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Photograph of a cracked concrete slab, significant shrinkage How to Distinguish Concrete Settlement Cracks from Shrinkage
Cracks in Concrete Foundations, Walls, Floor Slabs

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Concrete crack diagnosis: settlement vs shrinkage:

Here we describe how to tell the difference between slab settlement & slab shrinkage in concrete floors & foundations:

How to distinguish Settlement Cracks vs. Shrinkage Cracks in concrete slabs - a division of our article on How to Identify and Evaluate Settlement Cracks in Slabs in Poured Concrete Slabs or in concrete floors in basements, crawl spaces, or garages.

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Settlement Cracks Compared With Shrinkage Cracks in Poured Concrete Slabs

Photograph of a cracked concrete slab, significant shrinkage

This article series describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.

Types of foundation cracks, crack patterns, differences in the meaning of cracks in different foundation materials, site conditions, building history, and other evidence of building movement and damage are described to assist in recognizing foundation defects and to help the inspector separate cosmetic or low-risk conditions from those likely to be important and potentially costly to repair.

What about the cracks in these two photographs? They had been filled, and looked pretty significant.

At first we thought it might be a settlement problem, but that was probably wrong. We think these are shrinkage cracks too, from a really bad pour, probably with way too much water in the mix.

First: look at the photo above: that's a close up of some of the cracks in this floor where they were notfilled-in.

This is a classic discontinuous concrete shrinkage crack pattern. Shrinkage cracks range from hairline, less than 1/16" across to cracks so wide you can stick a gnarly Trumpian finger right into the opening.

Second: look at the photo below. It's hard to see, but there was no obvious difference in the slope nor level of the concrete throughout the basement.

If we were looking at settlement rather than shrinkage, or settlement combined with shrinkage cracks in the concrete, there ought to be some vertical dislocation or sloping among the broken up sections of slab.

Photograph of a cracked concrete slab, significant shrinkage

It is useful to keep in mind that diagnosing slab or any other building cracksor movement can be tricky since there may be more than one contributor to the problem.

These cracks may not be a structural concern, but there are caseswhere a serious hazard can be present, such as garage floor cracking when the floor was poured over soft, loose, inadequately-compacted fill and where the floor slab was not pinned to the garage foundation walls.

Soil settlement under a garage floor, perhaps aggravatedby groundwater which can increase soil settlement, can lead to first hollowing-out of space below the floor and second, sudden collapse of the floor structure.

How to find voids and settlement under a concrete slab: drag a chain?

It sounded a bit goofy when we heard this, but we tried it and it works: we use a heavy chain, dragging it across the garage floor andlistening to changes inthe sound it produces, to find areas of significant soil voids below the floor.

The pitch of the chain noise drops significantlywhen passing over a void below the concrete.

There are more sophisticated instruments that can also penetrate slabs and the earth to check for various conditions, and of course,before a professional slab-jacking firm starts pumping grout or inserting pins to lift a settled slab, the consultant will explorethe soils below the slab by drilling through it (or perhaps other means).

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Reader Comments, Questions & Answers About The Article Above

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On 2019-04-22 - by (mod) -

I can only speculate and I have to emphasize that diagnosing foundation cracks by a picture in a few words is always going to be incomplete, but with that apology, I can point out that it is common to see a crack like the one in your photo where garagej slab abuts the foundation wall. That can happen because the fill under the slab was not adequately compacted and perhaps al
A look so the slab was also not pinned to the wall.

You know those conditions that you wait of the slab combined with the weight perhaps of a vehicle parked on it can cause some settlement which then can push outward on the garage foundation wall.

Check to see how much the foundation wall leans outward ( ir kess common, obwards) and let me know.

Also look inside to see if the slab has settled uniformly or ir topoed or cracked. Take a look at the point at which the slab abuts the foundation wall to see if the original concrete pour Mark shows that they slab has actually settled here.

On 2019-04-21 by Cynthia O'Leary

A mountain home in Georgia we are considering purchasing has a straight horizontal crack on the outside of the foundation plus a few smaller diagonal cracks. The crack is located under the garage. What do you think may have caused this and how can it be fixed?

IMAGE LOST by older version of Clark Van Oyen’s Comments Box code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-04-14 - by (mod) -

Common, yes, often from an improper mix or placement or from cold or wet site conditions.

Good work and good results? Not really.

Use the picture frame icon to attach some photos.

On 2018-04-14 by Betty

I just had a new garage floor poured. In less than ten days the new floor was riddled with fine hairline honeycomb (irregular) shaped cracks. Is this normal?

On 2016-03-21 by (mod) - define & use terms "displacement" and "deflection" in assessing concrete structures

@MDC


The way I use the term "displacement" when talking about concrete foundations, walls, or slabs or floors, I mean that there has been some movement, either vertically or horizontally in the structural element itself: either the whole floor or wall has moved,leaned, heaved, or portions of it on either side of the crack have moved.

So, for example, at a structurally-harmless shrinkage crack in a concrete floor, you will see that the floor has remained level, and the floor has not lifted nor settled on either side of the crack.

Structural engineers use a similar word, deflection, to refer to bending under load; a foundation wall that has bulged or bowed might be described as having deflection.

The difference?

If a structural element remains in place but is bent, sagged, heaved, it's deflected, bulged, or bowed.

If a structural element or portions of it have moved with respect to portions of itself or with respect to the rest of the structure there has been displacement.

Types of displacement include leaning, heaving, settling. And in fact if a foundation wall is significantly bulged, as that means it has also gotten "shorter" there is likely to be displacement (*lowering) of the structure it was supporting.

On 2016-03-21 by MDC

What does 'displacement mean in relation to concrete cracks?

On 2016-03-17 by kamran

we have a rcc girder of 32m length in which we don't have cables when we launch the girder small shrinkage cracks produced due to its dead load. what are the safety precuatioons shoul be taken

On 2015-03-03 by Anonymous

what is the correction for a small crack less than 1/8 inch that follows the path of the grout between cinder block foundation.


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