Surface Index of Aggregates
Surface index of aggregates is another way to represent the specific surface of aggregate. This method was suggested by Murdock. Murdock provided some empirical numbers to represent the specific surface of different aggregates grading (as shown in the table below).
Surface Index Values for Different Aggregate Grading
| Sieve Size Within Which Particles Lie | Surface Index For Particles Within Sieve Size Indicated |
| 80 mm to 40 mm | -2.5 |
| 40 mm to 20 mm | -2 |
| 20 mm to 10 mm | -1 |
| 10 mm to 4.75 mm | 1 |
| 4.75 mm to 2.36 mm | 4 |
| 2.36 mm to 1.18 mm | 7 |
| 1.18 mm to 600 micron | 9 |
| 600 micron to 300 micron | 9 |
| 300 micron to 150 micron | 7 |
| < 150 micron | 2 |
From the above table it is clear that aggregate larger than 10 mm has less surface index value, and the value goes on increasing for aggregates within range 10 mm to 300 micron and surface index value starts to decrease with decrease in aggregate size.
Are there any studies on how to calculate the finished surface area of an exposed aggregate wall with relation to coatings application of either Latex or Pigmented Sealer?