Experimental Study on Internal and External Salt Attack from Seawater and Sea-Sand to Mortars

Seawater and sea-sand are potential material for concrete in marine environment. This paper aimed to study the influence of internal and external salt attack from seawater and sea-sand on the performance of mortars. Six groups of mortars with different salt attack types were designed. The length, mass, dynamic elastic modulus and pH value of all mortars were measured in the test. The hydrate phase was obtained by thermodynamic simulation, and the phase after 322 days attacked was detected by X-ray diffraction (XRD). Internal seawater and sea-sand attack could improve the early length change of mortars before 28 days. And the early mass growth rate of mortars of seawater mixed mortars was slow. While the influence of seawater and sea-sand on the early dynamic elasticity modulus was limited. The external environment was the main factor affecting the length, mass and dynamic elasticity modulus of mortars after 28 days. Differences of hydrate phases in different mortars were ettringite (AFT), monosulfate, hemicarbonate, monocarbonate, Friedel's salt and Kuzel's salt. The more salt in mixing materials, the larger the volume of hydration solid phase. The salt attack from seawater and sea-sand could increase pH of the simulated solution in mortars. Ettringite and brucite could be clearly observed by XRD in mortars attacked by external seawater, and gypsum and Friedel's salt could be observed in all mortars. It was more reasonable to use mass to evaluate the deterioration degree of the mortars attacked by seawater or sea-sand.

Automated summary

This study investigated the influence of seawater and sea-sand salt attack on the performance of mortars. It found that internal salt attack can improve early length change of mortars, while external environment is the main factor affecting mortars after 28 days. The volume of hydration solid phase increases with higher salt content in mixing materials.