cement - U-Cursos · Mehta and Monteiro: Concrete Review – Identify the crystal. Mehta and...

CE 60Instructor: Paulo Monteiro

Portland Cement

PortlandPortland CementCement

A hydraulic cement capable of setting, hardening and remaining stable under water. It consists essentially of hydraulic calcium silicates, usually containing calcium sulfate.

Manufacture

Raw Materials:

2/3 calcareous materials (lime bearing) - limestone

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


Raw Material


Crushing


Blending


Old Method


Kiln


Grinding


Production Process

Production of cementIs responsible for 7%CO2 production in theworld

Problem

Mehta and Monteiro: Concrete

Cement grains

Courtesy from Prof. Karen Scrivener, EPFL

Based on the following notation:Based on the following notation:C CaO

S SiO2

A Al2O3

F Fe2O3

H H2O

Cement MineralsCement Minerals

C3S : 3CaOSiO2C2S : 2CaOSiO2

C3A : 3CaOAl2O3C4AF : 4CaOAl2O3Fe3O4


Hydrationcement

+water

dissolution precipitation

Courtesy: Prof. Karen Scivener, EPFL

CHEMICAL REACTIONSCHEMICAL REACTIONS

2C3S + 6H --> C3S2H3 + 3CH + 120 cal / g2C2S + 4H --> C3S2H3 + CH + 62 cal / gC3A + CSH2 --> Ettringite + 300 cal / g


Hydrated Paste


Early Hydration

3 hours 10 hours

Courtesy: Prof. Karen Scrivener


Hydration Products

Hadley Grain

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)2Volume % : 20 to 25

low Van der Walls forceproblems with durability and strength


Calcium Hydroxide


-Calcium Sulfoaluminate HydratesVolume % : 15 to 20

first : ettringiteafter : monosulfate hydrated.


Ettringite


Review – Identify the crystal


Review 2 -- Identify the crystal


Review 3 -- Identify the crystal


Concrete has a complex microstructure

Cement grain

C-S-H

Sand Particle

Calcium hydroxide

pores

Courtesy Prof. K. Scrivener


Hydration process – Initial Condition

Let’s study a cement paste with w/c= 0.63Start with 100 cm3 of cement.

Compute the mass of cement: Mc = 3.14* 100 = 314 gCompute the mass of water: Mw = 0.63 * 314 = 200 g

Vc= 100 cm3

Vw= 200 cm3


Hydration Process

Miracle of hydration: Vp = 2 Vc

50%

Vc= 100 cm3

Vw= 200 cm3

Vc=50 cm3Vp = 100 cm3

Vw= 150 cm3


Once More…

75%

Vc= 100 cm3

Vw= 200 cm3

Vc=25 cm3Vp = 150 cm3

Vw= 125 cm3


Finally

100%

Vc= 100 cm3

Vw= 200 cm3

Vp = 200 cm3

Vw= 100 cm3


Exam question

• Calculate the water/cement ratio needed to obtain zero porosity in a fully hydrated cement paste.

100%

100 cm3

200 cm3100 cm3

W/c = 100/100*3.14

W/c= 0.32

Voids in the Hydrated Cement Paste (HCP)Voids in the Hydrated Cement Paste (HCP)

-Interlayer space in CSH* size = 5 to 25 Å* no adverse effect on strength and permeability* some effect on drying shrinkage and creep

-Capillary Voids> 50 nm : detrimental to strength and impermeability < 50 nm: important to drying shrinkage and creep.

-Air Voids* entrapped air: ~ 3 mm* entrained air: 50 to 200 mm


Water inside the pores


Orders of magnitude


Orders of Magnitude

Setting and HardeningSetting and HardeningStiffening is the loss of consistency by the plastic cement paste and it is associated with the slump loss phenomena in concrete.

Setting : Solidification of the plastic cement paste

Initial Set : Beginning of solidification (point in time when the paste has become unworkable) (>45 min.)

Final Set : Final solidification (< 375 min.)

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%) : mass concrete

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

cement - U-Cursos · Mehta and Monteiro: Concrete Review – Identify the crystal. Mehta and...

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