Idea Transcript
Manual for the Excel spreadsheet
Version 1.0 2013
IN PARTNERSHIP WITH:
WITH THE SUPPORT OF:
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TABLE OF CONTENTS Software introduction ................................................................................................................................................................ 6 Software structure ..................................................................................................................................................................... 7 Concrete mixture – step by step ................................................................................................................................................ 8 1 – Input material properties ............................................................................................................................................... 10 Cements and additions .................................................................................................................................................... 10 Fine and coarse aggregates ............................................................................................................................................. 11 2 – Demands of the mixture ................................................................................................................................................ 11 3 – Calculation...................................................................................................................................................................... 13 Inert structure ................................................................................................................................................................. 13 Strength model ................................................................................................................................................................ 15 Water demand ................................................................................................................................................................ 16 4 – Results concrete mixture ............................................................................................................................................... 18 Adjust the mixture ........................................................................................................................................................... 18 Save the mixture.............................................................................................................................................................. 20 5 – Optimization................................................................................................................................................................... 20
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SOFTWARE INTRODUCTION The Excel tool Mix Design is an adapted version of the existing software Mix Design – Mix Proportioning (March 2009) with the purpose of generating and comparing different concrete mixtures. The managing of materials and mix design is improved and the aim was a better user-friendly interface. The section mix proportioning is not implemented. The software gives the opportunity to create a limited material database that can be used to generate a concrete mixture. The mix design is based on several models, including grading curves and Dewar’s minimum voids ratio theory. Mix Design is compatible with Microsoft Excel 2010 and 2013 (VBA supported). The macro’s have to be enabled. Compatibility with other versions of Microsoft Excel or open source spreadsheets is not guaranteed.
SOFTWARE STRUCTURE
Figure 1 Software structure architecture
CONCRETE MIXTURE – STEP BY STEP Extract the .zip file and save all files (manual.pdf, MixDesign_v1.0.xlm and MixDesignicon) in the same folder. Then open the Excel file: MixDesign_v1.0.xlm. Make sure the macro’s are enabled, otherwise the software will not work.
Figure 2 Welcome screen
A welcome screen appears after opening the excel file. Two options are possible: Create a new project
The spreadsheet initializes by erasing all values in the worksheet Concrete mixture. Material properties, summary, saved ideal grading curves and strength models are retained.
Continue previous project
Opens the last saved project
For more information, open the manual by clicking on Read manual on the right side of the welcome screen. Make sure the manual is saved in the same folder as the Excel file. A step-by-step procedure explains how the excel tool Mix Design can be used. First a print screen gives you a quick view of the procedure.
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1 2
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4 5 Check requirements after calculations
Figure 3 Quick view of the procedure
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1 – INPUT MATERIAL PROPERTIES At the top of the worksheet Concrete Mixture, six material buttons linked to material databases are situated. Click on the material you want to input or change.
Figure 3 Material buttons
The corresponding worksheet will open. For every material there is a possibility to store maximum five different types. The yellow and red cells indicate the specific values related to the material. The red ones are obliged and they have to be filled in manually. After filling in a sieve set and the cumulative sieved aggregate (CSA), press the button Renew to generate dependent material properties of all inputted materials. The grading curves are graphically displayed on the right side of the table. Also a histogram of the sieved aggregates gives more information about the distribution of the particles. Remark If inconsistencies occur, e.g. sieve set is not sorted in ascending order or non-numeric values, a pop-up window will appear. Correct the error en press the renew-button again.
CEMENTS AND ADDITIONS Essential to continue:
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Name Real density Water content at standard consistency Sieve set (or Blaine value + Kf )
Explanation of the parameters: Real density
= overall particle volume, including the pores occupied by air or water (RD) (= korrelvolumieke massa = werkelijke volumemassa = masse réelle)
Water content
= water content of the paste at standard consistence in the Vicat test, calculated as a percentage of the mass of cement (= water demand for binding)
Air content
= air content in the paste [%]
Blaine value
= measure of fineness [m²/kg]
Kf
= constant typically 12 to 15 (14,4 from UK data; 12,2 from German data)
Mean size = Kf / (RD * Blaine)
k-value add
= k-value linked to a specific addition which will be used in the mixture. A table of values can be found on the right side of the grading curve graph in the worksheet Additions.
Max add/cement
= proportion of the addition/cement. Values can also be found in the same table.
