Anchor Corrosion Research Articles

Corrosion Investigation of Rock Anchors Served over 10 Years in Underground Powerhouse of a Hydropower Station

With the wide application of prestressed anchors in high slopes, underground structures, and bridge projects, the corrosion problems of the anchor structure during the long-term service have demanded more attention. Because of the environmental impact and structural characteristics, anchor cable corrosion is almost inevitable. To obtain the corrosion status of the anchors that have served over 10 years in the underground chambers of a power station, a field investigation was performed. The environment aggressivity was evaluated, and the anchor corrosion was inspected during the investigation. The results show that the effect of groundwater and stray current on anchor corrosion is slight. The main cause of the severe corrosion of the anchor heads is the high temperature and humidity in the chamber. To better evaluate the corrosion tendency and corrosion degree of the anchor head, a corrosion rating method was proposed based on the principles of existing investigation methods and the actual corrosion situation of anchors observed on-site. It was proved that the rating method can effectively reflect the corrosion characteristics and determine the areas prone to corrosion. This field investigation suggests that a regularly scheduled investigation is of great significance and meaning for accurately obtaining the corrosion status, assessing the failure risk, and issuing an early warning.

Review of corrosion test methods of prestressed anchor

Prestressed anchorage structures have been widely employed in water conservancy, hydropower, mining, transportation, and other industries as an essential reinforcement means in structures such as slope and underground cavities. The anchor corrosion during service caused widespread concern about the long-term durability of prestressed anchors. Corrosion tests, which can capture anchor corrosion initiation and development characteristics in various engineering environments, have gradually become an essential tool in the durability study of prestressed anchor structures. This study summarizes five commonly used testing methods for anchor corrosion and illustrates their applicability and defectiveness based on a comprehensive literature review and lessons learned from implementing anchor durability tests for prestressed anchors by several authors. This summary provides quick and practical guidance for those who will be studying anchor cable durability. Furthermore, the relevant literature is listed in this study for easy assessment by readers.

Effect of the chloride environmental exposure on the flexural performance of strengthened RC beams with self-anchored prestressed CFRP plates

Carbon fibre-reinforced polymer (CFRP) plates are widely used to strengthen reinforced-concrete (RC) structures. At present, most studies focused on the short-term performance of strengthened RC beams with a prestressed CFRP plate, and very limited information is available on their durability, which is of importance in certain cases, such as high-piled wharfs and bridges in marine environments. This study investigates the effects of chloride environment exposure on the flexural performance of strengthened RC beams with self-anchored prestressed CFRP plates. In total, seven RC beams, four of which were strengthened by a self-anchored prestressed CFRP plate, were fabricated and tested under three-point bending. The testing parameters included 25% and 40% prestress level of the ultimate tensile strength of the CFRP plate, 5% and 10% tensile steel rebar corrosion ratio of mass loss and 10% and 20% anchor corrosion ratio in the chloride environment. The evolution of time-dependent prestress losses in the strengthened beam was determined, and the flexural behaviour of the strengthened beams was analysed. A theoretical model is proposed to predict the flexural strength of prestressed CFRP strengthened RC beams in a chloride environment. The experimental results indicated that the coupling of the corrosion expansion of the metal anchor and rebar in the chloride environment had a large negative effect on the flexural performance of the beams strengthened by the self-anchored prestressed CFRP plates. After exposure to the chloride ion solution, the failure mode of the RC beams strengthened by the prestressed CFRP changed from concrete crushing in the compression section to anchor pullout. The proposed model, which considered the effect of a chloride environment to predict the flexural strength of the strengthened beams, agreed well with the test results.

Corrosion Characteristics of Anchor Cables in Electrolytic Corrosion Test and the Applicability of the Test Method in Study of Anchor Cable Corrosion

The selection of corrosion test method in the corrosion study of the prestressed anchors is an important issue. In this paper, the corrosion test of anchors was conducted with electrolytic corrosion test method. The corrosion characteristics of the anchor cables were examined. The effects of sodium chloride solution concentration, current, test time, and prestress level on corrosion were studied. The applicability of electrolytic corrosion method in anchor cable corrosion study is discussed subsequently. The results show that the corrosion of the anchor appears to be uniform corrosion. With the corrosion of the anchor, the central wire of the cable was basically not corroded, and the cross-sectional shape of the outer wire changes from a round to fan shape. The sodium chloride concentration and prestress level have no obvious effects on the corrosion of the anchor. The variation of test time does not affect the difference between the measured and theoretical calculated results, while a proper current in the electrolysis test may help reduce the difference. The measured corrosion rate fluctuates from −4% to 10% and tends to be higher compared with calculated results based on Faraday’s law. The study indicates that the electrolytic corrosion test is applicable in the anchor corrosion study.

Failure Analysis of the Strain Clamp Steel Anchor Corrosion of a 500 kV Transmission Line

By macroscopic observation, composition analysis, mechanical properties test, SEM, energy spectrum, overall grip tensile test and finite element mechanics calculation method, the strain clamp steel anchor corrosion failure of a 500 kV transmission line is analysed. The results show that the corrosion of steel anchor for 31 years are the result of the natural corrosion, steel anchor corrosion rate is accelerated due to the galvanic corrosion, crevice corrosion, stress and damaged surface of the galvanized layer, and achieve C4 environment (zinc 2.1–4.2 um per year, carbon steel 50–80 um per year). The hardware are qualified. It is suggested to replace the steel anchor with yellow rust on the surface after 5 years, and to reevaluate the next maintenance cycle of the gold fittings without yellow rust on the surface at present, and replace it when the corrosion depth reaches 10%. Before replacement, all fittings should be monitored, especially steel anchor.

