A house with a cement life of only 50 years has a service life of 70 years. Are you beginning to distrust the house you live in? First, we need to know what cement is.
The birth of cement 1756, British engineers found that only limestone containing clay can be fired to obtain hydraulic lime, which provided an important theoretical basis for the research and development of modern cement.
1824, a British construction worker invented modern cement and obtained the patent right of portland cement. He mixed limestone and clay in a certain proportion, calcined mature materials in a kiln, and then ground them into cement. Because the color is similar to the color of building stone in Portland, England, it is named Portland cement.
Secondly, we need to know what the purpose of cement is.
The role of cement Cement is a kind of powdery hydraulic inorganic cementing material. This "cementing material" is stirred into slurry and mixed with a certain proportion of stones, sand and other materials. After hardening, it not only has high strength, but also can resist the erosion of salt water. For a long time, it has been used in water conservancy, national defense, civil construction and other projects.
According to the performance and use, cement is divided into three categories:
First, general cement; Ordinary cement is used in most civil construction projects. It includes portland cement, slag portland cement, ordinary portland cement, fly ash portland cement, composite portland cement and pozzolanic portland cement.
Second, characteristic cement; High performance special purpose cement. For example: low-heat slag portland cement, expanded sulphoaluminate cement and quick-hardening portland cement.
Third, special cement; And some special cement. Such as G-class oil well cement (specially used for cementing oil wells and gas wells) and road portland cement (suitable for surface concrete of expressway pavement, airport runway and crowded squares in cities). ).
Factors affecting the service life of cement 1. Manufacture and formula of cement. There are strict standards for cement production in China. Based on different types of cement, the service life of cement is also different. The service life of inferior cement is about 30 years, that of general cement is about 50 years, and that of some special cement is over 100 years.
Second, the storage environment of cement raw materials. If the raw materials of cement are exposed to the sun, frozen at low temperature and wet, it will lead to the hardening and quick drying of cement, which will lead to the loss of cement hardness and the phenomenon of powder brittleness after freezing.
Third, the use environment of cement. Because cement contains calcium hydroxide, high temperature and thermal environment will lead to its decomposition or volume change. Therefore, in some special construction sites, it is necessary to clean and clean the key points of construction to prevent cement from sticking to the base.
Acid rain will dissolve calcium hydroxide and hydrated calcium silicate, leading to the destruction of cement structure and the collapse of buildings under certain pressure. The formation of acid rain is closely related to human activities, so the service life of cement will be greatly reduced in areas with large industrial pollution. Cement carbonization will lead to cement expansion, and long-term carbonization will easily lead to cracking. The service life of cracked cement will also be greatly reduced.
Fourth, the construction method of cement. Cement is widely used in civil construction projects. In addition to the standard construction, materials such as steel bars and wooden sticks will be added to cement to increase the overall strength of cement buildings and prolong the service life of cement. However, if the standard operation is not strictly followed in the construction process, the service life of cement will be greatly shortened.
Because in the process of construction, the use method of cement, construction environment, condensation cycle and so on will affect the service life of cement. Moreover, if there are many impurities or foreign bodies in cement mixed with other materials, it will also affect the strength of cement.
Then the life of our household cement is only 50 years. What shall we do when our house expires?
The relevant national norms are indeed clear, and ordinary civil buildings are indeed designed according to the 50-year life. A 50-year-old house has a service life of 70 years. In addition, we often see houses cracking and outdoor pavement sinking. Are you more worried about your house?
First of all, let's understand the factors that affect the life of a house. First, the design standard of the house refers to the frequency and intensity of earthquakes and typhoons. Usually, the life of a house is calculated according to a typhoon once every 50 years and an earthquake once every 50 years. Structural load and earthquake load standards are considered according to major typhoons and earthquakes that have occurred in the history of the Meteorological Bureau.
Therefore, the structural design of different places is different, and the structural design of Shenzhen and Beijing is also different, because Beijing has a high level of seismic fortification, and it is necessary to strengthen earthquake prevention when designing. In fact, the housing standards of 50 years and 100 years are also calculated according to western science, so the service life does not mean that it can only be used for so long.
Taking typhoon as an example, only 50 years or 100 years is taken as the statistical time period, the maximum typhoon intensity is inferred, and finally it is applied to the design standard of residential structure. In some places, there has never been a typhoon since human records, so it is basically unnecessary to consider the typhoon resistance and to design conservatively according to the minimum typhoon resistance.
If a once-in-a-thousand-year typhoon happens when the house is completed, the house may disappear directly.
Second, the carbonation of concrete leads to the corrosion of steel bars. Steel is always wrapped in concrete, because it will not encounter air and will not be oxidized, so it will not rust. Under general natural conditions, concrete is more durable and stable than rock. As long as it is not serious corrosion and temperature difference, it is completely possible for concrete to be preserved for thousands of years.
If the steel bars are corroded, the house may be broken in 10 years. If reinforcement measures are adopted, it can be repaired if it is broken. However, if the main stress components are damaged in a large area, the repair cost is too high, and sometimes it will not be worth the candle. This is also the main factor that affects the life of the house.
How long will it take for carbon dioxide in the air to completely carbonize concrete and lose its protective effect? All kinds of data show that the shortest is several hundred years, some say thousands of years, or even 1 10,000 years. But since the invention of cement and concrete, we have never seen them lose their lives.
Third, the foundation life of the building. According to research, the life of concrete is shorter than the building itself. In the design, the protective layer thickness will be strengthened, and the protective layer thickness of many basement layers will reach 5~ 10 cm. Because the concrete structure is not as dense as the above-ground structure, it is more susceptible to corrosion.
Generally speaking, the average life span of high-rise residential buildings with concrete frame and shear wall is more than 300 years, that of multi-storey residential buildings with concrete frame is more than 1000 years, and that of villas with concrete frame is even more than 1000 years.
It can be said that wooden houses can be used for hundreds of years, and masonry houses can be seen everywhere for thousands of years. The life of reinforced concrete houses should be much longer than these two. Therefore, everyone can completely avoid worrying.
Finally, the life of cement does not represent the life of residence, and the design life of residence does not represent the actual service life of residence. Even if the life span of cement is only 50 years and the property right of the house is 70 years, these 70 years refer to the right to use the land where the house is located, so even if the house collapses unexpectedly, you can still live in the house rebuilt on this land and continue to use this land.