Modular construction techniques are some of the fastest growing practices used in infrastructure projects. Roads & Infrastructure Magazine explores why the processes have become so popular.
Many infrastructure companies take advantage of the ability to construct elements offsite to improve how projects are delivered.
Mehrdad Arashpour from Monash University’s Department of Civil Engineering says this method of construction provides significant benefits when it comes to maximising speed and safety and minimising disruption.
He says that this is what made prefabricated construction so attractive to the Victorian Government as part of Melbourne’s Level Crossing Removal Project.
The project’s aim was to remove nine level crossings between a stretch of railway between the south-eastern suburbs of Caulfield and Dandenong. In 2016, the state government announced that they would be using ‘an innovative and modern design’ that would be constructed using pre-fabricated segments to build a new elevated rail system over one of Melbourne’s busiest train lines while it continued to run.
Dr. Arashpour says the only feasible option in the project was to use prefabricated construction elements to maintain normal operations of the metropolitan railway, which sees hundreds of thousands of passengers every week.
“Any interruptions to such a busy rail line would be very problematic, both socially and economically. In this situation, there was a need for minimum site disturbances which using prefabricated concrete beams could achieve,” he says.
“Precast beam segments had been created offsite and were trucked in before being assembled and installed with a gantry crane. This meant any safety risks for the construction of the elevated rail were redirected towards the manufacturing plants. These are controlled environments, meaning there is much less that can go wrong when it comes to safety.”
The speed of the construction was a significant factor for the government as it enters an election year. The Victorian Government announced in 2016 it would remove nine level crossings and that the five new stations would be operational by 2018.
“The election created a hard deadline for this project, meaning the project needed to be completed very quickly. Additionally, the longer a project takes, the more unexpected costs from inflation, labour costs and the lack of revenue from the completed project can add up,” Dr. Arashpour says.
“Precast segments also benefit from being manufactured in a factory environment, avoiding the complications that can arise on a construction worksite. For example, there is little risk of bad weather interrupting production and creating a delay.
“It also means that the production of the materials is more predictable when it comes to the costs.”
He says in a manufacturing environment processes can be automated so the material can be used more optimally. This means less waste is created and modern materials can be used to ensure the optimal servicability.
“There are also fewer labour elements necessary for constructing a project. For instance, there’s no need for expert carpenters and other tradesmen in the construction of the materials onsite. This is a significant benefit when it comes to projects in congested or remote areas,” Dr. Arashpour says.
“In remote or regional areas where there may not be enough specialised trade contractors, prefabrication of elements is the only viable option.”
Dr. Arashpour says that the future of infrastructure construction could be in the form of prefabricated construction, thanks to time and money saving manufacturing techniques.
“Using prefabricated and modular construction techniques are now very popular, especially in bridges. In most concrete or steel truss bridges, the majority of elements are now made off site.”
Building with precast
The practise of using precast materials in construction began shortly after World War II, where it was used to build houses quickly. In the following decades, the process has become more advanced and can be used for a variety of construction situations.
“Because precast is manufactured away from the site, it can be cast while ground works are being prepared. Delivery can be just in time and in accordance with a project’s schedule, resulting in continuous uninterrupted onsite erection of elements,” she says.
“Reducing site congestion by avoiding the need to cast huge elements onsite, precast offers faster construction, with no materials deliveries, no formwork, no need to set up expensive stressing beds and no post-tensioning.
“This total saving in time equates to lower interest paid on construction finance, earlier commissioning of the structure and a quicker return on the owner’s investment.”
She says some of the reasons precast construction has become so popular are the material’s durability, strength and spanning capacity in the case of flooring and bridges.
Additionally, she says that precast is low maintenance, with a variety of aesthetic finishes that can be applied to civil products like bridge beams, retaining walls, arches and noise walls, to commercial construction products like walling.
“These days almost any colour, pattern, shape and texture can be achieved,” she says.
“The more traditional finishes such as sandblasting or polishing are of course still available, but so are some of the newer finishes like staining, which offers myriad colours and a very low maintenance result. There are also products that will protect structures from being soiled by pollution.”
Precast elements also tick the box when it comes to social, economic and environmental benefits, according to Ms. Bachmann.
“There are fewer disruptions to neighbouring properties, which is especially important in residential areas. As there are less deliveries and activities being performed onsite, there’s also less dust, noise and traffic,” she says.
“The high quality of the precast elements means that structures will last for longer and a building’s energy cost can also be reduced.”
Concrete strengths used in the factory can range from 35 to 60 megapascals and can be both conventionally reinforced and use prestressed elements, which Ms. Bachmann says provide higher quality and precision compared to casting onsite
“With the majority of a building’s carbon emissions occurring over its lifespan, precast can offer energy savings that will benefit the environment in the long run. When a building is well designed, a precast building can perform exceptionally well from a thermal perspective and deliver significant energy savings,” she says.
Ms. Bachmann says precast materials have been used in major infrastructure projects around Australia, pointing to their use on the Mitchell Freeway extension in Western Australia.
Precast concrete manufacturer and National Precast member PERMAcast, made a multi-million-dollar contribution to the major road project. It manufactured the beams required for the construction of four bridges as part of the project.
The Mitchell Freeway project required 54 beams of varying sizes, with the largest being 25 metres-long, 5.5 metres-wide and weighing 100 tonnes. To accommodate the public rail network, which had to be shut down temporarily, many of the beams were installed overnight.
The company had no room for error and was required to adhere to strict curfews, transporting the beams 80 kilometres while being escorted by special hydraulic trailers.
Alberto Ferraro, PERMAcast’s Managing Director, says there was a lot of pressure to meet delivery timelines.
“The bridge beams are designed to last at least 100 years and we had to ensure they are produced to meet that expectation. We know we’ve achieved that, which is extremely satisfying.”
Ms. Bachmann says the importance of durability when it comes to the civil environment can’t be understated.
“Nobody wants bridges that don’t last their intended lifespan or begin to crack during a structure’s life. Being manufactured by skilled staff, using advanced concrete mixes and curing methods, plus being subjected to strict quality testing regimes, precast can guarantee a specified strength, quality and durability,” she says.