Pavement preservation treatments: the field guide to keeping good roads good

Pavement preservation, and what it is not

Pavement preservation is a planned program of treatments that keeps good pavement good, applied while the surface is still sound, so the pavement reaches the end of its real life instead of failing early. The FHWA frames it as a network-level, long-term strategy that extends pavement life cost-effectively, and the trade shorthand for it is the right treatment, on the right road, at the right time. The phrase sounds like a slogan. It is actually the whole job.

The thing to understand first is what preservation is not. It is not reconstruction, it is not a structural repair, and it is not a rescue for a road that has already failed. You preserve pavement that still has life in it. You cannot preserve a road that is already broken, and the most reliable way to waste a maintenance budget is to try. A thin treatment over a failed base buys one season and the owner pays for the same fix twice.

The other half of the definition is timing. A preservation treatment laid at the wrong point on the condition curve does nothing useful, no matter how well it is built. The treatments in this guide pay only when they go onto pavement that is still in good to satisfactory shape, which is why every one of them starts with a condition survey, not a coat of material.

When is pavement cheapest to treat?

Pavement is cheapest to treat while it still looks fine, and that is not a slogan, it is the shape of the deterioration curve. Condition holds high for years, drifts down slowly, then falls off a cliff. The widely cited figure from the AASHTO and FHWA pavement-management work is that the first 40 percent drop in quality takes about 75 percent of the pavement's life, and the next 40 percent drop takes only about 12 percent. The decline is not a straight line. It accelerates.

That curve sets the money. The same body of work puts the return on the order of 6 to 10 dollars of avoided rehabilitation or reconstruction for every dollar spent on preservation at the right point in the curve, with some agency figures higher and some lower. Treat that as the direction and the order of magnitude, not a contract guarantee, because it moves with climate, traffic, and how far down the curve you start. The lesson holds regardless. The dollar is spent best on pavement that is still high on the curve, where a treatment protects sound material.

The field version is simpler than the economics. The best time to treat a pavement is when it does not look like it needs anything yet. Wait until a road looks bad enough that the complaints come in, and it has usually already gone over the cliff, where preservation does nothing and the cheap fix is off the table. The deterioration curve and the condition survey behind it are covered in the companion PCI guide. This guide is what you do with the answer.

Preventive, corrective, and reconstruction

Three categories of work sit under the larger heading of taking care of pavement, and preservation is only one of them. Preventive maintenance is the planned work applied to good pavement before a deficiency shows up, to slow the deterioration and hold the functional condition without adding structural capacity. That is preservation proper. Crack sealing a sound road, fog sealing a dry surface, micro-surfacing before the cracks open: all preventive.

Corrective maintenance is reactive. It happens after a deficiency appears, to fix a problem that is already there. Patching a pothole, repairing a failed section, fixing a spot that is hurting safety or ride: that is corrective work, and it is not the same thing as preservation, even though crews often do both on the same visit. The distinction matters because a program built on corrective work is a program that is always behind, fixing what already broke.

Rehabilitation and reconstruction are the heavy end. Rehabilitation restores structure and ride to a pavement that has dropped past what a thin treatment can save, typically a mill and overlay or a structural overlay. Reconstruction tears the pavement out and rebuilds it from the subgrade up. Neither one is preservation, and conflating them is how budgets get misread. Preservation is the cheap work you do early to push the expensive work later. Once you are paying for rehab or reconstruction, the preservation window for that section is already gone.

Matching the treatment to the road

The right treatment depends on two things together: how much life the pavement has left, and what kind of distress it is showing. Condition alone is not enough, because a road at the same overall score can need very different work depending on whether the distress is age on the surface or a failure in the base. You read the condition to know how much intervention the section can carry, and you read the distress to know what kind it needs.

Measuring the condition is its own discipline, and it is the subject of the companion PCI guide. The short version is that a Pavement Condition Index from 0 to 100, surveyed under ASTM D6433, gives a repeatable number you can plan against, and the number maps to treatment families: high scores get preservation, middling scores get rehabilitation, low scores get reconstruction. The survey also names the distress, which is the part that overrides the score.

