PAVEMENT CONSTRUCTION GUIDELINES
General
Construction of permeable concrete pavements is similar to that of concrete segmental pavements.
However, the aim with permeable pavements – in contrast to traditional pavement construction principles and methods – is to allow water to infiltrate the pavement structure, while simultaneously ensuring structural stability in terms of load bearing capacity.
Installers should adhere strictly to design and material specifications to ensure long term performance of the permeable pavement in terms of infiltration capacity, stability and treatment of contaminants.
A cross section of a typical HydroCon permeable pavement for vehicle traffic is illustrated below.
Downloads
Set out below are (1 page) downloads for key construction steps for different types of HydroSTON permeable pavement. Choose the download applicable to the proposed project – by type of pavement (pedestrian v. vehicle traffic) and whether purpose is infiltration (unlined system) or harvesting for reuse / discharge into waterways (lined system). For greater appreciation of construction requirements, HydroCon advises that the download material be read in conjunction with the construction guidelines detailed in this section.
| Pavement Type | Infiltration – Unlined System | Harvesting / Discharge – Lined System |
| Pedestrian Only | Download | |
| Vehicle Traffic | Download | Download |
Subgrade Preparation
The extent of subgrade preparation will depend on whether the pavement is to be used for pedestrian or vehicle traffic.
The subgrade should be formed to the required depth below the pavement design surface. The finished subgrade foundation for the provision of subbase and/or base course should be subject to the approval of the Project Supervisor.
Generally, it will be sufficient in non-vehicle applications to excavate and trim to levels ready to receive the sub-base and base course. The subgrade surface should be cleaned of any loose soil or rock debris.
Where infiltration is not intended, the surface should have a slight cross-fall of 1 to 2% to the sides of the pavement or to the proposed drainage positions.
For vehicle applications, it is recommended that a geotechnical investigation be undertaken. The geotechnical report will generally advise on appropriate subgrade preparation.
It is recommended that a geotechnical engineer inspect all cut subgrades to confirm or vary design CBR values, and to identify weak ground that may require remediation.
Base/Subbase
Depth of, and type of material required for, the base/subbase will vary from site to site, depending on expected loadings, level of treatment and rate of infiltration required.
The base/subbase should be constructed to the specified thickness, compaction and depth below finished pavement surface and to the design grade and crossfalls of the finished surface.
Minimum base thickness for light traffic applications should be 250 mm, while a minimum of 300mm is applicable to heavier and more frequently used traffic situations.
Material should be compacted in 100 mm layers until stable. The topmost layer should be filled to approximately 50 mm above the target height and compacted until stable. Depending on the compacted height achieved, further fill may be necessary or compacted fill removed. In both situations, material should be compacted within ± 10 mm. The level of the finished base course should be the combined thickness (mm) of the paver and bedding layer below the design surface of the pavement.
The base/subbase should be compacted to not less than 98% of standard maximum dry density according to AS 1289.5.1.1. Because of the low fines requirement, the base/subbase will be harder to compact than normal road basecourse DGB20.
Only contractors with experience in compacting low fines basecourse should be engaged for installing trafficable permeable pavements.
The finished base/subbase should be individually inspected and approved by the Project Supervisor.
Edge Restraints
Edge restraints should be constructed along the perimeter of HydroSTON paving in accordance with approved Project Drawings. See CMAA T46 and CMAA MA44 for more information.
Bedding Layer
5 mm single size crushed aggregate should be spread in a single uniform layer over the base course and screeded in a loose condition to a depth necessary to achieve a uniformly thick layer (40 mm for vehicle traffic, 30 mm for pedestrian traffic) after laying and compaction of the pavers.
The appropriate depth of screeded material may be determined by laying a trial area before construction. 5mm single size basalt layer will generally reduce by 10mm after compaction of pavers.
Surfaces of the base course and bedding layer should be uniform with no irregularities in levels. The bedding layer should not be used to compensate for irregularities in the base course, since any unevenness in the bedding layer may cause deformation of the pavement during compaction, which could later increase under traffic load.
