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7 Pavement Preservation and Maintenance Terminology The first set of terms for pavement maintenance terminology that apply to microsurfacing are defined by the FHWA (Geiger 2005) as follows: Pavement preservation is "a program employing a net- work level, long-term strategy that enhances pavement performance by using an integrated, cost-effective set of practices that extend pavement life, improve safety, and meet motorist expectations." FIGURE 2 Microsurfacing environmental footprint compared Preventive maintenance is "a planned strategy of cost- with two types of pavement preservation overlays (Takamura effective treatments to an existing roadway system and et al. 2001). its appurtenances that preserves the system, retards future deterioration, and maintains or improves the functional condition of the system (without significantly increasing gases by keeping good roads good (Chehovitz and Galehouse the structural capacity)." 2010). Microsurfacing's environmental footprint is lower than Routine maintenance "consists of work that is planned most common pavement preservation and maintenance treat- and performed on a routine basis to maintain and pre- ments (Takamura et al. 2001). Figure 2 is from a study on the serve the condition of the highway system or to respond environmental impact of several commonly used pavement to specific conditions and events that restore the high- preservation and maintenance treatments. The study devel- way system to an adequate level of service." oped "eco-efficiency" indices for the five categories shown Corrective maintenance "activities are performed in in the figure and found that microsurfacing had a substan- response to the development of a deficiency or defi- tially lower environmental footprint than the other options (Takamura et al. 2001). This study does not include the reduced ciencies that negatively impact the safe, efficient oper- greenhouse gas emissions resulting from microsurfacing's ations of the facility and future integrity of the pavement ability to greatly reduce traffic delays in work zones (Johnson section. Corrective maintenance activities are generally et al. 2007). Additionally, the "risk potential" and "health reactive, not proactive, and performed to restore a pave- effects" categories did not include the reduction in work zone ment to an acceptable level of service due to unforeseen accident risk inherent to microsurfacing (Erwin and Tighe conditions." 2008). Therefore, microsurfacing's "true" footprint may be even smaller in relation to hot-mix asphalt options for The report will refer to various specific applications of pavement preservation and maintenance programs. When microsurfacing using these terms where appropriate and as looking at options to address pavement preservation and a "pavement preservation and maintenance program" when maintenance issues, the engineer can use the environmen- discussing it in general terms. tal and safety benefits of microsurfacing as possible justi- fication to offset any marginal increase in construction cost Microsurfacing Versus Slurry Seal Terminology versus other alternatives. The issue of whether or not microsurfacing is merely a polymer-modified slurry seal has yet to be settled. ISSA's KEY DEFINITIONS Inspector's Manual for Slurry Systems (2010a) differenti- The report uses a number of technical terms in a precise sense ates each technology in the following manner: that is important for the reader to understand. The technical vocabulary of this field has undergone a radical transformation Slurry seal--A mixture of aggregate, emulsified asphalt, as new products and new concepts have been developed. The water, and additives properly proportioned, mixed, and major terminology challenges found in the literature revolve spread over a properly prepared surface. Slurry seal is around two major areas. The first is the terms applied to vari- applied in a mono-layer. A mono-layer is considered one ous activities associated with pavement maintenance. The sec- stone thickness (based on the largest stone in the grada- ond is the fundamental definition of microsurfacing versus tion) spread on the pavement surface. slurry sealing. The lack of uniformity of microsurfacing ter- Polymer-modified slurry seal--A slurry seal designed minology exists not only in the technical literature but also in with an asphalt emulsion that has been modified with a the standard specifications of state DOTs in the United States. polymer or other special purpose additive to enhance one The specific definitions have been controversial and oftentimes or more properties of the slurry to better meet a par- rooted in local construction jargon. The terminology discussed ticular project requirement. Modifying emulsions may here will be used throughout the report and a Glossary is improve the bond between the asphalt and the aggregate included following the References. and may improve durability and toughness of the seal.