Distress type is the veto. Surface distress from age, block cracking, raveling, oxidation, light cracking, is exactly what preservation is built to handle. Structural distress, alligator cracking and deep rutting, is a base failure, and no surface treatment fixes it. A road can carry a respectable surface score and still be failing structurally underneath, which is why the matching step always pairs the score with a look at the cause. Get the cause wrong and the right-looking treatment fails anyway.

Crack sealing: the first line

Crack sealing is the first treatment in the toolbox and usually the highest return per dollar, because it stops water at the one place water gets in. A crack is an open door to the base. Surface water runs into it, softens the support underneath, and the road starts to fail structurally from a defect that began as a hairline. Seal the working cracks early with a flexible hot-pour material and you keep the base dry, which is most of the battle.

The distinction that matters is sealing versus filling. Crack sealing puts a rubberized, flexible hot-pour sealant into working cracks, the ones that open and close with the seasons, so the material moves with the pavement. Crack filling puts a stiffer material into non-working cracks that barely move. Put a rigid filler in a working crack and the next cold snap tears it out. The full process, routing, cleaning, the kettle temperature, the overband question, is covered in the crack-seal and sealcoat guide.

Crack sealing has a hard limit, and it is the same limit every treatment in this guide shares. It does not fix alligator cracking. The interconnected chicken-wire pattern is a base failure, not a crack you seal, and chasing it with a kettle is money poured into a hole. You handle the structural failures as patches first, then seal the working cracks in the sound pavement around them.

Fog seal: rejuvenating a dry surface

A fog seal is a single light application of diluted asphalt emulsion sprayed over the surface, with no aggregate, to put binder back into pavement that has dried out. As asphalt ages, the binder oxidizes and the surface goes gray, loses its fines, and starts to ravel. A fog seal soaks in, restores some of the lost binder at the surface, seals fine cracks and the raveling, and buys time on a pavement that is structurally fine but cosmetically and superficially aging.

It is the lightest treatment here, and the lightest commitment. A fog seal is fast and cheap and it returns to traffic quickly once it has broken and cured, but it adds nothing structural and it wears off, so it is a short-life treatment measured in a year to a few years depending on traffic and climate. On a low-volume road, a shoulder, or a recently chip-sealed surface that needs its aggregate locked down, it earns its place. On a busy lot it scuffs and tracks if traffic comes back before it cures, so the timing matters the same way it does for sealcoat.

The common error with a fog seal is the rate. Spray it too heavy and the surface stays slick and tacky, a skid problem and a tracking problem at once. The application rate is light by design, and the manufacturer and the spec set it for the surface texture and the dilution. A dry, porous, raveling surface takes more than a tight one, so the rate is read off the pavement, not off habit.

Seal coat: the parking-lot treatment

Seal coat, the sealcoat most people picture on a parking lot, is a thin protective coating of refined coal tar or asphalt emulsion mixed with water, sand, and additives, squeegeed or sprayed over the whole surface. It blocks UV, sheds water, and resists the fuel and oil that drip on a lot, and it gives the lot the uniform black look an owner wants. It is the dominant preservation treatment on commercial and institutional parking, and on driveways, where the loads are light and the appearance matters.

Sealcoat protects the surface, it does not add strength, and it goes on sound pavement only, the same rule as everything else here. The full job, the mix design, the sand loading, the two-coat application rate, the coal-tar versus asphalt-emulsion choice and the bans that increasingly decide it, the cure window before traffic, is the subject of the crack-seal and sealcoat guide. The short version for a preservation program is that sealcoat is the parking-lot member of the toolbox, on a re-seal cycle of every few years, run after crack sealing and patching and before striping.

