14 Oktober, 2010

Honeycomb and Void Repairs.

Reinforced concrete - one of the most commonly used construction materials - is a combination of concrete (cement and aggregates) and reinforcing steel. The cement mortar portion of this composite material (approx 25% of the concrete) acts as a paste or glue that binds all of the many sized aggregates together. When properly designed and placed these three materials create a unique composite that can be cast into thousands of different infrastructure applications. In order to have a reinforced concrete beam, column, slab or wall function properly, the concrete must be properly consolidated in the forms, i.e. it must completely encapsulate the reinforcement and be free of voids or "honeycombs". Voids are completely empty or hollow spaces in the form in which no concrete exists. Honeycombs based on a Portland Cement Association definition, are voids left in concrete due to failure of the cement mortar to effectively fill all the spaces between the coarse aggregate particles.  Severe honeycombs (sometimes known as rock pockets) occur when an excessive amount of aggregate is found without the presence of cement paste. (See Figure 1)
Honeycomb in Concrete Column
Figure 1: Honeycomb in a column from excessive lift depth.


Causes


 Void created by rebar congestion
Void created by rebar congestion
Primary causes of voids or honeycombs in reinforced concrete:

  • Rebar Congestion - if rebar is placed too close together or too close to formwork it will trap the larger pieces of aggregate while the mortar in the mixture may or may not pass through.  Other causes related to rebar congestion include excessive reinforcement splices that prevent the concrete from properly filling the forms.
  • Mix Design - Improper mix design can lead to low workability, early stiffening or an aggregate that is too large to properly consolidate the concrete for a given application. A good mix design should take in consideration the issues noted for rebar congestion and lift depth.
  • Lift Depth - When single concrete placements or "lifts" are too deep, proper vibration can become very difficult or impossible. Excessive lift depths can also allow too much free-fall of the concrete that can create a separation of the cement mortar and aggregate as the aggregate impacts the reinforcing steel when falling through the forms.
  • Inadequate Vibration - When the concrete is properly vibrated it acts more like a liquid allowing it to better settle in the form, consolidate around the reinforcement and completely fill the forms. It also helps in releasing any of the air voids in the mix to the surface. Improper vibration can be related to:
    • Too small or large a vibrator for the size of the pour and mix design
    • Too low a frequency or amplitude of the vibrator for the size of the pour and mix design
    • Too short or long an insertion time of the vibrator in the concrete in a single location
    • Too wide of a spacing between each insertion of the vibrator
    • Lift depths too deep to actually vibrate the concrete
    • Congested reinforcing that will not allow a standard vibrator to reach all areas required
  • Form Leaks - Leaks in the formwork can allow the cement paste to escape out of the form leaving behind only unbonded aggregate and rock pockets.

    Repair Process
    There are several factors to consider when repairing honeycombs and voids:
    • Void size and depth
    • Access to the repair area
    • Rebar details and congestion within the repair area
    • Quality assurance (how do you determine actual void size and prove the problem is fixed)
    • Costs from a "repair or replace?" perspective ... which is more cost effective?
    These critical items will clearly define the following key steps and sequential order of repairing a void which are:
    1. Define the size of the repairs
    2. Define the depth of the repairs
    3. Is shoring required?
    4. Select the type of removal
    5. Select the material for repairs
    6. Select the proper placement technique of this material to ensure filling of the void AND create a composite bond with the substrate.

    Defining the size and depth
     NDT Testing
    Figure 2: NDT Testing measuring response time in a concrete section. A void will appear as a shorter response time.
    The actual repair process starts with defining the removal geometry - i.e. size and depth of the area requiring repair. Methods used can include chipping, sounding and Non Destructive Testing (NDT) such as Impulse Response or Pulse Echo testing. These tests measure response times or frequency of a wave or impulse though a concrete section. If a void exists, the wave or travel time is of course greatly affected. (See Figure 2)  In many cases the area of repair is going to be larger than what is noticeable to the eye from the surface of the concrete. This difference is based on several items:
    • The presence of unseen voids.
    • The concrete materials around the void may not be sound and typically must be removed deep enough to reach a sound substrate.
    • The final repair shape is normally larger than the rough shape of the actual void. Per ACI and ICRI repair specifications the final surface shape should be rectilinear in shape vs the rough, multi-shaped void left after removal of unsound concrete. Rectilinear can be defined as a combined series of rectangular and/or square shapes. (See Figure 3)
    • Additional removal requirements, in relation the depth of the repair, must be considered. Typical repair specs call for a uniform depth throughout the repair area and where there is any exposed reinforcing steel (50% of the bar exposed), the concrete should be removed at a minimum of ¾" behind the bar. (See Figure 4)
     Final repair shape
    Figure 3: The final repair shape (in yellow) is often larger than the rough shape of the actual void.
    Careful thought must be given to the size, depth and location of the void as removal may affect the structural capacity of the element being repaired. If enough material is missing or is being removed from critical sections of a beam or slab, shoring should be installed when the void is detected or prior to removal. This is especially true with gravity elements such as columns. For example, any chipping or removal on a column  inside the structural core (any section inside the horizontal rebar ties) will dramatically affect the load carrying capacity.  As a rule of thumb, it is better to err on the side of safety and shore the element.

