Lecture 1 - UW Courses Web Server

Advanced Construction Techniques

Lecture 1

Professor Kamran M. NematiFall Quarter 2016 1

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CM 510


Fall Quarter 2016

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CM 510- Course Description

The course will introduce unique construction methods involved with several types of complex construction projects. The construction process will be discussed as a system to provide a background for examining various types of projects including modern concretes and infrastructure, high-rise construction, deep foundations, dams and bridges, tunneling and shotcrete, and other complex construction issues.


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CM 510- Text

P.K. Mehta and P.J.M. Monteiro “Concrete : Microstructure, Properties, and Materials,” Fourth Edition, MacGraw Hill, 2014 (reserved at both Engineering and Architecture Libraries).

Handouts and other reference materials will be distributed in class.

Class presentations and notes will be available through the course web site at:

http://courses.washington.edu/cm510/

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Faculty Office Hours:

Thursdays 5-6 PM or by appointment, 130J Architecture Hall. Voice-mail: 685-4439, Email: [email protected]

Assignments:

There will be three homework assignments in this class. All assignments are due at the beginning of the class on the date due. 20% will be deducted for each day late.

Exams:

One midterm test will be given on Thursday, November 17th.


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Term Project:

Each student will work on a term project that is pre-approved by the instructor. The term project should involve an analysis of an innovative technique or the use of an innovative building material in a construction project. Students are required to submit a one-page description of the project to the instructor by October 13th. The project is due on Thursday, December 8th at the beginning of the class. Students are expected to work individually.

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Sample Projects in the Past

Floating bridge construction processes and techniques

Construction process in Experience Music Project

Micro-tunneling

Mast climbing construction system

The use of robots in the construction industry

Mechanically stabilized earth retaining wall

Precast Seismic Structural Systems (PRESSS)

Mobile Bridges


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Grading:

Homework 20%

Midterm 25%

Term Project 25%

Term Project Presentation 20%

Class Participation 10%

Participation: Students are expected to maintain an active role in class discussions. By completing assignments on time and being prepared for class you demonstrate your interest in the class.

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CM 510 - Lecture Topics Sept. 29 Introduction to Concrete as a

Construction Material October 6 Alaskan Way Viaduct Replacement project;

Progress in Concrete Technology October 13 Field Trip to Spokane Street Swing Bridge October 20 Site Improvement and Deep Foundations;

Ground Freezing; Bridge Construction October 27 Dams; Cofferdams; Construction

Dewatering; Shotcrete November 3 High-rise Construction November 10 IDX Tower Tunnels November 17 Pavement Construction, Presentations,

Midterm November 24 Thanksgiving Holiday December 1 Presentations December 8 Presentations


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CM 510Advanced Construction Techniques

HYDRAULIC CEMENTSAND THEIR PROPERTIES

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Definitions

Cement Powder

Cement + Water Cement Paste

Cement Paste + Fine Aggregate (FA) Mortar

Mortar + Coarse Aggregate (CA) Concrete


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Concrete is initially plastic, allows one to mold into desired shape.

Chemical reaction (hydration) and paste set of concrete - producing strength and stiffness.

Definitions

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Cement

Cement is a pulverized material that develops binding forces due to a reaction with water

Hydraulic Cement Stable under water

Nonhydraulic Cement Products of hydration are not resistant to water (i.e. limestone)


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Cements that harden by reaction with water and form a water-resistant product.

Portland Cement (P.C.)

Portland cement is a hydraulic cement capable of setting, hardening and remains stable under water. It is composed of calcium silicates and some amount of gypsum.

Hydraulic Cements

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Cement Chemistry

Short Hand Notation

C (CaO, calcium oxide)

A (Al2O3, alumina)

S (SiO2, silica)

S (SO3, sulfate)

H (H20, water)

Reactive Compounds

C3S (tricalcium silicate)

C2S (dicalcium silicate)

C3A (tricalcium aluminate)

CSH2 (gypsm)

C4AF (tetra-calcium alumino ferrite)

In cement chemistry, the individual oxides and clinker compounds are expressed by their abbreviations


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C3S 3CaO . SiO2

C2S 2CaO . SiO2

C3A 3CaO . Al2O3

C4AF 4CaO.Al2O3.Fe2O3

C4A3S 4CaO.3Al2O3.SO3

ferrite aluminate mTetracaciu AFC

aluminate Tricalcium A C

Silicate Dicalcium SC

Silicate Tricalcium SC

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3

2

3

Compounds of Portland Cement

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Hydration Reactions

2C3S + 6H C-S-H + 3CH (120 cal/g)

