Deterioration Process of Concrete Exposed to Internal Sulfate Attack

Abstract

Damage to concrete structures with gypsum-contaminated aggregate occurs frequently. Aggregates in much of the southern part of China are contaminated with gypsum. Therefore, in this study, the effects of using different quantities of gypsum-contaminated aggregate on the expansion and compressive strength of concrete were investigated over a period of one year. Two groups of concrete were designed with the gypsum-contaminated aggregate containing different parts of fine and coarse aggregate, respectively. The SO3 contents were 0%, 0.5%, 1%, 1.5%, 3%, 5%, and 7% by weight of aggregate. X-ray diffraction (XRD), thermogravimetry (TG), and differential scanning calorimetry (DSC) were used to analyze the change in mineral composition over time. The microstructure was also studied by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that significant expansion and great loss in compressive strength did not occur in concrete if the content of SO3 lay below 1.5% and 3% in fine and coarse aggregates, respectively. The concentration of sulfate ions in concrete was not enough to form new a phase of gypsum. During the process of internal sulfate attack, the content of gypsum decreased and the content of ettringite increased. Ettringite was the main reason for the expansion damage of concrete. Additionally, the fracture mode of internal sulfate attack on concrete was the crack extension from gypsum to paste; finally, the aggregate separated from the paste.

Determining the Mineral Admixture and Fiber on Mechanics and Fracture Properties of Concrete under Sulfate Attack

“…As shown in the Table 7, the overall cracking load and instability load increase first and then decrease with the increase of dry-wet cycles, and the ratio of the two is 0.7 to 0.9. At the initial stage of corrosion, part of the sulfate radicals enters the concrete to form expansive products such as gypsum and ettringite, which fills the crevices of the concrete, increases the density, improves the crack resistance and limits cracking performance of concrete, and therefore increases the fracture toughness [26,27]. With the increase of corrosion age, the volume of crystallization products expands and exceeds the bearing capacity of the pores, resulting in a large number of micro-cracks, and these micro-cracks form new channels, which accelerate the corrosion rate of sulfate [28].…”

Influence of Different Waste Materials on Resistance of Cement Mortars against Carbonation and Chloride Ingress

“…It is worth noting that the elevated content of free CaO causes soundness problems in concrete as well as significant temperature increase, (Schlorholtz, 1998). At the same time, high amounts in sulfate ions cause concrete expansion (Zhang et al, 2013), (Ramezanianpour et al, 2020), (Chen et al, 2020). It is well known that the composition of fly ash mainly includes oxides SiO 2 , Al 2 O 3 and Fe 2 O 3 .…”

Study on Corrosion Mechanism of Different Concentrations of Na2SO4 Solution on Early-Age Cast-In-Situ Concrete

“…When the RA aggregates get closer, the corrosion products AFt and Gyp is increasing as well. Weifeng [ 24 ] used SEM and EDS to study the microstructure of concrete with different amounts of gypsum-contaminated aggregates. The results showed that the internal cracks of concrete propagate from gypsum to paste during the process of sulfate internal erosion, causing the aggregate to move from the grout and separated from the matrix.…”