review concrete الاسمنت البورتلاند.pdf

7/24/2019 review concrete االسمنت البورتالند.pdf

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CE 60Instructor: Paulo Monteiro

PortlandPortland CementCement

A hydraulic cement capable of setting, hardening and

remaining stable under water. It consists essentially ofhydraulic calcium silicates, usually containing calcium

sulfate.




Manufacture

Raw Materials:

2/3 calcareous materials (lime bearing) - limestone

1/3 argillaceous materials (silica, alumina, iron)- clay




Based on the following notation:Based on the following notation:

C CaO

S SiO2A Al2O3

F Fe2O3

H H2O




Cement MineralsCement Minerals

C3S : 3CaOSiO2

C2S : 2CaOSiO2

C3A : 3CaOAl2O3

C4AF : 4CaOAl2O3Fe3O4




CHEMICAL REACTIONSCHEMICAL REACTIONS

2C3S + 6H --> C3S2H3 + 3CH + 120 cal / g

2C2S + 4H --> C3S2H3 + CH + 62 cal / g

C3A + CSH2 --> Ettringite + 300 cal / g




SOLIDS IN CEMENT PASTESOLIDS IN CEMENT PASTE

-Calcium Silicate Hydrate

Notation: C-S-HC/S Ratio: 1.5 to 2.0

Main Characteristics: High Surface (100 to 700 m2/ g) ----> High Van

der Walls Force -----> Strength.

Volume % : 50 a 60




C-S-H





-Calcium Hydroxide ( portlandite)

Ca(OH)2

Volume % : 20 to 25low Van der Walls force

problems with durability and strength




Calcium Hydroxide





-Calcium Sulfoaluminate Hydrates

Volume % : 15 to 20

first : ettringite

after : monosulfate hydrated.




Ettringite




Hydration process – Initial Condition

Let’s study a cement paste with w/c= 0.63

Start with 100 cm3 of cement.

Compute the mass of cement: Mc = 3.14* 100 = 314 g

Compute the mass of water: Mw = 0.63 * 314 = 200 g

Vc= 100 cm3

Vw= 200 cm3




ASTM Portland CementsASTM Portland Cements

Type I- General Purpose

Type II- moderate heat of hydration and sulfate resistance (C3A <

8%) : general construction, sea water, mass concrete

Type III- high early strength (C3A < 15%) : emergency repairs,

precast, winter construction.

Type IV- low heat ( C3S < 35%, C3A < 7%, C2S > 40%) : massconcrete

Type V- sulfate resistant ( C3A < 5%) : sulfate in soil, sewers.




Significance:

• cost

• provide dimensional stability• influence hardness, abrasion resistance,

elastic modulus




Aggregate Type

•Coarse aggregate ( > 3/16 in. - 4.75 mm of No. 4)

•Fine aggregate < 3/16 in. and > 150 (No. 200)




Aggregate Type -mineralogy

•Sedimentary Rocks (cost effective - near the surface),

•about 80% of aggregates

•Natural sand and gravel•Sandstone, limestone (dolomite), chert, flint, graywacke

•Metamorphic Rocks: slate, gneiss : excellentto poor




Density

(pcf) concrete (pcf)

Normal weight aggregate 110 150

Lightweight Aggregate perlite - thermal insulators

expanded shales - structuralconcrete

< 70 90-115

Heavyweight Aggregate 115-200 <200




• Fineness modulus is the sum of the totalpercentages retained on each of thespecified sieve divided by 100. The

specified sieves are 3, 1 1/2, 3/4 and 3/8in and Nos. 4, 8, 16, 30, 50 and 100.




Characteristics of coarse aggregate Characteristics of fine aggregateType Used:________________ Type Used: ______________

Max. Size:______ 1 ______ inch F.M. _____ 2.93 ______________ B.S.G: 168 ______lb/ft3 B.S.G: 167 ______lb/ft3

Moisture deviation from S.S. D.=_-0.4%__ Moisture deviation from S.S. D.=0.7%__ Dry-rodded unit wt.__ 104 _lb/ft3____

B.S.G of cement = 196 lb/ft3




Effect of moisture




TestingTypes of Elastic Modulus

ASTM Testing




Introduction




Importance




Concrete Relaxation




Summary




Compressive Strength

• Fundamental relationship

• S = So exp (-kp)

• Where So is the strength at zero

porosity, p is the porosity and k aconstant.




