Core Tip: 3D printed concrete buildings aim to shorten the delivery cycle of residential products, realize intelligent manufacturing in the housing industry, improve housing quality, and achieve transformation and upgrading of the construction industry. This article will mainly discuss the structure and materials of 3D printed concrete.
Industrialization of housing is the future development trend of China’s construction industry, and 3D printed concrete buildings are an important sign of the housing industrialization moving closer to manufacturing, marking a significant step towards sustainable development in China’s real estate industry. In this regard, developed Western countries have already taken the lead, while in China, this area is just beginning and still faces many difficulties and challenges. It is precisely because 3D printed concrete buildings are still in their infancy in China that there is vast development space and a bright future. 3D printed concrete buildings aim to shorten the delivery cycle of residential products, realize intelligent manufacturing in the housing industry, improve housing quality, and achieve transformation and upgrading of the construction industry. This article will mainly discuss the structure and materials of 3D printed concrete.
Introduction
In recent years, housing industrialization has rapidly developed with the support of national policies, and batches of industrialized housing have sprung up, propelling housing industrialization onto the fast track of development, especially with the advancement of information technology, which drives housing industrialization towards automation, integration, and intelligence.The emergence of 3D printed concrete buildings fully demonstrates the promising future of industrialized housing development. The realization of intelligent manufacturing in the construction industry is not a castle in the air; just recently, a construction company in Shanghai used a 3D printer to build two buildings, one being an 1100-square-meter villa in Shanghai and the other a six-story apartment building in Suzhou, which is currently the tallest 3D printed building in the world.
3D printing technology is an advanced manufacturing technique, and its characteristic of not being limited by product structure determines its applicability in many industries. From another perspective, 3D printing is merely an advanced manufacturing technology, a tool. Its inherent value as a product is not high; it needs to realize value through industry applications, which is a process of gradually aligning technical advantages with user demands. For 3D printed concrete buildings, cost, raw materials, and structural safety are the key points for future development.
Analysis of 3D Printed Concrete Structures
Currently, 3D printed concrete buildings are modularly designed, with 3D printers printing out the industrialized modules of the building, which are then transported to the construction site for assembly. Therefore, the production and construction process is fundamentally the same as that of PC component industrialized housing. The difference lies in that there are no steel bars in these 3D printed walls, slabs, and other modules; instead, cement and glass fibers are used to enhance the tensile strength of the entire concrete structure, allowing for the construction of six-story buildings with unreinforced concrete structures.
Currently, the domestic housing industrialization PC structural system is divided into two categories: one is fully prefabricated structures, and the other is partially cast-in-place and partially prefabricated structures. For example, Wan Ke’s research and development of a prefabricated overall housing structure system is actually imported from Japan, where its beams, columns, and shear walls are cast-in-place as load-bearing structures; the floor slabs are prefabricated slabs with cast-in-place overlapping layers; only the exterior walls, stairs, and balconies are fully prefabricated components. The fifth-generation integrated housing from Yuanda also resembles this. Thus, from the current situation in China, most adopt a semi-prefabricated structural system, with only Yuanda’s sustainable buildings using fully prefabricated steel structures, which are all bolted together and can erect six floors in a day. Various new types of prefabricated building structural systems continue to emerge.
As the forefront and pinnacle of housing industrialization technology, 3D printed concrete buildings aim to break through the semi-prefabricated structural system, adopting a fully prefabricated structure, or even a completely 3D printed process, to transform the construction industry entirely from traditional construction to manufacturing. Aside from the foundational components, in the future, even the entire foundation could be 3D printed, achieving true intelligent manufacturing and utilizing virtual assembly technology. Virtual assembly employs computer simulation and virtual reality technology, using a simulation model to achieve optimal plans for product process planning, manufacturing, and on-site assembly.
For 3D printed building modules, the use of unreinforced structures is partly to facilitate printing, and partly to leverage the advantages of lightweight, thin, and strong 3D printed concrete modules, utilizing a wider variety of concrete to print different functional and structural building modules. Therefore, the raw materials for 3D printed concrete come from a broader range and have more varieties, and the mechanisms of setting, hardening, and strength development will also break through the theoretical boundaries of traditional concrete, with durability and safety still requiring research and validation.