One thing separates lot work from road work here. The treatments an agency uses on a highway, chip seals and slurries and micro-surfacing, are aggregate systems built for traffic and skid. Sealcoat is a thinner coating built for the lighter duty and the appearance of a lot. A lot owner reaching for a chip seal and a highway agency reaching for a parking-lot sealcoat are both using the wrong member of the family for the duty.

Chip seal and surface treatment

A chip seal, also called a surface treatment or seal coat in DOT language, is a sprayed layer of asphalt binder covered immediately with a layer of embedded aggregate chips, rolled in and then swept of the loose stone. It seals the surface against water and oxidation and it lays down a fresh wearing surface with good skid resistance, which is why it is one of the most-used preservation treatments on low- and medium-volume roads. It is cheap per square yard and it covers a lot of ground fast.

What a chip seal does well is seal and protect. What it does not do is add structure or fix anything underneath. It is a surface treatment in the literal sense, a skin over the existing pavement, so it goes on a road that is structurally sound and showing surface aging and light cracking, not on a road with rutting or alligator cracking. Laid on a failing base, the chip seal cracks straight back through within a season, tracing the failure it could not fix.

The two complaints owners have about chip seals are both real and both manageable. Loose stone after construction is the first, which is why the sweeping and the initial speed control matter, and why the brooming on a scrub seal exists. Noise and ride are the second, since a chip surface is coarser than a slurry or an overlay. On a road where the ride and the loose-stone risk are a problem, a cape seal or a slurry covers the chip, which is the next section.

Slurry seal and micro-surfacing

Slurry seal and micro-surfacing are both cold-applied mixtures of asphalt emulsion, fine aggregate, water, and additives, spread over the surface as a thin layer that seals and re-textures the pavement. They look similar going down and they get confused constantly, but they are not the same treatment, and the difference decides which jobs each one suits. The simplest way to keep them straight is that micro-surfacing is the engineered, polymer-modified, faster-curing, heavier-duty version of a slurry.

Slurry seal is about one stone thick, a thin emulsion-and-fine-aggregate coat that seals the surface, fills minor surface voids, and restores skid on a sound pavement. It cures by the water evaporating, so it leans on sun and low humidity and dry weather, and it returns to traffic in hours under good conditions. It is a good fit for low-speed, lower-volume surfaces, residential streets and parking, where the duty is light. What it cannot do is fix ruts; a slurry follows the shape it is laid on.

Micro-surfacing always uses a polymer-modified emulsion with chemical additives that force the water out and let it break and set without relying on the weather, so it cures fast and can be opened to traffic in about an hour under a range of conditions. It goes down thicker, in one or more stone thicknesses, and because it is engineered and tougher it can be placed in a thicker rut-fill pass to take minor wheelpath rutting back out of a surface that a slurry would just coat over. On a higher-volume road, a road with light rutting, or a job that has to reopen fast, micro-surfacing is the one that fits. Neither treatment adds structure, and neither fixes a base failure.

Scrub seals and cape seals

Scrub seals and cape seals are combination treatments, built by stacking the simpler ones to cover more distress than a single seal can. A scrub seal is a chip seal with a brooming step: the distributor pulls a broom sled that scrubs the sprayed emulsion down into the cracks before the aggregate goes on, so the binder works into the cracking instead of just bridging it. It seals a more cracked surface than a plain chip seal handles, and it is a way to get a few more years out of a road that is a step past a clean chip-seal candidate.

A cape seal is a chip seal covered by a slurry seal or a micro-surfacing layer. You get the sealing and the fresh aggregate of the chip seal, then the slurry or micro on top locks the stone down, smooths the ride, and quiets the surface, which answers the two usual chip-seal complaints in one treatment. A cape seal seals moderate cracks, restores skid and the uniform black look, and typically buys more years than either layer alone, which is why agencies reach for it on roads in fair-to-good shape that need more than a single seal.

The reason these combinations exist is that the single treatments each cover a narrow band of condition, and real pavement does not always land neatly in one band. The combination treatments are still preservation, though, with the same hard limit. A cape seal on a base failure is two treatments wasted instead of one. The stacking buys range across surface distress, not a pass on a structural problem.

