There are a considerable number of technical, commercial and environmental advantages of using PFA as a fill material over naturally occurring materials.
PFA is lightweight in comparison to other fill materials which brings savings in material and transport costs and reduces settlement in underlining soils. When properly compacted PFA settles less than 1% during the construction period, with no long-term settlement.
The self-hardening properties of PFA offer considerable strength advantages over natural clay and granular materials. These can exceed the design strength immediately after compaction, which means simple shallow trenches have a reduced need for shoring.
PFA is usually placed in accordance with the Department of Transport Specification for Highway Works that classifies it as a cohesive material for general fill (type 2E) or as a structural fill (type 7B).
The moisture content of PFA is an important factor of achieving the desired compaction and density values. Providing the PFA has been adequately compacted there are no long-term settlement problems.
The low permeability of PFA makes it a flexible substitute material that contractors are able to use when adverse weather conditions occur A key benefit being that this assists in surface water run-off during placing and compaction, which ensures construction work can continue.
Quick drainage of surface can be further enhanced by laying each layer to falls. And where PFA is laid and finished level even after heavy rain the surface will recover quickly again, allowing work to restart sooner than is the case with other fill materials.
In addition, with proper profiling PFA fill can be trafficked in all weathers, making it a versatile option that avoids potential delays in site delivery.