Thin and long Cracks on slab

Hi everyone, our slab has been poured for 3 weeks and now we spotted some thin and long cracks on the slab. They locate across the centre of the slab, from one side to the other, even extend to the edge of slab. Is that normal? Should we ask the builder to repair it? Will it cause any structural issue?






Please assist?

Thank you
TF

I think I read somewhere saying it's common for cracks appearing in newly poured concrete because it's still curing but I would definitely be concerned and would want to question my SM about it.

That looks like a normal shrinkage crack and nothing to worry about.

if you want to finf out more check out this link: https://anewhouse.com.au/2012/02/concrete-cracking/

The reason why i am worry is because the cracks extend from one edge to the other，so feel like the whole slab has been broken into half eventhough they are very thin.

Once a crack starts it tends to run until it either reaches an edge or another crack.

They look to be less than 1mm which is fine.

The slab uses the reinforcing steel, plus the interlocking effect of the irregular crack surface, to maintain the structural strength.

Thank you for clearing our minds!! Seem we worried too much:)

Hi,

I tend to disagree with the recommendation when saying the cracks at 3 months are 1mm and no cause for concern.

Firstly - do you have a soil report and who did the soil sample?
Secondly - what is the slab classification based on that soil report?
These are two very critical factors that you need to ensure are accurate due to potential issues that can occur if it has been classified incorrectly. The classification determines the appropriate thickness and depth of footings. If they are not correct, the potential of slab heave is very possible.

Bashworth has given a good answer.
Concrete shrinks, they are the physical properties of concrete. Shrinkage is controlled with reinforcing steel to ensure that instead of large cracks there are thousands of small cracks mostly invisible to the eye.
Presently there is no evidence pointing to defects requiring further attention.

It's not that the answer is invalid, the response I have provided is based on my own experience where hairline cracks where visible and I was given the same answer 12 years ago. Yes, I have slab heave and yes the soil report incorrectly classified the site resulting in more than just cracks to the slab. There is no harm in checking and questioning to ensure that the foundations are sound. It's also good to understand what each classification means. My property had large trees and an existing premises which was torn down and the property sub divided. The site has a "H classification and 3 structural engineers agreed it should have been "P" at a minimum "E". Therefore the slab was undersized for its purpose.