Influence of the multiple element ions contained in seawater and sea sand on the freeze-thaw resistance of cementitious materials

Preparation of concrete with seawater and sea sand can increase the pore solution salinity due to the introduced multiple ions, which can affect the freeze -thaw resistance of concrete by changing the crystallization pressure and freezing temperature. This study aims to investigate the influence of these multiple element ions in seawater and sea sand on the freeze -thaw damage characteristics of cementitious materials. The seawater sea -sand mortar (SSM) samples and reference specimens (Freshwater and river sand-FRM) were first prepared with same mix design. The accelerated freeze -thaw tests were then conducted in an environment chamber under the temperature range of [-20 degrees C, 7 degrees C]. The surface spalling, mass loss, and mechanical performance (Compressive strength, stiffness and fracture resistance) evolution during freeze -thaw cycles were characterized to examine the freeze -thaw resistance. The influence mechanism is analyzed through characterization of pore solution and structure, and Discrete Element Method (DEM) simulation. It is indicated that the introduced multi -element ions from seawater and sea sand accelerate the freeze -thaw deterioration of cementitious materials. After 150 freeze -thaw cycles, the mass loss rates of SSM and FRM samples reach above 10 % and 8 %, respectively. And the corresponding reduction rates for dynamic modulus are 51 % and 36 % for the SSM and FRM specimens. The deterioration in compressive strength is slightly higher than the loss of fracture resistance. The mechanism analysis indicated that deteriorated freeze -thaw resistance due to the introduced multi -element ions from seawater and sea sand mainly originated from the degradation of pore structure and the increase in freezing pressure. This study can serve as a solid base for the durability design and application of seawater sea -sand concrete in cold regions.