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The corrosion of rock bolts and a method to quantify the corrosion potential in mines A. J. S. Spearing, K. Mondal, and G. Bylapudi Southern Illinois University Carbondale, Carbondale, Illinois, USA

J. Hirschi Illinois Clean Coal Institute, Carterville, Illinois, USA

ABSTRACT Rock bolts are the main form of defence against rockfalls in mines. Conditions underground are conducive to corrosion. A perception exists about American coal mines that bolt corrosion is not an issue, especially when bolts are fully grouted. This perception is not necessarily accurate due to the formation of micro-cracks as the resin sets and to subsequent rock movement that breaks the resin column’s continuity. Corrosion should be considered when designing rock bolt support in long-term excavations. This paper explores the problem of corrosion, outlines a method to determine the corrosion potential of bolts, and suggests ways to mitigate such effects. KEYWORDS Acid, Alkali, Rock bolt, Chlorides, Corrosion, Iron, Nitrates, pH, Sulphates, Water

RÉSUMÉ Les boulons d’ancrage constituent le principal moyen de défense contre les chutes de roches dans les mines. Les conditions souterraines sont cependant propices à la corrosion. Il existe une perception dans les mines de charbon en Amérique que la corrosion n’est pas un problème, surtout lorsque les boulons sont encaissés dans un coulis. Cette perception n’est pas nécessairement juste en raison de la formation de micro-ﬁssures alors que la résine se solidiﬁe et que des mouvements subséquents du roc brisent la continuité de la colonne de résine. La corrosion doit être prise en compte lors de la conception du soutien par boulons d’ancrage dans les excavations à long terme. Cet article étudie le problème de la corrosion, décrit une méthode pour déterminer le potentiel de corrosion des boulons et suggère des manières de minimiser de tels effets. MOTS CLÉS Acide, Alcalin, Boulon d’ancrage, Chlorures, Corrosion, Fer, Nitrates, pH, Sulfates, Eau

INTRODUCTION In the American coal mining industry, underground The figures for the annulus when using cables are mismines produce about 30% of the total production of 1.1 leading because, depending on the hole diameter used, the billion tons, and use about 100 million rock anchors per ends of the cables would be bulbed (i.e., the strands open year (Tadolini & Mazzoni, 2006). The rock bolts used in and separated for improved mixing and resin bonding) in American mines are covered by ASTM International various places and to specific diameters to ensure good (2004a), which specifies properties, test methods, and resin mixing and adhesion to the cable. Table 3 gives typithe minimum performance of rock bolts, ancillaries, and cal mill certificates for rebar used in U.S. coal mines. resin grout. A relatively wide variety of steel members are routinely used as Table 1. Commonly-used steel for rock bolting, and the hole diameters used rock bolts in the United States, as Steel material Minimum yield stress Recommended anchor hole Annulus detailed in Table 1 (Spearing & (diameter and grade) (MPa) diameter (mm) (mm) Mueller, 2008). 16 mm (#5) Gr 60 414 25.4 4.7 The grade in Table 1 refers to the 19 mm (#6) Gr 40 276 25.4 3.2 19 mm (#6) Gr 60 414 25.4 3.2 minimum yield strength for the steel in 19 mm (#6) Gr 75 517 25.4 3.2 thousands of pounds per square inch 22 mm (#7) Gr 40 276 28.6 to 34.9 3.3 to 6.5 (psi; e.g., a Grade 40 bolt has a 40,000 22 mm (#7) Gr 60 414 28.6 to 34.9 3.3 to 6.5 psi minimum yield strength). The steel 22 mm (#7) Gr 75 517 28.6 to 34.9 3.3 to 6.5 used in cable bolts is given in Table 2.

