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CemGEMS web app tutorial

Defining simulations of cement hydration, blending and degradation

Process templates

In order to facilitate process simulations, the CemGEMS web app provides a number of process templates compatible with most of the provided input recipe templates. The available process types and control variables can be selected when the user creates a new Process simulation document (Process with New Process option). These two choices combined form the process template document key to save it under the user-entered name (default is "MyProcess") in the user's profile database.

The process simulation uses the current recipe as the initial state ("parent"), from which the code will create a number of "step recipes" by automatically cloning and modifying the parent recipe ad defined in the process document. The generated step recipes will be saved into the user's profile database as JSON documents, whose metadata contain the key of the parent recipe and the process.

Indexation of process steps begins from 0; recommended number of steps (to obtain relatively smooth diagrams and plots as in process templates) is about 100. A process document may optionally contain more than one process definition (work in progress).

Any Process definition can be adjusted/modified by the (expert) user, as described in redefining-processes page. After the process simulation is finished, its results will be (re)sampled into a Plot document (child to the process) and plotted in a graphical frame (created from default plot templates).

Cement hydration

This group of process templates, applicable only for CEM-I Portland cement types, uses the built-in modified Parrot-Killoh hydration kinetics model (Lothenbach et al., 2008) with stepping in linear (hours) or decimal logarithmic time scales. Parameters for controlling the degree of reaction (ReactExtent) of main cement clinker constituents are not hard-coded, but provided in process templates, where they can be modified by the expert user, as described in redefining-processes page.

  • Hydration-PK::Time-linear This template sets 100 steps of partial equilibrium state calculations from 0 to 24 hours time, with time step length of 0.24 hours (14.4 min). Optionally, after modification of the Process definition, another temperature or even a stepwise trend of increasing temperature can be set (by default, calculations are performed at 20 C, 1 bar). This applies also to three other variants of CEM-I hydration process.

  • Hydration-PK::Time-log Sets 100 steps of partial equilibrium state calculations from 0.01 to 10^3 hours (ca. 42 days) time, with time step length of 0.05 log10 units relative to the previous time point. In fact, the time stepping is set from -2.0 until 3.0 at increment 0.05 linearly for the decimal exponent, so that the time step #0 corresponds to 0.01 h (0.6 min), and time step #100 - to 1000 hours.

  • Hydration::Change-Rxt This template does not use the built-in Parrot-Killoh kinetics model because it works also with recipes where Cement (clinker) material is given by the bulk chemical analysis, without splitting to amounts and degrees of reaction of clinker constituents. Hence, cement clinker can only dissolve as a whole, controlled by a single ReactExtent value. This value is incremented in 100 steps starting from exp(-10), ending at exp(0) = 1.0 (full hydration), and incremented as exp(n+0.1)-exp(n). The results can be plotted against step index or against lead variable ReactExtent taken as an abscissa.

  • Hydration::Change-WB This template performs the effect of changing w/b mass ratio (in any cement) from 0.3 to 1.0 linearly in 101 steps. To keep the mass of Cement and SCMs solid part constant, the second and third spans set Quantity of the Water material and of the whole recipe to 0 (both are calculated automatically during the equilibration).

Blending of cement with SCMs

This group of process templates implements various "blending" of (usually Portland) cement recipe of any data type by stepwise adding increasing amounts of SCM (supplementary cementitious materials). In most recipe templates, of both "min" and "xrf" type, the SCM Material consists of several Constituents in the following order: Limestone, SF (silica fume), GGBFS (ground granulated blast furnace slag), CC(MK) (calcined clay, mainly metakaolin), FA-amorphous (reactive part of coal fly ash), FA-inert (non-reactive part of coal fly ash), PZL (pozzolana Bacoli (Italy) composition), Anhydrite, Gypsum. By default in most CEM-I recipes, Limestone has 100 %mass content in SCM and the SCM material contributes 0 g to the recipe. We recommend to check in the parent recipe the ReactExtent values for SCM constituents of interest (set by default for 28 days hydration time) and set them to 1.0 or other desired value, as these are not checked or modified in the "Blending" process templates. Also set the desired SCM composition in %mass of required constituents before creating a process simulation.

  • Blending::Add-SCM Sets 100 linear steps of blending a cement recipe by adding SCM, starting from 0 until 50 g with increment of 0.5 g, all per 100 g of cement, keeping the initial w/b mass ratio constant and temperature at 20 C. Optionally, temperature can be changed to another value or even increased or decreased linearly along with blending (this can be set in the process definition using jsoneditor in Expert view mode, along with the maximum addition of SCM).

  • Blending::Arbitrary This process template is similar to the previous one, and should be used by experts to edit with jsoneditor and to set up custom blending with addition of SCM or Salts and with parallel changes in w/b ratio and/or temperature.

Cement dilution and leaching in water

This group of process templates can be used for simulating changes in partially equilibrated hydrated cements upon adding Water or changing w/b mass ratio in a wide range. Composition of Water material to act on cement should be set in the parent recipe before running the process. The results (volumes or masses of phases) should be plotted for solids only, skipping aqueous solution and gas from the ordinate.

