The Construction Inspection, Appraisal, Repair And Reinforcement Industry Is Flourishing, And Zhongyan Technology Is Providing Support For Special Projects
China has a huge and rapidly developing stock of existing buildings and structures, with nearly 70 billion square meters of civil buildings, 450000 bridges, over 29000 kilometers of high-speed rail operation, and a total length of 4.8465 million kilometers of highways. There are 2444 berths of 10000 tons or more in ports nationwide, 235 civil aviation airports, and 98795 reservoirs of various types, including 732 large reservoirs, 306000 kilometers of various embankments, and more than 100000 water gates.
Looking at the development trends of the construction industry in various countries around the world, the development of the construction industry can be divided into three major historical stages: large-scale new construction stage - stage of balancing new construction and maintenance and renovation - stage of mainly renovating, repairing, and reinforcing old buildings.
Since the 1960s, European and American countries have entered a stage of large-scale reinforcement and renovation, while China has now entered a historical development stage of balancing new construction and maintenance. In recent years, the construction inspection, appraisal, repair and reinforcement industry has emerged and flourished, becoming a pillar industry for the development of the national economy.
China National Academy of Building Materials Science and Technology Zhongyan Technology Co., Ltd. (hereinafter referred to as Zhongyan Technology) is the birthplace of research and application of special engineering materials in China. In recent years, the team of Zhongyan Technology in engineering protection, repair, and reinforcement has been like a key, solving one key technical problem after another, and safeguarding the safe operation of various projects.
3-hour maintenance window to safeguard the safety of high-speed rail
Since the opening of China's first 350 km/h Beijing Tianjin intercity railway on the eve of the 2008 Olympics, China's high-speed rail has completed the construction of four horizontal and four vertical lines, accelerating its progress towards an eight horizontal and eight vertical network.
From following and leading the world, China's high-speed rail has also become a beautiful business card for China in the international arena.
However, behind the high-speed railway achieving a speed of 350 kilometers in China is the unremitting efforts of tens of thousands of science and technology workers and engineering personnel, and the concentrated embodiment of countless innovative technologies.
High speed railways have the characteristics of high smoothness, high stability, and high durability. A stable and smooth track bed structure is a prerequisite for achieving high-speed rail speed, and maintenance of the track bed structure is an essential part of ensuring its hundred year design life.
The high-speed railway uses a reinforced concrete longitudinal continuous track bed structure. Under the comprehensive effects of temperature difference, 1000 Hz high-frequency dynamic load, freeze-thaw cycles, corrosive environment, and other factors, the continuous and stable track bed structure cannot be separated from necessary protective measures, a large number of routine inspections, and daily maintenance work. However, due to the vast territory and long operating hours of trains in our country, the window of time left for inspection and maintenance every day is only 3-5 hours at night. Excluding online and offline time, the daily working hours are only about 1.5-3 hours.
Rapid repair has become a daily part of high-speed rail maintenance, and it also puts forward stricter requirements for materials, machinery, and work efficiency compared to civil engineering and highway engineering.
In 2017, severe concrete cracking occurred in the base plate of the roadbed structure of a certain section of a high-speed railway, which may cause concrete detachment and affect driving safety. Moreover, the disease is developing rapidly, and if not repaired as soon as possible, it may cause a wider range of concrete cracking. After investigation, it was found that there were problems with insufficient thickness of the protective layer and insufficient slope of the reverse slope during the construction process of this section. However, increasing its concrete protective layer will make the upper structure unable to drain water, and the traditional concrete replacement method can no longer meet the needs of this project.
Commissioned by a high-speed railway engineering department and engineering section, Zhongyan Technology conducted research on relevant repair materials and formulated technical solutions. Finally, the project problem was solved by using self-developed rapid curing epoxy based concrete damage repair materials (hereinafter referred to as repair materials). This material has good interface adhesion and waterproof performance, which can prevent secondary material detachment, improve structural waterproof performance, and prevent further freeze-thaw damage to the base plate concrete when the protective layer thickness is insufficient. According to authoritative testing institutions, the test results show that the bearing capacity of 1 centimeter repair material is equivalent to that of 4 centimeter mortar, and it can restore the structural bearing capacity of the base plate without increasing the structural thickness.
