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40 CHAPTER SEVEN CONSTRUCTION PRACTICES INTRODUCTION face Treatments--Construction Techniques). Because the adhesion process is closely related to the viscosity of the To a great extent, the construction phase drives the quality binder, warmer ambient air temperatures result in better and performance of chip seals during their service life. There- adhesion obtained between not only the aggregate and binder, fore, it is critical that the construction system be well defined, but also between the chip seal and pavement surface. It is also controlling the construction means and methods critical to the accepted that roadway surface temperature at the time of con- performance of the chip seal. Construction practices and pro- struction closely affects the quality of chip seals. General cedures vary from region to region and are generally associ- consensus among the majority of respondents is that ambient ated with local equipment availability and empirical knowl- air temperature should be a minimum of 50F (10C) when edge of its use. This chapter draws information from both the using emulsions, and 70F (21C) when using asphalt cements. survey responses and the standard chip seal specifications Responses from Caltrans and a number of counties in Cali- from several highway agencies to identify those construction fornia specify a maximum ambient air temperature of 110F practices that are associated with successful chip seal proj- (43C) for their chip seal construction projects. The Indiana ects. Special attention has been paid to method specifications DOT allows placement in air temperatures from 40F to 60F that prescribe specific construction equipment or that serve to only if the aggregate has been heated to a temperature of enhance equipment operation. 120F to 150F (Seal Coat Placement 2004). WEATHER Roadway Surface Temperature It is widely recognized that weather-related factors are often The surface temperature of the existing roadway is also a crit- responsible for the failure of a newly constructed chip seal ical factor, because energy transfer between the binder and the (Asphalt Surface Treatments--Construction Techniques 1988; pavement surface greatly affects the resultant viscosity of the Asphalt Seal Coats 2003). Because the performance of emul- binder and the speed at which it will break. In regard to sur- sions depends on evaporation for developing their adhesion face temperature, the survey responses showed that signifi- characteristics, ambient and pavement temperatures, relative cant variation in requirements between agencies and trends on humidity, wind velocity, and precipitation all have an impact a regional basis were difficult to develop. This is a concern, on the constructability of emulsion chip seals. Ideal chip seal because low surface temperatures can lead to poor adhesion weather conditions are those with low humidity, without wind, of the chip seal to the existing pavement surface (Asphalt Sur- and with sustained high temperatures (Maintenance Chip face Treatments--Specifications undated). The Asphalt Insti- Seal Manual 2000). Chip seals constructed with hot asphalt tute recommends that the temperature of the surface be a min- cements have been shown to experience serious adhesion imum of 70F (21C) when constructing a chip seal (Asphalt problems when there is high humidity or moisture present Surface Treatments--Specifications undated). If the surface during construction (Wegman 1991). High humidity is a detri- temperature were low as, for example, during the morning, ment to any chip seal operation mainly because of the result- asphalt would be more viscous than desired to attain appro- ing poor adhesion between the binder and the aggregate. The priate adhesion between aggregate and binder. On the other MDT recommends that binder be shot only if the humidity is hand, excessive pavement temperatures can also be a prob- 50% or lower (Maintenance Chip Seal Manual 2000). The lem, particularly with the emulsions. In such a case, viscosity Minnesota DOT (Mn/DOT) allows chip seal placement with a would be so low that binder could not secure the aggregate in relative humidity of up to 75% (Minnesota Seal Coat Hand- place. The survey results indicate that Michigan limits con- book 1998). Additionally, when using emulsions, break times struction to a pavement surface temperature of less than are significantly increased with high humidity (Asphalt Surface 130F (54C), whereas Ohio specifies a maximum surface Treatments--Construction Techniques 1988). temperature of 140F (60C). Ambient Temperature Rain It is accepted that ambient temperatures at the time of con- Chip seals should never be constructed when rain is likely. A struction closely affect the quality of chip seals (Asphalt Sur- rainfall, during or shortly after the construction of a chip seal,