Expansion Joints

The use of segmental paving in walkways and roadways does not necessarily negate the use of the expansion jointing in the pavement.

 

 

There are several detailing issues which need careful consideration when designing the pavement in question, and these are as follows:

1) What size paving unit or module is to be used?

 

 

In theory, a segmental pavement does not need any gaps to be left in the pavement to allow for expansion and contradiction of the paving units themselves.

That is, any expansion and contraction that takes place due to changes in atmospheric temperature is taken up by the jointing sand in the joints between each individual paving unit. This is particularly true when dealing with each individual paving units close to or of common brick dimensions and layed correctly.

However, as the unit dimension is increased, the number of joint gaps in the pavement will decrease proportionally. For this reason special attention needs to be given to this area of pavement design.

That is, assuming a length of segmental paving of 100 metres, and adapting an average linear coefficient of expansion of the concrete units of 0.0000108 per degree of change in temperature, and assuming a 30°C change in temperature, then the linear expansion would be in the order of 100000mm x 0.0000108 x 30°C = 32.4mm.

This expansion would need to be taken up in the pavement joints.

Thus, there are situations where it is advisable to allow for expansion joints in the segmental pavement to accommodate the excessive movement that will not be fully taken up by the jointing sand in the joints.

2. The shape of the area to be paved.

In general, a large uniform rectangular area, such as a courtyard as previously illustrated, when adequately restrained on all sides by buildings, will perform adequately with no allowance for expansion jointing in the paving.

However, where a pathway may lead away from this large mass of courtyard paving (and in particular where the pathway is extensive in length and not well restrained) consideration should be given to allowing for expansion joints within the paving along the length of the pathway.

When expansion of the paving mass occurs due to changes in ambient temperature, the extensions will always occur in the direction of least resistance. That is, the paving will always give where the weakest edge restraint is, or will break an edge restraint to release stress in the pavement.

 

3. Dimensional accuracy of the selected paving.

Most specifications of segmental paving call for high dimensional tolerances in the manufacturing process to be achieved.

This good dimensional accuracy of individual paving units, can lead to 'tight' installation of the segmental paving.

Generally speaking, the paving installer will use the dimensional accuracy of the paving units themselves to locate and maintain the laying bond or pattern of the paving, and consequently lay the paving with little to no joint-gap.

Thus, jointing sand will not be able to be fully installed into the segmental paving joints and individual paving units will touch each other, causing chipping, spalling and in most cases, jacking of the pavement in question when expansion occurs due to changes in atmospheric temperatures.

It is believed that this 'tight' installation of the individual units can contribute to the phenomenon of sand jacking in segmental paving - (see section on sand jacking).

 For this reason - expansion jointing in the pavement design should receive serious consideration.

 

 

 

4.Laying technique

Maintenance of joint gaps

Because UrbanStone's paving units are manufactured with excellent dimensional accuracy, as well as near vertical sides, the maintenance of adequate joints during installation may inadvertently be overlooked.

This is again a result of the installer using the dimensional accuracy of the paving units to maintain the laying bond, as well as using the vertical sides of each paving unit to slide the adjacent unit accurately and neatly into position.

Thus, each unit is accurately placed into position instead of being gently dropped into position, as described in, "Developing the Laying Face", section 2 of, "A guide for the installation and laying of UrbanStone segmental paving units in a flexible pavement application".

Again, a zero joint gap may occur giving rise to the possible problems as described above. For this reason, the installation of expansion joints may need to be considered.