CIM Journal | Vol. 1, no. 3


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A. J. S. Spearing, k. Mondal, G. Bylapudi, and J. Hirschi

The Charpy V-notch test is an inexTable 2. Cable properties and recommended hole diameters pensive mechanical test that produces Minimum Recommended anchor Theoretical Steel material data to assist with steel selection (ASTM yield stress hole diameter annulus (diameter International, 2007). This particular (MPa) (mm) (mm) and grade) impact testing has been widely used in 1862 25.4 to 34.9 5.2 to 10.0 15 mm Gr 270 the mining industry for selecting more 1862 25.4 to 34.9 3.7 to 8.5 18 mm Gr 270 corrosion-resistant steels. The Coal Authority (formerly known as British corrosion are independent of pH, corrosion kinetics of interCoal) used this technique to specify more corrosion-resismediate reactions is very much dependent on the pH of the tant, high tensile strength steels. Hebblewhite, Fabjanczyk, and Gray (2003) studied rock solution. The oxidation of metallic iron to Fe2+ (that results bolt failures due to stress corrosion cracking (SCC). The in its dissolution) is the primary step in corrosion. The rate of study used 44 failed rock bolts from different coal mines in dissolution of iron thus depends on the pH and the rate-determining step. In acidic solutions, it is observed that the pH of Australia. Experiments were conducted to examine the fractures using magnetic particle inspection, to analyze the the solution will increase due to a loss of protons. In neutral or alkaline solutions, however, the change in pH of the soluchemical composition using atomic emission spectroscopy, to determine fracture toughness using the Charpy impact tion is dependent on the rate-controlling step, the local pH (at the corrosion site), and the rate-determining step. tests (generally the higher the fracture toughness, the lower The corrosion takes place at a rate determined by a balthe susceptibility for SCC), and to test for hardness and evalance between opposing electrochemical reactions. The first uate the micro-structures. According to Hebblewhite et al., is an anodic reaction, which oxidizes the metal, releasing high Charpy values are expected to provide lower susceptielectrons into it. The second is the opposite cathodic reaction bility to SCC. The use of this test explained the behaviour of in the solution, which removes electrons from the metal. a few steel grades (840, 15M25, 15M30, 15M35), with When these reactions are in balance, there is no net flow of Charpy values ranging from 12 to 40 (depending on the steel electrons. This relationship can be shown on a Tafel plot, producer and the production batch). These steel grades have with the horizontal (x) axis being the log of the absolute curcarbon from 0.2 to 0.4% and some micro alloying elements, rent (I), and the vertical (y) axis being the electrode potential such as vanadium. The study’s report concluded that there (Ep). The intersection of the extrapolated anodic current and was no evidence of premature rock bolt failures of the grade potential with the cathodic current and potential provides the 840, but for these grades the costs are comparatively high corrosion current (Icorr) and corrosion potential Ecorr reaction due to expensive alloying elements and a complicated process that uses accelerated cooling and heating techniques. balance values, as shown in Figure 1. The Ecorr value can be compared with the open circuit J. Pile (personal communication, July 28, 2009) reports potential readings from underground to determine if the that San Juan colliery (owned by BHP) in new Mexico also adopted this method to specify more corrosion-resistant rock anchor steels. The San Juan colliery is the only mine in the United States that appears to use this test and specific special bolt steels. Almost all the rock bolts used in coal mines are made from steel and, hence, the corrosion of iron needs to be understood. The corrosion of iron is an electrochemical phenomenon with the overall equation: 2Fe + H2O + 1.5O2 → Fe2O3.H2O

(1)

Hydrated ferric oxide (Fe2o3.H2o) is also known as rust. It is the most tangible evidence of corrosion and is the leading cause of several issues related to corrosion in rock bolts and anchors in underground mines. Although the overall reaction shown above and the equilibrium potential of iron

Figure 1. Sample Tafel plot.

Table 3. Chemical composition of rock anchor steel (wt%) Grade #5 Grade 60 #6 Grade 40

C 0.41 0.26

Mn 0.99 0.60

P 0.01 0.01

S 0.06 0.04

Si 0.19 0.21

Cu 0.40 0.41

Ni 0.13 0.14

Cr 0.16 0.15


Mo 0.032 0.034

V 0.009 0.001

Cb 0.002 0.001

Sn 0.017 0.021

C. E. 0.61 0.67


The corrosion of rock bolts and a method to quantify the corrosion potential in mines bolt is in danger of corroding. Corrosion will occur if oCP ≥ Ecorr (i.e., a more negative voltage potential exists). The need to control corrosion mainly stems from safety issues coupled with economic considerations. The inherent benefits of corrosion control include the reduction in corrosion costs due to lower maintenance and repair/rehabilitation costs, and the lower risk of long-term failure, resulting in enhanced safety and reduced liability.

