114 / 2022-04-26 10:47:38

Chloride diffusion resistance of Sulphoaluminate cement based composite characterized by alternating current section method

sulphoaluminate cement; ultra-high molecular weight polyethylene fiber; chloride diffusion; marine concrete; concrete durability

Sulphoaluminate cement (SAC) has many excellent characteristics such as fast hardening, early strength, high strength, frost resistance, good durability and low alkalinity. SAC is often used for reinforcement of concrete structures. If short fibers were integrated with SAC, the compressive strength and tensile strength of fiber reinforced SAC concrete are significantly improved. However, the current researches on fiber reinforced SAC mainly focuses on its mechanical properties while its chloride permeation resistance had not been studied. The purpose of this paper is to study the SAC-based composites in order to be used for the reinforcement of concrete structures in the sea environments, and to extend the service life of marine concrete. Ultra high molecular weight polyethylene (UHMWPE) fiber was used in this study, because it has good durability in alkaline environment as well as good compatibility with cement paste. The SAC composite was prepared through adding UHMWPE fibers to SAC and its microstructure as well as durability were investigated. Chloride ion permeability coefficient were tested with the method of alternating-current sectioning, Because  alternating-current sectioning is a new method for Cl^- charactering diffusion coefficient of  cement based materials, helped by a electrodeless resistance meter, therefore, and rapid chloride migration (RCM) method was also adopted for comparing.  



Some positive results obtained as the following. During the hydration of SAC, a large amount of ettringite will be produced which can chemically react with Cl^- to form 3CaO·Al₂O₃·CaCl₂·10H₂O when Cl^- penetrate in concrete, resulting in chemically stabilizing of free Cl^-. Compared with ordinary Portland cement-based materials, the pore structure of fiber reinforced SAC is significantly improved, and the harmful pore volume is obviously reduced (Fig. 1 and Fig. 2). This is mainly because SAC hydrates and hardens along with a large amount of ettringite, chloroaluminate, etc. are precipitated in the pores during SAC hydration, which is beneficial on the improvement of the pore structure.



By measuring the resistivity of concrete impregnated with NaCl solution, the Cl^- diffusion coefficient of SAC and Portland cement based samples measured by alternating-current sectioning method can be calculated. Fig. 3 and Fig. 4 are respectively the chloride ion diffusion coefficient of SAC composites at the age of 7d and 28d. Under the same age, the Cl^- diffusion coefficients of SAC-based fiber composites are significantly reduced compared with normal Portland cement-based samples (Fig. 5). The results showed that both the methods have the same regularity and the data are very close, which are in the same order of magnitude. This indicates the new method can be effectively applied to SAC based composite to measure the Cl^- diffusion coefficient. Fig. 6 shows that the diffusion depth of Portland cement is larger than that of SAC based composite. Thus, as a reinforced material, SAC based composite might prolong the service life of concrete structures in chloride environments.