Paver Surface Maintenance Guide

Surface Maintenance

It may seen from Table 1 that, where chipped, cracked or worn pavers significantly affect the appearance of the surface, they can be removed and replaced. In this respect it is emphasised that individual cracked pavers seldom impair the structural integrity of a segmental pavement even though the aesthetics may be adversely affected.

Where pavers stand proud of the surface they must be replaced before they constitute a trip hazard. The technique of opening and re-instating segmental pavements is discussed below.

Opening and Reinstatement of Segmental Pavements

To lift an area of paving it is first necessary to remove two or three pavers from the pavement. This creates sufficient space so that levers can then be used to prise out the remaining units over the full area to be repaired. In a properly constructed pavement the initial removal of pavers is seldom easy. Special extraction tools are available for paver removal but may be ineffective unless the joints are wide or are free of sand. In many cases it is necessary to attempt to lever out a paver using tools such as screwdrivers. If the pavement is tightly laid this will often cause chipping of the pavers and a quicker solution is simply to smash one or more blocks to establish an opening in the pavement.

It is normally found that, because of weathering, wear and staining, pavers removed from a pavement will differ in appearance from those in the maintenance stockpile. For this reason, as the pavement is lifted, all undamaged pavers should be retained for later re-use. Where it is necessary to replace smashed or damaged pavers with units drawn from the maintenance stockpile it is important to blend the old and new pavers over the area being repaired to reduce the visual impact of any colour variation.

The bedding sand exerts a crucial influence on segmental pavement performance under traffic. For this reason, where it is necessary to excavate the bedding sand, it should be discarded rather than be retained for re-use, as it is likely that the sand will become contaminated or degraded during the repair process. Before removing the sand its thickness should be measured because it is important that the replacement layer be reinstated to as near the same thickness as practical. This will avoid variations in the behaviour of the pavement under traffic due to changes in the bedding sand thickness. This usually requires screeding the replacement sand to a loose thickness about 10—15% greater than the target thickness.

Joint Filling

Segmental pavements develop their structural capacity by wedging action between the individual pavers caused by traffic. The forces generated by this wedging action can only be transmitted through the pavement if the joints remain full of sand. Maintenance of the joints is therefore very important in maintaining the structural performance of segmental paving. Any loss of sand in the joints below the level of the chamfers should be promptly rectified. This is best accomplished by using dry bagged jointing sand meeting the requirements of T45 Concrete Segmental Pavements - Guide to Specifying, CMAA 1997. This sand should be brushed repeatedly across the joints until they are completely filled. Excess sand should be broomed off and the pavement should be compacted by at least 3 passes of a plate compactor. This process may need to be repeated several times until the joints are completely filled. This is best accomplished when the pavement is completely dry.

Joint Stabilisation

In areas where there is an occasional flow of water across the pavement surface and where vacuum sweepers are used, consideration should be given to stabilising the jointing sand using a sealant. Alternatively, proprietary jointing sands are available to fill the joints. These normally bind together upon wetting.

Weed Control

Best controlled by periodic applications of weedicide. Best results will often be achieved in dry weather when the pavement is dry prior to using the weedicide.

Table 1

Symptom Possible principal cause Extent Principal maintenance options

occasional cracked pavers Poor construction quality control of base layers A few individual isolated pavers Replace only if asethetics are impacted

Occasional chipped pavers Laid with too narrow joint widths individual pavers Replace ony if aesthetics are impacted.
If joints are < 2mm, lift and relay so that all joints are approx 3mm.

Worn or abraded pavers Incorrect specification, or poor quality pavers Individual or in groups Replace ony if aesthetics are impacted.
Replace with units that meet standards.

Joints have lost sand Joints were not completely filled during construction, vacuum sweepers or water jets were used or insufficient chamfers were provided on pavers Sand loss < 10mm
Sand loss > 10mm <10mm, suspend vacuum sweeping/water jetting.
>10mm, refill joints using dry jointing sand and re-compact entire surface.
Consider use of bonded jointing sand.

Weed growth in joints Windblown seeds have propagated in the jointing sand ------ Spray with herbicides

Surface is stained Normal surface conditions or insufficient routine cleaning Individual or groups of pavers Clean or replace if aesthetics are impaired.
Clean surface in situ for groups.

Surface shows efflorescence Soluble salt deposits Groups of pavers Will disappear over time with vigorous brushing or acid wash. No long term maintenance necessary.
Do not seal surface.