Common types of corrosion in mining The main types of corrosion that can affect rock bolts and cables, in their estimated order of significance with the most important first, are:

Aqueous corrosion Mine water, which is generally acidic, is frequently present underground, can cause significant damage to installed supports, and can even cause premature failure. This can create unsafe conditions. Major contributors present in mine water that exacerbate the corrosion problem are: • pH (acid and alkali conditions both cause problems). • Concentrations of chloride (Cl-) and sulphate (So42-) ions. • Dissolved oxygen concentration. • Concentration of hydrogen (H+) ions. • Concentrations of calcium (Ca2+) and magnesium (Mg2+) ions. Stress corrosion cracking Stress corrosion cracking (SCC) and subsequent failure are potential issues in many mines. SCC is the slow and progressive crack growth under the application of a sustained load in a corrosive environment, with complete failure occurring significantly below the ultimate tensile strength of an equivalent bolt that is unaffected by corrosion. With SCC, bolt failure under relatively high loads can occur with little actual corrosion visible to the naked eye, as shown to some degree in Figure 2. This problem can be overcome, or at least alleviated, in the following ways: • Reduce bolt strength (this method is not practical in most instances). • Increase bolt toughness (increase the energy that can be absorbed before failure). • Reduce pre-stress on bolts (often this method is not a desirable strata control option). • Alter the bolt surface by galvanizing or epoxy coating. • Provide cathodic protection to bolts or cables. • Use a corrosion inhibitor mainly if grout is cementitious (this method is primarily applicable in hard-rock mines). • Provide complete and effective full column grouting, with the understanding that subsequent rock movement, either in tension or shear, can crack this column at a later stage.

Atmospheric corrosion Atmospheric corrosion generally occurs only when relative humidity is at or above 80%.

215

Thus, this type of corrosion is mainly an issue in summer and in deep mines. However, when high humidity conditions occur, atmospheric corrosion effects can be significant and cause potentially hazardous conditions.

Microbial/bacterial corrosion Bacteria that consume (oxidize) sulphur and steel can be found in typical underground conditions. The importance of these bacteria is unknown due to a lack of research, but it is assumed not to be significant. Sundolm (1987) suggested that corrosion should be one of the main factors considered when selecting a rock bolt. In American coal mines, effects of corrosion are seldom given serious consideration, though they should be. Corrosion phenomena are observed either as uniform corrosion (corrosion that takes place uniformly over the entire surface) or localized corrosion, which is more important in rock anchors in mining. Localized corrosion may be divided into the following categories: • Pitting corrosion • Crevice corrosion (including corrosion under deposits and tubercles, which are large impervious structures) • Galvanic corrosion • Cavitation corrosion • Intergranular corrosion • Stress corrosion • De-alloying • Corrosion fatigue The inherent benefits of corrosion control include improved long-term safety and a reduction in maintenance and repair/rehabilitation costs. A corrosion cell may be considered a square with four critical components: • Anodic site • Ionic current path • Cathode site • Electronic path Removal of any one of these components stops corrosion, while the increase in the resistance to the ionic or electronic path reduces the corrosion rate. There are five primary methods (or combinations) of corrosion control: • Material selection • Coatings • Inhibitors • Cathodic protection • Design

Figure 2. Typical failure due to SCC (Hebblewhite et al., 2003).



216


Figure 3. Corrosion chamber with different rock anchors.

LABORATORY CORROSION TESTS

Figure 4. Simple schematic for oCP readings in the mine.

