The sustainability of cement paste is today one of the most topical areas where economic rigor and conservation will remain the rule of the day. The term “degradation” means that the cement paste does not serve its intended purpose for the intended duration. It should be noted that normally cement paste often has an essentially indefinite lifespan, in the absence of degradation processes [32]. The physicochemical degradation of cement can be considered in two categories. It is a physical action which breaks hardened cements into smaller fragments and a chemical action which modifies their components into different species and a chemical action generally consisting of a dissolution of the material and the formation of a new phase [45]. Among the degradation mechanisms of cement paste due to chemical and physical factors are alkali-silica reaction, sulfate attack, chloride reaction, carbonation, leaching, and freezing and thawing [45 ]. An example of chemical degradation processes can be seen in alkali-aggregate reactions such as dissolution of silica and formation of silica gel. This reaction involves a breakdown of the bonds between the aggregate and the paste [32]. An example of a physical degradation process is the reaction of Ca(OH)2 and CSH with CO2 which causes shrinkage by carbonation. This can lead to loss of structural integrity such as volume instability, cracking and loss of strength [32]. Laboratory experiments have shown that cement degradation will occur once exposed to such CO2-rich environments [10]-[12], [16], [22], [72]-[74], [30]. . It tends to degrade rapidly once exposed to such acidic gas by reacting with Ca(OH)2 and CSH. The degradation process mechanism starts when the CO2 gas is exposed in a humid environment, it will occur...... middle of paper ......3 occurring by acid attack after complete removal of Ca (OH)2 at low pH as shown in equation 2.10.CaCO3 + H2CO3 → Ca(HCO3)2 (2.10) In these reactions, CaCO3 is converted to water-soluble calcium bicarbonate (Ca(HCO3)2) which can then react with Ca(OH)2 to form CaCO3 and additional water as shown in equation 2.11. Ca(HCO3)2 is two orders of magnitude more soluble than Ca(OH)2 [33]. Thus, the water produced in equation 2.11 will dissolve more Ca(HCO3)2. As leaching of this material continues from the cement matrix, a dramatic increase in porosity and permeability would occur. Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + H2O (2.11) Additionally, the additional water produced by each reaction can allow the production of H2CO3 upon reaction with CO2 as in equation 2.4 and so a continuous carbonation process could occur.