Structural Maintenance

Structural maintenance becomes necessary when the pavement has been trenched or where the cause of pavement distress lies either in a poor choice of paver shape, laying pattern or because of problems in the base, sub-base or sub grade of the pavement.

Trenching

In opening an area of pavement to be trenched or repaired the width of paving lifted should provide an adequate working space of at least 1 m and should extend beyond the edge of any excavation by at least two runs of pavers. Because of the horizontal forces that develop in block pavements during construction and under traffic it is good practice to insert toms and spreaders across the excavation as shown in Figure 1. These prevent the pavement creeping horizontally inwards towards the area being repaired. If this is not done it may be difficult or impossible to reinstate the pavers once repairs to the pavement substructure are complete. In restraining the pavers it is not necessary to support the entire length of pavers around the repair. Usually it is adequate to space the toms and spreaders, shown in Figure 1, at intervals of 2—3 m.

Figure 1 Use of Toms and Spreaders at an Excavation.

Concrete segmental paving is unique amongst surfacings in that repairs can be made without leaving traces of the excavation. However, to accomplish this needs care in backfilling the excavation. Where possible clay material should be discarded and the excavation should be backfilled with layers of granular material. Each layer should be not more than 150-mm thick and should be fully compacted before placing subsequent layers. Occasionally, it is advantageous to add small quantities of cement (1% to 1.5% by weight) to help reduce subsidence. A common mistake by maintenance crews is to pay insufficient attention to the finished levels of the backfill on the assumption that errors in level can be corrected by varying the bedding sand thickness. However, this is poor practice and efforts should be made to maintain the sand thickness uniform to avoid differential deformations under traffic. As noted above, fresh sand should be installed to the original thickness. This normally means screeding the sand to a loose thickness some 10 to 15 percent greater than the target thickness.

The pavement should be relaid using those pavers removed from the excavation blended with essential replacements drawn from the maintenance stockpile. Toms and spacers should be removed progressively as the reinstatement of the surface proceeds. The compaction applied to the reinstated pavers should be as heavy as practical.

In the case of major rehabilitation where the entire pavement must be reconstructed the costs of lifting the paving can be reduced by a suitable choice of paver shape. For example, where rectangular blocks are used it is possible to lift the pavers en-masse using the bucket of a front-end loader without causing significant damage to the pavers. By contrast, dentated pavers may suffer considerable damage if excavated in this manner.

Creep in the Joint Lines

Distortion or creep of the joint lines is usually caused by traffic and is most evident in the wheel paths. Unless this is allowed to progress to a point at which the pavers become loose and are able to rotate, creep is primarily a problem of aesthetics and has little effect on the structural integrity of the pavement. As a rule of thumb, creep movements of 10 mm or less can usually be ignored unless aesthetic considerations are paramount.

Creep in the joint lines can only be remedied by lifting and relaying all or part of the surface. Unless the creep movements of the joint lines are accompanied by rutting it is normally not necessary to disturb the pavement substructure. Rather, following removal of the pavers it is sufficient to loosen and re-screed the bedding sand and then re-lay and compact the pavers. Often this will need to be done kerb to kerb but, as a minimum requirement, the pavers should be removed back to areas where the joint lines remain straight

However, simply to lift and re-lay the pavers may not permanently fix the problem of creep which, especially in the wheel paths, can be caused by the choice of paver shape or laying pattern. Where the pavers have been laid in stretcher bond the problem of creep may be sometimes be corrected by lifting the pavers and relaying them in herringbone pattern. However, where rectangular or other Category C shapes according to T44 (1) and T45 (2) have been used this may prove futile in the long term. It is then usually necessary to lift and discard such pavers and to replace them with Category A shape pavers installed in herringbone bond.

Joint Pumping

Occasionally water may pump from the joints of a segmental pavement. Usually this is an indicator than the bedding sand drainage is not working correctly or has not been installed. This may also indicate the use of an inappropriate bedding sand not meeting the requirements of T45 (2) for pavers or MA44 (4) for flags. To remedy this problem normally requires the pavers or flags to be lifted so that the drainage system can be inspected and repaired. However, where the problem is minor and intermittent, consideration should be given to sealing the surface. This is discussed further in Chapter 7.