Interfacial Transition Zone




REASON




Microstructural improvement

• Use of silica fume

reduce the porosity of the ITZgeometrical effect (no space)

reduces the amount of CH due topozzolanic reaction




Humidity

• Great importance of moist curing.




Temperature

• Cast and cured at the same temperature

• Cast at different temperature but cured atthe same temperature

• Cast at normal temperature but cured atdifferent temperatures.




Testing parameters

• Specimen Size: Fracture mechanics will

explain the importance of size effect.

• Loading Rate: Increasing rates lead toincreasing strength.




Thermal Stresses in Concrete

• Introduction

• Importance

• Technological Aspects

• Case Study – LA Cathedral




Thermal stresses

where:

σt: tensile stressKr: degree of restraint

E: elastic modulus

α: coefficient of thermal expansion∆T: temperature change

ϕ: creep coefficient

σ t =K r E

1 + ϕ

α∆T




Temperature Evolution

T = placement temperature of fresh concrete + adiabatic temperature rise- ambient or service temperature - heat losses.




DurabilityDurability

•Durability of concrete: ability to resist

weathering action, chemical attack,abrasion, or any process ofdeterioration




Water Structure




Abrasion - Erosion

•Note: the deterioration starts at the surface,

therefore special attentions should be givento quality of the concrete surface.

•Avoid laitance (layer of fines from cement and

aggregate).

The problem




The problem

The transformation of ice from liquid water generates a volumetric

dilation of 9%. If the transformation occurs in small capillary pores,

the ice crystals can damage the cement paste by pushing the capillarywalls and by generating hydraulic pressure.




Air-Entraining




Deterioration by fire

•Concrete is able to retain sufficient strength

for a reasonably long time.




Effect of High Temperature on

Cement Paste

•(a) degree of hydration

•(b) moisture state

•de-hydration:

•ettringite > 1000C

•Ca(OH)2 500-6000C

•CSH ~ 9000C




Electrochemical process of steel corrosion in concrete




Volumetric change

Th h i i i l




The chemistry is simple

1) The high pH in the cement paste promotes the hydrolysis of silic

Si-OH+ Si-OHSi-O-Si + H OH aggregate paste

2) Si-OH react with the paste to form Si-O-

3) Si-O-, adsorbs Na, K, and Ca to form a gel.




Expansive Reaction

• C3A + gypsum C3A.3C$.H32 (ettringite)

C3A.C$.H18 (monosulfate)

In the presence of sulfates




Sodium sulfate attack:

• Na2SO4 +Ca(OH) 2 +2H2O

CaSO4.2H2O + 2NaOH

the formation of sodium hydroxide as a by-product

of the reaction ensures the continuation of highalkalinity in the system, which is essential for thestability of the cementitious material C-S-H.

M i lf t tt k




Magnesium sulfate attack

• MgSO4 +Ca(OH) 2 +2H2OCaSO4.2H2O + Mg(OH) 2

• 3 MgSO4 + 3CaO .2SiO2 .3H2O + 8 H2O 3 CaSO4.2H2O + 3Mg(OH) 2 + 2SiO2.H2O

• the conversion of calcium hydroxide to gypsum is accompaniedby the simultaneous formation of relatively insoluble magnesiumhydroxide.

• In the absence of hydroxyl ions in the solution C-S-H is nolonger stable and is also attacked by the sulfate solution.• The magnesium sulfate attack is, therefore, more severe on

concrete.



CE 60

Factors influencing sulfate attack

• amount and nature of the sulfate present,

• level of the water table and its seasonalvariation,

• flow of groundwater and soil porosity,• form of construction,

• quality of concrete.

review concrete الاسمنت البورتلاند.pdf

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