Corrosion tests were conducted in five large plastic tanks with different conditions based on the water quality cable bolt, the plain galvanized one-Step Bolt, and a thread results obtained from analyzing ground waters of different stripping with a torqued bolt, the strength reductions caused coal mines in the Illinois Coal Basin. Figure 3 shows the by the corrosion were not statistically significant based on experimental setup for these long-term tests and Table 4 AnoVA analyses. A test period of at least 18 months would lists the conditions for each tank. The pHs used in three seem necessary and a proposal for funding such a project tanks were designed to cover the extremes and the average has been submitted to a suitable funding agency. of pHs found underground (6.6 to 8.4). Two additional tanks (4 and 5) were designed for accelerated testing, with MEASURING THE CORROSION POTENTIAL elevated temperatures of approximately 50°C in alkaline OF BOLTS IN SITU solutions. All the tanks had a cross-sectional area of 0.9 by The determination of bolts’ corrosion potential in a mine 1.8 m. Tanks 1 to 3 were filled to a depth of 30 cm, which or in a particular mine section consists of two steps: (a) underprovided a water volume of 510 l. Tanks 4 and 5 were filled ground measurements and (b) laboratory analyses and tests. to 45 cm to cover the immersion heater in each tank. over a period of nine months, weekly water samples Underground equipment needs and measurement were taken from the tanks and the pH, iron, sulphate, and procedure chloride contents were determined. In addition, bolts were The following equipment is needed for the underground destructively tensile tested every three months. The bolts measurements when taking the open circuit potential tested were: (oCP): • number 5 (⅝” diameter, 16mm) forged head (FH) Grade • A multimeter, approved by the United States of America 60. Department of Labor’s Mine Safety and Health Admin• number 6 (19 mm) forged head Grade 60. istration (MSHA), that has connecting cables, a meas• number 6 coated forged head Grade 60. urement range of 3.2 volts maximum, and an accuracy • number 7 (22 mm) forged head Grade 60. of 0.001 volts. • number 6 threaded head (TH) with a nut-Grade 60. • A standard copper-sulphate electrode or a thin copper • number 7 threaded head with a nut-Grade 60. rod. • Threaded number 6 Grade 60 rock anchors were • Connecting wires with known resistivity. installed in perforated pipe frames and loaded to 240 oCP voltage readings between a rock bolt type and the coal ft/lbs for monitoring of SCC failure. The load was deterroof are taken by establishing the circuit shown in Figure 4. mined within the torque range of a typical coal mine The MSHA-approved multimeter is used to measure the rock-bolter. These anchors were installed in Tank 5 voltage between a rock bolt and the reference electrode. under accelerated conditions, with heated water at oCP voltage measurements are recorded for different roof approximately 50°C. bolt types (if used) and for different roof conditions (wet and dry areas). Corrosion is obviously more likely to be • Hilti oneStep self-drilling rock anchors (plain, grouted, and galvanized). • 15 mm plain black cable — Grade Table 4. Experimental conditions for long-term tests 270. Condition Tank 1 Tank 2 Tank 3 Tank 4 Tank 5 • 15 mm epoxy coated cable — Grade pH 5.5 7 9 10 10 270. Temperature (°C) Ambient Ambient Ambient 50 50 • 18 mm galvanized cable — Grade Fe2+ (mg/L) 2.8 2.8 2.8 2.8 2.8 270. SO42- (mg/L) 950 950 950 950 950 The research test period was too Cl- (mg/L) 1,150 1,150 1,150 1,150 1,150 brief: with the exceptions of a black



The corrosion of rock bolts and a method to quantify the corrosion potential in mines severe in wet areas. The data are recorded after each separate reading, as illustrated in Table 5. Water samples are collected from mines or mine sections where oCP measurements are taken. They undergo chemical analyses to determine pH, sulphates, nitrates, and chlorides, which are responsible for the corrosion potential of roof bolts underground.

217

Table 5. Sample OCP readings from underground tests Roof bolt type #6 Grade 60 rebar

Location

Installation date

1

02/04/2004

OCP differential (mV) -675

#6 Grade 60 rebar #6 Grade 60 rebar

2

09/04/2004

-550

3

02/04/2005

-503

Note: Location 1 was in an area with water in the roof.

