Large surface area
Choosing hardstanding means balancing capex costs with maintenance savings. Felicity Landon reports
Making a decision on the right type of hardstanding for a port or terminal may not attract the same attention as high-ticket, critical infrastructure like quay walls - but if something does goes wrong later, it can have a devastating impact on operations.
Maybe the port environment can cope with a few minor potholes, cracks or uneven patches where an airport runway clearly could not. But no one would want to consider the partial or full closure of a busy container terminal because the pavement is cracking up all over the place.
“Most port clients would not consider paying a lot of money for a surface that lasts 50 years without a problem. The risk context is very different to an airport runway; for a port, within reason, it doesn't have to be that perfect,” says Jonathan Tyler, director at Royal Haskoning DHV. A specialist in port hardstanding solutions worldwide, he says ports have to consider all angles and then try to get the balance right between designing as cheaply as possible but getting a result that meets their requirements.
“It's about durability. You need to ask questions about climate, magnitude of use, loading and repetition. If you are an operator designing a container terminal, you will have a pretty good idea as part of your business case how many units you will be handling over a period of time and what sort of equipment you will be using; that will translate into the design.
“But if you are a port authority looking to develop an area and then put it out to tender, you don't want to go and invest in very heavy duty paving for handling steel ingots and then have someone the following week wanting to sign up to use the area for trade cars, which would only need a glorified car park. For me, it is very important to explain clearly the possible impacts of the design you might make and the cost associated with it and with future maintenance.”
Climate is a factor to consider. In temperate climates, concrete, asphalt or block paving would all be appropriate, he says. “But in places subject to very low temperatures and sustained freezing, you are more likely to see concrete paving, because otherwise there are issues to do with durability. If it's an incredibly wet area, you wouldn't go for block paving because the blocks are unlikely to maintain a stable surface - you are more likely to go for concrete or asphalt.”
Geography plays another part in finding a cost-effective solution. “You try to design bearing in mind what could be a relatively local supply of high-quality aggregates,” says Mr Tyler. “When you design a quay wall and need two-metre diameter steel piles, it is what it is and they will come from the most economic place - you won't try to dream up different materials to achieve a good result. But with paving, you would see within a relatively small radius what the supply of aggregate is likely to be, then take a view on what is likely to be suitable, and factor that into the design.
“You give a lot of thought to the economics of shipping aggregates, which are a very low-value item. You are not going to ship expensive granite across oceans from Norway. By using local aggregates you might have a thicker layer to meet the needs, but overall it will be cheaper.”
Ten years ago, typically asphalt would have been the cheapest, followed by block paving and then concrete slab, he says. However, the rise in bitumen prices over the past few years, particularly compared with cement, means asphalt paving is now expensive.
“Therefore most clients have more interest in block paving and in-situ concrete paving.”
Coupled with that, he says, clients are looking to get more out of the footprint of the terminal. “For a few years, clients only wanted to stack containers four-high and perhaps push to five-high. But a lot of projects are being planned for stacking six-high and that often leads more to concrete as a more robust solution.
“It isn't to say that block paving doesn't work for those particular heights but another factor is speed of laying.”
Yes, concrete can crack - designs must allow for expansion and contraction, and extreme temperature variations can be a problem. “Correctly designed, detailed and built concrete can last a very long time. However, on the flip side, if it's incorrectly done, you can end up with something that cracks a lot. With asphalt you can reheat and reroll; with block paving, you can lift them out, do repairs and put them back. But concrete is the least tolerant of bad design and construction.”
Maintenance is crucial. The construction and expansion joints in concrete paving are usually filled with a pliable sealant. If a small stone or piece of metal gets in, the joints can lock up and cause damage. “If a stone gets stuck - take it out. If any sealant is coming adrift, repair it. If you don't walk around and do low level maintenance like this, it can quickly escalate to cracking - then the water gets underneath and undermines the foundations, and the whole thing can fairly rapidly fall apart.”
As for maintenance in the broader context, yes, it is possible to leave things until you have a few potholes and then repair them all at once, says Mr Tyler. However, there are health and safety implications - those driving equipment can suffer from vibration and impact injuries if they are constantly using rough and damaged surfaces. That can be an issue in more claims-conscious locations. On top of that, a bad pothole could cause a driver to swerve, with significant risks of accident and injury. “There are important reasons why it is a good idea to keep things well maintained,” he says.
One trend noted by Royal Haskoning DHV is that commercial clients are increasingly asking for an 'early start-up' paving design. “What that means is, can we come up with something as cheaply as possible which enables them to take heavy loadings from day one but at some point, if things ramp up as expected, we could built on top or upgrade in some way. Within this there is a particularly interesting challenge in terms of having a good dialogue with the client. If business does ramp up, the client wants to take the paving and turn it into a more robust, more durable piece.”
That could mean designing a firm early start-up layer, and later removing the top few inches and adding a more robust layer on top of the existing foundations.
Weighing up the options
Many factors dictate the type of surface used in a terminal or port, says Eugene Cheah, business development manager for energy, mining and ports at Australian construction company Fulton Hogan.
“These include the existing ground conditions, the container and cargo loadings, the traffic of the various port operations, the environment, the budget, and operational and time constraints. Because each case is so different, we put together a design, programme and costing to suit the client's needs.
How would he weigh up the options? “Concrete is durable but also the most expensive to construct and replace - and it has the longest curing time, which affects operations. Asphalt can be less expensive but risks damage from high loadings, channelised wheel paths, destruction from fuel and hydraulic spills and deformation from container corner castings.
“There are other options, though - we have a number of proprietary products that can meet the specific needs.” These include RigiPhalt, a flexible open-grade asphalt with its voids filled with a stiff cementitious grout, to provide resistance against steel castings, high static and channelised wheel loads. This surface was used by Fulton Hogan for the Port of Newcastle's common user facility. PortPhalt is a highly modified asphalt designed for deformation resistance and load spreading capacity, and was used by at Patrick's Port Botany, Sydney terminal.
Among the challenges for port surfacing, Mr Cheah lists rutting or channelisation, which normally happens either side of container stacks, at truck grids and sometimes on runways where straddles are automated.
“Hitting a rut when you are sitting on a straddle carrier a few storeys high can provide OH&S issues for the driver.”
Indentations happen when the corner castings of containers place high loadings on the pavement - a five-high stack of 25-tonne containers equates to more than 30 tonnes' loading per small casting.
As for operational disruption: “The cost of downtime to repair hardstands is very high. When no containers or equipment are being moved, then no income is being made. We are often called in to fix up pavement failure and work closely with operations to minimise downtime.
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