Resources

Revised 2023

North American cities have thousands of utility cuts made in their streets each year. Figure 1 shows a daily occurrence in most cities: repairs to underground utility lines for water, sewer, gas, electric, steam, phone, fiber-optic, or cable services. A sample is given below of the number of annual utility cuts in a few cities.

• Billings, Montana: 650–730
• Boston, Massachusetts: 25–30,000
• Chicago, Illinois: 120,000
• Cincinnati, Ohio: 6,000
• Oakland, California: 5,000
• San Francisco, California: 10,000
• Seattle, Washington: 10 –20,000
• Toronto, Ontario: 4,000

The Cost of Utility Cuts

The annual cost of utility cuts to cities is in the millions of dollars. These costs can be placed into three categories. First, there are the initial pavement cut and repair costs. These include labor, materials, equipment, and overhead for cutting, removing, replacing, and inspecting the pavement, plus repairs to the utility itself. Costs vary depending on the size and location of the cut, the materials used, waste disposal, hauling distances, and local labor rates.

Second, there are user costs incurred as a result of the repair. They include traffic delays, detours and denied access to streets by users, city service and emergency vehicles.

User costs depend on the location of the cut. A repair blocking traffic in a busy center city will impose higher costs and inconvenience from delays than a cut made in a suburban residential street. There are downstream costs to users from utility repairs such as lost productivity due to delays, and damage to vehicles from poor pavement riding quality. While these losses are difficult to quantify, they are very present.

The third cost is subtle and long term. It is the cost of pavement damage after the repair is made. Cuts damage the pavement. Damage can range from negligible to substantial, depending on the quality of the reinstated area and the condition of the surrounding pavement. The damage reduces pavement life and shortens the time to the next rehabilitation. The need to rehabilitate damaged pavements earlier, rather than when normally required, has costs associated with it.

Several studies have demonstrated a relationship between utility cuts and pavement damage. For example, streets in San Francisco, California, typically last 26 years prior to resurfacing. A study by the City of San Francisco Department of Public Works demonstrated that asphalt streets with three to nine utility cuts were expected to require resurfacing every 18 years (1). This represented a 30% reduction in service life compared to streets with less than three cuts. Streets with more than nine cuts were expected to be resurfaced every 13 years. This represents a 50% reduction in service compared to streets with less than three cuts.

The report concludes that while San Francisco has some of the highest standards for trench restoration, utility cuts produce damage that extends beyond the immediate trench. “… even the highest restoration standards do not remedy all the damage. Utility cuts cause the soil around the cut to be disturbed, cause the backfilled soil to be compacted to a different degree than the soil around the cut, and produce discontinuities in the soil and wearing surface. Therefore, the reduction in pavement service life due to utility cuts is an inherent consequence of the trenching process.”

A 1985 study in Burlington, Vermont, demonstrated that pavements with patches from utility cuts required resurfacing more often than streets without patches. Pavement life was shortened by factors ranging between 1.70 and 2.53, or 41% to 60% (2). Research in Santa Monica, California, showed that streets with utility cuts saw an average decrease in life by a factor of 2.75, or 64% (3). A 1994 study by the City of Kansas City, Missouri, notes that “street cuts, no matter how well they are restored, weaken the pavement and shorten the life of the street.” It further stated that permit fee revenue does not compensate the city for the lost value resulting from street cuts (4). A 1995 study by the city of Cincinnati, Ohio, showed that damage to the pavement extends up to three feet (1 m) from the edge of properly restored cuts (5).

The cost of pavement damage includes street resurfacing and rehabilitation to remedy damage from cuts. Permit fees charged by cities to those making cuts often do not fully account for pavement damage after the cut pavement is replaced. Some cities, however, are mitigating the long-term costs of pavement cuts by increasing fees or by charging a damage fee. They seek compensation for future resurfacing costs to remedy pavement damage. The rationale for fees to compensate for early resurfacing can be based on the following formula in Table 1.

Reducing Costs With Interlocking Concrete Pavements

Life cycle analysis comparisons between asphalt, cast-in-place concrete and interlocking concrete pavements (ICP) show ICP have lower maintenance costs (6). Several of the benefits inherent to ICP that lower maintenance costs also help reduce pavement cut and repair costs, and the associated user costs, as well as reduce long term pavement damage including the associated fees to rehabilitate them.

• Ease of paver removal. Tools exist to assist with the removal of the first few pavers; once the area is opened, the extraction of the remaining pavers is very simple – reference Tech Note PAV-TEC-006. Cost savings occur because sawcutting equipment or pneumatic jack hammers typically used for monolithic pavements like asphalt or poured concrete are not required for surface layer removal.
• Ability to reinstate pavers. The extracted pavers can be stacked to the side and then reinstated, eliminating the need for the purchase of replacement surfacing materials.
• Reduction in Waste Material. Reinstating the same pavers creates additional saving in haulage of waste material from the site, and disposal (landfill) costs. Replacement materials also do not need to be hauled to the site.
• No delay for curing. User costs due to traffic interruptions and delays are reduced because the reinstated concrete pavers require no curing onsite; they can handle traffic immediately after reinstatement.
• Maintaining site aesthetics. With many projects, concrete pavers are originally used to help define the character of these areas, with the character influencing property values and taxes. Reinstated concrete pavers preserve the aesthetics of the street or sidewalk surface. There are no patches to detract from the character of the neighbourhood, business district or center city area. Conversely, visible patches with other materials will detract from the aesthetics and likely result in requests for earlier area restoration.
• Modular characteristics. Since interlocking concrete pavements are modular and not monolithic, they do not suffer the same accelerated wear from cuts.

Any break in monolithic pavement, e.g., joints, cuts or cracks, normally shortens pavement life because the continuity of the material is broken as shown in Figure 7. In contrast, the joints of the modular units in interlocking concrete pavements maintain structural continuity.

Figures 2, 3, 4, 5 and 6 show the process of repair and illustrate the continuity of the paver surface after it is completed. The reinstated units are knitted into existing ones through the interlocking paving pattern and sand filled joints. Besides providing a pavement surface without cuts, the joints distribute loads by shear transfer. The joints allow minor settlement in the pavers caused by discontinuities in the base or soil without cracking.

When pavers are reinstated on a properly compacted base, there is no damage to adjacent, undisturbed units. Unlike asphalt, concrete pavers do not deform, because they are made of high strength concrete. The need for street resurfacing caused by repeated utility cuts is eliminated because concrete pavers are not damaged in the reinstatement process. In addition, the use of low density concrete fill can help reestablish the broken continuity of the base and subgrade. This reduces the likelihood of settlement and helps eliminate damage to the pavement.

Therefore, long term costs of pavement damage from utility cuts to interlocking concrete pavement can be substantially lower when compared to monolithic pavements. This makes interlocking concrete pavement cost effective for streets that will experience a number of utility repairs over their life. Furthermore, lower costs from less damage can mean lower fees for cuts when compared to those for cutting into monolithic pavements.

Construction Recommendations When Reinstating Pavers

Excavation of the base and soil must be within the limits of the removed pavers, and care must be taken to not undermine the adjacent pavement. Trench excavation, bracing, shoring, and/or sheeting should be done in accordance with the local authority. Equipment should be kept from the edges of the opening as loads may dislodge pavers around the opening. Excavated soil and base materials should be removed from the site. The trench should be kept free from standing water. Tech Note PAV-TEC-006 – Operation and Maintenance Guide for Interlocking Concrete Pavements provides additional guidance on repairs to utility cuts.

Unshrinkable fill being poured into a trench is shown in Figure 8. The fill flows into undercuts providing additional support, and in places where the soil or base has fallen from the sides of thetrench. These places are normally impossible to completely fill and compact with aggregate base or backfill material.

There are many mixes used for low-density concrete fill (7)(8) (9). Proprietary mixtures include those made with fly-ash that harden rapidly. Others are made with cement. A recommended mix can be made with ASTM C150 Type I Portland cement (or Type 3 for winter repairs), or CAN3-A23.5-M type 10 (or type 30 Portland cement). The slump of the concrete should be between 8 and 12 in. (200 and 300 mm) as specified in ASTM C143 or CAN3-A23.2.5C. When air entrainment is required to increase flowability, the total air content should be between 4 and 6% as measured in ASTM D6023 Standard Test Method for Density (Unit Weight), Yield, Cement Content, and Air Content (Gravimetric) of Controlled Low-Strength Material (CLSM) or CAN3-A23.2-4C. Air content greater than 6% is not recommended as it may increase segregation of the mix.

A strength of 10 psi (0.07 Mpa) should be achieved within 24 hours. The maximum 28 day compressive strength should not exceed 50 psi (0.4 Mpa) as measured by ASTM C39 or CAN3-A23.2-9C. Cement content should be no greater than 42 lbs/cy (25 kg/m3). The low maximum cement content and strength enables the material to be excavated in the future. Mixes containing supplementary cementing materials should be evaluated for excessive strength after 28 days.

Repaired utility lines are typically wrapped in plastic prior to pouring the low density fill. This keeps the concrete from bonding to the lines and enables them to move independently. When the fill is poured, it is self-leveling. It should be poured to within the thickness of the paver, plus 20 mm (thickness of the bedding layer once compacted), of the riding surface; for example, with a 3.125 in. (80 mm) thick concrete paver, the fill would be 4 in (100mm) from the surface.

Bedding sand can be installed when the concrete is firm enough to walk on, generally within a few hours after placement. The bedding sand should be as hard as available and should conform to the grading requirements of ASTM C33 or CSA A23.1. Mason sand, limestone screenings or stone dust should not be used. The sand should be moist, but not saturated or frozen. Screed the bedding with 1 in. (25 mm) diameter screed pipe. Remove excess sand from the opening.

Since the low-density concrete fill is self-leveling, it will create a flat surface for the bedding sand. In most cases, there will be a slope on the surface of the street. The flowable fill can be screeded to slopes while stiffening. Drain holes at lowest elevations can be cut into the curing material using a metal can. This can be done when the material supports walking but has not yet completely cured. The approx 2 in. (50 mm) diameter holes are filled with washed pea gravel and covered with geotextile to prevent ingress of bedding sand. Adjustments to the thickness of the bedding sand may be necessary for the finished elevation of the pavers to follow the slope on the surface of the street. This can be accomplished by adjusting the height of the screed pipes.