2C2S + 4H C-S-H + CH (62 cal/g)

C3A + 3CSH2 +26H C6AS3H32 (300 cal/g)

2C3A + C6AS3H32 + 4H 3C4ASH12

C4AF + 10H + 2CH C6AFH12

C3S2H3 (C-S-H gel)

CH (calcium hydroxide)

C6AS3H32 (ettringite)

C4ASH12 (monosulfate)

Cement Chemistry


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Hydration of Portland Cement

Cal/g 1203CHHSC6HS2C3

Cal/g 26CHHSC4HS2C2 e)(Ettringit HSACHSC AF,C A,C 43

Compound Composition Morphology Amount (% Vol.)

C-S-HVariable

C/S 1.5 to 2

Poorly crystalline

High surface area: higher

bonding energy

50 – 60%

CH Ca(OH)2

Large hexagonal crystals,

low surface area, and poor

bonding energy

20 – 25%

C-A-S-HC6AS3H32

Ettringite

C4ASH12-18

Monosulfate

Long, well crystallized

needles

Hexagonal – small

crystals

15 – 20%

Hydration: Reaction with water

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Calcium silicates are the primary constituents of portland cement.

Raw material for P.C. Calcium Silica

Calcium: Limestone, chalk, etc (CaO+CO2)

Silica: Clays and shales (SiO2+Al2O3+Fe2O3+H2O)

Clay 1/3

Calcium 2/3

ment heat treat

thebefore dhomogenize

wellbe shouldmix Raw

Manufacturing Process


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Aerial Photo of a Cement Manufacturing Plant(Colorado)

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Raw Mill Feed


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Kiln Line Overview

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T = 1400CRaw

(Limestone

+Clay)

Clinker+Gypsum

Grind

Portland CementGrind Mill

AFC

AC

SC

SC

O.FeO4CaO.Al

O3CaO.Al

2CaO.SiO

3CaO.SiO

OHOFeOAlSiOClay

COCaOLimestone

4

3

2

3

3232

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2

2

232322

2


Rotary Kiln


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Reactivity of cement with water is a function of its fineness.

Generally, the finer a cement, the more rapidly it will react, and the strength development will be enhanced (expensive).

Fineness

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Types of Portland Cement

ASTM C 150, Standard Specifications for Portland Cement

Type I: General purpose. For use when the special properties specified for any other types are not required.

Type II: For general use, more specially when moderate sulfate resistance or moderate heat of hydration is desired.

Type III: For use when high early strength is desired. (limit the C3A content of the cement to maximum 15%)

Type IV: For use when low heat of hydration is desired.

Type V: For use when high sulfate resistance is desired.(Maximum limit of 5% on C3A)


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In classic research from over fifty years ago Bouge and Lerch* found that of the four portland cement phases only C3S and C2S developed appreciable compressive strength when pure samples of each were hydrated.

The compressive strength found by Bogue and Lerch** are plotted in the next Fig. as a function of age. Compressive strengths of C3A and C4AF, hydrated alone “A” and have not been plotted explicitly.

Effects of Chemical Composition of Portland Cements of Strength

* T.C. Powers, “The Non-Evaporable Water Content of Portland Cement Paste: Its Significance for Concrete Research and Its Method of Determination,” ASTM Bul., No. 158, (May 1949) pp. 68-76.

** R H Bouge and W Lerch “Industrial Engineering, Chem. 26 873 (1934)

The compressive strength found by Bouge and Lerch** for hydrated samples of the pure cement phases C3S and C2S are plotted as a function of age. The compressive strengths of C3A and C4AF, hydrated along and with gypsum, fall within the cross-hatched region labeled “A” and have not been plotted explicitly. The time scale is linear. The time scale is logarithmic, which has the effect of expanding the early ages, and this shows the differences between strength gain of C3S and C2S pastes.

Effects of Chemical Composition of Portland Cements of Strength


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The Structure of Concrete

The type, amount, size, shape & distribution of phases present in a solid material constitute its structure.

Concrete Consists of aggregates, paste and voids.

The macrostructure of concrete is shown below:

A polished section of concrete

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The structure of the aggregates in concrete is important but it can be characterized as a macrostructure which is visible to the human eye.

