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ASK Experts – Standard Q&A

Product and Service related:

Sr. No Questions Suggested Answer

1 - Why should I buy Tiscon rebars? - How Tiscon rebar is better than others? - What are the properties of Tiscon rebars?

Tata Tiscon 500D is made out of pure iron ore using best of the steel making processes as per IS 1786:2008 ensuring following benefits

Process: Neither re-rolling nor, scrap based process which completely lacks any refining ability. Refinement achieved in secondary metallurgical refinement process is our strong point which controls the cleanliness achieved in final product. Clean steel ensures a lot of hidden properties such as fatigue and impact resistance.

Services: Include various customer centric drives/ services that we offer. Including statement that if there was to be a problem then this will be addressed by a team of technical experts including Civil and Metallurgical engineers.

1. Uniform strength across the length of rebar 2. Constant diameter across the length of rebar 3. Superior ductility with soft inner core and hard outer layer 4. High bonding with concrete 5. Even rib pattern throughout the rebar length 6. Lowest impurities resulting in higher strength & ductility

Apart from these benefits you also get the following -

1. Buy in pieces 2. Free home delivery within municipal limits 3. Free technical supervision in select cities 4. Readymade rings or stirrups for minimum 10% savings

2 - Do you have any discount for TATA group

employees?

We would like to inform you that as of now we do not have any discount offers for the TATA group

employees. However, we assure you of our best services to enable hassle free buying experience. Also,

if you want we can arrange for a customer service executive visit to your site.

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3 - What is the weight of Tiscon rebar? - Why Tiscon rebar is lighter than other rebars? - What is the weight of 10 mm Tiscon?

We would like to inform you that TATA Tiscon rebars are sold in pieces and not by weight. All our rebars

are manufactured through a superior quality controlled TMT process and adhere to latest BIS (Bureau of

Indian Standards) norms which specify the nominal weight of rebar per metre and weight tolerance.

Weight per metre as per BIS standard is mentioned below –

Section (Dia in mm) Weight/Metre Range (In Grams)

6 206 - 238

8 367 - 423

10 586 - 648

12 844 - 932

16 1501 - 1659

20 2396 - 2544

4 - What is the difference between Fe500 and

Fe500D? - Why Fe500D is better than Fe500?

Both Fe500 and Fe500 D are supposed to offer a minimum of 500 MPa of Yield Strength (YS), where

they differ is the ductility parameter.

Fe500 D grade offers higher ductility (measured as UTS/YS ratio & % elongation) than Fe500 rebars due

to lower impurities like sulphur and phosphorus. Ductility is critical for the performance of rebar within

a structure especially during extreme loading conditions (like earthquakes).

5

- Does Tata Steel manufacture all rebars at its own facilities?

- Are Modern, Beekay, and BMW mills of Tata Steel or are conversion agents?

Manufacturing of rebar requires two main steps to be followed -

Step 1 - Steel making which entails conversion of raw iron ore into semi-finished product called billets

Step 2 - Rebar rolling which entails rolling of billets into ready to use rebars through TMT process

TATA Steel has its own facilities for both the steps at Jamshedpur, Jharkhand. However, to cater to the

rising demand of rebars at times we also utilize services of some agencies that only take care of rebar

rolling process (step 2) under strict supervision and quality control of TATA Steel.

6 - How to check originality of Tiscon rebars? - What is the identity of original Tata Tiscon rebars?

TATA Steel manufactures rebars under brand TATA TISCON. To verify the originality of rebars please check on the following three points -

1. TATA TISCON embossing should be there on every metre of rebar 2. TATA TISCON rebars comes with proper Test Certificate stating the chemical and mechanical

properties of rebar 3. You will always get an original invoice on every purchase of TATA TISCON rebars 4. Strength of rebar (500, 600) and type (D, SD etc) are embossed on the product

7 - What is the life of Tiscon rebars? The life of rebars depends upon two factors – 1. Quality of the concrete construction

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2. Atmospheric exposure of RCC structure Therefore, it is difficult to predict the actual life of rebar. However, under normal circumstances a RCC structure is designed for a minimum life of 50 years.

8 - I need an estimate for cost of constructing my

house? - What is the range for cost of construction?

