Who is responsible for durability of the concrete structure

Dnyan Deshmukh

Eternal Member
Staff member
Sep 7, 2017
2,632
4,580
Pune
When it comes to Durability of the structure, what we understand is structure is termed as durable when it can carry all load throughout its service life without failing. it means it gives the same performance till its end of design life as it perform Today.

Durability of Structure.jpg

The durability of the structure is taken very seriously by designers of structure and designers of concrete. when it comes to designing of something, there are norms which gets followed to get a specific characteristic in design product.

But in actual who governs the durability of the structure, who can certify that structure will perform as same at its end of the life, its still a question which i have on my mind as there is no technology Today known to human being which can predict the life of the structure to which it can last and by looking at any structure no one can predict what is going on inside in terms of integrity. even if there is any technology available in market it can not be popular to be used by any house owner to check the remaining life of its home.

Structural designer did the job of designing a structure to a specified life by following codes in respective countries, Concrete designer did the designing of concrete to ensure the concrete is durable and is not a permeable, also the other attacks which can spoil concrete are also taken care during designing process of concrete by doing trials and test on it.

Up to this it looks OK and all the parameters are considered to ensure the durability or serviceability of structure for design life. After the designing is over, the next job is to execute the project and complete the structure to make it serviceable for intended users of it.

When i ask questions to executors of the job mostly a Civil Engineers who works at actual field, what is the durability of the structure, in most of the cases i found that, this is the subject which is not given to them for understanding in details.

A general answer which mostly everyone could get is, when the reinforcement bars get corrode, concrete gets cracked the durability of the structure get reduced, to achieve the durability one need to protect the reinforcement bars from rusting.

I do not find any difficulty in understanding above lines to understand the durability of the structure, but those lines are only lines and in practical application those are got forgotten or given second priority in work schedule because nobody put thoughts on it in greater details to make it understand in more practical way.

Basically durability can be achieved by ensuring there is no rusting of bars or degradation of concrete due to any kind of attack in the service life of structure. if it happens, structure will remain durable for its intended service life and beyond.

The corrosion of reinforcement bars is electro mechanical process where one end of the bar is act as a cathode and another as anode, during the medium of water or air, ends get charged with negative and positive charge which accelerate the process of corrosion of reinforcement steel bars. to make this happen the medium need to break the concrete.
Breaking of concrete or disintegration in concrete could happen due to various reasons like attacks from air, water etc. concrete is not compacted and have porousness inside of it or do have honeycombing which creates direct contact of medium with reinforcement bars.

No material on this earth is immortal, every material disintegrates over time according to exposure conditions, it would take several thousands of years to make steel as soil. only the longest surviving material which we see is stone and its a main reason why ancient civilization used it to build there structures and keep written records of their writings.

Coming back to the subject, to ensure the durability of the structure one should ensure the reinforcement bars are not getting rusted and concrete is not susceptible to any kind of attack during construction of the structure.

So in my opinion to make a durable structure, supreme responsibility lies with the Civil Engineers who are actual executing those job at construction site to build a structure. I will put some lights on basic things which could improve the durability of structure.

When a structural designer do designing of the structure, base on the exposure conditions, decides on how much cover should be given to reinforcement, so that it can survive till its design life. In case when you do not find the specifically mention cover to reinforcement bars on structural drawing, you should ask your structural consultant for details of covers to be provided. For a smaller projects or individual houses structural drawing given have notes on cover to be provided to reinforcement bars which has 3 or more tables which prescribe on cover to each member of structure as per exposure condition. If you are building such project, you should also need to take the details of cover in writing from structural consultant to avoid customer dissatisfaction in later stage.

Now i know what cover to be provided to reinforcement bars, when a structure is actually getting built, are we serious about the intensity of what happens when there is less cover than the specified, is i am reducing the life of structure? or we just so ignorant that we make it as a its OK to have less cover.
Cover to reinforcement bars.jpg
Here we fail to understand the structural designers point of view on having cover to reinforcement bars, this will inordinately going to lead in reduction of durability and by the time we may or may not be on this earth to see its refercations. So after understanding it, i Hope every Civil Engineer will give importance to give adequate cover to reinforcement bars.

We should also check for the correct size of the cover blocks used for doing construction of the project.
Cover Block Size.jpg

Cover block should be of same strength as of concrete which is being poured in structure, using weaker cover blocks will also lead to healthy and faster attacks on reinforcement bars which will reduce the durability of structure.
Weak cover blocks.jpg
It is now trend to use PVC cover block due to its cheaper price but we should also think from the durability point of view to use those PVC cover Blocks or not. PVC never stick to cement, over the time it will form a separation cracks and make access to reinforcement bars.