    Removal Techniques
    Removal of the unsound material can be accomplished using hydrodemoltion techniques, or typically with 15# chipping hammers.  Why use such a small hammer?  When using anything greater than a 30# chipping hammer, the impact forces of the bit will microfracture the substrate and damage it. Also in may cases due to the concentration of rebar in the void, a smaller hammer is easier to accomplish the "dental" like removal without breaking the bond of the concrete around the rebar outside the repair area. Chipping is done until a uniform depth and shape is achieved and a "Fractured Aggregate Profile" is present in the substrate. This chipping profile is achieved when the aggregate in the concrete is sound and so well bonded that it will shear in half while being chipped with a 15# hammer.  At this point it is clear that the substrate is sound as the cement paste is well bonded to the aggregate.  This is a typical gauge to determine when sound substrate has been reached.
    Hydrodemolition on the other hand utilizes water pressure up to 50,000 psi to literally explode the cement in order to remove it. This is advantageous in situations where the concentration of rebar is so high that it is impossible to remove the concrete with a chipping gun. It also requires a water collection process due to the volumes of water required which can be difficult in some environments.
     Proper Surface Preparation
    Figure 4: Proper surface preparation.
    The last step of surface preparation requires that the concrete substrate has an "open pore structure". During chipping or Hydrodemolition, the pores of the concrete have been impacted and filled with concrete dust and slurry. Removing this is imperative as the bond between the repair material and substrate can only be achieved by forcing the repair material into these pores. The concrete can be properly prepared by abrasive blasting or high pressure water after demolition.

    Repair Material and Placement Techniques
    Now that the size and depth of the repairs are know, the next step is to determine the optimum repair material and the best technique for placing it into the void.  For most honeycomb and voids repairs, the Form and Pump Technique (See Figure 5) is the best choice to fill the repair area and ensure a good bond to the existing concrete.  Form & Pump, as the name suggests, pumps the repair material into a closed form. This guarantees two key requirements noted above. One is making certain that the repair material has entirely filled
    Form & Pump 2
         Figure 5: "Form & Pump"
    the formwork and is consolidated around all rebar. The second relates to the fact that once the form is full and all air voids removed, it is pressurized. This assures that the repair material has been literally driven into the open pores of the existing prepared concrete. This will achieve a bond sufficient to make the two materials act as one. Use of vent tubes and bleed locations in a Form & Pump repair operation are important in order to make sure that material is reaching all the sections of the repair area. Selection of repair material must consider the required flowability and aggregate size for void size, shape and rebar clearances.  For smaller, more minor honeycombs or voids, a Form and Cast in Place placement technique and vibration may be an option for a repair method.

    Quality Control
    Lastly, depending on the size and complexity of the repair, the same NDT type test methods can be used to make sure that no voids still exist.  Similar to finding a void in concrete, the testing can be used to measure the frequency or travel time through the concrete.  Results can be compared to initial testing and confirm a void free section





     Before Column - Fig 5A
     During Column - Figure 5A
     After Column - Figure 5A
    Figure 5 A-C

    Case Studies

    New High Rise Building Column Repairs
    A new twenty story high rise building project was being constructed. During inspection it was discovered that several columns and shear walls located throughout the structure had various levels of honeycombing.  There appeared to be two possible causes of the honeycombs:
    1. The lift depth for placements was excessive and segregated the cement and aggregates as they fell through the formwork and rebar
    2. The vibration process was very difficult to accomplish in the bottom 4 feet of the elements due to the lift depth.
    For most cases, it was determined that the unsound material would need to be removed inside the structural core (area inside the horizontal reinforcing bars). As such, columns and shear walls were shored up prior to the removal of material.  Removal was done using 15# chipping hammers and the surface was high pressured washed to open the pores.  Form & Pump or Form and Cast in Place was then used to fill the repair area depending on repair size and geometry.  NDT type tests or sounding was conducted to ensure that no voids or honeycombs existed after the forms were removed. (See Figure 5 A-C)




    Army Base Incinerator Wall Repair
     Before Project - Figure 6
     After Project - Figure 6
     Figure 6 A-B
    A very thick, heavily reinforced concrete incinerator wall located on an army base in the southeastern region of the United States had a large void that was observed after the forms were removed.  The combination of excessive reinforcing steel, a through wall penetration and placement techniques appeared to have caused the void.




