is mortar?
Mortar is a mix of cement, sand and water, to be used for brick works/block
works and plaster.

Q. How much water should be added in a concrete mix of one bag
of cement for normal construction work?
Normally the amount of water that is required per bag of cement is 25 -28
liters only.

Q. How does color affect the quality of cement & its concrete?
Quality of cement has nothing to do with its color.

Q. What precautions should one take for water to be used in concrete
construction?
It is good to use potable quality of water. It should be free from impurities
and harmful ingredients. Seawater isn’t recommended. The water fit for mixing
is fit for curing too. Use of minimum quantity of mixing water, consistent with
the degree of workability required to enable easy placing and compaction of concrete,
is advisable Ensure that water is measured and added Low water to cement ratio is
essential for good performance of the structure in the long run.

Q. What is the minimum recommended concrete mix proportion for
RCC works?
1:1.5:3, where 1 part of cement is to be mixed with 1.5 parts of sand and
3 parts of coarse aggregates. Water requirement for the mix would be less than 25
liters per bag of cement.

Q. What are the common mistakes, which affect the quality of concrete?
The ways in which concrete maybe spoilt are many, most common of them being: Use
of too much or too little water for mixing, or water carelessly added during mixing.
Incomplete mixing of aggregate with cement Improper grading of aggregates resulting
in segregation or bleeding of concrete. Inadequate compaction of concrete 
Using concrete which has already begun to set. Placing of concrete on a dry foundation
without properly wetting it with water. Use of dirty aggregate or water containing
earthy matter, clay or lime. Too much troweling of the concrete surface. Leaving
the finished concrete surface exposed to sun  and wind during the first ten
days after placing without protecting it and keeping it damp by proper methods of
curing.

Q. What are the factors responsible for governing the compressive
strength of concrete?
The compressive strength is governed by
the following factors:

Q. Within how much time the freshly prepared mortar / concrete
should be consumed?
The mortar / concrete should be consumed as early as possible after addition
of water to it. The hydration of cement starts the moment water is added to it.
As the hydration progresses the cement paste starts stiffening and loses its plasticity.
The concrete should not be disturbed after this. Normally, this is about 45 –
50 minutes.

Q. Why is compaction essential?

Green concrete has all the three phases – solids, water air. In order
to make the concrete impervious & attain its maximum strength it is required
to remove the entrapped air from the concrete mass when it is still in plastic state.
If the air is not removed completely, the concrete loses strength considerably.
It has been that 5% voids reduce the strength by about 30% and 10% voids reduce
the strength by over 50%. Compaction eliminates air bubbles and brings enough fine
material both to the surface and against the forms to produce the desired finish.
One can use such hand tools as steel rods, paddling sticks, or tampers, but mechanical
vibrators are best. Any compacting device must reach the bottom of the form and
be small enough to pass between reinforcing bars. Since the strength of the concrete
member depends on proper reinforcement location, be careful not to displace the
reinforcing steel.

Q. What is ‘curing’ and why is it so important?

The term ‘curing’ is used to include maintenance of a favorable
environment for the continuation of chemical reactions, i.e. retention of moisture
within, or supplying moisture to the concrete from an external and protection against
extremes of temperature.

Q. What is the correct method of curing?
If a concrete mix is placed in and around a cage of steel rods, it is called
Reinforced Cement Concrete (RCC).

Walls                          
:Water should be sprinkled from the top such that it covers the whole
area of the wall and it should be remain wet.

Slab                           
:Ponding should be done on the slab by constructing bunds of mortar
of approximately 1mX1m and water should be
                                   
stored.

Beams and columns   :The beams and columns can be maintained
wet by tying gunny bags around the periphery and by maintaining it wet
                                   
always.

Q. What methods are commonly employed to ensure sufficient
moisture for curing?
Ponding, continuous sprinkling, covering with wet cloth, cotton mats or
similar materials, covering with specially prepared paper, polyethylene, sealing
coat applied as a liquid commonly known as ‘curing compound’ which hardens
to form a thin protective membrane, are some of the methods by which concrete is
cured.

