Pavement Preservation Journal - Spring 2012 - (Page 37)

Why to Cut Back on Cutback Asphalt by M. Bahadir Erten and Umid Azimov P rime coat is used to penetrate and bond the loose material on the sub-base before subsequent hot mix asphalt or surface treatment is applied. As Stephen et al. stated, “Low viscosity medium curing (MC) grades of liquid asphalt are generally used for prime coat when dense, hard to penetrate bases are to be primed, typically an MC-30 or MC-70” (Stephen & Shrestha, 2005, p. 28). MC-30 is a type of cutback asphalt which is prepared by blending high viscosity asphalt cement with petroleum solvent to lower the viscosity in order to achieve better penetration. However, engineers are concerned with the use of cutback asphalt as prime coat for at least three reasons: environmental issues, fi re hazards and potential health risks posed to construction workers. ENVIRONMENTAL ISSUES The main environmental concern with prime coat applications is air pollution associated with the release of volatile organic compounds (VOCs) into the air (Freeman, Button, & Estakhri, 2010, p. 17). VOC emission results from the evaporation of the petroleum solvent used to reduce viscosity of the asphalt cement. The restriction on VOCs is intended to reduce ground level ozone (smog) formation. VOCs are a group of photochemically reactive pollutants that combine with nitrogen oxides in the presence of sunlight to form ozone. Stephen & Shrestha also noted that cutback asphalts are the major source of VOCs as only minor amounts of VOCs are emitted from emulsified asphalts and asphalt cements (Stephen & Shrestha, 2005, p. 61). According to the Resource Conservation and Recovery Act (RCRA), asphalt cement is not considered a hazardous material. However, RCRA defined diluents used to make cutback asphalts or additives added to emulsifying agents or performance enhancing agents in asphalt emulsions as hazardous materials (Stephen & Shrestha, 2005, p. 15). The use of cutback asphalt is regulated in many jurisdictions to help reduce VOC emissions (Asphalt Institute, 2009). In the state of Texas, the Texas Natural Resource Conservation Commission has established strict guidelines to prohibit the use of cutback asphalt for most applications between April 16 and September 15 of any year. The regulation affects major metropolitan areas in Texas (O’Leary, p. 2; Texas Natural Resource Conservation Commission, 2002, p. 3). FIRE HAZARD MC-30 may pose a potential fire hazard during manufacture and construction. According to Material Safety Data Sheet (MSDS), the flash point of MC-30 cutback asphalt material varies from 120 to 140 deg F. It is flammable and needs special handling and storage consideration to prevent fire and explosion (Martin Asphalt Company, 2007; Valero Marketing & Supply Company and Affiliates, 2011). According to Stephen & Shrestha (2005), fire can be a concern when using MC for prime coat or rapid cure cutbacks (RC) for tack coat as application often involves heating the material above its flash point (p.15) (Valero Marketing & Supply Company and Affiliates, 2011). HEALTH RISK MC-30 cutback asphalt may pose a health risk to the pavers. Inhalation of vapors, mist or asphalt fumes will cause headaches, nausea, dizziness and intoxication. Additionally, vapors or mist may irritate eyes. Prolonged dermal exposure to kerosene (petroleum solvent for MC-30 cutback asphalt) may produce dermatitis. Asphalt fumes contain substances that are known to cause cancer in humans. Stephen & Shrestha (2005) note that worker’s health safety issues stem from exposure to the cutback and stability or reactivity of the cutback. The majority of the materials typically used for prime or tack are reactive or pose more than a slight health risk (p.15). Erten and Azimov are affiliated with the Department of Civil, Architectural and Environmental Engineering, University of Texas at Austin. Opinions expressed are those of the authors. Contribute Your Technical Paper to Pavement Preservation Journal Prospective authors are invited to present articles on original research on any topic relevant to pavement preservation, such as preservation techniques, materials, construction, testing, performance, recycling and pavement management to Pavement Preservation Journal. Papers discussing best practices for pavement preservation treatments, including asphalt overlays, scrub and fog seals, crack sealing, chip seal, hot in-place recycling, micro surfacing, and slurry seals, would be welcome as well. Authors must prepare their manuscripts in accordance with the guidelines outlined by the Pavement Preservation  Journal. All articles should be submitted as an  e-mail attachment to Dr. Yetkin Yildirim, P.E., at For more information, including style guidelines, please  visit the Pavement Preservation Journal’s home page at Spring 2012 pavement preservation journal 37

Table of Contents for the Digital Edition of Pavement Preservation Journal - Spring 2012

President’s Message
National Preservation Conference: Make Plans Now
Pavement Preservation is ‘Sustainable’ Choice
Deck Micro Surfacing Cuts Accidents, Wins Award
Enhanced Fog Seals Boost Chip Retention
Sophisticated ‘Seal Coats’ Enhance Texas DOT Pavement Preservation
Rejuvenating Treatment Preserves Runway, Grooving
Fine-Mill Pavements for Smooth Thin Overlays
Puerto Rico, Southeast States Focus on Preservation
Maryland Identifies Right Fix for Right Road, Right Time
‘Thin is In’ for New Texas Center Courses
Why to Cut Back on Cutback Asphalt
Test Sections Constructed at Virginia Smart Road
Ground Penetrating Radar Fills Gaps in PMS

Pavement Preservation Journal - Spring 2012