Talk:Creep and shrinkage of concrete
|WikiProject Civil engineering|
"The creep originates in the calcium silicate hydrates (C-S-H) of hardened Portland cement paste. It is caused by slips due to bond ruptures, with bond restorations at adjacent sites."
Actually, there is no clear evidence, it is only a hypothesis (in fact, it is stated in the next paragraph that the physical mechanisms are debated).