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What will happen if we use too much rebar in concrete?


The main principle is that concrete has strong resistance to compression failure therefore it is strong in compression however it is weak in tension resistance to bending that is why steel compensates this weakness hence its strong in tension Having more percentage than the specified will cause the concrete to act as steel structure which is basically is not steel aimed structure besides that the area occupied by more reinforcement will weaken the concrete to act in compression resistance and punching shear and brittle failure may occur especially in the perpendicular structure such as columns at the time of ultimate strength, in conclusion, the standards have undergone plenty of experiences by experts to bring forward simple references for a designer I hope you have gained insight hints.

Rebar or reinforcement is expensive. Using more than recommended will be uneconomical. Moreover, providing adequate spacing between the rebars will be difficult. IS 456:2000 recommends minimum and maximum spacing which has to be fulfilled.

One more disadvantage of providing excess rebar is that the placement of concrete will become difficult. The concrete should be placed uniformly in the framework which would be affected by the presence of excess rebar.

Then the concrete will fail first, which is a brittle material so you will not get any warnings of failure beforehand, which means a sudden failure without warning and it can therefore cause loss of lives… this is a very unwanted situation. The rebar should be below a certain limit so that when the failure will happen, the rebar will start to fail, which is a ductile material so it gives a warning before the collapse and can save lives.


What is the difference between T rebars and H rebars?

 

There is no difference between ‘T’ rebars and ‘H’ rebars, as they both refer to high tensile steel. The letter ‘T’ comes from older codes of practice and ‘H’ is the more modern or current standard. Always use H to avoid confusion with T = Top and B = Bottom. So for example:

5H10 T&B means five 10mm diameter rebars top and five 10mm rebars bottom of the slab or beam. Also you can place two lines above one another as so:

4H16 T

4H25 B

Which would be a common way of showing a beam had different bar sizes top and bottom.

Note that the grade of rebar should be specified in your calculations and drawings using the tensile strength and ductility grade, B500A, B500B and B500C.


Which is the best cement used for plastering?


Rather than advising you on which brand of cement to be used, I would advise you on the type of cement to be used because that plays an important role in the quality of construction

For plastering works, use blended cement like PPC or PSC. These cement have less heat of hydration. That means during the cement reaction with water, they produce less heat. Less heat means less cracks on the wall surface. Less cracks and less porosity will decrease any water seepage.

As far as brand is concerned, most of the brands provide cement of good quality these days. You can go with the brand that is locally well known and gives you the best rate. Big brands claim huge premium and it is not worth a value for individual house constructions.

As different stages of construction require different types of cement, Understanding the types of cement, its substitutes, and the availability of local brands should empower you to choose the right cement required for your work thus avoiding any concerns on the availability of cement.

As Cement has a limited shelf life and loses strength over time, cement should be best consumed within a month or at most within two months of its production. The rate at which cement loses its strength depends on the storage conditions.


What is a rebar coupler?

 


What is a rebar coupler?

Rebar couplers are used in reinforced concrete structures to the connection steel bars that replace a normal rebar lap joints. The rebar couplers are very useful for reinforced concrete structure columns and walls. The rebar coupler comprises a piece of rebar furnished with a string, and a coupler sleeve at the correct end as seen toward an establishment. In development joints, rebar couplers can be utilized to supplant all bits of the rebar experiencing the form work. Rebar couplers are utilized for joining rebars with a full tensions capacity. The closures of bars to be joined are furnished with strings, and the bars are joined utilizing a coupler sleeve that moves the power on the rebar across the association.

Type of rebar coupler




Workability of concrete

 


Concrete is one if the most used construction materials in the world today. It can be placed in forms to create almost any shape, or placed in flat slabs thousands of feet long and inches or feet thick, it can be structural columns and beams supporting tall buildings or bridges, or it can be the hull of a boat that floats underneath the bridge and out to sea.

Concrete is a mixture of cement, usually Portland cement, coarse and fine aggregates (think of coarse as gravel and fine as sand, though other materials may be used). When cement is mixed with water and the appropriate aggregates, it becomes plastic (fluid), and it is placed in forms (molds) to create the shape the user is building. Hydration, a reaction between the dry components of the cement and water causes the concrete to set up, or harden into a stone like material that is the foundation (literally) of the construction industry today.

