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Questions and Answers
What type of aggregates should range in size to give a more workable mix?
What type of aggregates should range in size to give a more workable mix?
- Rounded aggregates (correct)
- Fine aggregates
- Coarse aggregates
- Crushed aggregates
Which type of aggregates make concrete stronger but harder to place, work, and compact?
Which type of aggregates make concrete stronger but harder to place, work, and compact?
- Coarse aggregates (correct)
- Fine aggregates
- Crushed aggregates
- Rounded aggregates
What percentage of the concrete mixture do well-graded aggregates generally account for?
What percentage of the concrete mixture do well-graded aggregates generally account for?
- 40% - 45%
- 20% - 25%
- 30% - 35% (correct)
- 10% - 15%
What is the primary reason to avoid using sea water in concrete mixtures?
What is the primary reason to avoid using sea water in concrete mixtures?
Which type of admixture improves workability, density, and long-term strength of concrete?
Which type of admixture improves workability, density, and long-term strength of concrete?
What do poorly graded aggregates result in?
What do poorly graded aggregates result in?
What is the primary function of water reducers in concrete mixtures?
What is the primary function of water reducers in concrete mixtures?
'Harder to place, work, and compact' refers to which type of aggregates?
'Harder to place, work, and compact' refers to which type of aggregates?
Which admixture should be used if you want to speed up the setting process?
Which admixture should be used if you want to speed up the setting process?
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Study Notes
Concrete Defects
- Crazing: fine cracks across the surface, caused by rapid drying conditions and dust
- Dusting: surface deterioration due to water bleeding, especially during rain and improper curing
- Rain Damage: surface erosion or small dents caused by rainwater running across the concrete surface
- Spalling: chipping or breaking of concrete, leaving an elongated cavity, due to poor compaction and external heavy loads
- Efflorescence: white crystalline deposits on the surface, caused by chemical reactions with salt content in cement
- Honeycombing: coarse aggregates appearing on the surface, caused by excess bleeding and poor concrete mix
- Blistering: formation of air-filled or water-filled bubbles, caused by access to water or air entering the concrete
Cracking Concrete
- Presetting Cracks: cracks that occur before concrete hardens, including:
- Plastic Settlement Cracks: caused by revibration of concrete in its plastic state
- Plastic Shrinkage Cracks: caused by hot days or low humidity
- Formwork Movement Cracks: caused by inadequate formwork strength
- Thermal Shock Cracks: caused by using warm water
- Hardened Cracks: little can be done with cracks after hardening, but can be covered or reinforced with structural members
- Fiber Saturation Point: the point at which cell cavities are empty but cell walls are full of water, approximately 28% moisture content
Wood Performance
- Wood performance depends on various characteristics, including:
- Strength
- Stiffness
- Hardness
- Finish Retention
- Treatability with Preservatives
- Resistance to:
- Shrinkage and swelling
- Checking
- Decay
- Color changes
- Warping
- Weathering
- Photodegradation
- Insect attack
Wood Deterioration
- Deterioration refers to the loss of ability of a wood product to serve its intended purpose
- Causes of wood deterioration include:
- Exposure to light, leading to surface erosion or photodegradation
- Exposure to moisture and heat cycles
- Changes in moisture content
- Attack by insects and decay fungi
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