With the improvement of building construction level, the situation of multi-story and high-rise buildings using reinforced concrete structure is developing well and is widely used in many projects. However, due to the differences in the technical quality of the construction personnel, less understanding of the operating procedures, in the construction of easy to produce phenomena affecting the quality of these conditions if not paid attention to or can not be resolved in a timely manner, will directly affect the quality of the project.
1 reinforced concrete construction prone to quality defects
Reinforced concrete structure is the most widely used in the construction of a structural form, the quality of its construction, determine the quality of the main project, affecting the roof and basement leakage and the use of users. Unqualified reinforced concrete works are bound to cause unsafe use, and reinforced concrete works to be rectified and repaired, which will also bring great trouble to the design unit and construction unit.
1.1 Surface damage, flute corner is not neat
Concrete surface local lack of pulp rough, or many small pits, but no reinforcement and debris exposed. This is a common quality problem in reinforced concrete construction, arising mainly from: the surface of the formwork is not coated with isolating agent, the surface of the formwork is not cleaned up and stuck with concrete, the surface of the formwork is not flat, warped and deformed, poor pounding, the corners are not vibrated, impact knocking, strong pry hard don’t, damage to the corners of the flute; the structure is collided after demolition of the formwork, etc.
1.2 Internal looseness, not dense
Concrete local loose, mortar less gravel more, between the stone gaps, the formation of concrete pockmarked, honeycomb, exposed tendons, holes. The reasons for this are: poor formwork joints, running slurry at the slab joints, formwork not coated with isolating agent; touching the surface of the plate is not cleaned up; not compacted, leakage vibration; improperly designed concrete mix ratio or on-site measurement errors; concrete mixing is not uniform, poor compatibility. Too much material at one time, not layered pounding. The bottom mold is not put in the bedding block, or the bedding block is dislodged, resulting in the reinforcement clinging to the formwork. Pry bad concrete protective layer when demoulding; reinforced concrete nodes, due to dense reinforcement, concrete with too large grains of stone, difficult to pour and not carefully pounded.
1.3 Microcracks in concrete
Reinforced concrete elements are working with cracks. To be exact, micro-cracks exist in concrete during the process of setting and hardening, which is due to the uneven volume deformation of cement stones and aggregates in concrete under the conditions of temperature and humidity changes, and they are bonded together and cannot be freely deformed, so the mutual restraint stress is formed; once this restraint stress is greater than the bond strength between cement stones and aggregates, and the tensile strength of cement stones themselves, micro-cracks are produced.
1.4 Exposure of reinforcement
The reinforcing steel in the reinforced concrete structure is exposed on the concrete surface. Causes: concrete pouring and pounding, reinforcing steel pad displacement or pad is too little or even missed, reinforcing steel close to the template; reinforced concrete structure section is small, reinforcing steel is too dense, such as in the case of large grains of gravel stuck in the reinforcing steel, concrete cement slurry can not fill the reinforcing steel around, due to improper mix ratio concrete segregation, or serious leakage of the template, concrete protective layer pounding is not dense, or wooden template wetting is not enough, the concrete table too much water loss, or premature demolition of the mold, etc., when the mold is removed, the concrete is missing edges and corners.
2 Measures for reinforced concrete building construction management
In recent years, with the continuous development of the economy, China’s construction industry has gained more space for development, and at the same time, the construction quality requirements for construction projects have also been continuously improved. The rapid development of urbanization construction has promoted the increasing number of high-rise buildings, and the building structure with reinforced concrete building frame structure as the main structure has also received more and more attention.
2.1 Material quality management
Materials, mainly steel, cement, sand, stone and formwork, etc. Reinforcing steel is the “bones” of reinforced concrete structures, and is one of the most important materials. If its quality is not qualified, it may get “cartilage disease” and fail to reach a certain tensile and compressive strength, which directly affects the quality and service life of the structure. Therefore, the diameter, level, shape, surface quality and intrinsic composition of the reinforcement must meet the design requirements. When entering the site, it must be re-checked and tested, and only those who are qualified are allowed to enter the site, and those who are not are never allowed to use. Concrete is the “flesh and bone” of the reinforcement project, mainly refers to cement, stone, sand and other materials.
The incoming must be second re-inspection, especially some small cement plant production of cement, the quality is unstable, should pay special attention. The sand and stone used should be strictly controlled in terms of mud content, and the requirements for stone should be graded with reasonable, the surface should not be attached to clay, dust and organic impurities, and the crushing value must meet the specification requirements. So for formwork materials, strict inspection should be made when entering the site, and the wood which is rotten and excessively wet and not easy to cause deformation should not be used so as not to cause quality accidents.
2.2 Pouring control of concrete
Concrete pouring operation is very easy to lead to cracks if it is improper, so it must be controlled well. The pouring work should be carried out continuously without stopping in the middle to ensure that it is done in one go. If the construction requires the concrete to be poured in layers, attention should be paid to the fact that the previous layer of concrete must be poured before the next layer is first set and pounded to the end to ensure that the upper and lower layers of concrete can be closely combined together.
When pouring the column, if the height of the column is less than 3.0m and the side length of its section is more than 400mm, and there is no cross reinforcement, it can be poured directly from the top of the column. If the poured member is both narrow and deep, then a layer of cement mortar should be poured at the bottom before pouring, with a thickness of about 50 to 100mm. The pouring of the beam should be started from one end of the beam and poured, and when it is about to reach the other end, then reversed to re-pour the other end first, so that the two sections of concrete are brought together before the initial set.
2.3 Concrete maintenance and defect treatment after pouring
Natural curing is most commonly used in cast-in-place reinforced concrete, requiring the concrete to be covered and watered within 3 to 15 hours after pouring with materials with strong water absorption and moistening capacity to keep the concrete in a sufficiently moistened state frequently. Some defects in the appearance of concrete structures or members destroy the structural integrity, reduce the stiffness of members and affect the structural load-bearing capacity, while some have little effect on the load-bearing capacity, but can cause corrosion of reinforcement, reduce durability, or occur leakage, affecting the use.
Therefore, according to the size of the concrete appearance defects, the nature of the difference between the situation, timely processing. For structural geometric deformation, running mold and other defects, without affecting the use of the building function, reinforcement does not deform the premise, can be chiseled excess part, chisel fine chisel flat, do not need to repair; for the smaller leakage of slurry, wrong platform and other defects, available flat shovel to remove the rough part; for small area of leakage of slurry, leakage of vibration, slag and other defects, can be timely repair, repair material is appropriate to use the same mortar with the structure of concrete ratio;. For the larger area of honeycomb, exposed stone and exposed reinforcement, should chisel away the weak concrete layer and individual protruding aggregate particles, and then choose steel wire brush or pressurized water to rinse the surface, local support mold, fill with a higher strength level of fine aggregate concrete than the original concrete, and carefully pounded.
Conclusion
Traditional construction technology can no longer meet the needs of modern construction projects, in order to achieve modern construction projects fast, high quality, low cost and smooth construction, is to use the function of management and scientific methods to promote the technical work. With the continuous development of structural forms, the rapid development of the science of reinforced concrete construction technology and the gradual improvement of people’s requirements for the use of building engineering functions, reinforced concrete and the scope of application is expanding.