Concrete pavers, if being replaced, should be at least 3.125 in. (80 mm) thick and meet ASTM C936 or CSA A231.2. They should be delivered in strapped bundles and placed around the opening in locations that don’t interfere with excavation equipment or ready-mix trucks. The bundles should be covered with plastic to prevent water from freezing them together. The bundles need to be placed in locations close to the edge of the opening. Most bundles have several rows or bands of pavers strapped together. These are typically removed with a paver cart. The paver bundles should be oriented so that transport with carts is done away from the edge of the pavement opening.

Rectangular concrete pavers [nominally 4 in. by 8 in. (100 mm x 200 mm)] should be placed against the cut asphalt sides as a border course. No cut paver should be smaller than one third of a unit if subject to tire traffic.

Place pavers between the border course in a 90 degree herringbone pattern (Figure 12). Joints between pavers should be between 1/16 and 3/16 in. (2 to 5 mm). Compact the pavers with a minimum 5,000 lbf (22 kN) plate compactor. Make at least four passes with the plate compactor. A small test area of pavers may need to be compacted to check the amount of settlement. The bedding sand thickness should be adjusted in thickness to yield pavers no higher than 1/8 in. (3 mm) above the edge of the undisturbed pavers.

Spread and compact sand into the joints. The joint sand is typically finer than the bedding sand, and should conform to the grading requirements of ASTM C144 or CSA A179. The joints must be completely full of sand after compaction. Remove excess sand and other debris. The pavers may be painted with the same lane, traffic, or crosswalk markings as any other concrete pavements. Plastic markings are not recommended. Light colored pavers can be used for pavement markings. This can save re-painting costs.

References

Refer to the latest published ASTM and CSA standards and CMHA Tech Notes.

ASTM–American Society for Testing and Materials International, Conshocken, PA. www.astm.org

CSA–Canadian Standards Association, Rexdale, ON. www.csagroup.org

CMHA–Concrete Masonry and Hardscapes Association, Herndon, VA. www.MasonryAndHardscapes.org

1. Tarakji, G., “The Effect of Utility Cuts on the Service Life of Pavements in San Francisco, Volume I: Study Procedure and Findings,” Department of Public Works, City and County of San Francisco, California, May 1995.
2. Shahin, M.Y., Crovetti, J. A. and Franco, J. L., “Effects of Utility Cut Patching on Pavement Performance and Rehabilitation Costs,” report prepared by ERES International for the City of Burlington, Vermont in 1985 and published with revisions for the 1986 Annual Meeting of the Transportation Research Board, December 23, 1985.
3. Comprehensive Study to Evaluate Repair Patches for Asphalt Paved Streets, a report prepared for Southern California Gas Company by ARE Engineering Consultants Inc., Scotts Valley, California, December 1989, p. 7.
4. Performance Audit—Public Works Department Utility Cuts Program, City Auditor’s Office, City of Kansas City, Missouri, March 1994.
5. Bodocsi, A. et al., Impact of Utility Cuts on Performance of Street Pavements, The Cincinnati Infrastructure Research Institute, Department of Civil & Environmental Engineering, University of Cincinnati, Ohio, 1995.
6. Stantec Consulting Ltd, “Interlocking Concrete Pavement Life Cycle Cost Analysis,” Waterloo ON, 2023
7. Union Gas Limited, “Unshrinkable Backfill Study,” Union Gas London Division, London, Ontario, 1994 with revisions in 1995.
8. “Unshrinkable Fill for Utility Trenches and Streets,” Canadian Portland Cement Association, Publication No. CP004.01P, Ottawa, Ontario, 1989.
9. Emery, J. And Johnston T., “Unshrinkable Fill for Utility Cut Restorations,” Transportation Research Board Annual Meeting, paper SP93-10, Washington, D.C., 1993.

Sources for additional information on low-density flowable fill include the Cement Association of Canada and the American Concrete Institute offers publication 229R-13, report on “Controlled Low Strength Materials (CLSM)”.

Figure 1 is from iStock.com and Figure 8 is courtesy of Gavigan Contracting Ltd., London, Ontario.

Interlocking concrete pavement (ICP) provides an attractive, durable, low maintenance pavement system. However, like any pavement system, if one of the elements fails to perform, the entire system can be compromised. Performance issues can arise from inadequate design, inappropriate materials, ineffective construction techniques or absence of proper maintenance. This Tech Note provides best practices for maintenance and illustrates actions that should be taken when the system underperforms. The methods utilized apply to commercial and residential interlocking concrete pavement applications. Following the guidance provided in this Tech Note can help ensure the optimum performance.

This Tech Note does not address maintenance of permeable interlocking concrete pavement (PICP) systems. This is provided in CMHA Tech Note PAV-TEC-023–Maintenance Guide for Permeable Interlocking Concrete Pavements.

Preventive Maintenance

CMHA recommends that interlocking concrete pavement systems should receive routine preventive maintenance in the spring and fall to ensure optimum performance, just like any other type of pavement.

Remove surface debris:This can be done using a mechanical street sweeper, as shown in Figure 1, or push broom depending on the size of the area. A spring sweeping to remove any remaining deicing chemicals and winter sand and a fall sweeping to remove accumulated dirt and leaves are recommended. A power washer or leaf blower can do this very effectively but be careful not to remove the joint sand.

Top up joint sand as required: During normal use, the sand filled joints receive sediment and debris from traffic. This settles into the top of the joints and helps hold the sand in place. Installations exposed to driving winds, concentrated runoff flows, or excessive cleaning, may result in some joint sand loss, which can be replenished with dry masonry sand. If the joint sand has dropped more that 1/2 in. (12 mm), measured similar to Figure 2, top up the joint sand immediately. While effective when the joint is filled, using polymeric sand for topping up joints is not recommended.

• After removing surface debris, the pavement surface should be dry.
• Using a wide push broom, spread dry masonry sand back and forth over the paver surface allowing it to fall into the joints and fill them to the bottom of the paver chamfers.
• When all joints are filled, remove excess sand from the surface.

Use of stabilized joint sand: During construction, stabilized sand can be used instead of masonry sand to reduce the potential for joint sand loss. Sealers can also help hold the sand in the joints. These are applied over the entire paver surface as a liquid and allowed to soak and cure in the joints. Further details are provided in CMHA Tech Note PAV-TEC-005–Cleaning, Sealing and Joint Sand Stabilization of Interlocking Concrete Pavement.

Apply sealers for easier stain removal: Sealers reduce intrusion of water, stains, oils, and dirt into paver surfaces as shown in Figure 3. Sealers are useful around barbeques, trash receptacles, fast food restaurants, driveways, other areas subject to stains, and where oil drippings are not wanted. Application of a sealer follows stain removal, efflorescence removal, and overall surface cleaning. Further detail is provided in CMHA Tech Note PAV-TEC-005–Cleaning, Sealing and Joint Sand Stabilization of Interlocking Concrete Pavement.

Inspect for distress: As part of the routine preventive maintenance inspection, check for the various distresses identified in the Types of Distress and Remedies section. If a distress is noted, schedule additional maintenance that remedies the distress and restores the pavement to optimum performance. Inspection be conducted twice a year. Once in Spring during or immediately after a rain event and again in late Summer or early Fall. The rain on the pavement surface will readily identify rutting, settlement and ponding, as well as run-on from adjacent vegetated areas. Table 1 is provided as a template that can be used to record the results of an inspection.

Winter Maintenance

Given durable aggregates and high densities, concrete pavers can offer outstanding resistance to freeze-thaw and deicer deterioration. The texture of the concrete paver surface with slight surface variations created by the joints can contribute to reduced slips and skids during winter conditions. The amount of slip resistance depends on the surface texture and joint widths.

Snow Shovels/Snow Blowers/Snowplows: Snow can be removed from interlocking concrete pavers using shovels, snow blowers or snowplows like any other type of pavement. Experience indicates easier snow removal by shoveling and plowing in a direction diagonal to the joints to prevent catching the edge of the pavers as shown in Figure 4. Prior to the winter season, heaved or slightly lifted units creating lippage of greater than 1/8 in. (3 mm) should be repaired.

With more powerful equipment like plows, excessive lippage and working parallel / perpendicular to the joints may lead to chipping the paver edges. In extreme cases where lippage is not addressed, pavers may be removed which would require further maintenance.

Snow blowers and snowplows can have shoes under them that skid across the pavement surface and raise the blade just above the pavement surface. See Figure 5. Over time, these shoes wear and need to be adjusted to ensure the blade rides at a height that removes as much snow as possible without catching paver edges. Excessive snow blowing and snow plowing operations can embed metal filings from worn shoes into the paver surface that can lead to rust stains. These can be removed with rust removal cleaners. See CMHA Tech Note PAV-TEC-005–Cleaning and Sealing interlocking Concrete Pavement–A Maintenance and Protection Guide. Synthetic shoes are available which prevent rust staining created by shoe wear.

As with any pavement, snow removal operations can scratch the paver surface. This could be more noticeable on textured or smooth (polished) pavers. Removing debris from the pavement surface before the snow season can reduce scratching. Using plastic snow shovels or synthetic blades edges should be considered in areas where the appearance of the paver surface is important.

Winter Sanding: Sand applied to improve slip and skid resistance also helps keep the joints filled thereby reducing preventive maintenance. CMHA recommends removing excess sand from the pavement surface in the spring. If left on the pavement surface year after year, sand can lead to excessive surface abrasion and wear. This may accelerate colour changes and overall deterioration of the paver units.

Snow and Ice Melt Systems: These systems are an effective way to prevent snow and ice accumulation. Electric and hydronic snow melt systems can be incorporated into interlocking concrete pavement systems. See Figure 6 and 7. Further information can be found in CMHA Tech Note PAV-TEC-012–Snow Melting Systems for Interlocking Concrete Pavements.

Deicer Use: Deicer chemicals that help prevent, reduce, or eliminate ice buildup as well as slips, falls and loss of vehicular control are often essential in many winter climates. Deicers mixed with ice and snow can increase damage to concrete. Pavers made with low absorption aggregates and high densities tend to have higher resistance to degradation caused by deicers. These properties help limit deicers from entering a concrete paver. In addition, a high cement content helps a paver resist damage from the stress of expanding ice. Units manufactured with these characteristics typically yield a high density and low absorption, as well as high compressive strength, thereby increasing winter durability.

