Cement

CE 60Instructor: Paulo Monteiro

Portland Cement

Portland Cement

A hydraulic cement capable of setting, hardening andremaining stable under water. It consists essentially ofhydraulic calcium silicates, usually containing calciumsulfate.

Manufacture

Raw Materials:

2/3 calcareous materials (lime bearing) - limestone

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

CE 60Instructor: Paulo Monteiro

Raw Material

CE 60Instructor: Paulo Monteiro

Crushing

CE 60Instructor: Paulo Monteiro

Blending

CE 60Instructor: Paulo Monteiro

Old Method

CE 60Instructor: Paulo Monteiro

KilnThis image cannot currently be displayed.

CE 60Instructor: Paulo Monteiro

Grinding

CE 60Instructor: Paulo Monteiro

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:C CaO

S SiO2

A Al2O3

F Fe2O3

H H2O

Important

Cement Minerals

C3S : 3CaOSiO2C2S : 2CaOSiO2

C3A : 3CaOAl2O3C4AF : 4CaOAl2O3Fe2O3

CE 60Instructor: Paulo Monteiro

Hydrationcement

+water

dissolution precipitation

Courtesy: Prof. Karen Scivener, EPFL

CHEMICAL REACTIONS2C3S + 6H --> C3S2H3 + 3CH + 120 cal / g

2C2S + 4H --> C3S2H3 + CH + 62 cal / gC3A + --> Ettringite + 300 cal / g

Extremelly important!!!

2CSH

CE 60Instructor: Paulo Monteiro

Hydrated Paste

CE 60Instructor: Paulo Monteiro

Early Hydration

3 hours 10 hours

Courtesy: Prof. Karen Scrivener

CE 60Instructor: Paulo Monteiro

Hydration Products

SOLIDS IN CEMENT PASTE

-Calcium Silicate Hydrate

Notation: C-S-HHigh Surface (100 to 700 m2/ g) ----> High Van

der Walls Force -----> Strength.Volume % : 50 a 60

CE 60Instructor: Paulo Monteiro

C-S-H

SOLIDS IN CEMENT PASTE

-Calcium Hydroxide ( portlandite)

Ca(OH)2Volume % : 20 to 25

low Van der Walls forceproblems with durability and strength

CE 60Instructor: Paulo Monteiro

Calcium Hydroxide

SOLIDS IN CEMENT PASTE

-Calcium Sulfoaluminate HydratesVolume % : 15 to 20

first : ettringiteafter : monosulfate hydrated.

CE 60Instructor: Paulo Monteiro

Ettringite

Mehta and Monteiro: Concrete

Review – Identify the crystal

Mehta and Monteiro: Concrete

Review 2 -- Identify the crystal

Mehta and Monteiro: Concrete

Review 3 -- Identify the crystal

CE 60Instructor: Paulo Monteiro

Concrete has a complex microstructure

Cement grain

C-S-H

Sand Particle

Calcium hydroxide

pores

Courtesy Prof. K. Scrivener

CE 60Instructor: Paulo Monteiro

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

CE 60Instructor: Paulo Monteiro

Hydration Process

Miracle of hydration: Vp = 2 Vc

50%

Vc= 100 cm3

Vw= 200 cm3

Vc=50 cm3Vp = 100 cm3

Vw= 150 cm3

CE 60Instructor: Paulo Monteiro

Once More…

75%

Vc= 100 cm3

Vw= 200 cm3

Vc=25 cm3Vp = 150 cm3

Vw= 125 cm3

CE 60Instructor: Paulo Monteiro

Finally

100%

Vc= 100 cm3

Vw= 200 cm3

Vp = 200 cm3

Vw= 100 cm3

CE 60Instructor: Paulo Monteiro

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

ASTM Portland CementsType 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.

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

CE 60Instructor: Paulo Monteiro

Water inside the pores

CE 60Instructor: Paulo Monteiro

Orders of magnitude

CE 60Instructor: Paulo Monteiro

Orders of Magnitude