Study on sewage erosion resistance of nano titanium modified coral concrete

Abstract

Sewage environments can significantly erode and degrade coral concrete, impacting its structural longevity. Moreover, the curing water environment greatly influences coral concrete's resistance to sewage erosion. This study investigated the modification of coral concrete with nano TiO2 to enhance its sewage erosion resistance. Concrete specimens with four different mass fractions of nano TiO2 were prepared and cured in three environments. Tests for compressive strength, flexural strength, and mass loss were conducted before and after 180 days of sewage exposure, and a corrosion coefficient was defined to evaluate resistance to sewage corrosion. While nano TiO2 significantly improved the mechanical properties and sewage erosion resistance of coral concrete, oxalic acid and seawater environments had adverse effects. Furthermore, increasing the nano TiO2 mass fraction initially enhanced and then reduced strength and resistance, while mass loss rates first decreased and then increased. The optimal nano TiO2 dosage of 4 % resulted in a maximum increase of 22.2 % in compressive strength, 33.2 % in flexural strength, a 0.06 increase in the compressive corrosion resistance coefficient, and a 0.1 increase in the flexural corrosion resistance coefficient. At this dosage, compressive strengths of coral concrete cured in oxalic acid and seawater were 97.8 % and 93.9 % of those in freshwater, while flexural strengths were 97.8 % and 94.4 %, respectively, with slight decreases in corrosion resistance coefficients, accompanied by higher mass loss rates. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that nano TiO2 promotes cement hydration, forming a dense structure by filling matrix pores. However, oxalic acid reacts with Ca(OH)2 to form calcium oxalate, slowing cement hydration, while MgCl2 in seawater reacts with Ca(OH)2, forming expansive Mg(OH)2, which increases internal concrete pores.

Keywords

• Modified coral concrete
• Nano TiO2
• Sewage erosion
• Mechanical property