Moisture Damage Evaluation of Asphalt Mixes containing ...docs.trb.org/prp/13-4613.pdf · Moisture Damage Evaluation of Asphalt Mixes containing Mining By-products (Taconite Tailings)

Moisture Damage Evaluation of Asphalt Mixes containing Mining By-products (Taconite Tailings) using Traditional and Fracture Energy Tests

By

Eshan V. Dave Department of Civil Engineering University of Minnesota Duluth

1405 University Drive Duluth, MN 55812, USA

[email protected]

Justin Baker Department of Civil Engineering University of Minnesota Duluth

1405 University Drive Duluth, MN 55812, USA

[email protected]

Submitted for Presentation and Publication Transportation Research Board

National Research Council, Washington, D.C.

August, 2012

Word count: 5430 words, 5 figures and 2 tables (1750 equiv. words) = 7180 total

TRB 2013 Annual Meeting Paper revised from original submittal.

1

ABSTRACT 1 The availability of mineral aggregates for pavement construction is continuously 2 depleting. The aggregate manufacturing process requires significant amount of energy 3 ranging from 10-30 MJ/ton. The process also produces 5 kg/ton of CO2 causing 4 significant amounts of greenhouse gas emissions. With annual consumption of 5 approximately 1.2 billion tons of aggregates in the United States, significant 6 environmental impact is caused. Annually more than 125 million tons of fine grained 7 crushed siliceous material is generated through iron ore mining in Northern Minnesota. 8 This material is typically referred to as “taconite tailings” and usually ends up as landfills 9 near mining operations. 10

This paper describes moisture damage evaluation of asphalt mixes containing significant 11 fraction of aggregate as taconite tailings. The evaluation is conducted using conventional 12 AASHTO T-283 test procedure as well as fracture energy based approach. The paper 13 presents comparative results for two mixes, one made with taconite tailings and other one 14 using conventional granite aggregates. The results indicate that mix containing taconite 15 has acceptable moisture damage resistance. The results also point out the limitations of 16 AASHTO T-283 procedure, especially the process of moisture conditioning. The fracture 17 energy results indicate that while mixes undergo reduced tensile strength, the overall 18 capability of mix to strain without cracking significantly increased after AASHTO 19 recommended moisture conditioning process. The study also included a set of samples 20 that were field conditioned over the period of winter and spring months. The mechanical 21 behavior of field conditioned samples was quite different as compared to those 22 conditioned in lab using the AASHTO procedure. 23

24

KEYWORDS: Taconite, by-product aggregate, moisture damage, fracture, renewability.25


2

INTRODUCTION AND MOTIVATION 1 2

Approximately 1.2 billion metric tons of crushed aggregates were manufactured in the 3 United States in 2010 at the cost of about $11 billion [1]. The crushed aggregate 4 resources for use in infrastructural applications are depleting and use of alternative 5 resources is necessary to meet the demand [2]. The environmental cost of producing 6 crushed aggregates is quite significant [3]. The outcomes of mining and crushing 7 operations further lead to greater ecological and sociological problems [4]. Mining by-8 products can be utilized to substitute the new crushed aggregates utilized in manufacture 9 of asphalt concrete. 10 11 Annually, approximately 40 million tons of high grade iron ore, rich in the mineral 12 hematite, is produced in the North-Central portion of United States at the Minnesota 13 Mesabi Iron Range mining operations. This production is about 75% of the total United 14 States’ production of iron ore. During processes to enrich the ore, the large blasted rock 15 particles are crushed to finer sizes and iron rich ore particles are extracted through use of 16 magnets. The left behind crushed siliceous aggregate is commonly referred to as 17 “taconite tailings”. Typically the tailings are used as backfill material at the open pit 18 mines. Previous studies have indicated that the mechanical properties of taconite 19 aggregate, in particular their crushing resistance and hardness, make them well suited for 20 use in asphalt concrete. 21 22 While previous studies have explored viability of using taconite tailing in asphalt mixes 23 and conducted research on aspects related to logistics of using tailings, there is limited 24 information available on mechanical properties of asphalt mixes containing taconite 25 tailings and their performance. Due to siliceous nature of this aggregate one potential 26 problem can arise from moisture induced damage. Moisture damage primarily occurs due 27 to penetration of moisture between asphalt mastic film and aggregate surface causing 28 stripping of the asphalt film leading to material disintegration. Especially for colder 29 climates where effects of moisture induced damage are exaggerated due to freezing, the 30 material damage can significantly increase the amount of pavement cracking leading to 31 premature failure. This study evaluates moisture damage potential in asphalt mixtures 32 containing taconite tailings against a traditional mix with perspective on pavement 33 cracking. 34 35 The standard test method for determining moisture induced damage potential in asphalt 36 concrete is AASHTO T-283 [5]. The AASHTO method is required as part of the 37 Superpave asphalt mix design which has been adopted by several State and local 38 transportation agencies. In recent years the AASHTO procedure has received criticism 39 for being too empirical and not representative of the actual field moisture damage; this is 40 briefly discussed in the background section of this paper. The mechanical property 41 evaluation for the AASHTO procedure is conducted through indirect tensile strength test 42 conducted at 25°C. For regions of older climate, such as Minnesota, the indirect tensile 43 strength test at 25°C is not representative of typical conditions present during winter and 44 spring months. The use of fracture energy based measurements of asphalt concrete’s 45 cracking resistance has gained popularity in recent years. In this work both the AASHTO 46


