Properties of Aggregates and its Values for use in Construction
This article presents information on various properties of aggregates, including bulk density, specific gravity, voids, water absorption, and their corresponding values. These properties are important to consider in the construction industry when selecting and using aggregates for various applications.
Bulk density refers to the weight of the aggregate per unit volume, while specific gravity is the ratio of the density of the aggregate to the density of water. The voids of an aggregate refer to the space between the particles and can affect the workability and strength of concrete. Water absorption, on the other hand, is the amount of water that an aggregate can absorb and can impact the durability of concrete.
It is essential to know the values of these properties to determine the suitability of aggregates for a particular construction project. The selection of aggregates with appropriate properties can affect the strength, durability, and overall performance of concrete structures. Therefore, understanding these properties and their values is crucial for engineers, contractors, and anyone involved in the construction industry.
1. Aggregates: Bulk Density, Specific Gravity and Voids
| Bulk Density | |
| River sand | |
| Fine | 1.44 |
| Medium | 1.52 |
| Coarse | 1.60 |
| Beach or river shingle | 1.60 |
| Broken stone | 1.60 |
| Stone screenings | 1.44 |
| Broken Granite | 1.68 |
| Specific Gravity | |
| Trap | 2.9 |
| Granite | 2.8 |
| Gravel | 2.66 |
| Sand | 2.65 |
| Voids, Percent, Average | |
| River sand | |
| Fine | 43 |
| Coarse | 35 |
| Mixed and moist | 38 |
| Mixed and dry | 30 |
| Broken stone, graded | |
| 25 mm maximum size | 46 |
| 50 mm maximum size | 45 |
| 63 mm maximum size | 41 |
| Stone screenings | 48 |
Note: Above values are indicative only
2. Aggregates: Limiting Values of Mechanical Properties
| Properties | Limiting Values (Percentage) | |
| For Wearing Surfaces | Other Than for Wearing Surfaces | |
| Crushing value | 30 | 45 |
| Impact value | 30 | 45 |
| Abrasion value (Los Angeles) | 30 | 50 |
| Soundness (Average loss of weight after 5 cycles) | When tested with Na2SO4 | When tested with MgSO4 |
| Fine aggregates | 10 | 15 |
| Coarse aggregates | 12 | 18 |
*Source- IS: 383 – 1970
3. Approximate Water Absorption of Aggregates, by Weight
| Average sand | 1.0 percent |
| Pebbles and crushed limestone | 1.0 percent |
| Trap rock and granite | 0.5 percent |
| Porous sandstone | 0.5 percent |
| Very light and porous aggregates may absorb as much as | 25 percent by weight |
Note:
When referring to aggregates, it is observed that as the size of the aggregate increases, the amount of free water it holds decreases. In other words, the coarser the aggregate, the lower the amount of free water it can carry. This means that if one were to compare two aggregates of different sizes, the larger aggregate would have less free water present than the smaller one. It is important to keep in mind that the amount of free water present in an aggregate can have an impact on the properties of the concrete or other materials it is used in. Therefore, choosing the appropriate aggregate size for a particular application is crucial for achieving the desired result.
4. Limits of Deleterious Materials (Percentage by Weight, Maximum)
(Clause 3.2.1 of IS: 383 – 1970
| Deleterious Substances | Fine Aggregates | Coarse Aggregates | ||
| Uncrushed | Crushed | Uncrushed | Crushed | |
| Coal and lignite | 1.00 | 1.00 | 1.00 | 1.00 |
| Clay lumps | 1.00 | 1.00 | 1.00 | 1.00 |
| Materials finer than 75-micron sieve | 2.00 | 15.00 | 3.00 | 3.00 |
| Shale | 1.00 | – | – | – |
| Total of percentages of all deleterious materials ** | 5.00 | 2.00 | 5.00 | 5.00 |
**Mica is excluded.
5. Bulking of Sands for Various Moisture Contents
| Moisture, percent | Percentage bulking in | ||
| Fine sand | Medium sand | Coarse sand | |
| 1 | 16 | 8 | 6 |
| 2 | 26 | 16 | 12 |
| 3 | 32 | 22 | 15 |
| 4 | 36 | 27 | 17 |
| 5 | 38 | 29 | 18 |
| 6 | 37 | 28 | 18 |
| 8 | 35 | 26 | 16 |
| 10 | 32 | 22 | 12 |
| 12 | 28 | 19 | 8 |
| 15 | 22 | 12 | 2 |
| 17 | 18 | 7 | 0 |
| 20 | 9 | 0 | 0 |
| 27 | 0 | 0 | 0 |
6. Surface Water Carried by Aggregates
| Aggregates | Approximate Qty of Surface Water | |
| Percent by mass | Ltr./cu.m | |
| Very wet sand | 7.5 | 120 |
| Moderately wet sand | 5.0 | 80 |
| Moist sand | 2.5 | 40 |
| Moist gravel or crushed rock | 1.25 – 2.5 | 20 – 40 |
Note:
According to Table 10 of the IS: 456-2000, it is stated that as the aggregate size becomes coarser, the amount of water that it can carry will decrease. This means that larger aggregates have less capacity to hold water compared to smaller ones. Therefore, if a construction project requires a certain amount of water in the mix, the appropriate aggregate size must be selected to ensure that the desired water-cement ratio is achieved. Choosing the right aggregate size is essential to ensure that the concrete mix has the desired workability and strength. Hence, it is important to consider the aggregate size carefully to ensure that the final product meets the required specifications.