How effective is concrete sticking together

Almost everything that needs to be said about concrete, cement, hand-mixing, uses and prices has been said on this forum. Please check out the contributions before posting new questions.

Moderators: Sometimewoodworker, MGV12, BKKBILL, pattayapope

How effective is concrete sticking together

Postby fluffykeith » Thu Apr 11, 2013 6:34 pm

Hi

I'm busy reading and learning - this site is great. But I have one nagging question that I can't see any reference to so maybe it's just one of those stupid questions.

Concrete posts, concrete beams, concrete floors, even concrete cupboards in the bathroom and kitchen, so, between each pour there is a joint, what keeps the joints from failing?
I know you can wet the previous concrete to aid adhesion, and I just read about some product that can be painted on (I guess water with some additive),
but is the joint stength purely in the rebar or is there strength in the concrete join between old and new concrete.

I'm asking as I see the posts get made and then the following in order of ground beam, floor beam, next floor post, next floor, seamingly in an ad hoc fashion. Does this result in castings being made such that a beam joins a post resulting in the old to new concrete joint being on the post side, that is, the joint is shearing rather that compressive, which would be the case if the beam was cast on top of the post.

Is it possible that the old to new joint will crack? and if the joint is shearing then it's only rebar holding up the floor.

Sorry - bit long winded to explain and hopefully you get the gist fo what I'm saying.
fluffykeith
 
Posts: 9
Joined: Fri Nov 16, 2012 7:17 pm
Location: UK

Re: How effective is concrete sticking together

Postby Roger Ramjet » Thu Apr 11, 2013 7:06 pm

fluffykeith,
The short answer is Lanko 751. Available at all big stores. You can either mix it with the concrete, but the best option is splashing it on liberally. It will bond old concrete to new and new to new. If your interested in what it looks like I'll search my build.
User avatar
Roger Ramjet
 
Posts: 5252
Joined: Tue Apr 27, 2010 12:55 pm

Re: How effective is concrete sticking together

Postby Roger Ramjet » Thu Apr 11, 2013 7:09 pm

fluufykeith,
Here's the page and the photo is about half way down: viewtopic.php?f=3&t=1864&p=31479&hilit=Lanko+751#p31479
User avatar
Roger Ramjet
 
Posts: 5252
Joined: Tue Apr 27, 2010 12:55 pm

Re: How effective is concrete sticking together

Postby fluffykeith » Thu Apr 11, 2013 7:13 pm

Hi thanks for the info.

I also see in your pictures how the column and beams join. Another good picture is
download/file.php?id=662&mode=view
on apetley's build which I have read from back to front so only just arrived at the column forming.

cheers

Keith
fluffykeith
 
Posts: 9
Joined: Fri Nov 16, 2012 7:17 pm
Location: UK

Re: How effective is concrete sticking together

Postby thailazer » Thu Apr 11, 2013 8:34 pm

Best thing to do is to attach new reinforcing rod to the existing reinforcing steel. You might have to chip away some concrete to get at it. If you can't do that, drilling holes and inserting your steel rods is better than nothing. Having all the steel bonded together helps distributes the loads the best. New builds are easy as you just leave the steel sticking out as those photos show.

Back in a previous life I remember using a special two part epoxy mix for pouring concrete onto existing 40 year old footings. We still drilled deep holes and used that same epoxy to hold the new steel. I was a summer worker putting new pads and supports on a 12 foot diameter pipeline.
thailazer
 
Posts: 650
Joined: Sun Jun 26, 2011 9:55 am

Re: How effective is concrete sticking together

Postby jazzman » Fri Apr 12, 2013 4:26 am

How to build a $20,000 / £14,000 house and a $???? MOTEL Updated 21 March 09 - with BOQ and costs
Don't let this happen in YOUR house.
jazzman
 
Posts: 2161
Joined: Wed Dec 06, 2006 9:11 pm
Location: Thailand

Re: How effective is concrete sticking together

Postby MGV12 » Fri Apr 12, 2013 5:40 am

A step by step guide to the above pin method ... and with the bonding agent applied you are good to go:

http://www.ehow.com/how_5882399_attach- ... -pins.html

“Some days I am an optimistic pessimist ... other days I am a pessimistic optimist”
User avatar
MGV12
 
Posts: 5349
Joined: Wed Jan 23, 2008 4:23 pm
Location: Chiang Mai

Re: How effective is concrete sticking together

Postby thailazer » Fri Apr 12, 2013 3:55 pm

fluffykeith... You are not asking a stupid question at all and I think you have the right concerns. A non-continuous pour interface is no good in sheer. Re-rod is a stop-gap but that interface will not be strong. The Thai building method is pretty good about keeping interfaces between old and new only in compression, but it is still something you have to watch out for. All the horizontal beams should be poured in one session for instance.

Are you building currently?
thailazer
 
Posts: 650
Joined: Sun Jun 26, 2011 9:55 am

Re: How effective is concrete sticking together

Postby fluffykeith » Fri Apr 12, 2013 6:39 pm

Thanks for the links. I also found a site with some pics that basically shows the columns being keyed with a dip in the top or rough end so that the beam locates in it.
I was also looking at some websites on precast columns, beams and floor slabs. Guess that is more expensive and needs a bit more acuracy in the build to get it fitting together.