ASTM C936 Standard Specification for Solid Concrete Interlocking Paving Units includes freeze-thaw durability criteria and resistance to deicing salts. ASTM C936 references the test method ASTM C1645 Standard Test Method for Freezethaw and De-icing Salt Durability of Solid Concrete Interlocking Paving Units. ASTM C936 includes an optional lower freezing temperature in ASTM C1645 for regions of the United States that experience severe freezing conditions based on a climatic zone map. The optional testing in 3% saline and the lower freezing temperature for these regions is equivalent to that required in the Canadian concrete paver standard, CSA A231.2 Precast Concrete Pavers. To obtain a copy of ASTM C936 or ASTM C1645 visit www.astm.org. The CSA standard is available from www.csagroup.org.

A key to successfully using deicing materials on unit concrete pavers is using only as much as needed to do the job, not as shown in Figure 8. This maximizes their benefits while minimizing damage to the concrete pavers and surrounding environment. The following guidelines can help limit the exposure of deicing chemicals while maintaining a safe environment:

• Apply sand first to increase traction, then apply deicers as needed. Sand should not be applied to permeable interlocking concrete pavements.
• Rock salt (sodium chloride, NaCl) is the least damaging to concrete materials and should be used whenever possible.
• If a more effective, quicker acting deicer is necessary, consider the judicial use of calcium chloride.
• Magnesium chloride and CMA are not recommended because they can chemically degrade all types of concrete, significantly increasing potential damage. The potential for damage from CMA increases with the amount of magnesium in the formulation.
• Do not over apply deicing chemicals; follow the recommended dosage.
• Do not use deicing chemicals in place of snow removal but reserve them for melting ice formed by freezing precipitation or freezing snow melt.
• Once loosened, snow, ice and excess deicing salts should be promptly removed by plow or shovel to avoid a buildup in concentration of the deicing chemical(s). If excess snow, ice and deicing salts is to be stored on-site do not store on concrete paver pavement.
• Protect vegetation and metal from contact with deicing chemicals as most can impair vegetation and corrode metals.

CMHA recommends adequate pavement slopes (typically a minimum of 2%) to facilitate surface water drainage and to help remove deicing materials. While not essential, reduction of water entering jointing sand can be further enhanced with joint sand stabilization materials and/or sealers. Table 2 compares common deicing chemicals and their effective temperatures to their impact on degradation of the concrete. DISTRESS TYPES AND REMEDIES Some distresses are aesthetic in nature and others affect the structural integrity of the pavement system. Identifying the type of distress points to repairs that can return the pavement to a high-performance level. Aesthetic (Visual) Aesthetic distresses typically do not affect the structural performance of the interlocking concrete pavement system. Efflorescence Efflorescence is a white haze that may appear on the surface of pavers sometime after installation as seen in Figure 9. It forms from Portland cement reacting with water. This reaction creates water-soluble calcium hydroxide (lime). When water enters the microscopic capillaries in the pavers, calcium hydroxide is dissolved and carried to the paver surface, where it reacts with the carbon dioxide in the air to become calcium carbonate. This forms a white haze on the surface of the pavers when the water evaporates. The appearance of efflorescence stops when the calcium hydroxide supply is exhausted. Efflorescence is not a structural, but rather an aesthetic concern. The white haze may give the impression that the color of the pavers is fading but this is not the case. Efflorescence may occur randomly or be concentrated in certain areas. Dark colored pavers show efflorescence more than lighter colored ones. Most paver producers put chemical additives in the concrete to reduce the likelihood of efflorescence occurring. In most cases the additives prevent efflorescence. However, completely eliminating the chance of efflorescence isn’t possible because it’s a natural by-product of curing concrete. If efflorescence occurs, it can be removed with cleaners specifically made for concrete pavers. Careless or improper cleaning can result in damage and discoloration to paver surfaces. Contact the paver supplier for further information on commercially available cleaners. CMHA Tech Note PAVTEC-005–Cleaning and Sealing interlocking Concrete Pavement–A Maintenance and Protection Guide provides additional details. Dirt and Stains Numerous companies sell products designed specifically to clean concrete pavers. Some are general cleaners and some are specific to the type of stain being removed. As an example, there are cleaners designed to remove only rust stains like those shown in Figure 10. Pressure washers, shown in Figure 11, are a commonly used tool used to clean pavers. Professionals use specialized equipment shown in Figure 12 to maximize the cleaner’s effectiveness and minimize any damage to the pavement. Concrete pavers generally aren’t damaged by petroleum products, but oil stains from vehicles can be difficult to remove. Oil stains should be treated as soon as possible. The longer they remain on the surface, the deeper they penetrate making them harder to remove. First, wipe oil from the surface and apply liquid detergent. Allow it to soak for several minutes, scrub, then rinse the pavers with hot water. Several treatments may be necessary to remove particularly stubborn stains. For best results use cleaners specially made for removing oil stains from concrete pavers. Keep in mind that due to their modular nature, replacing stained pavers might be simpler and less expensive than attempting to removed stubborn stains. Cleaning and sealing concrete pavers can make removing stains easier, since sealers prevent stains from soaking into the surface. The sealers may need to be reapplied from time to time due to wear and weather. Concrete pavers should be cleaned prior to sealer application to obtain the best performance and appearance. It is generally recommended that pavers be sealed after any efflorescence issues are under control. If there are concern about the reoccurrence of efflorescence, use of a “breathable” sealer is recommended. Removing oil and many other stains is discussed in CMHA Tech Note PAV-TEC-005–Cleaning and Sealing Interlocking Concrete Pavement—A Maintenance and Protection Guide. The paver supplier can provide information on cleaners and sealers specifically made for concrete pavers. Weeds and Ants Contrary to some views, weeds don’t grow from the bedding sand, base, or subgrade. Weeds can germinate between pavers from windblown seeds lodged in the joints. See Figure 13. Weeds can be removed by hand or killed using steam or a herbicide. Take care in using herbicides so that adjacent vegetated areas are not damaged. Use biodegradable products that won’t damage other vegetation or pollute water supplies when washed from the pavement surface. Besides stabilizing the joint sand, sealers can prevent seeds from germinating, and prevent ants from entering. Color Fading Color in concrete pavers is achieved by adding pigment to the concrete mix during production. The cement in the concrete mix holds the pigments in place. Normal wear from traffic or weather gradually erodes the cement and pigment particles, exposing more of the aggregate and sand, causing a color change over time. Like all pavements, concrete pavers receive dirt from foot or tire traffic which changes the surface color. See Figure 14. Cleaning and sealing the surface of the concrete pavers can moderate the rate of color change. Besides enhancing the pavers’ color, sealers can help prevent dirt from lodging in their surface. Minor Abrasion and Wear Including Scratches Over time traffic will cause wear and abrasion of the paver surface just like all other pavements. As mentioned in the winter maintenance section, sand or gravel left on the paver surface year after year can lead to accelerated abrasion and wear shown in Figure 15. As noted in the section on Preventive Maintenance, a routine maintenance program should include removal of surface debris to minimize surface wear and abrasion. Structural ASTM E2840 Standard Practice for Pavement Condition Index Surveys for Interlocking Concrete Roads and Parking Lots provides descriptions of distresses, severities and deduct values for calculating a pavement condition index (PCI), a fundamental tool for managing pavement preservation. This standard can be used to calculate a Pavement Condition Index (PCI) which is a value between 0 (very bad) and 100 (perfect) for an interlocking concrete pavement surface. Figure 16 shows how a typical pavement’s PCI value will reduce over time. The severity and extent of eleven distresses (some unique to interlocking pavements) and deduct curves indicate the functional and operational condition of the pavement surface while providing clues to structural integrity. Moreover, the PCI establishes the pavement deterioration rate and helps forecast preservation activities, especially rehabilitation timing. Although not typically used in residential applications, the distresses in ASTM E2840 can be useful for identifying performance problems in residential interlocking concrete pavements. The following list provides information about the eleven interlocking pavement distresses identified in ASTM E2840 and provide guidance for repair. Damaged Pavers Description: Damaged pavers distresses such as chips, cracks, or spalls. Damage may indicate inadequate support causing shear breakage, etc. Figure 17 Identification: One or more chips, cracks, or spalls. Cracked pavers with little to no opening generally will not affect performance. Repair: Replace with new pavers, compact, refill joint sand, compact. Depressions Description: Depressions are lower areas than those around it. Depressions are caused by settlement of the underlying subgrade or granular base, often from inadequate compaction. Other factors can be a saturated base or soil, excessive bedding sand thickness deformed from wheel loads, or washed out bedding and joint sand. Loose or inadequate edge restraints will cause pavers to move apart. Settlement is common on utility cut patches and adjacent to road hardware. Depressions can cause roughness in the pavement, and when filled with water, can cause hydroplaning of vehicles or slippery ice patches in the winter. Identification: Depression are measured by placing a 3 m (10 foot) straight across the depression and measuring the high depth from it to the pavement. Changes in shades of color on a pavement surface can give the impression of differential elevation where none exists. The apparent depth of differential elevation is often exaggerated by shadows in the early morning and late afternoon, as well as the chamfer on the paver edges. Standing water and stains can be used to visually identify depressions, like Figure 18, however, the boundaries and depth should be established using the straight edge or string line. Be careful to distinguish heaves from depressions. Repair: Identify source (typically not load-related): Bedding, base or subgrade and repair per rutting distress described below. Pavers in uneven areas with low severity depressions can be removed, the settlement adjusted, and the units reinstalled with no wasted paving materials or unsightly patches. Edge Restraint Description: Edge strips and curbing are restraints that provide lateral support for pavers. Lateral restraint is considered essential to resisting movement, minimizing loss of joint and bedding sand, and preventing paver rotation as seen in Figure 19. Edge strips/curbs can comprise prefabricated metal or plastic supports, concrete curbs, etc. This distress is accelerated by repeated traffic loading. Identification: Loss of lateral restraint is characterized by widening of the paver joints at the outer pavement edge or at the transition of pavement types. Pavers at the perimeter can exhibit vertical and horizontal rotation as well as local edge settlement. The distress is most notable within 0.3 to 0.6 m (1 ft to 2 ft) of the pavement edge. Repair: Repair/replace edge restraint/curb & adjacent pavers, compact, refill joint sand, compact. Excessive Joint Width Description: Excessive joint width means the joints between pavers have widened. Excessive joint width can occur from several factors including poor initial construction, lack of joint sand, poor edge restraint, adjacent settlement/heave, lateral movement of the pavers, etc. As joints get wider, the layer becomes less stiff and can lead to overstressing the substructure layers. Identification: Optimal paver spacing is typically specified as 1.5 to 3 mm (0.05 to 0.12 inches). Significant variation in joint width will highlight excessive joint width as shown in Figure 20. As joints get wider, the individual blocks may show signs of rotation. Repair: Identify reason for paver joint movements. Remove the pavers and remediate the cause. Reinstate pavers to specified joints widths, compact, refill joint sand, compact. Faulting Description: Faulting happens when the elevation of adjacent pavers differs or have rotated. Faulting can be caused by surficial settlement of the bedding sand, poor installation, pumping of the joint or bedding sand. Local roughness can reduce the ride quality. Faulting can pose a safety hazard for pedestrians. Identification: Faulting is characterized by small areas of individual units standing slightly proud above their neighbors. This can bee seen in Figure 21. This distress is often associated with more severe distresses such as settlement, heave, rutting, etc. Repair: Faulting may be corrected by resetting the blocks. However, faulting may be caused by differential base movement. In this case repair base, replace bedding, reinstate pavers, compact, refill joint sand, compact. Heave Description: Heaves exhibit elevations higher than surrounding areas. Heaves are typically caused by frost heave of the underlying soils as shown in Figure 22. Heaves can also occur because of subgrade instability and can also occur in conjunction with settlement / rutting. Identification: Visual examination is not always a reliable technique for detection of heaves, especially for low severity depressions. The most reliable method is using a 3 m straight edge. Repair: If from frost, install frost-resistant subbase materials. Consult w/ geotechnical engineer if not frost related. Horizontal Creep Description: Horizontal creep is the longitudinal displacement of the paving pattern caused by repeated braking, accelerating, or turning tires. Identification: Regardless of the paver pattern, the pavement surface should have a uniform pattern. Shifting of the joints or pattern signify horizontal creep as seen in Figure 23. Repair: Remove and reinstate pavers in original laying pattern. Apply steel, anti-creep reinforcement under the pavers in severe cases. Compact, refill joint sand, compact. Joint Sand Loss/Pumping Description: Joint sand loss/pumping typically includes removal of some or all joint sand, an essential component of interlock and pavement stiffness. Joint sand loss can occur from pressure washing, saturated bedding sand that pumps under traffic loading, etc. Identification: Surface of the joint sand is well below the paver chamfer or the top of the paver if there is no chamfer as shown in Figure 24. Stains on the pavers indicate a saturated bedding layer. Repair: Provide bedding layer drainage, replace with washed bedding sand, provide bedding layer drainage, reinstate pavers, compact, refill joint sand with MHA recommended material, compact. Missing Pavers Description: Missing pavers, as the name implies, refers to sections of pavement without pavers resulting from removal or disintegration/damage. Missing pavers compromise the integrity of the pavement structure and promote surface roughness like potholes in flexible pavements. Identification: One or more missing pavers as illustrated in Figure 25. Repair: Replace with new pavers Patching Description: Patching includes missing pavers replaced with a dissimilar material. Patch quality can compromise the integrity of the pavement structure and promote surface roughness. Identification: Sections of dissimilar materials such as asphalt, etc as shown in Figure 26. Repair: Remove the patch materials and replace with new pavers. May require establish a new bedding layer. Rutting Description: Rutting is a surface depression in the wheel path. Rutting is typically caused by settlement of the underlying subgrade or granular base under repetitive wheel loads. Rutting can cause roughness in the pavement and when filled with water can cause hydroplaning of vehicles. Identification: Locate rutting by visual assessment and measure rutting with a straight edge. See Figure 27. Rutting in a single wheel path is usually quite evident. However, depressions caused by static wheel loads are measured as rutting. Repair: Minor rutting typically occurs in bedding from excessive fines in the bedding sand and lack of surface and/or bedding drainage. Check slopes, drainage, and sand durability. Major rutting often indicates insufficient base thickness/stiffness loads – repair/ replace base, install bedding, reinstate pavers, compact, refill joint sand, compact. RESTORATION This section provides steps to remove pavement layers to address the underlying issue and reinstate the pavement. Evaluate the Design Before reconstructing what was originally constructed, consider the structural design and determine appropriateness for the application. This is particularly important if any distress is present that cannot be explained. Specific details reviewed include: • Paver aspect ratio • Paver laying pattern • Base thickness • Adequate slope and drainage During the disassembly process it may be appropriate to confirm the materials being removed meet specifications and thicknesses. The CMHA Construction Tolerances and Recommendations for Interlocking Concrete Pavements guide is an excellent reference to confirm construction details. Hire an CMHA Concrete Paver Installer CMHA Certified Concrete Paver Installers receive training about the most effective and efficient materials and methods recommended for the construction of segmental concrete pavement systems. Certified installers are recommended for restoration of concrete paver installations. A Certified Concrete Paver Installer’s credentials can be confirmed at www. masonryandhardscapes.org.