The cost of constructing a house depends upon following three factors -

1. Quality of construction

2. Place of construction

3. Quality of finishing work

On an average per square feet cost of construction for economy finish is Rs. 350-450, for medium finish

is Rs. 750-900, and for superior finish is Rs. 1200-1700. These costs are just indicative and may vary on

basis of material and labour costs. Also, this does not include the land price.

9 - Is cross rib bar better than Tiscon?

Regarding your query on cross rib steel bar please note that Government regulations require every

manufacturer to ensure a bond strength which is more than a specified minimum. Any rib pattern

leading to bonding below this level is not fit for use and any other rib pattern giving bonding much

beyond this specified minimum would be a wasted effort.

A good analogy of this situation could be as below:

A person below 18 years of age is not allowed a driving license however being of age 19 or 35 or 55 does

not imply that person with 55 years of age (highest among three) is having best driving skills. How good

a driver one is depends on many factors other than age.

Coming to X ribbed bars, if we compare them on rib pattern only, they are as good as any other rebar as

long as X-ribs ensure the minimum bond strength. However only 'X' pattern of ribs does not guarantee

compliance to minimum bond strength criterion, certain other variables like how spaced out the ribs

are, (mean) height of ribs, angle at which ribs are slanted etc. are as critical. In case of rebars bonding

capability beyond the specified minimum is of no practical significance. Amount of rebar consumed in

any structure depends only on one factor that's rebar's Yield Strength (YS).

10

- I want to know steel requirement for my house? - How much steel will be used in my house? - Can you give me an estimation of steel

requirement for my house construction?

To help you in generating an estimate of the material quantity Tata Tiscon has come up with an

application called Product Estimator. Through this application you can get a fair idea of quantity of

material and its cost towards building of your dream home. Please access the application at -

http://www.tatatiscon.co.in/home-builders/product-estimator.aspx. You can get the size of the rebars

and the quantity required by choosing location as Patna which is adjoining district of Saran.

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We also suggest that you should take help from a qualified local Engineer.

11 - I want to become Tiscon dealer? We have forwarded your query to our sales team. They will get in touch with you in next 72 working

hours.

12 - Which grade of rebar Tata Steel produces? Tata Steel makes Fe 500D and 600 grades of rebars. Within the family of 500D category – there are two variants also available namely, Super Ductile (SD), Corrosion resistant (CRS).

13 - What are the harmful effects of sulphur and

phosphorus?

(i) Higher quantities of impurities (S and P) introduce brittle behaviour of rebar (ii) High S, enhances the corrosion of rebar (iii) High S and P levels adversely impact fatigue and impact strength of rebar

14 - What is the difference between Fe 415 and Fe

500D grade rebar?

(i) Fe 500D has higher yield strength and elongation than Fe 415 which allows you to use less steel for reinforcement (ii) Also, Compared to Fe 415, Fe500D has lesser impurities like sulphur and phosphorus

15

- Local supplier of rebar also manufactures Fe 500D grade. Why should I buy the costlier rebar of Tata Steel?

A rebar is expected to have consistent properties of tensile and yield strengths along its full length. This can be ensured only when good quality control is exercised during steel making and rolling. Why Tiscon? Superior Ductility Tata Tiscon rebars are rolled in modern rolling mills which are equipped with computerized controls. Every critical parameter is continuously monitored to deliver best quality rebar. Superior ductility rebars are better to work with on site, easy to bend and cut. This feature also helps during earthquake by preventing any brittle failure.

Input from Masons

Slab does not sag when cast with TISCON but it sags when constructed with secondary bars

TISCON is very good quality

TISCON rebar is more ductile than other local rebars

Low impurities (Sulphur and Phosphorus content) Tata TISCON rebars are made from steel which uses virgin iron ore route as the back end

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process. Further during manufacturing, the steel is refined in several stages using best of intermediary processes (Hot metal desulphurisation, On-line purging, Secondary refining, Calcium injection etc). Lower impurity content gives it uniform properties along its length.

16 - How to judge whether the rebar I am using is of

good quality?

Following are critical parameters to judge the quality of rebar:

Rebar manufacturing route

Raw material used for making steel

Consistency of physical properties along the rebar length

Better ductility

Lower impurities

Easy to work with at site (ease of fabrication)

Good bonding with concrete

Reliable and transparent pricing and offerings (TISCON sold by piece)

17 - What is the role of rebar during earthquake

shaking?

