Maintenance and repair of pavers
By Brian Burton
|In some cases, a re-application of joint sand after power washing and cleaning is recommended.|
Small element segmental paving units have been used to construct durable surfaces for roadways for over 5,000 years using a variety of materials such as natural stone setts, wooden blocks and clay bricks. Some Roman roads built in this manner were so well designed and constructed that they are still in serviceable condition today, and could easily be used — except for the fact that they are more valuable as tourist attractions.
Segmental ICPs, as we know them today, were developed in the Netherlands in the 50s as a replacement for clay bricks, which were frequently used to pave roads and streets. The long established tradition of segmental paving in Europe resulted in tremendous growth in the industry and quickly established ICPs with design engineers. Currently there are over 500 million m2 installed annually around the world.
According to Robert Burak, P.Eng, director of engineering for the Interlocking Concrete Pavement Institute (ICPI), ICPs can accommodate constant traffic and large loads over long periods without cracking or deformation. The pavement typically consists of pre-cast concrete pavers laid to a prescribed pattern over a thin layer of bedding sand and a well-drained, compacted aggregate base. ICPs are typically the size of a house brick, approximately 200 x 100 mm in plane and 80 mm in thickness for structural pavements and 60 mm for pedestrian areas not subject to traffic. The ICPI recommends an aggregate base thickness of 100 mm for pedestrian areas over well-drained soils, 150 mm for residential driveways and 200 to 250 mm for parking lots or residential streets.
They are mass-produced using machinery that applies a combination of vibration and high pressure to a zero slump low water-cement ratio concrete mix. The resulting pavers have uniform dimensions and exhibit high compressive strength, usually in excess of 50 MPa. ICPs have been used in many residential, industrial and commercial applications including driveways, parking lots, patios, cart paths, airports, ports and factories.
Routine visual inspection
The arrival of the first signs of spring is the perfect time to take the time to check your ICP installations. You will want to pay particular attention to chewing gum residuals and oil stains, which can be removed with some of the newer proprietary cleaning products. As a rule, the longer these stains are left in place, the harder they are to remove. Power washing of ICPs in prominent locations definitely improves their appearance. Here are some pointers on what to look for when inspecting ICP installations, and how to make repairs where required.
It is a recommended practice to conduct a routine visual inspection of ICPs once a year in the spring to identify any ICP units that may have been damaged or displaced. (Unlike conventional pavements, stained or damaged ICPs can be replaced.) The joints between the pavers should be inspected to determine if any sand has been lost. Joints with low or no sand should be topped up with bedding sand and swept clean. Cleaning and sealing will discourage ants and weed growth in the joints and enhance the colour of the surface. It is a great way to add new life to a refurbished area.
Controlling moss, lichens and algae
Under most conditions moss, lichens, and algae should not grow on ICPs unless the area is heavily shaded. If such growth does occur, the area should be treated with a weed killer, applied in accordance with the manufacturer's instructions. Such products normally take several days to eliminate the problem and are most effective when applied during a spell of dry weather. These products are also more useful if any thick growths are scraped off first and herbicide is then applied to the surface. Most treatments leave a residue to discourage the re-growth of the moss and algae, but this will only be of limited value if the environmental conditions are such that the pavers remain damp and in the shade.
Efflorescence is a temporary phenomenon that occurs naturally (to a varying extent) on all products that contain cement. It usually appears in the form of a white deposit on the surface of the paver, which often shows up in the first or second season of service. (This thin film can lighten the surface colour of the paver.)
Efflorescence is caused when soluble salts within the concrete evaporate and deposit on the surface or when the concrete reaction components (calcium hydroxide) react with the atmosphere to produce the white film (calcium carbonate). The efflorescence crystals, due to their nature, are not visible when wet but become visible again as the crystals dry out. Any concrete product is generally somewhat more susceptible to efflorescence under damp conditions as the moisture aids the migration of the soluble salts to the surface of the paver. However, efflorescence does not have any effect on the structural integrity or durability of ICPs.
Efflorescence is temporary and will disappear in time as a result of normal weathering. It can be removed chemically by using an acid washing agent (diluted hydrochloric acid). In applying the product, the pavers should be thoroughly soaked first with clean water. After soaking the pavers apply the commercial acid wash (available from most building suppliers), according to the manufacturers' instructions. The best efflorescence cleaners are those specifically made for ICPs. These cleaners are diluted to the appropriate strength.
When a cleaner with acid is applied, there will be some frothing or effervescence. After this has finished, the entire paver surface should be rinsed thoroughly with clean water, taking care to dispose of the runoff safely. In the vast majority of cases, one treatment should be all that is required. Be sure to follow all label directions.
