Degradation Mechanism of Coal Gangue Concrete Suffering from Sulfate Attack in the Mine Environment

Abstract

Recycling coal gangue as aggregate to produce concrete in situ is the most effective way to solve the problem of deposited coal gangue in mines. Nevertheless, the mine environment underground is rich in sulfate ions, posing a threat to the durability of coal gangue concrete (CGC). Hence, the degradation process of sulfate-attacked CGC is investigated. A series of tests is performed to evaluate its variation law of mass, dynamic elastic modulus, compressive strength and sulfate ion distribution. Meanwhile, the microstructure and phases of sulfate-attacked CGC are identified by scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. The results indicate that the residual compressive strength ratio of CGC is higher than that of normal concrete after a 240 d sulfate attack, implying a superior sulfate resistance for CGC. Additionally, the higher the sulfate concentration, the more severe the degradation. Except for the secondary hydration of CGC itself, the diffused sulfate ions also react with Ca(OH)2, forming gypsum and ettringite; this plays a positive role in filling the pores at the early stage, whereas, at the later stage, the generated micro-cracks are detrimental to the performance of CGC. In particular, the proposed sulfate corrosion model elucidates the degradation mechanism of CGC exposed to a sulfate-rich environment.

Evaluating Sustainable Colored Mortars Reinforced with Fly Ash: A Comprehensive Study on Physical and Mechanical Properties under High-Temperature Exposure

“…The alterations in crystal phases of the R0, R1, R4 and R7 samples under ambient conditions and subsequent exposure to high temperatures were determined through X-ray diffraction (XRD) analysis, as illustrated in Figure 12a-d. The primary phases in all samples under ambient conditions were identified as portlandite (CH), calcium-silicate-hydrate (C-S-H), and quartz (Q) [64,65]. However, distinct from the R0 control sample, the FA-doped R1, R4, and R7 samples exhibited crystal phases of calcite (CaCO 3 ) and mullite (Al 6 Si 2 O 13 ) in addition to these primary phases [66,67].…”

A Finite Element Method Integrated with Terzaghi’s Principle to Estimate Settlement of a Building Due to Tunnel Construction

“…Analysing the invert of the tunnel, especially for type 1 soils, the decompressions in the tunnel contour and the infiltration flows suggest the possibility of a liquefaction of the sands. In the case of using segments in the tunnel lining, the joints must be treated with a specific fibre-reinforced concrete [65,66], suitable for the type of soil (particularly in mining tunnels) [67,68], or water-repellent additives [40].…”

“…Analysing the invert of the tunnel, es- flows suggest the possibility of a liquefaction of the sands. In the case of using segments in the tunnel lining, the joints must be treated with a specific fibre-reinforced concrete [65,66], suitable for the type of soil (particularly in mining tunnels) [67,68], or water-repellent additives [40]. It was observed that in the less compact soils (Figure 7a,c), the decompressed zones in the contour and adjacent areas of the crown and invert tunnel were somewhat larger.…”

Influence of Curing Temperature on the Performance of Calcined Coal Gangue–Limestone Blended Cements

“…In this process, pore structure distributions in the hydrated binder have also been refined [13], which is reflected in the reduction in the large pores and formation of more gel pores with lower size. More importantly, the pore structure refinement and ion consolidation ability of C-A-S-H gel are also favorable for resisting the penetration and transmission of corrosive ions, such as Cl − and SO 4 2− [14]. Therefore, CCG-blended cement also secure satisfactory long-term durabilities in severe environments as compared with the corresponding reference samples.…”