The durability of cement paste is one of the most current issues today in which economic containment and savings will remain the rule of the day. The term “degradation” means that the cement paste fails to serve its intended purpose for the intended time. It should be noted that normally cement paste often has a substantially indefinite lifespan, in the absence of degradation processes [32]. The physicochemical degradation of cement can be thought of in two categories. They are a physical action that breaks down hardened cements into smaller fragments, a chemical action that alters their components into different species, and a chemical action that usually consists of the dissolution of matter and the formation of a new phase [45]. Degradation mechanisms of cement paste due to chemical and physical factors include alkali-silica reaction, sulfate attack, chloride reaction, carbonation, leaching, freezing and thawing [45]. An example of chemical degradation process can be observed in alkali-aggregate reactions such as dissolution of silica and formation of silica gel. This reaction involves breaking the bonds between the aggregate and the pulp [32]. An example of a physical degradation process is the reaction of Ca(OH)2 and CSH with CO2 which causes withdrawal from carbonation. It could lead to loss of structural integrity such as volume instability, cracking and loss of strength [32]. Laboratory experiments have shown that concrete degrades when exposed to CO2-rich environments [10]-[12], [16], [22], [72]-[74], [30]. It tends to degrade rapidly once exposed to this acidic gas by reacting with Ca(OH)2 and CSH. The mechanism of the degradation process begins when CO2 gas is exposed to a humid environment, it...... middle of paper ......3 occurs by acid attack after a 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]. Therefore, the water produced in equation 2.11 will dissolve more Ca(HCO3)2. As leaching of this material continues from the cement matrix, significant increases in porosity and permeability would occur. Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + H2O (2.11) Furthermore, the additional water produced by each reaction may allow the production of H2CO3 when reacting with CO2 as in equation 2.4 and thus a process of continuous carbonation.