Hydrated cement paste shrinks since it loses moisture from its exceptionally smaller pores. As being the dampness is lost in these small pores, the surface stress on the remaining water tends to pull the pores collectively which ends up in a lack of quantity with time. Curing also impacts cracking. https://www.tjcyindustrialchem.com/news/cement-additives-and-concrete-admixtures-key-differences.html