Let us first understand the difference between brittle and ductile materials. Take two bars of same length and cross-sectional area – one made of a ductile material and another of a brittle material. Now, pull these two bars under tensile loading until fracture. You will notice that the ductile bar elongates by a large amount before it breaks, while the brittle bar breaks suddenly on reaching its maximum strength at a relatively small elongation (Figure 1).

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During an earthquake, very high amount of force/energy is generated on a structure. To absorb this energy, a good ductile material is needed. The area under the force-elongation graph (Figure 1) is a measure of the amount of energy absorbed by the material. So one can easily deduce that because of their higher elongation, a ductile material will absorb higher amount of energy before failure than the one with lower ductility. Importantly, among all building construction materials, steel is the ductile one, while bricks and concrete are brittle.

18 - What is the effect of temperature on the strength

of steel? There is no effect on the strength of steel at atmospheric temperature conditions. Only at very high and low temperatures the rebar strength gets adversely impacted. Such kind of

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temperatures are generally not experienced during the normal service life of a structure.

Usually, when exposed to a temperature higher than 600 C, the steel (structural or rebar) loses its strength significantly. It is the combination of temperature and time that determines the time for failure of the building. RCC structures using concrete and with a good clear cover, is considered to be a suitable protection against sudden fire. By controlling harmful residual element (such as S) the low temperature (sub-zero) impact properties (i.e. ability to resist propagation of cracks) is improved.

19 - My neighbour has used local rebar in his house but

there is no problem at his home?

For analogy, a car driver wearing a seat belt will have lesser probability of grave injuries during an accident than the one who does not wear a seat belt. Of course till the time there is no accident both the drivers might remain safe. Therefore, prevention is always better than cure. Similarly, it is very important to have rebars with good ductility so that structure suffers minimum damage in an event like earthquake. Earthquakes are unpredictable and till the time they don’t occur, your neighbour’s house might also remain safe. But when they do strike, a house built with a rebar of good ductility and having consistent properties will have lesser probability of collapsing. Your neighbour may have also been forced to use higher steel due to both: a) wastage due to cracking during bending and other fabrication and b) higher steel reinforcement due to commonly observed low strengths of these rebars.

20 - How savings are achieved using Fe 500 over Fe

415?

The no of bars to be placed in a particular member depends on the area of steel reinforcement required. For e.g. if a beam requires 400 mm2 area and 12 mm bars are used. Then no of bars required = Area of steel reqd/Area of 12 mm bar = 400/113 = 3.5. So we provide 4 no of rebars.

Area of steel reinforcement (Ast) required in a beam is calculated by:

√

fck = Characteristic strength of concrete fy = Yield strength of steel Mu = Factored Moment b, d = width and effective depth of beam section. This indicates that, Ast =1/fy i.e. steel reinforcement requirement goes down with increase in yield strength (fy) of

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rebar. However one should keep in mind that the above formula does not hold good for columns.

21 - What is the importance of carbon in steel?

Carbon is an element which is present in all steels although in varying concentrations. It is a hardening element of steel and determines the level of hardness or strength that can be attained. Carbon in steel is responsible for increasing tensile strength, hardness, resistance to wear and abrasion etc. However, when present in high quantities it affects the ductility, toughness and the machinability of steel.

22 - What is the temperature of rebar after quenching? Between 200°C - 300°C

23 - What is the role of tungsten carbide in rolling?

The different type of roll materials available for rolling process of rebars. Tungsten carbide rolls are used because of following advantages: a) High wear resistance: Rib geometry remain controlled within narrow tolerance b) Long lifespan: Un hindered production and, less surface defects on the rolled product c) High efficiency in high speed rolling

24 - How is TMT process of secondary different from

primary producers?

Following are the critical differences between Primary and Secondary producers: Raw materials: Primary producers use virgin iron ore (TATA Steel uses its own captive mines) on the other hand, secondary producers use scrap steels (often with unknown origin). Process: Secondary producers often do not have refinement facilities and also rely heavily on labourer’s skills for the manual methods of production Consequently, Rebars from primary producers possess: a) less impurities like sulphur and phosphorus b) proper combination of strength and ductility (cross-section exhibit uniform hard ring with soft core)

25 - How is extra elongation achieved in Fe 500SD over

Fe 500D? Targeted to control the rim thickness, the higher ductility properties are achieved by suitably controlling the lay head temperature and chemical control.