Remark If various additions are used, it is recommended to store a new cement for each addition with the corresponding values. E.g. Cement 1 = CEMI/42.5 – fly ash (k = 0.2 and max add/cem = 0.33) and Cement 2 = CEMI/42.5 – slag (k = 0.9 and max add/cem = 0.45)
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FINE AND COARSE AGGREGATES Essential to continue:
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Name Real density Loose bulk density Sieve set
Press the button Back to return to the main page. Repeat this procedure for every material to generate a complete material database.
Figure 4 Material properties - Fine aggregates
2 – DEMANDS OF THE MIXTURE After inputting the material properties, now the concrete requirements may be imposed by clicking on the button Demands of the mixture. A userform will open.
Figure 5 Demands of the mixture
The requirements are mainly based on the Belgian Standard NBN B 15-001 (2012) and secondary on the European standard EN 206-1:2000. For the environment class, table F.3 and table F.1 from NBN B 15-001 (2012) are used. The exposure classes are linked corresponding table F.2 and F.1 of the same Belgian standard.
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Figure 6 Demands of the mixture
After pressing Process, the possible concrete requirements linked to the selected environment or exposure classes are displayed. Choose the one that fits the demands and press Choose. Only one choice can be made. Also the language (Dutch or French) for the annotations corresponding the selected demands need to be chosen.
Figure 7 Demands of the mixture
The requirements are now displayed on the main screen and linked to the control cells (see page 19). Here, only three cells can be changed manually, namely the entrapped air, slump and total air. The value for entrapped air is standard 1,5 % and for the slump the average value of the chosen consistence class is displayed.
Figure 8 Overview - demands of the mixture
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3 – CALCULATION Now the mix design may begin. By clicking on Material selection different cements, additions, fine and coarse aggregates, admixtures and water can be chosen. Only aggregates from the databases with a valid name are assumed. A maximum of three materials can be selected. For cement and additions, the limit is also three materials in total. E.g. two cements and one addition or one cement and two additions. Start choosing a material in the left box and select if necessary more materials by using the two other boxes one by one moving to the right.
Figure 9 Material selection
Figure 10 Material selection
Press the OK button to start processing the mixture. This may take a few seconds. The last material selection is saved so it’s easy to change one or several materials during modeling. After processing, the names of the chosen materials appear on the main screen.
INERT STRUCTURE To define the inert structure, two methods can be used: ideal grading curves and minimum voids ratio (Dewar-model). Select the option button of your choice on the left side of the inert structure frame and press OK. Dewar:
after clicking the OK button, the software will calculate automatically the material proportions with the least voids ratio based on the theory of Dewar.
Grading curve:
a new window appears wherein the maximum aggregate size can be filled in and an existing ideal grading curve can be chosen. It’s also possible to enter a new ideal grading curve. When activating this option and after pressing OK, a new worksheet will open.
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Figure 11 Select an ideal grading curve
Enter a new ideal grading curve: The new ideal grading curve can be filled in manually in the yellow cells or with the help of the buttons on the right of the worksheet Grading curves. A graphical visualization is given on the right side of the table. Based on the maximal aggregate diameter, ABC-curves are plotted to give a guideline to create the new ideal grading curve. To complete, press the large button with the arrow to interpolate the values into the standard sieve set. On top of the worksheet, four buttons are situated: Import, Save, Clear and Back. Back:
Go back to the main screen Concrete mixture (no actions are undertaken, the grading curve is not used).
Import:
Imports the grading curve into the method of the least squares and the program automatically returns to the main screen where the material proportions are calculated.
Save:
Save the new grading curve and give it a name. The values are saved next to the last ideal grading curve. From now on, it’s possible to select this curve when opening the user form Grading Curve.
Remark The ideal grading curve is not imported in the least squares worksheet, if needed, press Import.
Clear:
Erases all saved ideal grading curves, excluding Füller
Interpolates the new ideal grading curve.
Figure 12 New ideal grading curve
After the proportions have been calculated, it’s possible to use them immediately in the concrete mixture or they can be modified in the second column Definite volume %. The inert mixture is visualized in a graph on the right side of the inert structure frame. When changing the proportions, the curve instantly changes corresponding to the new values. By activating the checkbox Show ABC-curves, these ideal curves associated with the specified diameter appear in the graph.
