Reinforced Concrete Wall - use of poker

rampantbunny

I've a reinforced concrete retaining wall on my site.
Engineer designed this and specified the steel schedule.

Should a poker/vibrator be used to settle the poured concrete?
If not used what is the net effect? (engineer not consulted on this yet, but plans don't suggest poker should or should not be used).

Czhornet

rampantbunny wrote: »

I've a reinforced concrete retaining wall on my site.
Engineer designed this and specified the steel schedule.

Should a poker/vibrator be used to settle the poured concrete?
If not used what is the net effect? (engineer not consulted on this yet, but plans don't suggest poker should or should not be used).

Definitely, without a doubt. Poorly compacted concrete leads to honeycombing, poor surface finish, poor overall strength, lets water through and can lead to corrosion of the steel eventually leading to failure of the structural wall as the steel strength is lost. You can hire either petrol or electric (110v) for E30/40 a day. Don't pour concrete without it, you will regret it so much in the future if you dont!

Metric Tensor

Agree with the above 100%.

To be honest if the person installing your concrete doesn't know that a poker/vibrator is necessary in ALL cases you should be looking elsewhere because they clearly haven'ta clue what they are at.

Calahonda52

rampantbunny wrote: »

I've a reinforced concrete retaining wall on my site.
Engineer designed this and specified the steel schedule.

Should a poker/vibrator be used to settle the poured concrete?
If not used what is the net effect? (engineer not consulted on this yet, but plans don't suggest poker should or should not be used).

The others have summed it up very very well.

Just a question here: why did you expect to see poker specified on the drawings?
Does the sketch for foundations say how it will be achieved?

The key design issue here is getting the required strength in the concrete and it will have to be vibrated in some way, not necessarily by a traditional poker: they can also be attached to the side of the shuttering if the steel placing is very concentrated and the retaining wall is high with a tapering formwork..

The big concern here is when the concrete arrives, the engineer may have specified a slump and cube test.

Typically the builders regard the concrete as being too stiff to work with so after the slump test and cube test is done they tell the driver to " wet her up there" Mick, or Joe or Mary or whoever. This weakens the concrete......

I first rejected such a wetted up load in October 1975 so its not a new problem

rampantbunny

Thanks for the replies.

Before hiring this guy I asked him would he be using a poker. He said he would be. I wasn't at site on any day of the concrete pour and I left him to it.

Spoke with a previous client of his last night. He wasn't on site when his job was being done either but he was informed by the men driving the concrete trucks that the poker was not used on his job at all. Plus when this client did return to site the poker was always 'clean' and in the same spot.

I rang concrete worker this morning;
Me: did you use the poker
Him: uhm, I did...but even if I didn't it wouldn't matter because the concrete was like cream going in and would be well compacted
Me: not using a poker makes a big difference, but as long as you used it, then fine
Him: oh yea, OK, chat later

I'm just suspicious. Any way of determining if wall was pokered. The finished surface is very smooth to be fair but I know this is not proof the poker was used.

gctest50

Just get lads in that are used to doing concrete, since it is such an important thing and very expensive and messy to remedy

Metric Tensor

rampantbunny wrote: »

Any way of determining if wall was pokered. The finished surface is very smooth to be fair but I know this is not proof the poker was used.

It's not easily done. X-Ray surveys, etc. It's a pretty costly undertaking.

You could do the old fashioned way and pick an out of the way corner the wall and smash it up - see what you find inside!

rampantbunny

Again thanks for the responses.

Firstly, the job is done/complete.
There was a poker onsite, but I've no evidence to suggest it was or was not used except for my suspicions based on work carried out by same guy for a neighbor (I didn't know until last night that he worked for neighbor so never went looking for neighbors opinion).

Secondly, his work 'looks' good. Smooth finish to walls, but his boards are very smooth and although it would take a long time, I'm sure copious taps of a hammer would get him the smooth result I see.

Calahonda52 wrote: »

Just a question here: why did you expect to see poker specified on the drawings? Does the sketch for foundations say how it will be achieved?