Q. When should curing be started and when is it complete?


Curing should be started just after the surfaces begin to dry. Normally
7 to 14 days curing is considered adequate.

Q. What is steel reinforcement? Why is it required in a
concrete structure?
Steel reinforcements are used, generally, in the form of bars of circular cross
section in concrete structure. They are like a skeleton in human body. Plain concrete
steel or any other reinforcement is strong in compression but weak in tension. Steel
is one of the best forms of reinforcements, to take care of those stresses and to
strengthen concrete to bear all kinds of  loads.

Q. What is bar-bending-schedule?

Bar-bending-schedule is the schedule of reinforcement bars prepared in advance before
cutting and bending of rebars. This schedule contains all details of size, shape
and dimension of rebars to be cut.

Q. What are the different types of steel reinforcements
being used in a reinforced concrete structure?
Mild steel bars conforming to IS: 432 (Part I) and Cold-worked steel high strength
deformed bars conforming to IS: 1786 (grade Fe 415 and grade Fe 500, where 415 and
500 indicate yield stresses 415 N/mm2 and 500 N/mm2 respectively) are commonly used.
Grade Fe 415 is being used most commonly nowadays. This has limited the use of plain
mild steel bars because of higher yield stress and bond strength resulting in saving
of steel quantity. Some companies have brought thermo mechanically treated (TMT)
and corrosion resistant steel (CRS) bars with added features. Bars range in diameter
from 6 to 50 mm. Cold-worked steel high strength deformed bars start from 8 mm diameter.
For general house constructions, bars of diameter 6 to 20 mm are used.

Q. Why cover blocks are required to be placed before concreting?
What are their sizes?
Cover blocks are placed to prevent the steel rods from getting exposed to the atmosphere,
and to place and fix the reinforcements as per the design drawings. Once the steel
is exposed to the atmosphere, corrosion starts. Sometimes it is commonly seen that
the cover gets misplaced during the concreting activity. To prevent this, tying
of cover with steel bars using thin steel wires called binding wires (projected
from cover surface and placed during making or casting of cover blocks) is recommended.
Covers should be made of cement sand mortar (1:3). Ideally, cover should have strength
similar to the surrounding concrete, with the least perimeter so that chances of
water to penetrate through periphery will be minimized. Provision of minimum covers
as per the Indian standards for durability of the whole structure should be ensured.

Shape of the cover blocks could be cubical or cylindrical. However, cover indicates
thickness of the cover block. Normally, cubical cover blocks are used. As a thumb
rule, minimum cover of 2” in footings, 1.5” in  columns and 1”
for other structures may be ensured.

Q. How important are transverse reinforcements like links
and stirrups? What precautions should be taken while tying them?
Transverse reinforcements are very important. They not  only take
care of structural requirements but also help main reinforcements to remain in desired
position. They play a very significant role while abrupt changes or reversal of
stresses like earthquake etc. They should be closely spaced as per the drawing and
properly tied to the main/longitudinal reinforcement.

Q. What is a lap or development length? Where and how should they
be provided?

Lap length is the length overlap of bars tied to extend the reinforcement length..
Lap length about 50 times the diameter of the bar is considered safe. Laps of neighboring
bar lengths should be staggered and should  not be provided at one level/line.
At one cross section, a maximum of 50% bars should be lapped. In case, required
lap length is not available at junction because of space and other constraints,
bars can be joined with couplers or welded (with correct choice of method of welding).

Q. What is anchorage length?

This is the additional length of steel of one structure required to be inserted
in other at the junction. For example, main bars of beam in column at beam column
junction, column bars in footing etc. The length requirement is similar to the lap
length mentioned in previous question or as per the design instructions.