After doing concreting, it is important to do construction joint preparation to ensure good bonding between old and new concrete we pace in structure. if the lattice not removed from the concrete surface, it may lead to weaker bond in concrete.
Construction Joint Preparation.jpg
The smooth surface at the top of the concrete could be cause due to over vibration or fine particle accumulation during process of compaction of the concrete. It is important to remove all those lattice from the top of the concrete. this can be achieved by various ways, such as using water jet, roughening the concrete surface by making aggregate exposed without dislodging or you can press the 20mm size aggregates halfway into top surface to form a mechanical key for bonding of the concrete.

Same way construction joints in slab are also important and they are weaker sections in structure from where durability of the structure can get reduce. the joint should be made in a straight line and at locations as specified by the structural consultant only. it do happens that concrete get flowed beyond the stopper which was placed to arrest the concrete. in such cases all concrete which flowed beyond the stopper should be removed when its fresh or by breaking on very next day.
Construction Joint Preparation Slab.jpg

The bond between the concrete and reinforcement steel bar is very important part from durability point of view, during practical application, it is commonly observed that, some concrete do get stuck to reinforcement bars during concreting activity. it should be removed from steel bars to ensure proper bonding of concrete with reinforcement steel bars.
Reinforcement bars cleaning.jpg
It is also observed that, during application of oil to shutters, some oil do also get spilled on slab and reinforcement bars get coated with it, we should no allow oiling of shutter on slab top once the reinforcement work is started. in case oil spillage observed over reinforcement bars, we should get it clean with detergent by washing.
Oil Spillage over reinforcement bars.jpg

When it comes to top slab reinforcement bars, we often use rebar chair / ghodi and it do have many local names, there is a possibility that rebar chair is directly placed on shutter as the bar bender do think that it will give more stability to keep top reinforcement bars in place but it will have negative impact on durability of the structure, the rebar chairs should be always kept on bottom reinforcement bars of slab. for tying each lag of chair should be tied to 2 reinforcement bars of the slab which will ensure no toppling of chair during movement.
Rebar Chair.JPG

The most prone area for all kind of loads on structure is the column beam junction which are most busiest part of the structure doing actively load transfers. we should ensure the lapping of column reinforcement bars should never fall in this junction which will increase the life of the structure.
Lapping in column beam junction.jpg

Also, during tying of reinforcement bars the cage of beam reinforcement is made above the slab level and then lowered in the position. for columns which have slabs and beams all around and shuttering work is done, it is practically not possible to tie all stirrups of column in that junction. we should ensure those stirrups in column beam junction are tied properly as per spacing as this is most prone zone to cracking.
Column Beam Junction Ring.jpg

Low or inadequate cover to reinforcement bars lead to exposed reinforcement bars after concreting of structural members as the concrete does not pass due to low space. it can create another problem of honey combing too.
Honeycombing and exposed reinforcement bars in column do receive a patching with either cement paste or mortar or mortar with aggregate depending on the depth, in most of the cases those patching jobs are done by mason and mostly in hurry to ensure no one looks at it and make issue. also those patch wont get cure properly which can developes cracking and the source for reducing the durability of structure, if we do ensure proper covers are installed to reinforcement bars, those issues gets eliminated and durability of the structure is ensured.
Honeycombing in columns.jpg
Exposed reinforcement bars can also be observed in slab bottom when the adequate cover to reinforcement bars are not installed.
Rebar exposed in slab.jpg

Exposure of reinforcement bars could also happen due to the workability of the concrete, if the concrete when received at site do lack in required amount, it will also create a problems of rebar exposure and honeycombing in structure due to no able to pass and reach each corner with efforts taken for doing compaction of concrete.

Slump of concrete.jpg
It is important to ensure the concrete does not lack in workability which is required to pour the concrete in structure. pressurizing the workforce to do the concrete pouring with concrete lacking in workability is not only asking for trouble but begging for it to come.

Ensuring the compaction of concrete and cover to reinforcement bars is the prime responsibility of execution engineer to ensure the durability of structure is achieved. Concrete which is not compacted properly will also lead to have porous structure in it which will lead to weaker zone which can initiate rusting of reinforcement bars.