Undulating Surface

The most common cause of an undulating surface is poor control of the levels on the top of the base course leading to uneven thicknesses of bedding sand. Occasionally in pedestrian pavements, it may be possible to correct this problem by rolling the pavement with heavy pneumatic tyred rollers. More commonly it is necessary to lift the pavers, remove and discard the bedding sand and to carefully re-profile the base course to meet the tolerances set out in T45 (2) . Fresh bedding sand can then be spread and the original pavers relayed. Such techniques should only be used where there is no rutting in the pavement, i.e where there is no cause to question the structural adequacy of the base/sub-base. If rutting is present complete reconstruction of all or part of the pavement may be necessary (see Clause 5.5).

Rutting, Potholing or Extensive Surface Damage

Rutting or extensive cracking of pavers is symptomatic of inadequate support from the pavement sub-structure. If widespread, this may be the consequence of poor design, sub-standard materials or inadequate compaction. In such cases it is usually necessary to completely rebuild the affected lengths of pavement. This is beyond the scope of this Guide and reference should be made T45 (2) , MA44 (4) or other Design Guides. If the problems are localised, eg as potholes or depressions, it is often adequate merely to excavate the affected areas and to backfill these with well-compacted cement-treated granular materials and then to reinstall the pavers on fresh bedding sand. However, before implementing such relatively expensive maintenance procedures it is advisable to check that the pavement is adequately designed to resist the prevailing traffic conditions.

Symptom Possible principal cause Extent Principal maintenance options

Large areas of chipped pavers with joint widths <2mm Pavers laid with too narrow joint widths or surface was installed on under designed or poorly constructed sub structure. Groups of pavers Lift pavers, repair sub structure and relay with new pavers.
Ensure joint widths are between 2 & 5 mm

Extensive areas of cracked pavers Inadequate pavement sub-structure Groups of adjacent pavers Lift pavers, repair sub-structure and relay with new pavers

Surface has been trenched Normal service conditions ----- Check and compact trench backfill, reinstate origional pavers and compact

Joints are pumping Drainage of bedding sand is blocked or inadequate and/or incorrectly graded bedding & jointing sands were used Localised areas of distress
Widespread problem lift & relay area using origional pavers with the new bedding and jointing sand
Check and, if necessary, lift pavers, rectify drainage and/or replace bedding sand, relay origional pavers, refil joints with correctly graded or proprietary bonded jointing sand and recompact pavement.
Consider sealing pavement surface.

Joint lines are distorted horizontally Incorrect choice of paver shape or laying pattern to suit traffic Displacement <10mm
Displacement >10mm <10mm, if aesthetics are impaired lift pavers, loosen and rescreed sand, relay pavers.
>10mm, relay using pavers in herringbone pattern.

Surface shows undulations but no rutting Base course was incorrectly profiled or toleranced during construction leading to variable bedding sand thicknesses Localised areas of distress
Widespread distress Lift and relay only if aesthetics and/or riding quality is impaired.
Lift pavers, remove & discard bedding sand, reprofile base and relay original pavers.

Surface shows rutting along wheel paths Sub-structure is inadequate due to poor design, sub-standard base materials or insufficient compaction. Ruts are continuous along pavement If aesthetics or riding quality is impaired then lift pavers, remove bedding sand, repair sub structure and relay original pavers on fresh bedding sand

Symptom	Possible principal cause	Extent	Principal maintenance options
occasional cracked pavers	Poor construction quality control of base layers	A few individual isolated pavers	Replace only if asethetics are impacted
Occasional chipped pavers	Laid with too narrow joint widths	individual pavers	Replace ony if aesthetics are impacted. If joints are < 2mm, lift and relay so that all joints are approx 3mm.
Worn or abraded pavers	Incorrect specification, or poor quality pavers	Individual or in groups	Replace ony if aesthetics are impacted. Replace with units that meet standards.
Joints have lost sand	Joints were not completely filled during construction, vacuum sweepers or water jets were used or insufficient chamfers were provided on pavers	Sand loss < 10mm Sand loss > 10mm	<10mm, suspend vacuum sweeping/water jetting. >10mm, refill joints using dry jointing sand and re-compact entire surface. Consider use of bonded jointing sand.
Weed growth in joints	Windblown seeds have propagated in the jointing sand	------	Spray with herbicides
Surface is stained	Normal surface conditions or insufficient routine cleaning	Individual or groups of pavers	Clean or replace if aesthetics are impaired. Clean surface in situ for groups.
Surface shows efflorescence	Soluble salt deposits	Groups of pavers	Will disappear over time with vigorous brushing or acid wash. No long term maintenance necessary. Do not seal surface.