Driveways

Hot Mix Asphalt: Best for Your Driveway

·  Frequently Asked Questions About the Paving Season

A Consumer's Guide

Inviting, Attractive
The appearance of your driveway creates an impression about your home and way of life. An inviting driveway provides a focal point as passersby and visitors approach your home. And certainly an attractive driveway, one with “curb appeal,” adds value to your home investment. So it is worthwhile to plan your driveway carefully. With Hot Mix Asphalt as your material—and some attention to design and construction—your driveway will provide years of lasting service and an excellent return on the investment.

Just What is Hot Mix Asphalt?
It’s an engineered mixture of aggregate, or stones and sand, with liquid asphalt cement, a petroleum product. Varying sizes of aggregates are heated, then mixed, in exact proportions, with asphalt cement that has been liquefied at about 300 degrees. While the mixture is still hot, it is delivered to your driveway and paved on top of a base or subgrade that has already been prepared. Very soon after paving, the mixture cools and hardens and you can drive on it right away.

What You Receive with Hot Mix Asphalt
You’ll recognize several benefits with Hot Mix Asphalt, compared to other, more costly options.

• It is strong and durable.
• It is engineered to withstand freezing and thawing.
• No need to worry about salting your driveway in winter. Hot Mix Asphalt is unaffected by salt. and
• Unlike other, more rigid materials such as concrete, Hot Mix Asphalt is designed to flex and “give” with slight settlements or frost heave. Hot Mix Asphalt lends itself readily to the types of service that are usual in residential areas. If a utility line must pass under your driveway, repairs are more easily and quickly performed than with alternative materials such as concrete. The same is true if undue ground settlement should occur naturally.

And Hot Mix Asphalt is the most cost-effective option you can choose. Just as it has for millions of homeowners the world over, Hot Mix Asphalt can last many years for you—with only minimal maintenance.

About Quality Control
There are hot asphalt mixtures of various types. Some mixtures are smoother on top than others; some have a higher content of asphalt cement than others. A special type of asphalt mixture is even colored and imprinted to resemble paver blocks. Consult with your homebuilder or contractor to assure that your mixture will provide the surface and performance characteristics you want. Unfortunately, all consumers do not closely monitor their driveway design and construction. So it is possible for some builders and/or subcontractors to try to boost their profits at the expense of your driveway’s quality. Getting multiple bids, if possible, and having the willingness to work with your builder or contractor to control quality will serve you well. A word of warning: If someone knocks on your front door and says, “We have a load of asphalt that was left over from paving nearby, and we can pave your driveway at a bargain rate if you’ll pay cash,” don’t take him up on it. Asphalt that is “left over” from another job will be too cool to make a good pavement at your house. Anyway, as with any other business transactions, you want to know who you’re dealing with before proceeding, so making a deal on the spot doesn’t make sense for you. Checking references can save you money in the long run.

Full-depth Asphalt: The Best Option
Full-depth Hot Mix Asphalt driveways are built entirely of Hot Mix from the soil subgrade up. Full-depth driveways keep water out of the pavement. So water never enters the pavement to swell when it freezes. Full-depth asphalt provides a better balance of strength and flexibility—plus durability—than any other material. For improved soil stability, it is recommended that topsoil containing clay be removed or modified. A solid subgrade requires thorough compaction. Paving with Hot Mix follows. A 4-inch thickness may be adequate, but 5 or even 6 inches of full-depth Hot Mix will assure you of a stronger, stable driveway under a wider range of climate and loads. As an option, some contractors use 6 to 8 inches of compacted aggregate, or gravel, as a base under 3 inches of Hot Mix.

“We recommend full-depth asphalt for driveways,” says Dave Newcomb, NAPA Vice President of Research and Technology. “We calculate that Hot Mix Asphalt can replace aggregate on a ratio of 1:3 in thickness. That is, 1 inch of Hot Mix is equivalent to 3 inches of aggregate base.” Hot Mix Asphalt is best placed in “lifts,” or layers. For example, a total of 2 to 3 inches may be spread as two layers each 1-1/2 inches thick when compacted. A good way to pave a 4-inch “mat” is first to place 2-1/2 inches, compact it, then pave the remainder and compact again.

“If possible, we apply only the first course of Hot Mix during new-home construction,” says Jeff Terp of Merit Asphalt Inc., a Wisconsin-based NAPA Member. “We wait until construction is finished to pave the surface course. That way construction traffic, dirt, and little dents all happen on the base course. At the end we clean the base and pave the surface course, and it looks good.”

