Comparative study on the durability of ultra-high toughness cementitious composites and mortar under salt attacks

Abstract

The high fly ash replacement (50%–85% by weight of total cementitious materials) and the use of polyvinyl alcohol fibers have improved the durability of ultra-high toughness cementitious composites (UHTCC) and reduced its life-cycle costs and CO₂ emission, which give UHTCC higher sustainability than that of normal concrete. To get a comprehensive understanding of the durability of UHTCC, a comparative study on the salt resistance was conducted between UHTCC and Portland cement mortar. Specimens were exposed to NaCl, MgCl₂, Na₂SO₄, and MgSO₄ solutions with 5% anion concentration and high-salinity (35%) seawater, which are the common aggressive substances in actual engineering environments. Physical and mechanical properties of specimens were characterized periodically and microscopic analyses were also conducted. After exposed to MgCl₂ solution and seawater, an Mg-containing layer was formed on the surface of specimens, which acted as a barrier to retard external ions from penetrating but significantly impaired the mechanical properties of mortar specimens. Magnesium salts generally showed more serious degradation effects than sodium salts. The addition of PVA fibers could improve the salt resistance of UHTCC, and the salt resistance of UHTCC was greater than that of mortar, which suggests the promising applications of UHTCC to civil infrastructures under aggressive environments to extend the service life of structures.