After placing of the concrete and finishing the surface to desired finishing details, it is very much important to start early curing on the concrete surface by sprinkling water and covering with hessian cloth or plastic sheets. else will lead to shrinkage cracking in the concrete, shrinkage cracks can also go through the whole thickness of structural member. shrinkage cracks creates the entry for mediums to do corrosion of reinforcement bars.
Shrinkage cracks.jpg

Those cracks will also take one of the medium which is water from top to down through it and make a permanent way for it which could actively do corrosion.
Leakage from slab.jpg

As i have written many articles on concrete, i have not gone in details of concrete from durability point of view.
You might have noticed during reading the article, many times i written reinforcement steel bars. because it is important to protect it to ensure the durability of the structure.
After reading article, you might have understood that, who is responsible for ensuring durability of the structure which is actual executor of that job in field and they should therefore must certify the durability of the structure.

Wait a minute, how could they certify the durability?

Well it is the basic process in any construction company and comes in Total Quality Management.

Civil Engineers do certifies the durability of the structure by filling and signing the checklist for executed works by them, this articles is just for them to understand, what they do fill and sign in checklist is not just a point or not just a formality its a Responsibility of them.

I hope after reading this article, when you work at site and see a situation like any above point discussed, you will first get struct with the durability point of view and later the schedule time for completion.

I would also request other members to do post on points to be considered and look after during execution from durability point of view.

Also would like, many scholars to make this subject as your Project to be submitted in collage and try to understand the practical things and how we can improve it to meet the requirement of Owners, Designers and Build the structures for intended users which could last beyond the design life.
 

HockeyPuck

Active Member
Feb 3, 2019
118
88
Chicago, Illinois (USA)
Excellent article, Dnyan Deshmukh !!!

Details matter. Precision matters. Conscientiousness matters. Construction engineers & contractors need to attend to the details.

The pictures & descriptions in the article show several instances where the installations required corrections. As engineers, we need to be constantly on the look-out for opportunities to educate those we are working with. Not everyone in the industry has the same knowledge-base as we do - Always be willing to share your knowledge with others so that the entire project team can benefit - Cheers!!!
 
Last edited:

Walufu

Newbie
Sep 8, 2019
2
1
Kampala Uganda
It depends on how or what has made the structure to fail, firstly look at who has designed the structure if he made his calculations very well ie the loads on different members and specified every aspect as per specifications to make the design code of all that is involved in construction.
Secondly, look at the engineer and his team doing the work at the site, have they followed what was stated in the structural plans.
Finally, look at the end user, has he or is he using the structure in the right way like in terms of load and care of the structure.

So all these groups of people have to be accessed in case a structure fails, thanks
 
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Rokysed

Newbie
Jul 31, 2019
2
1
Johor Malaysia
The answer is simple.
The Owner/Developer.
The designer/architect/engineer/QS/contractor et.al. (all bound by laws, codes and standards) are only EVER as good as the owner wants, is willing to pay or how subservient they are, but 20 years down the track it is still the Owner, even if it wasn't the original one. If a bean counter says a building is a good buy and his client is STOOOPID enough to buy it without a full engineers report the caveat emptor kicks in.
 
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AMMAR BAIG

Newbie
Nov 27, 2019
1
2
PAKISTAN
This really help me in understanding some causes which leads to the less durable structure.
The whole discussion is focused on the rebar and clear cover.
But some other consideration are important.
1) serviceability
2) Rebar placement and number.
Concrete durability also depends upon its stiffness. Concrete having less stiffeness may leads to the disintegration of whole structure i-e spalling.
Rebar number also matter,like if calculation says 2 #9 bars in beams,now its better to place more bar of less dia like no 6 or 7,says 4 bars.it will help the crack to be arrested,because every reinforcement bar has its own area of arrest so more bars of less dia means greater area for crack to be arrested in it.But not exceeding the under reinforcement condition.
I really appreciate your effort.
 

Bandya

Apprentice
Jul 10, 2019
14
5
MUMBAI
When it comes to Durability of the structure, what we understand is structure is termed as durable when it can carry all load throughout its service life without failing. it means it gives the same performance till its end of design life as it perform Today.

View attachment 3211

The durability of the structure is taken very seriously by designers of structure and designers of concrete. when it comes to designing of something, there are norms which gets followed to get a specific characteristic in design product.