Professional cleaning methods
Professional cleaning of ICPs may be required on a periodic basis in some heavily trafficked areas or prominent entrance locations. For most jobs, a professional company experienced in the use of cleaners and spray equipment should handle cleaning. These companies typically use a pressure washer and an applicator to apply efflorescence cleaner (when needed).
A high-pressure sprayer typically applies cleaner and water between 600 and 2,000 psi (4.1 and 13.8 MPa), and at a rate between 22 and 45 litres per minute. 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 influence 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.
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 and then rinsed away with a high-pressure sprayer. The final rinse should be with water only.
For small areas, such as in residential patios, walks or small driveways, an adequate cleaning job can be achieved without this equipment. First, the pavers should scrubbed to remove dirt and efflorescence, and 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. Brushes with plastic bristles are acceptable. This method of cleaning is for do-it-yourselfers who wish to re-furbish 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.
|The contractor reinstalls concrete pavers in an area where bedding sand was lost due to heavy rainfall.|
When an ICP is installed according to the installation procedures recommended by the ICPI, there will be little need for repair. Like any pavement however, there are times when repair is required. The difference with an ICP, however, is that the repairs are done quickly and with the least impact on your maintenance budget.
Pavements in Canada are particularly susceptible to the combined effects of frequent freeze-thaw cycles and moisture. This, combined with repetitive loads from vehicular traffic, over time, can result in an ICP exhibiting noticeable settlement of the base, bedding sand and pavers.
A common problem is settlement of individual pavers or groups of pavers near curbs, site fixtures, walls, or at locations where pavers meet other surfacing materials. Settlement is often due to insufficient compaction of base materials. This is often the case in confined areas that are difficult to reach with mechanized compaction equipment during installation.
Settlement can also occur as a result of loss of bedding sand or base materials as a result of insufficient drainage. Settlement can also occur near downspouts where water flows directly on to the pavers during rainstorms. Fortunately, this is not a permanent defect, and can be rectified.
To repair settlement, the shifted paving units (and those in close proximity) must be removed and set aside for re-installment. If the settlement is minor, say fewer than 10 mm, additional bedding sand can be installed, the pavers reinstated at slightly higher elevations than their neighbours and compacted level with the pavement surface. If settlement is greater than 10 mm, then remove the bedding sand; fill the depression with base material such as (MTO Granular A) and compact. Replace the bedding sand and pavers as previously described.
When there are many cut pavers to re-instate, it is a good idea to number the pavers with chalk prior to removal to facilitate re-installment. +When re-instating pavers, keep the joint between pavers tight (2 to 4 mm). After installing the pavers and compacting them, fill the joints with sand and compact the pavers again.
Replacement of damaged pavers
Although cracked or chipped pavers are rare occurrences, accidental breakage occurs occasionally. One of the benefits of ICPs is the ability to remove individual units and replace them with new ones. At the completion of the initial project, the contractor should leave extra pavers at the site for this purpose, thereby avoiding any noticeable variation in colour. Slight variations in colour may occur from traffic-borne dirt on surrounding pavers.
Removal can be accomplished by carefully wedging individual pavers out of position using hand tools such as a metal pry bar or screwdriver. Special tools are now available to remove pavers. Removal can be made easier by removing as much joint sand as possible with a putty knife and/or shop vacuum and wetting the joint sand. Begin prying on the short ends of the paver. The paver will rise a small distance with each pry. When it rises high enough, grasp the unit and pull it free. Once the first paver is removed, additional units can be easily removed if required. In some cases, the stubborn pavers may need to be broken with a cold chisel and maul. Always wear protective eye goggles during this procedure.
Weed growth between pavers
Should weeds appear, it might be due to excessive space between pavers. The widened joints may be from lack of a stable edge restraint or loss of bedding or joint sand. When separation occurs and joint spaces between pavers enlarge over time, soil can enter. This process creates conditions that can support weed growth. Although weed growth can be controlled by application of herbicides, this maintenance activity will have to be repeated unless the joints widths are tight, soil between the pavers is removed and replaced with joint sand, and a sealer is applied to the joints. An ounce of prevention creates a pound of cure: stabilizing the joint sand with a sealer upon completion of the installation is the best measure for preventing weed growth. Always use sealers and joint sand stabilization materials that are specifically recommended for ICPs.
Brian Burton is a Certified Instructor for the ICPI Certification Program and is a member of the Standing Committee for Technical Evaluations for the Canadian Construction Materials Commission (CCMC). He is also responsible for development of Corporate Sponsorships for the Communities in Bloom program.
For further information on the Interlocking Concrete Pavement Institute (ICPI) or for a list of ICPI members, call the ICPI at (202) 712-9036, or write to the ICPI, P.O. Box, 23053, 55 Ontario Street, Milton Ontario, L9T 4M0. The E-mail address is ICPI@bostromdc.com and the website is www.icpi.org/ICPI