Introduction Dr Magnus Currie From Scotland, UK MEng Civil Engineering PhD Wind Energy Systems...
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Transcript of Introduction Dr Magnus Currie From Scotland, UK MEng Civil Engineering PhD Wind Energy Systems...
![Page 1: Introduction Dr Magnus Currie From Scotland, UK MEng Civil Engineering PhD Wind Energy Systems (Concrete Monitoring) Class Tutors > Ms Liu and Ms Gau.](https://reader035.fdocuments.net/reader035/viewer/2022081519/56649cf15503460f949c0596/html5/thumbnails/1.jpg)
Introduction
• Dr Magnus Currie• From Scotland, UK• MEng Civil Engineering• PhD Wind Energy Systems (Concrete Monitoring)
• Class Tutors > Ms Liu and Ms Gau
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ENG1010 Resources
• Powerpoints (PPTs) will be uploaded after each lecture
• Tutorials will also be uploaded• Web address >
http://www.uwcentre.ac.cn/sbc/
• There is no textbook for this course• Please take notes in a note book• If you don’t understand something please ask
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ENG1010-Reinforced Concrete Design
Week One – Basic Principles of ConcreteWeek Two – Reinforced Concrete ConstructionWeek Three – Concrete ConsiderationsFinal Day – Exam
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Week 1
1. Introduction to Concrete2. Concrete Design and Properties3. Concrete Chemistry4. Concrete Admixtures5. Properties of Materials
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Tutorial Times
• Monday – ThursdayEnglish 14:30-15:30Chinese 15:40 – 16:40
• FridayEnglish 08:30-09:30Chinese 09:40-10:40
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Lecture 1Introduction to Concrete
Dr Magnus Currie
ENG-1010: Reinforced Concrete Design
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Objectives
• To explain the basic concepts of concrete• To explain the properties of fresh concrete• To explain the properties of hardened concrete
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Concrete
• A mixture of two components
1. Paste (25% - 40%)2. Aggregates (60% – 75%)
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Paste
• Paste compromises of:
1. A binder (such as cement)2. Water3. Air (either entrapped or entrained)4. Other admixtures depending on the mix
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Aggregates
• Compromises a mix of:
1. Fine aggregates (such as sand)2. Coarse aggregates (gravel or crushed stone)
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Making Concrete
• When paste and aggregates are mixed together the particles of aggregates get coated with the paste.
• Because of the chemical reaction of the cement and water the paste hardens and binds the aggregates together to form a rocklike mass called ‘Concrete’
• We will discuss this reaction later
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Volume Distribution
• The volume of each material in concrete depends on the design strength, the use of the concrete and the environment in which it will be used.
• Air and water become trapped inside a concrete element
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Quality of Concrete
• Aggregate requirement• Paste requirement
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Aggregate Requirement
• Aggregates should consist of particles with adequate STRENGTH against compression, impact and abrasion.
• Aggregate particles should have RESISTANCE against aggressive exposure conditions such as highly fluctuating temperature and humidity.
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Aggregate Requirement
• Aggregates should NOT contain deleterious materials such as chloride, sulfates, etc. That will cause deterioration of concrete.
• The size, shape and particle size distribution (gradation), of the aggregates should be such that the least amount of paste is required to fill the spaces between aggregate particles
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Paste Requirements
• Quality of paste greatly affects the quality of the concrete
• Paste should be sufficient enough to completely coat each particle of aggregate and to fill spaces between aggregate particles completely
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Paste Requirements
• The quality of hardened concrete is determined by the amount of water used in relation to the amount of cement.
• This is called the W/C ratio of the paste
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Advantages of reducing the W/C ratio of the paste
• Increase compressive strength and flexural strength
• Lower permeability, thus increased water-tightness and lower absorption
• Increased resistance to weathering• Better bond between successive layers and
between concrete and reinforcement
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Advantages of reducing the W/C ratio of paste
• Less volume change from wetting and drying• Reduced shrinkage cracking tendencies
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Effect of w/c ratio on compressive strength of concrete
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Uses of admixtures to improve the Quality of concrete
• Adjusting setting time or hardening in abnormal conditions of concreting such as cold and hot.
• Reducing water demand• Increasing workability in case of a very low
w/c ratio• Intentionally entrained air in concrete
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Mixing Requirements
• All the ingredients of concrete should be mixed properly so as to achieve a homogenous mixture
• The sequence of charging ingredients into the mixer plays an important part in the uniformity of the finished product
• Size of the batch in relation to the size of the mixer
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Mixing Requirements
• The elapsed time between batching and mixing
• Design, configuration and condition of the mixer drum and blades
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Consolidation Requirements
• Consolidation of the freshly placed concrete removes voids in concrete and improves the quality of concrete as a result of increased density.
• For a highly workable concrete the consolidation should be done by hand rodding (vibration)
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Consolidation Requirements
• For stiffer mixtures having low w/c ratio the consolidation should be done by vibration.
• Vibration sets in motion the particles in freshly mixed concrete, reducing friction between them and thereby increasing the mobility of concrete which helps in removing the voids even at low w/c ratio.
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Consolidation Requirements
• Consolidation by vibration permits the lower w/c ratio which in turn results in improved quality.
• Vibration of highly workable concrete should be avoided as it can cause segregation of the concrete.
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Effect of Consolidation
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Curing requirements
• Curing of a placed and finished concrete is done for maintaining a satisfactory moisture and temperature in concrete for some defined period after placing and finishing, to allow the complete hydration of the cement.
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Curing Requirements
• Following are various methods commonly used for concrete curing:
- Ponding or immersion- Spraying or fogging- Wet covering- Plastic sheets and impervious paper
coverings- Membrane-forming curing compounds- Steam curing
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Advantages of Curing
• More strength and abrasion resistance• More water tightness• Less volumetric changes• More volume stability• More resistance to freezing and thawing and
deicer salts• More durability
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Effect of Curing on Strength
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Properties of freshly mixed concrete
• Workability• Hydration• Setting Time• Hardening
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Workability
• The Slump Test
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Properties of Hardened Concrete
• Strength• Unit Weight• Resistance to freezing and thawing• Permeability and water tightness• Abrasion Resistance• Volume Stability• Control of Cracking
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Compressive Strength
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Summary
• Explain the basic concepts of concrete• Explain the properties of fresh concrete• Explain the properties of hardened concrete
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Questions?
Pantheon, Rome, Italy (27BC)