But in actual who governs the durability of the structure, who can certify that structure will perform as same at its end of the life, its still a question which i have on my mind as there is no technology Today known to human being which can predict the life of the structure to which it can last and by looking at any structure no one can predict what is going on inside in terms of integrity. even if there is any technology available in market it can not be popular to be used by any house owner to check the remaining life of its home.

Structural designer did the job of designing a structure to a specified life by following codes in respective countries, Concrete designer did the designing of concrete to ensure the concrete is durable and is not a permeable, also the other attacks which can spoil concrete are also taken care during designing process of concrete by doing trials and test on it.

Up to this it looks OK and all the parameters are considered to ensure the durability or serviceability of structure for design life. After the designing is over, the next job is to execute the project and complete the structure to make it serviceable for intended users of it.

When i ask questions to executors of the job mostly a Civil Engineers who works at actual field, what is the durability of the structure, in most of the cases i found that, this is the subject which is not given to them for understanding in details.

A general answer which mostly everyone could get is, when the reinforcement bars get corrode, concrete gets cracked the durability of the structure get reduced, to achieve the durability one need to protect the reinforcement bars from rusting.

I do not find any difficulty in understanding above lines to understand the durability of the structure, but those lines are only lines and in practical application those are got forgotten or given second priority in work schedule because nobody put thoughts on it in greater details to make it understand in more practical way.

Basically durability can be achieved by ensuring there is no rusting of bars or degradation of concrete due to any kind of attack in the service life of structure. if it happens, structure will remain durable for its intended service life and beyond.

The corrosion of reinforcement bars is electro mechanical process where one end of the bar is act as a cathode and another as anode, during the medium of water or air, ends get charged with negative and positive charge which accelerate the process of corrosion of reinforcement steel bars. to make this happen the medium need to break the concrete.
Breaking of concrete or disintegration in concrete could happen due to various reasons like attacks from air, water etc. concrete is not compacted and have porousness inside of it or do have honeycombing which creates direct contact of medium with reinforcement bars.

No material on this earth is immortal, every material disintegrates over time according to exposure conditions, it would take several thousands of years to make steel as soil. only the longest surviving material which we see is stone and its a main reason why ancient civilization used it to build there structures and keep written records of their writings.

Coming back to the subject, to ensure the durability of the structure one should ensure the reinforcement bars are not getting rusted and concrete is not susceptible to any kind of attack during construction of the structure.

So in my opinion to make a durable structure, supreme responsibility lies with the Civil Engineers who are actual executing those job at construction site to build a structure. I will put some lights on basic things which could improve the durability of structure.

When a structural designer do designing of the structure, base on the exposure conditions, decides on how much cover should be given to reinforcement, so that it can survive till its design life. In case when you do not find the specifically mention cover to reinforcement bars on structural drawing, you should ask your structural consultant for details of covers to be provided. For a smaller projects or individual houses structural drawing given have notes on cover to be provided to reinforcement bars which has 3 or more tables which prescribe on cover to each member of structure as per exposure condition. If you are building such project, you should also need to take the details of cover in writing from structural consultant to avoid customer dissatisfaction in later stage.

Now i know what cover to be provided to reinforcement bars, when a structure is actually getting built, are we serious about the intensity of what happens when there is less cover than the specified, is i am reducing the life of structure? or we just so ignorant that we make it as a its OK to have less cover.
View attachment 3212
Here we fail to understand the structural designers point of view on having cover to reinforcement bars, this will inordinately going to lead in reduction of durability and by the time we may or may not be on this earth to see its refercations. So after understanding it, i Hope every Civil Engineer will give importance to give adequate cover to reinforcement bars.

We should also check for the correct size of the cover blocks used for doing construction of the project.
View attachment 3213

Cover block should be of same strength as of concrete which is being poured in structure, using weaker cover blocks will also lead to healthy and faster attacks on reinforcement bars which will reduce the durability of structure.
View attachment 3214
It is now trend to use PVC cover block due to its cheaper price but we should also think from the durability point of view to use those PVC cover Blocks or not. PVC never stick to cement, over the time it will form a separation cracks and make access to reinforcement bars.

After doing concreting, it is important to do construction joint preparation to ensure good bonding between old and new concrete we pace in structure. if the lattice not removed from the concrete surface, it may lead to weaker bond in concrete.
View attachment 3215
The smooth surface at the top of the concrete could be cause due to over vibration or fine particle accumulation during process of compaction of the concrete. It is important to remove all those lattice from the top of the concrete. this can be achieved by various ways, such as using water jet, roughening the concrete surface by making aggregate exposed without dislodging or you can press the 20mm size aggregates halfway into top surface to form a mechanical key for bonding of the concrete.

