Sometimes relatively simple steps can be taken to correct or improve drainage problems. Asphalt is more easily resurfaced than concrete. However, some shortcomings of original design and construction can be difficult, if not impossible, to overcome entirely.
I have received different bids/proposals/recommendations from different contractors as to the scope of work. How do I evaluate different points of view from supposed experts?
Our expertise is in consultation and making sound technical recommendations based on your needs, preferences, and budget. Very often different points of view come from some combination of variances in technical knowledge, perspective on the pavement’s stage of the lifecycle, or the aforementioned needs, preferences, and budget.
Crack filling is a bit of a double-edged sword. Cracks that are left unfilled allow water intrusion that can compromise the base structure of pavements. Most soils in the Bay Area have low R-values meaning they lose stability and strength when wet, so keeping water intrusion to a minimum is important, especially if the pavement ever needs to support heavy loads. Cold applied crack fillers tend not to protect and last as long as hot applied rubber, but they are also less noticeable, less expensive, and can be done the same day as sealcoating. Hot rubberized crack fillers are much more effective for wider cracks and longer lasting, but they also cost more, are more noticeable and unsightly, and are best performed on a separate day in advance of sealcoating. Depending on the volume and type of traffic, width of cracks, quantity of cracks, age of the pavement, and aesthetic considerations, we can make a recommendation that balances cost, effectiveness, and appearance. Because crack filling without sealcoating or slurry sealing afterwards tends to be unsightly, we generally recommend completion after repairs and prior to the surface treatment.
Very small projects can be completed in one day while larger projects may take multiple days. Small to mid-size projects often have a phase/day for demolition and form setting and a separate phase/day for pouring and finishing. Most commonly used concrete mixes take a minimum of a day to cure for foot traffic, a few days to cure sufficiently for car traffic, and 5-7 days for truck traffic. The PSI rating of concrete mixes is based on strength at 28 days. The curing process over time plots as a curve with most of the curing takes place after placement and gradually slowing. Concrete continues to strengthen incrementally even well past the 28-day rating.
The work can be phased to re-direct traffic during demolition, placement, and curing. If this approach is not practical, metal trench plates can be used to cover and protect new concrete while it cures. For some other applications, use of a “high early strength” mix which contains chemical additives to speed the curing process may be advisable. The approach which makes the most sense depends on factors such as type and thickness of concrete, target strength, time available for curing, size of areas, cost of plates versus additives, and other variables.
Most concrete mixes are referred to by the amount of cement (the “glue” or binder) holding the aggregates together in each cubic yard of the mix. Most mixes for sidewalks, curbs, gutters, driveways, slabs etc range from 5 to 7 sacks and have a 28 day PSI rating of 3,000 to 5,000 psi.
Rebar serves several purposes. Dowels and longitudinal strands are simple means of typing together new concrete with existing so that they move together rather than independently. Rebar grids, commonly at 12”-24” on center are placed in load bearing slabs to provide tensile support. Concrete has high compressive strength but low tensile strength. The inclusion of the rebar compensates for the tensile strength deficiency, more broadly distributes loads, and prevents vertical displacement when/if cracks develop.
As a general rule, most sidewalks and driveway approaches do not contain rebar. With all concrete structures (whether slabs, curbs, etc) if there is vertical displacement at cracks, there is no rebar.
In general, yes. Good design and construction result in fewer cracks and more predictable and controllable location of them. Concrete structures generally consist of a combination of expansion joints to allow for expansion and contraction of the concrete and control joints to encourage cracking in specific, straight, and controllable areas of the slab or structure.
Given proper conditions (air temp, surface temp, sunlight exposure, wind, humidity, etc) many new sealcoat applications dry quickly and can be open to low to medium traffic within hours. If ideal conditions are not meant or the sealcoat will be subject to higher traffic volumes (e.g. main entrances to large communities or complexes) or tight turning from parking ingress/egress (as in shopping center parking lots) it may be desirable for the sealcoat to cure overnight before it is open to traffic again.