Thin and ultra-thin overlays

A thin overlay is a new layer of hot mix asphalt placed over the existing pavement, generally 1.5 in or less, with the ultra-thin version at about 1 in or less, laid as a fresh wearing course on a prepared surface. It is the heaviest treatment that still counts as preservation, and it sits right at the line between preservation and rehabilitation. It restores the ride and the surface, seals the pavement, and corrects minor surface irregularities in a way the thinner seals cannot.

What makes a thin overlay preservation rather than rehab is that it is a functional treatment, not a structural one. A true structural overlay is thick enough to add load-carrying capacity to the pavement and is sized for it. A thin or ultra-thin overlay is too thin to add meaningful structure; it addresses the surface, the ride, and the sealing, and it is placed on pavement that is still structurally sound. The bonded ultra-thin version uses a heavy tack or membrane to lock the thin lift to the surface below, because a thin lift that does not bond will not last.

The temptation with a thin overlay is to use it to hide a problem the owner does not want to pay to fix. A thin overlay over alligator cracking reflects the crack pattern straight back through the new mat within a season or two, because the bad base is still flexing under it. That reflection crack is the signature of paving over a structural failure. You patch the failed sections full-depth first, then overlay the sound pavement, or you accept that the section needs rehabilitation and stop calling it preservation.

Cold and hot in-place recycling

In-place recycling reuses the existing asphalt where it lies instead of hauling it off and trucking in new mix, and it shows up at the edge of the preservation conversation because it can renew a surface or a structure without a full reconstruction. Cold in-place recycling, CIR, mills off the top several inches of the existing asphalt, mixes the reclaimed material with an emulsion or foamed binder, and lays it back down and compacts it, treating cracked but structurally sound pavement and slowing the cracks from coming back through.

Hot in-place recycling, HIR, heats the existing surface in place, scarifies and remixes it, sometimes with a little added mix or rejuvenator, and recompacts it, renewing the top of the pavement without removing it. Both methods cut hauling and material cost and reuse what is already on the road, which is why agencies use them on the right candidate. The honest classification is that the lighter, surface-renewal versions act like preservation while the deeper, structural versions shade into rehabilitation.

These are specialized treatments with specialized equipment and a real engineering step behind candidate selection, so this is the boundary where a preservation program hands the decision to a pavement engineer. The point for a program manager is that recycling is a tool for a structurally sound but badly cracked pavement, a candidate that is past the thin seals but that you would rather not tear out. It is not a fix for a failed subgrade either. The base still has to be sound.

What is not preservation: rehab and reconstruction

Knowing what falls outside preservation keeps the budget honest, because the heavy treatments cost many times what the thin ones do and they answer a different problem. A mill and overlay, grinding off the top of the existing asphalt and replacing it with new mix, is rehabilitation when the new lift is thick enough to restore structure and ride to a pavement that has dropped past preservation. It is not a preservation treatment, even though it shares a paver with the thin overlay.

Full reconstruction is the heaviest of all: the pavement and often the base come out and the section is rebuilt from the subgrade up. That is what a failed pavement needs, a road down in the poor and very poor range where the base is gone and no surface treatment carries the load. Reconstruction is the expensive end of the curve, the bill preservation exists to push as far into the future as possible.

The reason to draw the line clearly is that the treatments are not interchangeable, and the failure mode runs one direction. Use a preservation treatment where rehabilitation is needed and it fails fast, because you treated a structural problem with a surface fix. Using reconstruction where preservation would have done the job is rarer, and it only wastes money. The discipline is to spend the cheap treatment early, on the sound pavement, and reserve the heavy treatments for the sections that have genuinely failed, not the sections that merely look tired.

How do you pick a pavement treatment?

