Fiber Additives in Asphalt Mixtures (2015)

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24 CHAPTER THREE SURVEY RESULTS: CURRENT U.S. AND INTERNATIONAL EXPERIENCE This chapter presents the results of the survey of U.S. states, summarizing their experiences with the use of fibers in asphalt mixes. It also summarizes the information that has been gathered on fiber use in other countries. See the appendices for a copy of the survey, a list of those who completed it, and the tabulated survey responses. U.S. SURVEY RESULTS An electronic survey was distributed to all 50 states in April 2014. Responses were received from 48 states, for a response rate of 96.0%. The survey responses are summarized here. Of the two states that did not respond to the survey, an online search of their specifications and special provisions found that one (Massachusetts) does not mention fibers in its documents, so it appears they do not currently use fibers in asphalt. The other state (Vermont) does include fibers in its specifications but only for asphalt curb mixtures, so, again, it is likely that their experience is limited. The District of Columbia had been identified in a 2011 AASHTO Subcommittee on Materials survey (Nelson Gibson, FHWA communication, Nov. 1, 2013) as not using fibers in asphalt. Figure 8 lists the states that responded and the status of their use of fibers. Montana responded that it does not allow fibers but pointed out that its specifications are silent on the matter, so contractors would presumably have the option to use them if they felt the need. West Virginia has been open to vendors demonstrating their products but has not yet implemented the use of fibers. Hawaii does not routinely use fibers, but the state placed one SMA project with fibers in 2004 and another in 2014. Of the states that do use fibers, by far the most common applications are in stone matrix asphalt and porous mixes (open-graded or porous friction courses) (see Table 3). Fibers are used in these mixtures to prevent draindown of the asphalt binder from the mixture. Eleven states use fibers in both SMA and porous mixes; 12 use them in SMA only; and eight use them only in porous mixes. This likely reflects the types of mixes used in those states. For example, so far North Carolina has used fibers only in porous mixes; the state has a draft specification for SMA but has not yet placed any. In addition to preventing draindown (cited by 27 of the states that use fibers), there are a few other reasons to use fibers. Georgia, Oklahoma, Tennessee, and Virginia also use them to reduce rutting and cracking. Idaho uses them only on an experimental basis to reduce rutting and cracking. New Hampshire uses fibers to reduce cracking and draindown, while Ohio uses them to reduce rutting and draindown. Maryland indicated that fibers allow more binder in the mix, while Oklahoma says they allow more mastic. Washington State has had limited experience with fibers, having used them on only a few SMA projects. FIGURE 8 State responses to “Does Your Organization Currently Specify or Allow the Use of Fibers in Asphalt Mixes?” (Source: Survey responses). TABLE 3 STATES AND PROVINCES INDICATING USE OF FIBERS IN VARIOUS APPLICATIONS Application States and Provinces Indicating Use SMA or gap-graded mixes AL, CO, CT, IL, KS, KY, MI, MO, OH, PA, SD, WI Porous or open-graded mixes CT, FL, ME, NC, NH, NY, OR, SC Both SMA and open-graded friction course (OGFC) DE, IN, GA, LA, MD, MS, NJ, OK, TN, TX, VA Dense-graded hot mix asphalt overlays ID Other applications • CT – cold mix • NH – curb mixes • OH – supplemental spec for dis- tricts desiring to use fibers • PA – curb mixes • VA – thin hot mix overlays and sta- bilized mixtures Source: Survey responses. Three states reported using fibers in the past but not currently. New Mexico used them in SMA but has not placed

25 any SMA since at least 2000. Arizona also formerly used fibers in SMA but is not currently placing SMAs. PennDOT reported past use and is studying the potential of using fibers again through 12 pilot projects. Several states report declining use, as indicated in Table 2. In most cases, this is because of a decrease in the amount of premium surface (SMA and porous) being placed under reduced budgets. In other cases, such as Illinois, other materials are being used in lieu of fibers. Table 4 shows the approximate annual tonnage of asphalt being placed in the states that use fibers and responded to the question. The tonnage varies greatly depending on the size of the program, number and size of projects with the mix types using fibers, and availability of alternative methods to reduce draindown. TABLE 4 STATE ESTIMATES OF ANNUAL TONNAGE CONTAINING FIBERS State Approximate Annual Tonnage Containing Fibers (tons) CT 1,500 DE 20,000 FL 500,000 GA 208,586 ID Very few currently IL Minimal with use of reclaimed asphalt shingles (RAS) and ground tire rubber (GTR) KS 10,000 KY 50,000–100,000 ME Less than 1,000 MD In 2012, 396,379; in 2013, 10,212 NC 60,000 tons NH Less than 5,000 NJ 100,000 NY Less than 2,000 for DOT work OH Less than 10,000 OK 20,500 OR Currently under 500; before 2009, approximately 30,000 SC Approximately 250,000 OGFC per year SD 100,000–150,000 TN 2012, 197,000 OGFC; 2013, 197,000 OGFC; no SMA for last 4-5 years TX 700,000 AL, IN, LA, WI Unknown or unavailable without research Source: Survey responses. Some states require the use of fibers and others allow it. For example, Kansas reported that it currently requires cellulose or mineral fibers in SMA but is considering removing that requirement as long as a draindown limit is met. Illinois allows the use of fibers, but the amount actually