Thanks thailazer - yep my concern was there is a lot (the whole floor) relying on the column to beam joints. I see now that the columns are only made up to the level just under the beams, then beams cast all in one on top.

thailazer - I'm not building yet - I'm at the "what should I be doing and how do I finance it" stage. We had wanted to be in the Chaing Mai area but MIL gave us some land in Udon Thani and she wasn't too happy when I suggested selling as she sees it as an investment although the selling was in the context of her having money to live on rather than re-investing in a different area.
Not sure what to do with it. We're in the UK, so anything we do to will be a holiday home, until I retire or have an alternative income. That's probably a way off as I'm just at the extended mid-life crisis stage.
A holiday home is ok for us but if we wanted to rent it out I don't think it's in a desirable area - don't ask where it is as I have no idea, we did visit it the last time out, but as we had a man-with-van transport I didn't take much notice of the route. Are there GPS coordinates on the channote? (waiting for that too!). There were some posts, I have a pic of some posts and a lot of grass but not sure how whoever put the posts in figured that's where they should be.
So basically as I decide what to do I'm reading up on the whole construction thing (as well as finishing our uk house updates).
fluffykeith
 
Posts: 9
Joined: Fri Nov 16, 2012 7:17 pm
Location: UK

Re: How effective is concrete sticking together

Postby gliffaes » Tue Apr 30, 2013 6:56 am

MGV12 wrote:A step by step guide to the above pin method ... and with the bonding agent applied you are good to go:

http://www.ehow.com/how_5882399_attach- ... -pins.html


But but but look at the rules....ah its ok number 3 rule negates all the rest :lol: :lol:



Wear gloves, a dust mask and boots when working with concrete.

For structural repairs on buildings and in situations where a concrete repair failure will be dangerous, consult with an engineer for the proper design.

Follow all local building codes.
gliffaes
 
Posts: 1943
Joined: Sat Apr 03, 2010 6:45 pm

Re: How effective is concrete sticking together

Postby MGV12 » Tue Apr 30, 2013 4:53 pm

gliffaes wrote:


Wear gloves, a dust mask and boots when working with concrete.




Thais aren't bothered by a slight skin irritation :roll:

Safety3.jpg

“Some days I am an optimistic pessimist ... other days I am a pessimistic optimist”
User avatar
MGV12
 
Posts: 5349
Joined: Wed Jan 23, 2008 4:23 pm
Location: Chiang Mai

Re: How effective is concrete sticking together

Postby pipoz » Wed May 01, 2013 12:25 am

fluffykeith wrote:Hi

Concrete posts, concrete beams, concrete floors, even concrete cupboards in the bathroom and kitchen, so, between each pour there is a joint, what keeps the joints from failing?
I know you can wet the previous concrete to aid adhesion, and I just read about some product that can be painted on (I guess water with some additive),
but is the joint stength purely in the rebar or is there strength in the concrete join between old and new concrete.

I'm asking as I see the posts get made and then the following in order of ground beam, floor beam, next floor post, next floor, seamingly in an ad hoc fashion. Does this result in castings being made such that a beam joins a post resulting in the old to new concrete joint being on the post side, that is, the joint is shearing rather that compressive, which would be the case if the beam was cast on top of the post. Is it possible that the old to new joint will crack? and if the joint is shearing then it's only rebar holding up the floor.



If the joint doesn't have reinforcement from one pour to the next, the best way to get a good bond between the two concrete surfaces is,

1. After the first conc pour, just roughen the exposed surface that will connect to the second pour. A simple way to do this, is to brush some Retarder onto the first pour surface when finished (say an hour after the pour), then wait another 6-10 hours until the concrete has gone off/is partly set, then hit it with an air compressor or garden house to remove some of the surface concrete. This will give it a roughened appearance - We call it "Green Cutting", as the concrete is still green at that point (Green meaning its gone off/set somewhat, but not hardened).
2. Then before the second pour, mix up a concrete slurry and add in some BONDCRETE. (Bondcrete and many other similar products is just an Additive). Brush the mix on the exposed/roughened surface of the first pour and then proceed with the second concrete pour on top.

Even without any reinforcement between the two pour joints, thus will give you a pretty solid bond between the two concrete pour surfaces

pipoz
User avatar
pipoz
 
Posts: 1879
Joined: Mon Jan 23, 2012 10:41 pm
Location: Udon Thani Sometimes

Re: How effective is concrete sticking together

Postby Tanlic » Thu Dec 11, 2014 2:23 pm

Hope someone can answer this quickly.

When fitting/building a wall between to columns should steel bars be used for strenth or are the blocks just held by the cement glue. Thanks in advance
Tanlic
 
Posts: 92
Joined: Fri May 09, 2014 4:39 pm

Re: How effective is concrete sticking together

Postby MGV12 » Thu Dec 11, 2014 4:02 pm

Tanlic wrote:Hope someone can answer this quickly.

When fitting/building a wall between to columns should steel bars be used for strenth or are the blocks just held by the cement glue. Thanks in advance


Rebar should have been incorporated into the columns for this. However the columns can be drilled and rebar bonded [2-pack anchor bond the best] in every couple of courses ... or at very least ninety degree angle brackets screwed to the columns and laid between courses.

“Some days I am an optimistic pessimist ... other days I am a pessimistic optimist”
User avatar
MGV12
 
Posts: 5349
Joined: Wed Jan 23, 2008 4:23 pm
Location: Chiang Mai

Re: How effective is concrete sticking together

Postby thailazer » Thu Dec 11, 2014 4:04 pm

Tanlic wrote:Hope someone can answer this quickly.

When fitting/building a wall between to columns should steel bars be used for strenth or are the blocks just held by the cement glue. Thanks in advance

You need to drill holes and insert steel rods that will go into the brick work joints for maximum strength. Spacing should be about half a meter between the rods, although the Thai builders go over a meter and some walls are lucky to have one.
thailazer
 
Posts: 650
Joined: Sun Jun 26, 2011 9:55 am

Next

Return to cement, concrete and mortar

Who is online

Users browsing this forum: Bing [Bot] and 2 guests