Author: Richard Bowyer - National Sales Manager, Car Parks and Infrastructure
Structural safety and integrity are a legal duty of car park owners and operators. Asphalt has long been used in the waterproofing and protection of car parks. Failed asphalt can allow water and chlorides to ingress to any underlying structure, risking long-term structural damage, and ultimately structural failure.
Once asphalt coverings show signs of deterioration, there are four key choices car park owners, operators and facility managers face to maintain structural protection.
Repair asphalt for temporary solution
Temporary or patch repairs can be appealing financially. But, using asphalt as a repair material for failed asphalt can be problematic. Patch preparation requires cutting an area with vertical sides to ensure a neat edge. The patch repair then requires a staggered joint to maintain waterproofing integrity, ideally with the stagger at the interface between the paving and mastic asphalt layers. Unfortunately, as these layers are or should be fully bonded, creation of this staggered joint is difficult and therefore not always undertaken. Shrinkage of the old and new materials places tension at the repairs’ perimeter. Here cracks can form posing further water ingress risks.
Using hot asphalt for car park repairs requires areas to close for adequate preparation and ensure the safety of car park users. Opening the surface for patch repair also introduces a risk of water ingress during the works, with a period of dry weather required. Cold mix asphalts may be suitable for short term emergency patches to mitigate health and safety risks but are only ever a very temporary solution as they will not reinstate the waterproofing.
Completely remove asphalt and replace with new asphalt
The removal of asphalt is a major undertaking given the sheer weight and volume of material. Methods of removal are dictated by the site conditions, as well as the size and ease of access for any associated plant machinery for mechanical removal. Great care must be taken to avoid the risk of damage to the substrate, before it’s removed from site via chutes, skips or similar means.
Whilst uncontaminated mastic asphalt can be recycled, the fact that the build-up comprises both mastic and paving asphalt makes this challenging. In practice, asphalt regularly goes to landfill. Extrinsic costs such as site set up, removal costs, transport, waste management and waste separation procedures all add up. Keeping the car park open is challenging in such a major construction project with considerations for pavement closures, town centre access issues, scaffolding, and site security.
The removal of any waterproofing also introduces significant risks of water ingress. In car parks that are over occupied spaces, there are added risks. If lightweight insulating concrete (Lytag or similar) is present, its form is more susceptible to damage and saturation from weather.
The works are disruptive, time consuming and lead to widespread closure of car parks areas. As the amount removed at a time is typically that which can be replaced in a day, the programme can be complex and fair-weather dependent.
Remove asphalt and replace with liquid applied membrane
There are important considerations for removing asphalt from car park decks. Firstly, the underlying, unseen substrate must be suitable for the liquid membrane and must not be lightweight insulating concrete or an unreinforced screed.
Structural loadings are calculated as part of the engineering design and specification for the car park construction. A typical 40mm asphalt build-up imposes a c.a. 100Kg/m² load. For a 5,000m² car park deck, this equates to approximately 500 tonnes.
A replacement liquid applied membrane may only weigh 10% of this resulting in a very significant reduction in dead load, requiring structural engineer advice.
Structures can exhibit elastic recovery following long term dead load removal. This movement or ‘springing’ can lead to new, unforeseen cracking in the concrete deck and a potential weakening of structural integrity. Unfortunately, these cracks can take time to form as they may be influenced by the reintroduction of live loads (car movements) to the structure.
And it’s not only weight, but also the depth of the replacement system. Now a thinner build up, the impact on levels can be significant for numerous details, upstands and thresholds as well as drainage points. To avoid potential risks and reinstatement of details etc. the asphalt should be left in situ.
Sustainable asphalt overlay with PMMA liquid coatings
Overlaying the existing in situ asphalt with technologically advanced PMMA (Polymethyl Methacrylate) liquid delivers minimal disruption and, as the life of the asphalt is extended, presents a more sustainable option. Over 2 million m² of asphalt have been overlayed with Triflex waterproofing and protection systems in the UK alone.
Overlay of asphalt offers a more sustainable option. Negating the removal and recycling of tonnes of asphalt shortens the programme of works and moves up the waste hierarchy with a solution that reuses existing materials. With no hot works, the cold solution satisfies insurers too.
Project efficiency and minimal disruption with Triflex PMMA asphalt overlay
Overlay systems based on Triflex cold PMMA resin technology rapidly cure, even at low temperatures. The waterproofing, surfacing and protection systems are seamless and self-terminating but tough and durable for longevity. The systems deliver proven outstanding waterproofing with full or partially reinforced and crack bridging options for peace of mind. The technology is also available in Triflex PMMA repair mortars enabling rapid surface preparation.
Quickly trafficable, the car park is soon back to full use, minimising interruption to users and revenue generation.
For more information, expert advice, survey, and sustainable solutions contact us today.