Q. What is the checklist for steel reinforcement before
the placement/pour of concrete?
Reinforcement should be free from loose rust, oil paints, mud etc. it should
be cut, bent and fixed properly. The reinforcement shall be placed and maintained
in position by providing proper cover blocks, spacers, supporting bars, laps etc.
Reinforcements shall be placed and tied such that concrete placement is possible
without segregation, and compaction possible by an immersion vibrator.

Q. For a given diameter, how do we calculate the weight
of steel per meter length of the steel bar and vice versa?

For any steel reinforcement bar, weight per running meter is equal to d2/162
Kg, where d is diameter of the bar in mm. For example, 10 mm diameter bar will weigh
10×10/162 = 0.617 Kg/m.

Q. Can we receive the quality test certificate of steel 
from the supplier?
Yes. We can receive the test certificate of the batch of materials supplied
at our site. The certificate will confirm the compliance of quality of supplied
materials as per the requirement of relevant Indian standard code.

Q. Why plastering is required?

Plaster protects structure from temperature variations; external attacks
of sulphates, chlorides, etc. Plaster also provides smooth & aesthetic surface
on RCC & Brickwork surface.

Q. What precautions should be taken during plaster works?
Preferably use cement which releases low heat of hydration. A blended Cement
is a good choice.

      a) Use optimum water at the time of mixing.

      b) Do not use dry cement on the plaster surface.

      c) At the junction of Brickwork & RCC, chicken
mesh or fiber mesh may be used.

      d) Wet the surface before plastering.

      e) Cure the surface for at least 10 to 12 days.

Q. What are carpet area, built-up area & super built-up
area?

Carpet Area: This is the area of the apartment/building, which does not
include the area covered by the walls. Built up Area: The carpet area plus the area
of the walls. Super Built up Area: This includes the built up area along with the
area under common spaces such as the lobby, lifts, stairs, etc. 

Q. What are the things one should keep in mind before finalizing
a land deal?
Some points which one must pay attention to prior to land deal –

a)    House plot should not be under any acquisition proceedings
of any government bodies .
b)    Verify from the planning authorities whether the land was designated
for residential use.
c)    The survey number of land is critical.

d)    Certificate obtained from registrar’s office should confirm
that there is no encumbrance on the property.

e)    The title deed of the land should be clear and an advocate
should be consulted for this.

f)     Verify the rates after contacting some property consultants
and some people who have purchased their plots recently. You
       should also refer guidelines and the market
rates published in the government manual of your city/town.

g)    Stamp duty at the time of registration is mandatory.

Q. What are the important considerations before selecting
a piece of land?

While selecting the land one should give importance to following issues
–

a)    Required size of plot and construction area

b)    Existing rates area wise

c)    Distances from Railway Station, Bus Stand and Air Port.

d)    Distance from your work place.

e)    Distances from hospital and medical clinics.

f)    Available infrastructure like water supply, drainage, road
etc

Q. What are the points, one should pay attention to while
awarding the contracts for house construction?

Whatever the type of contract, one needs to pay close attention to the
following aspects –

a)    Type of materials

b)    Quality of work

c)    Advance payment, if any

d)    Progress & time schedule

e)    Future measurement & payment conditions

Q. What would be an approximate cost per sq.ft of my house
construction?

To give an idea, depending on the finishes you choose, the construction
cost should be as follows –

Type of finish in the construction                            
Cost (in rupees) per sq.ft of construction

Top Class Finish                                                        
750 – 1000

Medium Class Finish                                                  
480 –   700

Simple Class Finish                                                    
350 –   550

Q. What is the ratio of material, labor and other expenditures
for house construction?

60:30:10

Q. What would be the approximate cost break up for various
works in terms of percentage of construction cost of house?

Q. Give me break up of stage wise construction cost to
plan my financial requirement.

Q. What is the EMI in house loans?

Once you take house loans, you will repay your amount in monthly installments
depending upon the loan amount, total duration and interest rate. This means you
have to pay certain amount per lakh rupees during the entire period. This is called
Equated Monthly Installments (EMI). The longer is the repayment period smaller will
be the EMI. Generally, EMI doesn’t exceed the 50% of household income.