Same way construction joints in slab are also important and they are weaker sections in structure from where durability of the structure can get reduce. the joint should be made in a straight line and at locations as specified by the structural consultant only. it do happens that concrete get flowed beyond the stopper which was placed to arrest the concrete. in such cases all concrete which flowed beyond the stopper should be removed when its fresh or by breaking on very next day.
View attachment 3216

The bond between the concrete and reinforcement steel bar is very important part from durability point of view, during practical application, it is commonly observed that, some concrete do get stuck to reinforcement bars during concreting activity. it should be removed from steel bars to ensure proper bonding of concrete with reinforcement steel bars.
View attachment 3217
It is also observed that, during application of oil to shutters, some oil do also get spilled on slab and reinforcement bars get coated with it, we should no allow oiling of shutter on slab top once the reinforcement work is started. in case oil spillage observed over reinforcement bars, we should get it clean with detergent by washing.
View attachment 3218

When it comes to top slab reinforcement bars, we often use rebar chair / ghodi and it do have many local names, there is a possibility that rebar chair is directly placed on shutter as the bar bender do think that it will give more stability to keep top reinforcement bars in place but it will have negative impact on durability of the structure, the rebar chairs should be always kept on bottom reinforcement bars of slab. for tying each lag of chair should be tied to 2 reinforcement bars of the slab which will ensure no toppling of chair during movement.
View attachment 3219

The most prone area for all kind of loads on structure is the column beam junction which are most busiest part of the structure doing actively load transfers. we should ensure the lapping of column reinforcement bars should never fall in this junction which will increase the life of the structure.
View attachment 3220

Also, during tying of reinforcement bars the cage of beam reinforcement is made above the slab level and then lowered in the position. for columns which have slabs and beams all around and shuttering work is done, it is practically not possible to tie all stirrups of column in that junction. we should ensure those stirrups in column beam junction are tied properly as per spacing as this is most prone zone to cracking.
View attachment 3221

Low or inadequate cover to reinforcement bars lead to exposed reinforcement bars after concreting of structural members as the concrete does not pass due to low space. it can create another problem of honey combing too.
Honeycombing and exposed reinforcement bars in column do receive a patching with either cement paste or mortar or mortar with aggregate depending on the depth, in most of the cases those patching jobs are done by mason and mostly in hurry to ensure no one looks at it and make issue. also those patch wont get cure properly which can developes cracking and the source for reducing the durability of structure, if we do ensure proper covers are installed to reinforcement bars, those issues gets eliminated and durability of the structure is ensured.
View attachment 3222
Exposed reinforcement bars can also be observed in slab bottom when the adequate cover to reinforcement bars are not installed.
View attachment 3223

Exposure of reinforcement bars could also happen due to the workability of the concrete, if the concrete when received at site do lack in required amount, it will also create a problems of rebar exposure and honeycombing in structure due to no able to pass and reach each corner with efforts taken for doing compaction of concrete.

View attachment 3224
It is important to ensure the concrete does not lack in workability which is required to pour the concrete in structure. pressurizing the workforce to do the concrete pouring with concrete lacking in workability is not only asking for trouble but begging for it to come.

Ensuring the compaction of concrete and cover to reinforcement bars is the prime responsibility of execution engineer to ensure the durability of structure is achieved. Concrete which is not compacted properly will also lead to have porous structure in it which will lead to weaker zone which can initiate rusting of reinforcement bars.

After placing of the concrete and finishing the surface to desired finishing details, it is very much important to start early curing on the concrete surface by sprinkling water and covering with hessian cloth or plastic sheets. else will lead to shrinkage cracking in the concrete, shrinkage cracks can also go through the whole thickness of structural member. shrinkage cracks creates the entry for mediums to do corrosion of reinforcement bars.
View attachment 3225

Those cracks will also take one of the medium which is water from top to down through it and make a permanent way for it which could actively do corrosion.
View attachment 3226

As i have written many articles on concrete, i have not gone in details of concrete from durability point of view.
You might have noticed during reading the article, many times i written reinforcement steel bars. because it is important to protect it to ensure the durability of the structure.
After reading article, you might have understood that, who is responsible for ensuring durability of the structure which is actual executor of that job in field and they should therefore must certify the durability of the structure.