You’re the Boss
If you’re having a new home built, you can specify to your builder that you want a Hot Mix Asphalt driveway—as do millions of homeowners, across all new-home price ranges. If your builder hasn’t done so when you buy, he likely will soon hire an asphalt contractor to pave driveways. As the owner, though, you are still the boss. You can plan for, request, and obtain top-quality performance. If your driveway is in bad shape and needs either a complete reconstruction or resurfacing with Hot Mix Asphalt, you’ll want to talk directly with two to four contractors. Consult the Yellow Pages or ask your neighbors for names of firms. You can ask their advice about what’s to be done, but once you decide upon and define your project, it is good business to obtain at least two bids.

Here’s a cost saving tip: If you can arrange with some neighbors to have all your driveways paved at the same time by the same contractor, savings will result for all owners—because that gives a paving contractor economies of scale.

Placing an Overlay
Driveways of either asphalt or concrete can be overlaid with Hot Mix Asphalt—with excellent results. Usually for driveways, a surface course of 1-1/2 to 2 inches thick will suffice. Before paving, be sure the contractor patches any serious holes or cracks with Hot Mix and compacts it. Otherwise the trouble spots may carry upward through your
new pavement.

How to Hire a Contractor
All reputable contractors who seek your business in good faith will provide references and phone numbers of satisfied customers. Some firms even maintain a list of recent customers and phone numbers. A few quick calls will help protect your investment. Ask references about qualifications such as contractors’ quality of work, attention to details, on-time performance, and ability to finish work completely. Here are some other points to consider:

• Check gates for clearance; know who’s responsible for re-hanging them, if needed.
• Decide whether you, a plumber, or someone else will raise any water valves or sewer inlets to meet the asphalt around them.
• Assign specific responsibilities and make notes.
• Surface drainage is very important. Make sure your contractor plans and builds adequate surface slopes to produce good drainage. So-called “ponding,” or standing water, on or near the driveway, is undesirable. Once you have taken bids and selected the contractor you want, you’re ready for the contract. A construction contract should detail such items as the responsibility for grading work and accuracy, for compacting the subgrade and base, for measuring compacted pavement thicknesses, for pavement slopes and smoothness, payment schedule, and guarantee of the finished product. It’s important to make sure your contractor has adequate liability insurance. Ask for written proof of it.

Maintaining your Driveway
If designed and built correctly, a Hot Mix Asphalt driveway will give you years of effective service. A high-grade asphalt emulsion sealer (sometimes called bituminous emulsified sealer) should be applied every two to five years, depending on your climate, wear patterns, and the like. Driveways that are sealed regularly look better and last longer. Emulsion sealers consist of asphalt cement treated to mix with water. Once applied, the water evaporates, the material hardens, and the surface is waterproof. For driveways on slopes, some sealers contain sharp sand that will provide added traction.

Your Best Buy
Just as with buying a new roof or deck, good business practices prevail with installing a new driveway. Be informed. Seek multiple bids. Get references. Surveys show that quality-conscious companies belong to trade associations such as the National Asphalt Pavement Association. Ask your contractor if he is a NAPA Member. With Hot Mix Asphalt and a NAPA contractor, you'll know you have the best buy, all of the time.

For a download of a brochure with this information, [click here].

For questions about driveways, please e-mail the engineering department.

Is there a paving season when I should have my driveway paved?

The main concern on when to pave a driveway is temperature. Asphalt must be placed and compacted while it is hot. Lift thickness and air and surface temperatures play significant roles in how fast the mix cools and therefore the time a contractor has to complete the work. Because seasonal temperatures vary throughout the U.S. temperatures serve as a better guide for paving. The following table, developed using MultiCool, illustrates the effect of temperature and lift thickness on time available for compaction.

Note: Table developed based on 300 degree F delivery temperature and 175 degree F final temperature.

Red areas indicate temperatures where these lifts of asphalt are not recommended and yellow indicates caution.

The amount of time that a contractor will require to place and compact your driveway will depend on the size of the job, amount of handwork and available equipment. As a general guide, you should probably allow over 20 minutes for the contractor to place and compact a lift. Therefore, if you are having a 1-1/2 inch lift placed the air and surface temperatures should be above 70 degrees F. For a 2-inch lift, there is a little more leeway, but the air and surface temperature should be above 40 degrees F. The above times are based on a mild wind condition (less than 10 mph) and should be decreased by about 5 to 10 minutes for every additional 10 mph of wind speed.

It is also important to ensure that the soil or rock on which the pavement is being placed is firm and dry. If this is not the case, then it is recommended that paving be delayed until it is.