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Questions and Answers
What is an atom?
Most atoms are what?
What is electron octet?
Ionic bonds are formed:
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Concrete and other brittle materials are mostly based on:
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The concept of the 'sea of electrons' is valid for:
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In solids, the molecules:
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Elastic deformation can be defined as:
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On a molecular level:
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Hooke's Law states that:
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Which cement phase would cause flash set after mixing with water if gypsum would not be added?
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Which Portland cement phase is responsible for the long-term strength gain?
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Plastic shrinkage is:
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Lowering the water-to-cement ratio will generally:
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Lowering the water-to-cement ratio will generally:
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The typical mixing duration of concrete in industrial pan mixes is:
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The maximum temperature of concrete during hydration is:
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Study Notes
Atomic Structure
- Atoms are the smallest building blocks of elements.
- Most atoms are nonmetals.
- The electron octet rule describes the tendency of atoms to have eight electrons in their outermost shell (valence shell) for stability.
Chemical Bonding
- Ionic bonds form between two ions with opposite charges.
- Covalent bonds involve the sharing of electrons between atoms.
- Metallic bonds involve the sharing of electrons in a "sea of electrons" that delocalizes between metal atoms.
Materials Science
- Concrete and brittle materials are primarily held together by ionic bonds.
- The "sea of electrons" concept is relevant to metallic bonding.
Material Behavior
- In solids, molecules can vibrate but cannot move freely.
- Elastic deformation is reversible, meaning materials return to their original shape after the removal of force.
- Pure compression can lead to greater repulsion forces between atoms, preventing complete failure.
- Hooke's Law states that for small deformations, displacement is proportional to the applied load.
Cement Chemistry
- Tricalcium aluminate (C3A) is a highly reactive cement phase that can cause flash set in concrete, leading to rapid hardening.
- Belite (C2S) is the phase responsible for long-term strength gain in Portland cement due to its slower reaction with water.
Concrete Shrinkage
- Plastic shrinkage is a process that causes the shrinking and cracking of freshly cast concrete due to moisture loss within the first few hours.
- This shrinkage can lead to clay-like cracking.
Concrete Properties
- Lowering the water-to-cement ratio generally increases compressive strength and also reduces the penetration of harmful substances into the concrete's microstructure.
- Typical concrete mixing duration in industrial pan mixes is 1-3 minutes.
- Optimal temperature for concrete hydration is below 25 degrees Celsius.
- High temperatures (above 25 degrees Celsius) can lead to accelerated setting times, reduced strength, and increased risk of thermal cracking.
- Secondary cementitious materials can replace part of the Portland cement in concrete mixes to manage hydration heat.
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Description
Explore the fundamentals of atomic structure, chemical bonding, and material behavior in this quiz. Understand the differences between ionic, covalent, and metallic bonds, as well as the principles governing material stability and elasticity. Test your knowledge on the electron octet rule and Hooke's Law.
