Blend up to four stockpiles and check the mix against the BC grading limits.
Blending of Aggregates: Bituminous Concrete (BC): Free Online Tool
Blending of aggregates means combining several stockpiles, such as 40 mm, 20 mm, 10 mm and stone dust, in proportions that give a gradation inside the specified band. Getting this right is essential for a bituminous concrete surfacing. A mix outside the band can cause segregation, poor strength or poor workability.
This calculator blends up to four materials, A to D. You enter each stockpile's percentage passing on the listed sieves and the proportion of each material, which must add up to 100 %. It shows the blended gradation against the limits sieve by sieve, marked OK or not OK. There is also a button that suggests proportions in 1 % steps, targeting the middle of the limits. Site engineers, lab technicians and students use it to avoid trial and error.
When to use this calculator
Use it when you have sieve analysis results for your stockpiles and need to decide in what ratio to feed them for Bituminous Concrete (BC). It is useful in the laboratory during job mix formula trials, at the plant when stockpile gradations change, and for checking whether a single material already meets the limits (put 100 % on A). It also helps students understand how each fraction shifts the combined curve. Whenever the sieve results of a stockpile change, enter the new values and check the blend again.
How to use the Blending of Aggregates: Bituminous Concrete (BC)
- Open the calculator above on your phone, tablet or computer. Nothing needs to be installed and no sign-up is required.
- Pick the option you need from the drop-down list (Grading 1 (19 mm nominal size); Grading 2 (13.2 mm nominal size)).
- Enter your values in the input boxes: Grading, Sieve (mm), Max, Sieve (mm), Material A, Material B, Material C, Material D. The boxes already hold sample values, so overwrite them with your own.
- Press Calculate. The result appears straight away under the button.
- Change any value and press Calculate again to compare options. Press Reset to go back to the sample values.
- Check the result against your drawings, project specification and local code before you order material or approve work.
How the calculation works
Each blended percentage passing is the weighted sum of the stockpiles: blend = sum of (proportion x percentage passing) / 100 for every sieve. Proportions are percentages by weight and must add up to 100. The blend is compared with the minimum and maximum of each sieve and marked OK or not. Limits are from MoRTH Table 500-17, Grading 1 and Grading 2. Default selection: Grading 1 (19 mm nominal size), with Grading 2 (13.2 mm nominal size) as the other option. Sieves: 26.5, 19, 13.2, 9.5, 4.75, 2.36, 1.18, 0.6, 0.3, 0.15 and 0.075 mm. The sample gradations are only an example; overwrite them with your own sieve results.
Worked example
When you open the page the calculator is filled with sample values. Pressing Calculate with those values gives the result below, which you can use to check that you are reading the output correctly.
| Proportions used | |
|---|---|
| Material A | 25.0 % |
| Material B | 25.0 % |
| Material C | 25.0 % |
| Material D | 25.0 % |
| Blend check | |
| Result | Within the limits |
Tips and common mistakes
- The grading limits are editable defaults. Confirm them against your project specification and edit the limit boxes if your contract is different.
- Enter percentage passing for every sieve of each stockpile from your own sieve analysis. The sample gradations are only an example and must be overwritten.
- Make sure proportions add up to exactly 100 %. Leave unused materials blank, and put 100 % on A when you use a single material.
- Treat the suggested proportions as a starting point. The search uses 1 % steps and targets the middle of the limits, so verify it in trials.
- Sample stockpiles correctly and repeat sieve analysis regularly, because handling and segregation change gradation and therefore the blend actually produced.
Frequently asked questions
Are the grading limits in this calculator final?
No. They are editable defaults. You must confirm them against your project specification or contract and edit them if they differ. The calculator checks only against the numbers shown in the limit boxes.
What does the Suggest best proportions button do?
It searches combinations of the materials in 1 % steps and picks the mix closest to the middle of the limits. It is a guide only, so confirm it by trials and check practicality.
Can I blend fewer than four materials?
Yes. Leave unused materials blank and give them no proportion. For a single stockpile, enter its gradation under material A and set the proportion of A to 100 %.
Why does it say the blend is outside the limits?
One or more sieves have a blended percentage passing below the minimum or above the maximum. Look at the sieve marked not OK, and change the proportions or the material that controls that fraction.
Are the sample gradations real data?
No. They are only an example, so you can see how the tool works. Replace them with your own sieve analysis results before using the answer for any decision.
Important note
This tool gives estimates for planning, study and quick checks. It does not replace design by a qualified engineer, site-specific testing, or the requirements of your project specification and local building code. Always confirm final quantities, test results and acceptance limits with the responsible engineer before using them for construction or payment.