With the continuous development of technology, in the future, giant 3D printers may emerge that can print entire buildings on-site, similar to the double dragon gate crane style structure, where the printer can rise and fall like a tower crane, with several variable-position trusses arranged at the top, each equipped with a printing head. Depending on the area size, dozens of printing heads may be arranged. The vertical structure of the building can be printed layer by layer, while modular structural steel bars are hoisted on-site for welding assembly. The printing head can use tools similar to ancient rammed earth wall tools to layer the steel mesh and stack concrete. Once such a giant printer appears, it will bring significant changes to the entire commodity concrete industry, while also posing a huge challenge for small and medium-sized commodity concrete enterprises, as this technology for 3D printing concrete is more complex and requires higher quality standards.
Analysis of Raw Materials for 3D Printed Concrete
According to publicly available data, the concrete used in Shanghai’s 3D printed buildings is glass fiber reinforced concrete, which features higher tensile, bending, and cracking strength compared to ordinary concrete, with improved toughness and impact resistance, thus widely used in non-load-bearing components like building exterior wall panels, ceilings, and partition walls. For instance, the white concrete grid on the exterior of the French Pavilion at the Shanghai World Expo was made using glass fiber concrete.
From the current trend of 3D printed concrete technology development, the proportion of ordinary concrete in 3D printed building raw materials will significantly decrease, while fiber concrete, foam concrete, lightweight aggregate concrete, cement-resin-based concrete, polymer concrete, and water glass concrete will see larger-scale applications, and even the emergence of new material concrete.
3D printed concrete differs from traditional concrete; since 3D printing does not use molds, it must meet the requirements for rapid forming, meaning it must quickly set after exiting the printing nozzle and flow outward. It must also ensure tight connections between each layer of concrete to avoid cold joints, so that 3D printed concrete components or buildings are seamless; additionally, it must allow the concrete to flow freely within the pipes and nozzles without clogging them. These three points necessitate that 3D printed concrete differs from traditional concrete, which in turn affects its raw materials and quality requirements.
In terms of binding materials, the binding materials used in 3D printed concrete are quite diverse and broadly defined as concrete, not just ordinary cement concrete. In addition to cement, materials like resin, water glass, gypsum, and geopolymer can serve as binding materials for 3D printed concrete, with geopolymer being particularly suitable due to its fast hardening and early strength characteristics.
Aggregates, which make up the largest portion of concrete, have higher requirements for 3D printed concrete compared to traditional concrete. Aggregates that are strong, low-density, and have a particle shape close to spherical are most suitable for 3D printed concrete. Additionally, since 3D printed concrete buildings are formed by stacking layers of concrete, with each layer being relatively thin, and due to the complex structure of the 3D printer nozzle, the particle size of aggregates in the concrete must be smaller than that of traditional concrete, with a maximum aggregate size of less than 10mm. Requirements for particle gradation, clay content, and harmful substances are stricter. These specifications are determined by the unique characteristics of 3D printed concrete.
Additives, while making up the smallest portion of concrete materials, significantly enhance concrete performance. 3D printed concrete requires higher workability, exhibiting excellent fluidity within pipes while setting quickly in the air after exiting the nozzle. This necessitates that additives possess multiple functions and must be complex superplasticizers. Moreover, the diverse materials used in 3D printed concrete require that additives have good adaptability, leading to the development of specialized series of additives for 3D printing.
Conclusion
The development of housing industrialization and information technology has given rise to new building forms, namely 3D printed buildings. 3D printed buildings represent a very complex system engineering that effectively inherits the ideas of assembly line production and intelligent manufacturing from the manufacturing industry, breaking the constraints that have historically prevented industrialized production in construction, providing infinite possibilities for the development of industrialized construction. Achieving 3D printed concrete buildings is an inevitable trend in the development of housing industrialization, a necessary demand to adapt to modern construction technology, and an important pathway to enhance the technical level and innovation of the entire construction industry.
The development of 3D printed concrete technology presents both an opportunity and an unprecedented challenge for the commodity concrete industry.Only by adhering to technological innovation and keeping pace with the development of construction technology can one gain an advantage in the competitive future commodity concrete market and achieve sustainable and healthy development.
Reprint with acknowledgment, this article and the images in it are transferred from China Concrete Network, cover image sourced from the internet
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