Study on the degradation mechanism of sulphoaluminate cement sea sand concrete eroded by biological sulfuric acid

Two different types sulfuric acids, i.e. the biological sulfuric acid (BSA) produced by T.t bacteria (Thiobacillus thiooxidans) and chemical sulfuric acid (CSA), were applied to simulate the corrosion. The sulphoaluminate cement (SAC) and the sea sand were mixed to made the concrete. The mass loss, compressive strength, chloride binding rate, pH value and pore structure were measured in the process of corrosion. Furthermore, X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were used to analyze the products of the reaction. It could be found that under the corrosion of sulfuric acid, the initial hydration products of SAC, including ettringite (AFt) and Friedels' salt, were decomposed continuously and the main corrosion product was dihydrate gypsum. Under corrosion of BSA, the corrosion became more intense due to the influence of bacterial effect. Moreover, the corrosion of BSA was more severe than that of CSA, which was obvious in terms of mass loss, strength decline and pore structure. The BSA has a more negative effect on the performance of SAC concrete.