WORKABILITY OF CONCRETE :

The property of concrete which determines the amount of useful internal work ,necessary to produce full compaction i.e workability is the amount of energy to overcome Friction while compacting. Also defined as the relative ease with which concrete can be mixed ,transported, moulded and compacted.

WORKABILITY TESTS:

SLUMP TEST: Slump cone of bottom dia 20cm, top dia 10cm and height 30cm at three layers of conrete .Each layer tamped for 25 times bya standard tamping rod of 16mm diameter and 60 cm length. The subsidence of concrete under gravity in “mm” is SLUMP.



What is Lap Length?

 


What is the lap length?

It is the length provided to overlap two rebars in order to safely transfer load from one bar to another bar and alternative to this is, to provide mechanical couplers. 

What are the general rules for lap length?

For the different diameter of bars

When the bars of different diameters are to be spliced the lap length is calculated considering the smaller diameter bars.

Suppose you are constructing a column, from bottom 20 mm diameter bar is coming and from here 16 mm diameter bar has to be spliced then for calculating lap length 16 mm diameter should be considered and not 20 mm.

What is the minimum lap length?

For direct tension, the straight length of the lapping bar shall not be less than 15d or 20 cm. While in the case of compression lapping should not be less than 24d.

What is the difference between lap length and development length?

Lap length is provided to safely transfer stresses from one bar to another, while development is needed to safely transfer the stresses from steel bar to concrete to make a continuous structure.

Where lap length is provided in column?

The bending moment at the middle portion of the column is zero it means the middle portion of the column is least stressed. Hence, lapping should be provided in the mid-section of the column.


Reinforcing Bar Couplers


Simplify the design and construction of concrete
Lapped joints are not always an appropriate means of connecting reinforcing bars. The use of laps
can be time consuming in terms of design and installation and can lead to greater congestion
within the concrete because of the increased amount of rebar used.
Ancon couplers can simplify the design and construction of reinforced concrete and reduce the amount of reinforcement required.
Lapped joints are dependent upon the concrete for load transfer. For this reason any degradation in the integrity of the concrete could significantly affect the performance of the joint. The strength of a mechanical splice is independent of the concrete in which it is located and will retain its strength despite loss of cover as a result of impact damage or seismic event.
The Ancon range of reinforcing bar couplers is the most comprehensive available and includes tapered threaded, parallel threaded and mechanically bolted couplers.
Rebar couplers. Rebar couplers are used in reinforced concrete structures to replace normal rebar lap joints. ... Each rebar coupler consists of a piece of rebar equipped with a thread and coupler sleeve at the right end as viewed in the direction of installation.



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Acceptable Rebar Rust | Rust on Reinforcing Steel


Q.: If reinforcing bars have been stored outside and have a coating of rust, how much rust is acceptable?

A.: Section 12 of ASTM A 615-96a, "Standard Specification for Deformed and Plain Billet Steel Bars for Concrete Reinforcement," says that rust shall not be cause for rejection provided the weight, dimensions, cross-sectional area, and tensile properties of a hand-wire-brushed test specimen aren't less than the ASTM specification requires.

Section 7.4.2 of ACI 318-95, "Building Code Requirements for Structural Concrete," has a similar statement indicating that reinforcement with rust shall be considered satisfactory, provided the minimum dimensions (including height of deformations) and weight of a hand-wire-brushed test specimen aren't less than applicable ASTM specification requirements.

Q: The project inspector is requiring us to wire-brush mill scale and rust off all our rebar. Although the rebar has been at the site for a couple of weeks, we don't think the rust is that heavy or will interfere with the bond between the concrete and steel. Any suggestion? We're tired of brushing rebar.

A: Fortunately, there are a couple of standards to assist you. The ASTM standard specification for deformed steel reinforcement and the Concrete Reinforcing Steel Institute (CRSI) Manual of Standard Practice both give the same information: Reinforcing bars with rust, mill scale, or a combination of both should be considered as satisfactory, provided the minimum dimensions, weight, and height of deformation of a hand-wire-brushed test specimen are not less than the applicable ASTM specification requirements. This inspection criteria recognizes studies that have shown mill scale and rust enhance the bond between concrete and steel. for document Concrete Reinforcing Steel Institute (CRSI) Manual of Standard Practice PDF download. 