3

procedure using indirect strength and fracture energy measurement using the disk-shaped 1 compact tension (DCT) test were employed. The DCT tests were conducted using the 2 ASTM D7313 [6] test procedure. The moisture conditioning for DCT specimens 3 followed the same process as the AASHTO T-283. This study also intended to make 4 preliminary comparisons between the AASHTO T-283 conditioning method against 5 conditions that asphalt mix undergoes in actual pavement. The comparison was 6 conducted by leaving compacted asphalt specimens in the field over the course of winter 7 and spring months. The samples were tested using the indirect tensile strength and 8 fracture energy tests at the end of field conditioning. 9 10 Background information through literature review on topics of using taconite tailings in 11 asphalt concrete and moisture damage evaluation are presented in the subsequent section. 12 The testing plan and details on materials are presented thereafter and followed by test 13 results and discussion. 14

BACKGROUND 15 16

The Minnesota Mesabi Iron Range (MMIR) generates approximately 125 million tons of 17 high quality crushed aggregate in form of taconite tailings [7]. Taconite tailings have 18 been used in Minnesota for roadway construction dating back as early as the 1950s [8]. A 19 study started in 2004 led to development of two pavement test sections that were 20 constructed at the Minnesota Department of Transportation’s (MnDOT) MnROAD 21 Facility [9]. This study explored both mechanical properties and economic issues 22 associated with use of taconite tailings as asphalt aggregate. Project tasks included 23 assessing pre-existing road sections with taconite tailings, constructing new test sections 24 with taconite tailings, maintenance treatments, demonstration projects, pothole studies, 25 and laboratory testing. Monitoring of distresses, rutting, ride quality, faulting, falling 26 weight deflectometer, and friction was completed for all test sections, where minimal 27 distresses were found. A summary of the project concluded that taconite aggregate can be 28 successfully used in pavement applications. Test sections constructed at MnROAD have 29 performed as well or better than conventional pavements, and further research will 30 continue [10]. The taconite tailings have been characterized for mechanical and physical 31 properties as aggregate and have shown excellent results [7]. While significant emphasis 32 has been on the characterization of aggregate, and on logistical and mix design aspects 33 associated with taconite tailings, there has been quite limited research on performance 34 evaluation of asphalt mixtures containing tailings. A study by Velasquez et al. [11] 35 reported that mixes with taconite tailings performed slightly better than granite and 36 limestone mixes when tested for indirect tensile strength and creep stiffness, fracture 37 strength, fracture temperature and dynamic modulus. One of the major failure 38 mechanisms for asphalt pavements is through the damaging effects of moisture. While 39 the previous study conducted performance tests on asphalt mixes with taconite tailings, it 40 did not look at effects of moisture. The moisture effects might be critical for mixes with 41 taconite tailings due to siliceous nature of taconite aggregate. The siliceous aggregates in 42 general tend to have greater affinity of moisture induced damage. 43 44


