Chapter 3Chapter 3

CementCement

– Production and Composition of Portland Cement– Hydration, Setting and Hardening of Portland

Cement– Technical Properties of Portland Cement– Corrosion and Prevention of Hardened Cement– Characteristics and Application of Portland

Cement

§3.2 Portland Cement

Corrosion and Prevention of Hardened Cement

• Introduction

• Representative Corrosion Types

– Denudation Corrosion

– Sulfate Corrosion

– Magnesia Corrosion

– Carbonate Corrosion

– Acid Corrosion

• Origin of Corrosion

• Prevention of Corrosion

Introduction

• The hardened cement paste can still be hardened and the strength can also increase in the normal condition (humid environment or in water).

• Corrosion of Hardened Cement• The structure will be destroyed. Strength and

durability will be decreased, or totally damaged in corrosive substance.

– Denudation Corrosion

– Sulfate Corrosion

– Magnesia Corrosion

– Carbonate Corrosion

– Acid Corrosion

– Alkali Corrosion

Representative Corrosion Types

Denudation corrosion

• Denudation corrosion– It refers to the

corrosion caused by dissolution of calcium hydroxide in soft water.

Preventive measureIn hard water, the following reaction happens

On the surface, dense calcium carbonate layer will On the surface, dense calcium carbonate layer will be formed to protect concretebe formed to protect concrete

Beforehand concrete should be carbonized in carbonizing apparatus-Artificial carbonation.Artificial carbonation.

Ca(OH)Ca(OH)22 + Ca(HCO + Ca(HCO33) ) 22 CaCO CaCO33 + H + H22OO

Denudation corrosion

Denudation corrosion

Artificial carbonationArtificial carbonationBeforehand concrete should be carbonized in carbonizing apparatus

Ca(OH)Ca(OH)22 + Ca(HCO + Ca(HCO33) ) 22

CaCOCaCO33 + H + H22OO

On the surface, dense Calcium carbonate On the surface, dense Calcium carbonate layer will be formed to protect concretelayer will be formed to protect concrete

Preventive measure

Sulfate Corrosion• Characteristics

– Sulfate medium-sea water, underground water and so on

– Sulfate reacts with ingredients in hardened cement to form dilatancy crystal and destroy the hardened cement

22432

24232

3133

203124

OHCaOHCaSOOAlCaO

OHCaSOOHOAlCaO

Crystallization and expansion

MgCl2+Ca(OH)2 = Mg(OH)2+CaCl2

MgSO4+ Ca(OH)2+H2O = Mg(OH)2+CaSO4·2H2O

Crystallization and expansionCrystallization and expansionFreely solubleFreely soluble

Magnesia Corrosion • Characteristics

– Magnesia medium-sea water, underground water and so on

– Magnesia reacts with ingredients in hardened cement to form freely soluble and dilatancy crystal , and destroy the hardened cement.

Carbonate Corrosion

Ca(OH)2+CO2+H2O CaCO3+2H2O

CaCO3+H2O+CO2 Ca(HCO3)2

Freely soluble

• Characteristics– Carbonate medium-sea water, underground

water and so on.– Carbonate reacts with ingredients in hardened

cement to form freely soluble and destroy the hardened cement.

Acid Corrosion

Freely soluble

Crystallization and expansion

OHCaSOOHCaSOH

OHCaClOHCaHCl

24242

222

2)(

2)(2

• Characteristics– Acid medium-industry environment and so on

– Acid reacts with ingredients in hardened cement to form freely soluble crystallization, expansion and destroy the hardened cement.

Alkali Corrosion

CHAlONaNaOHA 3223C Ｏ

OHCONaCONaOH 2322 Freely soluble

Dry air

Crystallization and expansion

• Characteristics Alkali reacts with ingredients in hardened

cement to form freely soluble crystallization, expansion and destroy the hardened cement

Origin of Corrosion

Hydrates such as CH, C-A-H are liable to react with some corrosion substance.The inner structure of hardened cement is not perfectly compact. Influence from environment.

Prevention of Corrosion

• Selection of cement varied with environment features.

• Improving denseness of cement.

• Prevented coating should be covered on the surface of concrete. Impregnated concrete should be employed for the special concrete project.