Study on the Deterioration of Concrete under Dry–Wet Cycle and Sulfate Attack

Abstract

In order to study the deterioration and mechanism of dry–wet cycles and sulfate attack on the performance of concrete in seaside and saline areas, the deterioration of compressive strength of concrete with different water cement ratios under different erosion environments (sodium sulfate soaking at room temperature and coupling of dry–wet cycling and sodium sulfate) was studied here. At the same time, ICT (industrial computed tomography) and NMR (nuclear magnetic resonance) techniques were used to analyze the internal pore structure of concrete under different erosion environments. The results show that the compressive strength under different erosion environments increases first and then decreases, and the dry–wet cycle accelerates the sulfate erosion. With the increase of dry and wet cycles, larger pores are filled with erosion products and developed into small pores in the early stage of erosion; in the later stage of erosion, the proportion of larger pores increases, and cracks occur inside the sample. In the process of sulfate soaking and erosion, the smaller pores in the concrete account for the majority. As the sulfate erosion continues, the T2 spectrum distribution curve gradually moves right, and the signal intensity of the larger pores increases.

Analysis and Prediction of Sulfate Erosion Damage of Concrete in Service Tunnel Based on ARIMA Model

“…However, due to the high sulfate concentration in the water sample detection of the test tunnel, the experiment requires a strict sulfate concentration. Therefore, sodium sulfate immersion concentrations of 2% and 10% are selected, which are also used in previous studies [ 40 , 41 , 42 ]. To ensure the concentration of the sodium sulfate soaking solution remains unchanged, we replaced it every 30 times.…”

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].…”

The Impact of Long-Term Physical Salt Attack and Multicycle Temperature Gradient on the Mechanical Properties of Spun Concrete

“…Experimental results presented by Liu et al [14] showed that following 80 CWD cycles of a sulphate attack, the compressive strength of ordinary concrete increased by 9.1 and 6.1% (subject to the water-cement ratio), while in the succeeding 120 CWD cycles, compressive strength decreased by 15.6 and 11.3%, respectively. Concrete soaking accelerated the corrosion caused by cyclic wetting and drying [14,37].…”

“…The scientific literature provides a number of studies on factors having an impact on concrete durability, including physical salt attack (PSA) [3][4][5][6][7][8][9][10][11][12][13], cyclic wetting and drying (CWD) [14][15][16], the water-cement ratio of the initial concrete mix [14,[17][18][19], chemical admixtures [20].…”

“…The impact of PSA and CWD on the physical-mechanical properties of vibrated concrete is considered in the research papers that state that exposure to saline initially improves the structure of concrete [14,37], while the damaging effects of pressure from salt crystals growing in concrete pores are noticeable only after long-term exposure to CWD.…”