revision of concrete technology (questions)

8/13/2019 Revision of Concrete Technology (Questions)

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CIV2226

Week 13Concrete Technology


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Concrete Technology - Topics Covered

in CIV2226 Mix Design Cements and Supplementary Cementitious Materials

Chemical Admixtures Fresh Properties Hardened Proprties

Specifying Concrete Handling & Placing Durability

Cracking and Crack Control


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Check:

Lecture presentations (MUSO) CIV2226 Recommended Reading & Library

Lists & Australian Standards that were

re erence n eac ec ure Laboratory Mix Design/Lab Classes/Reports Past examinations (MUSO)


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Constituents of Concrete: Cement

Supplementary Cementitious Materials Water

Coarse & Fine Aggregates

Chemical Admixtures


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Concrete Mix Design Purpose of mix design? Parameters used in Mix Design (workability,

strength, w/c, aggregate gradings, free water, ,

density of concrete, Fineness Modulus .)? Calculation to Road Note 4 British Method)

refer to Prac Class#1 and your laboratory notes


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Portland Cement What is it?

How is it manufactured? Components of Portland Cement &

their Characteristics/Influence on

MineralPhase

C3S

Behaviour of Portland Cement

Cement Types & Specification &

Characteristics Influences of cement types on concrete

properties

C3A

C4AF


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Strength DevelopmentFactors that Influence Strength (composition, fineness)

Heat of H dration

Portland Cement

What is it? Why is it important? Factors thatincrease/reduce the rate and peak heat of hydration.Influence on other engineering properties (e.g strength)

SettingWhat is it (initial set, final set)?Why is it important?

What factors influence setting?


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Supplementary Cementitious Materials

How are they used in concrete?

Sla

PortlandCement

+and/or Fly ashand/or

Silica Fume

Blended or Inter-ground

CementitiousBinder inConcrete


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Ground Granulated BlastFurnace Slag (or, slag)

What is it?

How is it manufactured &

Environmental benefits?


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Slag replacement of OPC

Slower reaction that 100% OPC

Lower heat of hydration

Lower Permeability Effect on strength (short & long-term?)

Effect on heat of hydration?


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Fly ash

What is it? How is it manufactured and used in concrete?

v Slow reaction Effect on fresh properties?

Effect on Permeability?

Effect on strength (short & long-term) ?


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What is it?

How is it manufactured and used in concrete?

Silica Fume

Rate of reaction?

Effect on fresh properties?

Effect on Permeability?

Effect on strength (short & long-term) ?


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Concrete Aggregates

How are they manufactured? Significant aggregate properties and how they

affect properties of concrete?

Size, gradings, shape, texture, porosity and waterabsorption - how they affect properties ofconcrete?


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Chemical Admixtures

What are they?Why are they added to concrete mixtures?

To achieve certain properties in concrete To ensure the quality during the stages of mixing,

transporting, placing, and curing in adverse

weather conditions. To overcome emergencies during operations


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Chemical Admixtures

Types? Classifications to the Australian Standards? Mechanisms of behaviour?

Applications in concrete construction?


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Admixture Classifications AS1478


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Properties of Fresh Concrete

Concrete Mixing

Transport

Importance

Adequatetime beforesetting

Ease of

acemen

Compaction

Finishing

o resProperties Compactionwith ease

Surfacefinishing withease

While also producing hardened concrete that is uniform (not segregated) & lowvoidage & homogeneous mass


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What is it?

Common methods of measurement (e.g. slump)

Workability

Factors influencing workability (e.g. concreteingredients and proportions, chemical

admixtures, temperature & humidity)


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Segregation

What is it?

Why does it occur?

at are t e e ects on strengt an ura tyMethods to reduce segregation?


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Bleeding

What is it?

Why does it occur?

at are t e e ects regar ng ura ty an strengtMethods to reduce bleeding?