• An experienced crew can reinstate pavers with little or no cutting, aligning reinstated pavers with existing joint lines, pattern, and spacing between the units.
• Although existing pavers can be reused in reinstatement, there may be projects where it is more cost effective to remove and replace the area with new pavers. Stabilized joint sand may be difficult to remove from the pavers and recycling the pavers may be more cost-effective. An experienced paver installation contractor can provide guidance on cost-effective approaches for each reinstatement project.

Disassembly Concrete pavers can act as a zipper in the pavement that facilitate underground repairs by removal and reinstatement of the same concrete pavers. Unlike asphalt or poured-in-place concrete, segmental pavement can be opened and closed without using jack hammers on the surface and with less construction equipment. This results in no ugly patches and no reduction in pavement service life. In addition, no curing means fast repairs with reduced user delays and related costs. Repair of a segmental pavement system might not require removal of the entire pavement area. It is possible only the area showing signs of distress would need to be repaired. It might also not be necessary to remove the full depth of the system. Depending on the type of distress identified, it might only be necessary to remove the top layers and leave the lower layers intact. The section on Distress Types and Remedies provides guidance on disassembly and reinstatement. The following step-by-step procedure covers how to “unzip and zip” interlocking concrete pavement. This procedure applies to any interlocking concrete pavement, including pedestrian areas, parking lots, driveways, streets, industrial, port and airport pavements. Identify Area to be Excavated The location and depth of existing utilities need to be established prior to excavating. Many localities have one telephone number to call for obtaining marked utility locations. Set cones, traffic signs, or barricades around the area to be excavated according to local, state, or provincial standards. Determine and mark the area of pavers to be removed. Remove pavers at least 18 inches (0.45 m) wider on each side of the trench opening. This shoulder around the opening should consist of undisturbed bedding sand. It will be used as a guide for reinstating the sand and pavers later (Figure 28). Paint or crayon should be used to mark the area of pavers for removal. The trench area can be marked on the pavers as well. Paint may be necessary to establish a more permanent marking than crayon, especially if there is vehicular traffic, or if there will be an extended period between marking and excavation. The same paving units will be reused, so in some instances paint on them may not be desirable, especially if there is little traffic to wear it away over time. Remove Joint Sand Scrape the sand from the joints around the first paver using a putty knife or small trowel (Figure 29). If joint sand stabilizer was used, it will take more effort to remove the paver. Alternately, a pressure washer can be used to dislodge the joint sand around the first pavers to be removed. Pavers Locate the first paver to be removed. This is typically at one end of the marked area. Use a paver extractor to remove the first paver and subsequent ones (Figure 30). They are designed to clamp the paver tightly. These work most efficiently in removing the first paver if some of the joint sand is removed before clamping and pulling. Water can be applied to lubricate the joint sand to facilitate extraction. Alternately, it is possible to carefully pry each side of a paver upward with one or two large screwdrivers. Begin prying on the short ends of the paver. The paver will rise a small distance with each prying (Figure 31). When the paver is high enough to grasp, wiggle it loose, pulling upward. If necessary, pry with a screwdriver using one hand while pulling upward with the other. Sometimes, one end of the paver can be pulled above the others so a pry bar can be inserted under it. The paver can then be pried out. If the pavement has been subject to vehicular traffic for a length of time, the pavers may be tightly locked together and the first paver may need to be broken for removal. A small sledgehammer (3 lb. maul) applied to an appropriate chisel will break a paver into small pieces. Protective eye goggles should be worn during this procedure. Remove all broken pieces from the space until the bedding sand is completely exposed. Pneumatic hammers or cutting saws are generally not required for this process. After the first paver is removed, surrounding pavers can be loosened and pried out (Figure 32). Grab the pavers by the short end, as it offers less resistance than the long side. Remove pavers to the marks on the pavement for the opening. Sand sticking to the sides and bottoms of pavers can interfere with their reinstatement and compaction into the bedding sand. Scrape off sand from each unit as it is being removed. A small trowel, wide putty knife, wire brush, or another paver works well. Again, if stabilized joint sand has been used, it will take more effort to remove the sand sticking to the paver. The direction of removal should consider where pavers are going to be stacked. Stack the pavers neatly near the opening, out of the way of excavation equipment such as backhoes or dump trucks. If the pavers need to be removed from the site, stack them on wooden pallets and secure them tightly so there is no loss during transit. Equipment used to move pallets with pavers should be capable of lifting more than 3,000 lbs. (1,365 kg). If the pavers need to be moved only a short distance, then stack them directly on a paver cart at the opening and set them nearby. They will then be ready for pickup by the paver cart when reinstated. For every project, a small stockpile of spare pavers should be stored and used for repairs during the life of the pavement. Weathering, wear, and stains may change the appearance of removed pavers compared to spares kept in storage for repairs. When pavers are removed, all undamaged units should be retained for future reinstatement. Pavers from the stockpile that replace damaged or broken units should be scattered among the pattern of the existing reinstated pavers. This will reduce the visual impact of color variations. Bedding The removed pavers will reveal compacted bedding sand. It may be removed and reused or removed during excavation of the base. For some projects with time constraints, the sand will probably be removed during excavation and not reused. If the sand is reused, it may need to be loosened with rakes before removal by shoveling. The sand should be neatly stockpiled and kept free from soil, aggregate base, or foreign material. If the sand is mixed with these materials, it should not be reused, and it should be replaced. Whether or not it is reused, always leave an undisturbed area of sand 6 to 12 in. (15 to 30 cm) wide next to the undisturbed pavers. This area will provide a stable support for temporary edge restraints and for screeding the bedding sand after the base is reinstated. Edge Restraint If the edge restraint is showing signs of distress. Is loose and not serving it purpose remove the section that is not performing adequately. When removing, consider how the reinstated edge restraint will connect back into the remaining edge restraint. Install Temporary Bracing Install temporary bracing with wood, plastic, or metal edge restraints around the perimeter of the opening. Using 2x4s placed on their side around the opening and braced with more 2x4s can be very effective. This is recommended practice. If the restraints are to be spiked in they can be pinned to the base using metal spikes (Figure 33), but damage to the base created by removing the spikes will need to be repaired during the reinstatement process. Bracing helps keep the undisturbed pavers in place during excavation and fill activities and will enable reinstatement of units into the existing laying pattern without cutting them to fit. Base and Subgrade If aggregate base material is removed, it may be possible to stockpile it near the opening for reuse. Keep the aggregate base material separate from excavated subgrade soil. Any soil removed should be replaced with base material unless local regulations require reinstatement of the native soil. The final shape of the excavated opening should offset from the bracing. (Figure 34). This helps prevent undermining and weakening of the adjacent pavement. Follow local codes for trenching requirements and the use of shoring, as it may need to be inserted to prevent collapse of the trench sides. Reinstatement Before placing any materials, it would be useful to review CMHA Tech Note PAV-TEC-002Construction of Interlocking Concrete Pavement and Construction Tolerances and Recommendations for Interlocking Concrete Pavements to ensure materials to be placed and methods used agree with industry best practices. Subgrade After the repairs are complete, soil at the bottom of the trench should be compacted prior to placing and compacting the base material. Repairs typically use the same base material that was removed. A crushed stone aggregate base should be placed and compacted in 4 to 6 inch (100 to 150 mm) lifts (Figure 35). If the excavated base material was stabilized with asphalt or cement, it should be replaced with similar materials. Monitoring density of the compacted soil subgrade and base is essential to reinstating any pavement, including interlocking concrete pavements. It will help prevent rutting and premature failure. A dynamic cone penetrometer is an effective means for monitoring the density of each lift while working in the opening. If the soil or base material is too dry during compaction, a small amount of water can be sprayed over each lift prior to compacting. This will help achieve maximum density. A nuclear density gauge is recommended for checking the