You pick a treatment from four inputs read together: the condition, the distress type, the traffic, and the climate. The condition, a PCI or an equivalent rating, tells you which band of treatment the pavement can carry. The distress type tells you whether the problem is surface or structural, and a structural problem vetoes every preservation treatment regardless of the score. Those two are the heart of the call, and the survey behind them is the companion PCI guide's subject.

Traffic and climate narrow it from there. A high-volume road needs a treatment that returns to traffic fast and stands up to load, which pushes toward micro-surfacing or a thin overlay over a slurry. A low-volume road can take a chip seal or a slurry. Climate decides the cure: a slurry that leans on sun and low humidity is a poor choice in a wet, cool window, while micro-surfacing breaks regardless of the weather. A cold climate with hard freeze-thaw beats up thin treatments faster, so the cycle shortens.

The matrix below is a starting frame, not a spec. It pairs the condition band with the distress and points to a treatment family, and it carries the same warning as the rest of this guide: the cause overrides the score. Confirm the call against the project specification, the agency treatment triggers, and the manufacturer's limits on the actual material before you commit. The matrix tells you where to start the conversation, not how it ends.

When is a road too far gone to preserve?

A road is too far gone to preserve when the failure is in the structure, not the surface, and that is the single most important judgment in this whole field. The tell is the distress. Alligator cracking, the interconnected chicken-wire pattern in the wheelpaths, is fatigue failure of the base, and deep rutting that lives down in the base or subgrade is the same story. Once you see widespread structural distress, the preservation window for that section has closed, whatever the surface score says.

Here is the limit stated plainly, because it governs every treatment above. None of these treatments add meaningful structure, and none of them fix a base failure. A seal, a slurry, a micro-surfacing pass, even a thin overlay, all sit on top of the pavement and protect or renew the surface. If the base is gone, the support the treatment needs is gone, and the treatment fails on the same schedule as the pavement it was laid over. Spending preservation money on a structural failure is the most common waste in the trade.

So the honest call on a badly failed section is to take it out of the preservation plan and put it in the rehab or reconstruction plan, then preserve the sound pavement around it. The mistake owners make is treating the worst-looking section because it is the one that bothers them, when that section is exactly the one where preservation does the least. Diagnose the cause before you spec the treatment. A pavement that is failing structurally is asking for a different budget line.

Timing windows and traffic return

Every preservation treatment has a weather window and a traffic-return time, and getting them wrong turns a good treatment into a callback. The seals and slurries are temperature-and-moisture jobs. Common practice for emulsion and sealcoat work is a surface and air temperature of at least 50°F and rising, no rain in the window before and after, and enough drying time for the water to leave the material. Lay any of them too cold, too wet, or too late in the day and the material does not break or cure, and it scuffs or washes off.

Traffic return separates the treatments and often decides which one a busy site can use. A fog seal and a slurry need their water to leave before traffic, hours under good drying conditions and longer when it is cool or humid. Micro-surfacing breaks chemically and reopens in about an hour, which is exactly why it wins on roads that cannot close for long. Sealcoat wants longer, on the order of a day before foot traffic and longer before vehicles. Crack sealant sets fast but can track in heat if the overband is not detacked.

The early-opening failure is the one owners blame on the product when it is really the schedule. The lot or the lane got reopened before the material cured because somebody needed it back, and now there are tire scars, bare spots, and tracking in the turns. The defense is to plan the closure honestly up front, phase a site that cannot fully close, and pick a fast-return treatment when the duty cycle is tight rather than rushing a slow one back into service.

The worst-first trap and the network argument

Worst-first is the instinct that wrecks pavement budgets, and beating it is the real argument for preservation. The instinct is to spend the money on the roads that look the worst, because those are the ones that draw complaints. The trouble is that the worst roads have already failed, so every dollar spent on them buys reconstruction, the most expensive fix there is, while the good roads that a cheap treatment would have held keep slipping down the curve untreated. Agencies that have run the numbers find that spending the whole annual budget worst-first reconstructs only a small slice of the network, somewhere around 2 to 4 percent, while the rest deteriorates.