I didn't mean to (and don't think I have) suggest that I did or did not expect the engineer to specify poker or not. The sentence I used was for those posters whose default response to questions of this nature might be 'what does your engineer say/what are your details'.
The sketch provided stipulates the steel schedule, dimension and layout of all bars.
I would expect to see a poker used, but I've never worked concrete personally hence the thread. Main thing for me now is to confirm poker was employed or not.

Metric Tensor wrote: »

It's not easily done. X-Ray surveys, etc. It's a pretty costly undertaking.
You could do the old fashioned way and pick an out of the way corner the wall and smash it up - see what you find inside!

Would I expect to see hollows, or stone not surrounded by concrete? If it went in wet I'm not sure there'd be obvious gaps. I do have a few ducts running through the bottom of the wall for draining any water build up. I could break these out and see what the concrete is like in those areas, but again, if the concrete was wet going in I'd expect see smooth finish regardless of poker use.


I'll be chatting to the actual concrete supplier at some point. I could ask them (their drivers) if the poker was used and take it from there.

mickdw

Pouring something like a retaining wall, it would generally make life easier for them to use the poker as the concrete will flow around the steel then.
If he has got a good finish on the wall and didn't use a poker, I'd suggest the concrete was like water going in which would be bad.
You really should have supervision on site for these works.
Did engineer sign off on wall before pouring?
Was he on site for pour?

Czhornet

mickdw wrote: »

Pouring something like a retaining wall, it would generally make life easier for them to use the poker as the cover will flow around the steel then.
If he has got a good finish on the wall and didn't use a poker, I'd suggest the concrete was like water going in which would be bad.
You really should have supervision on site for these works.
Did engineer sign off on wall before pouring?
Was he on site for pour?

+1 If you think the poker wasnt used and wall has a good finish, then it must have been like "pea soup" going in. Was there any evidence if runny concrete around the shutters, splashes on the ground etc. If water is added on site, this gives a high water to cement ratio which in turn means poor strength!

rampantbunny

mickdw wrote: »

Pouring something like a retaining wall, it would generally make life easier for them to use the poker as the cover will flow around the steel then.
If he has got a good finish on the wall and didn't use a poker, I'd suggest the concrete was like water going in which would be bad.
You really should have supervision on site for these works.
Did engineer sign off on wall before pouring?
Was he on site for pour?

Re. engineer; he was happy to sign off on wall from photos of the steel work. He wasn't on site to see the pour. He couldn't get to it despite it being planned in advance.

Fair point re. the supervision; I should definitely have learned my lesson by now, that absolutely no one on a building site can be trusted to do a proper job without being supervised. What was I thinking.

If I was to cut a piece of this concrete from the wall, could this be tested for strength?
I'm not saying I'd be able to gain much from this as it would become a case of blame game between concrete worker and concrete supplier.

rampantbunny

Czhornet wrote: »

+1 If you think the poker wasnt used and wall has a good finish, then it must have been like "pea soup" going in. Was there any evidence if runny concrete around the shutters, splashes on the ground etc. If water is added on site, this gives a high water to cement ratio which in turn means poor strength!

I was only able to see the job each evening after work so can't tell whether the concrete was sloppy or not. The surrounds are muddy so would hide all evidence of splashes.

The latest pour is actually the second half of the job. The first stage was completed this time last year. The wall poured is 6ft high, contains a right angle, and supports a garage in this corner. The wall is back-filled to about 5 foot so there is as much weight on this wall as there will be.

Question; if the concrete was weak for that pour, should I expect to see cracks or other at this point? Or is this something that will only manifest in 5-10 years etc.

Mahogany Gaspipe

To reiterate every point already made, yes the formwork should certainly have been vibrated.

Sampling the concrete for strength will only now tell you the strength of the concrete at a discrete point; whereas the issue in this situation is how the overall structure performs.

If the surface finish is acceptable and the structure wasn't designed to protect your property against some manner of rock slide up slope of the wall, well then I suggest you may just chalk this down as experience and move on.