density of the completed compaction of the soil and base layers. A qualified civil engineer should monitor compaction for conformance to local standards. If there are no local standards for compaction, a minimum of 98% standard Proctor density is recommended for the soil subgrade, and a minimum of 98% modified Proctor density for the base. Compaction equipment companies can provide guidelines on equipment selection and use on the soil and the base. For further guidance on compaction see CMHA Tech Note PAV-TEC-002–Construction of Interlocking Concrete Pavements. Geotextile Placing a geotextile between the subgrade and base can prevent the subgrade from contaminating the base aggregate and reducing the system’s long-term performance. Consult Tech Note PAV-TEC-022–Geosynthetics for Segmental Concrete Pavements for details of the selection of an appropriate material. Base The final elevation of the compacted base at the opening perimeter should match the bottom of the existing undisturbed sand layer that surrounds the opening (Figure 36). The elevation of the middle of the base fill placed in the opening should be slightly higher than its perimeter to compensate for minor settlement. CMHA Tech Note PAV-TEC-004–Structural Design of Interlocking Concrete Pavement for Roads and Parking Lots and ASCE 58-16 can provide guidance on the minimum recommended base thickness. Controlled low-strength materials (CLSM) (sometimes called slurry mix, flowable fill, or unshrinkable fill) can be used in some applications as a replacement for unstabilized base materials (1). The fill can be made from aggregate bound with fly ash, pozzolans, or cement. Because it is poured from a truck, the fill will form around pipes and underground structures where soil or base backfill and compaction are difficult. Low-strength fill can be poured into undercuts and under pipes where it is impossible to fill and compact aggregate base. The material is also selfleveling (Figure 37). Low strength flowable fill requires a short curing time and can be used in freezing weather. It requires no compaction and with some mix designs, can be opened to traffic in 24 hours. Low-strength fill is stiffer than aggregate base and offers higher resistance to settling and rutting. This reduces deterioration of the pavement surface over time. To facilitate re-excavation, flowable fill should be made with a small amount of cement. Check with suppliers on the strength of in-place fill that is at least two years old, and on ease of excavation of these sites. The strength of the fill should not exceed 300 psi (2 MPa) after two years of service. Low-strength fill has been used successfully in Toronto and London, Ontario; Colorado Springs, Colorado; Cincinnati, Ohio, Kansas City, Missouri; Peoria, Illinois; and many other municipalities. It is generally more cost-effective than using aggregate base by reducing job time and future pavement repairs. Local ready-mix suppliers can be contacted for available mixes, strengths, installation methods and prices. See CMHA Tech Note PAV-TEC-007–Repair of Utility Cuts within Interlocking Concrete Pavements for further information on low-strength fill. Edge restraint Ensure the edge restraint is constructed according to the details provided in CMHA Tech Note PAV-TEC-003–Edge Restraints for Interlocking Concrete Pavements and the system selected is recommended for the application. Remove Temporary Bracing Once the base has been reinstated it is appropriate to remove the temporary bracing. Repair any damage to the base this process might create. Bedding During the foregoing procedures, it is likely that the pavers and bedding sand around the opening were disturbed especially if no temporary edge restraints were placed to secure the pavers. If so, then remove an additional two rows of pavers, or back to an undisturbed course. Clean sand off of these pavers and set them aside with the others. Be sure there is at least 8 in. (200 mm) of undisturbed bedding sand exposed after removal of the course(s) of pavers. This area of undisturbed sand can be used to guide screeding of fresh bedding sand over the compacted and leveled base. Prior to screeding, carefully remove any temporary edge restraints so that adjacent pavers remain undisturbed. Place a straight edge or string line across the paver surface on either side of the opening. Measure down at several points along the string line to confirm the base follows the grade of the surrounding paver surface, with a slight crown near the center to account for future consolidation of the newly compacted base (Figure 38 and 39). It may be necessary to remove a few courses of pavers to straighten the edge of the pavers. Low areas should be filled with base material and compacted. Do not use the bedding sand to compensate for low places in the surface of the base. Use a string line to determine the undisturbed bedding sand thickness by measuring from the string line to the base surface then subtract the paver thickness. This should be approximately 5/8 in. (16 mm). Set screed rails below the string line the thickness of the pavers minus 50% of the undisturbed bedding sand thickness. The additional thickness of the bedding sand will account for compaction and sand moving into the joints. Screed sand to ensure uniform thickness is placed over entire base surface. It may be necessary to confirm this is the correct bedding thickness by placing pavers and compacting. The paver surface should be 1/16 to 1/8 in. (2 to 3 mm) above the adjacent paver surface to account for further consolidation. Further information regarding bedding sand is available in CMHA Tech Note PAV-TEC-017–Bedding Sand Selection for Interlocking Concrete Pavements in Vehicular Applications. Pavers Pull and secure string lines across the opening along the pavement joints every 6 to 10 ft. (2 to 3 m). By following the string lines, joints of reinstated pavers will remain aligned with undisturbed ones. Lay the remaining pavers in the original laying pattern from the smaller end of the opening, generally working “uphill,” i.e., from a lower elevation of the pavement to the higher one (Figure 40). Minor adjustments to the alignment and spacing of joints can be made with alignment bars (Figure 41), pry bars or large screw drivers. Adjust prior to compacting the pavers. Compact pavers with at least two passes of a minimum 5,000 lbf. (22 kN) plate compactor. The path of the plate compactor should overlap onto the undisturbed pavers (Figure 42). Joint Sand Spread dry joint sand and compact again until the joints can no longer accept sand (Figure 14). Sweep away excess sand. The elevation of the reinstated pavers after compaction should be no higher than 1/8 in. (2 mm) at the edges and 3/16 in. (5 mm) at the center. Traffic and minor settlement will compact the pavers to a level surface. After a short period of time, the repaired area will be undetectable (Figure 15). Applications prone to joint sand loss like steep slopes, concentrated surface water flow and continually windy areas are good candidates for joint sand stabilization. If an area is reinstated in such applications, then the use of a joint sand stabilization is recommended. See CMHA Tech Note PAVTEC-005-–Cleaning and Sealing Interlocking Concrete Pavements for advice on joint sand stabilization. Additional information about joint sand is included in CMHA Tech Note PAV-TEC-17–Bedding Sand Selection for Interlocking Concrete Pavements in Vehicular Applications. Surface Treatment At the end of the reinstatement process, it may be appropriate to clean and possibly seal the reinstated and surrounding undisturbed pavers. Information on this process is available in CMHA Tech Note PAV-TEC-005-–Cleaning, Sealing and Joint Sand Stabilization of Interlocking Concrete Pavement.

References

1. ASTM – American Society for Testing and Materials International, Conshocken, PA. www.astm.org
2. CSA–Canadian Standards Association, Rexdale, ON. www. csagroup.org
3. ASCE – American Society of Civil Engineers, Structural Design of Interlocking Concrete Pavements for Municipal Streets and Roadways. Reston, VA. www.ASCE.org
4. CSA – Canadian Standards Association, Rexdale, ON. www.csagroup.org
5. CMHA- Concrete Masonry and Hardscapes Association, Herndon, VA. www.masonryandhardscapes.org a. CMHA Construction Tolerances and Recommendations for Interlocking Concrete Pavements b. CMHA Tech Notes PAV-TEC 002, 003, 004, 005, 012, 013, 017, 022
6. Controlled Low Strength Materials (CLSM), ACI 229R-94, American Concrete Institute, Farmington Hills, Michigan, 1994.

Revised 2022

When properly installed, interlocking concrete pavements have low maintenance requirements and provide an attractive surface for decades. Under foot and vehicular traffic, they can become exposed to dirt, stains and wear. This is common to all pavements. This tech nical bulletin addresses various steps to maintain interlocking concrete pavements appearance. These steps include removing stains and cleaning, plus joint stabilization or sealing if required.

Stains on specific areas should be removed first. A cleaner should be used next to remove any efflorescence and dirt from the entire pavement. A newly cleaned pavement can be an opportune time to apply joint sand stabilizers or seal it. In order to achieve maximum results, use stain removers, cleaners, joint sand stabilizers, and sealers specifically for concrete pavers. These may be purchased from a manufacturer, contractor, dealer or associate member of the Masonry and Hardscapes Association.

Removing Stains

Commercial stain removers available specifically for concrete pavers provide a high degree of certainty in removing stains. Many kinds of stains can be removed while minimizing the risk of discoloring or damaging the pavers. The container label often provides a list of stains that can be removed. If there are questions, the supplier should be contacted for help with determining the effectiveness of the chemical in removing specific stains.

