10 Questions
Which type of aggregate exhibits the highest percentage of voids?
Angular Aggregates
What is the primary reason why elongated aggregates are not suitable for high-strength concrete?
Poor interlocking behavior and weak bond strength
What is the characteristic of flaky aggregates?
Least dimension is less than 60% of its mean dimension
Which type of aggregate is obtained by crushing rocks?
Angular Aggregates
What is the term for the size distribution of aggregates?
Grading of aggregates
What is the approximate percentage of total volume of concrete that aggregates make up?
60-75%
Which of the following is NOT a characteristic of rounded aggregates?
Result in the maximum percentage of voids
What is the term for the process of extracting aggregates from underwater sources?
Dredging
Which type of aggregate is formed from crushed concrete, bituminous or demolition debris?
Contrived aggregate
What is the name of the process of breaking down bedrock into smaller particles?
Crushing
Study Notes
Types of Aggregates
- Elongated aggregates: length > 180% of mean dimension, poor interlocking behavior, weak bond strength
- Flaky aggregates: thickness < 60% of mean dimension, poor interlocking behavior, weak bond strength
- Irregular aggregates: partially rounded, result in 35-37% voids, lesser workability, slightly higher bond strength
- Angular aggregates: well-defined edges, formed by crushing rocks, result in 38-45% voids, less workability, stronger aggregate-mortar bond
Classification of Aggregates
- Based on size: fine aggregates, coarse aggregates
- Fine Aggregates: sand and/or crushed stone
- Coarse Aggregates: gravel and crushed stone
Definition of Aggregates
- Mineral particles originating from rocks
- Inert filler materials used in making concrete
- Make up 60-75% of total volume of concrete (normal/ordinary concrete), 90% of asphalt pavements
Aggregate Sources
- Natural Aggregate: sand and gravel mine (pit), quarry (bedrock)
- Contrived Aggregate: recycled products, crushed concrete, bituminous, demolition debris, taconite tailings
Methods of Extraction and Processing
- Underwater Sources: dragline excavation, dredging
- Land Sources: track drills, blasting bedrock, crushers and screens
Classification of Aggregates Based on Shape
- Rounded aggregates: completely shaped by attrition, minimum voids (32-33%), more workability, lesser water-cement ratio
- Irregular or partly rounded aggregates: partly shaped by attrition, available in pit sands and gravel
- Angular aggregates: well-defined edges, formed by crushing rocks
- Flaky aggregates: thickness < 60% of mean dimension
- Elongated aggregate: length > 180% of mean dimension
- Flaky and elongated aggregates: combination of flaky and elongated shapes
Identify and understand the different types of aggregates, including elongated and flaky aggregates, and their effects on concrete strength.
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