An overlay is a new section of asphalt that is typically 1.5” to 2” and therefore has structural strength. A sealcoat is an emulsion – a mixture of asphalt oils, water, and particulates that has no strength and will reveal any limitations or structural deficiencies of the surface on which it is placed. A slurry seal is similar to a sealcoat but with aggregates added to the mix, most commonly ¼” (Type 2) or 1/8” (Type 1) in diameter. Sealcoats tend to perform best in parking lots and lower traffic roadways that may require a lot of vehicle turning while slurry seals tend to perform best on higher volume roadways with mostly directional traffic. In general, an overlay often costs 5-10 times the cost of a sealcoat and a slurry seal costs 1.5-2 times the cost of a sealcoat. The right application can depend on many factors including layout, traffic volumes, condition of the existing pavement, the stage of the lifecycle, costs, and other preferences and priorities.
Yes, but again they tend to be minor. The most commonly used producers in the SF Bay Area are Overkote (Reed & Graham), Graniteseal (Graniterock), Tri-American, and Western Colloid. As with many other products, there are pros and cons of each with variations in longevity, depth of color, effectiveness on new versus aged pavements, etc but they are similar enough in both appearance and cost that most customers are unlikely to notice a difference, particularly if surfaces are sealed regularly at 5-7 year intervals. On rougher surfaces, the addition of sand and latex additives can improve the longevity and performance of the sealcoat and replace fine aggregates lost to erosion/raveling. If conditions dictate, we may recommend one material over another or encourage the inclusion of additives.
The frequency of sealcoating depends on a number of factors. How long the sealcoat takes to wear off depends largely on the condition of the pavement underneath. Rougher surfaces absorb more, so the seal tends to last longer. Smooth surfaces absorb less, so the seal wears faster. Most pavements have areas that receive different amounts of traffic, sunlight, water flow, and other environmental elements that lead to wear. Sealcoating has two benefits – surface preservation and aesthetic improvement. We find that most customers prefer to be slightly proactive with successive sealcoats and re-seal surfaces when they start to look worn or streaky. In terms of functionality, many of these pavement surfaces are still largely protected adequately, but again customers tend to prefer a more proactive approach favoring aesthetics, particularly given the cost effectiveness and “cheap insurance” nature of sealcoating. We see many contractors claim 3-5 year windows (likely a bit of self-serving advice at play there), but a 5-7 year cycle is more common and reasonable for common two coat applications.
New asphalt absorbs a lot of striping paint, but even with a two-coat application, a “freshening up” is often warranted within a few years. Many customers proactively sealcoat at that time, so the two often go hand in hand. On most other pavement surfaces, the striping lasts about as long as the sealcoating so they can often be completed in tandem. Occasionally some markings wear out faster than the asphalt or sealcoat do, particularly in areas with large volumes of vehicle traffic such as entrances and exits to shopping centers or gated communities. Striping provides great bang for the buck and the paint tends to dry in around 10 minutes on a typical day, so even if your property needs an occasional mid-cycle refresh in some areas, it’s likely to be relatively inexpensive and painless.
Asphalt is made of approximately 5% oil/binder and 95% crushed aggregate, of which 10-20% is often recycled (RAP – reclaimed asphalt pavement). Materials engineers design mixes with varying combinations of aggregate sizes/gradations and oil content to achieve various performance criteria. The goal is to create strength through the interlocking aggregates with just enough (but not too much) binder to effectively bond the aggregates. The most common asphalt mix is a “1/2” medium.” In this mix, the largest aggregates are ½” diameter with other smaller aggregates (3/8”, ¼” etc) down to sand size particles.
Asphalt paving is equipment intensive and asphalt cools/cures quickly. Many projects can be completed in one day and ready for traffic that evening. Larger projects may take multiple days. Many customers are surprised at the speed and efficiency of completing asphalt work.
New asphalt can be driven on once the “cessation temperature” (point at which the binder has cooled and stiffened to the point that it can no longer be compacted) of around 150 degrees Fahrenheit or below has been reached. Generally by the time the crew has left the jobsite, the asphalt has cooled to the point that no damage can be done by routine traffic.
