*I am going to post this here and also in General as I am not sure where people in the know about concrete people will be looking.
We had a number of piles replaced under our house and have discovered a problem with the concrete used. Here are some images of what is happening at the top of the concrete and I was wondering if this is the result of having used the concrete that was recently in the news as being faulty. I have read the concrete was sold and has caused a large issue in a number of building sites due to its having too high an alkali content and the resulting failure meant it had to be replaced in some very high profile building sites.As you can see, the concrete appears to be swelling and crumbling, at the top you can knock pieces off with the concrete simply crumbling when put under stress. I haven't been able to find any online images of concrete suffering from this issue so was wondering if anyone here could give advice. https://trademe.tmcdn.co.nz/photoserver/full/432805617.jpghttps://trademe.tmcdn.co.nz/photoserver/full/432805527.jpghttps://trademe.tmcdn.co.nz/photoserver/full/432805478.jpg
survivalkiwi,
Dec 14, 7:06am
Did it come in a truck or mixed on site?
jphs,
Dec 14, 7:09am
Mixed onsite. 18 piles done in total. The concrete was high strength concrete and come in bags about 25kg I think . maybe 1/2 a metre high bags.
happychappy50,
Dec 14, 7:18am
Had exp of this in Oz,quick set concrete was the problem,Drys too quick & is apt to crack,that is why when a concrete slab is poured on a hot day you often see a sprinkler going on it to s l o w down the drying process,I only use standard bagged stuff these days,works just the same,recently did a colour steel fence no movement,but left installing panels for a week,all straight & the panels went in easy as.
The firth link you gave is 20 MPa Rapid Set. Rapid Set use to be only 12 MPa but now it is 20 MPa. I wouldn't use it myself, but in Firth's PDF selection tables say it's okay for structural foundations.
jphs,
Dec 14, 8:13am
Hi folks, thankyou for offering advice here! The concrete used was 25 NPA which is strong concrete.
jphs,
Dec 14, 8:21am
I have seen concrete crack due to it setting too quickly however this is something different. The concrete seems to be expanding and cracking. When you remove a piece of the surface, it seems to be light and crumbly and not at all hard as it should be. At the ground level, where there is moisture in the earth, the crumbled surface has absorbed moisture and is almost like a paste.
echoriath,
Dec 14, 8:25am
If you are certain it was mixed with the correct amount of water and batched before pouring in the forms, you may need to have it analysed professionally to assess what the actual problem is.
Who did the work? Have you contacted them? It's worth putting in writing to them immediately that there's a problem. They may already be aware of the problem. The sooner you let them know YOU are aware there's a problem, the sooner your issues are likely to be sorted out.
jphs,
Dec 14, 8:54am
Have contacted the person who did the work and have given them pictures as well so they are aware of the issue. It seems odd that the failed concrete has simply been expunged from the media here. If concrete used in the Waterview Tunnel off ramps had to be replaced and Auckland University's new Engineering School building had a floor removed as it contained the failed concrete then where else has it been used and why are there no public resources to check your work?
echoriath,
Dec 14, 9:34am
There's a LOT of concrete that gets poured. It's hard to check it all. What tends to get more scrutiny by building inspectors and the like is the boxing, slab thickness and reinforcing. In ten years in building in NZ, I have never heard of an inspector checking the chemical content of concrete on site. Thickness, yes, but not the chemistry.
Presumably that would happen at batching plants, and if the big plant in this town is anything to go by, I will only say they could do with a LOT more scrutiny at several levels. Just one example: since MPa is governed in part by water content, a simple thing like a slump test does not even need to be performed when the paperwork for three separate batches shows the same slump, but one is soup, the other is porridge, and the third is just right. In ten years, I think I have seen one slump test performed by someone other than myself.
jphs,
Dec 14, 9:40am
So the MPA is determined in part by the water content. Then would having the incorrect water content in your concrete mix cause weakening of the concrete? Also, would it cause what is seen in the pics I posted with my initial post? I have used ready mix to do mowing strips and edging and, if I may say so, have got quite good at doing so. All of the concrete I have used has set hard as a rock and I have never seen what has happened under our home with what i have done in the garden.
echoriath,
Dec 14, 9:57am
Too much water and too little are both problems. You want enough water for the mix to be uniformly mixed and wet right through, but the less water you can get away with, the harder the final product. Too much water prevents the concrete from properly curing.