26 - How is Fe 415D different from Fe 500?

S No Parameter 415D 500D

1 Min Yield Strength (N/mm2) 415 500

2 Min Elongation (%) 18 12

Importantly it is to be kept in mind that using Fe 500D over Fe 415D results in 10-12% savings in steel consumption.

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27 - What is the difference between rusting and

corrosion?

Rust is the oxide that is formed by open air oxidation of iron. Rusting is caused by the reaction of air and moisture, generally a slow process and is a very common phenomenon for most steel products and has practically no effect on the functional quality.

Corrosion on the other hand is the electrochemical reaction between a metal and its environment. The reaction causes formation of not only oxides but other compounds as well. Corrosion usually results in accelerated and uneven erosion of metal surface and is detrimental to its intended service performance.

28 - How quenching is done?

Quenching is done by passing the hot-rolled rebar through a water box/ cooling chamber where a jet of water is continuously passed at a very high speed.

29 - Will elongation of rebar reduce with passage of

time? No, elongation of rebar will not reduce with passage of time.

30 - Why Tiscon Superlinks be preferred by customers?

Normally it is seen at sites that same mandrel is used for bending rebars of different dia. This practice can render the bends brittle. Also, as per the codal provision the 135° hook is mandatory for structures lying in high seismic zones. But generally stirrups are bend at 90° hooks only. TISCON Superlinks are made using proper mandrel dia and hook which adds to the overall

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strength of the structural member. It also results in saving of time and cost.

31

- Comparison between Readymade (TISCON footing) and straight bar footings (on-site construction)

Use of Readymade TISCON footing will result in following savings (for a 1000 sq ft building): 1] Time saving = 1 day 2] Saving due to material cost = Rs 2000 3] Savings due to less labour = Rs 1500

32 - Dos and Don’ts of TISCON (Storage, handling etc.)

Guidelines given in BIS4082 for reinforcement storage/stacking applies to TI|SCON: a) Steel reinforcement shall ordinarily be stored in such a way as to avoid distortion and to prevent deterioration and corrosion. It is desirable to coat reinforcement with cement wash before stacking to prevent scaling and rusting. b) In case of long storage, reinforcement bars shall be stacked above ground level by at least 150 mm. Also in coastal areas or in case of long storage a coat of cement wash shall be given to prevent scaling and rusting.

33 - If some query is incomplete or it is unclear… We are unable to understand your query. Request you to elaborate a little further on your requirement.

It will help us in understanding your problem and enable us to give the solution possible at our end.

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Design related

Sr. No Questions Suggested Answer

1 - Which section should I use in roof? - Which steel should I use in slab? - Can you guide me on casting roof of my home?

Size of rebars used in slab casting depends upon the type of building construction. The rebar thickness

as per building construction types are given below –

1. Residential construction without basement - 8 mm

2. Residential construction with basement - 10 mm (for basement slab) and 8 mm for other slabs

3. Commercial construction - Mix of 8 mm and 10 mm

Apart from this, you also need to keep a tab on the following points –

1. Alignment of soffit formwork should be horizontal

2. Minimum clear cover of bottom layer of rebar should be 20-25 mm

3. Removal of slab formwork should be done only after a minimum of 14 days

4. 4. Slab should be cured for a minimum of 28 days using ponding (preferred) or jute cloth

2

- Which steel should I use for my house construction?

- What are the different sections used in different structural members of house?

Foundation - 10 mm or 12 mm

Column - 12 mm to 16 mm (in zone II, III, IV) ; 12 - 20 mm (in zone V)

Beam - 12 mm to 16 mm (in zone II, III, IV) ; 12 - 20 mm (in zone V)

Roof - 8 mm & 10 mm

Ring/Stirrup size: 6 - 8mm; however 8 mm recommended in Zone III, IV, V

3

- Tata Tiscon is rusted. Should I use it? - Can I use rusted rebar for construction? - How can I stop rusting of rebar? - How can I remove rust from rebar surface?

