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EGB270 (completed)
Concrete Aggregates
| Question | Answer |
|---|---|
| A Civil Engineering material is any material used in the construction industry. Examples: | Concrete, cement, masonry, steel, soil, stones, aggregates, wood, plastics, and asphalt. |
| Aggregates are defined as: | Inert, granular, inorganic material, which normally consist of stone or stone-like solids |
| Types of Aggregates based on source | - Natural: rock or stone; - Artificial: - Industrial waste products; - Manufactured aggregates; and - Reused waste materials |
| Types of Aggregates based on size | - Coarse: – Retained on 4.75𝑚𝑚 sieve. - Fine: – Passing through 4.75𝑚𝑚 sieve and retained on 150𝜇𝑚 sieve. - Silt and clay: – Passing through the 75𝜇𝑚 sieve. |
| Aggregates can also be classified based on... | - Geology; - Physical characteristics; - Chemistry; and - Hardness |
| Geological Classification of Aggregates: | Igneous Sedimentary Metamorphic |
| Igneous | Formation: Cooling from a liquid phase Examples: Granite, basalt, rhyolite, pumice |
| Sedimentary | Formation: Deposition by mechanical or chemical means Examples: Sandstone, shale, limestone, breccia |
| Metamorphic | Formation: Transformation of existing rock by heat and pressure Examples: Marble, gneiss, quartzite, phyllite |
| Physical Characteristics of Aggregates: | • Shape and Texture; • Appearance; • Size gradation; • Moisture content; • Strength; • Density; • Toughness; • Abrasion resistance; • Freeze-thaw resistance; • Soundness; and • Alkali-silica reactivity |
| Shape of Coarse Aggregate: | - Ideal shape is close to spherical; - Rounded is best for concrete (workability); - Angular is best for asphalt and high strength concretes (mechanical interlock); |
| Shape of Coarse Aggregate (2): | - Minimal flaky/elongated agg (<𝟏𝟓%) otherwise workability is decreased; - A high proportion of flaky/elongated particles in the agg could indicate weak rock |
| Rough agg surface creates a better bond with... | cement paste, which increases strength, but workability is decreased; |
| The bond between a rough agg surface and cement paste is thought to be a combination of... | mechanical interactions and chemical bonds between the paste and some minerals in the aggregate |
| Higher roughness means more... | surface contact between the agg and the cement paste, which means a better mechanical and chemical bond ∴ higher strength |
| Maximum Aggregate Size | • Smallest sieve opening through which the entire sample passes; • Influences paste requirement; |
| Maximum Aggregate Size (2) | • Must be able to fit between formwork, steel reinforcement and minimum cover; and • Large agg size causes higher internal stresses ∴ lower concrete strength |
| Fineness Modulus is an... | index to define the fineness or coarseness of aggregate It represents the average aggregate size in a sample It normally ranges from 2 to 8 |
| Aggregates are... | inert, granular, inorganic material, which normally consist of stone or stone-like solids |
| Types of Aggregates based on source and size: | – Natural: rock or stone & Artificial: Industrial waste products, Manufactured aggregates, and Reused waste materials – Coarse: retained on 4.75𝑚𝑚 sieve, Fine: passing 4.75𝑚𝑚 sieve and retained on 150𝜇𝑚 sieve, and Silt/Clay: passing 75𝜇𝑚 sieve |
| Classification of Aggregates based on geology and physical properties: | – Igneous, Sedimentary and Metamorphic – Shape and texture, Gradation, Moisture content, Specific gravity and Unit weight |
| Summary - Aggregates (Classifying aggregates) – Source: | • Natural, • Artificial |
| Summary - Aggregates (Classifying aggregates) – Geology: | • Igneous, • Sedimentary, and • Metamorphic |
| Summary - Aggregates (Classifying aggregates) – Physical characteristics: | • Shape and texture, • Size gradation, • Moisture state, and • Density |
| Summary - Aggregates - Grading: | – Sieve analysis, and – Grading curves |
| Summary - Aggregates | - Fineness modulus; - Unit weight and specific gravity |
| Summary - Aggregates - Moisture content: | – Absorption capacity – Effective absorption – Surface moisture |
| Course Agg + Water + Cement + Fine Agg | Concrete |
| Coarse Agg => | Stone |
| Water => | Water Reservoir |
| Cement => | (Clay + Limestone) + Heat |
| Fine Agg => | Sand |
| Moisture Content: | the amount of water present in a sample in any specific condition |
| Absorption Capacity: | maximum quantity of water that aggregates can absorb |
| Effective Absorption: | the amount of water required to bring a sample from the air-dry to the saturated-surface-dry state |
| Surface Moisture: | the amount of water on the surface of the aggregate particles |
Created by:
Asher - S
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