Comments for International Summit on Cement Hydration Kinetics http://blogs.cae.tntech.edu/hydration-kinetics July 27, 28 and 29, 2009 Sat, 22 Aug 2009 17:46:28 -0500 http://wordpress.org/?v=2.8.4 hourly 1 Comment on 1.2 Session Topic Modeling by Richard A. Livingston http://blogs.cae.tntech.edu/hydration-kinetics/workshop-program/session-sub-topic-no-12-modeling/comment-page-1/#comment-415 Richard A. Livingston Sat, 22 Aug 2009 17:46:28 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=261#comment-415 I would like to clarify my comment at the workshop on the importance of temperature in the kinetics models. We know from calorimetry that the early age reaction is very exothermic and that the rate constant has a strong Arrhenius relationship. It also appears that the structure and water content of the C-S-H gel is temperature dependent. Therefore, the model needs to include a feedback loop for the effect of temperature on the rate of the reaction. This also implies that the thermal boundary conditions - adiabatic , isothermal etc - for the concrete object need to be specified. Computer models that simulatesimultaneously chemistry, temperature, stress (electromagnetics ect) are called multi-physics. COMSOL is a commercial version. We have been using it for a problem that involves induction heating. It is very powerful, but also expensive. I would like to clarify my comment at the workshop on the importance of temperature in the kinetics models. We know from calorimetry that the early age reaction is very exothermic and that the rate constant has a strong Arrhenius relationship. It also appears that the structure and water content of the C-S-H gel is temperature dependent. Therefore, the model needs to include a feedback loop for the effect of temperature on the rate of the reaction. This also implies that the thermal boundary conditions – adiabatic , isothermal etc – for the concrete object need to be specified. Computer models that simulatesimultaneously chemistry, temperature, stress (electromagnetics ect) are called multi-physics. COMSOL is a commercial version. We have been using it for a problem that involves induction heating. It is very powerful, but also expensive.

]]> Comment on Dolado – A Molecular Dynamics Study of the Formation of Calcium (Alumino) Silicate Hydrate (C-A-S-H) Gels by Dr Balakrushna Padhi http://blogs.cae.tntech.edu/hydration-kinetics/conference-papers/a-molecular-dynamics-study-of-the-formation-of-calcium-aluminosilicate-hydrate-c-a-s-h-gels/comment-page-1/#comment-375 Dr Balakrushna Padhi Thu, 13 Aug 2009 15:51:37 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=366#comment-375 I need the full paper I have seen the presentation it is a very good presentation in pdf form I need the full paper I have seen the presentation it is a very good presentation in pdf form

]]> Comment on 4 Session Topic – Admixture Interactions by Josephine Cheung http://blogs.cae.tntech.edu/hydration-kinetics/workshop-program/session-topic-no-4-admixture-interactions/comment-page-1/#comment-188 Josephine Cheung Fri, 24 Jul 2009 21:33:39 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=268#comment-188 Here are some questions that I think will be important to bridge the knowledge gap to build a model: 1) How do chemicals impact Al-SO4 balance? 2) Which model can simulate undersulfated cement hydration? Can the models also simulate or predict impact of admixtures? 3) What is the impact of dosage rates? 4) What is the impact of chemicals on cement with finenesses? 5) What is the impact of chemicals on the different cement phases ortho-C3A vs. cubic-C3A different alite phases (monoclinic vs. triclinic and others) 6) What is the impact of interstitial phase hydration, including the ferrite phases, affect the silicate phase hydration? 7) Need data on realistic dosage rates. Most literature focused at over-dosed ranges. Here are some questions that I think will be important to bridge the knowledge gap to build a model:

1) How do chemicals impact Al-SO4 balance?
2) Which model can simulate undersulfated cement hydration? Can the models also simulate or predict impact of admixtures?
3) What is the impact of dosage rates?
4) What is the impact of chemicals on cement with finenesses?
5) What is the impact of chemicals on the different cement phases ortho-C3A vs. cubic-C3A
different alite phases (monoclinic vs. triclinic and others)
6) What is the impact of interstitial phase hydration, including the ferrite phases, affect the silicate phase hydration?
7) Need data on realistic dosage rates. Most literature focused at over-dosed ranges.

]]> Comment on 1.2 Session Topic Modeling by Jeff Bullard http://blogs.cae.tntech.edu/hydration-kinetics/workshop-program/session-sub-topic-no-12-modeling/comment-page-1/#comment-187 Jeff Bullard Fri, 24 Jul 2009 18:27:50 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=261#comment-187 Is the "reaction volume" another way of saying that nucleation and growth of C-S-H only occurs on C3S surfaces? If you assume that no nucleation can occur in the bulk solution, but only on C3S surfaces, then that would seem to explain both the lack of influence of w/c ratio, but the significant influence of C3S surface area. If so, then the mechanism would be heterogeneous nucleation of C-S-H on C3S surfaces or growth on existing C-S-H surfaces. This latter mechanism is the only one that has ever produced results consistent with published experiments when simulating the full chemistry and microstructure evolution with HydratiCA, and it is also the mechanism assumed by the Dijon model. Is the “reaction volume” another way of saying that nucleation and growth of C-S-H only occurs on C3S surfaces? If you assume that no nucleation can occur in the bulk solution, but only on C3S surfaces, then that would seem to explain both the lack of influence of w/c ratio, but the significant influence of C3S surface area. If so, then the mechanism would be heterogeneous nucleation of C-S-H on C3S surfaces or growth on existing C-S-H surfaces.

