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Durability of concrete
In this presentation I’m focusing on the durability of concrete. First I’ll give a brief overview of concrete, we have to know what does it actually means and where is it used? (slide) Basically concrete is a construction material composed of cement , aggregate (generally gravel, limestone , or granite, plus a fine aggregate such as sand ) also water, and chemical admixtures.(slide) Concrete is used to make pavements, architectural structures , foundations, roads, bridges, marine - and parking structures, brick /block walls and footings for gates , fences and so forth . Mainly it is used because of its high durability and availability, but also because it is cheaper than to use wood for example. Concrete is used more than any other man-made material in the world.(slide)
Moving on, the durability of concrete can be defined as the ability to remain serviceable for at least the required lifetime of the structure of which it forms apart. However there are many factors which shorten the lifetime of concrete (slide) such as: physical attacks, including frost damage, fire , wind and water waves and chemical attacks including sulfates, sea water, acids, alkali-silica reactions and of course corrosion of embedded steel .
That’s why the durability of concrete needs to be tested. (slide) Firstly, the concrete contains pores and capillaries which fulfill with water. In laboratories several test have been worked out to measure the permeability but in real life we have a similar situations in marine areas .
Next, there are three major types of flow constants for concrete. (slide) Firstly there is permeability which is a rate of flow of fluid into a porous solid of concrete. Then comes diffusivity- a situation where gas or liquid will be transmitted through the substance. And finally there is sorptivity which is a process where liquid is absorbed by capillarity. When the concrete is drying, it is very important to cure it well. (slide) It means watering the concrete to keep all the previous factors as low as possible.
(slide) Degradation of concrete is mainly caused by chemical affects such as reactions with sulfates, sea water, acids and alkalis and physical affects including frost, fire, wind and water erosion. The chemical processes are complicated and need special circumstances to react . As a result of those, concrete usually cracks. (slide) Sea water, however, may fill the pores of concrete in marine areas, which makes it even more durable.
And finally, concrete usually contains steel constructions to shear strength and compensate stressed areas. (slide) But if the concrete gets damaged, the steel is also affected by corrosion. The corrosion is mainly caused by CO2 or chlorides, which can be found in sea water and road de-icing salts. To avoid these problems stainless steel and chemical admixtures should be used. (slide) That’s all. Thank you for listening !