Experts on Global Dialogues for a Sustainable Built Environment - Session 2
In the 2nd session of the Experts on Global Dialogues for a Sustainable Built Environment webinar series, our experts discussed new low-carbon smart materials from their respective areas of expertise. Thanks to the co-organisers of this webinar event, the China Ecological Building Material Association at the China Building Material Federation, China State Key Laboratory of Green Building Materials and RECONMATIC.
In this session, we invited 4 experts to give us presentations on phase change materials, mycelium building materials, energy-saving windows and 3D printing technology in the development of low-carbon building materials.
Energy Storage and Radiation Protection Building Materials
With the improvement of people's living standards, people are paying more and more attention to the comfort of the indoor environment, however, the efficiency of energy use at the current stage remains a problem. How to store and utilise energy in a more reasonable way has become the focus of future development. As a new material, phase change energy storage building materials can help to achieve the purpose of saving energy.
Phase change energy storage is a type of thermal energy storage. This material was used to store or release heat to regulate and control the temperature of the surrounding environment and improve the efficiency of energy use. Shuai Xie introduced the commonly used phase change materials: organic aliphatic hydrocarbons and inorganic hydrated salts, and material performance optimisation techniques like the nucleating agent method, which uses substances with the same crystalline shape as the phase change material and within 15% difference in lattice parameters to effectively solve the subcooling problem. The use of small-size nucleation centres (seed) of nanomaterials to adsorb and nucleate eutectic salts and crystallise them, reducing their supercooling.
Thickener method (phase separation control method) which is based on the stabilization mechanism of the thickening phase, the thickener can form a network structure to increase solution viscosity, preventing the density distribution of crystalline particles from being uneven, and slowing down the occurrence of phase separation. It can also provide nucleation sites to promote crystallization. He also uses attapulgite to improve phase separation, and the results showed that the latent heat retention rate of CaCl2⋅6H2O and CH3COONa⋅3H2O could reach more than 90%.
All nano-carbon materials can enhance thermal conductivity, and flake nano-graphene has the best enhancement effect. Xie Shuai’s team developed a sugar alcohol PCM using expanded graphite to enhance thermal conductivity. The thermal conductivity reached 2.155, and the enthalpy of the phase change only decreased by 5.5%. The ordered structured design of thermal conductive fillers can significantly improve the thermal conductivity of phase change materials, such as the directional arrangement of CNT, metal foam, etc.
Beixin Building Materials Group Co., LTD., a subsidiary of China Building Materials Group, took the lead in realizing the industrial preparation and engineering application of phase change heat storage gypsum board. We are looking forward to more applications of his phase change heat storage technology, but meanwhile, the authorities also need to quickly establish relevant standards to promote the development of the phase change material industry.
Digital Fabrication of Low-carbon Concrete
Building construction, one of the main industries, is currently the least digitised and automated, it faces inefficiencies, low productivity and wasted resources. Although the revolution in construction may not be here yet, many research projects and experiments such as 3D printing, digital manufacturing and others have raised possibilities for construction.
Dr Seyed introduced two different 3D printing techniques, one being the extrusion-based type, where a hose is connected to a pump system, the pump is connected to a mixer that delivers the concrete and the robot extrudes layer by layer. This type is ideal for on-site practice and large-scale construction, and it is one of the most widely used techniques in 3D concrete printing. The second one is the particle-bed, which has the advantage of being small-scale and highly accurate, allowing for very complex geometries to be printed, ideal for off-site applications and without having to worry about the printing environment. It is also easier to adjust if something goes wrong, which is an advantage over the extrusion-based type.
Dr Seyed says that there is nothing futuristic about 3D printing, it is just a combination of different disciplines such as robotics control, printing systems, and material control. The focus of carbon reduction should be on the use of low-carbon materials. Seyed tries to create concrete suitable for 3D printing by adding some additives to the treated organic or inorganic waste. The inorganic waste comes mainly from processing waste and building demolition waste. The other advantages of using 3D printing include reduced material waste and labour. As the whole process is automated through robotic printing, we can also increase the speed of construction and do not need moulds. The reduction in the use of mould materials helps to reduce the building's carbon footprint and the possibility of worker injury.