    • The repair process began by defining the size and depth of the repair area through a combination of chipping, sounding and NDT Testing (which was larger than what appeared to the eye). The next step was to define the removal geometry with the final surface shape being rectilinear.  Material was then removed using 15# chipping hammers and hydrodemolition.  The repair area surface was then prepared to open the pores of the concrete. Form & Pump was used to fill the void with repair material. Finally, QC was again performed using NDT testing to make sure that the no voids existed after the forms were removed. (See Figure 6 A-B)

50 ulasan:

Tanpa Nama berkata...

Ѕhe bought the unԁerstanding frοm cooking pioneeг Baгbaга Kerг.
Thesе items аre οrdinarily viewed in all varietiеs
οf reѕidеncеs, even individuals that usuаlly
are not intenԁed to be 'green'. (You are аiming for the regularity of ρeanut butter.
Here is my weblog - old stone oven

Tanpa Nama berkata...

Hеllo there, You've done an excellent job. I will certainly digg it and personally recommend to my friends. I'm confіdent they will be bеnefited from
this websіte.
Also visit my web-site : Chemietoilette

Tanpa Nama berkata...

Hеy there just wаnted to givе you a quіcκ hеаdѕ up
and let you know a fеw of the іmages аren't loading correctly. I'm not surе ωhу but I thіnk
its a linking issue. I've tried it in two different web browsers and both show the same results.

Stop by my webpage - Chemietoilette

Tanpa Nama berkata...

It happens to be a chef's term for 'a position for аll kinds of thingѕ
and all in itѕ place'. At minimum 51 % have to be com, whilst usually up to 75% is implemented. "In culture, I signify 50 % the time quite a few everyone have in no way been by yourself, undeniably alone, without the need of some sort of distraction.

Also visit my web-site; Www.si-news.It

Tanpa Nama berkata...

Sweet blоg! I found it whilе searching on Yahoο Neωs.
Do you hаve anу tірѕ on how tо get
lіsted іn Yahoo News? I've been trying for a while but I never seem to get there! Thank you

My web blog - Chemietoilette

Tanpa Nama berkata...

This is а slеek desіgneԁ dіgital conνection tοaster
ovеn thаt ωill cοnsistently ԁeliveг ρerfect tastіng fοod eνerу time.
That's right, no buying that sorry excuse for pizza dough at your local grocery store; we'гe talking thе real deal here.
Most breаd machіnеs comе ωіth
a reсipе bоοκ includеd.


Alѕo visit my web ρage :: pizza pan ashtabula

Tanpa Nama berkata...

I'm really enjoying the design and layout of your blog. It'ѕ a very easу on the eyes ωhich maκeѕ it much mοre
pleasant foг mе to come here аnd vіsіt more
often. Did you hire out а devеlopеr to create
yοur theme? Fantastic work!

My site; augenoperation

Tanpa Nama berkata...

Ηello, уeѕ this paгagгaph is actually fastiԁiοus and ӏ have leагned lot
of thingѕ from it concernіng blοgging.
thanks.

Ηеrе is my blog - artikel-sains.blogspot.ru

Tanpa Nama berkata...

Highly descriptive article, I liked that bit.
Will there be a part 2?

Feel free to visit my web page fda Dietary Supplements

Tanpa Nama berkata...

Wow, superb blog layout! How long have you been blogging for?
you made blogging look easy. The overall look of your web site is excellent,
let alone the content!

Have a look at my web blog; buy volume pills

Tanpa Nama berkata...

Its like you read my mind! You seem to know so much about this, like you wrote
the book in it or something. I think that you could do with a few
pics to drive the message home a little bit, but other than that, this is magnificent blog.

A great read. I will definitely be back.

My webpage - abercrombie and fitch

Tanpa Nama berkata...

The best part about this plan is, you get the natural benefits of
diet cleanse.

Stop by my web-site drinks to clear your system

Tanpa Nama berkata...

These are in fact wonderful ideas in regarding blogging.
You have touched some pleasant factors here. Any way keep
up wrinting.

Have a look at my blog post ... Cheap Jerseys

Tanpa Nama berkata...

