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CemGEMS web app tutorial

Level Engineer

Working with recipes and results

CemGEMS computes physical properties in a bottom-up manner, starting from the values assigned for Constituents. For instance, to recalculate the densities, you may enter zeros in the Density column for the whole recipe and for all Materials. After clicking Equilibrate Recipe, you should see non-zero values there. Only if there are no Constituents in the Material or their properties are set to zeros, the entered properties of the Material will not be re-calculated. The same rule holds for the properties of the whole recipe with respect to the properties of Materials.

For Constituents in Cement and SCM materials, real elemental compositions (for clinker minerals Alite, Belite etc.) are provided in the recipe template of "min" type. You can check them by expanding the recipe down to the Constituent level and expanding Formulae for a chosen Constituent. If you need to use a different composition in this place, feel free to change the numbers and mention this in the Comment. Be careful with tweaking on the formulae containing iron (Fe), as this can have a strong effect on the calculated redox potential (pe, Eh) and equilibrated Fe-containing phases.

In recipe templates of "xrf" type, the "Cement" material composition is given as %mass values of oxides (SiO2, CaO, Al2O3, ...) as reported in XRF or other bulk chemical analysis data. Templates of "xrf" type cover many cases when clinker phase characterization data (i.e. amounts of clinker constituents and their bulk chemical compositions) are not available. In such recipes, the "Cement" material contains no Constituents, therefore hydration kinetics models of Parrot-Killoh type cannot be applied. The properties of "Cement" are provided in the template, and the extent of hydration can only be controlled by setting the value of ReactExtent for the "Cement" material.

Regarding Reaction Extents for constituents and materials. If you have a different idea about reaction extents/degrees (assuming the full hydration extent 1 for the whole recipe), feel free to change them. Reaction extents are calculated top-down, which means that if the recipe-level value is set to 0.1 then all reaction extents of Materials will be multiplied by 0.1. Likewise, if a Material reaction extent value is less than 1 then all values for constituents of this materials will be multiplied by this value.

The resulting ReactExtent values on all levels will be shown in the Residual part of the Result (the ReactExtent values in the Input recipe remain as they were initially entered). The values of Reaction Extent are used for spliting the elemental composition of a Constitutent or Material to a residual part and to add the rest to the equilibrating part. Note that, without regard of what value was assigned to fluid constituents and materials (water, air), they will be treated as having ReactExtent equal to 1 in all cases.

Controls using the input w/b ("W/B_ratio")

The water/binder mass ratio (w/b) is one of the main controls on cement paste preparation and cement hydration. Cement recipes are usually set in terms of w/b (sometimes w/c water-cement) ratio; addition of SCMs, activators, etc.; and the initial temperature.

In CemGEMS, it is assumed that three materials are used regarding the w/b ratio: “Cement”, “SCM”, and “Water”. The WBmassRatio (w/b or wb, "W/B_ratio") value should be in the interval {0.1; 10000}. The "binder" includes the Portland cement (clinker) together with any SCMs or activators, but excludes the filling in mortar or concrete (sand, pebbles) and any constituents in the "Salt" or "Other" materials.

If masses (Quantity) of Cement, SCM and Water materials are specified in the recipe by positive values then, upon "Equilibrate Recipe", the w/b value will be automatically computed or corrected, and will appear in the inputRecipes widget. However, CemGEMS lets the user to enter the desired "W/B_ratio" value and let the masses of Water or Cement and/or SCM materials be adjusted automatically upon "Equilibrate". Several cases are possible (assuming that "Cement" is the first material in the recipe, "SCM" is the second one, and "Water" is the third material).

In the recipe input, the masses (Quantity) of all of the above mentioned materials, the total recipe Quantity, and the w/b ratio can be all set to non-zero values; some values can be inconsistent with the others; or any or all values may be zeros. Note that setting of all mentioned Quantities in %mass or %vol is not allowed (only mass or amount units are possible). The GEMSW back-end code uses the following prioritization to analyze possible cases:

  • WBmassRatio (wb): priority 1
  • Cement Quantity (cq): priority 2
  • SCM Quantity (sq): priority 3
  • Salts (other) Quantity (oq): priority 3
  • Water Quantity (wq): priority 4
  • Recipe Quantity (rq): priority 5

This prioritization resolves into the following cases.

If all quantities and w/b ratio are entered as positive values, then (with necessary units converisons)

  • wq = wb * (cq + sq)
  • rq = wq + cq + sq + oq

This also includes cases when initially wq = 0 and/or rq = 0.

If wb = 0 and (cq > 0 or sq > 0) and wq > 0 then

  • wb = wq / (cq + sq)
  • rq = wq + cq + sq + oq

If wb = 0 and (cq > 0 or sq > 0) and wq = 0 and rq > 0 then

  • wq = rq - oq - cq - sq
  • wb = wq / (cq + sq)

If wb = 0 and cq = 0 and sq = 0 and wq = 0 and rq > 0 then wb = 0.5 is assumed, and

  • wq = rq/3
  • cq = rq*2/3
  • rq = wq + cq + sq + oq
  • wb = 0.5

Finally, if all values wb, cq, sq, wq and rq are zeros,

  • cq = 100 g
  • wb = 0.5
  • wq = cq * wb
  • rq = wq + cq + sq + oq

This algorithm allows the user to change w/b ratio with automatic adjustment of wq, rq while keeping cq and sq values as given, if possible.

For example, if Cement Quantity is given as 0.09 kg and SCM Quantity as 10 g then any adjustment of w/b will retain these values and change the Water Quantity and the recipe total Quantity.


Last update: June 8, 2020