Rusting is a natural process for rebars which happens due to exposure to atmosphere. It is not harmful and can be removed by using a hard wire brush or sand paper. However, prolonged exposure leads to corrosion wherein the ribs of rebar start wearing off and the reduction in size of rebar takes place. There is no process of reversal for corrosion. At large construction sites it is customary to sprinkle water on the rebar to allow a certain degree of reddishness to appear before using it for concrete casting. The benefit of this is in the development of fine pits on the rebar surface which results in strong bonding of rebar with the concrete.

Thus, prevention of rebars from getting corroded needs to be taken care of. You can follow the steps mentioned below for the same -

1. Rebar should be stacked at least above 150 mm from ground level using wooden sleepers to avoid direct contact with moisture of ground surface. Also during rainy season, stacked rebar should be covered with tarpaulin sheets.

2. In places where rebar is exposed for 1-2 months during construction apply cement:water slurry in 1:3 ratio on rebar surface. This will prevent direct contact of rebar with atmosphere to create

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rust. This cement layer is not a waste since it goes inside the concrete when construction resumes.

3. In case of expansion in future after 2 months you may pour loose concrete on rebar, which should be demolished off when construction resumes in future. Chip off the construction joint and resume construction with fresh concrete.

4 - Give an example showing comparison between

savings of Fe 500 and Fe 415?

An example of structure designed using both Fe 415 and Fe 500 is shown below:

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5 - Why column bars are extended into the footings?

Very high stresses are developed at the column–footing interface. If the column rebar are not extended into the footings then there is a high probability that the structure will fail at the column footing interface. The extension of column rebar in footing is called as development length and is used for efficient transfer of loads (coming via column) to ground.

6

- What is the importance of soil on structural design?

Any load that is acting upon the structure has to be finally transferred to the soil via the foundation. The basic function of foundation is to transmit the loads in a manner that the transferred stress does not exceed the soil strength. So unless the value of soil strength is known, the foundation design is an approximation.

The load carrying capacity of soil (i.e. soil bearing capacity) is determined by various tests conducted under the supervision of a Civil Engineer. Based on this value and other factors like loads being transferred to the soil from the building, position of the water table, the general nature of the terrain, the past use of the land and the stress history, the structural engineer then decides the type of foundation to be provided.

7 - Why 6 mm is to be used for stirrups?

According to BIS456; Stirrup diameter to be used in Column is the maximum of: a) 6 mm, b) 1/4 × maximum dia of longitudinal column reinforcement. Therefore, for column reinforcement ≤ 25 mm diameter, the use of 6 mm rebar for stirrup dia will be sufficient. Stirrups made of 8 mm rebar will be required for column reinforcement using ≥ 25mm dia rebar. Typically for IHB constructions (up to G+2 or, G+3) 20 mm dia is sufficient for column reinforcement,

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therefore 6mm is a potential option. In beams, by a proper design engineering, the use of 6 mm dia stirrup will find application specially when used with lower spacing between the stirrups. However, if clear span of beam exceeds 5 m then 8mm dia stirrup is mandatory as per BIS 13920. However, in non-loaded structures such as tie-beam, lintel, the use of 6mm for stirrup may be recommended.

8 - What is a typical calculation to get suitable section

of Slab ?

No typical calculation or shortcut known to exist. Slab design follows calculation steps such as: 1] DL (dead load) + LL (live load), 2] Bending Moment calculation, 3] Rebar calculation (Area of required steel and nos of bars), 4] Short term and long term deflection checks, 5] Crack width calculation. However in

residential framed structure, 100 125 mm depth using 8 mm rebar spaced @ 150mm centre to centre between main and binder is sufficient (this may change depending on slab panel size i.e. length and width). STAADPRO is one of the available design tools which is used for carrying out the mentioned calculations. With the user input of slab's geometrical dimensions; Step 1 calculates DL and LL, then, Step 2 is calculated using the values obtained in Step 1 which in turn serves as input for the calculation of step 3 and then step 4 serves as checking criteria (deflection and crack width; as prescribed in IS456). This is an iterative procedure, which when converged (i.e. fulfilling the deflection and crack width criteria), makes the quantity of rebar known.

9 - What is a typical calculation to get suitable section

of Beam?