Laboratory methods The following materials and equipment are needed for conducting electrochemical tests in the laboratory: • Glass flask to contain the electrochemical cell. • Sample of specific rock bolt steel tested underground to be the test electrode. • Counter electrode (platinum mesh). • Reference electrode: standard calomel electrode (SCE). • Epoxy resin and hardener for mounting the test specimen of the specific rock bolt. • Mould release used for test specimen preparation. • Mounting cups used for mounting the test specimen. • Voltmeter for oCP readings. • eDAQ Potentiostat for the application of potential pulses while observing the current as a function of the potential. • e-corder, which is the data acquisition system used for collecting test data with the help of e-chem software. • PC for data recording. • Water and distilled water for electrolyte preparation. • Acetone for cleaning the test specimen (bolt steel) before testing. • Chemicals (ferric nitrate, sodium chloride, and sodium sulphate; the selection depends on findings from the water samples taken during the underground oCP tests).

• A stirrer for mixing chemicals for electrolyte preparation. • A water heater used for electrolyte preparation. • Filter paper for filtering the chemical solution for a clear electrolyte. • Machine shop equipment for sample preparation (lathe, drill, cutter, grinder, polisher, and soldering machine).

Laboratory measurement procedure 1. Steel bolt sample preparation A disc-shaped sample is cut from the selected roof bolt steel and is then wet-ground and polished. Before testing, the sample is cleaned with acetone and a microscopic image is taken for material reference. The sample is then soldered to a wire with an approximate diameter of 2 mm. The sample is covered with an epoxy resin and hardener mixture (approximately 85% epoxy resin and 15% hardener), leaving one side of the sample surface exposed to the electrolyte for testing in the electrochemical cell, as shown in Figure 5. Before installing the sample in the cell, the sample is polished using 240 and 600 grit for a fine surface and cleaned with distilled water. Figure 6 shows a completed sample ready for testing. 2. Water preparation The analysis of mine water samples will provide the chemical data needed to prepare a water sample for the laboratory test. The sample is prepared by adding chemicals, as per the calculated weight ratios found from the analysis. The water is preheated to 50°C to help

Figure 6. A #6 rebar section ready for testing (Chandra & Daemen, 2005).

Figure 5. Bolt steel sample preparation for lab tests.



218


Figure 7. (a) Equipment used for test sample preparation; (b) Schematic showing the test sample; (c) Equipment used for electrochemical testing; and (d) Schematic showing the electrochemical test setup.

chemical salts dissolve and the water solution is stirred for 30 minutes. It is then filtered and the clear water solution is used for testing. 3. Laboratory testing The laboratory testing layout is shown in Figure 7 and the test procedure is as follows. The test is conducted

using the eDAQ potentiostat (Figure 7), equipped with a data acquisition system (e-corder) and e-chem software (eDAQ Inc). The prepared test specimen (rock bolt steel) is immersed in the solution that has been prepared to imitate conditions found at a specific, underground test site. The oCP is recorded after ten minutes and used as the “start” oCP. This start oCP is used as the initial voltage setting and the final voltage setting value for the potentiodynamic scan is set -400 mV lower. The potentiodynamic scans are conducted at a scan rate of change of 0.5 mV/s. Figure 8 shows the potentiodynamic polarization scan and the corresponding modified Tafel plot (Table 6), which is used for reading the Ecorr in mV and ln|icor| in mA/cm2. The corresponding corrosion rate is calculated employing available standard methods (ASTM International, 2004b, 2004c, 2009). The corrosion (or penetration) rate is calculated by: IcorrEW PR(mm/yr) = –––––––––– 3272 ρAs

(2)

where Icorr is the corrosion current in mA, EW is the equivalent weight (atomic weight/charge per atom) in gm/equivalent, As is the surface area of the sample exposed to the electrolyte in cm2, and ρ is the density of the material in gm/cm3. Figure 8. Tafel plot for a test steel sample.