used is limited because the state also allows the use of reclaimed asphalt shingles (RAS) and ground tire rubber, which also control draindown. North Carolina also allows RAS to prevent draindown in OGFCs. New York allows the fibers “if needed.” Ohio has had success with polymer-modified binders to reduce draindown in many districts. Ohio also has a supplemental specification for fibers that can be used at a district’s option to produce a rut-resistant mix for high-stress applications. Ohio reports that in high-strength mixes with high crushed aggregate contents, fibers can actually reduce strength by interfering with aggregate interlock, though they do improve lower-strength mixes. Oklahoma is allowing the use of a warm mix technology (Evotherm) on one SMA project in lieu of fibers. Only Idaho currently reports using fibers in dense-graded asphalt overlays to reduce rutting and cracking. One project has been completed, and research is under way to compare the field performance of three brands of fibers. In addition to using fibers in SMA and porous mixes, Virginia uses them in thin asphalt surfaces and stabilized mixtures. Connecticut uses fibers in cold mix in addition to SMAs. New Hampshire reports using fibers in curb mixes, and the Vermont specifications indicate that it does too. Most of the states that use fibers in SMA and porous mixtures allow either cellulose or mineral fibers. Table 5 summarizes the reported fiber types specified or allowed. Florida’s specifications allow the use of either cellulose or mineral, but the agency reports that the vast majority of the use is of mineral fibers. Georgia uses synthetic polymer fibers (polyethylene and poly para-phenylene terephthalamide) experimentally. Pennsylvania does not currently use fibers routinely but is researching the use of aramid and polyethylene fibers in 12 pilot projects. Indiana used to use large quantities of polymer fibers in dense-graded mixes but now uses limited quantities of cellulose or mineral fibers in SMAs (see chapter four for details). Asked to name any additional tests, specifications, mix designs, or acceptance criteria required for fibers or fiber mixes, six states said they did not require anything additional: Connecticut, Idaho, Indiana, Louisiana, Mississippi, and Oklahoma. The remaining 22 states that use fibers do have some additional requirements, most often a maximum limit on draindown. More details are provided in the following section on state specifications and test methods. No states reported having any safety or health issues when fibers are used. Almost all said they rely solely on the Material Safety Data Sheet/Safety Data Sheet. Nine states reported that they have conducted or are conducting research into the use of fibers in asphalt. The completed reports were included in the literature review

26 presented in chapter two. As indicated previously, Idaho and Pennsylvania have ongoing research efforts in this regard. Alaska is considering an experimental use of fibers in pavement preservation in 2014 or 2015. TABLE 5 TYPES OF FIBERS SPECIFIED OR ALLOWED BY STATES State Fiber Types Specified or Allowed AL Polymer, cellulose, mineral CT Polymer DE Cellulose, mineral FL Cellulose, mineral GA Cellulose, mineral, polymer (experimentally) ID Polymer IL Cellulose, mineral IN Cellulose, mineral KS Cellulose, mineral KY Cellulose, mineral LA Cellulose, mineral ME Cellulose, mineral MD Polymer, cellulose, mineral MI Cellulose MS Cellulose, mineral MO Cellulose, mineral NY Polymer, mineral NH Polymer (polyester) NJ Cellulose, mineral NC Cellulose, mineral OH Polymer, cellulose, mineral OK Cellulose OR Cellulose, mineral PA Cellulose SC Cellulose, mineral SD Cellulose TN Cellulose TX Cellulose, polymer VA Cellulose, polymer WI Polymer, cellulose Source: Survey responses. Life cycle cost analyses or benefit–cost ratios for the use of fibers are almost nonexistent. Very few states report having any such data available. Oregon said it essentially eliminated the use of OGFCs in 2008 after an evaluation revealed that the life cycle costs were not favorable; the use of fibers immediately dropped. Oregon’s response mentioned the possibility of using more fibers in the future because the state is considering increasing the use of porous asphalt to reduce water runoff from the pavement. South Carolina is the only state to mention constructability issues with fiber mixes in its survey response, though other states are known to have encountered difficulties. South Carolina respondents indicated that the service life of OGFC mixes has been less than expected, which they attribute, in part at least, to mix consistency and constructability issues. They have experimented with using warm mix technology (Evotherm) and ground tire rubber to control draindown without fibers in hopes of improving uniformity and constructability. Alabama reports that it is currently updating its specifications to allow reclaimed asphalt shingles (RAS) in place of fibers in SMA mixes. RAS contains fibrous materials from the backing material on the shingles; it also includes a stiff asphalt binder, which may help to reduce draindown. STATE SPECIFICATIONS AND TEST METHODS One survey question asked whether the agencies have any specifications, test methods, mix design methods, or acceptance criteria for fibers or fiber-modified mixtures. A total of 22 states reported having specifications or test methods specific to fibers or fiber-reinforced asphalt mixes. Most require a maximum allowable draindown, typically no more than 0.3% by weight of the mix. AASHTO T 305 is frequently cited as the test method used; Kansas and South Carolina have their own draindown test