4

The most widely accepted moisture damage evaluation method is the modified Lottman 1 procedure that utilizes the tensile strength ratio (TSR). The original method is based on 2 work by Lottman [12]. The method has been revised to make it suitable for Superpave 3 mix design procedure through work by Epps et al. [13]. The current method is specified 4 as the AASHTO T-283 test procedure [5]. There has been some criticism of the test for 5 its high variability [13,14]. In recent years, researchers have explored the use of dynamic 6 modulus for determining moisture induced damage [15,16]. This has been partly driven 7 by as a result of poor repeatability on part of the AASHTO T-283 procedure and due to 8 non-fundamental nature of the test [15]. The NCHRP study also indicates that while 9 dynamic modulus measurement has great potential for moisture induced damage 10 evaluation there is need for simplification. The use of wheel tracking devices for 11 evaluating moisture induced damage is also popular [17]. The wheel tracking tests, 12 however, are more suited for moisture damage in roadways during warmer season and 13 may not be relevant to the effect of moisture damage on cold climate cracking. The work 14 by Arambula et al. [18] used the concepts of damage and fracture mechanics to explore 15 the moisture susceptibility in asphalt concrete. This work demonstrated the importance of 16 moisture on cracking performance of roadways. Effect of moisture induced damage on 17 fatigue cracking has also been explored [19]. The previous research has clearly shown 18 that the reduction in durability of asphalt mixes due to moisture induced damage can have 19 direct adverse effects on pavement’s cracking performance. 20 21 In recent years the use of fracture energy concepts have become exceedingly popular in 22 linking pavement cracking performance with asphalt mix’s mechanical properties. A 23 variety of fracture energy tests and procedures have been proposed, for example, use of 24 indirect tension test [20], disk-shaped compact tension (DCT) test [21], and semi-circular 25 bend (SCB) test [22]. The work by Apeagyei et al. [23] showed the applicability of DCT 26 test in evaluating moisture damage in asphalt mixtures. Use of energy ratio concept was 27 utilized by Birgisson et al. [24] using IDT fracture tests, the results from this study 28 showed very promising results for using fracture energy ratios. 29 30 The DCT and SCB tests have been extensively used for evaluating thermal cracking 31 performance of asphalt pavements [25-27]. The DCT test has also been used extensively 32 in study of reflective cracking in asphalt overlays [28,29]. The DCT fracture energy test 33 has shown very promising results in distinguishing different asphalt mixes in terms of 34 their cracking performance [25,27] and has been applied to a variety of asphalt mix 35 applications, such as investigating the effects of recycling [30]. Through comprehensive 36 survey of performance tests and material specifications, Dave and Koktan [17] 37 recommended fracture energy tests as most suitable candidates for use as performance 38 test in Minnesota. The fracture energy of material is the amount of necessary energy 39 consumed before a crack or discontinuity is formed. It is differentiated from tensile 40 strength in the sense that strength simply gives the peak stress limit at which failure is 41 initiated, whereas, fracture energy is a mechanical property that includes formation of 42 damage, accumulation of damage and formation of a crack. This is especially important 43 in quasi-brittle material like asphalt concrete which exhibit significant material capacity 44 even after the peak stress threshold (strength) is reached. 45 46


5

Based on the review of published literature the following key points were observed: 1 2 - No previous study has conducted comprehensive evaluation of moisture damage in 3

mixes containing taconite tailings. 4 - For regions of colder climate, such as Minnesota, it is important to focus on the 5

moisture induced damage distress from perspective of cracking distress. 6 - The AASHTO T-283 is the most widely accepted test procedure for determining 7

moisture damage potential in asphalt concrete. 8 - Fracture energy test, such as DCT, has been successfully utilized in recent years to 9

determine cracking potential of asphalt materials. There is limited amount of 10 information available as to how moisture damage affects the fracture properties of 11 mixes, especially for mixes with taconite tailings. 12

13 The review of previous research described in the preceding write-up helped develop the 14 testing plan for this study. Based on the review it was decided that two types of mixes 15 will be studied; one that utilizes significant fracture of mineral aggregate in form of 16 taconite tailings and another one that uses commonly used aggregate source from 17 Minnesota. The AASHTO T-283 conditioning procedure was selected due to its 18 popularity and usage over past several decades. For indirect tensile strength tests 19 conducted at 25°C, (AASHTO T-283 procedure) the lab conditioning process 20 recommended by AASHTO T-283 has been used. However, not much information is 21 available as to how this empirical lab condition process fares with fracture properties of 22 materials determined at low temperatures. Thus, it was decided that replicate specimens 23 be conditioned in field by leaving them next to a roadway for duration of one winter and 24 spring season. 25

TESTING PLAN AND MATERIALS 26 27 The testing plan for this study included three types of material conditions, two types of 28 mechanical tests, and two material types. The material conditioning methods included: 29 30

- Unconditioned: No conditioning was conducted for these specimens. 31 - AASHTO Conditioning: The conditioning was conducted according to the 32

AASHTO T-283 procedure which includes moisture saturation of specimens 33 to between 70 and 80%. The saturated samples were conditioned at -18°C for 34 16 hours followed by thawing period at 60°C for 24 hours. The samples were 35 thereafter placed in water bath at 25°C. 36