You actually make it seem so easy with your presentation
but I in finding this matter to be actually something which I think I might never
understand. It kind of feels too complicated and extremely huge for me.
I'm having a look ahead in your subsequent publish, I'll try
to get the cling of it!

Look at my blog post :: buy semenax

Tanpa Nama berkata...

This design is steller! You most certainly know how to keep a
reader amused. Between your wit and your videos, I was almost moved to start my
own blog (well, almost...HaHa!) Wonderful job. I really loved what you had
to say, and more than that, how you presented
it. Too cool!

Also visit my web page - vigrx plus

Tanpa Nama berkata...

We offer lower rates for complete Home Business packages which web
businesses can consider. You can make good money by attracting the targeted customers then you have good chance to make money online MMO.
It has the ability to provide affinity data?



Feel free to surf to my web page: top search engine optimization companies

Tanpa Nama berkata...

Fantastic items from you, man. I have keep in
mind your stuff prior to and you're just too magnificent. I really like what you've received here, really like what
you're saying and the way in which during which you assert it. You make it entertaining and you continue to care for to stay it sensible. I can not wait to read much more from you. This is actually a wonderful web site.

My web blog ... Louis Vuitton Handbags Outlet

Tanpa Nama berkata...

I’m not that much of a internet reader to be honest but your blogs really nice,
keep it up! I'll go ahead and bookmark your website to come back later. Cheers

my web site ... genf20 plus review

Tanpa Nama berkata...

Every now seasons reasons some shoes is probably[url=http://niketrainersuksale.webeden.co.uk]Nike UK[/url]
fleetingly command not hold the adeptness to[url=http://tomscanadaoutlet.snappages.com]Toms Shoes Outlet[/url]
use such shoes all of us[url=http://addnikecanadastore.snappages.com]Nike Canada[/url]
becomingly position them in[url=http://louboutintrainersuk.blog.co.uk]Christian Louboutin Outlet[/url]
set upright set up order to circumvent superfluous wickedness to shoes[url=http://salelouisvuittonuk.webeden.co.uk]http://salelouisvuittonuk.webeden.co.uk[/url]

If your insole is accurately poor, it is must manipulate a subdued engagement and sea water gently scrub. Can be noted that, don't usability chemical cleaning agents cleaning, or may result in the insole the superficies of cloth off.[url=http://shoppradabagsuk.webeden.co.uk]Prada UK[/url]

Tanpa Nama berkata...

Simply wish to say your article is as surprising. The clearness in your put up is simply nice and that i can suppose you
are a professional on this subject. Well along with your permission let me to clutch your feed to stay up to date with coming near
near post. Thank you one million and please
carry on the enjoyable work.

My blog post; Evgeni Malkin Jersey

Tanpa Nama berkata...

Hi just wanted to give you a brief heads
up and let you know a few of the pictures aren't loading properly. I'm not sure
why but I think its a linking issue. I've tried it in two different internet browsers and both show the same outcome.

Also visit my web-site: Get the Facts

Tanpa Nama berkata...

This site was... how do you say it? Relevant!! Finally I've found something that helped me. Thanks!

My webpage ... web site

Tanpa Nama berkata...

Amazing! Its truly amazing piece of writing, I have got much clear idea concerning from
this paragraph.

Take a look at my website - Total Curve

Tanpa Nama berkata...

Post writing is also a excitement, if you be familiar with after that you can write if not it is difficult to write.


Check out my web site; Louis Vuitton Outlet

Tanpa Nama berkata...

We are a group of volunteers and opening a new scheme in our community.
Your website provided us with valuable information to work
on. You've done an impressive job and our whole community will be grateful to you.

my blog More hints

Tanpa Nama berkata...

Hi my friend! I wish to say that this article is amazing,
nice written and come with almost all significant infos.
I would like to peer more posts like this .

My website - slc-wireless.com

Tanpa Nama berkata...

Hi! Someone in my Facebook group shared this website with us so I came to
give it a look. I'm definitely loving the information. I'm book-marking and will be
tweeting this to my followers! Terrific blog and great design and style.



my website ... volume pills review

Tanpa Nama berkata...

I'm not sure why but this blog is loading incredibly slow for me. Is anyone else having this problem or is it a problem on my end? I'll check back later on and see
if the problem still exists.

my web page ... zetaclear

Tanpa Nama berkata...

Thanks for another informative website. Where else could I
get that kind of info written in such a perfect manner?
I have a undertaking that I am simply now working on, and I've been at the look out for such info.

Here is my page :: Louis Vuitton Outlet

Tanpa Nama berkata...

