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The service life of reinforced concrete is not permanent. Although it seems to be solidified on the surface of concrete, it still continues to function. As time goes on, hydration heat will continue to occur, and concrete will gradually reduce its strength or damage due to weathering. So 30 years of concrete houses are old houses, equivalent to 60 years old; 50 years of concrete houses are almost the end of their life. And wood itself has gone through the test of years. Every piece of wood has grown for more than 100 years, and wood will not change with the growth of time. Wood has only physical expansion and contraction changes, and there is no chemical change due to the growth of time. Wood has only physical expansion change, but not chemical change or even damage.