The function and control method of reinforcement protection layer
Source: | Author:lichengcn | Publish time: 2017-08-09 | 36 Views | Share:
      How does steel and concrete work?What kind of relationship is it?Will tell from the physical and mechanical properties of the material, reinforced with strong tensile, compressive strength, and concrete has high compressive strength, tensile strength is lower, but the elastic modulus of the two is close, and good adhesive power, both play their mechanical performance, and can coordinate well, share structure component of external loads.

      Because there is sufficient adhesion between steel reinforcement and concrete, the reinforced concrete members are as a whole to bear external forces in the calculation of structure.Since the tensile strength of concrete is very low, in order to simplify the calculation, the general concrete is only considered to bear the compressive stress, while the tensile stress is fully assumed by the reinforcement.For the cross section design of the stressed member, the farther the steel bar is from the compression zone, the greater the external bending moment can be borne by the steel bar of its unit area, so the efficiency of reinforcement will be higher.So generally speaking, the tensile steel bar should always be near the edge of the concrete member of the tensile side.If the stress bar of the girder should be located at the upper part of the component.If the placement error or the protective layer is too large, the weight of the beam will be reduced, and the heavy accident will occur.

      So, the more you pull the bar, the better?The answer, of course, is no.This is because the main component of the steel is iron, which is easily oxidized at room temperature, not to mention in high temperature or humid conditions.Was wrapped in concrete members reinforced form passivation protective film, not contact with the outside world is relatively safe, but if reinforced protective layer thickness is too small, also is the tension zone of the steel bar too close to a side, on the one hand, easy to cause exposure or force between steel surface spalling of concrete, on the other hand, with the passage of time, the surface of the concrete will gradually carbonization, it won't be long before, outside the reinforced concrete loses the protection, leading to reinforcement corrosion, cross section is reduced, strength is reduced, loss of bond between steel bar and reinforced concrete, component integrity is damaged, serious when still can lead to the destruction of the whole structural system.Usually, the protection layer of the foundation beam is 2.5 cm. 

      In the engineering practice, the quality problems caused by the thickness of the protection layer of steel bar are too numerous to enumerate.Prominent as now commodity residential construction floor big negative bending moment of reinforced protective layer and cast-in-site frame structure in the primary and secondary girder of the beam at the junction of the upper part of the negative bending moment of reinforced protective layer is big problem.Take residential building as an example, nowadays the residence area is bigger and bigger, the floor span also grows bigger, especially the living room floor board.I have seen a building with a span of 5.7 meters and a thickness of 15cm. The design is a double - duplex steel mesh.From structure mechanics calculation, negative bending moment of the bearing is across the bottom of the plate bending moment is small, but because of bearing negative bending moment reinforced construction when the unit did not cause enough attention, the project has just completed has not been used can be found on the floor near the surface of which appeared a lot of cracks.After the authoritative test department found that after check the test joints of negative reinforcement layer is generally more than standard 2 -- 4 cm, the biggest more than 7 cm, to the upper floor of negative moment reinforcement effect is greatly reduced, some even completely out of action, and finally had to be under the condition of local reinforcement reinforcement measures agreed by design, even though this is itself caused great economic loss to construction unit.According to relevant statistics, about 70% of the reasons for the cracks are caused by the incorrect location of the protection layer.

      So how should the protective layer be controlled?I personally think the focus should be on two aspects, one is to grasp the pre-construction technology;The second is the control of elements in the process of grasping.Before construction, the correct reinforcement protection layer should be determined according to the design drawing and construction acceptance specification.The thickness of the protection layer is not the same. Generally speaking, the protection layer of the cast-in-place slab is 1.5cm thick, while the foundation layer is usually 5cm thick and sometimes even 10cm.Therefore, this thickness must be clearly defined in the technical disclosure of the operator, otherwise it will be easy to rework.During the construction process, it is important to standardize the operation, especially during the concrete pouring process.Is often steel binding when the position is correct, but the concrete is poured into the situation changed, and is not treading on instruments on the above, as a result of the support bar horse pier is stepping down, the upper reinforced concrete bending deformation, the thickness of the protective layer is not guaranteed.So in the construction process, should do the standard operation, strictly prohibit operator to walk on the rebar;The upper steel bars shall be effectively fixed;The water should be checked frequently and solved in time.

      It is true that the thickness of the reinforcement layer is not decisive to the quality of the single project, but if it does not pay attention to it, the harm caused cannot be ignored.In order to understand the mechanism of reinforcement and concrete, we should fully realize the importance of the reasonable thickness of the reinforcement layer to the engineering structure.Only if we can make our engineering construction technical level to a higher level.