No typical calculation or shortcut known to exist. Beam designing involves calculation steps such as: 1] DL + LL + WL (wind load) + SL (slab load), 2] BM/ SF (shear force) calculation, 3] Rebar calculation (Area of steel and nos of bars), 4] Deflection check. STAADPRO is one of the available design tools which is used for carrying out the mentioned calculations. With the user input of beam's geometrical dimensions; Step 1 calculates DL, LL, WL, SL then, Step 2 is calculated using the values obtained in Step 1 which in turn serves as input for the calculation of step 3 and then step 4 serves as checking criteria (deflection). This is an iterative procedure, which when converged (i.e. fulfilling the deflection criteria; as prescribed in IS456), makes the quantity of rebar known.

10 - Is it correct that more steel harmful? Why?

Consider a slab panel size = 16' × 11' (Assumptions: Depth = 100 mm; DL [self-weight (s/w) of slab, Floor finish (F/F)] + LL = 6 kN/m2; Rebar = 8 mm dia @ 150mm c/c both ways) then, after using the deflection criteria (total calculated deflection = 11.8 mm; Allowable ≤ 13.4 mm), long term calculated deflection (due to creep + shrinkage) = 3.6 mm; Allowable < 9.6 mm, hence it is OK (i.e. using correct concrete strength (≥M20) and correct construction procedure - no cracks would be developed). Now, If main rebar (along X-direction or shorter direction) increased to 10 mm dia @ 150mm c/c, binder (along

Ydirection) 8 mm dia @ 150mm c/c, then the total calculated deflection = 13.75 mm exceeds the allowable deflection and, the calculated long term deflection = 6.8 mm (< allowable). Since the proposed design fails in total deflection criteria therefore, it is likely that by just partial substituting lower dia with high dia rebars - a no fulfilment of deflection criteria may cause the formation of cracks on the slabs.

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11 - Fundamentals of crack width No fundamental calculation could be explained. Crack width increases with increase in main reinforcement or decrease of slab depth.

12 - Fundamentals of preventing crack (vibration crack

impermeability etc)

Crack mainly develops on RCC due to: 1) Faulty design engineering and, 2) Faulty construction practice (improper vibration/ compaction, inferior concrete mix, insufficient clear cover, improper shutter/props, shorter period curing). If crack appears due to any of these reasons, no means can reverse the mechanism. However, some remedies may be taken to repair the same temporarily depending on nature and severity of crack. Recommended method is to chip off the concrete adjacent to crack, and fill with fresh concrete (with 3/8'' chips) or cement: sand mortar of 1:3, with/without waterproofing compound.

13 - Concrete Mix for roof and its significance Minimum recommended RCC grade is M20 (as per IS456), i.e., Cement : Sand: Graded stone chips = 1 : 1.5 : 3 to 1 : 2 : 3 (max). This is sufficient for slab. Depth of slab (required as per panel size) and rebar detailing (arrangement, grade of rebar) and grade of concrete are of major significance.

14 - Concrete Mix for beam and its significance Minimum recommended RCC grade is M20 (as per IS456), i.e, Cement : Sand : Graded stone chips = 1 : 1.5 : 3 to 1 : 2 : 3 (max) is sufficient for beam. Depth of beam and rebar detailing (longitudinal and stirrups, grade of rebar) and grade of concrete are among the significant variables.

15 - Concrete Mix for Column and its significance

Minimum recommended RCC grade is M20 (as per IS456), i.e. Cement : Sand : Graded stone chips = 1 : 1.5 : 3 to 1 : 2 : 3 (max) is required. Higher the grade of concrete - higher is the compressive strength of column. Therefore, either column dimensions or rebar quantity is saved for high storey constructions (for any nature of occupancy: residential/ commercial/ institutional) with the use of high strength concrete for a constant design load. Other than cross-sectional area and rebar (longitudinal and stirrups), concrete grade has very high significance in columns.

16 - Concrete Mix for Foundation and its significance Minimum RCC grade M20 (as per IS456), i.e, cement: sand: graded stone chips=1:1.5:3 to 1:2:3 (max) sufficient for footings, no significance. Plan dimension and depth of footing are only significant.

17 - Lap Length and its significance

Minimum length of bonding of rebar with concrete, so that rebar don't come out during pulling to desired stress (0.55fy in working stress method, and 0.87fy in limit state method of design). No significance for footing, tie beam, lintel, chajja or non-loaded members (30 × D is recommended in such cases). For other members, 57 × D may be followed for M20/ Fe500 case [as per Clause 26.2 of BIS456].

