Mechanical behavior of ultra-high toughness engineered cementitious composite using seawater coral sand exposed to elevated temperature

Abstract

Island construction poses new challenges to material development. High-performance Seawater Coral Sand Engineered Cementitious Composite (SC-ECC) with high toughness can achieve by using polyethylene (PE) fibers. However, when suffering from high temperature, PE fibers tend to melt and plug the pores, blocking vapors from escaping the matrix and causing it to crack. To address this problem, in this paper, polyoxymethylene (POM) fibers with good thermo-mechanical property are explored to replace the PE fibers in the SC-ECC to remain a good mechanical feature exposed to elevated temperature. The high-temperature tests were conducted to obtain the cracking temperature variations of SC-ECC with different fiber content. The bursting resistance mechanism of POM fiber was revealed by means of thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosity (MIP) microstructural analyses, and the bursting probability was discussed from the perspective of pore structure. The mechanical performance tests of SC-ECC with various fiber replacement rates at different temperatures were carried out, and a tensile constitutive model was proposed. The results indicated that the specimens with POM fibers did not experience spalling or fracture within the temperature range of 20–700°C, while those with only PE fibers exhibited fracture at 300℃. After melting, POM fibers easily volatilize without agglomeration and blockage of pores, leaving behind larger diameter voids. This facilitates the alleviation of high vapor pressure generated from water loss between 200 and 300℃. The tensile properties of POM-incorporated specimens slightly decrease with increasing POM content, while the compressive strength gradually increases. Regardless of the fiber type, strain hardening behavior of SC-ECC was lost at 200℃. Beyond 300℃, ECC with pure PE completely lost its mechanical performance due to bursting, while that with POM fibers consistently maintained good compressive and tensile strength up to 400°C. The addition of POM significantly enhances the compressive strength of SC-ECC at any temperature (20–400℃). A comprehensive evaluation demonstrated an excellent mechanical performance and high temperature spalling resistance of SC-ECC with 1.5 vol% PE and 0.5 vol% POM.