Any screeded bedding material left exposed should be checked for depressions and levels and, where necessary, rescreeded before further pavers are laid.
Bedding material should not be screeded more than two metres in advance of the laying face at the completion of work on any day.
Unwoven geotextile may be laid between the base course and the bedding layer to improve structural stability and/or prevent migration of bedding and base course materials.
Laying Pavers
There are three main laying patterns – herringbone, stretcher and basketweave. Zig-zag running bond is a variation of stretcher pattern. Each pattern may be laid at either 90 degrees or 45 degrees to the line of edge restraints.
HydroSTON 50 pavers should be laid in either stretcher or herringbone bond. In certain residential applications, HydroSTON 50 may be laid without joints in basketweave bond.
HydroSTON 80 should be laid in standard herringbone pattern or variants such as ‘elbow interlock’.
Pavers should be placed uniformly on the screeded bedding to the nominated laying pattern. Except where specified otherwise, pavers should be placed so that they are not in direct contact with each other and should have uniform 4 mm nominal joint widths.
Pavers should be laid with string lines rather than joint spacers since string lines provide better pattern control and allow for minor variations in paver dimensions.
As concrete pavers may exhibit minor variations in colour, it is recommended that pavers be selected from 3 pallets and from different levels of each pallet. This widely recommended procedure avoids concentrations of colour and gives a more harmonious appearance.
The first row should be located next to an edge restraint or an established straight line, and laid at a suitable angle to achieve the required orientation of pavers in the completed pavement.
Consideration should be given to working off a ‘header’ row of pavers laid at a 90 degree angle to the edge restraint.
In each row, full units should be laid first. Closure units should be cut with a brick cutting power saw and fitted subsequently. Where possible, edge restraints should be adjusted to minimize cutting, as shown below.
Except where necessary to correct any minor variations occurring in the laying bond, paving units should not be hammered into position. Where adjustment of position is necessary, care should be taken to avoid premature compaction of the bedding material.
To prevent disturbance to the pavement, no construction traffic should be allowed prior to compaction and joint filling. Boards should be used for foot or barrow traffic.
Information on surface detailing, including edge restraint and edge detailing, organization of the worksite, commencement and development of the surfacing pattern and treatment of features, can be found in CMAA T46 – Concrete Segmental Pavements: Detailing Guide.
Joint Filling
Joints should be filled continuously during placement to prevent movement of pavers. Filling material should be spread over the pavement and the joints filled by brooming.
Joint filling material shall be clean dry crushed aggregate having a particle size of between 1–3 mm. The material should contain low fines. HydroCon is able to supply a specially graded 1-3 mm virgin basalt aggregate suitable for 4 mm joints.
Care should be taken to ensure that joints between individual paving units, and between paving units and edge restraints, are fully filled with joint material.
Careful attention to joint materials and clearances is important in allowing deflections of pavers under traffic load. Deflections are typically less than 2 mm for loads less than 2 kN. As deflections increase, jointing material is progressively drained by gravity during successive cycles of loading and unloading. This action can destabilize the pavement and cause deformity.
Compaction of Pavement Cover
As soon as a section of pavement has been laid and joints filled, the pavement should be swept to remove excess filling material.
The pavement should then be compacted to achieve consolidation of the bedding layer (approximately 10 mm settlement). The surface should be brought to design levels and surface profiles by not less than two passes of a high frequency, low amplitude mechanical flat plate vibrator fitted with a rubber or plastic apron to protect the paved area.
Joints should be refilled after compaction to fully close gaps in the joints.
Paving operations should be arranged so that use of the plate compactor proceeds progressively behind the laying face without undue delay, and such that compaction is completed prior to cessation of construction activity on any day. Compaction should not be attempted within 1 metre of the laying face except on completion of the pavement against an edge restraint.
Paving units, which are structurally damaged during compaction, should be removed immediately and replaced. The pavement should then be recompacted for at least 1 metre surrounding each replacement unit.
