Pavement Seminar
Section 3: Solutions to pavement deterioration
Once a property manager (with or without the help of an estimator, pavement consultant, or geo-technical engineer) has analyzed a pavement system to determine the level of deterioration, there are always various solution options to consider. This seminar will explore the specific solutions that Carolina Asphalt has proposed to its customers throughout the Carolinas since 1982.
Which option to choose: The greater the level of deterioration, the larger the expense and the greater number of solution options. The purpose of this seminar is to educate property managers so they can make the best pavement expense decisions for the properties they manage.
Trade offs: For every level of pavement deterioration there are many possible solutions to consider. While one solution may be cheaper than another, invariably there are trade-offs to evaluate in order to make the best decision. Be aware of the trade-offs that are made when selecting a particular option so there are no surprises in the long run.
Geo-technical engineers: A geo-technical engineer can be used to analyze a pavement and determine its level of deterioration. Depending on the depth of their analysis, they may conduct a series of tests on the pavement to measure existing pavement compositions and strength. On larger projects, geo-technical engineers can provide a projected life expectancy of various options and fully define the work in a series of specifications.
Although there can be significant expenses involved in retaining a geo-technical engineer, there is great value delivered when a third party takes responsibility for the design of a project. Solutions to pavement problems are only as good as the rationale behind them; the greater the level of deterioration, the greater the need for expert advice.
Specifications: Once you have chosen an option and understand the trade-offs, a clearly-defined specification should be created that includes standard units of measurement for pricing and payment purposes. It should also be very clear as to who is responsible for the performance of the job specifications. See our Tools section for sample specifications.
Who is responsible?: What is the warranty on the job and if the pavement does break, who is going to take responsibility? If a geo-technical engineer has written a pavement design for a project and the work fails under expected traffic conditions, the engineer is responsible. If a contractor volunteers to write a design specification and the work fails within the stated warranty period, the contractor is responsible.
Solution: Sealcoating
In most cases, the solution to the problem of surface raveling is to sealcoat the pavement, especially if it is under 5 years old and is structurally sound (no visible alligatoring or block cracking). The economic benefits of sealcoating are difficult to determine because there are many variables that contribute to asphalt failure. Generally speaking, the greatest returns in extended life of a pavement can be made from a sealcoat expense when the pavement is 1-2 years old.
The sealcoat material should have at least 3 pounds of sand added per undiluted gallon of sealer to provide adequate skid resistance. Sand is cheap, but it is very difficult to pump without the right equipment.
Procedure:
1) Notify tenants! A sealcoating project must be properly planned since it involves taking large sections of a parking lot at a time (usually 5,000 square yards per section) and each section takes 2 days to seal and stripe. If possible, post a map with each section highlighted in a public place and send out individual notices. Make sure to explain your policy on moving cars (ie: who will pay for a tow truck)
2) Weather delays: Since a sealcoating emulsion is water-based, it must dry completely before it sets. The advent of web site weather maps has improved the process, but if rain is imminent, the sealcoat job will be delayed and tenants need to be clear about how each delay affects the scheduling of each section. The better the communication, the less chance there will be of upset tenants!
3) Barricade each section: The type of barricade devices is dependent on site constraints but the more obvious the better. If the barricade is easily moved or if there is a gap to fit a car through, tenants will drive through the wet material and create a mess.
4) Surface preparation: All dirt, vegetation and silt must be removed from the surface with blowers, scrapers or broom tractors. A sealcoat will not stick to dirt!
5) Tape off the entrance to get a better edge.
6) Primer coat (optional): If a surface is heavily oxidized, priming is recommended to maximize adhesion of the sealcoat material.
7) Oil spot primer: The oil spots must be scraped and primed with a special oil spot primer. A sealcoat will not adhere to untreated oil spots.
8) Sealcoat application: A minimum of 2 coats should be applied to the surface. Each coat should be cured before the next coat is applied. The sealcoat can be sprayed or squee-geed onto the surface of the asphalt at a rate of .1 gallon of undiluted material per square yard per application. Each sealcoat manufacturer has different requirements for the amount of water added to provide proper viscosity but the important measure is the amount of undiluted material applied to the pavement. It is imperative that all cars are removed from each section prior to applying material.
