Precast concrete structures in the future

Concrete is the most commonly used building material in the world, and precast concrete components and structures provide a creative way to extend the use of concrete. Facing the increasing challenges on the construction industry, including climate change, energy saving and environmental protection, structural engineers need a new vision for the potential of precast structures as well as for the sustainable use of concrete in general. In thinking about sustainable construction, we need to find innovative ways to reduce the impact of construction activity on our environment. Civil engineering provides human beings with essential support of their everyday life: housing, workplace, transport, communications and utility supplies (electricity, gas, water, etc.). Precast structures are well-recognized as environmentally friendly structural systems, so there is no doubt that precast technology will play a very important role in future construction activities. In the 21st century, construction needs that will use precast concrete include: – tall residential buildings – tall office buildings – advanced modern factories – online shopping warehouses – large-scale infrastructure. New residential and office buildings are widely required in the developing world for improving the living and working conditions of the local people. High quality – especially in terms of sustainability and durability – is a very critical aspect for construction, and precast technology can provide this. Advanced modern factories for IT-based manufacturing and online shopping warehouses currently provide many challenges for civil engineers. The high pressure on the construction period and the use of special facilities are common features, and precast technology usually provides the best solution. For large scale infrastructure, such as long-span bridges, high speed railway lines, subways, and stadiums, precast components and systems are already widely used and will find more applications in the future. Requirements for sustainability are being constantly updated, and innovation is the best driver to keep precast concrete structures moving on the right track. Concrete is easy to produce, cheap, robust, shapeable and suitable for almost all kinds of construction, and using precast technology is the best way to bring concrete into practical engineering. Further consideration of the sustainability aspects of precast concrete structures will always be necessary. For instance, life cycle energy saving strategy is essential for precast concrete structures, as with other materials, at both the component and the structure level. Use of lightweight concrete and embedding heatproof material may significantly reduce energy consumption in the everyday use of structures. Precast concrete structures, composed of prefabricated concrete members that are reinforced or prestressed are the best known form of structural system. However, the main stream of precast concrete structures will soon include other hybrid materials and even more sustainable concrete members, such as steel-reinforced or fiber-reinforced concrete members and concrete members using recycled aggregate. Modular construction has always been seen as the highest application level of precast technology. A primary benefit of modular construction is its rapid delivery. The process of creating modules in a factory can take place even while the site work is continuing, so modular buildings can be constructed much faster than buildings constructed with a cast-in-situ strategy. This allows the buildings to be occupied sooner and allows owners to see a faster return on investment. The expression "concrete forest" indicates that people are worried about the uncontrolled use of concrete. Therefore reducing the amount of concrete used is important from the public perspective. In this regard, recycled aggregate concrete should be used for future precast concrete structures by recycling prefabricated concrete members, components or whole subassemblies. We also realize that precast concrete structures reflect the local construction culture, so precast concrete structures in different countries and regions can show different cultural characteristics. The future development of structural systems will be colorful and will enrich the local cultural environment. In areas that are prone to seismic activity, the extensive use of precast concrete structures may be limited due to the lack of proper understanding of the complex seismic behavior. In order to extend the engineering application of this kind of structural system and to evaluate the seismic behavior of existing precast concrete structures in seismic zones, some research has been carried out around the world in the past few decades, such as the series of investigations in the 1990s in USA and Japan, and consideration of the seismic behavior of precast concrete structures with respect to Eurocode 8 in Europe. More efforts need to be focused on the seismic behavior of precast concrete structures worldwide in the future. Precast concrete is an important topic for "Structural Concrete". In this issue, two papers introduce the experimental investigation and new developed calculation model for reinforced concrete members with hollow circular cross-section. One paper deals with shear failures of concrete structures under dynamic loads. Three papers look at steel fiber reinforced concrete columns, staggered lap joints, and reinforced concrete beams strengthened with carbon fiber composites. Another paper describes the renovation retrofitting work carried out on the 100-year-old reinforced concrete dome of the centennial hall in Wroclaw, which has been listed as a UNESCO world heritage site. One paper presents a state-of-the-art review of the long-term properties of recycled aggregate concrete, while another describes the application of a precast concrete immersed tunnel for the Hong Kong–Zhuhai–Macao Link project, mainly focusing on the early-age behavior of the tunnel. The final paper deals with the behavior of plain concrete ground supported slabs under step loading conditions. We can easily find the precast aspects in most of the papers. I believe, precast concrete structures, with constant innovation, are available and qualified for a better construction in the future. Xilin Lu, Professor and Vice-Director State Key Laboratory of Disaster Reduction for Civil Engineering, Tongji University, Shanghai, P. R. China