While inspecting aggregate for quality control purpose, it is required to describe its physical properties, because physical properties of aggregate have an effect on the property of concrete. The physical properties of aggregate which should be described are given below.
- Name of parent rock & Group name
- Particle Shape
- Surface Texture
Let us see how to describe above mentioned properties of aggregate.
Physical Characteristics of Aggregates
1. Name of Parent Rock & Group Name
All aggregates are produced due to disintegration of rocks. Due to this the property of aggregate is comparable to the property of its parent rock. If we can know the name of parent rock then we can definitely get some facts regarding its strength properties. But this is not the case always. Sometimes the property of aggregate differs completely from its parent rock.
There are 3 primary types of rock on the basis of origin, such as
- Igneous Rock
- Sedimentary Rock
- Metamorphic Rock
To know more about these rock types click here
In order to know the name of parent rock, we can take help of a professional geologist.
After identifying the name of the parent rock, next step is to place it under certain trade group. Some of the trade group names for different type of parent rocks are given below.
| Parent Rock | Trade Group | Example |
| Igneous Rock | Granite Group | Granite, Granophyre, Diorite, Syenite |
| Igneous Rock | Gabbro Group | Gabbro, Norite, Peridotite |
| Igneous Rock | Aplite Group | Aplite, Porphyry |
| Igneous Rock | Dolerite Group | Dolerite, Lamprophyre |
| Igneous Rock | Rhyolite Group | Rhyolite, Trachyte, Felsite |
| Igneous Rock | Basalt Group | Andesite, Basalt |
| Sedimentary Rock | Sandstone Group | Sandstone, Quartzite, Grit |
| Sedimentary Rock | Limestone Group | Limestone, Dolmite |
| Metamorphic Rock | Ganulite & Gneiss Group | Ganite gneiss, Amphibolie, Granulite |
| Metamorphic Rock | Schist Group | Slate, Schist |
| Metamorphic Rock | Marble Group | Marble, Crystalline limestone |
2. Particle Shape
Shape of the aggregate is an important characteristic of aggregate, since it affects the following property of concrete.
- Workability
- Strength
- Cement requirement
Aggregates are available in many different shapes. To know which shape the aggregate conforms with, use the following table.
| Particle Shape | Description | Example |
| Rounded | Fully water worn, or completely shaped by attrition | River or seashore gravels; desert and seashore sand |
| Irregular or partly rounded | Naturally irregular or partly shaped by attrition, having rounded edges | Pit sand & gravel; land or dug flints; cuboid rock |
| Angular | Possessing well defined edges formed at the intersection of roughly planer faces | Crushed rocks of all types |
| Flaky | Thickness is small relative to the width and/or length | Laminated rocks |
| Elongated | Length is considerably larger than the other two dimensions | Crushed rocks |
| Flaky and elongated | Material having the length considerable larger than the width and the width is relatively larger than thickness | Laminated rocks, crushed rocks |
3. Surface Texture
In concrete, the bone between aggregate & cement paste, is largely influenced by the surface texture of aggregate. An aggregate having rough surface texture will have better bond than with a smooth surface.
By making a thorough visual inspection, we can describe its surface texture. Use the following table to describe the aggregate for its surface texture.
| Surface Texture | Description | Example |
| Glassy | Having the surface made shiny and nonporous | Black flint |
| Smooth | Water worn or smooth due to fracture of laminated or fine grained rock | Gravel, chert, slate, marble |
| Granular | Fracture showing more or less rounded grains | Sandstone |
| Rough | Rough fracture or fine or medium grained rocks containing no easily visible crystalline constituents | Basalt, felsites, limestone |
| Crystalline | Containing easily visible crystalline constituents | Granite, gabbro, dolomite |
| Honey comber & porous | With visible pores and cavities | Brick, pumice |