9) Third coat in drive lanes (optional): A sealcoat is primarily worn off the surface by the sheer force of tires on the pavement. The sealcoat will wear fastest in the drive lanes of a parking lot, especially in the entranceways. A third coat can be applied in these heavy wear areas to maximize the service life of the sealcoat.
How to specify a sealcoating project
Unfortunately there are no DOT guidelines for sealcoating and so most specifications are vague and incomplete. Many times, the manufacturer’s specifications are copied and given to each contractor but if the contractor doesn’t carry this material, he will submit an "as equal." The worst-case scenario however, is when a property manager requests a bid for a sealcoat project without providing any guidance. Since there are no accepted standards in the industry, the property manager will get very different proposals which will be impossible to compare objectively.
Carolina Asphalt has provided a sample sealcoating specification to be used in creating a scope of work for a pavement project. This specification can be modified by the property manager for each project, but it is important to clearly state the specifications expected for the project so each contractor bids the same job. This makes it much easier to compare bids "apples to apples."
Standard vs. "Premium" sealcoat materials:
It is very clear that various sealcoat materials applied at the same application rate will wear differently depending on the quality of materials used in the manufacture of the sealer. There is a scrub test used by ASTM (American Society of Testing Materials) to measure relative wear. The following conclusions can be made about the best sealcoat materials based on these tests:
1) Premium sealers have twice the service life of standard materials.
2) Premium sealers leave a thicker coating on the pavement.
A property manager can request a base bid for standard material with an option for a premium product. After the bids are submitted, a cost/benefit analysis can be run to determine the merits of each. In many cases, an extended warranty may justify the marginal difference in cost.
Property Manager hint: Make sure that each bidder state the following on a sealcoating bid:
1) Type of sealcoat material to be used and the name of the manufacturer.
2) Specific reference to latex polymers. Whether they are hot-blended at the manufacturer or added cold on the job site.
3) Proposal should quote on a unit price for easy comparison. The standard unit is square yard.
4) Proposal should state how many coats will be applied and whether a primer coat will be applied.
Solution: Cracksealing
The solution is to apply a cracksealer into these cracks that will adhere to the walls of the crack through the pavement expansion/contraction rate experienced for that location.
Minimal width:
It is generally accepted that cracks must be at least 1/4" wide to be sealed but this measurement should be taken on the coldest day possible when the void is forced open by the contraction of the pavement.
Cold vs. hot pour cracksealers:
Cold materials are much easier to apply and are therefore less expensive but they do not have the same elasticity as hot pour products in all temperature extremes. Hot pour cracksealer must be heated to a constant temperature of 350-375¾o F in an oil jacked machine and injected into the crack using a specialized machine.
Routed vs. non-routed:
A specialized routing machine will cut a 3/8" by 3/8" channel into the crack in the pavement. Crackseal material can then be injected through a wand from the bottom of the void to the top (as opposed to dripping cracksealer into an untreated crack that fills from the top to the bottom). The routed crack will reduce the rate of expansion of the crack in weather cycles.
Example: A 1/4" crack that expands 1/4" in the winter will stretch the cracksealer 100%. If the same crack is routed to 3/8" and expands the same 1/4" , the cracksealer will only stretch 50%. Since the total cost of cracksealing is usually not a significant expense, the marginal increase to rout is well worth the cost.
Overband vs. filling flush:
The longest lasting crack repair is an overband of material on top of the crack but some property managers don’t like the appearance of a raised 2-3" wide band of material. In this case, the crack should be routed and material injected to fill routed void only. This method will not last as long.
Procedure:
1) Routing (optional but recommended by Carolina Asphalt): Rout out all random cracks 1/4" or wider to a uniform width of 3/8".
2) Heat lance: Blow out debris, vegetation and moisture with a hot air lance. Air flow at surface must be 3000° F and 3000 psi.
3) Cracksealing: Inject prepared crack with cracksealant designed for expected temperature variation. Material can be overbanded or filled flush depending on the preference of the property manager.
4) Sanding (optional): Sand or similar aggregate substance can be spread on crack to minimize tracking of crackseal material.