- Field Conditioning: In order to compare AASHTO conditioning with field 37 situations, gyratory compacted specimens were stored in field. The specimens 38 were placed on plywood sheet at a closed weigh-station on Interstate 35 (I-35) 39 located near Cloquet, MN. Figure 1 shows the specimens at the end of 40 conditioning which took place from January 2012 to June 2012. 41

42


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Minnesota thnd a twelve

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AASHTO T-2

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F

DISCUSSIO

The previouslseries of ratnconditioned

DCT peak loauperpave mi

AASHTO T-oth mixes. etention of IT

The fracture resented pre

manner, the righer ductiliecommendedhus if we asequirement aconite mix etter retentiaconite mix

AASHTO T-ield conditiond not greate

Figure 5: Di

ON OF RESU

ly presentedtios; the propd specimensad. The ITS ix design me-283 as wellThe mix prTS.

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ULTS

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(b) Peak L

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Loads

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of the two asnormalized atios for ITSrred to as teninimum TSRmet the rec

ith granite a

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fter AASHTOn establishedhe granite must one win

f fracture eneDCT peak lo

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th testing.

CT) Test Res

sphalt mixesagainst the sS, DCT fracnsile strengthR of 0.80. Thcommended aggregates s

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11

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et this . The have

w that going after

small


12

Table 2: Mechanical property Ratios for Conditioned Materials 1 2

Type of Conditioning

ITS Ratio (TSR) DCT Fracture

Energy Ratio (FER) DCT Peak Load

Ratio (PLR) Granite Taconite Granite Taconite Granite Taconite

AASHTO T-283 0.95 0.85 2.09 3.35 0.58 0.65 Field 0.90 0.89 0.75 0.90 1.09 1.02

3 The following key points can be inferred from the experimental findings: 4 5

- The traditional TSR measurement using AASHTO T-283 specifications shows 6 that the granite mix has slightly better damage resistance as compared to taconite 7 mix; however, both mixes meet the recommended thresholds. The field 8 conditioning show different trends for TSR as compared with AASHTO 9 recommended conditioning. In this case the taconite mix shows slightly better 10 damage resistance. Once again, the indirect tensile strength measurement at 25°C 11 is a composite measure of material’s resistance to deformation, indirect tensile 12 failure and crushing and shearing failure. Thus it may not be a well suited 13 property to determining the resistance to cracking as a fracture test conducted at 14 low temperatures. 15

- The fracture energy ratios indicate that the AASHTO T-283 conditioning process 16 might be ill-suited for determining changes in cracking resistance of material due 17 to environmental effects associated with moisture. The taconite mix showed 18 superior retention in fracture resistance of asphalt mixtures after field 19 conditioning as compared to control mix developed using granite aggregate. This 20 is a significant finding as it provides confidence in use of taconite aggregates 21 from mining operations without worry of accelerated deterioration in cracking 22 resistance due to effect of moisture and climatic cycling. 23

- The reduction in material strength at low temperatures is expected to be 24 comparable between the granite and taconite mixes. Once again the AASHTO T-25 283 conditioning shows too severe drop, whereas field condition shows slight 26 improvement. The slight improvement in DCT peak load for field conditioned 27 samples is in agreement with previous research on the topic. 28

SUMMARY AND CONCLUSIONS 29 30

A comparative lab evaluation of moisture induced damage potential for asphalt mixes 31 produced with high amount of taconite tailings against a mix produced with traditional 32 granite aggregates is conducted in this study. The taconite tailings are a by-product from 33 mining and ore enrichment process. The results of laboratory testing led to the following 34 conclusions: 35 36

- The asphalt mixture produced with taconite tailings is not expected to have 37 moisture induced problems. This is based on modified Lottman test (AASHTO T-38 283) as well as fracture energy tests. The field conditioned specimens showed that 39


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mix with taconite tailings has slightly better performance than granite mix when 1 evaluating moisture damage using fracture properties. 2 3

- The conditioning process recommended by the AASTHO T-283 test may not 4 closely replicate the moisture damage occurring in field. Fracture testing at low 5 temperatures show significantly different behavior of unconditioned and 6 conditioned specimens. It is anticipated that the curing of specimens at 60°C 7 causes significant amount of healing and may not be realistic for propensity of 8 pavement cracking occurring during colder climates. During colder climates the 9 freezing of absorbed moisture in asphalt concrete would cause significant 10 microscopic damage. 11