I lean away from readymix, personally. With a little research, it's possible (and cheaper) to mix your own. The most overlooked point when batching from scratch is that most ratios you see assume you will measure quantities by weight and NOT by volume. You also have to allow for the possibility that there is moisture in the sand and gravel, especially if the aggregates have been out in the rain recently.
You can get by with pre-mix stuff for a lot of things, but I have seen some of it turn out very poorly even when mixed right. This is especially true when it is poured into a hole and the "right" amount of water is poured on top. It mostly ends up as powder with lumps of concrete in it.
Trade secret: dishwashing liquid is a cheap, easy and effective plasticiser, meaning you can make a workable mix without using as much water. One squirt per barrow before you start adding water does the trick nicely.
jphs,
Dec 14, 10:07am
Awesome, I will try that when I next get into garden edging mode. As for our piles, I am not sure what to do. The builder is in the South Island and is unsure of the cause of the concrete's situation.
newtec1,
Dec 14, 10:17am
And has been outlawed for 30 years. We used to use it to fill party walls to make it slide down the cavity,but it was soon banned.
newtec1,
Dec 14, 10:19am
Get him to replace the lot.Piles are an important load bearing design of any house,you will only continue to have problems if you don't.
echoriath,
Dec 14, 10:44am
Sorry, what has been outlawed, exactly?
mm12345,
Dec 14, 11:18am
That's bloody terrible. I hope that the contractor left propping in place - and didn't remove it. Just to be clear though, as described the concrete is all still friable and spalling away? If not and the concrete looks good under the parts which have spalled away, I guess it's possible that the damage is superficial from them buggerising around under the house with barrows and planks etc while the concrete was still green, but it doesn't look or sound like it. Replacing the lot will be a big job but looks like it's needed. Did the contractor get building consent (probably needed for 18 piles)? Whatever the cause, it shouldn't be the OP's problem to investigate how or why.
jphs,
Dec 14, 11:41am
Unfortunately the concrete didn't go like that because of buggerising around rather it just cracked, swelled and crumbled over time. I am beginning to think I should take a spade and dig a bit to see if this "spalling" goes underground as well. I might do that tonight. In the pile inside the door under the house it thought that rain may have done that as it seemed very bad so i took off the top crumbled layer and mortared nice and tidy over the top so I could shut the door again. Unfortunately see this photo, you can see my mortaring is now cracked and looking on the top it looks as though moisture may be coming up through the concrete beneath it so the mortaring I did is going pear shaped as well. Here's a pic . https://trademe.tmcdn.co.nz/photoserver/full/432848672.jpg
tintop,
Dec 14, 1:26pm
There is so much misinformation, bad advice and old wives tales so far in this thread I dont know where to start.
Suffice to say that the op has a job that the contractor has not done properly.
Read up on the Consumer Guarantees Act and get the contractor back to repair the work.
brigette6,
Dec 14, 1:41pm
I use to be a concrete batcher and tester many moons ago. it looks like there was too much water in that mix. if too much water is added one sign is segregation of the stones and sand. the stones make their way to the bottom and the sand slurry sits on top.
mm12345,
Dec 14, 1:47pm
Well you should start somewhere, otherwise what you're saying could fall into the same category.
tintop,
Dec 14, 2:03pm
Fair enough comment - but I am pushed for tI'm right now. Suffice to say I spent a number of years in concrete laboratories, concrete testing, concrete construction supervision
Whatever the problem the op has - in the end the CGA applies.
mm12345,
Dec 14, 2:20pm
The Building Act also applies - and it's along those lines I'd be chasing up the guys who did this rather than CGA, especially if the total cost of the job was over $15k and beyond Disputes Tribunal powers. But if they don't recognise there's an "issue", then some expert advice / site inspection is needed. That may be achieved as simply as by calling the Council - whether or not the work was extensive enough to trigger requirement for building consent, it's a structural issue and must still meet code even if consent-exempt. With 18 piles replaced, I doubt whether it should have been exempt. The size of the penalties and other actions that they could face might be a hell of lot more of an incentive for them to remediate that mess - if that's what's needed.
tintop,
Dec 14, 2:24pm
Good advice mm12345
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