The limit of resolution of the unaided human eye is approximately 1/5 millimeter which is 200 microns.

The Microstructure of Portland Cement Concrete


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The use of both light and electron microscopes allows the study of the microstructure of concrete at the submicron level.

The microstructure of concrete can be divided into regions:

Cement Paste

Transition Zone between Aggregate and Cement paste


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Structure of “un-damaged” Concrete

Macrostructure

Aggregates (CA, FA)

Hydrated cement paste (hcp)

Entrapped air voids

Microstructure

Hydrated cement paste

(Hydration products:C-S-H, ettriginite; monosulfate; porosity: gel, capillary pores entrained/ entrapped air voids)

Transition zone (TZ)


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Microstructure of Concrete

(Hydration products)

CH C-S-H

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Ettringite


(Hydration products)


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Characteristics of the TZ

Large crystals of Ettringite and CH with preferred orientation

Porous Structure


(Transition Zone)

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One way to view cement paste is to consider the hydration of one grain of cement.

The partial hydration of one grain of cement is schematically represented in the next slide.

There are many details in this process that are not yet understood, but there is sufficient information available to allow a consistent mental picture to be considered.



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The hydration products formed inside and outside the cement grain are schematically represented.

The multiple nature of the cement grain is neglected and assumed to be a single phase that shows two types of products.

P1 refers to the “primary” portlandite which appears early in the originally water-filled space.

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The hydration of a number of cement grains is schematically represented in the next slide at different degrees of hydration.

The fresh paste (i.e., the initial combination of water and cement grains) is drawn to approximately represent the 0.4 water/cement ratio, and thus there are not enough hydration products to fill the originally-water-filled space and a capillary porosity remains in the final microstructure.

The Microstructure of Portland Cement Paste


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A schematic representation of the hydration of a number of cement grains. The multiphase nature the cement grains has been neglected as this is like the hydration of tricalcium silicate alone. (a) Fresh paste of water-to cement ration of 0.4 is shown cement grains in the originally water-filled space. (b) After 33% hydration, the cement grains now have inner hydration regions and outer products which form a “columnar zone” around each grain. (c)After 67% hydration, the un-hydrated cores are clearly surrounded by thick “rims” of inner hydration products and the columnar zone of outer products is growing on the surface of each grain. The primary portlandite, P1, is shown with the dendrite morphology. (d) At 100% hydration, the un-hydrated cement has been consumed but the shape of the original cement grains can be distinguished if the inner product differs from the columnar zone of outer products. The intergrowth of the columnar zones from two different grains is shown at several points, but this would be larger at low water/cement rations.

Originally water-filled space = clear, unhydrated cement = , inner hydration products = ,

outer hydration products = , & primary portlandite = P1.

///

The Microstructure of Portland Cement Paste

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The originally-water-filled space within the cement paste becomes the capillary pores which act as stress concentrations and reduce the strength significantly.

The strength of most engineering materials is increased with a decrease in porosity, and by controlling the water/ cement ratio the engineer is assured that the basic porosity of the paste is also controlled. That is not to say the other sources of porosity will not occur, but at least the cement paste will have a given porosity.

Capillary Porosity


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Figure below shows a graphical representation of the relative volumes of hydration products during hydration.

Graphical representation of the relative volumes of hydration products during hydration. The initial w/c is 0.5, and one unit of cement is shown to produce two volumes of hydration products.

Capillary Porosity

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If cement paste specimens are prepared with a range of w/c ratios it is apparent that the density of high w/c samples is much lower than low w/c samples.

This is illustrated in the next slide in a presentation originally given by T.C. Powers*.

*T.C. Powers, “The Non-Evaporaable Water Content of Portland Cement Paste: Its Significance for Concrete Research and Its Method of Determination,” ASTM Bul., No. 158, (May 1949) pp. 68-76.

Capillary Porosity Over a Range of W/C Ratios


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Composition of Cement Paste at different stages of hydration. The percentage indicated applied only to paste with enough water-filled space to accommodate the products at the degree of hydration indicated.

Capillary Porosity Over a Range of W/C Ratios

Advance Construction Techniques

CM 510

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Admixtures

in Concrete


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Concrete TechnologyAdvanced Construction TechniquesCM 510

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ADMIXTURES

A material other than water, aggregates, and hydraulic cements used as an ingredient of concrete or mortar and added to the batch immediately before or during mixing.