LINK HERE 

The Weight of Reinforced Concrete Hume Pipe



How to calculate the Weight of Reinforced Concrete Hume Pipe
RCC Hume Pipes are used for culverts, irrigation, drain and Sewer Lines. The Various Diameter of RCC Hume pipes available such as 100 mm, 150 mm,200 mm,250mm,300mm, 350mm,400mm,450mm, etc. RCC Hume pies are Placed across the culverts, drainage, sewer, Irrigation for easily drain the water. This pipes are very much difficulty in installation and acquire heavy equipment for movement and placing of Hume pipes.
RCC Hume pipe has some advantage and disadvantage. These Hume pipes area much better than the metal pipes because in metal pipes there will be more chances of rusting. Precast Concrete pipes may not be suitable in acidic, alkaline and temporary hard water But Reinforced concrete Hume pipes are useful for black cotton soils.

Weight of Reinforced Concrete Hume Pipe

Let us consider:

Inner radius of Hume pipes (R1) = 20 cm = 0.2 m

Outer Radius of Hume Pipe (R2) =25 cm =0.25 m

Length of RCC Hume pipe (L) = 1 m

Density of Reinforced Cement Concrete = 2500 kg/ m3

The volume of R CC concrete Pipe =?

We know that

The volume of outer radius =π r12 x L

Volume of Inner radius = π r22 x L

So Total Volume of RCC Hume Pipe = π x (r22 – r12 )x L = π x [ (0.25)2 – (0.2)2] x 1 = 0.07068 m3.

Now, let us calculate the Weight of Reinforced Concrete Hume Pipes

So Weight of Hume Pipes = Volume of Hume Pipes x Density of Material used = 0.07068 x 2500 = 176.714 kg.

Hence, the weight of R CC Hume pipes is 176.714 kg.

How To Check Quality Of Sand On Site

Sand is one of the most important constituents of concrete. The main purpose of mixing sand (fine aggregate) in concrete is to fill the voids between Coarse aggregate. And the voids between fine aggregate is filled with cement. Sand bulks the concrete and helps to increase the workability of concrete.


Sand is formed by the weathering of rocks. Well, different regions use the variety of sands (Pit sand, River sand, Sea Sand) in construction according to the availability. A good fine aggregate used in construction should be well-graded (all particles that have almost the same size). The fine aggregate used for construction should pass 4.75mm sieve and retain on 150 microns sieve.

So mainly we perform 5 physical tests on the sand at the site

1- Clay Test.
The presence of clay in the sand effect the performance of the concrete strength. So the presence of clay in the sand can be detected by doing two physical tests on sand
 - Take some amount of sand into your hand and drop it into the glass which contains water. After dropping the sand than shake the glass. If the clay is present in the sand it will make a separate layer above the water surface. So it indicates sand is not good.

- In another simple test take some amount of sand in your hand and then drop it. If sand stick into your fingers it indicates the presence of clay in the sand.

2- Organic impurities Test.
To detect the organic impurities in the sand, you may perform this test.

- Take some amount of sand and drop it into the solution of sodium hydroxide or you may use the solution of caustic soda both work the same. After adding sand into the solution then shake it. If the solution colour appears to a brown it indicates the presence of organic impurities in the sand.

3- Silt Test.
Basically presence of silt in the sand is very dangerous because silt reduces the strength of the concrete. To detect the silt presence we mainly perform this basic physical test on the sand.

- Take a glass bowl and add some amount of sand into the bowl. After adding sand add some amount of water as well as salt into the bowl and then shake it well. After shaking it leave it for at least 24 hours. If silt is present it will make a separate layer above the sand layer.

4- Salt Test.
To check the presence of salt in the sand we perform a very simple and easy test.

- Take very little amount of sand and then taste it. If salts are present in sand it tastes will be salty.

5- Earthy Matters.
The earthy matters are commonly mixed in the sand. So to check the presence of earthy matters in the sand we mainly perform this physical test.

- Take some amount of sand in your hand. After taking sand to rub it by using your other hand. If light marks appear in your hand it indicates the presence of clay.

Note: These all physical test on the sand you can perform it at the site. But when your experience increases in upcoming years in construction work you can ably to check the quality of sand without using these tests.


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