An overlay is a new section of hot mix asphalt, usually 1.5”-2”, placed over the existing pavement surface, often utilizing an interlayer made of specialized fabric and/or fiberglass. This type of rehabilitation is commonly seen on city streets and can be both cost effective and structurally effective on parking lots and private roadways as well. Drainage profiles and the condition of the existing pavement must be considered when planning for an overlay. An overlay IS in fact a new asphalt surface and to most people will have the same appearance of asphalt that has been fully replaced. There are pros and cons, cost implications, and longevity considerations with determining whether an overlay, replacement or a hybrid approach is best. That’s where we can provide guidance.
Properly placed and compacted asphalt appears somewhat porous to many people. This appearance is normal and will smooth with the kneading action of rubber tire traffic. It is also normal for the new asphalt to attract dirt immediately after placement, for water flow lines to be conspicuous and appear as stains, and for it to gray considerably in the first year or two following installation. However, new asphalt should not slough off and produce loose aggregate. It should also be relatively uniform in appearance without concentrated pockets of large aggregates. Both of these conditions can be indicative of improper workmanship and/or compaction, the most crucial element of quality asphalt placement. Whether it’s our own work or that of another contractor, we’re always happy to provide inspections and no-nonsense appraisals of quality.
Are there differences in quality (good/better/best) in terms of asphalt mixes from different plants and suppliers?
Yes, but they tend to be minor and inconsequential to most projects. Experienced asphalt crews will often notice small differences in the workability of asphalt mixes, subtle variations in oil content, and concentration of large and fine aggregates (called gradations). However, most plants produce hundreds if not thousands of tons of asphalt each day, so they must monitor quality closely to protect their own interests. Virtually all modern plants are computer controlled and oil content and gradations meet rigid quality control standards, often to CalTrans (in CA anyhow) standards. There is always an acceptable range for oil content and gradations. Some producers shoot for the lower end of the acceptable range as a means of reducing costs while others prefer to be safely in the middle. For parking lots and low volume roadways, the quality of materials is likely to be comparable regardless of which producer supplies the material. With asphalt, the quality of the placement and compaction has a much larger impact on quality and longevity than the small variations in the material.
On many large projects that involve oversight by engineers and/or government agencies, specifications can literally fill a thick book. Check out this link to CalTrans specifications. Most smaller private works projects involve no measure of quality by the owner at all. The quality of an asphalt installation generally depends on compaction, accomplished with vibratory rollers. Asphalt should generally be placed at 250-300deg F and compacted in stages until it cools to 150-175 degrees. Testing of air voids / compaction / density by use of a nuclear gauge and/or core samples in a lab are the most common methods. Generally compaction of 92-97% (3-8% air voids) is most desirable to ensure a long lasting surface that is impervious to water and will not age and oxidize prematurely. A difference of only 2 percentage points in air voids can affect longevity by 15%. Often on larger, full rehabilitation projects we will include third-party testing as an option to ensure that quality is in line with a major investment in new pavement. On smaller projects, testing may be overkill and not cost effective, but proper care should always be taken to monitor temperatures and compaction methods.
As previously discussed, proper compaction is the most crucial element of ensuring quality asphalt installation. The various stages of compaction – breakdown rolling at high temps (high 200’s), intermediate rolling at medium temps (low to mid 200’s), and finish rolling at cooler temps approaching cessation temperature (150-200) are critical. Factors such as wind speed, sun/UV exposure, air temperature, ground temperature, thickness of asphalt, distance to the asphalt plant, and others relate to how fast the asphalt will cool once place and how much time is available for compaction. During summer months when placing a 4” section with a paver, for example, conditions are right and generally make compacting new asphalt much easier to manage. In winter months, placing a thin section of asphalt requiring a lot of handwork on a cool, breezy, cloudy day at a site far from the asphalt plant may make proper compaction extremely difficult. In terms of precipitation, some mist, fog and even drizzle generally aren’t detrimental to quality but a steady rain should absolutely be avoided.