Concrete is the most used material in the construction sector, reaching approximately 30 billion tonnes of annual global consumption levels. Ordinary Portland cement (OPC), which is the main binder used to produce concrete, is responsible for 6 to 9% of global GHG emissions. Seyed suggests that a way to address these carbon emissions is to use geopolymer cementing, which is made from aluminium silicates, such as coal combustion by-products, fly ash, and steel manufacturing by-products, slag. As long as they contain an aluminosilicate source, we can activate them and use them as a substitute for Portland cement. The geopolymers also build structural solidity as they have very high mechanical properties, and they have a very low drying shrinkage, are durable, heat and cold resistant and fire resistant. After testing the potential of these polymers by printing them in 3D, it was possible to see the high quality and resolution of the prints.
Seyed is also doing research on whether PVC and rubber have the potential to replace natural sand, and current research suggests that for non-structural loading applications we can use 70% PVC or rubber to replace natural polymers. These findings are very encouraging and show that we need creative ideas to reduce waste in the construction sector and to develop a strong circular economy in order to save more of the earth's natural resources and to bring the building construction industry to a net zero target.
Smart Energy-saving Glass
Buildings account for about 51% of the world's electricity and about 33% of the carbon emissions. How to reduce the energy consumption of buildings is a problem that scientists urgently need to think about. Windows, the least energy-efficient and the most complex part of the building, consume 4% of the total primary energy consumption in the United States. Smart windows are one of the possible ways to reduce energy consumption. Dr Yi Long’s group has been working on thermochromic windows since 2012, from early vanadium dioxide to hydrogels, and more recently "hydro-condensate" and smart windows regulated by passive radiative refrigeration. We report on some research progress and reflections on future work.
The solution that they have worked out is - Liquid Smart Windows. In between two layers of glass, instead of gas, a smart liquid phase change material is poured in to control the temperature by intelligently adjusting the transmission of sunlight. If the temperature is below 29 degrees, it becomes very transparent, which means that sunlight can pass through and thus provide heat to the room. However, if the external temperature exceeds 30 degrees, it becomes opaque or translucent, thus reducing sunlight penetration and preventing the interior from absorbing too much heat.
Why liquid? Firstly, as the liquid can flow, it has no restrictions on the size and shape of the glass, which greatly reduces the requirements of the process, you just need to mix the liquid and pour it in, which makes it easier to scale up production. Secondly, water itself is one of the materials with a very high specific heat capacity and thermal energy storage capacity, and the liquid phase change material is a mixture of special liquid materials and over 98% water. Also liquid provides excellent sound insulation, with double glazing with liquid providing a 15% improvement in sound insulation compared to double glazing using air.
Her second project is radiative cooling regulated passive smart windows. Ideally, for humans, we want to be able to receive as little heat as possible from the sun in summer and reflect as much as possible back into outer space, whereas in winter you need to receive as much heat as possible and at the same time suppress the cooling from outer space.
Windows need to maintain a certain level of visibility otherwise they lose its purpose. In summer we need to make the view visible from indoors and also block near-infrared radiation, which is what makes the room warm, while enhancing the radiative cooling and sending excess heat back into outer space. In winter, on the other hand, we absorb as much NIR as possible to heat the room, while suppressing the radiative cooling, thus reducing the amount of heat being sent back to outer space and allowing the heat to be retained. As this is a passive control, it does not require any external circuitry to control it, it will automatically respond to the temperature regulation. The concept was selected by the German Ministry of Science and Technology as one of the top ten breakthroughs in the world for 2022.
Mycelium Fungi Building Material
There are already some examples of the use of fungi in building construction materials. Depending on the strain and substrate, scientists can produce insulating panels, furniture, fittings, fabrics, packaging materials and even bricks, which have good thermal and acoustic properties and strong fire resistance. However, mycelium composites are currently dry, meaning that the mycelium inside is dead, it does not respond to external information.
As the leader of the Fungal Architectures project, Professor Andy has pushed the boundaries of our perception by showing us that fungi have the ability to differentiate between different types of stimuli. By experimenting with and recording the resistance spikes of mycelium, we were able to see that mycelium responds to weight in an on-off manner and to light stimuli in a sustained manner. In his experiments, Andy prepared a fungal block with electrodes inserted into the side and then experimented with different weights of 8kg, 16kg and 32kg dumbbells and found that the block was able to adapt to the application of weight by changing the pattern of electrical activity. Andy is also trying to experimentally verify if it is possible to find logic circuits from a living fungal matrix or even to decipher the language of fungi.
These discoveries aim to use the fungal mycelium to develop a fully integrated structural and computational living matrix that can be applied to buildings in the future to facilitate their growth. The project marks the first time that intelligent biomass has been used as a building material. If we leave some living mycelium on the building structure, then we can use these mycelium to sense information, transmit information, and make decisions, using the mycelium to create a brain, thus making the building body itself smarter.