Chapter 3 Cement

§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

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.

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

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

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) 2 CaCO3 + H2O

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

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

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

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+CO2 Ca(HCO3)2 Freely soluble

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 ) ( ® +

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

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.