Why are crack formed at an angle of 45 degrees in slabs?
The two most common causes of concrete slab cracking are:
1. Temperature or curing cracking – this type of crack is caused by shrinkage of the concrete during curing. Concrete is weak in tension, so as the concrete shrinks and tension forces are set up within the concrete, cracks will form to relieve the stress. This is why “sawcutting” is done at periodic intervals in large slabs – not to prevent the cracking which is going to occur, but to control where it occurs, and hide it. The sawcuts make weak lines in the concrete, so the cracks occur within the sawcut area, relieving the stress. The cracks in the sawcut cannot be seen from the surface, so it appears to the end user that the concrete is not cracked.
2. The second most common reason you would get cracking in the concrete slab is that the slab is bearing on material that is not properly compacted or leveled. This is akin to a foundation type failure, where the loading conditions are exceeding the bearing capacity of the sla
