Here’s the science behind 3D printing in construction

A mock-up of 3D printers building a bridge in Amsterdam. Image: MX3D.

It’s often claimed that 3D printing – known in the trade as “additive manufacturing” – will change the way we live. Most recently, a team from Eindhoven University of Technology announced plans to build the “world’s first” habitable 3D printed houses. But it’s one thing to build small, prototype homes in a park – it’s quite another to successfully use additive manufacturing for large scale projects in the construction sector.

Additive manufacturing uses a combination of materials science, architecture and design, computation and robotics. Yet in some ways, it’s not as futuristic as it sounds. The simple approach of layer-wise construction – where building materials are layered on top of each other to create a facade – has already been practised for a long time in the construction sector, for example in conventional brick layering techniques.

The true novelty of additive manufacturing lies in its ability to combine new, highly efficient and sustainable materials with architectural design software and robotic technology, to automate and improve processes that have already been proven manually. In this sense, additive manufacturing holds many potentially groundbreaking benefits for the construction sector.

3D printing can produce up to 30 per cent less material waste, use less energy and fewer resources, enable in-situ production (which in turn cuts transport costs), grant greater architectural freedom and generate fewer CO₂ emissions over the entire lifecycle of the product.

Printable feedstocks

But there is still some way to go before additive manufacturing technology can deliver on its potential. There are several different components of additive manufacturing, each of which must be developed and refined before the process can be successfully used in large-scale construction.


One component is printable feedstocks – the materials which are actually “printed” to create the final product. There are many types of printable feedstock, but the most relevant one for large scale construction is concrete. Printable feedstocks are typically made from a combination of bulk materials – such as soil, sand, crushed stone, clay and recycled materials – mixed with a binder such as Portland cement, fly ash or polymers, as well as other additives and chemical agents to allow the concrete to set faster and maintain its shape, so that the layers can be deposited rapidly.

In a project I am currently working on at Brunel University, we are focusing on producing a printable cement feedstock. To create materials for 3D printed constructions, scientists must carefully control the setting time of the paste, the stability of first few layers and the bonding between the layers. The behaviour of the materials must be thoroughly investigated under a range of conditions, to achieve a robust structure which can take load.

The combination of cement, sand and other additives must be just right, so that the feedstocks don’t set while still in the printer, and don’t stay wet for too long once they have been deposited to form a structure. Different grades of feedstock need to be formulated and developed, so that this technology can be used to build a range of different structural elements, such as load-bearing and large-scale building blocks.

Building blocks

Another component is the printer, which must have a powerful pump to suit the scale of manufacturing in the construction industry. The pressure and flow rate of the printer must be trialled with different types of feedstocks. The speed and the size of the printer is key to achieving a good print quality: smooth surface, square edges and a consistent width and height for each layer.

How quickly the feedstock materials are deposited – typically measured in centimetres per hour – can speed up or slow down construction. Decreasing the setting time of the feedstock means that the printer can work faster – but it also puts the feedstock at risk of hardening inside the printer system. The printing system should be optimised to continuously deliver the feedstock materials at a constant rate, so that the layers can fuse together evenly.

The geometry of the structures produced is the final piece of the puzzle, when it comes to using 3D printing in construction. When the printer and the feedstock have been properly set up, they will be able to produce full-size building blocks with a smart geometry which can take load without reinforcements. The shape stability of the truss-like filaments in these blocks is an essential part of printing, which provides strength and stiffness to the printed objects.

The ConversationThis three-pronged approach to adapting additive manufacturing for construction could revolutionise the industry within the next ten to 15 years. But before that can happen, scientists need to fine tune the mix ratios for the feedstocks, and refine a printing system which can cope with the rapid manufacturing of building blocks. Only then can the potential of 3D printing be harnessed to build faster, and more sustainably, than ever before.

Seyed Ghaffar, Assistant Professor in Civil Engineering and Environmental Materials, Brunel University London.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

The Tory manifesto promises to both increase AND decrease the rate of housebuilding

Housing secretary Robert Jenrick. Image: Getty.

In his 2014 Mansion House speech, the then-chancellor George Osborne expressed with uncharacteristic honesty the motives at the heart of how the Conservatives see British housing politics: “The British people want our homes to go up in value, but also remain affordable; and we want more homes built, just not next to us.”

Five years later these contradictions remain unreconciled and present in their manifesto, which contains two different and contradictory – but clearly extensively targeted and focus-grouped – sets of policies.