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Construction practice related

Sr. No Questions Suggested Answer

1 - Need your advice on starting construction - What should I do to start construction?

- First and foremost is that your house must be designed by a professional (structural engineer)

- You need to check with him whether he has taken local seismic zone and resulting forces thereof

into design

- The RCC reinforcement detailing should incorporate sufficient ductility to the structure by

controlling member stiffness at design and detailing stage.

- Lastly, you should engage an experienced contractor who shall do 'quality work' on-site to ensure

quality of concrete as well as reinforcement placing

We should mention of a few typical cares to be exercised encompassing storage of rebars at site to

minimum concrete cover to development length to typical cares prescribed for column – beam/ slab

joints construction.

However, if you have already developed the design of your house we can arrange for a customer service

executive (CSE) visit to assist you in your construction.

Please let us know for arranging CSE visit.

2

- Should I use binding wire for lapping or do welding?

- What type of welding should I do in my house construction?

In Indian subcontinent welding is not recommended in RCC Construction as it impacts the strength of

the rebar. However, under special circumstances it can be used only in those areas that lie in seismic

zone II, with adherence to BIS norms.

We may include a line on our coupler offering here as an alternate measure.

3 - What is RCC? - What type of RCC should I use in columns? - What type of RCC should I use in slab?

Reinforced Cement Concrete is a composite material consisting of concrete (cement, sand, stone chips,

and water) & reinforcement bar with excellent strength and durability characteristics. Judicious

selection of materials is required for achieving desired strength.

The concrete should be of minimum M20 grade for residential construction. Proportion of

cement:sand:graded stone chips in M20 concrete should be 1:1.5:3. The best steel grade to use for

reinforcement bars is 500D and in high seismic zones it is SD.

4 - What is RMC? - Is RMC better than manually prepared concrete? - Should I use RMC for my house construction?

Ready mix concrete is better than manual concrete because of the uniformity in mix proportion and control over quality. Usage of concrete solely depends on the type of occupancy. For a commercial occupancy minimum of M25 grade should be used. And, for residential occupancy upto G+4 minimum of M20 grade should be used and for building above G+4 minimum M25 should be used. However, we recommend you to

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consult your structural engineer for usage of concrete grade as per the building design.

5 - Which cement should I buy? - How to determine the quality of cement?

Following points should be kept in mind while selecting cement for your construction - 1. Minimum 43 grade cement should be used 2. On rubbing cement between fingers it should give a smooth and cold feeling 3. If a small quantity of cement is thrown into a bucket of water it should sink and not float on the

surface 4. Lastly, it should be free from any hard lumps

6

- Why historical buildings such as Taj Mahal and Qutub Minar having no rebars are still standing strong even after being subjected to many earthquakes during their lifetime?

Rebars are not the only way to resist earthquake loads. Seismic resistance of a structure depends on many other factors like quality of workmanship, quality of raw materials and most importantly the architectural configuration. These factors formed a critical part in the design of historical structures.

Desire to create aesthetically and functionally efficient structures drive architects to conceive wonderful and imaginative structures. Sometimes the shape of building catches the eye of the visitor, sometimes the structural system appeals, and in other cases both shape and structural system work together to make the structure a marvel. However, each of these choices of shapes and structure has significant bearing on the performance of the building during strong earthquakes. The wide range of structural damages observed during past earthquakes across the world is very educative in identifying structural configurations that are desirable versus those which must be avoided.

The importance of the configuration of a building was aptly summarised by Late Henry Degenkolb, a noted Earthquake Engineer of USA, as:

“If we have a poor configuration to start with, all the engineer can do is to provide a band-aid - improve a basically poor solution as best as he can. Conversely, if we start-off with a good configuration and reasonable framing system, even a poor engineer cannot harm its ultimate performance too much.”

7 - Why is brick layer added before casting the

foundation?

The purpose of brick layer is: a) To provide firm and flat level for laying of concrete

b) To hold the moisture content of footing concrete without the soil soaking it

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- Why is gypsum added in cement? Gypsum is added to control the “setting time of cement”. If not added, the cement will set immediately after mixing of water leaving no time for concrete placing.

8 - For how much duration curing of concrete should

be done?