Solution: French drain
The most important function is to intercept the water before it gets under a pavement section and channel it with pipes into a drainage swale or catch basin on the property. In many cases, it is obvious where the water is coming from but in some cases investigative work must be done. This is especially true if a high water table is suspected. Water table gauges, (piezometers), must be installed and monitored for several weeks to accurately define this problem.
The least expensive solution to a water problem is to eliminate the source. A cracked irrigation line or broken water pipe or roof drain once repaired can save thousands of pavement system repairs dollars.
Property Manager Hint: Monitor water usage each month and immediately investigate unusual increases. Ask tenants and contractors to monitor the property for damaged irrigation systems and fix problems as soon as possible.
If it is clear that the water source under the pavement cannot be prevented, then a french drain can be installed under the surface to channel the water through a piping system. It is important to note that french drain systems can be expensive and so a cost/benefit analysis should be done in each case. What is the cost of the drain relative to the amount of pavement system repairs it will eliminate? This is usually a function of how far the piping system has to travel before reaching an outlet, if there is only one water problem on a property in an irrigated island but the nearest catch basin is 500 linear feet away, the cost will not be worth the benefit.
It is always less expensive to build a french drain system in the landscaping than it is in the pavement system. Many times, however, irrigation lines run right along the back of the curb making it impossible to construct the drain in the landscape area.
Prefabricated french drains are much less expensive and are most effective in landscape applications but can be used in pavement systems as perimeter drains during initial construction. Carolina Asphalt recommends the installation of traditional french drain systems as opposed to cheaper pre-fabricated system. A traditional french drain consists of a trench, wrapped with a special filter fabric, washed stone, and a slotted pipe. The drain system must be constructed at a 1% slope for water to flow in a pipe in the bottom of the Prefabricated french drains.
Procedure:
1) Have all public underground utilities located prior to the start of work and have locate order updated as needed. Have private services such as water, sewer and irrigation lines located as well.
2) Block off the area and notify the tenants. The crew will need room to dig through the pavement system, load trucks and bring new materials to the site.
3) Sawcut the edges of the excavation to provide a uniform edge.
4) Dig a trench 24"-36" deep and 12"-18" wide. Maintain a constant grade of 1% at the bottom of the trench so that water does not stand.
5) Place a layer of geo-textile filter fabric in the entire trench and place a slotted pipe in the bottom of the excavation.
6) Fill fabric-lined trench with washed stone and wrap filter fabric over top of stone layer to prevent silt or fine aggregate from clogging the system.
7) Compact the stone layer and install asphalt layer. The asphalt should be at least 6" in depth and the width of the top of the trench should be at least 4’ wide to get maximum compaction.
French drains can be very effective solutions to a water problem if designed and constructed properly. The most common problem encountered is insufficient compaction of the trench and the result is a concave section that holds water creating further problems.
Care must also be taken to completely investigate all sources of water so that the cause of the problem can be determined. A property manager can monitor a water problem over time to uncover clues. It is certainly worth the time to invest before spending money to correct the wrong problem!
Solution: Full depth asphalt repair
Alligator cracking is a visual sign that the existing pavement structure can no longer support the loads exerted on it. The entire area must be excavated and replaced with a full-depth layer of new asphalt. It would be less expensive to cut out the damaged areas and replace with a layer of crushed stone and new asphalt, but it takes several days for stone to set up properly and it must be flooded with water to achieve density. This is usually not feasible in a repair scenario for a pavement system that is currently in use (see seminar section of new construction).
The networked cracks on the top surface are an indication of instability in the lower levels of the pavement system. For this reason, the area must be excavated 1’ beyond the cracks on the surface. Each patch should be a minimum of 4’ wide to accommodate the full width of a small steel wheeled roller.
Areas to be repaired should be rectangular and encompass the entire cracked area. Wherever feasible, it is best to combine several small areas in to one large repair. A series of small patches with uncracked asphalt in between, left untouched, will usually create more repairs in the near future. The base layer in the untouched areas will be less stable than the repaired areas and will be pounded by traffic that rolls from a strong to a weaker surface.
