Three phase of concrete

Cincrete have three phases they are aggregates, cement paste and transition zone.
When you see graph between the stress and strain of that three phase. The graph of aggregate is linear that mean to say if stress

is increasing then also strain is not increasing more. However you seen the graph of cement paste that is not linea, it may bend that means to say that is result of micro cracking. As similar the cement pase we can see when the stress is increasing then strain will also increasing at same rate.
If we summerized graph between the stress and strain, it may cleared that when the line is non linear may result to form cracks.

The concrete will not retain to its original load due to creep and micro cracking. Simply, there will be a residual strain at zero load. This is called hysteresis loop.