The corrosion of rock bolts and a method to quantify the corrosion potential in mines The corrosion rate in Table 6 is the uniform corrosion rate; however, research has found that localized corrosion is more of a problem than uniform corrosion (Spearing & Mondal, 2009). The pH has an effect on the corrosion rate, as shown in Table 7. It seems that the more acidic the water, the higher the corrosion rate. Generally, mine water tends to be acidic because of the pyrite that is often present. Repetitive tests are required to obtain more reliable uniform corrosion rate results for commonly used bolt steels (including rebar) and localized corrosion rates (of threads, for example).

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Table 6. Polarization test data Material type #5 Grade 60 rebar #6 Grade 60 rebar #7 Grade 60 rebar

Ecorr (mV)

ln |Icorr|

Icorr (mA/cm2)

-643

-17.53

2.436E-06

0.018

-654

-14.26

6.417E-06

0.031

-661

-17.51

2.493E-06

0.016

Corrosion rate (mm/yr)

Table 7. Uniform corrosion rate of rebar in acidic conditions (pH of 5) and alkaline conditions (pH of 8) Material type #5 rebar

Corrosion rate (mm/yr) pH 8

Corrosion rate (mm/yr) pH 5

0.013

0.018

#6 rebar

0.011

0.030

#7 rebar

0.010

0.016

Table 8. Comparison between underground OCP readings and Ecorr from the lab tests

Result evaluation and interpretation

Material type

OCP vs SCE (mV)

Ecorr (mV)

-675 -550 -503

-653 -653 -653

#6 Grade 60 rebar #6 Grade 60 rebar #6 Grade 60 rebar

Using the in situ and lab tests, the following detailed corrosion potential results can be obtained. Table 8 compares the underground and lab results for #6 Grade 60 rebar tested underground in three locations (two in dry conditions and one in wet conditions). These results are shown graphically on Figure 9. From the readings taken, it was observed that the oCP values in Locations 2 and 3 had lower negative voltages than the Ecorr of -654 mV; hence, corrosion would not be an issue, which is an indication that the roof bolts had not started corroding. At Location 1, the oCP value is -675 mV, which is more negative than the Ecorr (mV) value measured in the lab for similar bolt steel. This finding indicates that this particular bolt in the specific conditions will be subject to corrosion over time.

corrosion protection is needed; otherwise, galvanized or epoxy-coated cables should be used. Protecting (with bitumen, for example) the barrel and wedges, as well as the cable around them, may be beneficial. This technique is sometimes practiced in Australia (Villaescusa, Hassell, & Thompson, 2007). • In known areas of high corrosion potential, using a larger diameter bolt will be advantageous because the life will be increased.

MITIGATING THE EFFECTS OF CORROSION once corrosion has been identified as a potential issue in the long-term, the methods to mitigate it can be relatively simple. The following recommendations can be made for long-term excavation support: • Where active bolts are deemed necessary, use forged headed bolts with mechanical shells and resin, rather than threaded bolts and two-speed resin. The threads are areas for accelerated localized corrosion. • Use only full-column, resin-grouted bolts. Using additional resin helps coat and protect bolt ends. • Cable bolts in coal mines are always partially grouted (typically for 1.2 m). Where black cables are used, some form of

Figure 9. Plot showing the oCP from mines and Ecorr from lab tests of #6 Rebar.



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• If water is present underground then it should be tested to estimate corrosive potential.

CONCLUSIONS AND RECOMMENDATIONS Localized corrosion can be a safety issue in long-term excavations. The corrosion potential of bolts in mines can be reliably obtained and quantified. This information can then be used to improve the safety and long-term stability of excavations, and can actually lower overall costs by reducing rehabilitation expenses. For key long- term excavations in coal mines, it is recommended that the corrosion potential of rock bolts be determined using the method outlined or any other method deemed suitable and reliable. In addition, the following research is recommended: • Longer-term corrosion tests in tanks (for at least an 18month period). • Repetitive tests to reliably establish uniform and localized corrosion rates for commonly used bolt steel. • Underground oCP and Ecorr tests in locations where bolts have been installed for several years to determine if the bolts are stable or corroding. Bolts should then be over-cored to determine whether the method is reliable and meaningful.