Wait a minute, how could they certify the durability?

Well it is the basic process in any construction company and comes in Total Quality Management.

Civil Engineers do certifies the durability of the structure by filling and signing the checklist for executed works by them, this articles is just for them to understand, what they do fill and sign in checklist is not just a point or not just a formality its a Responsibility of them.

I hope after reading this article, when you work at site and see a situation like any above point discussed, you will first get struct with the durability point of view and later the schedule time for completion.

I would also request other members to do post on points to be considered and look after during execution from durability point of view.

Also would like, many scholars to make this subject as your Project to be submitted in collage and try to understand the practical things and how we can improve it to meet the requirement of Owners, Designers and Build the structures for intended users which could last beyond the design life.
In my opinion, site control on quality of construction shall be the main entity in ensuring the durability of the structure. The designer goes on the basis of certain assumptions as regards to the Grade of concrete, Grade of Steel, working loads on the structure based on the related code provisions and parameters. Based on the analysis and design thereof, drawings are issued for erection/construction as the case may be. Next comes the execution part wherein the ingredients play a major role. It is often observed that the raw material like sand which is a rare commodity in concrete construction is not washed or the metal that is used in concrete mixing is not up to the mark since it is not possible to check up complete delivery of material to site, stacking and actual time lapsed in using the same. The reinforcements once placed in position are not coated with anti corrosive coat and lay exposed to atmosphere for a number of days causing rust and scales on surface which are rarely removed in bulk constructions. Anti corrosive coat is considered to be difficult to remove during construction stages and ignored. In case of bulk constructions, RMC is used wherein concrete can be relied upon for proper composition as per design mix if automated. In case of shortage of power supply, it cannot be relied upon. Next comes the curing where water is used. The quality of water used is concrete mixing and curing may not be up to the mark as specified in codes. Formwork and workmanship also play important role in assuring proper cover, binding wires etc. In case of major projects like road bridges and dams etc it is possible to obtain a good durable structure. But it again comes to the contractor and his margin considerations.

In addition to above, it is observed that the designers today use computer aided design software but at times fail to read and interpret the results correctly leading to durability lapses.

I know this is not a complete and satisfactory reply but an attempt to reply to some extent.
 
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Narasimhudu

Newbie
Feb 9, 2020
1
1
Kurnool
When it comes to Durability of the structure, what we understand is structure is termed as durable when it can carry all load throughout its service life without failing. it means it gives the same performance till its end of design life as it perform Today.

View attachment 3211

The durability of the structure is taken very seriously by designers of structure and designers of concrete. when it comes to designing of something, there are norms which gets followed to get a specific characteristic in design product.

But in actual who governs the durability of the structure, who can certify that structure will perform as same at its end of the life, its still a question which i have on my mind as there is no technology Today known to human being which can predict the life of the structure to which it can last and by looking at any structure no one can predict what is going on inside in terms of integrity. even if there is any technology available in market it can not be popular to be used by any house owner to check the remaining life of its home.

Structural designer did the job of designing a structure to a specified life by following codes in respective countries, Concrete designer did the designing of concrete to ensure the concrete is durable and is not a permeable, also the other attacks which can spoil concrete are also taken care during designing process of concrete by doing trials and test on it.

Up to this it looks OK and all the parameters are considered to ensure the durability or serviceability of structure for design life. After the designing is over, the next job is to execute the project and complete the structure to make it serviceable for intended users of it.

When i ask questions to executors of the job mostly a Civil Engineers who works at actual field, what is the durability of the structure, in most of the cases i found that, this is the subject which is not given to them for understanding in details.

A general answer which mostly everyone could get is, when the reinforcement bars get corrode, concrete gets cracked the durability of the structure get reduced, to achieve the durability one need to protect the reinforcement bars from rusting.

I do not find any difficulty in understanding above lines to understand the durability of the structure, but those lines are only lines and in practical application those are got forgotten or given second priority in work schedule because nobody put thoughts on it in greater details to make it understand in more practical way.

Basically durability can be achieved by ensuring there is no rusting of bars or degradation of concrete due to any kind of attack in the service life of structure. if it happens, structure will remain durable for its intended service life and beyond.

The corrosion of reinforcement bars is electro mechanical process where one end of the bar is act as a cathode and another as anode, during the medium of water or air, ends get charged with negative and positive charge which accelerate the process of corrosion of reinforcement steel bars. to make this happen the medium need to break the concrete.
Breaking of concrete or disintegration in concrete could happen due to various reasons like attacks from air, water etc. concrete is not compacted and have porousness inside of it or do have honeycombing which creates direct contact of medium with reinforcement bars.