Reason:

Improve or modify some or several properties of portland cement concrete.

Compensate for some deficiencies.


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A. Chemical Admixtures

Type A: Water-reducing (WR)

Type B: Set retarding (SR)

Type C: Set accelerating (SA)

Type D: WR + SR

Type E: WR + SA

Type F: High-range water-reducing (HRWR)

Type G: HRWR + SR


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B. Mineral Admixtures

Class N: Raw or calcined pozzolans

Class F: Fly ash produced from burning bituminous coal

Class C: Fly ash normally produced from burning lignite (subbituminous) coal.

(both pozzolanic and cementatious)


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1) Admixtures for Durability

Frost action: Air-entraining agents

Sulfate and acidic solutions: Pozzolans, polymer emulsions

Alkali-aggregate expansion: Pozzolans

Thermal Strains: Pozzolans


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2) Admixtures for Increasing Strength

Water reducing agents

Pozzolans

Consistency: Flowability, slump

Workability: High cohesiveness and high consistency

(Advantage of fine particle size Cohesiveness)

To reduce the water content while

maintaining a given consistency


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Chemical AdmixturesSurfactants (Surface-Active Chemicals/ Agents)Air-entraining surfactants:

At the air-water interface the polar groups are oriented towards the water phase lowering the surface tension, promoting bubble formation and counteracting the tendency for the dispersed bubbles to coalesce.

At the solid-water interface where directive forces exist at the cement surface, the polar groups become bound to the solid with the non-polar groups oriented towards the water, making the cement surface hydrophilic so that air can displace water and remain attached to the solid particles as bubbles.


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Chemical AdmixturesSurfactants (Surface-Active Chemicals/ Agents)Air-entraining surfactants:


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Air-Entrained Concrete


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Mechanism of Frost damage in concrete

Only concrete that is above the critical saturation is vulnerable to frost damage.

Critical saturation occurs when more than 91.7% of pores in concrete is filled with water.

Water Expands 9% on freezing.


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Mechanism of Frost damage in concrete

If 91.7% of the pores in concrete are filled with water prior to freezing, then all of the pores will be completely filled upon freezing.

Water is forced ahead of the advancing freezing front.

Internal hydrostatic pressure can disrupt the concrete.


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Freeze-Thaw Deterioration


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Mechanism of Protection by AE


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Air Content Specifications ACI 318 – Building Code

ASTM C 94 – Specs for Ready-Mixed Concrete


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Chemical Admixtures

When water is added to cement, a well-dispersed system is not achieved, because:

The water has high surface tension.

Cement particles tend to cluster together or form flocs.When a surfactant with a hydrophilic chain is added to the cement-

water system, the polar chain is adsorbed alongside the cement particle, and thus lowering the surface tension of the water, and making the cement surface hydrophilic.

Surfactants (Surface-Active Chemicals/ Agents)Water-Reducing surfactants:


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Chemical AdmixturesSurfactants (Surface-Active Chemicals/ Agents)Water-Reducing surfactants:


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Mineral Admixtures

Definition: Mineral Admixtures are insoluble siliceous materials, used at relatively large amounts (15-20% by weight of cement).

Fine particle size, siliceous materialthat can slowly react with CH at normal temperatures, to form cementitious products.

Aq

Normal Temp.CH CSH+ S


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Mineral Admixtures

Low heat of hydration

Transform large pores to fine pores

Historically, mineral admixtures are volcanic ashes.

Significance: Durability to thermal cracking, chemical attack, sulfate attack, workability.


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By-Product Mineral Admixtures

Fly Ash (FA) 1-40m Particle Size; Surface Area=0.5 m2/g

Blast Furnace Slag (BFS) 1-40m; SA=0.5 m2/g

Condensed Silica Fume (SF) 0.1m; SA=20 m2/g

Rice Husk Ash (RHA) 10-20m; SA=60 m2/g

Internal bleeding is reduced Reduced Microcracking

Effect of Pozzolans:

It will reduce the available space for formation of large crystals

Pozzolans will convert CH into C-S-H


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The Slump Test


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The Slump Test Consistency of concrete is generally measured by

the slump test (ASTM C143). This test is performed by measuring the slump (subsidence), in inches, of concrete after removal of the truncated cone mold in which the freshly mixed concrete was placed. Details of the test procedure and the dimensions of the cone and tamping rod are given in ASTM C143, and summarized in this figure:

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