methods, which are similar to the other methods. Table 6 is a summary of the properties specified by agencies that have particular requirements for fiber mixes. The specifications are very similar. Requirements for cellulose fibers typically include fiber length, sieve analysis, ash content, pH, moisture content, and oil absorption. The requirements for mineral fibers sometimes specify the mineral types that can be used (virgin basalt, diabase, and slag, most often) and usually include length, thickness, and shot content. The limits placed on these properties are also fairly standard, though there are some deviations. For cellulose fibers, the fiber length and thickness relate to the ability of the fibers to reinforce the binder or mixture. The length and the percentage that passes specific sieve sizes are typically determined using one of two methods, the Alpine method or the sieve analysis method. Both are described in chapter two, in the section on methods of testing fibers and fiber mixtures. In either case, the percentage of fibers by mass that pass the specified sieve size is determined. The pH, oil absorption, and moisture content all relate to the bond of the fiber and asphalt. The pH must be compatible with the binder. The cellulose fiber absorbs oil (typically five times the mass of fiber) to retain binder and ensure good adhesion. And the moisture content is limited to avoid adding water to the mix and interfering with the bonding of the fiber and binder. Similar requirements frequently apply to cellulose pellets, with additional limitations on pellet size and binder penetration.

27 percentage that passes two small sieve sizes (typically 0.250 mm and 0.063 mm). Besides draindown, no additional tests are required for fiber mixes. INTERNATIONAL EXPERIENCE Two survey responses were received from Canadian provinces. Manitoba reported that it does not use fibers in For mineral fibers, the length and thickness are typically specified for the same reasons as they are for cellulose, but different test methods have historically been used. Thickness is determined by examining 200 fibers under a microscope. The fiber length is determined using a Bauer McNett fractionation; this process disperses the fibers in water so they can be sieved. In addition, the shot content is usually controlled. This property is a measure of nonfibrous materials contained in the fiber and is determined as the TABLE 6 SPECIFIED FIBER PROPERTIES REPORTED BY STATES/PROVINCES State Fiber Types Specified or Allowed AL Draindown (AASHTO T 305) DE Cellulose: ash content (D1282); pH, moisture content, and length (AASHTO MP 8). Mineral (from virgin basalt, diabase, slag, or other silaceous rock): length and thickness (MP 8), shot content (ASTM C612). FL Mineral (from virgin basalt, diabase, or slag) with cationic sizing agent for dispersal and adhesion: specified length, thickness, shot con- tent (ASTM C612). Cellulose: length, sieve analysis (Alpine or Ro-Tap methods), ash content, pH, oil absorption, moisture content. Certified test results required for each batch. GA Draindown, wet mixing time. Polymer: limit on unseparated fibers, length, form, specific gravity, tensile strength, melt temperature, acid/alkali resistance, packaging. Cellulose: ash content, pH, moisture contents. Cellulose pellets: pellet diameter, binder type, and content. Mineral (from virgin basalt, diabase, slag, or other silicate rock): shot content. IL Sieve analysis, length, ash content, pH, oil absorption, moisture content, shot content/gradation. KS Draindown (KT-63). KY Reference AASHTO M325 for design of SMA. Material certification to verify cellulose or mineral fibers. Dosage rate specified. MD Draindown, percent stabilizer. ME Cellulose: Alpine sieve analysis, ash content, pH, oil absorption, moisture content. Mineral: dosage rate, length, thickness, shot content. MO Draindown (AASHTO T 305). NH Polyester fibers from Qualified Products List, uniformly distributed in dry mix at ~0.25% of total batch weight. NJ Mineral or cellulose fibers conforming to AASHTO MP 8. Dosage rate specified. Fibers must be dispersed uniformly and proportioned to within ±10% of required rate. Certification required. Manufacturer’s representative present for first day of production. NY Mineral: length, thickness, shot content. OH For SMA–cellulose: length, sieve analysis (Alpine or Ro-Tap), ash content pH, oil absorption, moisture content. Cellulose pellets: cellulose fiber requirements above, pellet size, binder penetration. Mineral (from virgin basalt, diabase or slag with cationic sizing agent for dispersal and adhesion): length, thickness, shot content, degradation. For supplemental specification for rut-resistant mix: polyester or polypropylene from Qualified Products List: denier, length, crimps, ten- sile strength, specific gravity, melt temperature, certified test results. ON Cellulose: sieve analysis (Alpine or mesh screen), length, ash content, pH, oil absorption, moisture content. Mineral: sieve analysis, length, shot content. Draindown for SMA. OR Mineral: mineral (from virgin basalt, diabase or slag): dosage rate, length, minimum and maximum thickness, shot content (ASTM C612). Cellulose: dosage rate, length, gradation (Alpine or mesh screen), ash content, pH, oil absorption, moisture content. SC Draindown (SC-T-90, SC-T-91). SD Draindown (at design and once a day during production). Cellulose: length, sieve analysis (Alpine), ash content, pH, oil absorption, moisture content. TN Draindown (T 305). TX Draindown. VA Cellulose or mineral with supplier’s certification of properties and documented success in similar applications. WI Draindown. Source: Survey responses.