Property Manager hint: Walk the entire parking lot with an estimator and place small paint dots on the outer edges of all cracked areas. Once these have all been sprayed, stand back and create a series of rectangles to encompass the cracked areas. Number and measure each area and note on a site plan.
The design depth of the repair is dependent on the traffic loads, the strength of the sub-grade and the years it is expected to last. Evaluate these three factors for a particular pavement system when choosing a design depth of pavement.
The number of heavy truck axle loads exerted on the pavement system is a measure of the traffic loading. Car traffic is almost irrelevant in this consideration since heavy truck loads can be equivalent to 30,000 car loadings.
The strength of the sub-grade most often is visually measured in a proofroll process. The pavement system is excavated and removed and a loaded truck is slowly driven over the sub-grade. Any significant deflection is marked and measured.
The depth of the repair is directly related to the life of the repair. The deeper the repair the longer it will last. Carolina Asphalt has installed thousands of tons of asphalt repairs for over 20 years in the Carolinas, and our experience has given us the following guidelines for depth of repairs.
4" depth: Car traffic only, no truck traffic expected
Parking spaces in an apartment complex with a centralized dumpster in the front of the property would be a good example.
6" depth: Car traffic with occasional truck traffic
Drive lanes of commercial/retail/residential parking lots where dumpster trucks and delivery trucks are allowed to use.
8" depth: Regular truck traffic
Such as in front of a dumpster pad or in a loading dock of an industrial facility.
10-12" depth: High truck traffic
In marginal sub-grade areas.
Once the area has been sawcut and the existing pavement system has been excavated and removed to the design depth proposed, the bottom of the excavation should be proofrolled. Any weak areas should be removed and replaced with suitable fill material such as pit gravel or crushed stone. For marginal sub-grade conditions, a structural geo-textile fabric can be installed in the bottom of the excavation prior to the placement of fill material.
Property Manager hint: Make sure there are contingencies in your repair contract for undercutting bad sub-grade and replacing with suitable fill. This can be priced on a tonnage or cubic yard basis.
The major drive lanes are the first areas to crack and break into an alligator pattern. It is important to monitor these breaks and repair as soon as possible to retard further growth of the weakened area. This damage can accelerate if not addressed because water has a free path to the sub-grade through the random cracks in the asphalt surface.
Procedure:
1) Mark out all rectangular areas to be repaired with spray paint and number each area.
2) Notify tenants of schedule for each section and block off completely.
3) Sawcut the asphalt section of the pavement system on sprayed marks. (Do not allow area to be excavated without cutting because surrounding pavement system can be damaged.)
4) Excavate to the design depth and remove excavated material from site.
5) Proofroll the bottom of the excavation; undercut weak areas and replace with fabric and fill as needed.
6) Install layer of binder asphalt and compact.
7) Apply an asphalt emulsion to patch edges.
8) Install 2" layer of surface mix on binder and compact.
Working around tenant operations: It is very important to communicate with tenants concerning a repair project in a parking lot. While most isolated repairs are in drive lanes and not in parking stalls, tenants must be made aware of the repair process so they can plan accordingly.
Property Manager hint: Make sure your contractor provides a firm schedule so you can distribute to your tenants. It is not acceptable to prepare for a contractor to do a job then not show up or even call. Depending on your comfort level with your contractor, you might want to give your tenants a production coordination contact within the contracting company. If your contractor has an on-site superintendent, you may want this person to contact shipping coordinators for tenant deliveries.
Every load of asphalt produced in a state certified asphalt plant must have a ticket created to verify quantity of materials purchased. The final patch repair dimensions can be measured and the effective thickness of the asphalt can easily be calculated.
Property Manager hint: The largest expense in an asphalt project is materials. Asphalt is a petroleum-based product and continues to rise in cost. A property manager should know exactly how many tons of asphalt should be used for a project and should hold the contractor to this amount. Each bid for a patch repair project should clearly state the square yards, the depth of repair and the tons of asphalt required. Please use our online tonnage calculator for assistance.
