Not sure what went wrong here, have I used the wrong type of concrete ? 1

[MiniMe4Eng]

These are pictures for a small project, replacing a bath tub with a shower and changing the position
Short story: it is not drying out and I am wondering if the pipe/joins cracked when the concrete cured or
it is because of using the wrong type of concrete and too much water.
I poured the concrete (both types, see below) on March 29!!

Here is what is under concrete

Here is before pouring concrete

Here is within a week since I poured the concrete

And here is the situation as of yesterday

This is the concrete used for the now dried out area

And since I wrongly estimated how much I needed I used some left over concrete from a fence project
This concrete mix was used for the area that is not drying up after so long and I am wondering what is going on
It is true that the mix for the area that still looks wet was poured a little too liquid
For that type of concrete and for such a small patch should it take this long to cure ?

 

[jayrod12]

You're concerned because it's still that darker colour of grey? Looking like it's moist? I would say in 2 weeks I've seen some concrete still have that green (wet) look to it. It could also just be a different concrete mix/different aggregate is causing a different colour. Some of those bag mixes I've used have an extremely dark natural colour to them.

Is it hard when you press on it with a screwdriver? If so, I wouldn't worry about it too much if you're confident you have no plumbing leaks or source of water below the repair area. If there is a source of water below, you'd want to find out what's causing it, but it's affect on the concrete should be your least concern.

 

[miningman]

Why does photo #1 show what looks like dirt below the pipe whilst photo #2 shows crush??? What part of the construction sequence have you not documented??

 

[MiniMe4Eng]

@jayrod12
I am concerned with the fact that it feels wet
In one of the pictures you could guess a hair dryer that I used to dry up the patch -it turns lighter but then after a while it gets back to darker
and it forms that white efflorescence, so I am not sure if it still cures and it still dries up after so long or there is something else. Se my next comments for miningman

@miningman
As someone advised I added some gravel there to break the humidity propagation. That is why you see gravel in the second picture
Now having that gravel layer should prevent the humidity from ascending toward the surface and my wet like looing patch should dry up.

In beginning I suspected the curing concrete cracked open the cemented joins and I had a leak at the bottom end of the elbow
So I made sure that no water is flowing through the pipe anymore (I had just the condense pump from my furnace pumping like 1 liter of water once or two times in 24h. SO I disconnected that but the patch still feels wet and if I dry it up with a hair dryer it gets wet like

Don't get me wrong the concrete is rock solid but it does feel a little bit wet -leaving a piece of tissue on top of it hardly collects any humidity but I still see that efflorescence forming

 

[jayrod12]

To be fair, you did use a product intended for post fixing, so you shouldn't expect visually appealing concrete. Some concretes take long than others to fully cure and use up all of the water.

 

[MiniMe4Eng]

The visual aspect is not a problem, the possible ascending humidity could be
I plan to pour a layer of self leveling concrete on top of what you see so I can install tiles

 

[jayrod12]

The ascending humidity would be an issue regardless of the concrete used. I wouldn't expect that the post fixing stuff is overly different from the general use fast set from a porosity standpoint unless you mixed it significantly different.

I understand that you're likely in a time crunch, but I'd be leaving that area as long as possible to allow it to dry as much as possible prior to installing the leveling compound and tiles.

 

[MiniMe4Eng]

Not in a time bond, I can wait as long as needed we have two bathrooms
Is there any technique I can use to accelerate the drying up process?
I also cant make sense of the difference in behaviour regarding the humidity for the two concrete types

Still have this question: can the concrete, while it is drying up, crack an ABS join that it is cast in the respective concrete

Hope I am using the right terms here

 

[ATSE]

Post hole concrete pre-mix has a bit lower cement content. Definitely more permeable that a 4,000 psi mix. About $2 extra per bag, just to rub it in.
However, you might have a moisture problem, and you need to figure out the source before proceeding.
Drill a vertical hole or two through your new concrete, and before you apply a cementitious topping for observation. Make sure there is not positive pressure. Even if you tile over concrete that have positive pressure behind it, it will probably continue to give you problems.
At the end of the day, water always wins.

 

[jayrod12]

I wouldn't say the curing process for the concrete should of affected the pipe at all. If it did, this would be the first time I've ever heard of that.

