Shrinkage Cracking?

[Joseph Hagarty, CMI]

A few from a recent inspection.

Interesting one is the first where the crack fans out from the center.

[Joseph Hagarty, CMI]

And then there was this one......

[dmoore3]

Joe,

Those ARE NOT shrinkage cracks - those are structural in nature. The root cause may have been shrinkage cracking due to excessive water being added to the mix on site. Doing this results in a higher water/cement ratio and thus an increase in volume due to excessive water. When the shirnkage occours during curing, it weakens the matrix of the concrete slab (wall, slab or otherwise) resulting in a weakened structure unable to adequately hold the stresses for which it (the mix design)was intended. The result is a premature failure at stress points (such as window corners, doors and other areas where stresses are often bearing weight such as wall corners).

The simplified process is as follows:

Typically, freshly poured concrete will contain a significant amount of water in the mix design. As the concrete begins to hydrate and lose water through capillary systems created by moisture migrating to the nearest exterior surface. As the water migrates and evaporates voids are left behind and the mass of concrete begins to shrink. Rapid evaporation can cause shrinkage energies that exceed the tensile strength of fresh concrete. At this point micro-cracks form producing planes of weakness through the entire slab. As the matrix continues to shrink the micro cracks expand into larger, visible faults. Cracks of any dimension not only reduce the quality and durability of concrete, but are aesthetically unacceptable.

Therefore, you can understand how adding an excessive amount of water on the jobsite can adversly affect the long-term integrity of a structure.

Hope this helps!

[Jay Buzz]

As a homeowner who has a few hairline vertical cracks in the basement(appears to be shrinkage), I must say that some of those make me feel much better about the cracks we have. Our builder is still building and as I walk thorugh the houses under construction, 9 times out of 10, the corner of the egress window or daylight window has a crack coming off the corner down to the floor. I'd be pretty concerned about the crack that starts in the center of the wall and sprawls out.

[Marcel R. Cyr]

Houston, We have a problem. ha. ha.

Marcel

[dmoore3]

I'm also curious as to what type and design of reenforcement is within those walls.....

[Marcel R. Cyr]

Originally Posted by dmoore3

I'm also curious as to what type and design of reenforcement is within those walls.....

Chances are Doug, there is not enough, obviously.

The spider cracking is caused by the wall structurally giving in due to either not enough reiforcement or real bad backfill and hydrostatic pressure on a concrete wall that obviously was not capable to withstand.

I would bet money that this wall did not have proper horizontal reinforcement, no u-shaped reinforcement under the foundation window along with 45 degree reinforcement at the bottom of it and poor backfill and perimeter drainage and waterproofing.

I would check the exterior for grade and any evidence of perimeter drainage, sumps, floor drains, and write it up accordingly.

This is not an easy fix.

Marcel

[Keith Swift, PhD.]

I agree with Douglas, but would prefer a better view. In one picture it looks like moisture has penetrated as well. Depending on what your clients are like, and the history of lawsuits in your area, I'd paly it safe and defer to a specialist.

[rwand1]

Do a Google search "cement cracks"

These cracks may be the result of several different senarios.

Here is one link.

http://www.cement.org/tech/faq_cracking.asp

[ROBERT W. NEWLAND, JR.]

I would defer to a specialist in a heartbeat. I'm dealing with my very own foundation issue and picture 3 (water intrusion) is exactly what mine looked like a few years back....

[Marcel R. Cyr]

There is no doubt in my mind that this can only be diagnosed by a specialist.

If one wants to know the cause, that is the route to take.

So the report would read,

Observed numerous cracking patterns in the concrete foundation walls and bulging in areas that would indicate to me that a structural element exists.

There also seems to be some water intrusion from some of the visible cracks, and this would indicate that there might be a lack of water proofing membrane on the exterior side of the foundation and also a lack of foundation drainage and poor backfill material exerting pressures to a foundation wall that may be lacking the sufficient reinforcement to sustain those pressures.

I would highly reccommend a Structural Engineer to provide a clear evaluation to this condition.

Marcel
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[gbeaumont]

Originally Posted by mcyr

The spider cracking is caused by the wall structurally giving in due to either not enough reiforcement or real bad backfill and hydrostatic pressure on a concrete wall that obviously was not capable to withstand.

Hi to all,

Last time I saw a crack like that the engineer who was consulted called it out as the result of improper back filling, either from the concrete being insufficiently cured, or from very heavy equipment having been used too close to the foundation.

Regards

Gerry

Image courtesy Taunton Press,Fine home building

[Kenton H. Shepard, CMI]

Originally Posted by dmoore3

Joe,
Those ARE NOT shrinkage cracks - those are structural in nature.

Doug, they look a little excessive to me, I don't often see shrinkage cracks create that X, but without bowing (Joe didn't mention bowing or displacement) what makes you so sure they aren't shrinkage cracks? Shrinkage cracks typically point to opposite diagonal corners of rectangular walls, and although you describe how excessive water in the mix can adversely affect concrete, and I don't think anyone will argue with you on that point, I don't really see where you illustrate your original point.

Originally Posted by dmoore3

...Cracks of any dimension not only reduce the quality and durability of concrete, but are aesthetically unacceptable.

Actually concrete shrinkage is necessary to put the rebar under tension so that it can effectively do it's job. Some cracking is common during the shrinkage process, and in foundation work, asthetics are not usually high priority.

[Brian A. MacNeish]

Originally Posted by kshepard

Doug, they look a little excessive to me, I don't often see shrinkage cracks create that X, but without bowing (Joe didn't mention bowing or displacement) what makes you so sure they aren't shrinkage cracks? Shrinkage cracks typically point to opposite diagonal corners of rectangular walls, and although you describe how excessive water in the mix can adversely affect concrete, and I don't think anyone will argue with you on that point, I don't really see where you illustrate your original point.




Actually concrete shrinkage is necessary to put the rebar under tension so that it can effectively do it's job. Some cracking is common during the shrinkage process, and in foundation work, asthetics are not usually high priority.

Spot on, Kenton!!!