Abstract: To address the problem of the high cost of freshwater river sand transported over long distances from land in the construction of marine and island projects, and to make resourceful use of the reinforcing and toughening properties of coir fibers, the alkali-treated coir fiber-reinforced seawater sea sand concrete was proposed as a high performance, cost-effective and low-carbon building material. By designing three kinds of macroscopic destructive tests (compressive, splitting tensile and flexural tensile strength tests), and combination of macroscopic experimental damage phenomena and microstructural electron microscopic analyses, the effects of alkali-treated coir fiber’s length and content on the mechanical properties of seawater sea sand concrete were studied and verified. The absorptivity of natural and alkali treated coir fibers was tested in different solutions, and the microstructure of the fibers was observed by electron microscopy. It is proved that alkali treatment could not only improve the roughness of coir fibers,weaken the moisture absorption rate of the fibers, but also effectively enhance the bonding effect between the fibers and the concrete.

Key words: coir fiber, seawater sea sand concrete, alkali treatment, mechanical properties, composites