Identify the stains prior to applying the cleaner. A test application should be evaluated in a small, inconspicuous stained area for cleaning effectiveness. Some stains may require repeated applications of the remover to achieve effective cleaning. This is often the case for deep set oil stains. With all stain removers, cleaners, joint sand stabilizers, and sealers, the label directions and warnings should be read and carefully followed for all precautions.

Start removal of stains at the bottom of the pavement and work up the slope in manageable sections. By working up the slope, cleaning fluids will drain down the pavement. This technique assists in uniform removal while allowing the used cleaner to be rinsed away consistently. The surface remains dry ahead of the cleaner-soaked wet areas, allowing better visibility of the stains to be removed.

Take care in selecting and applying cleaning products, as acidic ones may harm vegetation and grass. These cleaners should not run onto vegetation. When using strong acidic stain removers or cleaners that might drain onto vegetation, saturate the vegetation with water prior to using acidic cleaners. This will minimize absorption of cleaner rinse water and reduce risk of damage to vegetation.

Removal of Common Stains

There are proprietary cleaning products specifically designed for concrete pavers. Many have been developed through extensive laboratory and field testing to ensure cleaning effectiveness. These chemicals should be used whenever possible. Using manufactured cleaning chemicals for specific stains relieves the user from the uncertainty of attaining the proper mixture of chemicals.

If no proprietary stain removal products are available, a comprehensive source of information on stain removal is found in Removing Stains from Concrete by William H. Kuenning. It describes chemicals, detergents or poultice (scrubbing) materials recommended for removing particular stains, and the steps to be followed in removal. This publication recognizes that some of the treatments involve hazardous chemicals and it advises specific precautions.

Removal of several common stains from Removing Stains from Concrete are listed below (1). Most involve typical household chemicals. Searching the internet using the key phrases mentioned below can provide additional information. CMHA disclaims any and all responsibility for the application of the information. The user is advised to use cleaners specifically made to remove stains that commonly occur on concrete pavers. They will likely be more effective.

Asphalt and emulsified asphalt—Chill with ice (if warm outside), scrape away and scrub the surface with scouring or abrasive powder. Rinse thoroughly with water.

Cutback asphalt and roofing tar—Use a poultice made with talc or diatomaceous earth. Mix with kerosene, scrub, let dry and brush off. Repeat as needed.

Blood, candy, ketchup, mustard, grease drippings from food— For stubborn stains, apply liquid detergent full strength and allow it to penetrate for 20 to 30 minutes. Scrub and rinse with hot water. Removal is easier if these stains are treated immediately.

Caulking—Scrape off excess and scrub with a poultice of denatured alcohol. Rinse with hot water and detergent.

Acrylic latex caulk—follow guidelines for removal of latex paint.

Chewing gum—Same as caulking, or scrub with naphtha.

Clay soil—Scrape off dry material, scrub and rinse with hot water and strong detergent.

Creosote—Apply a poultice with paint thinner and talc. Scrub and allow to dry. Scrape off, scrub with scouring powder and rinse with water.

Leaf, wood rot, or tobacco stains—apply household bleach and scrub with a stiff bristled brush.

Mortar—Let harden and carefully remove hardened spots with a trowel, putty knife or chisel.

Smoke—Scrub with a poultice of talc with bleach diluted 1:5 with water. Rinse with water.

Oil or grease that has penetrated—Mop up any excess oil with rags. Cover the area with oil absorbent (kitty litter). Talc, fuller’s earth, diatomaceous earth can be used. Leave it on the stain for a day then sweep up.

Paint—Fresh paint should be mopped up immediately with rags or paper towels by blotting. Do not wipe as this will spread the paint and extend the job of removal. If the paint is latex and water based, soak and then scrub the area with hot water, scouring powder and a stiff brush until no more improvement is seen. Let the remaining paint dry and remove as described below.

Dried paint—Scrape any excess oil based paint, varnish or water based latex paint off the surface. Apply a commercial paint remover and let it sit for 20 to 30 minutes. Loosen with gentle scrubbing. Do not rub the loosened paint into the surface of the paver. Instead, blot up the loosened paint and thinner. Repeat as necessary.

Tire skid marks—Scrub black area with water, detergent and scouring powder.

In the case of small stained areas, removal and replacement with new pavers may be an option.

Overall Cleaning

Overall cleaning of the pavement can start after stains are removed. In preparation for cleaning, low tree branches, shrubs and vegetation adjacent to the pavement should be tied back or covered to protect from overspray of cleaning solutions or sealers. The area should be inspected for any cracked or broken units. These should be replaced. Badly stained units can be replaced, but it is usually easier to clean stains and less costly than replacing the pavers.

When pavers have stains too difficult to remove, replace them with the same type of units. Refer to CMHA Tech Note PAV-TEC-006 Reinstatement of Interlocking Concrete Pavements, for a full description on replacing pavers. If pavers must be replaced, there may be a difference in color from the surrounding pavers. This variation should eventually disappear. If color variation is unacceptable, controlled use of proprietary cleaners designed to improve the color of concrete pavers can minimize variation.

Removal of accumulated dirt and efflorescence is the objective of cleaning. It is essential in preparing the pavers for sealing as well. Many cleaners effective in removing dirt and efflorescence are a mix of detergent and acid. Cleaners with strong acids will change the color of the pavers slightly. The degree of change can be controlled by the type of acid in the cleaner, its concentration and the length of time on the pavers. Proprietary cleaners will give specific instructions on their application. These directions should be followed. In order to achieve proper results, cleaners should be tried on a small area to test results and any color changes. The concentration and time on the pavement can be adjusted accordingly. Protective clothing and goggles should always be worn when using acidic solutions.

Anticipate where the cleaning fluids will drain, i.e, across the pavement and not onto grass or vegetation. Sediment or cleaners allowed to pond in low spots may stain the pavers. If unsure of the runoff direction, test drainage with ordinary water first to identify any trouble spots. Be sure to rinse these areas thoroughly. Turn off all automatic sprinkler systems during cleaning, sealing and drying.

Professional Cleaning Methods

For most jobs, cleaning should be handled by a professional company experienced in the use of cleaners and spray equipment. Professionals typically use a pressure washer and an applicator to apply efflorescence cleaner (when needed). The various methods for applying joint sand stabilizers and sealers are covered later. A high pressure sprayer applies cleaner and water between 1,000 and 4,000 psi (6.9 and 27.6 MPa), and at a rate between 2 and 6 gallons/minute (7.6 and 22.7 liters/minute). See Figure 2. The rate of flow is adjusted to ensure sufficient rinsing. The pressure loosens dirt and pushes water from the surface without the need for scrub brushes. The nozzle type and its distance from the paver surface influences the effectiveness of the cleaning as well. A nozzle that creates a wide spray enables a large area to be covered efficiently and prevents sand from being washed from the joints. A low angle of attack from a wide nozzle spray will also reduce the risk of dislodging joint sand.

Cleaners to remove efflorescence are applied with a low pressure pump spray 30 to 100 psi (0.2 to 0.7 MPa). A shower type spray nozzle will help ensure even distribution of the cleaner. Cleaning chemicals are applied, allowed to sit an appropriate time, then rinsed away with a high pressure sprayer. The final rinse should be water only. A large amount of water is more important to rinsing than high pressure.

For small areas, an adequate cleaning job can be achieved without this equipment. Such areas include residential patios, walks, or small driveways. Cleaners can be applied by hand, the pavers scrubbed to remove dirt and efflorescence, then thoroughly rinsed with water from a garden hose. Scrub brushes with steel bristles are not recommended. They will loosen from the brush, rust, and leave stains. Brass or plastic bristles are acceptable. This method of cleaning is for do-it-yourselfers who wish to refurbish a small area of pavers.

The additional time required to clean and seal pavers without the help of a professional should be weighed against investing in a competent company to do the job. Professionals have the equipment and experience with the various chemicals. They can achieve the highest level of results in the least amount of time.

Efflorescence and its Removal

Efflorescence is a whitish powder-like deposit which can appear on concrete products. When cement hydrates (hardens after adding water), a significant amount of calcium hydroxide is formed. The calcium hydroxide is soluble in water and migrates by capillary action to the surface of the concrete. A reaction occurs between the calcium hydroxide and carbon dioxide (from the air) to form calcium carbonate, then called efflorescence.

Efflorescence does not affect the structural performance or durability of concrete pavers. The reaction that takes place is the formation of water soluble calcium bicarbonate from calcium carbonate, carbon dioxide and water. It may appear immediately or within months following installation.

Efflorescence may reach its peak in as short as 60 days after installation. It may remain for months and some of it may wear away. If installation takes place during dry period of the year, the next cycle of wet weather may sometimes be necessary for efflorescence to materialize.

If there is a need to remove deposits before they wear away, best results can be obtained by using a proprietary efflorescence remover. The acid in proprietary cleaning chemicals is buffered and blended with other chemicals to provide effective cleaning without damage to the paver surface. Always refer to the paver supplier or chemical company supplying the chemicals for recommendations on proper dilution and application of chemicals for removal of efflorescence. They are generally applied in sections beginning at the top of slope of the pavement. If the area is large, a sprayer is an efficient means to apply the cleaner. The chemicals are scrubbed on the surface, then rinsed away. Results can be verified after letting the area dry for at least 24 hours. In most instances one application is sufficient. However, in severe instances of efflorescence, a second application may be necessary. Contact the manufacturer of the cleaning product to determine if a second application will not discolor the pavers or expose some aggregates. Note: Protective clothing, chemical resistant rubber boots and gloves, and eye goggles should be worn when applying acid or alkalies.

Joint Sand Stabilizers and Sealers

Stabilizer and sealers are two distinct products sometimes with overlapping functions. Joint sand stabilizers help secure sand in the joint after it has been installed. Their primary function reduces the risk of removal of joint sand from flowing water, wind, aggressive cleaning, tire action and intrusion of organic matter, seeds and insects.

Joint sand stabilizers come in liquid and dry applied forms. Some liquid stabilizers are made of the same materials as sealers, but with a higher solids content with additional wetting agents. When applied to the paver surface and joints, stabilizers can make the surface easier to clean and reduce staining in a manner similar to sealers. Depending on the chemical contents, liquid stabilizers may or may not change the appearance of the paver surface.