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Hardened Concrete Properties for

Structural Engineering

Strength Modulus of elasticity

Shrinkage

Creep Coefficient of thermal

expansion

Durability


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Compressive Strength

Major factors of influence:

w/c

Age Type of curing

Degree of compaction

Temperature Humidity


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Types of Shrinkage

plastic shrinkage autogenous shrinkage

Factors that influence shrinkage

aggregate content, w/c ratio

relative humidity (exposureenvironment)

surface to volume ratio

age of concrete


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Shrinkage What are the effects on concrete?

How does shrinkage-related crackingoccur?


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Creep what is it?Factors influence Creep

level of stress

relative humidity

strength of concrete at the time ofloading

average path length for moisture

movement duration of applied load


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Specification,

Ordering, and Supply ofConcrete

Manufacturing of Concrete

Batching

Mixing EquipmentSlump Control

Transport of Concrete

Concrete Placement and Finishing

R l i hi B h A li S d d


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Relationships Between the Australian Standards

Structural DesignAS3600 Concrete Structures

Specification of ConcreteAS1379 Supply of Concrete

Specification of

Concrete TestingAS1012 Methods of Testing Concrete

Aggregate TestingAS1141 Methods for Sampling

& Testing Aggregates

Portland & BlendedCementsAS3972

Cement TestingAS2350

AdmixturesAS1478

Aggregates

AS2758

Sampling and Testing Specifications


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Required Workability

Factors:

Type of structural member (e.g. ground slab,column, etc)

Size of form

Density, size & spacing of reinforcement Atmospheric conditions

Type of equipment


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Distribution Methods

Chute

Pump

Tremie

Barrow

Slip-form


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Concrete Slabs Placement

(example)

Place concrete as near to its final position as possible

Start placing from the corners of the formwork or, in

the case of a sloping site, from the lowest level.

Commence placingat one corner of the

formwork

Random placing can

cause segregation &

makes it more difficult to

achieve correct levels

C ti


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Compaction

2-stage process:1. aggregate particles are set in motion and slump

to fill the form giving a level top surface

2. entrapped air is expelled.

Stage 1

PROCESS: Liquefactionof the concrete whichallows it to slumpand fill the formTIME: 3 to 5 seconds

Stage 2

PROCESS: The expulsionof entrapped airTIME: 7 to 15 seconds


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Curing of Concrete

Importance of CuringMechanisms of Curing

ypes o ur ngEffects on Concrete Properties

D bilit f C t


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Durability of Concrete

From: Corrosion of Steel in Concrete.

Luca Bertolini, Bernhard Elsener, Pietro Pedeferri, Rob P. Polder, 2004.WILEY-VCH Verlag

GmbH & Co. KGaA, Weinheim

S lf t Att k


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Sulfate Attack

Mechansims of deterioration Effects on concrete?

How to avoid sulphate attack

Sulphate Salt Crystallization Mechansims of deterioration

ec s on concre e

How to avoid salt crystallisation attack

Acid Attack Types of acid and how they affect the mechansims of

deterioration

Effects on concrete?

How to avoid/reduce acid attack

Corrosion of Steel Reinforcement


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Why is Hydrated Cement A PerfectCorrosion Inhibitor?

Why does steel in concrete corrode?

Corrosion of Steel Reinforcement

Effects on Reinforced Concrete?

Prevention, Maintenance, and

Remediation


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How does AS3600 account for

durability?



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Sources of Tension in Concrete

External or Structural Sources Gravity loads: dead and live loads Lateral loads: wind and seismic


oa s rom su gra e sett ement or swe ng

Internal Mechanisms

Volume change restraint due to temperaturechanges or drying shrinkage

Expansion due to corrosion of reinforcingsteel or deleterious chemical reactions


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Example: Thermal Cracking


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Example: Thermal Cracking

Hydration of Cement Evolves HeatRisks of Cracking (sections > 1m thickness)

Temperature difference between internal & external

concrete Contraction of concrete after peak temperature (restrained

after hardening)


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Control of crackingDepends on the cause (e.g. dryingshrinkage; reduce external drying, reducefree water in the mix, lower cement content,

..)


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CIV2226

Concrete TechnologyExam

GOOD LUCK!

revision of concrete technology (questions)

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