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Figure 13 Example of an inert structure
It’s also possible to fill in the proportions manually in the column Definite volume %, without using ideal grading curves or the Dewar-model. In the lower right corner, the reference maximum aggregate diameter and the standard deviation of the initial and definite mixture are calculated. These values give the opportunity to criticize the coarse aggregate choice and the accuracy of the inert structure mix. σ
= standard deviation [N/mm²] ∑
=√
(
)
If reference Dmax is smaller than the upper nominal aggregate size, the box will turn green. In the other case, it will turn orange to indicate there might be an inconsistency between the demands and the selected coarse aggregate. Press the button Use definite to confirm the proportions of the inert structure. This is only possible if numerical values are filled in and the summation of the proportions is 100%. With the last button at the bottom of the inert structure frame, you can save a new defined mixture curve as a grading curve. In this way it’s possible to compare specific concrete recipes used in the concrete batch plants.
STRENGTH MODEL To generate the mean pressure strength, fcm, different models can be used by clicking on the button Strength model. The validation of the strength model is linked to a specific test specimen. To match the correct value of fck to the strength model, choose also a test specimen or enter a min fck corresponding the chosen strength model.
Figure 14 Pressure strength models
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The parameters can be changed according to the mixture. Click the button Change parameters to open the worksheet Strength models where several parameters can be saved next to the framed table and copied in the frame when necessary. The mean compressive strength is used to determine the characteristic compressive strength fck according to below formula:
With k σ
= factor corresponding to the wanted part of the theoretical compressive strength distribution = 1,64 [-] = standard deviation [N/mm²] ∑
=√
(
)
WATER DEMAND The last step to create the concrete mixture is the determination of the water demand. Again, there are two possibilities: -
Fixed water amount Dewar model (minimum voids ratio)
Remark Before selecting one of the option buttons, it can be useful to check the frame Admixtures and fill in the rate and factor if necessary. Remark When different cement types or additions are used, make sure the proportions in the last column (Dewar volume %) of the concrete mixture and the k-values are correct. If not, change these values before selecting one of the option buttons for water demand. If these values are changed after activating an option button, it’s necessary to click the button Renew in the water demand frame to recalculate the mixture. Fixed water amount When activating the option button Fixed water amount, a textbox appears. An amount of water can be filled in and the mixture is automatically calculated. In this situation it’s also possible to enter a fixed amount of admixtures in the last column of the Admixture frame. Dewar model – voids ratio When activating the option button Dewar, the program calculates the water demand corresponding to the proportions of the definite inert structure and the total cement and addition quantity of the concrete mixture specified in the text box. The results can be more accurate when raising the accuracy or make the step of the cohesion factor smaller. Beware that these actions can result in an infinite loop due to the necessity of rounding numbers which makes it impossible to generate a concrete mixture. Good values can be realized with an accuracy of 3 and a cohesion step of 0,01. Some other values are mentioned to give an idea of the properties of the mixture: -
Nx nx Ux CJ
= cement/mortar = mortar/concrete = voids ratio of the concrete = cohesion factor
An ideal Dewar mixture has a cohesion factor of 1. If higher, this indicates a more sandy mixture and a smaller value indicates a coarse mixture.
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Figure 15 Properties of Dewar
After selecting one of the option buttons, the water absorption of the aggregates is calculated. This is only possible if the water absorption of the aggregates is filled in in the material database. If not, a fixed water absorption can be applied. At the bottom of this frame, the total water demand due to water absorption of the aggregates and the one calculated by Dewar is given. Only the water demand calculated by Dewar is used to calculate the water-cement ratio and the design of the mixture.
Figure 16 Water absorption aggregates
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4 – RESULTS CONCRETE MIXTURE Now the concrete mixture is calculated and displayed in a table. The overview is subdivided in three frames: -
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Inert structure o Volume [%] linked to the last column (Dewar volume %) o Mass [kg/m³] Solid structure o Buttons to change the mixture o Volume [%] o Mass [kg/m³] Concrete mixture o Volume [%] o Mass [kg/m³] o Cost [€/m³] o Chloride [kg/m³] o Alkali [kg/m³] o Relative density [-]
For each column, the summation is made underneath the table.
ADJUST THE MIXTURE The proportions of the solid structure can be changed by clicking on the arrow buttons on the left side. The upper button changes the total cement percentage with 0,1 % while keeping the inert structure constant. After every click, the program recalculates the mixture and the new values are shown. In some cases, due to round off, the summation deviate by 0,1 % of 100 %. When clicking the smaller buttons, it’s possible to add more or less of this specific material also in steps of 0,1%. Notice the summation cell will turn red until the total amount of the proportions is 1. Only in that case, the program will recalculate the mixture. Inert structure = constant
Change the proportion of each material
Figure 17 Overview concrete mixture
Has to be 1.000 ± 0.001
Below the table, the grading curves of the chosen cement and additions, fine and coarse aggregates, inert and solid structure and the ideal grading curve of Bolomey are visualized in a graph. Changing the coefficient of Bolomey (A) and Dmax is immediately visible in the graph. Also varying the solid mixture will change the graph instantly.