All surface sealers are applied as liquids. Their primary function is providing additional protection to concrete paver surfaces. Such chemicals can be similar to products used to seal cast-in-place concrete slabs. Sealers are applied to the entire surface of an installation to add further protection from stains, oils, dirt, or water. Occasionally, sealers are applied to pavers during manufacturing. Whether applied in a factory or on a site, most sealers change the appearance of the paver surface by darkening it and enhancing the surface color. Since liquid sealers penetrate the joint sand to some extent during application, they secondarily provide some stabilization.

Joint Sand Stabilizers

Joint sand stabilization is generally optional and not required for many interlocking concrete pavements. Sand in joints will likely stabilize over time without additional treatment as a result of silts or other fines working their way into spaces between the sand particles. The rate of stabilization depends on the amount and sources of traffic, plus sources of fines that work their way into the joints from traffic over time.

Liquid and dry applied stabilizers provide initial protection against joint sand loss. They accelerate joint sealing that can normally occur from a combination of atmospheric dust deposits, dirt and sediment that finds its way to the pavement, and contributions from passing tires. Stain removal, efflorescence removal, and overall surface cleaning should precede application of liquid stabilizers in new construction. None of these preparatory treatments are needed prior to the application of a dry applied stabilizer. It is applied first with the joint sand to complete the paver surface and begin interlock. Stain and efflorescence removal, cleaning and sealing can be done subsequently.

Given the wide range of joint sand stabilizers and proprietary formulations, it is best to consult with the manufacture to determine expected lifespan and/or reapplication rates.

There are some applications where early stabilization of the joints is important to maintaining functional performance of the paver surface. For example, stabilization is recommended on high slope applications over 7%. Applications on high slopes will help prevent washout of joint sand. Stabilizers in very low slope or flat areas can help reduce infiltration of standing water.

Stabilization benefits pavements subject to aggressive, regular cleaning. Examples might include amusement parks and restaurant exteriors. Pavements that see regular, heavy rainfall can benefit from stabilization of the joint sand. Surfaces that experience concentrated water flow such as gutters receiving sheet flow from large areas or at the drip lines under the eaves of buildings will better resist erosion of joint sand if stabilized.

Stabilizers have been effective in securing joint sand in places subject to high winds such as in desert climates. They can prevent joint sand displacement from high-speed tire traffic. Like sealers, joint and stabilization materials reduce the potential for weeds and insects in the joints. In residential applications stabilization at downspouts and under eaves helps keep joint sand in place. Tumbled pavers (cobble stone-like units) and circular patterns have wider joints than other paver shapes. Tumbled pavers may require stabilized joint sand between them if they have slightly irregular sides and wide joints.

Studies on the permeability of the surface of interlocking concrete pavements have indicated ranges between 10% and 20% perviousness (2). The rate of permeability depends on several factors. They include the fineness of the joint sand (percent of material passing the No. 200 or 0.075 mm sieve), the joint widths, slope, consolidation of the sand plus the age of the installation. Newly placed pavers have higher permeability (as much as 25%) than installations trafficked for several years. Sealers and joint sand stabilizers can contribute to long-term performance by reducing infiltration of water to the bedding sand and base.

Liquid Penetrating Stabilizers

These are water or solvent-based with the primary resin or bonding agent being an acrylic, epoxy, modified acrylic, or other polymers as solids (by volume) typically 18% to 28%. Solvent or water carries the solids into the joint sand. They will evaporate and leave the solids behind as the binding agent. Modifiers such as epoxy resins may also add to the ability of the product to create a solid matrix in the joint sand. When initially applied, liquid stabilization materials should be allowed to penetrate at least 3/4 inch (20 mm) into the joint sand. A mockup is beneficial in determining application rates for specific products, joint sands, and for specific job site conditions.

Joint sand gradation can affect the depth of penetration of the liquid stabilizer. The amount of fines or material passing the No. 200 (0.075 mm sieve) can influence the depth of penetration. A joint sand gradation with less than 5% passing the No. 200 (0.075 mm) sieve can allow better penetration of liquid stabilizers. A job site mock-up should be tried to determine the penetration rate. The mock-up also will determine the appropriate application rate.

Prior to applying liquid materials, the surface should be clean and dry and any efflorescence removed from the pavers. Either a broom or leaf blower can efficiently remove excess sand. Some successful methods of application involve applying liquid joint stabilizers with low pressure, high volume spray, followed immediately by a squeegee to move the material into the joints. See Figure 3. Other methods use rollers, watering cans, or hand pumped, garden-type sprayers. Some equipment has multiple spray nozzles and mechanized rollers and/or squeegees. All application methods must provide uniform dispersion and effective penetration.

Liquid stabilizers bind the sand in the joint and secondarily provide sealing of the concrete paver surface. All liquid based stabilizers create some change in the appearance of the pavers. This ranges from a slight color enhancement, a modest sheen, to a high gloss. Like sealers, cured liquid stabilizers that remain on the surface of the pavers enhance their color, inhibit fading, and protect against staining. It also makes the paver surface easier to clean and maintain (Figure 4). However, joint sand stabilization will last significantly longer than the enhancement of the surface appearance.

Dry Joint Sand Stabilizers

These are dry additives mixed with joint sand. The additives are organic, inorganic, or polymer compounds that stiffen and stabilize the joints when activated by water applied to the joint sand. Additives come either pre-mixed with bagged joint sand, or are sold separately as an additive mixed with the joint sand on the job site per the supplier’s instructions. The additive is often mechanically mixed for consistency. Dry stabilizers are appropriate for residential settings, parking lots, bike lanes, plazas, and other areas with low velocity wheel loads or areas without concentrated water flow. They are convenient for application by homeowners.

The pavers are initially compacted into the bedding sand. Joint sand is applied to the surface with a stabilizer additive mixed in it. See Figure 5. It is then compacted into the joints with a plate compactor like all interlocking concrete pavement installations. After compaction and removal of all sand from the paver surface, the joints are wetted. When dry, the material in the sand stabilizes the full depth of the joint and it helps maintain interlock among the pavers. For either pre-mixed or job site mixed additives, a job site mock-up is beneficial for determining the depth of stabilization. The mock-up will determine the rate and application method of water to ensure full activation of the stabilizer. A mock-up will confirm a consistent method for uniform distribution of the additive in the sand for job site mixed additives in particular.

Prior to application, blowing or sweeping the surface clean is recommended. Use of a respirator and restricting access to the area must be addressed to comply with OSHA regulations. See Figure 6. Since water activates these products, no moisture should be present on the surface or in the joints until they are ready to be placed in the joints. Once the pavers and joint sand are compacted, the joints are full of sand, and all excess sand is removed from the surface, water is added to activate the bonding agent. The water is applied as a light, wide spray, and allowed to collect and soak into the joints (Figure 7). A narrow spray should not be used because it can dislodge sand from the joints. It is imperative to immediately remove any excess moist joint sand that inadvertently gets on the surface of the pavers. Otherwise, once it is moistened and allowed to cure on the surface, the sand will need to be removed with hot water. Some stabilizers may require removal with a wire brush or a pressure washer. Dry products will not leave a surface sheen like liquid stabilization products. This can be beneficial for a contractor or owner who needs to stabilize isolated areas through selected application of the product.

Installation, Functional, and Structural Considerations

Liquid and dry applied joint stabilizers are not a substitute for recommended installation practices. Prior to their application, all liquid stabilization products require that the joint sand be compacted and consolidated in the joints until full. Some dry stabilizers require mixing with joint sand then spreading, filling, and compacting the sand and pavers until the joints are full. Other stabilizers are premixed in bags and are ready for filling the joints. Stabilizers resist many of environmental conditions that lead to functional deterioration of the paver surface. However, stabilizers do not add to the structural (load bearing) capacity of the pavement. Therefore, structural calculations for base thickness design should not consider a joint sand stabilizer.

Sealers

Uses: Sealers reduce the intrusion of water, stains, oils and dirt into the paver surfaces. Like stabilizers, application of a sealer follows stain removal, efflorescence removal and overall surface cleaning. Sealers are used for visual and functional reasons. Sealers do not increase the structural properties of the paver nor do they impact the loading capacity of the paver system. They offer visual improvement by intensifying the paver colors. Some will add a glossy sheen or “wet” look to the pavement (see Figure 8). Other sealers offer some color enhancement and produce a low sheen, or a flat finish.

Sealers offer many functional advantages. They can protect pavers from stain penetration. They are useful around trash receptacles, fast food restaurants, driveways, other areas subject to stains, and where oil drippings are not wanted (see Figure 9).

Like stabilizers, sealers are also useful in stopping unwanted insects and weeds. Sealers can stabilize joint sand between pavers cleaned by vacuum equipment. They can help maintain the sand in the joints under high velocity water flows. Where solvents may be spilled onto pavers, elastomeric urethanes and certain water based sealers have been successfully used to prevent their penetration. Likewise, special urethane sealers have been used to seal and stabilize joint sand subject to propeller wash, jet engine fuels and exhaust in commercial and military airports.

Types of Sealers for Concrete Pavers: Table 1 lists the various types of sealer for concrete pavers. The table suggests applications and compares important properties. The sealer manufacturer or supplier should be consulted prior to using any sealer to verify that their product will perform in the environment planned for its use. Sealers not recommended for use with pavers are alkyds, esters, and polyvinyl acetates. Epoxies and silicones are generally not used on concrete pavers.

Solvent and Water Based Sealers: Like stabilizers, sealers can be either solvent or water based. Solvent based sealers consist of solids dissolved in a liquid. Solvent based products carry the dissolved solids as deep as the solvent will penetrate into the concrete paver. After the solvent evaporates, the sealer remains. Water based sealers are emulsions, or very small particles of the sealer dispersed in water.

Water based sealers penetrate concrete as far as the size of the particles will permit. After the water evaporates, typically at a slower rate than solvents, the remaining particles bond with the concrete and to each other. These particles cannot penetrate as deeply as those carried by solvents. Water based sealer curing time will vary with the temperature, wind conditions and humidity.

Silanes/Siloxanes: Silanes and siloxanes penetrate concrete well. Silanes are the simpler form that, when exposed to moisture, begin to link up to other silanes. Siloxanes do the same linking together. Both chemicals become a polymer, curing as a film in the capillaries of the concrete. A hydrophobic barrier to moisture is created, preventing moisture from entering but allowing the concrete to “breathe” or release water vapor.

Because silanes and siloxanes reduce moisture from entering the concrete, they can deter efflorescence from appearing on the surface of concrete pavers. They initially enhance colors and produce a flat, no-gloss finish on the paver surface. This makes silanes and siloxanes very suitable on exterior areas for resisting efflorescence when a glossy surface is not desired.

