Numerous studies have shown that sulfate is an important factor in damaging the durability of concrete structures. In practice, sulfate corrodes both concrete and steel reinforcement, causing great harm. The sulfate attack mechanisms on concrete mainly include two types:

　　① Physical attack. Under alternating dry-wet cycles, sulfate infiltrating into the concrete may crystallize. For example, Na2SO4 and MgSO4 crystallize from water to form Na2SO4·10H2O and MgSO4·7H2O crystals, respectively, which expand in volume by 4 to 5 times, generating crystallization pressure, causing cracks in the concrete and leading to deterioration of the concrete.

　　② Chemical attack. Sulfate intrudes into the concrete and reacts with cement hydrates such as calcium hydroxide, calcium aluminate hydrate, and monosulfate, as well as unhydrated tricalcium aluminate, to form expansive products—gypsum and ettringite—causing cracking and destruction of hardened concrete. The cracking of concrete in turn makes it easier for external sulfate ions to penetrate into the concrete. These processes promote each other and develop cyclically, causing rapid destruction of the concrete. The formation of gypsum also leads to a decrease in stiffness and strength of the concrete and surface softening. The deterioration of concrete performance caused by sulfate attack is mainly manifested as: strength loss, expansion and cracking, surface spalling, surface softening, mass loss, etc.
　　Technical Measures to Prevent Steel Corrosion
　　According to the Geotechnical Investigation Report, during the investigation period, the groundwater level was between 0.12 and 0.80 m, with an annual fluctuation of about 0.80 m, and the investigation was conducted during the wet season. Therefore, the design water level for corrosion protection is considered to be -0.68 to 0.00 m. According to Article 12.2.4 of the current national standard Code for Investigation of Geotechnical Engineering (GB50021-2001) (2009 Edition), steel reinforcement in reinforced concrete structures has weak corrosivity when immersed in water for a long time. The design ground elevation of the entire sintering plant area is 4.10 m. Therefore, in this design, only reinforced concrete piles with a pile cap embedment depth of not less than 4.80 m are in a long-term immersed state. Cl- has weak corrosivity to the steel reinforcement in the piles, and SO42- has moderate corrosivity to the reinforced concrete structure of the piles. Otherwise, according to Article 4.9.5 of the current national standard Code for Anticorrosive Design of Industrial Buildings (GB50046-2008), reinforced concrete cast-in-place piles should not be used under strong corrosive conditions. In view of this, if cast-in-place piles are to be used, the foundation embedment depth needs to be increased so that the cast-in-place piles are in a stable water level. However, construction requires dewatering measures, increasing the excavation volume, increasing construction difficulty, and greatly increasing project cost. According to the requirements of the construction unit, in order to reduce the excavation volume and reduce construction costs such as dewatering measures, after special subject analysis and research, the pile cap embedment depth was raised to 1.5 m to 2.5 m, and a comprehensive durability strategy and scheme centered on high-volume concrete technology was adopted for the cast-in-place piles. The following anti-corrosion and durability ideas were proposed:
　　(1) Use high-performance concrete. High-performance concrete not only has excellent steel protection performance, but also has excellent comprehensive durability, such as good sulfate resistance, wear resistance, chemical corrosion resistance, etc. In addition, high-performance concrete is relatively economical and construction quality is easy to guarantee. This cast-in-place pile uses high-volume mineral admixture concrete to improve the durability of the reinforced concrete structure. The cast-in-place pile uses C40 concrete, with a water-binder ratio not greater than 0.4 and an impermeability grade not less than P8.
　　(2) Increase the thickness of the concrete cover. In environments where chloride salts exist, the cover thickness shall not be less than 50 mm. Considering construction deviations, the steel reinforcement cover of the piles in this project is 70 mm.
　　(3) Use epoxy-coated steel reinforcement. For cast-in-place piles in alternating dry-wet areas, the corrosion of steel reinforcement by Cl- is strong. This part (about 5 m long) uses epoxy resin-coated steel reinforcement to isolate the steel reinforcement from contact with corrosive media and prevent Cl- corrosion of the steel reinforcement. If the coating quality is well controlled, it can effectively delay the onset of steel corrosion. However, once corrosion starts, the corrosion rate will accelerate. Therefore, the difficulty in construction quality control is to ensure that the coating is not damaged during construction.
　　(4) Appropriately use corrosion inhibitors. Corrosion inhibitors can prevent or delay the destruction of the passive film on steel reinforcement by chloride ions. However, the use of corrosion inhibitors in pile foundations increases the cost per cubic meter of concrete by about 10%, and the main component of corrosion inhibitors is calcium nitrite. Calcium nitrite is the main component of early strength agents and antifreeze agents and has the effect of accelerating the setting of concrete. Considering comprehensively, corrosion inhibitors should be added appropriately.
　　4 Conclusion
　　Chloride salts and sulfates are key factors in the corrosion of steel reinforcement and the durability of reinforced concrete structures. The comprehensive durability anti-corrosion technology centered on high-volume concrete technology has the advantages of reliability, ease of implementation, and economy.