According to the Unified Standard for Reliability Design of Building Structures (GB 50352-2005), the design service life of buildings is divided into four categories:
- The temporary service life is 5 years;
- The design service life of the easily replaced structural members shall be 25 years;
- The design service life of ordinary buildings (such as residential houses) and structures is 50 years;
- Monumental buildings and particularly important architectural designs (such as the Three Gorges Dam) have a service life of 100 years.
In fact, for concrete buildings, although the design life is only 50 years, However, its ultimate life is much longer than the design years, the key lies in the maintenance and maintenance of the building, as long as the repair in place, perhaps with a 100 years is no problem.
We often hear reports that a bridge designed to last 50 years is still in use after 70 years. Generally speaking, as long as after maintenance, the main structural strength of the building can reach the new standard, it can also continue to use.
“Design service life” means the period of time during which a structure or structural member specified in the design can be used for its intended purpose without major repairs. It means that during this period, even if I do not repair it, it will be used normally. And “service life” is simply the time of use, after the “design service life,” Concrete buildings due to wind erosion, force majeure damage (earthquake), rain water erosion, etc., cause the building needs a certain repair, in order to meet the design life of the building standards. So, even after the design of the use of the house, living in general is no problem.
Around the 3rd century BC, the ancient Romans discovered the hydraulicity of natural volcanic ash, using it to mix mortar that hardens to high strength. Therefore, in many of the remains of ancient Rome, we can see the “concrete building,” which is the prototype of ancient concrete.
In 1849, Joseph Monier, a French gardener, solved the problem of low tensile strength of concrete by combining wire with concrete to make flowerpots, and presented his new invention at the 1867 Paris Exposition. Since then, he has invented a similar structure of concrete pipes, water tanks and other products, and in 1875 designed the first reinforced concrete bridge. Now we are using steel, tensile and anti-twist performance is stronger.
Technically, the world’s first concrete building of modern significance was built in 1853, called “The house of Francios Coignet in Paris ” ， At present, it is still intact. Even after the shelling of World War II, the main structure can still meet the standard of normal use. So, the life of the concrete building has been 166 years. According to the concrete production process and raw material technology at that time, its service life has far exceeded its design service life.
Since concrete buildings built more than 160 years ago have achieved such a long service life, After more than 100 years of technological innovation, concrete production process is more scientific, the use of cement, admixtures and other raw materials are also through constant innovation. Therefore, according to the design requirements of modern reinforced concrete buildings, service life to achieve the design of 2-3 times is no problem.
At present, the average service life of the house is shorter than that of the developed countries in Europe and the United States, and some houses may not have been designed for use, it was removed. On the one hand, because of the rapid development of domestic cities, in order to create a modern urban atmosphere, the replacement speed of architectural style will also accelerate, so the life of the house is not long.
On the other hand, the rise of the domestic real estate industry, some of the more prosperous lots, In order to meet the needs of more high-grade commercialization, the constant demolition and construction, construction and demolition, resulting in just built a few years of the house was torn down, but this is also a great waste.
Concrete has become one of the basic materials of construction in modern urban construction. At the same time, with the increase of human demand for high-rise buildings, some ultra-high strength concrete is also being applied in a large number, Since the 1960s, the application of superplasticizer, polymer materials, a variety of fiber, developed increasingly high strength concrete materials, and these concrete life is longer.