This latter mechanism is the only one that has ever produced results consistent with published experiments when simulating the full chemistry and microstructure evolution with HydratiCA, and it is also the mechanism assumed by the Dijon model.

]]> Comment on 1.1 Session Topic Mechanisms by Jeff Bullard http://blogs.cae.tntech.edu/hydration-kinetics/workshop-program/session-sub-topic-no-11-mechanisms/comment-page-1/#comment-186 Jeff Bullard Fri, 24 Jul 2009 18:22:07 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=259#comment-186 Agreeing with Jeff Schweitzer, if we focus on alite for a moment, can we really nail down the mechanism of the "induction" period? We have one theory that C3S superficially hydrolyzes and has an apparent solubility product that is extremely low as a result. Another theory is that a metastable hydrate barrier layer forms as a separate phase and kinetically prevents C3S from dissolving rapidly. Yet another theory, I think, is that the mechanism of C3S dissolution itself changes dramatically as the driving force for dissolution changes, resulting in a large decrease in its dissolution rate. We often say that nucleation and growth of C-S-H are the rate-controlling steps during the induction period, and models of kinetics are often developed by assuming that the rate of nucleation of growth of C-S-H is equal to the rate of hydration for purposes of predicting calorimetry curves, etc. This is sufficient for such predictions (e.g. the BNG model) but we also need to understand what slows the rate of C3S dissolution to get a more complete picture of the chemistry. Agreeing with Jeff Schweitzer, if we focus on alite for a moment, can we really nail down the mechanism of the “induction” period? We have one theory that C3S superficially hydrolyzes and has an apparent solubility product that is extremely low as a result. Another theory is that a metastable hydrate barrier layer forms as a separate phase and kinetically prevents C3S from dissolving rapidly. Yet another theory, I think, is that the mechanism of C3S dissolution itself changes dramatically as the driving force for dissolution changes, resulting in a large decrease in its dissolution rate.

We often say that nucleation and growth of C-S-H are the rate-controlling steps during the induction period, and models of kinetics are often developed by assuming that the rate of nucleation of growth of C-S-H is equal to the rate of hydration for purposes of predicting calorimetry curves, etc. This is sufficient for such predictions (e.g. the BNG model) but we also need to understand what slows the rate of C3S dissolution to get a more complete picture of the chemistry.

]]> Comment on 2 Session Topic – SCM’s by Jeff Chen http://blogs.cae.tntech.edu/hydration-kinetics/workshop-program/session-topic-no-3-scms/comment-page-1/#comment-185 Jeff Chen Fri, 24 Jul 2009 15:54:38 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=265#comment-185 Proposed questions for the panel: KINETICS - How can we predict the hydration kinetics of any mineral assemblage? - How can we predict the reactivity of a given SCM, given its composition, physical characteristics, and composition of the surrounding pore solution? DEGREE OF REACTION - How can we better quantify the degree of reaction of SCMs in hardened cement pastes? THERMODYNAMICS - What hydrated phases form during the hydration of SCMs? What are the reaction stoichiometries? - What are the aqueous thermodynamic relationships? POZZOLANIC C-S-H - How can we model the nanostructure of pozzolanic C-S-H? - What is the impact of pozzolanic C-S-H on transport? Proposed questions for the panel:

KINETICS
- How can we predict the hydration kinetics of any mineral assemblage?
- How can we predict the reactivity of a given SCM, given its composition, physical characteristics, and composition of the surrounding pore solution?

DEGREE OF REACTION
- How can we better quantify the degree of reaction of SCMs in hardened cement pastes?

THERMODYNAMICS
- What hydrated phases form during the hydration of SCMs? What are the reaction stoichiometries?
- What are the aqueous thermodynamic relationships?

POZZOLANIC C-S-H
- How can we model the nanostructure of pozzolanic C-S-H?
- What is the impact of pozzolanic C-S-H on transport?

]]> Comment on 1.2 Session Topic Modeling by Jeff Thomas http://blogs.cae.tntech.edu/hydration-kinetics/workshop-program/session-sub-topic-no-12-modeling/comment-page-1/#comment-180 Jeff Thomas Wed, 22 Jul 2009 16:33:40 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=261#comment-180 A concept that I will discuss in my talk is that of a "reaction volume", which is a limited volume within which reaction product can form during the early nucleation+growth period. The reaction volume seems to extend outward from the surface of the cement or C3S particles by a fixed distance. The evidence for this is indirect, but pretty compelling. Increasing the w/c does not increase the amount of early hydration as one would expect if all of the water-filled space was available to N+G. On the other hand, increasing the surface area of the powder greatly increases the amount of early N+G hydration. So some questions I would like to raise for discussion at the workshop are: 1) Why does a reaction volume exist, i.e., what is the mechanism for limiting hydration product to form in this region? 2) Is there an alternative explanation for these observations? A concept that I will discuss in my talk is that of a “reaction volume”, which is a limited volume within which reaction product can form during the early nucleation+growth period. The reaction volume seems to extend outward from the surface of the cement or C3S particles by a fixed distance. The evidence for this is indirect, but pretty compelling. Increasing the w/c does not increase the amount of early hydration as one would expect if all of the water-filled space was available to N+G. On the other hand, increasing the surface area of the powder greatly increases the amount of early N+G hydration. So some questions I would like to raise for discussion at the workshop are:

1) Why does a reaction volume exist, i.e., what is the mechanism for limiting hydration product to form in this region?
2) Is there an alternative explanation for these observations?