Calahonda52

rampantbunny wrote: »

I've a reinforced concrete retaining wall on my site.
Engineer designed this and specified the steel schedule.

Should a poker/vibrator be used to settle the poured concrete?
If not used what is the net effect? (engineer not consulted on this yet, but plans don't suggest poker should or should not be used).

OP, the tense here left me with the impression that it was not built, hence my reply.

Should a poker/vibrator have been used to settle the poured concrete? etc

rampantbunny wrote: »

The latest pour is actually the second half of the job. The first stage was completed this time last year. The wall poured is 6ft high, contains a right angle, and supports a garage in this corner. The wall is back-filled to about 5 foot so there is as much weight on this wall as there will be.

Question; if the concrete was weak for that pour, should I expect to see cracks or other at this point? Or is this something that will only manifest in 5-10 years etc.

Lindt see this first time

Re What Gaspipe asks:
what material is it designed to retain.
are their drainage holes in it if holding back clay

This is key

what thickness is it at the base?.
Can u post any pics of the steel fixed and we will take a stab at the loading

whats the design of the garage floor?

Czhornet

rampantbunny wrote: »

I was only able to see the job each evening after work so can't tell whether the concrete was sloppy or not. The surrounds are muddy so would hide all evidence of splashes.

The latest pour is actually the second half of the job. The first stage was completed this time last year. The wall poured is 6ft high, contains a right angle, and supports a garage in this corner. The wall is back-filled to about 5 foot so there is as much weight on this wall as there will be.

Question; if the concrete was weak for that pour, should I expect to see cracks or other at this point? Or is this something that will only manifest in 5-10 years etc.

The corner (if the steel is tied properly) will be the strongest part as the L bars will tie in both walls. The middle section of a long wall is where a crack from a bulge or leaning of the wall may occur. This will be due to pressure from behind due to settlement of the fill. Testing of the wall at this stage is as you say will turn into a blame game, although all water added on site is supposed to be recorded on the concrete delivery docket, it might be a place to start looking first if you want to follow it up.

Stone Deaf 4evr

Concrete and its handling is an art - one that unfortunately 90% of they guys handling of it are ignorant of.

the poker is used to remove air bubbles which can cause weak spots, you'll often see this on the face of the wall once the formwork is stripped back and you can see stones looking out at you from little depressions.

wetting up the mix to get it to flow isnt the answer either. Paddy on the shovel loves it as it flows everywhere but you'll still get plenty of air trapped. also, you can have a problem where the overall constituency of the mix is so viscous, that all the larger aggregate in the mix will start to settle towards the bottom of the formwork, leaving nothing but fines up top. this is counter to mix design.

a proper contractor who understands steel drawings, mix design etc is worth their weight in gold, don't dismiss a fella if hes 'too expensive' - I'd query why someone else is cheaper.


At the end of the day, a retaining wall is a critical structural element, I'd be insisting your engineer be on site for the duration of the pour, to see slump tests being carried out on the loads and overseeing any addition of water to the mix.

rampantbunny

Calahonda52 wrote: »

Re What Gaspipe asks:
what material is it designed to retain.
are their drainage holes in it if holding back clay

This is key
what thickness is it at the base?.
Can u post any pics of the steel fixed and we will take a stab at the loading
whats the design of the garage floor?

Thanks for the interest and responses Calahonda but I won't post engineering detail (charter). I think pictures of the steel in situ could be considered the same thing. If interested I'll send you PM.

What am I retaining;
Crushed stone for the most part under the garage underneath which are larger boulders. Used larger boulders for better drainage and cost. All compacted down over a period of time with smaller stone and all inspected by engineer.
Directly adjacent to the wall I've large stone (500 to 1000mm). The wall has holes every 6-8 ft for drainage. I've also a 12" corri pipe under the wall in two locations to allow more drainage from water run-off from driveway etc. At the rear of the wall (not bearing any load) I have a shallow drain which is to be piped to take away any water on that side.

