Paving the way – Construction (Part 4)

The basic function of residential pavements, such as driveways, paths and patios, is to provide safe and easy access onto or around a property. Concrete is typically used to not only provide a durable paving surface (sloped, to provide surface water run-off), but one which can also incorporate a wide range of decorative finishes to complement the design and landscaping of the residence.

While creating a concrete pavement is relatively straightforward, there are a number of design and construction aspects that need to be considered in order to produce a finished product that satisfies the functional and aesthetic requirements of the homeowners.

Isolation joints

Figure 1, as would be used against the foundations of an adjoining structure for instance, should not impede any relative movement. This may be horizontal, vertical or both and may include rotation. While movement from concrete drying shrinkage will normally cause the joint to open with time, temperature changes may give rise to joint-closing movements.

Control joints

The control joint in Figure 2 (on next page) can be made by:

• Saw-cutting a groove with a conventional concrete cutting saw 12-18 hours after finishing.
• Green-cutting a groove with a Soff-Cut saw following finishing, when the concrete has hardened sufficiently to prevent unraveling.

Or alternatively:

• Inserting a pre-moulded strip into the concrete as it is being placed.
• Use of a grooving tool immediately after the concrete has been placed.

Note: If joints are saw cut, these should be installed prior to shrinkage cracking occurring.

As a guide, saw cuts should be made not more than 12 hours after finishing of the slab if temperatures exceed 25°C, and not more than 16 to 18 hours after finishing of the slab for lower temperatures.

To avoid delays, green-cutting (the same day) is possible using a Soff-Cut saw. The surface should be thoroughly cleaned after cutting.

If joints are wet-formed by scoring the plastic concrete with an edging tool (tooled joint), ensure that the groove does not fill with cement slurry and render the joint less effective.

Free movement joints

For free movement joints, the mesh should be terminated each side of the joint. To allow some tolerance in the location of the saw cut, crack inducer or tooled joint, cut the ends of the mesh wires at least 50 mm clear of the proposed joint location (Figure 3).

Construction joints

A construction joint Figure 4 is used to accommodate an unplanned break in concrete placement. The joint should be formed to allow adequate compaction and finishing of the concrete along the edge. Once the concrete has hardened, the formwork is removed, the edge roughened to provide aggregate interlock across the joint and the new concrete placed against the existing edge.

About CCANZ

This article contains information from CCANZ’s Information Bulletin 80 Residential Concrete Driveways and Paths, which provides guidance on the planning, design, construction, maintenance and specification aspects that need to be considered to ensure a successful concrete paving project. Content from Standards New Zealand in this bulletin has been reproduced by CCANZ with permission from Standards New Zealand under licence 000997. Any New Zealand Standard referred to in this bulletin can be purchased from Standards New Zealand by telephoning 0800 782 632 or visiting www.standards.co.nz

CCANZ would also like to thank Cement Concrete Aggregates Australia (CCAA) for their assistance in producing the bulletin. To download the full Bulletin visit the CCANZ website – www.ccanz.org.nz