Silanes and siloxanes do not resist penetration of petroleum stains unless they have additives specifically for that purpose. When required, proprietary mixtures with additives can increase petroleum stain resistance. Other additives can ensure greater consistency in the color of pavers and avoid a blotchy appearance.

Silanes have smaller molecules, so they penetrate farther into the concrete than larger siloxane molecules. However, they are more volatile (tend to evaporate) until they bond to the concrete paver. Silane sealers generally require a higher percent of solids to counteract their rate of evaporation. Therefore, silanes tend to be more expensive than siloxanes.

Silanes and siloxanes are typically used as water repellents for concrete bridge decks, parking garages, and masonry walls. Their primary use for reinforced concrete structures is to prevent the ingress of chloride ions from deicing salts. This intrusion causes reinforcing steel corrosion in the concrete, and a weakened structure. Their ability to decrease intrusion of chloride materials provides additional protection of pavers subject to deicing salts or salt air, such as walks, streets, parking lots, plaza roof and parking decks. They are also useful around pool decks to minimize degradation from chlorine.

Most silane and siloxane sealers are solvent based. Certain manufacturers offer water based products as well. These products may have a very short shelf life after the silane or siloxane has been diluted with water. The user should check with the manufacturer on the useful life of the product.

Acrylics: Acrylic sealers can be solvent or water based. They enhance paver colors well and create a gloss on the surface. Acrylic sealers provide good stain resistance. Their durability depends on traffic, the quality of the acrylic and the percentage of solids content. They provide longer protection from surface wear than silanes or siloxanes.

Acrylic sealants are widely used in residential and commercial paver applications. They generally last for a few years in these applications before recoating is required. Acrylics specifically developed for concrete pavers do not yellow over time. When they become soiled or worn, pavers with acrylics can be easily cleaned and resealed without the use of extremely hazardous materials.

Acrylics should not be used on high abrasion areas such as industrial pavements or floors. Water based acrylics perform well for interior applications. They may be allowed by municipalities that regulate the release of volatile organic contents (VOCs) in the atmosphere.

Urethanes: As either solvent or water based, polyurethanes produce a high gloss and enhance the color of pavers. Aromatic urethanes should contain an ultra-violet (UV) inhibitor to reduce yellowing over time. The product label should state that the sealer is UV stable. Urethanes themselves are more resistant to chemicals than acrylics.

While aliphatic urethanes can be used for coating the surface of pavers, elastomeric (aromatic or aliphatic) urethanes should be used where the primary need is to stabilize joint sand. For airfield and gas station applications, the urethane should have a minimum elongation of 100% per ASTM D2370, Standard Test Method for Tensile Properties of Organic Coatings. Urethanes resist degradation from petroleum based products and de-icing chemicals. This makes them suitable for heavy industrial areas, as well as airfield and gas station pavements.

Urethanes cannot be rejuvenated simply by re-coating. If urethane sealers must be removed, methylene chloride or sand blasting is often necessary. Methylene chloride is a hazardous chemical, and is not acceptable for flushing into storm drains. It should not be allowed to soak into the soil. Therefore, urethane removal is best handled by professionals.

Water Based Epoxy Sealers: Water based epoxy sealers combine other types of sealers with epoxy. They cure by chemical reaction as well as by evaporation. They have very fine solids allowing them to penetrate deep into concrete while still leaving a slight sheen to enhance the color of the pavers. They generally do not change the skid resistance of the surface. When applied, water based epoxy sealers create an open surface matrix that allows the paver surface to breathe thereby reducing the risk of trapping efflorescence under the sealer should it rise to the surface. They resist most chemicals and degradation from UV radiation. These characteristics make these types of sealers suitable for high use areas such as theme parks and shopping malls. The elasticity and adhesion of these sealers make them appropriate for heavily trafficked street projects and areas subject to aggressive cleaning practices.

Sealing Procedures: All dirt, oil stains and efflorescence must be removed prior to sealing. The cleaned surface must be completely dry prior to applying most sealers. Allow at least 24 hours without moisture or surface dampness before application. The pavers may draw efflorescence to the surface, or the sealer or liquid stabilizer may whiten under any one of these conditions:

• The surface and joints are not dry
• The pavers have not had an adequate period of exposure to moisture
• There is a source of efflorescence under the pavers (i.e, in the sand, base, or soil) moving through the joint sand and/ or pavers
• The sealer is not breathable, i.e., does not allow moisture to move through to the surface of the paver and evaporate.

If the base under the pavers drains poorly, the sealer is applied to saturated sand in the joints, or is applied too thick, the sealer can become cloudy and diminish the appearance of the pavers. In this situation, the sealer must be removed or re-dissolved. Consult your sealer supplier for advice on treating this situation.

Cover and protect all surfaces and vegetation around the area to be sealed. For exterior (low-pressure) sprayed applications, the wind should be calm so that it does not cause an uneven application, or blow the sealer onto other surfaces. For many sealers, especially those with high VOC’s, wear protective clothing and mask recommended by the sealer manufacturer to protect the lungs and eyes.

Sealers can be applied with a hand roller if the area is small (under 1000 ft2 or 100 m2). For larger areas, more efficient application methods include a powered roller, or a low pressure sprayer. Sealers are often applied with a foam roller to dry pavers having clean surfaces and chamfers. However, the use of a squeegee to spread the sealer will avoid pulling joint sand out of the joints. See Figure 10.

Sealer should be spread and allowed to stand in the chamfers, soaking into the joints. Penetration into the joint sand should be at least 3/4 inch (20 mm). The excess sealer on the surface is pushed to an unsealed area with a rubber squeegee. The action of a squeegee wipes most of the sealer from the surface of the pavers while leaving some remaining in the chamfers to eventually soak into the joints. Generally only one coat is required.

For other applications, follow the sealer manufacturer’s recommendation for application and for the protective gear to be worn during the job. With some sealers that recommend two coats, the first coat is usually applied to saturation. A light second coat, if needed, can be applied for a glossy finish. Be careful not to over apply the sealers such that the surface becomes slippery when cured. For water based sealers requiring two coats, always apply the second coat while the first coat is still very tacky. Prevent all traffic from entering the area until the sealer is completely dry, typically 24 hours.

If spraying sealer on the pavers, care should be taken to prevent the spray nozzle from clogging and causing large droplets to be unevenly distributed on them. This is most important for water based sealers. This can cause a poor appearance and performance.

Sealers normally require reapplication after a period of wear and weather. The period of reapplication will depend on the use, climate, and quality of the sealer.

Safety Considerations

Adequate slip (foot) and skid (tire) resistance of concrete pavers should be maintained with properly applied joint sand stabilizer or surface sealers. See CMHA Tech Note PAV-TEC-013 – Slip and Skid Resistance of Interlocking Concrete Pavements for test methods and guidelines. See www. masonryandhardscapes.org to obtain this and all CMHA Tech Note technical bulletins. The manufacturers of stabilization and sealers should be consulted concerning slip and skid resistance performance characteristics under wet and dry conditions.

Some commercial or industrial pavement use painted pavement markings. Consult with the stabilizer and sealer manufacturers for compatibility of their materials with pavement markings. Where there are pavement markings, applications using high gloss materials should be avoided as they can increase the difficulty of reading pavement markings under certain light conditions.

Federal, state/provincial, and some municipal governments regulate building materials with high volatile organic contents (VOCs). The restrictions usually apply to solvent based sealers. The VOC level of a sealer refers to the pounds per gallon (or grams per liter) of solvent which evaporates from the sealer, excluding the water. VOCs have been regulated since they can contribute to smog. Most water based sealers comply with VOC restrictions and some solvent based products may comply as well. The user should check with the sealer supplier to verify VOC compliance in those areas that have restrictions.

Many solvent based products are combustible and emit hazardous fumes. Therefore, flame and sparks should be prevented in the area to be sealed. Never use solvent based sealers in poorly ventilated or confined areas.

Persons applying joint sand stabilizers and sealers should wear breathing and eye protection as recommended by the manufacturer, as well as protective equipment mandated by local, state/provincial, or federal safety agencies. Follow all label precautions and warnings concerning handling, storage, application, disposal of unused materials, and those required by all government agencies.

The U.S. Federal Government and Canadian Government require that all shipments of hazardous materials by common carrier must be accompanied by a Safety Data Sheet (SDS). All chemical manufacturers must supply sheets to shippers, distributors and dealers of cleaners, joint sand stabilizers, and sealers if the materials are hazardous. The SDS must accompany all shipments and be available to the purchaser on request. The SDS lists the active ingredients, compatibility and incompatibility with other materials, safety precautions and an emergency telephone number if there is a problem in shipping, handling or use. The user should refer to the SDS for this information.

Maintenance of Interlocking Concrete Pavement

Occasionally interlocking concrete pavements will require maintenance for them to deliver peak performance. Refer to Tech Note PAV-TEC-006–Operation and Maintenance Guide for Interlocking Concrete Pavement for information on preventative maintenance, identifying and remedying aesthetic and structural distresses and best practices for the disassembly and reinstatement of interlocking concrete pavement.

References

Refer to the latest published ASTM and CSA standards and CMHA Tech Notes.

1. ASTM–American Society for Testing and Materials International, Conshocken, PA. www.astm.org
2. CSA–Canadian Standards Association, Rexdale, ON. www. csagroup.org
3. CMHA-Concrete Masonry and Hardscapes Association, Herndon, VA. www.MasonryandHardscapes.org
4. Kuenning, W., Removing Stains from Concrete, The Aberdeen Group, Addison, Illinois, 1993.
5. Madrid, G. G., et al., “Water Infiltration through Concrete Block Pavements up to 26 Years Old,” in Proceedings of the 7th International Conference on Concrete Block Paving, Concrete Manufacturers Association, South Africa, 2003.
6. Emery, J. A., Stabilization of Jointing Sand in Block Paving, ASCE Journal of Transportation Engineering, Vol. 119, No.1 January/February, 1993, American Society of Civil Engineers, New York, pp. 142-148.
7. Thorp, E., “Protection of Concrete with Sealers, Coatings and Membranes,” Concrete Repair Bulletin, March/April 1993, International Concrete Repair Institute, Des Plaines, Illinois, pp. 4 ff.
8. Cady, P.D., “Sealers for Portland Cement Concrete Highway Facilities,” Synthesis of Highway Practice 209, National Cooperative Highway Research Program, Transportation Research Board, National Academy Press, Washington, D.C., 1994.