The second pour is required to retain percolation area. Again, I plan on putting down large stone beside wall to bear some weight and allow drainage. There are holes in this wall also.

Both walls are supported about every 8 meters by pillars formed as part of the pour. Not something the engineer specified but which I asked for. Also, where engineer specified a certain thickness of steel I asked if it could be increased. He had no problem, and the cost was not much more.

First pour paid for, second pour outstanding (only finished pour two days ago). Before paying up I want to be sure a poker was used. I've enough of chalking it down to experience and moving on. If quarry confirm that no poker was used when they were onsite then it's looking like it was just taken out of the van for show.

Calahonda52

I don't think pics breach the charter in anyway...
Anyway sounds to me you are well on top of it, the drainage is key so its well taken care of, not that it ever rains here

the backfilling should wait at least 28 days and be done gently rather than horsed in from a height.

To be honest I don't know how you will prove that the poker was used.
Alos rarely are the delivery truck dockets marked up for added water accurately

I would focus on what you can prove rather than answers to questions.
In any event unless you have large dynamic loads on the driveway I wouldn't be concerned: we engineers tend to double the load, halve the material strength and add a bit for luck.

what width is wall at base

Metric Tensor

A core can be tested for strength if removed properly but to fully test the wall you would need a large number of cores.

Visual inspections of the cores will also help. You'll see a honeycombing effect related to poor vibration or you may see the aggregate separating into different bands if the mix consistency was not right. But again you will only see this at the point you check. You'll have no idea what's going on in the rest of the wall.

As others have said - if the slump was reasonable and he was pouring the wall from the top of a 6 foot shutter you'd expect to see series voids on the face of the wall if no vibrator was used. However, as others have said - a very high slump mix, or indeed a large depth of cover to the steel could give you a smooth face without vibrating - this is only lipstick on a pig though because the voids and separation will still exist internally within the wall.

The belt and braces super expensive way to do it is to use a series of specialist instruments that you roll along the face of the wall (or tap against it). They will provide you with a plot of the internal wall structure that will vary based on density, etc. And then based on the information from these you do a targeted series of cores - you shouldn't underestimate how expensive that would be!

Are you getting cores drilled elsewhere in the house for services? If so you could ask the core guy to take two or three along the length of the wall and inspect the cross-sections to see.

rampantbunny

Calahonda52 wrote: »

I don't think pics breach the charter in anyway...
Anyway sounds to me you are well on top of it, the drainage is key so its well taken care of, not that it ever rains here

the backfilling should wait at least 28 days and be done gently rather than horsed in from a height.

To be honest I don't know how you will prove that the poker was used.
Alos rarely are the delivery truck dockets marked up for added water accurately

I would focus on what you can prove rather than answers to questions.
In any event unless you have large dynamic loads on the driveway I wouldn't be concerned: we engineers tend to double the load, halve the material strength and add a bit for luck.

what width is wall at base

Posting pics won't breach the charter, but the discussion about loading that would follow would I think.

The footings for the wall are approx. 1300 wide and 245 deep. The front face of the wall (load bearing side) rises from this about 800 from front of footing, leaving about 250mm the other side (heel). The wall is of uniform thickness from top to bottom at 250mm. The individual pillars are 16" and increase the thickness of the wall by roughly 8".

I'm fairly satisfied that the wall is strong enough to bear what it is being asked to bear, especially considering that I'm using large stones to hold back some of the pressure on the wall.
What rankles is yet another trade onsite that cuts corners when your back is turned. Time to move on. Xmas party nite...yehaw.

rampantbunny

Metric Tensor wrote: »

Are you getting cores drilled elsewhere in the house for services? If so you could ask the core guy to take two or three along the length of the wall and inspect the cross-sections to see.

I'll be coring holes elsewhere later, but at that point it will be too late for redress.
Will have to see what the quarry says re. use of poker. They're local enough to be familiar with my build and I'm hoping will feel that they can tell me the truth. Time will tell, but no one will be paid until I have an answer.