28 asphalt. Ontario does use fibers in SMA mixes and some trial mixes. In the trial mixes, the purpose of the fibers is to help resist cracking over jointed concrete. Five trial sections were constructed in 2007 to compare the performance of a control section without fibers to four test sections with varying combinations of polymer-modified binder and polyethylene terephthalate (PET) fibers. The properties required of the fibers in Ontario are listed in Table 6. Aside from the Canadian experience, much of the other information on international use of fibers was obtained through the literature review. As noted in the Introduction, fibers were typically used in European stone matrix asphalts. When that technology was introduced to the states, the use of fibers was included. These were typically cellulose and mineral fibers, as they are today. The origin of the use of fibers in dense-graded mixes is harder to determine. There were some early reports of this type of application, but it was limited. Much of this experience is apparently in the United States. Although cellulose, mineral, and synthetic fibers are widely used in developed nations in Europe and North America, there has been quite a bit of work in developing countries to make use of locally available, plant-based fibers. This is a more economical practice and provides a market for local materials. The types of plant-based fibers that have been studied for use in asphalt mixes include coconut (Oda et al. 2012; Do Vale et al. 2014), sisal (Oda et al. 2012), hemp (Abiola et al. 2014), jute (Das and Banerjee 2013), straw (Qiang et al. 2013), and sisal oil palm (Muniandy et al. 2014). To supplement the literature review and obtain current information on fiber use internationally, individuals working in asphalt research and teaching or in asphalt mixture production/construction were contacted by e-mail. The responses obtained from these contacts are summarized in Table 7. These responses confirm that international use of fibers is predominantly in SMA and porous asphalt mixtures, and that the most widely used fiber is cellulose. TABLE 7 COMMENTS ON FIBER USAGE IN OTHER COUNTRIES/REGIONS Country/Region Comments Australia/New Zealand Cellulose fibers used in SMA, typically at 0.3% by mass of total mix. Other fibers, including fiberglass, rockwool, polyester and natural wool, are suitable for use but rarely used because cellulose is more cost-effective. Brazil SMA mixes require fibers, which are typically cellulose. SMA mixes are not widely used, perhaps <4,000 km total. There have been a few applications of microsurfacing with glass fibers. Finland Uses cellulose fibers in SMA. Does not use porous mixtures because of studded tire wear. Germany Continues to use fibers in SMA. One major supplier precoats cellulose fibers with binder to pelletize the fibers and aid in dispersion in the mix plant. Israel Netivei Israel, the national roads company, requires cellulose or mineral fiber in SMA and porous mixtures. Other Middle Eastern Countries No known use of fibers. Iran has used some SMA and porous asphalt, but typically uses SBS or crumb rubber to limit draindown. Poland Not used routinely. One company in Poland does use synthetic fibers in cold mix. Other European use is of fibers in SMA; about 99% of the fibers used are cellulose. Some European companies with operations in Poland (and other European coun- tries) have researched the use of fibers within the past 10 years or so, but current coordinated European research efforts (Frame- work Programs for Research and Technological Development and COST, European Cooperation in Science and Technology) are not addressing fibers in asphalt. There is a Polish patent for a process using fibers from waste tires, but there has been no practical application to date. There has been research on the use of polymer fibers in high-stiffness modulus base layers for heavy traffic applications. Spain Cellulose fibers are used in high binder content mixes to prevent draindown, but this is a limited application used mainly for airports. Spain rarely uses SMA. There has been some research on use of steel fibers for heating and self-healing asphalts. U.K. and Northern Ireland Cellulose fibers are used in SMAs to prevent draindown. Source: E-mail communications.