However I was at a house recently where a joint on plumbing below a slab wasn't glued. It had been dry fit up and no one went back and glued it together. Slow leak caused heaving of the subgrade (where I am our subgrade is highly susceptible to volumetric changes due to moisture content) to the point that there's a 5" tall 10 foot diameter cone of heaved concrete slab right above the plumbing joint.

 

[MiniMe4Eng]

@jayrod12 -I tested (no pressure testing though) the joint for leaks
The ABS cement is visible for each join if I zoom in in the first picture

@ATSE what is a sign that I have positive pressure there, sorry I am not familiar with the terminology
I am quite sure the humidity gradient is from under the slab toward the floor surface and into the room there is no question about that
How come the other path of concrete is not experiencing the same issue ?

One detail that is worth mentioning is that the humidity of the dirt in that opening changed over time
It stayed dry in the winter and it was a little bit more humid when the temperature raised (I live in Toronto)
I had to dig the dent to make room for the P trap and you can see that in the first picture; no water was observed during that time
The next day after the day when I finalized the dent to make it deep enough I could see some water collected in that gap
This also coincided with a very heavy rain (I think it rained the entire night)
Once the P trap was in I added dirt back to set the surface level and then I added gravel
However as you can see in the picture the space above the P trap was not sealed and it can bread so if any more water accumulates there I should see humidity or water around he drain where the gravel is visible. That spot is marginal to the entire wet areas

 

[miningman]

That is an obscene amount of water ponding only 6 inches below your concrete surface . Strongly suggest having a local contractor look at the area and making corrective suggestions. My guess is it will require extensive and expensive drainage before any more concrete is applied.

 

[MiniMe4Eng]

After removing that water it went away and it did not collect again
It was a one time since August since I opened that area and my guess is that it collected there because it was the lowest point and it percolated from the area around it.

 

[BridgeSmith]

Is there any technique I can use to accelerate the drying up process?

Probably, but that would interrupt the hydration (curing) process of the concrete, so it would not continue to gain strength like it's supposed to. The specified strength of the concrete is at 28 days of age. Granted, after 2 weeks it's probably 80-90% to that full strength, it's still curing and should be expected to still feel moist, and it's a good thing, since that helps the curing process.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[MiniMe4Eng]

I am in no rush but the other section is dry like Sahara...

 

[dik]

Concrete patches are nearly always ugly... just be careful what you paint it with...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[MiniMe4Eng]

I will pour self leveling concrete so I can install tiles and a shower base that needs to be level

 

[BridgeSmith]

Not sure what the plan is, but if you're using self-leveling concrete (or any mixture with actual cement) over the patched area, you don't have to wait until it's dry. It actually bonds better the sooner you do it. Concrete doesn't 'dry'; it cures by hydrating (growing intertwined crystals from dehydrated mineral). Therefore, a better bond between new concrete and old is achieved when the old concrete is in a condition called saturated surface dry (SSD), where the old concrete itself is as moist as it can be, but there's no water on the surface. So, your best approach, short of actually roughing up the concrete surface, is to keep the concrete wet for a few days before applying the self-leveling concrete, but be sure you keep any water off the surface for a few hours before pouring.



Rod Smith, P.E., The artist formerly known as HotRod10

 

[dik]

You have to be careful... best to encapsulate the stuff in gravel and add concrete over... if the concrete moves and the stuff is inside, it may cause it to break.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dauwerda]

As Bridgesmith stated, concrete does not dry, it cures. Concrete gets hard through a chemical process where the water reacts with the cement. If you don't have water you won't have a reaction, if you have too much water you will have excess water that will evaporate (causing excess shrinkage). Concrete will develop the most strength buy curing in 100% humidity (no loss of water that would have been needed for the curing process due to evaporation). Using a blow dryer to "dry" the concrete will simply result in evaporating water quicker than it would naturally and possibly removing the water that would have been required for the chemical reaction (i.e. reduces the strength of the concrete). It would also increase shrinkage - probably not a problem for a patch so small.

Why does your concrete patch appear so brown? Did you mix the concrete with water in a separate then place it? Or did you just pour the powder mix into the patch and ad water to it (I see this done with fence posts, but it results in a inferior product)? The brown appearance makes me think there is a bunch of dirt mixed in with the concrete (which is why I ask how you mixed it), which would certainly have negative effect on the final product.