I cannot detect changes between those images, but I am thinking the areas circled in yellow suggest some change in structure. For example, one would think the concrete (light colored) lines would be straight or linear. Well, is many areas or patches they are dark. Why? Did the concrete crumble or break due to stress fracture? One would think if it was extreme, we'd see water coming out, but if it gets to that point, then perhaps the whole structure would give away. Not even close to an engineer. Just an observation and thinking on crumbling concrete/stress. I might try to find a picture from a few posts ago and compare those particular areas…