Building houses in the UK is usually centred around traditional bricks and mortar which have been the backbone of the building trade for many years. When CEMEX were approached by an ambitious self-builder, Adrian Corrigall back in 2017, the challenge was set to help create a modern family home utilising one of the most commonly used materials on the planet…concrete. Usually the sole preserve of large commercial buildings, cast-in-situ concrete has rarely been the material of choice for self-builders, but Adrian’s vision was very different to that of your average self-builder. Inspired by a visit to a landmark property in Mexico designed by architects Reyes Rios + Larrain Studio and supplied by CEMEX, the idea for Concrete House was shaped by the henequen hacienda style and the intelligent fabric-first design principles.
Concrete House was designed by Graeme Laughlin of the award-winning practice RAW Architecture Workshop. His design gives Adrian, his wife Megan and their three children a functional yet stylish house, laid out in clearly defined ‘wings’ which spur off from the central kitchen and living areas. Each area of the house sits at a slightly different level, giving a greater sense of individuality and separation.
The over-riding design principles for the house were energy efficiency and use of disruptive methodologies. Adrian’s vision to create a high performing house for his family was equally matched by his willingness to challenge the accepted norms of house building in the UK, and perhaps even discover a way to revolutionise the way we think about building.
CEMEX provided early stage materials advice to Adrian and his design team to help to realise some of these goals. From the start it was clear that concrete was to be the primary material, but aside from structure, what other functions could concrete take on?
Working closely with the CEMEX Research Group in Switzerland, a range of innovative concrete solutions were proposed to Adrian and Graeme during a 2 day workshop. During this time, key principles of thermal and structural design were defined alongside an intensive materials selection process.
The design of the structure was centred around cast-in-situ ‘sandwich panels’, comprising 2 leaves of concrete with a central core of insulating material. This method of solid wall construction has a number of clear advantages including superior air-tightness and significantly reduced thermal conductivity values.
Building in this way usually requires tons of steel reinforcement, cranes to lift formwork which can take up valuable program time. In order to counter this, CEMEX proposed the use of its Resilia HP Fibre-Reinforced Self Compacting Concrete for the structural walls and horizontal elements. Selecting a high-performance fibre-reinforced concrete allowed Adrian’s design team to significantly reduce the amount of steel reinforcement, up to 60% less than in the original design. Resilia HP is not only a high strength product, it is also highly ductile, allowing for thinner sections to be cast. This design choice also had an added benefit in speeding up the cycle time between casting of the walls, as there was very little steel to detail and fix. Being a self-compacting concrete (SCC) also meant that the material could be placed into the forms with minimal intervention from the contractor, allowing them to pour each element quicker and more efficiently.
It is widely accepted that concrete performs equally as well as a thermal envelope, providing a great natural method of keeping houses at an even temperature, regardless of the external temperature. But even the most efficient houses can suffer from heat loss at key structural junctions. Following a thorough thermal modelling process assisted by CEMEX Research Group, some key areas of the structure were identified as being prone to heat loss, particularly where horizontal and vertical elements meet. The use of another advanced concrete was proposed to mitigate this. Insularis, a lightweight concrete, was developed by CEMEX to provide a thermal break in concrete structures. With a much lower thermal conductivity value than traditional concretes, Insularis gives designers the option of continuing the concrete through the junction without compromising on strength or adding in other materials. For Concrete House, Insularis was used to form the kickers at the base of the external walls, dealing with the heat loss issues and helping Adrian’s vision of an energy efficient build.
Speed and efficiency were also a huge part of the build, and to support this Adrian formed a partnership with Peri UK to use their new Duo® lightweight formwork system. Duo can be assembled by hand in much quicker times, due to its plastic composition and low overall weight. Traditional formworks often require a crane to lift each section into place, an expense not associate with the average self-build project. CEMEX worked closely with Peri and Adrian’s design team to make sure that the Resilia HP concrete would perform well in conjunction with the Duo system. Early site trials were conducted using both brand new products, which allowed CEMEX to optimise the mix design and also improve the production process.
Work began on site in September 2017, the site being levelled and foundations being prepared. CEMEX supplied 109m3 of traditional GEN3 concrete for what was probably the most straightforward part of the concrete works. In early November the work to the suspended slabs began in earnest. With a high water table and potential for clay heave, Adrian was forced to adopt additional measures to protect the ground slab, which included a level of steel reinforcement. For this element CEMEX designed the Resilia Conventional mix, taking account of the presence of the steel reinforcement and the reduced need for the concrete to perform to a higher flexural strength value. Around 120m3 of Resilia Conventional was supplied to form the ground slabs and upstands between level changes.
Into December and the first walls were ready to be poured. Due to the layout of the building, Adrian and his build team had to carefully select the build route around the site to avoid conflict between the formwork supports. Smaller sections of walls at low lying parts of the building were completed first, in a methodical sequence which then dictated the speed of build. As the build team became more accustomed to the Resilia HP, they were able to place lager volumes per pour.
Pouring the walls was not without its share of drama, with the supplying plant being located much further from the project than usually done. This distance caused some early stage issues with logistics and this was made clear when one CEMEX vehicle suffered a puncture whilst travelling to site. The resultant delay in getting the material to site caused a pour line along an external courtyard wall. Fortunately, the Resilia HP was designed with four hours of consistence retention, so the material was able to be placed after the short delay with only an aesthetic line on the courtyard wall. Following on from this CEMEX changed the timing and method of production at the plant, allowing more loads to leave for site earlier in the morning to beat the morning rush hour.
In January 2018 the first requirement for Insularis came around, another first for CEMEX UK to produce. Following trials with assistance from CEMEX Research Group, we prepared to pour the first set of kickers. The first attempt at pumping the material ran into issues, where the concrete would not immediately pump. The decision was taken to hand place the material due to the time limits in place. CEMEX went away and made some modifications to the mix for the second attempt some days later. Again, initially the material blocked the pump, but with some adjustments to the pump configuration the material finally flowed into place. Variations in the raw material alongside the configuration of the pump had caused the issues, but working together with the site team these were overcome.
The final structural elements were the roof slabs, where again the levels rose and fell across the building. More upstands and parapets were cast in an intricate sequence of pours planned by Adrian and his team.
Once structurally complete there was one more element that required assistance from CEMEX. The final floor construction called for underfloor heating pipes to be laid, with a finished concrete or screed floor. Working with Adrian again, CEMEX proposed a number of options including screeds, but finally it was another concrete which fit the bill. A bespoke version of our Evolution Self Compacting Concrete (SCC) was designed to allow a finished concrete surface, without compromising on the floor levels throughout the build and also allowing for a powerfloated finish. The mix, called Evolution F contained a range of CEMEX Admixtures which were added to aid the placement of the material whilst controlling the consistence retention to give the contractor time to work with the material.
At the completion of the project CEMEX had supplied 4 brand new mix designs all developed and modified to suit the project, with the ongoing assistance of the CEMEX Research Group, the wider CEMEX UK business and related supply chain partners. The project has served as a platform for development of not only new variations of mixes but also the range of applications and sectors which could benefit from utilising these new advances in concrete technology.