The do-nothing trap is the same mistake by inaction. Defer the cheap treatments to save money this year and the good pavement drops off the cliff on its own, and next year's bill is rehabilitation instead of preservation. Both traps spend more to get less, because both ignore the shape of the curve. The network argument is the answer: spread the budget so the good pavement gets cheap preservation that keeps it good, the fair pavement gets the right rehab before it fails, and the failed pavement gets reconstructed on a schedule rather than all at once.

Life-cycle cost is how you make that case to an owner with numbers. Instead of the cost of this year's project, you look at the total cost of keeping a section in service over decades, and on that ledger a preservation program almost always beats letting pavement fail and rebuilding it. The condition survey is what turns the argument into a plan, by telling you which sections are still high on the curve and worth preserving and which have already gone over it. That prioritized, multi-year plan is the deliverable the companion PCI guide builds, and it is what a preservation program runs on.

A single lot versus a road network

The same principles apply whether you own one parking lot or a thousand miles of road, but the scale changes the tools and the treatments. A facility owner with one lot is making a project decision: rate the lot, handle the failed sections as patches, crack seal and sealcoat the sound pavement, and re-seal on a cycle of a few years. The treatments are the lot-duty ones, sealcoat and crack seal, and the plan is short and concrete. The crack-seal and sealcoat guide is written for exactly this owner.

An agency with a network is making a portfolio decision: rate everything to a consistent score, then spread a fixed budget across the inventory so the network average holds or climbs instead of falling. The treatments are the road-duty ones, chip seals, slurries, micro-surfacing, cape seals, and thin overlays, chosen per section by condition and traffic. The hard part is not any single treatment, it is the allocation, deciding which sections get the cheap preservation that protects the network and which get the expensive rehab that cannot be avoided.

A campus or a data-center site sits in between and is worth calling out, because the pavement carries a duty most lots do not. Fire lanes, loading docks, generator yards, and the access routes that emergency and delivery vehicles use see heavier axle loads than a typical parking field, and a failure there is an operational problem, not a cosmetic one. The program for that kind of site rates the heavy-duty areas separately, holds them to a tighter standard, and times the treatments around access windows that cannot close. The scale is small, but the consequence of a failure is large, so the discipline runs closer to the network model than the simple-lot one.

The treatment toolbox and what to record

The toolbox runs from the lightest, cheapest treatment to the heaviest, and the table below lays it out against the condition it suits and the life it typically buys. The service-life figures are the commonly cited ranges from FHWA and agency experience, and they move with climate, traffic, and the quality of the work, so treat them as planning numbers and confirm them against your own pavement history and the manufacturer's data. The pattern across the table is the whole story: cheaper, lighter treatments for better pavement, and every one of them needs sound structure underneath.

What you record on a preservation job is what makes next cycle's plan possible. Capture the section, the condition you rated it at, the treatment you applied and why, the materials and rate, the weather and cure on the day, and the date. A treatment with no record behind it is a treatment nobody can evaluate when the section is re-surveyed, and the whole value of a preservation program is the loop of rate, treat, re-rate, and adjust. Recording the section map, the scores, the treatment, and the cost in a tool like FieldOS keeps the survey, the scope, and the history tied together, so this year's work becomes next cycle's baseline instead of a memory.

Note the sections you flagged as too far gone to preserve, specifically, because those are the ones that fail next and the note is what shows you called it. The same record that backs the preservation scope is the record that defends the rehab and reconstruction budget when those sections come due, and an owner who can see the history is an owner who funds the plan.

