Paving 101

Subgrade

Whether you are building a road or parking lot from scratch, the first step is to prepare the subgrade. Once excess materials are removed, the area must be finished and graded. This provides proper drainage for your finished product. Correct drainage is crucial, not only to the adjacent buildings, but water cannot be allowed to stand on the asphalt. Significant puddles will cause premature failure of the asphalt surface.

Compaction of sub soils is critical. Any movement, whether from nature or settling of soils, will translate into a surface failure. Every project, whether created from scratch or resurfaced, requires different techniques for preparation. Be sure to ask lots of questions so you feel good about the contractor's experience before you make a decision.

Baserock

Baserock thickness depends on the type of traffic or weight you expect to be having over the surface. When in question, thicker is always better up to a certain point. Budget constraints are always a factor that can lead to an inadequate base and asphalt thickness. We strive to give you all the options we feel are required for your project. When a company bids your job, they should include the compacted thickness, square footage, and tonnage of the baserock they will be using.

The baserock thickness is often the first thing that is reduced to cut costs. Always remember the asphalt surface is only as good as what is underneath it. Proper installation and compaction of the baserock section is crucial. Inadequate density or thickness in the baserock can lead to cracking and settling in the asphalt. Thin or used baserock can cause an uneven finish grade, resulting in an uneven asphalt surface. This means the asphalt will be thicker in some areas and thinner in others (the thin areas will be a future problem).

Customers sometimes wonder why the rock they have been dumping on their driveway for years cannot act as a proper baserock. The truth is that the rock currently on your driveway may be adequate, depending on quantity, age, and thickness. However, it may not be sufficient for stability, drainage, and a level course under the asphalt. Remember, once it is paved over, you bought it for better or worse.

Asphalt

The installation of asphalt is probably the most specialized and difficult part of the job. Weather, ambient temperature, and skill are all factors that can leave you with a high maintenance or low maintenance job.

Asphalt pavements are made up of stone (aggregate), fine stone or sand, and asphalt cement. The asphalt cement is what gives the pavement its black appearance and is the “glue” that holds everything together. When combined in the proper amounts and heated to around 300 degrees, it all comes together to form asphalt pavement.

Asphalt pavement is installed at various thicknesses using different methods, depending on the type of job. A typical driveway on flat ground should have a compacted asphalt thickness of no less than two inches. Steeper situations on hills, or steep corners, may require a thicker section of asphalt to prevent “stretching” or development of thin areas caused by the compaction process. Asphalt overlays or resurfacing typically require no less than 1 ½ inches, after compaction of asphalt pavement. Factors that alter these measurements include surface roughness or grade and slope.

Chipseal - Another Option

Chipseal is another type of surface that can be installed over asphalt, baserock, or even over existing chipseal. As a maintenance procedure, chip seal can be installed over worn asphalt or old chipseal to provide a new wear surface. As a new surface, chipseal can be installed over baserock, providing the grades are less than 10% and you don't live in an area over 2000 feet in elevation. Chipseal won't work in areas where it snows.

When chipseal is installed over baserock, the preparation is very important. The baserock must have a tight surface and drainage that is no less than 4% (1/2 inch per foot) in any direction. Water cannot be allowed to stand or it will break down the road oil very rapidly leading to a surface failure. The finished baserock surface must be as smooth as possible because the chipseal will follow any high or low spots, just like painting your car.

Chipseal used as a wear surface is very common. It is called a "chipseal overlay" whenever it is installed over existing chipseal or asphalt. City and county agencies use this as regular maintenance for many of the roads you drive on. Single layers are the most common but heavily worn roads can benefit from a double layer.

Chipseal is basically a layer of thick hot road oil with 5/16" to 3/8" crushed rock spread over it and then compacted into the oil. The oil hardens and retains the crushed rock to create a new wear surface. Chipseals that are done correctly are installed using an oil truck to spread the hot oil in front of a self propelled "Chip Spreader" machine. If an overlay is being done, a pneumatic rubber-tired roller is used to compact or impregnate the rock into the oil.

The common mistakes made in chipseal installation are:

#1. Installing the incorrect quantity of oil per square yard

The spread rate of the oil varies depending on different road conditions. A qualified professional will determine and install the correct quantity for your specific needs. Always ask about the type of oil that will be used and the spread rate (gallons per square yard). Ask that this be listed on the contract.

When the rock or "chips" are installed, it is important that they are not allowed to roll into the oil. A self-propelled chip spreader is needed to achieve this. A chip box on the back of a truck will work but will not prevent the chips from rolling into the oil. Also, the chips will not be spread evenly and will usually be installed too thick to compensate for lack of accuracy in the spread of the oil. When it comes to chips in a chipseal, thicker is not better!

A self propelled chip spreader will drop the chips into the oil from approx. six inches in height and prevent a rolling effect. A chip spreader will also install the chips in the correct proportion to the oil so loose chips will be kept to a minimum.

#2 Using the incorrect equipment to compact the crushed rock "chips."

The compaction of the chips is the last step in a chipseal job. When chipseal is installed over baserock, a steel drum roller is used. When a chipseal overlay is done over a hard surface, a pneumatic "rubber tired" roller is used. It is important to get the chips impregnated into the oil, especially in the low spots. The individual rubber tires will push into the low areas without "crushing" the chips on the high spots. This leaves a densely compacted and uniform surface.

The final step is to sweep off any loose chips approximately three to five days after the initial chipseal. Loose rock that is allowed to sit on top of the road surface will grind into the bonded rock, loosening it up and causing premature surface wear.

Chipseals that are done right, using the correct quantity of oil and type of equipment, will last for years at a fraction of the cost of asphalt.

Always choose a contractor with the right equipment and skills to do the job right the first time.

Here is where it all starts