Solution: Rehabilitation
The pavement system has widespread base failure and the surface conditions are very poor. The underlying causes of this condition must be determined in order to devise the most cost-effective solution. Once a pavement has reached this condition there are several rehabilitation options to pursue. There can be a tremendous variance in cost to construct each of these options so it is important to determine a specific specification so that comparable quotes can be given.
The three options to consider when a pavement system has reached this level are listed below in order of least expensive to most expensive:
1) Patch and Resurface
2) Patching and Resurface with crack membrane
3) Reclamation
It may not be readily apparent which method is most practical in each particular case. A geo-technical engineer can be hired to evaluate the existing condition and estimate the relative costs and benefits of each method of rehabilitation to determine the best approach. Many property managers will consult with a trusted estimator and rely on their practical field experience (even though the estimator will usually not have access to testing data to confirm his assumption).
Whatever method is chosen to determine a method of rehabilitation, it is best to have each bidder price the exact same job so a truly objective decision can be made. The higher the level of deterioration of a pavement system, the greater the chance of variability in the repair or rehabilitation method chosen will be. Be very clear about your expectations for the rehabilitation method in your discussion with a geo-technical engineer or paving estimator.
Property Manager hint: When a decision has been made, define the method in the form of a scope of work and give this to each bidder so that prices can be compared on an "apples to apples" basis. The more specific you can be in the definition, the less arbitrary the contractor selection process will be.
Option 1: Patch and Resurface
All broken areas that move under the weight of a loaded truck must be repaired with full depth asphalt at the depths stated earlier, less the thickness of the overlay layer. Isolated cracks must be sealed with a hot pour cracksealer to retard reflective cracking.
All repair areas should be clearly marked on the pavement, numbered and referenced on the proposal or scope of work. The tonnage for these repairs can be calculated by measuring the total area and multiplying by standard coefficients (tonnage calculator).
Procedure:
1) Notify tenants and distribute/post schedule. (All cars must be cleared from each work section.)
2) Excavate and repair marked areas using patch specifications. No surface mix is required, just binder.
3) Surface preparation: Completely clean surface of all vegetation and dirt with a broom tractor and forced air blowers.
4) Apply a liquid asphalt emulsion to old asphalt to bond the new layer.
5) Install asphalt surface mix and compact.
Thickness of resurfacing layer:
This is usually 1.5" to 2.0" depending on the use of the facility. Thickness is always after compaction. Proposal should state square yards, thickness of asphalt and unit price per square yard.
Drainage concerns:
The asphalt layer will create additional height to the pavement structure and this variance must be considered before the start of the project. It is possible to "feather" into concrete gutter pans and concrete loading docks and driveways but will this trap water?
Option 2: Patching and resurfacing with a crack membrane
This method is very similar to option 1 but instead of repairing every broken area, a crack membrane can be installed prior to the resurfacing process to retard reflective cracking of the lightly cracked areas. Areas that move significantly under the weight of a loaded truck will need to be cut out and replaced prior to placement of crack membrane.
There are two types of crack membranes:
a) geo-textile fabric (Petromat): A heavy layer of asphalt emulsion (.2 gallons per square yard) is applied to the prepared surface and the fabric is rolled into the liquid so that the emulsion is absorbed into the fabric before it sets up. Geo-textile fabric should only be applied to low shear areas of a pavement. If it is applied in turning areas or on a grade, the asphalt layer can "slip" on the fabric.
Procedure:
1) Proofroll entire surface and remove and replace areas that move significantly with full depth asphalt.
2) Completely clean paving surface with tractor broom
3) Apply a heavy coat of asphalt emulsion/tack (.2-.3 gallons per square yard)
4) Roll geo-textile fabric into the tack and secure corners.
5) Allow asphalt emulsion to bleed through fabric and let tack set up. Resurface over fabric and tack with surface asphalt. (1.5-2")
Property Manager hint: Do not consider using this method of repair in turning areas or on grades in a parking lot because the asphalt can "slip" on the fabric.
b) Flexible Asphalt Membrane (Perma-Flex): The Perma-Flex system consists of a heavy layer of asphalt emulsion (tack) followed by a thin lift of Perma-Flex asphalt; usually 1-1.5" in thickness. Another coat of tack is applied before the final lift of asphalt is installed (1-1.5" in thickness).
