The City of Cincinnati's Department of Transportation and Engineering (DOTE) has received some questions from residents about the preventive maintenance (PM) program. Below is a series of information to help you better understand the PM program and how it's used on Cincinnati streets.

About

Preventative maintenance work is not a traditional “grind and repave” project that includes a hard surface of asphalt. A preventive maintenance surface treatments is a thin layer of a liquid coating system that fills surface cracks and pores and seals the existing pavement in order to extend the life of the street beyond the usual 20 to 25 years between repaving.

Preventive maintenance is a cost-effective means to preserve structurally sound pavements, extend their life, and reduce roadway budgetary costs. Preventive Maintenance activities include pavement rejuvenation, crack sealing and surface treatments. Preventive Maintenance provides greater value to the roadway system, improves safety, enhances mobility, and provides a higher level of satisfaction of roadway users.

Surface treatments specifically are preventive maintenance techniques used to extend the longevity of roadways by sealing the pavement surface. They protect the pavement from the effects of aging and the environment. A planned pavement maintenance program with surface treatments can help us achieve considerable savings in rehabilitation costs. They provide a durable, all-weather surface, ready for use just hours after application. Surface treatments can be reapplied numerous times as long as the pavement is sound; extending the life of the pavement by seven years on average with each application. Another benefit of surface treatments is improved skid resistance; thereby increasing safety.

Types of Treatments

There are four types of surface treatments that DOTE uses:

• Slurry seal is a versatile and cost-effective surface treatment used to preserve and protect sound pavement which has oxidized with age. The principal materials mixed to create slurry seals are aggregate, asphalt emulsion, and filler, according to a laboratory mix design. Water is added for workability.  This treatment provides uniform color and texture and is suitable for most low volume residential roadways.
• Micro-surfacing is a rapid-setting mixture of polymer-modified asphalt emulsion, dense graded aggregate, and other additives.  Its chemical characteristics minimize user delays and make it an excellent choice for higher volume roadways.
• Chip seal is a combination of an asphalt emulsion and crushed and angular aggregate.  It is the most economical surface treatment.  Specifically designed to seal and protect the pavement from water intrusion, Chip Seal also provides increased traction for enhanced safety on low to medium volume roadways.
• Cape seals are designed for pavements that may not be ideal candidates for micro-surfacing or slurry seal. The cape seal process involves a two-step process: 1) an engineered polymer-modified Reflective Crack Retarding Interlayer (RCRI) is applied on the existing pavement, and then 2) covered with Micro-Surfacing or Slurry Seal after one to two weeks.  The RCRI helps retard reflective cracking in asphalt pavements.  This is a cost-effective process that provides the strength and durability of RCRI and the smoothness and texture of micro-surfacing and/or slurry seal.

Ins and Outs of the Process

It should be understood that the streets in the City's preventive maintenance contracts are not being paved with asphalt, but rather a thin layer surface treatment. These treatments are designed to seal the pavement to slow down overall deterioration of the pavement, they do not smooth out the riding surface as a typical grind and pave would. Surface treatments, specifically slurry seal and micro-surfacing, are not easy to work with where hand work is required, and imperfections in the finished product are to be expected.

Also, on narrower streets, adjacent applications on either half of the street may overlap due to fixed equipment width; causing a raised ridge down the middle. However, the appearance of all the surface treatments will change over time as the surface wears and becomes smooth. Furthermore, to help the surface treated street look better, no one should walk or drive on the treatment until after the roadway is opened by the contractor.  Most of the appearance issues we are seeing are damages caused by people and vehicles getting on the streets before they are ready for traffic.

Slurry seals and micro-surfacing take time to set; that is, become firm enough to allow traffic.  This time varies, depending upon the temperature, humidity, wind and sunlight/shade.  Typically, you should not drive on a slurry sealed or micro-surfaced street for four to six hours after the application of the treatment.  It can take over two months for both slurry seals and micro-surfacing to cure; that is, to become fully hardened.  Until fully cured, the treated surfaces can be marred by the turning of wheels.

For chip seals and the first phase of cape seals, driving on the surface can occur almost immediately after the chips are placed.

Also, keep in mind that “prevention” is important.  Even though a street may be in good condition now, it is constantly deteriorating.  The time to conduct preventive maintenance is now, when it is still sound.  It’s too late for preventive maintenance once the roadway has deteriorated beyond a certain point.

Education Next Steps

DOTE is working on additional public education piece to explain the PM process; a one-page flyer with photos that shows the major steps and will be distributed to residents who live are streets that are being treated.