1. Chapter 3
Cement

2. §3.2 Portland Cement 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. 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

4. 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.

5. Representative Corrosion Types
Denudation Corrosion
Sulfate Corrosion
Magnesia Corrosion
Carbonate Corrosion
Acid Corrosion
Alkali Corrosion

6. Denudation corrosion Denudation corrosion
It refers to the corrosion caused by dissolution of calcium hydroxide in soft water.

7. Denudation corrosion Preventive measure
In hard water, the following reaction happens
On the surface, dense calcium carbonate layer will be formed to protect concrete
Beforehand concrete should be carbonized in carbonizing apparatus-Artificial carbonation.
Ca(OH)2 + Ca(HCO3) CaCO3 + H2O

8. Artificial carbonation
Denudation corrosion
Preventive measure
Ca(OH)2 + Ca(HCO3) 2
CaCO3 + H2O
On the surface, dense Calcium carbonate layer will be formed to protect concrete
Beforehand concrete should be carbonized in carbonizing apparatus
Artificial carbonation

9. 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
Crystallization and expansion

10. Magnesia Corrosion MgCl2+Ca(OH)2 = Mg(OH)2+CaCl2
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.
MgCl2+Ca(OH)2 = Mg(OH)2+CaCl2
MgSO4+ Ca(OH)2+H2O = Mg(OH)2+CaSO4·2H2O
Crystallization and expansion
Freely soluble

11. Carbonate Corrosion Ca(OH)2+CO2+H2O CaCO3+2H2O CaCO3+H2O+CO2 Ca(HCO3)2
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.
Ca(OH)2+CO2+H2O CaCO3+2H2O
CaCO3+H2O+CO Ca(HCO3)2
Freely soluble

12. Acid Corrosion O H CaSO OH Ca SO CaCl HCl ) ( ® + 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.
Freely soluble
Crystallization and expansion O H
CaSO OH Ca SO
CaCl
HCl 2 4 ) ( +

13. Alkali Corrosion Dry air Freely soluble Characteristics
Alkali reacts with ingredients in hardened cement to form freely soluble crystallization, expansion and destroy the hardened cement
Freely soluble
Dry air
Crystallization and expansion

14. 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.

15. 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.