The Conservatives have two housing targets. The first is to make significant progress to hitting “our target of 300,000 houses built a year by the mid-2020s”. The second is their aim to build “at least a million new homes” during the next parliament, which implies a target of 200,000 homes a year. This is not only 100,000 lower than their initial target but also lower than the current rate of housebuilding: 213,660 new homes a year. They have therefore implied at separate points in the same manifesto that they intend to simultaneously increase and decrease the rate of housebuilding.  

There are similar conflicts in their approach to planning. They intend to make the “planning system simpler” while simultaneously aiming to introduce community-led design standards for development and planning obligations to provide infrastructure for the local community.

None of this is unsurprising, The Tories don’t seem to know if they want to build more houses or not – so of course they don’t know whether they wish to make it easier or harder to do so.  

Politicians like obfuscation on housing policy to placate NIMBY voters. Take for example prospective Conservative MP and ‘environmentalist’ Zac Goldsmith’s crusade to save treasured local car parks. The manifesto can equally be accused of pandering to NIMBY instincts, protecting their shire voters from all housing, including ones they might actually need or want, by promising to protect the greenbelt.  

Instead, Conservatives intend to foist development on Labour-leaning inner-city communities and prioritising brownfield development and “urban regeneration”. This requires massive, infeasible increases in proposed density on brownfield sites – and research by Shelter has shown there are simply not enough brownfield sites in cities like London. Consequently, it is not clear how such a policy can co-exist with giving these inner-city communities rights on local design. Perhaps they intend to square that circle through wholesale adoption of YIMBY proposals to let residents on each street opt to pick a design code and the right to turn their two-storey semi-detached suburban houses into a more walkable, prettier street of five-storey terraces or mansion blocks. If so, they have not spelt that out. 

Many complain of NIMBYism at a local level and its toxic effects on housing affordability. But NIMBYism at the national level – central government desire to restrict housebuilding to make house prices rise – is the unspoken elephant in the room. After all, 63 per cent of UK voters are homeowners and price rises caused by a housing shortage are hardly unpopular with them. 


There is anecdotal evidence that protecting or inflating the value of homeowners’ assets is central to Conservative strategy. When George Osborne was criticised for the inflation his help to buy policy caused within the housing market, he allegedly told the Cabinet: “Hopefully we will get a little housing boom, and everyone will be happy as property values go up”. More recently Luke Barratt of Inside Housing noted that most Conservatives he spoke to at the 2018 party conference were scared “they’d be punished by their traditional voters if the values of their homes were to fall”. He was told by a Conservative activist at the conference that, “If you build too many houses, you get a Labour government”.

But the senior figures in the Conservative Party are painfully aware that the continuing housing shortage presents major long-term problems for the Party. As the manifesto itself acknowledges: “For the UK to unleash its potential, young people need the security of knowing that homeownership is within their reach.” Perpetual increases in house prices are incompatible with this goal. The problem has greatly contributed to the Conservatives’ severe unpopularity with a younger generation priced out of decent accommodation. 

Equally, there is increasing evidence that ‘gains’ from rising house prices are disproportionately concentrated in the south of England.  The differences in housing costs between regions greatly reduce labour mobility, suppressing wage growth in the north and midlands, which in turn leads to greater regional inequality. The policy of coddling southern homeowners at the expense of the economic well-being of other regions is a major long-term stumbling block to Conservative desires to make inroads into the ‘red wall’ of Leave-voting labour seats outside the south.

Before dealing with the issue of where housing should go, you must decide whether you want to build enough housing to reduce the housing crisis. On this issue, the Conservative response is, “Perhaps”. In contrast, even though they may not know where to put the necessary housing, the Labour Party at least has a desire in the abstract to deal with the crisis, even if the will to fix it, in reality, remains to be seen. 

Ultimately the Conservative Party seems to want to pay lip service to the housing crisis without stopping the ever-upward march of prices, underpinned by a needless shortage. Osborne’s dilemma – that the will of much of his party’s voter base clashes with the need to provide adequate housing – remains at the heart of Conservative housing policy. The Conservatives continue to hesitate, which is of little comfort to those who suffer because of a needless and immoral housing shortage.

Sam Watling is the director of Brighton Yimby, a group which aims to solve Brighton’s housing crisis while maintaining the character of the Sussex countryside.