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
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
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.
Granite, Granophyre, Diorite, Syenite
Gabbro, Norite, Peridotite
Rhyolite, Trachyte, Felsite
Sandstone, Quartzite, Grit
Ganulite & Gneiss Group
Ganite gneiss, Amphibolie, Granulite
Marble, Crystalline limestone
2. Particle Shape
Shape of the aggregate is an important characteristic of aggregate, since it affects the following property of concrete.
Aggregates are available in many different shapes. To know which shape the aggregate conforms with, use the following table.
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
Possessing well defined edges formed at the intersection of roughly planer faces
Crushed rocks of all types
Thickness is small relative to the width and/or length
Length is considerably larger than the other two dimensions
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.
Having the surface made shiny and nonporous
Water worn or smooth due to fracture of laminated or fine grained rock
Gravel, chert, slate, marble
Fracture showing more or less rounded grains
Rough fracture or fine or medium grained rocks containing no easily visible crystalline constituents