Our basement flooded recently and we are in the process of redoing it. The slab floor has always had this hump in it, figured it just settled.
But I pulled off a piece of the hump and there is gravel below it and beneath the gravel you can see the original floor. You can see an outline where the cement was built up here.
Any ideas why this hump was built up like this? Planning on breaking it out so we can level and put new flooring down but concerned why anyone would do this.
The concrete could have been made out of using dirty sand, also, it could be the result of inadequate mixing, especially with the small capacity mixer, or too much mixing water that tends to wash out the cement and form honeycombs (loose aggregates with a little or no cement bond).
I suspect your floor has many such defects. You may try to detect the defective spots by knocking the slab with a metal rod. The quality hardened concrete will respond with a crispy banging sound, while the problematic location will respond with a muffled sound.
Depends on the quantity of the problemed concrete, you can fix a small number of bad spots by digging up the defective concrete and enlarging the hole by chipping until reaching the sound concrete, then refill clean gravel to level with the original bottom of the slab, give it a slight tamping, then place well-mixed concrete. However, for more than just a few bad spots, hiring a reputable contractor may be a better choice.