SC024

for what its worth I think even IF they did wet up the conrete to the point it was like soup & flows from one end of shutter to the other they would still get bubbles / aero bar effect againt the shutters except that the bubbles would be smaller but without a doubt still there without using the vibrator. Even at only 800 high its going to take a lot of beating shutters with a hammer all the way along & up & down both sides. If the poker was there why not just use it? it's alot less effort & will be done quicker to be quite honest. I know what I would be using.

Are the shuttters still there? you'll see hammer marks all over them.

rampantbunny

SC024 wrote: »

for what its worth I think even IF they did wet up the conrete to the point it was like soup & flows from one end of shutter to the other they would still get bubbles / aero bar effect againt the shutters except that the bubbles would be smaller but without a doubt still there without using the vibrator. Even at only 800 high its going to take a lot of beating shutters with a hammer all the way along & up & down both sides. If the poker was there why not just use it? it's alot less effort & will be done quicker to be quite honest. I know what I would be using.

Are the shutters still there? you'll see hammer marks all over them.

Shutters gone off site, but saw them while they were up and they didn't look beaten. The surface of my neighbours walls are pretty smooth to look at and he is adamant that the poker was not used on his.
Had a closer look at mine today. There are small bubbles on the face of the wall.
The first pour (year old) does look less 'fresh' - I think it's because where there were surface bubbles, they are now a little larger if that makes sense.

Question - should I expect no bubbles if the poker was used?

Could be my imagination but I think the bottom of the wall looks a shade darker than the top. It's as if heavier stone sank to the bottom and thinner at the top (as another posted alluded to re. wet mix).
Will get a picture up-close tomorrow and post back.

SC024

rampantbunny wrote: »

Shutters gone off site, but saw them while they were up and they didn't look beaten. The surface of my neighbours walls are pretty smooth to look at and he is adamant that the poker was not used on his.
Had a closer look at mine today. There are small bubbles on the face of the wall.
The first pour (year old) does look less 'fresh' - I think it's because where there were surface bubbles, they are now a little larger if that makes sense.

Question - should I expect no bubbles if the poker was used?

Could be my imagination but I think the bottom of the wall looks a shade darker than the top. It's as if heavier stone sank to the bottom and thinner at the top (as another posted alluded to re. wet mix).
Will get a picture up-close tomorrow and post back.

In an ideal world with poker being used you will have 0 bubbles at all but in my experiece this rarely happens you will always get a small couple here or there. Im just telling you what ive seen in my experience in the real world but I'm not an engineer or anything. I've poured a few walls & beams etc. etc.

Metric Tensor

It is possible to have small "bubbles" adjacent to the formwork even in well vibrated concrete. You are talking very small ones though. Only visible up close.

The surface is not really a good indicator because so many factors come into play such as curing, time of striking, type of formwork, greasing of boards, etc, etc. I've seen some rotten finishes (where the formwork was badly removed) and the concrete was still well vibrated and sufficient for structural purposes, terrible to look at though.

cork2

My first question is what are these guys into? As in are average ground workers? Do they specialise in shuttering walls, columns, floors? Is it agricultural tanks and sheds they're into? From what I'm reading on this thread people are jumping the gun. A poker is 110% required, to attempt such a pour without it would be ridiculous! But you say a poker was on site.Why have it and not use it? I mean I've poured walls even if you were a "chance it" type filling the pans without a vibrator would be very difficult. I reckon if there was no poker used you'd know the minute you strip the shutter, there'd be major holes in the face of the wall where the concrete didn't compact. By all means try and track down the truck drivers but I think at the end of the day if you're holding back money on these guys you better be able to back it up.Speak to your engineer, ask him to look at the wall and see what he thinks. That's what you pay him for and if these guys go the legal route to get paid then your engineers opinion will be very valuable, if you're that nervous I'd even suggest he talk to the lads that did the work but have him do so before you get an invoice from the lads who did the work.

rampantbunny

cork2 wrote: »

