عنوان مقاله [English]
Sulfate attack on concrete is one of the severe environmental factor in reducing the service life of concrete structures. Laboratory studies on sulfate attack, revealed the importance of physical factors such as porosity on the process. Formation of expansive reaction products, such as ettringite and gypsum, can lead to cracking, spalling, and other damaging effects. Based on the accepted findings, a correlation exists between the C3A content in Portland cement and the susceptibility of concrete to sulfate attack. Cements of type II and V, having limited C3A content, were introduced to the moderate and severe sulfate oncentrations, respectively. Nonetheless, in some cases, the use of Type V cement and even the use of zero-C3A cement may not prevent damage due to sulfate attack. These data encourage researchers to find out new materials for protecting concretes against sulfate attack. Also, chloride ions exist besides sulfate ions in seawaters. Therefore, chloride ions can affect the diffusion rate of sulfate ions in the concrete where a smaller amount of studies could be found.As a result, in the present study, Montmorillonite nano-clay particles were substituted as cement in the range of 0.2 to 0.4 percent. Surface of nano-clay particles that negatively charged can prevent sulfate ions diffusion in the concrete. Water-cement ratio and cement content were considered 0.42 and 325 kg/m3, respectively. In the experiments, cubic specimens were considered for sulfate and combination of sulfate and chloride attacks after 28 days of moist curing. Mass loss of specimens and compressive strength changes were measured during 6 months of immersion. Results showed that the nano-clay particles increase the durability of concrete mixtures against sulfate and combination of sulfate and chloride attacks. Also chloride ions decrease the rate of sulfate ions attack. Furthermore, the mixture containing 0.3\% of nano-clay particles showed the best performance.