introduction dr magnus currie from scotland, uk meng civil engineering phd wind energy systems...

Introduction

• Dr Magnus Currie• From Scotland, UK• MEng Civil Engineering• PhD Wind Energy Systems (Concrete Monitoring)

• Class Tutors > Ms Liu and Ms Gau

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

ENG1010-Reinforced Concrete Design

Week One – Basic Principles of ConcreteWeek Two – Reinforced Concrete ConstructionWeek Three – Concrete ConsiderationsFinal Day – Exam

Week 1

1. Introduction to Concrete2. Concrete Design and Properties3. Concrete Chemistry4. Concrete Admixtures5. Properties of Materials

Tutorial Times

• Monday – ThursdayEnglish 14:30-15:30Chinese 15:40 – 16:40

• FridayEnglish 08:30-09:30Chinese 09:40-10:40

Lecture 1Introduction to Concrete

Dr Magnus Currie

ENG-1010: Reinforced Concrete Design

Objectives

• To explain the basic concepts of concrete• To explain the properties of fresh concrete• To explain the properties of hardened concrete

Concrete

• A mixture of two components

1. Paste (25% - 40%)2. Aggregates (60% – 75%)

Paste

• Paste compromises of:

1. A binder (such as cement)2. Water3. Air (either entrapped or entrained)4. Other admixtures depending on the mix

Aggregates

• Compromises a mix of:

1. Fine aggregates (such as sand)2. Coarse aggregates (gravel or crushed stone)

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

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

Quality of Concrete

• Aggregate requirement• Paste requirement

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.

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

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

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

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

Advantages of reducing the W/C ratio of paste

• Less volume change from wetting and drying• Reduced shrinkage cracking tendencies

Effect of w/c ratio on compressive strength of concrete

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

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

Mixing Requirements

• The elapsed time between batching and mixing

• Design, configuration and condition of the mixer drum and blades

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)

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.

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.

Effect of Consolidation

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.

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

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

Effect of Curing on Strength

Properties of freshly mixed concrete

• Workability• Hydration• Setting Time• Hardening

Workability

• The Slump Test

Properties of Hardened Concrete

• Strength• Unit Weight• Resistance to freezing and thawing• Permeability and water tightness• Abrasion Resistance• Volume Stability• Control of Cracking

Compressive Strength

Summary

• Explain the basic concepts of concrete• Explain the properties of fresh concrete• Explain the properties of hardened concrete

Questions?

Pantheon, Rome, Italy (27BC)