XRD & Portland Cement Hydration

Reading materials on X-ray Diffraction & Portland Cement Hydration

XRD

A brief introduction (In Chinese)

http://www.labtoday.net/html/instrument/instrument/2018/1206/5762.html

Hydration of Portland Cement

Hydration of Portland Cement

Introduction
Portland cement is a hydraulic cement, hence it derives its strength from chemical reactions between the cement and water. The process is known as hydration.

Cement consists of the following major compounds (see composition of cement):

• Tricalcium silicate, C₃S
• Dicalcium silicate, C₂S
• Tricalcium aluminate, C₃A
• Tetracalcium aluminoferrite, C₄AF
• Gypsum, CSH₂

Chemical reactions during hydration
When water is added to cement, the following series of reactions occur:

• The tricalcium aluminate reacts with the gypsum in the presence of water to produce ettringite and heat:
• The tricalcium silicate (alite) is hydrated to produce calcium silicate hydrates, lime and heat:
• Once all the gypsum is used up as per reaction (i), the ettringite becomes unstable and reacts with any remaining tricalcium aluminate to form monosulfate aluminate hydrate crystals:
• The belite (dicalcium silicate) also hydrates to form calcium silicate hydrates and heat:
• The ferrite undergoes two progressive reactions with the gypsum:
  • in the first of the reactions, the ettringite reacts with the gypsum and water to form ettringite, lime and alumina hydroxides, i.e.
    • Ferrite + gypsum + water ® ettringite + ferric aluminum hydroxide + lime
    • C₄AF + 3CSH₂ + 3H ® C₆(A,F)S₃H₃₂ + (A,F)H₃ + CH
• the ferrite further reacts with the ettringite formed above to produce garnets, i.e.

• Ferrite + ettringite + lime + water ® garnets
• C₄AF + C₆(A,F)S₃H₃₂ + 2CH +23H ® 3C₄(A,F)SH₁₈ + (A,F)H₃

The garnets only take up space and do not in any way contribute to the strength of the cement paste.

The hardened cement paste
Hardened paste consists of the following:

Ettringite                                     – 15 to 20%
Calcium silicate hydrates, CSH     – 50 to 60%
Calcium hydroxide (lime)             – 20 to 25%
Voids     – 5 to 6% (in the form of capillary voids and entrapped and entrained air)

Conclusion
It can therefore be seen that each of the compounds in cement has a role to play in the hydration process. By changing the proportion of each of the constituent compounds in the cement (and other factors such as grain size), it is possible to make different types of cement to suit several construction needs and environment.

References:
Sidney Mindess & J. Francis Young (1981): Concrete, Prentice-Hall, Inc., Englewood Cliffs, NJ, pp. 671.

Steve Kosmatka & William Panarese (1988): Design and Control of Concrete Mixes, Portland Cement Association, Skokie, Ill. pp. 205.

Michael Mamlouk & John Zaniewski (1999): Materials for Civil and Construction Engineers, Addison Wesley Longman, Inc.,

Appendix:

ScienceDirect Topic page
https://www.sciencedirect.com/topics/engineering/portland-cement-hydration#:~:text=Ordinary%20Portland%20cement%20(OPC)%20hydration,the%20setting%20and%20the%20hardening.