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CemGEMS web app tutorial

Level Student

Working with recipe inputs and output results

The input cement recipe is a valid combination of materials (clinker, SCMs, water, etc.) and their constituents, defined using chemical formulae. Template recipes for main types of cement, provided by CemGEMS web app, were initially prepared by the development team using the data collected and recommended by top-level experts in cement chemistry (more about recipe templates here). Using triangles on the left side of the inputRecipes table to expand the recipe, the materials, the constituents, or the formulae, you can navigate into a desired level of the tree-like table, explore the data or edit them as necessary.

Calculating the hydrated equilibrium state

Even without entering any quantities, reaction extents, and formula compositions of materials and their constituents, you can compute a partial equilibrium in hydrated cement paste at given temperature, pressure and water/binder mass ratio (w/b). To do this calculation, activate the "Equilibrate Recipe" button.

The result will appear as a (collapsed) "outputResults" table, located below the two horizontal stacked bar charts showing composition (as volumes of phases and constituents) of the cement recipe before (inputRecipes) and after (outputResults) equilibration. The row under Speciation shows some total bulk properties of hydrated cement, as well as input temperature and pressure. Navigate using triangles to expand the Speciation into two tree-like sub-tables: Equilibrated and Residual.

Expand the Residual part to see what materials and constituents did not react completely, and in what amounts they remain present in hydrated cement. Note that all materials or constituents that were given in the recipe a zero quantity or a unity (1) reaction extent (degree of reaction), will not appear in the Residual part. Fluid materials (water, air) are always treated as fully equilibrated and, thus, never appear in the Residual part.

Now expand the Equilibrated part to see (hydrated) stable Phases; expand Phases to see their species, with amounts, concentrations, etc. The Phase column contains actually not the names of phases from GEMS chemical system, but phase name aliases that can be viewed and changed in the phaseAliases table (accessible in "Expert" view only). Each phase entry can be expanded (by clicking upon the triangle) to display the substances (chemical species, end members) comprising the phase. Note that only phases with Quantity exceeding 1e-9 g are present in the Equilibrated table. The last entry in the list of Phases shows the bulk values for the whole equilibrated system, with its elemental composition as (expanded) speciation.

Changing the W/B (water-binder) ratio

In cement recipe, it may be necessary to set or change the W/B mass ratio. CemGEMS makes this really easy. In the input recipe (top-level row), find the W/B_ratio column cell where you can set the desired ratio (usually not less than 0.3). Equilibrate the recipe and look at the effect in the Speciation, Equilibrated part, and on the stacked bar charts for Inputs and Results.

Following changes in temperature or pressure

In the input recipe, you can change the temperature (from 0 C to 99 C) and/or pressure (from 1 bar to 100 bar). Equilibrate and look at the effect of such change in the Speciation, Equilibrated part and on the stacked bar charts for Inputs and Results.

Changing the degree of hydration

You can explore different degrees of cement clinker (or the whole binder) hydration (values between 0 and 1) by editing and re-equilibrating the recipe. Go back to inputRecipes, expand a recipe, and check the ReactExtent cell content. "1" means a complete hydration extent. Change it to a small number (e.g. 0.01) and click Equilibrate.

In the outputResult, which now emulates some early hydration stage, you should see now more mass in the Residual part and less mass in the Equilibrated part. By cloning the recipe and increasing the whole-recipe ReactExtent value, you can follow changes in the hydrated assemblage due to more reaction progress. The impact of different degree of reaction for a chosen material or a constituent (of cement or SCM material) can be investigated in a similar way. This tedious work is automated in "Hydration"-type processes (more about process templates here).

Changing cement composition at materials level

To investigate the effect of e.g. addition of SCMs, expand the recipe to see materials and modify Quantity (masses) of Cement and/or SCM as desired (the mass of Water will be automatically adjusted according to given W/B ratio). Click on "Equilibrate Recipe" to see the results.

In the case of Portland cement, if you reduce the addition of SCMs to minimum (less than 1%) or set to zero and equilibrate, then Portlandite phase will surely appear in the Equilibrated part. At some larger addition of SCM (especially silica-rich), Portlandite will disappear because of more C-S-H that can form.

Keeping your task recipes and results traceable

To keep your recipe and results intact and to continue working with another recipe, just create a new recipe, or clone the existing recipe (by entering a new name). In the latter case, all changes that you have done in the recipe will be taken over into the cloned one, and you can continue modifying it further on. In the former case, the new recipe will be created "from scratch" using an appropriate template recipe from the provided selection.

Last update: June 8, 2020