Wow that was strange. I just wrote an incredibly long comment
but after I clicked submit my comment didn't show up. Grrrr... well I'm not writing all that
over again. Anyhow, just wanted to say excellent blog!


my page - Abercrombie and Fitch

Tanpa Nama berkata...

Amazing blog! Is your theme custom made or did you download it from somewhere?
A theme like yours with a few simple tweeks would really make
my blog stand out. Please let me know where you got your design.

Many thanks

My site ... Cheap Louis Vuitton Bags

Tanpa Nama berkata...

Hi there, this weekend is good for me, as this time i am reading
this wonderful informative paragraph here at my home.


Have a look at my blog :: Chaussure Air Max

Tanpa Nama berkata...

I think this is among the most vital information for me.
And i'm happy studying your article. However wanna statement on some normal issues, The site taste is ideal, the articles is in point of fact nice : D. Excellent job, cheers

my web blog; Wholesale NFL Jerseys

Tanpa Nama berkata...

Pretty! This has been an extremely wonderful article.
Many thanks for providing this info.

my website - Michael Kors Bags

Tanpa Nama berkata...

If the tread on your tyres has worn away, you could be in for more of these long lasting extremes cold, wet or hot depending on which Storm Chasing Sa system gets stuck and where.


My weblog; chasing the storm

Tanpa Nama berkata...

Wonderful blog! I found it while searching on Yahoo News.
Do you have any tips on how to get listed in Yahoo News? I've been trying for a while but I never seem to get there! Cheers

Look at my website ... nysacpr.org

Tanpa Nama berkata...

When someone writes an piece of writing he/she maintains the plan of
a user in his/her brain that how a user can know it. So that's why this piece of writing is great. Thanks!

Also visit my web site: Recommended Site ()

Tanpa Nama berkata...

Hey I know this is off topic but I was wondering if you knew of any widgets I could add to my blog that automatically tweet my newest twitter updates.
I've been looking for a plug-in like this for quite some time and was hoping maybe you would have some experience with something like this. Please let me know if you run into anything. I truly enjoy reading your blog and I look forward to your new updates.

Also visit my web site - Discover More

Tanpa Nama berkata...

Hi there to every body, it's my first visit of this web site; this weblog consists of amazing and in fact fine material designed for visitors.

Here is my web blog; Louis Vuitton Purses Outlet

Tanpa Nama berkata...

I couldn't refrain from commenting. Well written!

Here is my web page :: Air Jordan []

Tanpa Nama berkata...

When someone writes an post he/she retains the idea of
a user in his/her brain that how a user can be aware of it.
So that's why this article is amazing. Thanks!

Have a look at my webpage; Air Max

Tanpa Nama berkata...

When some one searches for his necessary thing, therefore he/she desires to be available that in detail, therefore that thing is maintained over
here.

My webpage - provillus for women ingredients

Tanpa Nama berkata...

I must thank you for the efforts you've put in writing this site. I'm
hoping to see the same high-grade blog posts from you later on
as well. In fact, your creative writing abilities has inspired me to get my own,
personal site now ;)

My web page ... NFL Jerseys Cheap

Tanpa Nama berkata...

Hi there! This post could not be written any better!
Reading through this post reminds me of my good
old room mate! He always kept talking about this. I
will forward this write-up to him. Fairly certain he will have a good read.

Thank you for sharing!

Review my blog post: New Kobe Bryant Shoes

Tanpa Nama berkata...

I'm really enjoying the theme/design of your weblog. Do you ever run into any web browser compatibility issues? A few of my blog visitors have complained about my website not operating correctly in Explorer but looks great in Opera. Do you have any advice to help fix this problem?

Feel free to visit my web site: Chaussures De Foot

Tanpa Nama berkata...

Everyone loves what you guys are usually up too.
This type of clever work and coverage! Keep up the amazing works guys I've added you guys to blogroll.

My webpage Air Max 1

Tanpa Nama berkata...

As the admin of this website is working, no question very soon it will be famous, due to
its quality contents.

Also visit my page - Boutique Air Max

Tanpa Nama berkata...

Hi my family member! I want to say that this article is awesome, nice written and come with
approximately all significant infos. I would like to look extra posts like this .


my weblog: Sac Louis Vuitton Pas Cher

Tanpa Nama berkata...

Hey there! Do you use Twitter? I'd like to follow you if that would be ok. I'm
undoubtedly enjoying your blog and look forward to new updates.


Also visit my weblog ... Mulberry UK

Tanpa Nama berkata...

Touche. Great arguments. Keep up the great effort.


Have a look at my web page ... Louis Vuitton Handbags Outlet