The duration of curing of concrete depends on the grade of cement (Grade 33, 43 and 53) and type of cement (Ordinary Portland Cement, Puzzolona: Granulated blast furnace slag or Fly ash based), mix proportion, desired concrete strength, shape and size of the concrete member and environmental & exposure conditions. The duration may vary (typically 14 to 28 days) depending on the condition:

IS-456: 2000 provisions for duration of curing (Indian Standard-Plain & Reinforced concrete-Code of Practice, 4th revision, page 27) are as follows:

Exposed surfaces of concrete shall be kept continuously damp or in a wet condition by ponding or by covering with sacks, canvas, hessian or other similar material and kept continuously wet for at least 7 days from the date of placing, in case of Ordinary Portland Cement (OPC) and at least 10 days when mineral admixtures or blended cements are used. In case of concrete where mineral admixtures or blended cements are used, it is recommended that the above minimum periods may be extended to 14 days.

9 - When should the curing process be started?

It is difficult to set a time frame on how early water curing can be started. It depends on, prevailing temperature, humidity, wind velocity, type of cement, fineness of cement, w/c used and size of member etc. The point to observe is that, the top surface of concrete should not be allowed to dry. Enough moisture must be present to promote hydration which is responsible for obtaining the strength of concrete. In hot arid regions, concrete used for road slab or roof slab may get dried up in a very short time (typically 2 hours). Often questions are asked whether water can be poured over the above concrete within two hours to prevent the drying. The associated problem is, if water is applied within say two hours, whether it will interfere with the water/cement ratio and cause harmful effects. In other words, question is how early water can be applied over concrete surface so that uninterrupted and continued hydration takes place, without causing interference with the water/cement ratio. The answer is that first of all, concrete should not be allowed to dry fast in any situation. Concrete that are liable to quick drying is required to be covered with wet gunny bag or wet hessian cloth properly squeezed, so that the water does not drip and at the same time, does

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not allow the concrete to dry. This condition should be maintained for 24 hours or at least till the final setting time of cement at which duration the concrete will have assumed the final volume. Even if water is poured, after this time, it is not going to interfere with the water/cement ratio. However, the best practice is to keep the concrete under the wet gunny bag for 24 hours and then commence water curing by way of ponding or spraying.

10 - When should the curing process be started?

It is difficult to set a time frame on how early water curing can be started. It depends on, prevailing temperature, humidity, wind velocity, type of cement, fineness of cement, w/c used and size of member etc. The point to observe is that, the top surface of concrete should not be allowed to dry. Enough moisture must be present to promote hydration which is responsible for obtaining the strength of concrete. In hot arid regions, concrete used for road slab or roof slab may get dried up in a very short time (typically 2 hours). Often questions are asked whether water can be poured over the above concrete within two hours to prevent the drying. The associated problem is, if water is applied within say two hours, whether it will interfere with the water/cement ratio and cause harmful effects. In other words, question is how early water can be applied over concrete surface so that uninterrupted and continued hydration takes place, without causing interference with the water/cement ratio. The answer is that first of all, concrete should not be allowed to dry fast in any situation. Concrete that are liable to quick drying is required to be covered with wet gunny bag or wet hessian cloth properly squeezed, so that the water does not drip and at the same time, does not allow the concrete to dry. This condition should be maintained for 24 hours or at least till the final setting time of cement at which duration the concrete will have assumed the final volume. Even if water is poured, after this time, it is not going to interfere with the water/cement ratio. However, the best practice is to keep the concrete under the wet gunny bag for 24 hours and then commence water curing by way of ponding or spraying.

11 - Which is the better option between welding,

lapping and couplers?

Due to the growing technical challenges faced in today’s construction industry, traditional methods for connecting rebar, such as lapping or welding, are no longer the best methods to connect rebars. Welding of rebar can hamper the high strength and ductility of the original rebar. Lapping on the other hand not only results in extra rebar length being used but also requires careful attention during the placement process. Couplers offer the following advantages:

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More reliable and more structural integrity than lap splices because the use of coupler eliminates the reliance on the concrete for load transfer between the two rebars being spliced

Reduces rebar congestion

Efficient and easy design options result in smaller and stronger columns with the maximum amount of useful area

No lapping length necessary – reduces inventory which lowers cost

Allows for same line splicing – no staggered splices

Minimizes rebar waste