Foundation Cold Joints
“Delays in concreting can result in cold joints. To avoid cold joints, placing should be resumed substantially before the time of initial set. For unusually long delays during concreting, the concrete should be kept live by periodically re-vibrating it. Concrete should be vibrated at approximately 15 minute intervals or less, depending upon job conditions. Concrete should not be over-vibrated to the point of causing segregation. Furthermore, should the concrete approach time of initial setting, vibration should be discontinued and the concrete should be allowed to harden. A cold joint will result, and suitable surface preparation measures should be applied.”
Both pour lines and cold joints are common in concrete construction, but cold joints have more serious consequences.
In the case of what I see in the pictures, this pour line came close to a cold joint where rat holes or segregation of the concrete would have been evident due to the subsequent layer being set and the consolidation made impossible between the two layers.
The pictures show, that although the pour line is extremely visible, consolidation between the two layers was accomplished. That is evident from the overlapping fat of the concrete that bled between the two pours and overlapped the previous pour.
That means that although the elapsed time between the pours was not to delayed, that the two were not able to bond together.
Now, at this point it becomes an aesthetic issue more than a defect.
If the exterior of the wall is waterproofed in this location, it should be adequate to prevent water intrusion in the future.
If the concern is of a structural issue, this can only be verified by having a core sample taken at the joint and tested.
The angle of the pour line in the pictures, also indicate a high slump concrete was used. Typically, a slump of no more than 4” is required to get optimum design strength of the concrete.
My rough estimation of this one is about a 6” slump. The high water to cement ration will decrease the design strength considerably. But this could only have been confirmed at the time of the pour using a slump cone and done by a Certified Field Concrete Testing Technician like I am.
Making a judgment based on pictures is not always accurate, so my advice would be to have a structural engineer to make the final determination.
A Windsor Probe can also be used to check the wall for estimated strength. Available through Concrete Testing Labs.
Good luck and hope this helps a bit.