Choose language:
Damage to stressing rising up works is due to the building material structure as well as the demands from the environment pretty often.
Concrete is as more economical and universal applicable building material a foundation-stone for modern building. A large part of the buildings is today from concrete.
Concrete does not grow however in nature, it by humans in different quality is manufactured and for the most diverse tasks used. The apparent unlimited application type this building material offers, as well as the circumstance that he is usually only manufactured in his final form on the building site, it lead pretty often to remark or planning faults.
Concrete actual even if one does not designate it often in such a way - a "universal building material". There are demands for which it is less suitable, is it because of its chemical composition, is it that one it in forms squeezes and by forces stressed, for which he is problematic by its material-conditioned brittleness.
After one for a long time the opinion was the fact that concrete buildings did not require any maintenance practically during their entire utilization period showed the experience of the last decades that also concrete constructions are to be maintained appropiately, and that smaller damage, if one does not eliminate it immediately reorganized and the causes of the damage attains full growth itself relative to fast larger damage, which are to be eliminated only at high expenditure.
There is today a whole set of special methods and the most diverse demands adapted materials, with which one can repair damage to concrete buildings. Before one goes however to the removal of an arisen damage, the cause of the damage must clarify. The recognition and disconnection of the causes of the damage requires however thorough knowledge of the behavior of building materials and construction units under the arising read, use and demands due to environmental factors.
see also durability of concrete
Concrete possesses a small tensile strength with very high pressure strength only. The tensions which can be taken up by a construction unit must be usually taken up therefore by inserted steel bars (reinforced concrete). Steel is a corrosion-susceptible building material, which rusts very fast, if it is exposed unprotected to atmospheric oxygen and dampness. Concrete is high alkaline and has the important characteristic to form by its passivation layer on the steel to protect and it in such a way against rust. By reaction with air carbonic acid the concrete loses its alkality (carbonating) however with the time and is then no more in the situation to protect the embedded steel bars against corrosion. The standards, e.g. DIN 1045, prescribe therefore depending upon demand and environmental condition and/or Expositionsklasseeine minimum thickness for concrete covering. With no longer sufficient protection by concrete covering the screen end corrosion product (rust) possesses itself the repeated volume of the original steel, the screen end pressure blows itself off the steel protecting concrete covering. This damage will all the rather occur, the more thinly, more porous and less alkaline the concrete covering of the steel is.
All materials, with exception of precious metals, are bent, as soon as they come with certain other molecules/atoms into contact be received new chemical compounds. Thereby the original material properties are more or less changed. That applies also to the building material concrete. Its inclination such new chemical compounds to be received and with it depends the danger that concrete construction units are attacked by chemical materials, apart from the chemical composition and concentration materials of the affecting the concrete also very strongly on the tightness of the concrete. Thus of the fact whether the materials affect only the surface or whether also into the construction unit can penetrate and influence it ago from the inside. Particularly the penetration of chemically aggressive liquids or gases is promoted by the air voids and tears of the concrete.
Differences will can after two different the solving attack and the driving attack.
Concrete exists essentially out by cement cemented nature rock. A little resistantly against chemical attacks particularly is the artificially manufactured cement, while existing in their current chemical composition since many millions the nature rocks years are substantially less susceptible to chemical effects. Hardened cement paste is particularly little resistable as basic product against acids. Since the components of the different cements are acid soluble nearly everything, in principle no stability can be expected opposite organic and inorganic acids by the confirmed cement, the hardened cement paste. The complicated lime alumina connections of the hardened cement paste are transformed by the acid attack into water-soluble connections, which can be cleared away then by water and atmospheric effects. Thereby the co-operation between addition and hardened cement paste is first loosened and destroyed with progressive attack. As long as the concrete skin is unimpaired, the attack can begin in each case from the surface. The larger the attack region with progressive opening and of the concrete outer skin however becomes, the faster progresses the destruction.
Driving attack is present, if materials the affecting the concrete form new products with substantially larger volume with reaction with the hardened cement paste, in some cases also with the (alkali-float). The larger space requirement leads out then for the breakup of the concrete from the inside. A typical example for this is also the sulfate driving. If sulfathaltige gases or solutions affect the concrete, then it comes by reaction between the sulfates and the tri calcium aluminate of the hardened cement paste (C3A) to the formation of Ettringit. The volume of the basic materials becomes larger on the eightfold, the concrete is from the inside out blown up. This damage arises frequently with sewers from concrete. Here forms under material organic before all conditions dominant with deep-seated duct systems (small velocity of flow, relatively high temperature and missing ventilation) by bacterial decomposition of the schwefelhaltigen contained in the waste water such as proteins, which can attack the concrete surfaces after putrid eggs smelling hydrogen sulfide gas and.
Concrete is not more inflammable and during fire load very resistant building material. Nevertheless damage arises also at the temperatures of up to 1000 degrees, typical for normal fires, whose effects of fire duration and kind of the construction (static system) are dependent.
The waste of the concrete firmness is minimal up to approx. 200 degrees. At higher temperatures the firmness drops faster, and can have dropped with 500 degrees up to 50% of the normal pressure and tensile splitting strength. Because of the bad heat conductivity relevant temperatures arise however only in the highest centimeters during normal fire load for stability, while the core of the concrete construction is usually less concerned. It comes usually to flakings due to a steam development by the residual moisture in the concrete.
Reinforcing steels are substantially temperature-more sensitive than concrete. Already at relatively small fire temperatures the steel begins itself to stretch. This happens all the faster, the smaller concrete covering is. By the stretch of the steel it comes to chipping off concrete covering, whereby the steel is exposed then directly to the fire effect. With approximately 500 degrees the steel reaches its yield point, high-quality steel is completely generally more sensitive to fire temperatures. With prestressing steel the critical border is only scarcely over 350 degrees. If the yield point of the steel sinks under the tension which can be taken up by it in a reinforced concrete compound unit, then the load-carrying capacity of the construction unit is exhausted. It will first deform and with further deformation will fail.
We found here 2 articles.
D» Damage to concrete buildings» Damp stain |
We found here 4 related websites.
Index | Privacy | Terms Of Use | Sitemap | Feedback
Printer Friendly Format
Bookmark this page
Back to "Building damage"
Back to top