Venting
Pavement systems designed for stormwater harvesting may need to be vented to avoid variable infiltration rate performance. Fully porous HydroSTON pavers provide maximum opportunity for air outflow at the surface.
Infiltration of rainfall involves water inflow and air outflow, and possibly air compression. Laboratory studies have shown that soil air compression can lead to a substantial decrease in the rate of infiltration. When air pressure is sufficiently high, air will escape from the soil surface, thereby causing a sharp decrease in air pressure and a major increase in the rate of water infiltration.
Infiltration rate is always equal to, and controlled by, the rate of air outflow from the soil (or pavement) surface. The infiltration rate varies inversely with the air pressure ahead of the wetting front and with the ponding depth over the pavement. A minor decrease in surface water head can cause a substantial increase in infiltration rate.
Air outflow dynamics has implications for the specification of system infiltration rates and for construction, particularly when permeable pavements are to be used for stormwater harvesting.
Drainage Pipes
Where drainage pipes are required, it is recommended they be laid at a gradient of min 0.5% (a minimum fall of 5 mm per metre) towards the discharge point. Slotted drainage pipes should be wrapped in unwoven geotextile.
Subbase or base course material should be placed evenly around each side of the drainage pipes. A light compactor should be used to ensure that the material under the pipes is stable and provides an appropriate support angle.
Cover above the drainage pipe should be at least 50 mm.
Liners & Membranes
Joints of impermeable liners and geofabrics should have 300 mm overlaps and be sealed with double sided tape.
Woven geofabric should be placed over impermeable liners to prevent damage from base/subbase material. Some subgrades may necessitate placement of woven geofabric under the liner.
Tolerances
A summary of dimensional limits and tolerances in respect to construction for pavers, joint widths and base course is set out in Appendix F.
Work sizes and dimensional deviations for HydroSTON pavers are given in Appendix A.
Protection of Work
Pavement construction should be carried out following completion of general site works. During construction, the pavement area should be protected from any materials eg sediments, site debris and ingress of foreign matter from areas adjacent to the construction site, that could contaminate the pavement structure.
Pavement under construction should be fully protected from machinery and traffic of all kinds until joint filling and compaction of the pavement cover has been completed. As noted in Section 4.6.12, boards should be used for foot or barrow traffic during the construction stage.
Selection of Contractors
Permeable pavements should be installed by experienced pavement contractors, who understand the processes of stormwater treatment and infiltration and the importance of adhering strictly to design and material specifications.
Installation of the base/sub-base is a critical aspect of trafficable pavement construction. A sub-contractor should be selected with experience in permeable sub-structure installation.
Supervision
Installation should be closely supervised by a representative of the commissioning body or client. The representative (Project Supervisor) should be responsible for certifying that construction has been carried out in accordance with specifications in this document. Failure of permeable pavements is invariably due to changes in recommended substructure materials and inappropriate substructure installation.
The Project Supervisor should ensure that contractors supply for approval samples and details of bedding, joint filling, base/subbase materials proposed for use at least 28 days prior to delivery of materials or commencement of construction of the pavement. Samples of 20 kg mass should be provided unless otherwise advised by the Project Supervisor. Samples should be supported with test results from a NATA registered laboratory, confirming that the constituents comply with the requirements of this Specification. Materials used should conform to approved samples.
The Project Supervisor should certify the appropriateness of samples of base/subbase, bedding and joint filling materials submitted by the Contractor.
The Contractor should take digital photographs of each stage of construction – subgrade, base/subbase and bedding layer. Photographs should be transferred to computer disk and provided to the Project Supervisor prior to commissioning. The photographs will provide a visual record of construction, helping to verify that construction was in keeping with relevant specifications.
Opening to Traffic
As soon as practicable after compaction, light vehicle use of the pavement should be permitted to assist in “lock-up”. The effectiveness of lock-up will depend largely on workmanship in laying of the pavement cover, particularly the filling of joints.
Pavements should be inspected by contractors at regular intervals up until the expiration of the Defects Liability Period to ensure that all joints remain completely filled. Any joints not completely filled should be topped up as necessary.
