Reason for these cracks is unknown

[arawinda]

Hi, I need expert opinion on possible reasons for cracks shown in attached pictures.

Element - basement ground slab
Thickness - 450mm
RF details - T1, T2, B1, B2-T16@200 (QT bars)
Clear cover - 50mm
Ambient temperature during casting - 27-30 Celsius. (Sri Lanka 6pm to 6am)
Mix design (kg/m³):
Cement - 391
Fly ash - 106
Coarse aggregate - 1003
Manufactured sand - 726
Water - 174

 

[HTURKAK]

I guess early age cracking . The reason should be early-age volume change due to thermal deformation , cement hydration and shrinkage .
Can you check the range of crack depths and measure the widths?

 

[ANE91]

That’s not how expert opinions work. You’re soliciting guesses. Crack causation determinations are extremely involved; there are literally dozens of reasons (often interrelated) why concrete might crack. It could be as simple as mapping/measuring cracks, or it could require petrography, identification of points of restraint as well as reactive aggregates or sources of sulfates/chlorides, consideration of temperature exposures and load cycles, an analysis of the mix and placement, etc.

Here’s my guess: it’s concrete, therefore it cracked. That’s the reason.

You might as well feed this to an AI until you get a preferable answer.

 

[arawinda]

I guess early age cracking . The reason should be early-age volume change due to thermal deformation , cement hydration and shrinkage .
Can you check the range of crack depths and measure the widths?

I will visit the site tomorrow and update. BTW, what are the simple methods of checking crack depth. I have a tool for measuring crack width.

 

[Smoulder]

First might be plastic shrinkage in small area. Last is crazing. Others look restrained shrinkage.