My first question is what are these guys into? As in are average ground workers? Do they specialise in shuttering walls, columns, floors? Is it agricultural tanks and sheds they're into? From what I'm reading on this thread people are jumping the gun. A poker is 110% required, to attempt such a pour without it would be ridiculous! But you say a poker was on site.Why have it and not use it? I mean I've poured walls even if you were a "chance it" type filling the pans without a vibrator would be very difficult. I reckon if there was no poker used you'd know the minute you strip the shutter, there'd be major holes in the face of the wall where the concrete didn't compact. By all means try and track down the truck drivers but I think at the end of the day if you're holding back money on these guys you better be able to back it up.Speak to your engineer, ask him to look at the wall and see what he thinks. That's what you pay him for and if these guys go the legal route to get paid then your engineers opinion will be very valuable, if you're that nervous I'd even suggest he talk to the lads that did the work but have him do so before you get an invoice from the lads who did the work.

The contractor owns all the gear so not just an average ground-worker. If you're asking does he specialise in commercial sort of car-park type or bridge shuttering jobs versus agri tanks then I don't know. His is not a big outfit so I imagine he is not tendering for large contracts.

Just back from a site this morning where the same guy absolutely did not use a poker (confirmed by client). Wall was not structural insofar as not required to retain or support load therefore engineer not employed. Regardless of wall integrity, it is the finish that interests me and it is exactly as mine is. So, without poker it is entirely possible to achieve a finish which does not have major holes it would appear. Light taps of the hammer up and down the shutters.

Nervous is not how I'd see myself at this stage but I am suspicious given previous clients experiences. Anyhow, will sort it one way or other. Face to face conversation might be enough.

mickdw

I think you will stress yourself over this and achieve little.
If you are happy with finish and Engineer has no issue with the structural side, forget about it.
If the Engineer had any worries about the design he would have been on site checking everything from placement of steel to cube testing and slump testing concrete.
As you said previously, you increased steel compared to what was called for so I'd say the wall is 100 percent.

rampantbunny

Thanks mick. Ah no, there'll be no stress.

I earlier wrote:
I'm fairly satisfied that the wall is strong enough to bear what it is being asked to bear, especially considering that I'm using large stones to hold back some of the pressure on the wall.
What rankles is yet another trade onsite that cuts corners when your back is turned. ...

There'll be some questions and hopefully answers and it remains to be seen what will be achieved in the end. Hopefully it's not disappointment with yet another tradesman taking shortcuts. It's too common and that's really the crux if it. Will see how it goes.

cork2

I'm honestly not being smart in the slightest and I may be after completely missing the point but if you're not worried about the structural integrity of the wall and you're pretty happy with the finish face of the wall what is the issue?

As for the poker these guys must love hardship if they gave it a skip, I vibrate everything even where it's not require just for how much it simplified the moving and levelling of the concrete.

You're dead right about the face to face chat though, that is the way to go as it's much easier to get your point across from both sides when you're standing in front of the project in question.

rampantbunny

cork2 wrote: »

I'm honestly not being smart in the slightest and I may be after completely missing the point but if you're not worried about the structural integrity of the wall and you're pretty happy with the finish face of the wall what is the issue?

As for the poker these guys must love hardship if they gave it a skip, I vibrate everything even where it's not require just for how much it simplified the moving and levelling of the concrete.

You're dead right about the face to face chat though, that is the way to go as it's much easier to get your point across from both sides when you're standing in front of the project in question.

It's a retaining wall, the back of which will not be seen, the front of which will be hidden - so although it looks OK, this is secondary to structure/performance.
So, I'm happy that the wall will stand but not necessarily because of the work done. I posted that I increased the steel in the wall above engineers spec, plus I'm installing large rock in-front of the wall to lessen the load on the wall (also not required by engineer).

When I pay for something I've two considerations, not in any particular order:

1. Get what you paid for
2. Look after it

The rock in-front of the wall satisfies the 'looking after it' point. It doesn't have to be done but it can only help especially with drainage.
That leaves getting what I paid for and if a poker wasn't used the job falls short on this count. That's the issue.

PS..no offence taken from your post.