Paving performance can be influenced by a combination of factors, including installation methods, weather conditions, placement of control and expansion joints, and interaction with the service environment. In this article, we’ll discuss methods to safeguard against cracking and paver failure.
Did you know:
Concrete expands by 10-15 micrometres per °C for every linear metre. That means that a 10m paved area could expand by up to 6.75mm on a 45°C day!
This thermal expansion of concrete causes movement in the paving, which, if not properly planned for, can lead to the development of unsightly cracks. So what are the best ways to prepare for this?
Adequate jointing of paving
The inclusion of control joints and expansion joints is a key consideration that should be given thought as early as the design phase, especially for large areas of paving. The purpose of these joints is to allow flexibility for movement within the concrete paving and base slab.
Control Joints
Control joints are man-made weakened areas in the concrete slab. Saw cuts are made vertically and horizontally into the top quarter of the slab, inducing cracks to form directly beneath.
It is important for control joints to be tooled into the concrete as soon as the slab has been placed. The longer that sawing is delayed, the higher the possibility of cracks to form naturally within the concrete. Unfortunately, including sawcuts after cracks have already formed does not fix the problem, and it is likely for the cracks to continue expanding.
Expansion joints
Well-planned paving areas will have continuous horizontal and vertical lines that occur at intervals throughout the paving. These are expansion joints, which accommodate independent movement between adjoining paving areas. Spacing of expansion joints should be engineered and properly constructed. Without these joints, the restrained movement or expansion of the paving would be likely to cause cracking.
A flexible material, such as grey foam, should be used to infill expansion joints, not cementitious grout which tends to harden and become brittle. It is also important that expansion joints extend beyond the grout line and align with the sawcut control joints in the concrete base slab.
Storing and handling of paving
Every care is taken when packaging SVC pavers onto pallets, and the pavers are carefully shrink-wrapped and sealed for protection during transportation. Once the pavers are on-site, it is important to exhibit the same level of care when moving pavers around by hand or by forklift. Slow, smooth movements and careful placement will minimise damage from high impact loads.
Remember that the pavers at the bottom of a pallet can have up to one tonne of weight above them!
Paver laying techniques
We generally recommend that pavers are laid on a concrete base. This should be constructed as an engineered slab, meaning that the concrete is appropriately reinforced, laid on a well compacted base and installed with a waterproofing membrane. A strong, stable foundation will reduce the likelihood of any movement or failure transferring to the pavers above.
When laying pavers, proper care must be taken to prevent potential damage. Pavers laid carelessly may result in micro cracks, invisible to the naked eye, which later become larger, visible cracks.
Particularly when laying large format or rectangular paving, it is necessary to handle the pavers carefully to avoid impact loads. These loads can occur when placing, or when tamping down at either end with a rubber mallet.
Summary
Providing that pavers are sound before laying, cracks in paving can be avoided by good design planning and proper handling during installation. Otherwise, cracking can generally be attributed to a sub-standard paving base, inadequate jointing of the base or paving, or issues relating to laying techniques.
