With the initial completion of China’s modernization and construction tasks, the major cities have also been better developed, especially in recent years with the changes in diet, architecture, economy, lifestyle, etc., so that people’s needs for living gradually shift to the direction of quality.

However, in the actual real estate industry, conflicts between residents and construction companies often occur, and the key factor that causes these disputes lies in the quality of the building or in after-sales maintenance. In order to solve such problems, although China has introduced a number of policies, however, due to the continuous disputes in the real estate industry in recent years, coupled with the market downturn, such issues have also received the attention of all sectors of society, the following specific description of this aspect of the problem.

　　Overview

　　Concrete structure is currently more widely used in the field of construction of building construction methods, from the application and development experience in recent years shows that the application of this structure, due to the influence of materials, technology, environment, management, technology and other factors, there are still problems such as water leakage, cracks, structural strength weakening, etc., and therefore should strengthen the exploration of these common problems, from which to find the causes of such problems, and accordingly To find specific solutions to improve the quality of buildings and provide safe and reliable living and office conditions for the public.

　　Causes of concrete cracks

　　1 From the aspect of material quality

　　However, due to unqualified cement, sand, stone, etc., not meticulous market research in the material purchase, insufficient material experiments, greedy for cheap to buy “relationship materials, cheap materials”, etc., but did not choose the real standard materials suitable for the project requirements, or unreasonable ratio In addition, the quality of the building is caused by the combination of the materials, and then the formation of what is commonly known as “tofu dregs project”.

　　2 From the deformation of the foundation

　　Due to the existence of uneven settlement, the problem of cracking in the reinforced concrete structure will occur. Usually, the cracks are related to the foundation deformation in terms of size, shape and direction, and when the stress of the foundation deformation increases, it will result in penetrating cracks.

　　3 Structure loading view

　　Generally speaking, if the load on the structure exceeds the bearing capacity, it will cause cracks, and the formation of these cracks is also closely related to construction, use and other factors. In daily practice, it can be seen that the reinforced concrete beam and slab bending members in use will have cracks due to excessive load, and although the degree varies, it will bring more potential accidents due to the increase of time.

　　4 From the design construction

　　In the concrete structure, sudden changes in the cross-section of structural members, or unreasonable openings, grooves, etc., will cause the stress to gather, and therefore in the ring beam or hoop, hanging bars and other structural joints set unscientific, easy to cause concrete cracking.

　　5 From the influence of humidity

　　From the perspective of physics, the principle of thermal expansion and contraction is suitable for concrete materials, so when the concrete is hardened in the air, the volume will naturally shrink, which is related to the tensile stress generated in the component, especially in the early stage of concrete, the strength is low, so the shrinkage value will also reach the maximum; by inference, if the early maintenance work is not in place will naturally cause shrinkage cracks, from the form of expression, to Cast-in-place shear walls and pool bottom projects are more common.

　　6 From the aspect of creep

　　The main structural components, when its internal stress function, will be instantaneous so that the concrete structure in the elastic deformation, coupled with the extension of time, will produce the phenomenon of cracking, which is usually referred to as rheological deformation. If this happens, it will bring many stress losses to the prestressed members, and the crack resistance of the structure itself will be sharply reduced, and the more common area is in the tensile zone of the bending members.

　　7 From the construction side

　　Concrete structures are mainly used in building construction, but the cracking problem can be caused by the lack of safety and quality management, unreasonable construction process, strict supervision or unqualified material ratio, uneven vibrating during pouring, unscientific proportion of reinforcement, untimely maintenance, lack of protective measures in the construction environment, together with temperature and humidity, seasonal changes, and material transportation.

　　Repair design

　　In the principle of repair design of building concrete structure cracks, it is necessary to evaluate the judgment results of repair and reinforcement, and then implement restoration design for cracked structure function and durability. On the other hand, consideration of material, repair method and repair time should be paid attention to repair, and repair design work should be carried out based on these basic conditions. The details are as follows.

　　First, the scope and scale of repair should be set and the site should be investigated and studied.

　　Secondly, the cause, condition and degree of cracking, such as crack width, depth and type, should be recorded and analyzed, and the importance of the building, its general environment, factory area, salt environment, hot spring area, cold area and special use should be identified and distinguished.

　　Thirdly, in the repair, there should be clear regulations and restoration goals set to ensure that the selected repair materials, methods and time meet the scientific and reasonable repair design; it is also necessary to compare the environmental conditions and give a higher grade repair design, preferably in the case of stable cracks to start the repair work, because various conditions will have different effects on the cracks, such as temperature, humidity, time, etc. changes in the repair affecting the cracks.