No material on this earth is immortal, every material disintegrates over time according to exposure conditions, it would take several thousands of years to make steel as soil. only the longest surviving material which we see is stone and its a main reason why ancient civilization used it to build there structures and keep written records of their writings.

Coming back to the subject, to ensure the durability of the structure one should ensure the reinforcement bars are not getting rusted and concrete is not susceptible to any kind of attack during construction of the structure.

So in my opinion to make a durable structure, supreme responsibility lies with the Civil Engineers who are actual executing those job at construction site to build a structure. I will put some lights on basic things which could improve the durability of structure.

When a structural designer do designing of the structure, base on the exposure conditions, decides on how much cover should be given to reinforcement, so that it can survive till its design life. In case when you do not find the specifically mention cover to reinforcement bars on structural drawing, you should ask your structural consultant for details of covers to be provided. For a smaller projects or individual houses structural drawing given have notes on cover to be provided to reinforcement bars which has 3 or more tables which prescribe on cover to each member of structure as per exposure condition. If you are building such project, you should also need to take the details of cover in writing from structural consultant to avoid customer dissatisfaction in later stage.

Now i know what cover to be provided to reinforcement bars, when a structure is actually getting built, are we serious about the intensity of what happens when there is less cover than the specified, is i am reducing the life of structure? or we just so ignorant that we make it as a its OK to have less cover.
View attachment 3212
Here we fail to understand the structural designers point of view on having cover to reinforcement bars, this will inordinately going to lead in reduction of durability and by the time we may or may not be on this earth to see its refercations. So after understanding it, i Hope every Civil Engineer will give importance to give adequate cover to reinforcement bars.

We should also check for the correct size of the cover blocks used for doing construction of the project.
View attachment 3213

Cover block should be of same strength as of concrete which is being poured in structure, using weaker cover blocks will also lead to healthy and faster attacks on reinforcement bars which will reduce the durability of structure.
View attachment 3214
It is now trend to use PVC cover block due to its cheaper price but we should also think from the durability point of view to use those PVC cover Blocks or not. PVC never stick to cement, over the time it will form a separation cracks and make access to reinforcement bars.

After doing concreting, it is important to do construction joint preparation to ensure good bonding between old and new concrete we pace in structure. if the lattice not removed from the concrete surface, it may lead to weaker bond in concrete.
View attachment 3215
The smooth surface at the top of the concrete could be cause due to over vibration or fine particle accumulation during process of compaction of the concrete. It is important to remove all those lattice from the top of the concrete. this can be achieved by various ways, such as using water jet, roughening the concrete surface by making aggregate exposed without dislodging or you can press the 20mm size aggregates halfway into top surface to form a mechanical key for bonding of the concrete.

Same way construction joints in slab are also important and they are weaker sections in structure from where durability of the structure can get reduce. the joint should be made in a straight line and at locations as specified by the structural consultant only. it do happens that concrete get flowed beyond the stopper which was placed to arrest the concrete. in such cases all concrete which flowed beyond the stopper should be removed when its fresh or by breaking on very next day.
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The bond between the concrete and reinforcement steel bar is very important part from durability point of view, during practical application, it is commonly observed that, some concrete do get stuck to reinforcement bars during concreting activity. it should be removed from steel bars to ensure proper bonding of concrete with reinforcement steel bars.
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It is also observed that, during application of oil to shutters, some oil do also get spilled on slab and reinforcement bars get coated with it, we should no allow oiling of shutter on slab top once the reinforcement work is started. in case oil spillage observed over reinforcement bars, we should get it clean with detergent by washing.
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When it comes to top slab reinforcement bars, we often use rebar chair / ghodi and it do have many local names, there is a possibility that rebar chair is directly placed on shutter as the bar bender do think that it will give more stability to keep top reinforcement bars in place but it will have negative impact on durability of the structure, the rebar chairs should be always kept on bottom reinforcement bars of slab. for tying each lag of chair should be tied to 2 reinforcement bars of the slab which will ensure no toppling of chair during movement.
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The most prone area for all kind of loads on structure is the column beam junction which are most busiest part of the structure doing actively load transfers. we should ensure the lapping of column reinforcement bars should never fall in this junction which will increase the life of the structure.
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Also, during tying of reinforcement bars the cage of beam reinforcement is made above the slab level and then lowered in the position. for columns which have slabs and beams all around and shuttering work is done, it is practically not possible to tie all stirrups of column in that junction. we should ensure those stirrups in column beam junction are tied properly as per spacing as this is most prone zone to cracking.
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Low or inadequate cover to reinforcement bars lead to exposed reinforcement bars after concreting of structural members as the concrete does not pass due to low space. it can create another problem of honey combing too.
Honeycombing and exposed reinforcement bars in column do receive a patching with either cement paste or mortar or mortar with aggregate depending on the depth, in most of the cases those patching jobs are done by mason and mostly in hurry to ensure no one looks at it and make issue. also those patch wont get cure properly which can developes cracking and the source for reducing the durability of structure, if we do ensure proper covers are installed to reinforcement bars, those issues gets eliminated and durability of the structure is ensured.
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Exposed reinforcement bars can also be observed in slab bottom when the adequate cover to reinforcement bars are not installed.
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Exposure of reinforcement bars could also happen due to the workability of the concrete, if the concrete when received at site do lack in required amount, it will also create a problems of rebar exposure and honeycombing in structure due to no able to pass and reach each corner with efforts taken for doing compaction of concrete.

