HOW TO INSPECT PHYSICAL CHARACTERISTICS OF AGGREGATE USED IN CONCRETE?

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.

  1. Name of parent rock & Group name
  2. Particle Shape
  3. 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.

Angular aggregate
Angular aggregate
Flaky aggregate and Elongated aggregate
Flaky aggregate and Elongated aggregate
Irregular aggregate
Irregular aggregate
Rounded aggregate (gravel)
Rounded aggregate (gravel)
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

 

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