　　Fourth, according to the practical experience of repair can be divided into stages in terms of repair recovery target; such as performance recovery, it is usually appropriate to restore it to the same performance of sound components, which is due to the cracks triggered by the cement aspect as the repair object, and generally can set its warranty life at 10 to 15 years; then the degree recovery, because the aggregate triggered by steel corrosion, alkaline aggregate will deteriorate, coupled with cracking causes, the analysis of all the causes is not yet clear, so usually the repair degree recovery time can be set at 5 to 10 years; there is also in the safety and reliability of the recovery situation, you can ensure the degree of personal safety as the basic standard, to start the emergency repair works.

　　Fifth, it is necessary to pay attention to the matter that in the repair operation, adequate and specific research should be carried out, and the safety and security measures of mechanical materials, scaffolding, project site and surrounding people should be done.

　　Repair methods and characteristics analysis

　　There are many repair methods for cracks in building concrete structures, and the following is a specific description from the basically more common coating covering method, filling method, pre-stressing method and grouting method. 　　

 1 Coating method

　　In the repair operation, in accordance with the requirements and relevant practical experience, usually for the concrete surface there are a large number of surface cracks line manual method or mechanical spraying method; principle is the repair material coated on the surface of the concrete, closed protection; in general, 0.3mm ~ 2.5mm thickness can meet the requirements of the coating film, note that the greater the thickness, the ability to adapt to changes in the crack will also be followed by increase; when using this method, the selected repair materials should be differentiated, such as in indoor, outdoor, different environments, different media, crack activities, etc., requiring careful analysis and strict selection.

The materials chosen in the usual repair construction should be targeted, such as the choice of epoxy asphalt-like rigid coatings in wear-resistant flooring, while for unstable cracks, polyurethane cool-like coatings with strong elastomeric properties should be the main focus.

　　2 Filling method

　　The filling method is mainly used to expand the cracks with steel brazier, wind pick and high-speed cutting discs to form a V-shaped or trapezoidal groove; then, epoxy mortar, cement mortar, PVC mastic and asphalt grease are used to form a closed protection by layering pressure smear.

This method is very suitable for repairing general cracks and water seepage cracks, for example, V-shaped can be applied to general cracks, while trapezoidal can be applied to water seepage cracks; in terms of material analysis, epoxy mortar can be chosen when high structural strength is required, while polyvinyl chloride and asphalt plaster are suitable for repairing leakage only.

　　3 Prestressing method

　　The application of prestressing method is mainly through it to achieve nut tightening to reduce cracks or make them close; for example, after drilling holes for members with drilling machine and penetrating bolts, it can increase the prestressing force to prompt nut tightening and achieve the purpose of crack repair; if the relevant conditions and standards are met, the two-way prestressing method can be applied with better effect, for example, when the direction of hole formation and the direction of cracks form vertical or not prevails.

　　4 Grouting method

　　The so-called grouting method is to pour cement or other chemical slurry into the concrete joints to play the purpose of curing when spreading, thus forming a buried strength to increase the integrity of the member, promoting the recovery of the use function, allowing its durable strength to increase, and achieving the goal of plugging and preventing rust. From the material aspect, epoxy resin slurry and methacrylate-based can be widely applied to structural repair; water glass, acrylic phthalan, polyurethane cool, acrylic salt-based, can be widely applied to prevent and stop leaks; from the functional point of view, the filling of such insoluble materials can effectively increase the strength of the building, so that its water barrier performance is strengthened.

　　Conclusion

　　In conclusion, from the perspective of development, in the new era, we should insist on keeping pace with the times, adapting to the times and the local conditions. Because from the current market situation of the real estate industry, there is an oversupply and an obvious problem of excess stock, but on the other hand, it should be recognized that the people’s demand for housing quality and the concern of after-sales service quality.

Therefore, construction enterprises should summarize and analyze all aspects of the problems through property, treat all aspects of things seriously, and solve the real problems of residents in a timely manner, so as to further promote the harmonious relationship between enterprises and the public, and make a citizen’s obligation for a socialist harmonious society.

At the same time, it is also necessary to have a systematic study and setting of solutions to such problems, so as to make some useful achievements in this aspect, thus enhancing people’s interest in the real estate industry and further boosting the demand for buying houses.