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It is important to ensure the concrete does not lack in workability which is required to pour the concrete in structure. pressurizing the workforce to do the concrete pouring with concrete lacking in workability is not only asking for trouble but begging for it to come.

Ensuring the compaction of concrete and cover to reinforcement bars is the prime responsibility of execution engineer to ensure the durability of structure is achieved. Concrete which is not compacted properly will also lead to have porous structure in it which will lead to weaker zone which can initiate rusting of reinforcement bars.

After placing of the concrete and finishing the surface to desired finishing details, it is very much important to start early curing on the concrete surface by sprinkling water and covering with hessian cloth or plastic sheets. else will lead to shrinkage cracking in the concrete, shrinkage cracks can also go through the whole thickness of structural member. shrinkage cracks creates the entry for mediums to do corrosion of reinforcement bars.
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Those cracks will also take one of the medium which is water from top to down through it and make a permanent way for it which could actively do corrosion.
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As i have written many articles on concrete, i have not gone in details of concrete from durability point of view.
You might have noticed during reading the article, many times i written reinforcement steel bars. because it is important to protect it to ensure the durability of the structure.
After reading article, you might have understood that, who is responsible for ensuring durability of the structure which is actual executor of that job in field and they should therefore must certify the durability of the structure.

Wait a minute, how could they certify the durability?

Well it is the basic process in any construction company and comes in Total Quality Management.

Civil Engineers do certifies the durability of the structure by filling and signing the checklist for executed works by them, this articles is just for them to understand, what they do fill and sign in checklist is not just a point or not just a formality its a Responsibility of them.

I hope after reading this article, when you work at site and see a situation like any above point discussed, you will first get struct with the durability point of view and later the schedule time for completion.

I would also request other members to do post on points to be considered and look after during execution from durability point of view.

Also would like, many scholars to make this subject as your Project to be submitted in collage and try to understand the practical things and how we can improve it to meet the requirement of Owners, Designers and Build the structures for intended users which could last beyond the design life.
Durability of structure is ensure site execution engineer only.the above instructions must and should follow site engineer who is giving permission to pour the concrete.every body should follow above instructions.
 
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Civil4M

Company Info
Staff member
Sep 7, 2017
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though it is designed by many, finally it ends up in hands of executor.

so peoples who do execute the work and check prior to concreting might be more responsible and highly responsible from durability point of view.
 
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kranjan

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May 18, 2020
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In my opinion, even though Durability of structure, the responsibility lies with all stake holders who associated with work viz design/Implement/end users, but in majority the durability of structure is at execution level, the reason may be plenty one among them is cover to rebar is simple, but getting ignored at many a time and that decides the life of structure.

If we revisit the whole process of product delivery 1. Designer go by the codal requirement and best industrial practice where we have no chance to doubt on durability adequacy 2. End users if at all make any modification and undesired loading, result of reaction easily known and well measurable what went wrong, hen they never do such mistakes. 3. Execution where work left with too many workforce, many material involved with lot of interfaces viz external climatic / logistic / skill set and level of experience and their supervision

Best example factory made precast element more durable than in-situ (on site) cast element. Reason behind factory work with dedicated team under enclosed controlled environment whereas site cannot.
 
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