]]> Comment on 1.3 Session Topic Instrumentation and Experimentation by George Scherer http://blogs.cae.tntech.edu/hydration-kinetics/workshop-program/session-sub-topic-no-13-instrumentation-and-experimentation/comment-page-1/#comment-170 George Scherer Mon, 20 Jul 2009 18:50:01 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=263#comment-170 Suggested topics for discussion: 1. What is the nature of the initial product? (LD C-S-H or something with a different Ca/Si ratio...?) 2. What is the nucleation process? 3. What are the transport properties of the initial product? (Is it a diffusion barrier, so that ions are fed to the product by dissolution of the free surface, or does dissolution continue just as fast below the product?) 4. Where does the product deposit? (Is it uniformly deposited on the clinker particle, or does it form near the site that provided the ions? Does it all form on the clinker or does some precipitate or gel in the liquid phase?) 5. How do the particle size and shape distributions affect the percolation process? 6. What combination of methods can answer these questions? 7. What would we do with the information if we had it? Suggested topics for discussion:

1. What is the nature of the initial product? (LD C-S-H or something with a different Ca/Si ratio…?)
2. What is the nucleation process?
3. What are the transport properties of the initial product? (Is it a diffusion barrier, so that ions are fed to the product by dissolution of the free surface, or does dissolution continue just as fast below the product?)
4. Where does the product deposit? (Is it uniformly deposited on the clinker particle, or does it form near the site that provided the ions? Does it all form on the clinker or does some precipitate or gel in the liquid phase?)
5. How do the particle size and shape distributions affect the percolation process?
6. What combination of methods can answer these questions?
7. What would we do with the information if we had it?

]]> Comment on 1.3 Session Topic Instrumentation and Experimentation by jeff.schweitzer http://blogs.cae.tntech.edu/hydration-kinetics/workshop-program/session-sub-topic-no-13-instrumentation-and-experimentation/comment-page-1/#comment-168 jeff.schweitzer Mon, 20 Jul 2009 15:00:48 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=263#comment-168 I would like to get our discussions going for coming up with a relevant set of topics and questions for our two panel discussions. These can be either things you plan on addressing in your talk or those you will not be addressing but think would be useful to discuss. Here are a few items that I hope will prompt your thinking on what would be useful to include: 1. How do we define the end of the early hydration period? 2. How well do we know the experimental conditions and what is needed to translate the experimental results into useful information for modeling? 3. What is the form of the sample during the experiment and are there issues to translate the measured results into useful constraints on the modeling? 4. Are there any techniques that have not been used that are promising to consider for future experimentation? 5. What are the best ways to benchmark the modeling approaches so that the data obtained from experiments are actually useful for modeling? I would like to get our discussions going for coming up with a relevant set of topics and questions for our two panel discussions. These can be either things you plan on addressing in your talk or those you will not be addressing but think would be useful to discuss. Here are a few items that I hope will prompt your thinking on what would be useful to include:

1. How do we define the end of the early hydration period?
2. How well do we know the experimental conditions and what is needed to translate the experimental results into useful information for modeling?
3. What is the form of the sample during the experiment and are there issues to translate the measured results into useful constraints on the modeling?
4. Are there any techniques that have not been used that are promising to consider for future experimentation?
5. What are the best ways to benchmark the modeling approaches so that the data obtained from experiments are actually useful for modeling?

]]> Comment on 3 Session Topic – Post Peak Hydration by Question for the panel http://blogs.cae.tntech.edu/hydration-kinetics/workshop-program/session-topic-no-2-post-peak-hydration/comment-page-1/#comment-167 Question for the panel Mon, 20 Jul 2009 14:31:27 +0000 http://blogs.cae.tntech.edu/hydration-kinetics/?page_id=284#comment-167 I'd like to see a discussion of the possible mechanisms that determine kinetics in this later stage of hydration. It's assumed that it is diffusion limited. But there are other factors involved that need to be considered such as the availability of space and reactants (particularly water, and especially locally due to regional self-desiccation). How do these controlling factors interact to control the reaction rate and how does modeling take these into account? I’d like to see a discussion of the possible mechanisms that determine kinetics in this later stage of hydration. It’s assumed that it is diffusion limited. But there are other factors involved that need to be considered such as the availability of space and reactants (particularly water, and especially locally due to regional self-desiccation). How do these controlling factors interact to control the reaction rate and how does modeling take these into account?

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