Corrosion resistance and modification mechanism of modified anchoring grouting material in carbonaceous mudstone environment

Abstract

In the corrosive environment of carbonaceous mudstone, the mechanical properties of grouting materials in the anchorage section of anchor bolts continue to deteriorate. In response, a cement-based modified anchoring grouting material (MAGM) with high corrosion resistance was developed. The results reveal that compared with those of ordinary Portland cement (OPC) grouting material, the compressive strength, tensile strength, and shear stress peak of the MAGM increased by 85.9%, 44.4% and 45.4%, respectively, after 28 d of corrosion in a carbonaceous mudstone solution. Waterborne epoxy resin and curing agent create a network membrane structure under the action of nano-Al2O3 to protect the cement hydration products. In the corrosive environment of carbonaceous mudstone, corrosion products formed on the surface of the stone body have adsorbed onto the reticular membrane structure, filling the pores of the stone body and slowing the erosion rate of ions. After 365 d of application of MAGM and OPC in the corrosive environment of a carbonaceous mudstone slope, the peak shear stress of MAGM is, on average, 55.3% greater than that of OPC.

1. Introduction

With rapid economic development, many excavated slopes have formed during the construction of railways, highways, and other projects [1, 2]. Anchorage grouting technology [3−7] has become an important method for ensuring the long-term stability of slope engineering, with the advantages of high efficiency and low cost. Carbonaceous mudstone slopes [8] are widely distributed in southwestern China. Under the action of rainfall, rainwater easily dissolves free ions in the soil. When anchor grouting technology is used to reinforce slopes, traditional cement grouting materials cannot effectively resist the corrosion of various ions. As a result, they are prone to cracking and failure, which causes the anchoring section of the anchor bar to lose its anchoring performance [9]. In contrast, free ions penetrate the surface of the anchor bar through the capillary pores in the surrounding cement paste. This causes corrosion of the anchor bar and ultimately leads to slope instability [10]. Therefore, the development of new anchoring grouting materials suitable for specific corrosive environments has become an urgent issue to be addressed in engineering construction.

Scholars have conducted extensive research on how to improve the mechanical properties of traditional cement-based anchoring grouting materials. For example, MEI et al [11] modified a cement slurry by adding fly ash. Research has shown that fly ash can improve the compactness of the cement grouting slurry; however, the strength of the cement slurry stone body decreases after the addition of fly ash. To address the limitations of fly ash-modified cement slurries, many scholars have used waterborne epoxy resin (WER) to modify cement slurries [12 −14]. ANAGNOSTOPOULOS et al [15] discussed the effect of WER on the performance of cement slurries. The test results reveal that adding WER to a cement slurry increases its viscosity, stability, and compressive and tensile strength. However, it also reduces the slurry drainage rate, resulting in slow setting and hardening, low early strength, and a significant impact on the construction period. To address the problem of low early strength, ZHANG et al [16] reported that nano-Al2O3 (NA) can increase the early strength of cement-based materials and decrease the setting time on the basis of the principle of an ultrafine dense system. WER and nanomaterials modify the mechanical properties of cement-based grouting materials effectively. However, unlike ordinary slopes, the anchoring grouting material used for carbonaceous mudstone slopes must address two key issues: first, improving the stability and mechanical properties of slurry stones, and second, resisting the corrosive effects of the environment.