ACKNOWLEDGMENTS The authors gratefully acknowledge the funding provided by the Illinois Department of Commerce and

Economic opportunity through the office of Coal Development and the Illinois Clean Coal Institute. They would also like to acknowledge the test materials and testing equipment that were provided by Jennmar Corporation. Paper reviewed and approved for publication by the Rock Engineering Society of CIM. A. (Sam) Spearing is an associate professor in the Department of Mining and Mineral Resources Engineering at Southern Illinois University Carbondale (SIUC). His interests include rock engineering, support design, mine design, and risk management. He has designed various supports that are routinely used in the mining industry, including the Rocprop and Roofex (the yielding rock bolt). Kanchan Mondal is an associate professor in the Department of Mechanical Engineering and Energy Processes at SIUC. His expertise is in the area of electrochemical engineering, surface science, catalysis, energy management, coal processing, and materials. He has published over 50 peer-reviewed journal papers and has delivered over 80 presentations at professional conferences. Gopi Bylapudi is a recent graduate from SIUC with an M.Sc. in mechanical engineering. He has a green belt in Six Sigma from the American Society for Quality and his thesis investigated bolt corrosion in mines. He completed his B.Sc. in mechanical engineering at Anna University, in India. Joseph Hirschi is a project manager with the Illinois Clean Coal Institute and a PhD candidate in engineering science at SIUC. His research interests include mine and power plant optimization, mining methods, coal processing, and miner health, safety, and training. He has a B.Sc. and an M.Sc. in mining engineering, and an MBA from the University of Utah.

REFERENCES ASTM International (2004a). F432 Standard specification for roof and rock bolts and accessories. West Conshohocken, PA: Author. doi: 10.1520/F0432-04

industry. Paper presented at the University of Wollongong and the Australasian Institute of Mining and Metallurgy Coal operators Conference, new South Wales, Australia.

ASTM International (2004b). G5 Standard reference test method for making potentiostatic and potentiodynamic anodic polarization measurements. West Conshohocken, PA: Author. doi: 10.1520/G0005-94R04

Spearing, A. J. S., & Mondal, k. (2009). Corrosion of rock anchors in coal mines (Project no. 07-1/US-3). Carterville, IL: Illinois Clean Coal Institute.

ASTM International. (2004c). G102 Standard practice for calculation of corrosion rates and related information from electrochemical measurements. West Conshohocken, PA: Author. doi: 10.1520/G010289R04E01

Spearing, A. J. S., & Mueller, A. (2008, September). State of the art intersection support in coal mines in the USA. Paper presented at the First Southern Hemisphere International Rock Mechanics Symposium, Perth, Australia.

ASTM International (2007). E23 Standard test methods for notched bar impact testing of metallic materials. West Conshohocken, PA: Author. doi: 10.1520/E0023-04

Sundholm, S. (1987, August). The quality control of rock bolts. Paper presented at the Sixth International Congress on Rock Mechanics (pp. 1255-1264), Montreal, Canada.

ASTM International (2009). G59 Standard test method for conducting potentiodynamic polarization resistance measurements. West Conshohocken, PA: Author. doi: 10.1520/G0059-97R09

Tadolini, S., & Mazzoni, R. (2006, July). Understanding roof bolt selection and design still remains priceless. Paper presented at the Twentyfifth International Conference on Ground Control (pp. 382-389), Morgantown, West Virginia.

Chandra, D., & Daemen, J. (2005). Sub-surface corrosion research on rock bolt system, perforated SS sheets and steel sets for the Yucca Mountain Repository. Quarterly Technical Report, April-June, 4. Hebblewhite, B., Fabjanczyk, M., & Gray, P. (2003, February). Investigations into premature rock bolt failures in the Australian coal mining

Villaescusa, E., Hassell, R., & Thompson, A. G. (2007). Corrosion of rock reinforcement in underground hard rock mining excavations (Research Report no. 263). Perth, Australia: Minerals and Energy Research Institute of Western Australia.

©2010 Canadian Institute of Mining, Metallurgy and Petroleum. All rights reserved.

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