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Figure 18 Bolomey, fine particles and standard deviation of the inert structure
Associated with the curve of Bolomey, the amount of fine particles is calculated and visualized in a frame. This table indicates if there are too little or too much fine particles in the mixture and can be changed by adding or removing specific aggregates. Because the inert structure can be changed while varying the solid structure, a new standard deviation of the inert structure is calculated. As part of step 3 – calculation, some values need to be inspected: fcm w/c cement content chloride content alkali content When these values comply with the demands of the mixture, the cells will turn green, otherwise they will be red. ( ∑
)
Mass of cements (Dewar)
Mass of cements + additions = cem + ∑
= requirement linked to environment class
Figure 19 Control cells => check requirements
= requirement linked to environment class
= cmin – k * (cmin -200)
= requirement linked to environment class (= cmin)
If an addition is added, the water/cement ratio and cement amount are automatically adapted and two new demands need to be checked out: a new minimum cement content and a maximum addition/cement ratio. Only the k-value can be changed. The mass and reduced mass are calculated automatically. Remark The purposed k-factor is only valid when using standard cements as mentioned in the Belgian standard. These factor has to be filled in in the material database Cement. A table with guide values is displayed in the worksheet Additions (on the right sight of the grading curve). Every other cement or addition needs special attention, especially when combining several additions and cements. Remark When more addition is added then permitted, the k-value turns 0. Remark The new minimum cement content is standard calculated with the formula c min – k (cmin – 200). This is only valid when using fly ash or silica fume. When blast furnace slag is used, the formula has to be c min – k (cmin – 175), but this is not taken into account.
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SAVE THE MIXTURE After a concrete mixture is completed, the properties can be saved in the worksheet Summary by clicking on the button Save mixture. First give a reference name and press OK. The summary will open and all previous mixtures appear, including the new one.
Figure 20 Results of the concrete mixture
It’s also possible to save a print screen of the mixture as a pdf file by clicking on the button Save as pdf. This file will be stored in the same folder as the Excel file. Click on the button Go to summary to open the overview of the saved mixes. Underneath the table, different graphs are shown. They can be used to compare or optimize the mixtures. The boundaries are related to the most recent requirements of the mixture, displayed in the first frame of the worksheet Concrete mixture.
Selected mixture
Figure 21 Summary
On top of this worksheet, three buttons can be found: Clear all mixtures Clear selected mixtures Back
Erase all saved mixtures Only mixtures with a selected checkbox will be erased Return to the main page Concrete mixture
5 – OPTIMIZATION Additionally, it is possible to optimize a concrete mixture on the basis of two methods. The first one is linked to the minimum voids ratio model by Dewar while the other one visualizes the optimum of the saved concrete mixtures. These two methods are useful to draw conclusions, but keep in mind it is important to interpret the results properly.
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Optimization of water demand (minimum voids ratio – Dewar)
Figure 22 Optimization of water demand
Five different graphs are visualized: Free water versus cement Fine aggregates versus cement Density versus cement w/c versus cement cost versus cement These graphs are linked to a table based on the theory of minimum voids ratio by Dewar. Click on the button Show table to have a look. In this table, the material proportions vary as function of the minimum voids ratio. E.g. the cement amount with a minimum water content can be found in the graph and table. This table is linked to the cohesion factor displayed in the frame Water demand. Keep in mind that the inert structure is not fixed. Optimization of summary
Figure 23 Optimization of the summary
A second method gives more flexibility but is also more difficult to interpret. Seven properties are taken into account to optimize a concrete mix design: -
cement content fine aggregates content coarse aggregates content water content density strength cost
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Depending on the purpose of the optimization, different weight factors can be given to the properties. The summation of the weight factors has to be 1 (= 100%). Now a general purpose function for all combinations can be calculated:
∑
With:
ηi = weight factor ∑ Φi = individual purpose function (linear interpolation between minimum and maximum value)
The better the concrete mixture fulfills the demands, the higher the general function will be. A graph visualizes these results. It is obvious that this method requires insight into the matter to make good and accurate comparisons.