Property Manager hint: The Perma-Flex system will add 2-3" of total thickness to the existing pavement system. Make sure this does not adversely affect drainage before considering this option!
In cases where an existing parking lot is too far gone to consider patching and resurfacing or the structure is showing signs of base failure and the existing structure is not adequate to support current needs, reclamation of the parking lot can become the most cost-effective and evironmentally-friendly means of rehabilitation.
The reclamation process involves grinding up the entire existing pavement system in place with a large machine. The reclaimed material will look just like crushed stone. If the existing pavement system is not thick enough in places, the reclaimer may grind up some dirt in the process and mix it with the asphalt and stone. (This is why core samples should be taken before this process is considered).
The reclaimed material is then graded in place and set up just like stone is in new construction. If there is too much reclaimed material to allow for proper drainage, this material must be moved to another part of the parking lot or removed from the site.
Once the reclaimed material has been graded, compacted and set to proper grades, the surface is paved with the proper thickness of asphalt.
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Level 6: Complete failure of the pavement
Solution: Remove and replace
The pavement system is at the end of its service life and it has been determined that rehabilitation options are not feasible. There are several options to consider at this point but as the entire pavement must be replaced, each option is expensive and it is recommended that a geo-technical engineer be consulted to design the best specification (depth of each material to be used). The three options to consider when replacing the pavement system at this level are:
1) Full depth asphalt
2) Stone and asphalt
3) Geo-textile fabric, stone and asphalt
Option 1: Full Depth Asphalt
The entire pavement section is removed to a sufficient depth to accommodate a full depth section of asphalt. The remaining stone base is compacted and proofrolled prior to placement of the asphalt.
This solution can be implemented very quickly especially if a milling machine is used to excavate the original pavement structure. It is very important to know the exact thickness of the existing structure as new asphalt should be placed on some appreciable thickness of stone base (not directly on sub-grade). It is also important to know the strength of the sub-grade prior to removal of the original pavement system to minimize unexpected change orders. When the existing pavement is excavated to the design depth, there is a limited time window to complete the project and if poor sub-grade is encountered it must be immediately removed and replaced. This can significantly increase the cost of the entire project.
Property Manager hint: Make sure you know exactly how many tons of asphalt will be required for the project and include a bidder requirement to provide asphalt plant receipts to benchmark the job.
Option 2: Stone and Asphalt
This is very similar to option 1 except that after excavation of the original pavement, a layer of stone is installed and compacted prior to the placement of the asphalt layer. Since stone has a much lower strength coefficient than asphalt, more materials are required and more excavation and removal will be required (which can be offset by the cost savings of stone vs. asphalt materials). Another consideration is timing; stone installation and compaction can take several days per section as was described earlier in this seminar. For this reason, this option is usually not acceptable to use around active tenant operations.
Property Manager hint: Compare the cost of constructing option 1 vs. option 2 using a base line strength coefficient so you can compare “apples to apples.” Be sure to factor in the potential cost over-runs/change orders and opportunity costs to delaying tenant operations.
Option 3: Geo-textile Fabric, Stone and Asphalt
This option is very similar to option 2 except that after initial excavation of the original pavement system, a geo-textile fabric is installed directly on the exposed base layer to “bridge” over marginal sub-grades. This option is especially effective when pavement tests (conducted prior to start of job) reveal marginal sub-grade conditions. For this reason, a geo-technical engineer with experience in pavement design can customize a job specification to maximize the return on investment. This option can also include a provision to recycle the original pavement system by allowing milled aggregates to be used as the new stone base on top of the geo-textile fabric. A bridge lift of milled aggregate can be placed directly on the geo-textile fabric and dry rolled to place the fabric in tension to adequately support the projected traffic loads. The new asphalt layer is then placed and compacted over the milled aggregate to complete the project. The key advantages to this option are: the potential for change orders is not as great and these projects are completed much more quickly than the other options.
Property Manager hint: Calculate the strength number of this option and compare it to the cost of equal strength numbers for the previous options. Again, factor in the potential for change orders and the opportunity costs associated with delaying tenant operations.
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