Investigations of rock anchor corrosion and its influence factors by exhumations in four typical field sites

With the abundance application of rock and soil anchors in high slope and underground projects, more concerns have been paid to the working condition and durability of the anchorage system. To effectively evaluate the corrosion of anchors in service and the influence factors, field exhumations were performed in four typical application sites and tests of samples were conducted in laboratory. Chemical composition, metallurgical structure and mechanical performance of anchors are tested. Microstructure and component of corrosion byproducts and grout were analyzed. The environmental influence factors are also assessed. The results demonstrate that the anchor head is most liable to corrode in comparing to other section of the anchor. Presence of damaging ions can accelerate the initiation and development of corrosion. Chemical and mechanical properties of anchors remain basically unchanged after 1.5 to 20 years' service. Groundwater and stray currents in the underground do not induce noticeable influence on the corrosion of anchors. This research accomplished a set of evaluation methods of influencing factors and the general law of anchors' corrosion in field environments, which may provide a reference framework for evaluating the environmental effects, durability and service life of rock anchors.

A Resilience Model for Engineered Slopes Subject to Anchor Corrosion

Many high engineered slopes are stabilized using anchors, which may corrode over time. Proper maintenance is essential to recover the system performance and upkeep slope functions. This paper presents a resilience model for maintenance decision by analysing the degradation of an anchor-stabilized slope due to corrosion and evaluating the recovery of slope performance after maintenance. Failure probability is used as an indicator to characterize the evolution of slope performance within its service life. The timing for maintenance is determined when the failure probability reaches an intolerable value. Information obtained from regular inspections is used to reduce the uncertainty in the determined maintenance time. The effectiveness of possible repair schemes is measured by a resilience index for the slope attained after maintenance, which considers the reduction in the failure probability and the duration over which the failure probability remains acceptable. A benefit index, which incorporates both the effectiveness and cost of a repair measure, is defined and used to quantitatively evaluate possible maintenance schemes. The proposed model is illustrated using an anchor-stabilized rock slope example, which provides a means to quantitatively assess different repair measures and enables engineers to select an effective and economic measure for slope maintenance.

Ground anchors corrosion - the beginning of the end

Ground anchor corrosion is a common problem for anchored slopes in Taiwan. It is partly due to the humid climate condition and abundant groundwater in the slope and partly due to poor corrosion protection of anchor design and construction. In 2010, an anchored slope at Taiwan National Freeway No. 3 failed suddenly after 13 years of service. It buried 3 cars and killed 4 people. It caught the public’s attention and initiated the island-wide program on over hauling the anchors slopes in Taiwan. Since this event, the Ministry of Transportation and Communication (MOTC) of Taiwan government had launched an extensive inspection and maintenance program for the existing anchored slopes along the freeways, highways, and railways. Totally, more than 100,000 ground anchors had been inspected. This paper will evaluate the findings from this inspection program. It includes (1) the status quo of the anchors regarding the corrosion condition and the residual load that remained on the existing anchors; (2) remedial measures taken to sustain the serviceability of existing corroding anchors; (3) measures taken to enhance the long-term durability of new anchors without changing the strand material and the practice of anchor construction commonly used by the local contractors.

Problems and detection of line anchor and substation ground grid corrosion

Corrosion due to electrochemical reactions and methods for dealing with it are discussed. To estimate the rates of substation ground grid and guy anchor corrosion, four tests are suggested, namely: (1) earth resistivity (2) guy current, (3) grid-to-earth potential; and (4) polarizing current. An analysis of test results will give the degree of corrosion and the form of correction necessary. >

Analysis of Anchor Corrosion on Two Parallel Coastal Transmission Power Lines

A number of recommendations were made concerning the solution of the corrosion problems on Williams-Mt. Pleasant #1 and #2 lines, and for future line construction in low resistivity soils. These recommendations were tempered by the fact that corrosion is an extremely complex problem. Transmission lines cannot economically be built to withstand every attack. Instead, general protective measures, with individual hotspot treatment, can provide secure anchoring systems.

Analysis of Anchor Corrosion on Two Parallel Coastal Transmission Power Lines

Corrosion problems of two 230 kV overhead transmission lines located in extensive coastal zones are analyzed. The lines are parallel on the same rights-of-way, but use different grounding techniques. Step-by-step testing procedures are introduced. The data is presented in a table with corresponding charts and figures. Economic analysis is used to study possible solutions. Three examples are given which address the cost of anchor protection vs. the existing situation continuing. Recommendations are made for the lines studied, and for future construction in low resistivity soils.

Problems and Detection of Line Anchor Corrosion

For estimating the rates of guy anchor corrosion, four tests are suggested, namely 1) earth resistivity, 2) guy current, 3) grid-to-earth potential, and 4) polarizing current. An analysis of test results will give the degree of corrosion and the form of correction necessary.