Common mistakes

• Preserving a failed road, putting a thin treatment over alligator cracking or a base failure that needs rehabilitation or reconstruction.
• Spending worst-first on the roads that look the worst, reconstructing a few while the good pavement slips down the curve untreated.
• Matching the treatment to the score but ignoring the distress type, so a structural failure gets a surface fix.
• Treating too late, after the pavement has gone over the cliff, where preservation does nothing and the cheap fix is gone.
• Skipping the crack sealing, so water reaches the base and turns a surface problem into a structural one.
• Skipping the condition survey and speccing a treatment off the windshield, so the cause is never diagnosed.
• Confusing slurry seal with micro-surfacing and using a slurry where the road has rutting or needs a fast reopen.
• Calling a thin overlay a structural fix, then watching the old crack pattern reflect through the new mat in a season.
• Reopening to traffic before the treatment cures, leaving tracking and bare spots in the wheelpaths and turns.

Field checklist

Standards and references

The framework for pavement preservation comes from the FHWA, which defines preservation as a network-level strategy and distinguishes preventive maintenance, corrective maintenance, and rehabilitation, with the preventive category being preservation proper. The FHWA pavement preservation program, the AASHTO Transportation System Preservation work run through the National Center for Pavement Preservation, and the industry group FP2 are the bodies that publish the guidance behind the deterioration curve, the cost case, and the treatment definitions. Cite them for the concept, and confirm the current document, because the guidance is updated on a cycle.

The individual treatments answer to their own references. The condition survey behind treatment selection follows ASTM D6433 for roads and parking lots, covered in the companion PCI guide. Hot-applied crack and joint sealant is specified under ASTM D6690, and the slurry and micro-surfacing systems are covered by the International Slurry Surfacing Association guide specifications that many agencies adopt. For asphalt mix, placement, and the overlay and recycling work, the Asphalt Institute references are the trade source. Name the standard that controls the specific treatment, not a generic list.

What actually governs a given job is the owner or agency specification on top of the standards. A state DOT, a city, a campus, or a private owner sets its own condition thresholds, treatment triggers, application rates, and material rules, and those control the plan where they are stricter or simply different. The coal-tar sealcoat bans are the clearest example of a local rule that overrides preference, and they keep changing. Treat the figures in this guide as the commonly cited numbers, and verify the controlling values and the local rules before you bid or build.

Units and terms

Preservation work gets described in a stack of terms that mean specific things, and using them loosely is how a plan loses its authority. Condition is a PCI, a unitless index from 0 to 100. Treatment coverage is in gallons per square yard for the sprayed and slurry treatments, pounds of aggregate per square yard for chip seals, and inches of compacted thickness for overlays. Temperatures are in °F for the weather window and the material. Service life is in years, and the cost case is a ratio of dollars saved per dollar spent.

The terms carry the distinctions that decide the work. Preservation protects sound pavement and adds little or no structure. Rehabilitation restores structure and ride to pavement that has dropped past preservation. Reconstruction rebuilds failed pavement from the subgrade up. Preventive maintenance is the planned work on good pavement, while corrective maintenance is the reactive work after a deficiency shows up. An emulsion is asphalt or coal tar suspended in water that breaks and cures as the water leaves. Get the term right and the scope follows.

Pavement preservation

A planned program of low-cost treatments on sound pavement to keep good roads good and delay reconstruction; not a structural repair

Preventive vs corrective maintenance

Planned work on good pavement before a deficiency versus reactive work after a deficiency appears

Rehabilitation / reconstruction

Restoring structure and ride to failed-down pavement, versus rebuilding failed pavement from the subgrade up; neither is preservation

Deterioration curve

The accelerating drop in pavement condition over time, flat at the top and steep at the bottom, that sets treatment timing

Chip seal / scrub seal / cape seal

Sprayed binder with embedded chips; a chip seal broomed into the cracks; a chip seal covered by a slurry or micro-surfacing

Slurry seal vs micro-surfacing

Cold emulsion-aggregate seals; micro-surfacing is always polymer-modified, cures chemically, reopens faster, and can fill minor ruts

Thin / ultra-thin overlay

A new HMA wearing course about 1 to 1.5 in or less, a functional surface treatment that adds little structure

PCI

Pavement Condition Index, a 0 to 100 surface-condition rating under ASTM D6433 used to choose the treatment

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