  • Leaching::Add-Water This template sets the addition of Water material stepwise from 10^2 g to 10^7 g with linear stepping of logarithmic values (101 steps). In order to keep the mass of Cement+SCMs constant at 0.1 kg, each step (before equilibration) zeroes off the W/B mass ratio and the total recipe Quantity.

  • Leaching::Arbitrary This process template is similar to the previous one, and should be used by experts to edit with jsoneditor and to set up custom leaching with addition of Water or Salts and with parallel changes in cement composition and/or temperature.

Salt ingress ("attack") into cement

The salt ingress into cement is a reactive transport phenomenon, in which dissolved anions and cations from the external aqueous electrolyte solution diffuse into cement mortar or into concrete due to concentration gradients, and react there with hydrated cement phases. Ions present in high concentration in cement porewater (Ca+2, Na+, OH-, SO4-2) in some cases may diffuse in the opposite direction out of cement. Water, as such, does not move much in the absence of advective transport (which only occurs in fractures). These complex processes can only be qualitatively and approximately simulated in a simple stepwise process of mixing (addition of Salt composition to cement) with chemical equilibration.

In ingress process templates below, the addition of NaCl or another salt or of CO2 as a Constituent of the Salts Material is implemented. Note that this material is not accounted for in cross-checking of the w/b mass ratio. At large additions of salt, the thermodynamic model of cement may become incorrect due to very high ionic strength of the pore water, which is beyond the range of applicability of Debye-Hueckel equation for ionic acrtivity coefficients, or because some soluble salt minerals were not included in the GEMS thermodynamic system. The Salts material composition should be set in the parent recipe before the process of "ingress" type is simulated.

  • Ingress::Add-Salts In this process template, a stepwise linear addition of Salt from 0 to 40 g with increment 0.4 g (per 100 g cement) is implemented, using the Quantity of Salts Material. The last process span sets the Quantity of the whole recipe to 0 in order to retain constant w/b mass ratio after the equilibration calculation. To simulate carbonation of cement, first set the Salt material composition to contain some %mass of CO2 in the parent recipe.

  • Ingress::Arbitrary This process template is similar to the previous one, and should be used by experts to edit with jsoneditor and to set up custom salt ingress or carbonation with addition of Water or Salts and with parallel changes in cement composition and/or temperature.

Degradation: Carbonation of cement

Carbonation, i.e. reaction of cement with atmospheric CO2 or dissolved carbonate species diffusing into cement or concrete, is essentially a reactive transport phenomenon, which in CemGEMS can only be qualitatively and approximately simulated in a simple stepwise process of mixing (addition of CO2) with chemical equilibration. To implement this kind of simulation, first set the Salt material composition to contain 100 %mass (or different but significant percentage) of CO2 in the parent recipe, equilibrate it, and then make a "salt ingress" process and simulate it.

Other (ad hoc) processes

Various simple process simulations can be set by incrementing state variables such as temperature (between 0 and 99 C) and pressure (1 to 100 bar). As an example, one process template for stepwise increase of temperature is provided.

  • Other::Stepwise Sets a stepwise linear increase of temperature from 0 to 99 C with step 1 C in InputSpan 0. As an option, the input span 1 can be used for changing the 28-day reaction extent of Cement Constituent Belite according to changing temperature (i.e. to make a higher reaction extent at higher temperature). If needed, the jsoneditor can be used (in Expert view) to add more InputSpan blocks for analogous change of ReactExt for other clinker phases or SCM constituents.

  • Other::Arbitrary This process template is similar to the previous one, and should be used by experts to edit with jsoneditor and to set up custom stepwise change of arbitrary input properties of recipe materials or constituents and/or temperature or reaction extent.

References for process simulations

  • Avet, F., Li, X., & Scrivener, K. (2018). Determination of the amount of reacted metakaolin in calcined clay blends. Cement and Concrete Research, 106, 40-48, Table 1, col.1.

  • De Weerdt, K., Ben Haha, M., Le Saoût, G., Kjellsen, K., Justness, H., Lothenbach, B. (2011) Hydration mechanisms of ternary Portland cements containing limestone powder and fly ash, Cement and Concrete Research, 41(3), 279-291.

  • Lothenbach, B., Le Saout, G., Gallucci, E., Scrivener, K. (2008) Influence of limestone on the hydration of Portland cements. Cement and Concrete Research, 38(6), 848-860.

  • Massazza, F. (1998). Pozzolana and Pozzolanic Cements. Ch. 10 in Lea's Chemistry of Cement and Concrete (Fourth Edition), Ed. Hewlett, P., Butterworth-Heinemann, p.471-635.

  • Olsson, N., Lothenbach, B., Baroghel-Bouny, V., Nilsson, L.-O. (2018) Unsaturated ion diffusion in cementitious materials – The effect of slag and silica fume, Cement and Concrete Research, 108, 31-37.

  • Savastano Jr., H., Warden, P.G., Coutts, R.S.P. (2005) Microstructure and mechanical properties of waste fibre–cement composites Cement and Concrete Composites, 27, 583-592, Table 1.

Last update: June 10, 2020