Portland Cement: Hydraulic Reactive Components, By-Product

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Discussion Overview

The discussion centers on the major hydraulic reactive components in Portland Cement and the undesirable by-products produced during the cement hydration reaction. It explores both the chemical composition and implications of these components in various applications.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants identify alite and belite as the major reactive phases in Portland Cement.
  • There is a question regarding the definition of "undesirable" by-products, with some suggesting that every application may have its own corresponding undesirable by-product.
  • One participant speculates that Sodium Hydroxide might be an undesirable by-product, recalling a mention from a lecture.
  • Another participant argues that sodium compounds do not play a role in Portland Cement, emphasizing that calcium and silicon dominate, and that after mixing with water, the cement paste is primarily composed of calcium-silicate-hydrate and Ca(OH)2 (portlandite).
  • A participant questions whether calcium hydroxide is an undesirable product, noting that calcium-silicate-hydrate contributes to the strength of cement.
  • One participant mentions that in specific applications, such as storing nuclear waste, the presence of Ca(OH)2 is highly undesirable due to its effect on pH and potential for leaching radionuclides.
  • It is acknowledged that cement cohesion and strength are mainly due to calcium-silicate-hydrate.

Areas of Agreement / Disagreement

The discussion reflects multiple competing views regarding the classification of by-products as undesirable, particularly in different applications. There is no consensus on the implications of calcium hydroxide in all contexts.

Contextual Notes

Participants express uncertainty about the specific implications of by-products in various applications, and the discussion highlights the dependence on context for determining what constitutes an undesirable by-product.

Who May Find This Useful

Individuals interested in the chemical properties of cement, applications in construction and waste management, and the implications of cement hydration reactions may find this discussion relevant.

SherlockOhms
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Could someone tell me the major hydraulic reactive components in Portland Cement and also the undesirable by-product during the cement hydration reaction? Thanks.
 
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I believe alite (and to some extent belite) are the majot reacive phases in portland cement.
See: http://en.wikipedia.org/wiki/Alite

Regarding the other question, "undesirable" in what sense? For every application there is a corresponding undesirable byproduct.
 
Useful nucleus said:
I believe alite (and to some extent belite) are the majot reacive phases in portland cement.
See: http://en.wikipedia.org/wiki/Alite

Regarding the other question, "undesirable" in what sense? For every application there is a corresponding undesirable byproduct.

Thanks for that. To be honest, I'm not sure. I was just reading a past exam question and it stumped me. I have a feeling it may be Sodium Hydroxide because I think I remember our lecture mentioning that before. Does that sound correct?
 
Sodium compounds do not play a role in portland cement. Calcium and Silicon dominate the scene in cement. Before mixing with water, the klinker is mainly alite and belite. After mixing with water, the cement paste is dominated by calcium-silicate-hydrate and Ca(OH)2 (portlandite).
 
Is calcium hydroxide an undesirable product in the cement? I know that CSH is what gives it it's strength, right?
 
I cannot give a general statement about Ca(OH)2 in all applications. But one application I'm familiar with is storing nuclear waste in cementitious waste forms for ultimate disposal in geological repositories. In such application it is highly undesirable to have Ca(OH)2 because its presence elevates the pH in the system and so can facilitate the leaching and migration of radionuclides.

And you are right cement cohesion and strength is mainly due to C-S-H.
 
Thanks for the help. Great stuff!
 

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