12 - While the AASHTO T-283 recommended conditioning process seems not 13

applicable when using fracture energy testing as the recommended performance 14 test, if it were applicable the increased potential for pavement cracking due to 15 moisture damage is not anticipated. Both granite and taconite mixes showed 16 significant increases in strain tolerance and ductility after undergoing lab 17 conditioning. 18

19 - The taconite mix has relatively lower fracture energy and has some propensity for 20

premature pavement cracking. Note that this is based on low fracture energy prior 21 to lab or field conditioning. 22

RECOMMENDATIONS 23 24 While, the focus of this study was to evaluate moisture induced damage potential for 25 asphalt mix with taconite tailings, several observations were made during the course of 26 this research that enable the authors to make practical as well as research related 27 recommendations: 28 29

- The taconite tailings in asphalt mixes should be used to substitute mineral 30 aggregates and increase sustainability of pavement infrastructure. Such mixes are 31 not anticipated to have durability problems due to moisture induced damage. 32 33

- The AASHTO T-283 conditioning process should be modified to account for 34 actual climatic conditions of the pavement site. The thaw period of the current 35 procedure might be too severe for mixes in colder climates that use softer binder 36 grades. 37

38 - The AASHTO procedure only simulates a single freezing and thawing cycle. 39

Typically an asphalt mix undergoes several freeze-thaw cycles during each winter 40 season. The effects of multiple freeze-thaw cycles on asphalt mix durability 41 should be explored. 42

43 - The DCT fracture energy test show very good promise for use as a proof test to 44

screen mixtures with potential for moisture induced damage. The DCT test has 45


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recently been recommended by a national pooled fund study for specification 1 purposes to ensure good low temperature cracking performance. The moisture 2 damage testing using the DCT test should be added to this proposed specification. 3

4 - The preliminary field condition effort in this study was limited to one course of 5

winter and spring season. Typically asphalt mixture is left in place for several 6 years, thus future research efforts should consider longer field conditioning times. 7 Also, in this study the mix in field as not subjected to traffic loading which should 8 be considered in future research. 9

ACKNOWLEDGEMENTS 10 11 This material is based upon the work supported by the Grant in Aid program of the 12 University of Minnesota. The authors also express sincere gratitude to Mr. Eddie Johnson 13 from Minnesota Department of Transportation in his help with procurement of materials 14 and for providing the technical advice. The views expressed in this paper are that of the 15 authors and do not reflect those of sponsors. 16 17 REFERENCES 18 19 [1] USGS (2011), “Mineral Commodity Summaries 2011,” United States Geological 20 Survey, U.S. Department of Interior, 198 p., Reston, VA. (Available online: 21 http://minerals.usgs.gov/minerals/pubs/mcs/) 22 23 [2] Tepordei, V. V., and Bolen, W. P. (2006), “Aggregate Economics: Natural 24 Aggregates – A Fundamental Building Block of Modern Society ‐ Are a Major 25 Component of the U.S. Economy”, Aggregates Manager, 11(4), pp. 14‐23. 26 27 [3] McIntyre, J., Spatari, S., and MacLean, H. L. (2009), “Energy and Greenhouse Gas 28 Emissions Trade-Offs of Recycled Concrete Aggregate use in Nonstructural Concrete: A 29 North American Case Study”, Journal of Infrastructure Systems, 15(4), pp. 361-370. 30 31 [4] Barksdale R. D. (Ed.) (2005), “The Aggregate Handbook”, National Stone, Sand and 32 Gravel Association, 800 p., Alexandria VA. 33 34 [5] AASHTO (2011), “Standard Method of Test for Resistance of Compacted Hot Mix 35 Asphalt (HMA) to Moisture-Induced Damage,” AASHTO T 283-07, American 36 Association of State Highway and Transportation Officials, 8 p., Washington DC. 37 38 [6] ASTM (2011), “Standard Test Method for Determining Fracture Energy of Asphalt-39 Aggregate Mixtures Using the Disk-Shaped Compact Tension Geometry,” ASTM 40 D7313-07a, ASTM International, 7 p., West Conshohocken, PA. 41 42 [7] Zanko, L., Oreskovich, J. A., and Niles, H. B. (2003), “Properties and Aggregate 43 Potential of Coarse Taconite Tailings from Five Minnesota Taconite Operation,” 44 Minnesota Department of Transportation, Report MN/RC-2004-06, 294 p., St. Paul MN. 45


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Moisture Damage Evaluation of Asphalt Mixes containing ...docs.trb.org/prp/13-4613.pdf · Moisture Damage Evaluation of Asphalt Mixes containing Mining By-products (Taconite Tailings)