Editing Portland cement (section)

==Setting and hardening==
Cement sets when mixed with water by way of a complex series of chemical reactions that are still only partly understood.<ref>{{cite journal|url=https://www.sciencedirect.com/science/article/abs/pii/S0008884623002466|last1=Scrivener|first1=Karen|last2=Matschei|first2=Thomas|last3=Georget|first3=Fabien|last4=Juilland|first4=Patrick|last5=Mohamed|first5=Aslam Kunhi| title=Advances in hydration and thermodynamics of cementitious systems|journal=Cement and Concrete Research|volume=174|year=2023|pages=107332|doi=10.1016/j.cemconres.2023.107332|issn=0008-8846|access-date=20 Feb 2023}}</ref> A brief summary is as follows:

The clinker phases—calcium silicates and aluminates—dissolve into the water that is mixed with the cement, which results in a fluid containing relatively high concentrations of dissolved [[ions]]. This reaches [[supersaturation]] with respect to specific mineral phases: usually first [[ettringite]], and then [[calcium silicate hydrate]] (C-S-H)—which precipitate as newly formed solids. The interlocking of the C-S-H (which is crystallographically disordered, and can take on needle or crumpled-foil morphologies) and the ettringite crystals gives cement its initial setting, converting the fluid into a solid, and chemically incorporating much of the water into these new phases.<ref>{{cite book |last1= Mehta |first1= P.K.|last2=Monteiro |first2=P.J.M. |date=2013 |title= Concrete: Microstructure, Properties and Materials |publisher= McGraw Hill|isbn= 9780071797870}}</ref>

[[Gypsum]] is included in the cement as an inhibitor to prevent flash (or quick) setting; if gypsum is not present, the initial formation of (needle-shaped) ettringite is not possible, and so (plate-shaped) hydrocalumite-group ("AFm") calcium aluminate phases form instead. This premature formation of AFm phases causes a rapid loss of flowability, which is generally not desirable because it means that placement of the cement or concrete is very difficult.<ref>{{cite web |last= Monteiro |first= P.J.M. |title= Lectures - Cements |url= http://monteiro.ce.berkeley.edu/display.php?img=32&imgdir=lectures/cements |publisher= UC Berkeley |access-date= 2025-02-25}}</ref> 

Hardening of the cement then proceeds through further C-S-H formation, as this fills in the spaces between the (still-dissolving) cement grains with newly formed solid phases. [[Portlandite]] also precipitates from the pore solution to form part of the solid microstructure, and some of the initially-formed ettringite may be converted to AFm phases, releasing part of the sulfate from its structure to continue reacting with any remaining tricalcium aluminate<ref>{{cite journal |last1= Lothenbach |first1= Barbara|last2= Le Saout|first2= Gwenn|last3= Gallucci|first3= Emmanuel|last4= Scrivener|first4= Karen|date= 2008|title= Influence of limestone on the hydration of Portland cements|url= https://doi.org/10.1016/j.cemconres.2008.01.002|journal= Cement and Concrete Research|volume= 38|issue=6 |pages= 848–860|doi= 10.1016/j.cemconres.2008.01.002}}</ref>