After a long period of argumentation and investigation, in order to avoid further aggravation of the disease, the plan was officially implemented in the winter of 2017.
However, the construction temperature close to zero is far from the test environment temperature, and the material curing time is greatly extended. Under the premise of appropriately accelerating the material curing speed, it is urgent to improve the construction process.
Zhongyan Technology has organized technical forces to develop intelligent temperature control templates in a short period of time. This template not only increases the temperature during the material curing stage and shortens the curing time, but also ensures that the temperature does not drop rapidly during the cooling stage after material curing, effectively avoiding temperature cracks caused by high temperature curing of materials and large temperature differences during template removal. At present, the project has been running steadily for more than two years.
Repair of damage to the base plate of high-speed rail engineering, photographed by Zhang Shuai
Repair and reinforce the "key blocks" of the subway
High speed rail is a good companion for people's travel, while subway and rail transit running through cities are closely related to the daily lives of most people.
As of the end of 2018, a total of 35 cities had opened 185 urban rail transit operating lines, with a total length of 5761.4 kilometers. Among them, underground lines accounted for 63.2%, pavement lines accounted for 14.4%, and elevated lines accounted for 22.4%.
Subways have advantages in saving land resources, energy, and high commuting efficiency, but they also have disadvantages such as long construction cycles, high costs, and high waterproofing disasters. Due to the fact that most subways belong to underground engineering, although a lot of work will be carried out in waterproofing and drainage design at the beginning of construction, concrete cracks and water leakage may still occur in some sections under the influence of unfavorable geological conditions, long-term dynamic loads, stray currents, and other factors.
The subway shield tunneling construction adopts the technology of splicing precast concrete segments into circular tunnels. During the construction process, some key blocks (also known as key blocks) may have hidden cracks due to factors such as the head of the shield tunneling machine. After long-term operation, cracks gradually expand and there is a risk of small concrete blocks falling off.
Subway engineering is similar to high-speed railways in that it adopts a skylight maintenance system, which can be repaired using high-speed railway related repair materials and technologies. But unlike high-speed trains, K blocks in subway engineering are usually located on the side walls or top of tunnel segments, belonging to high-altitude operations. The strict time limit for skylights and simple scaffolding techniques cannot meet the repair needs, and the top operation puts higher requirements on the material's sagging properties. Especially when working on side walls, the track lifting car cannot reach the work site and can only be forced to use diagonal scaffolding. However, the stability of the scaffolding and the personal safety of workers have become a constant concern for managers.
Another disease of subway engineering is water leakage. Due to different geological conditions and stress concentration at the joints, different structural forms of joints are areas and locations with severe water leakage.
Leakage water treatment usually adopts a combination of repair and drainage methods, using sealing materials to seal and stop leaks, and adding drainage facilities to drain water.
Traditional sealing materials can be divided into two categories: one is foamed polyurethane material, which has low strength and is limited to temporary sealing and cannot be used for reinforcement and repair; the other is special cement sealing material, which has a fast reaction speed but will continue to expand in a water environment. It needs to be removed after sealing before proceeding to the next step of construction. However, neither type of material can achieve reinforcement and repair of cracks, nor can it effectively connect the two structural forms.
Relying on a certain subway project, Zhongyan Technology has carried out research and application of related materials. This is a further expansion of materials for high-speed rail repair engineering. The reliability of epoxy based grouting materials and repair materials used for dry crack repair and dry substrate bonding has been widely recognized in the engineering community, but the bonding performance of wet substrates will be greatly compromised.
Researchers modify the curing agent to improve its wettability at the concrete interface, squeeze out moisture at the moist interface, and achieve reliable bonding with concrete. This product is applied in the fields of tunnel engineering, water conservancy engineering, underwater pile foundation pier and column repair and reinforcement. It not only solves the problem of adhesion and repair of wet and underwater concrete, but also becomes a sharp sword for corrosion protection in marine engineering.
The protection, repair and reinforcement team of Zhongyan Technology has developed underwater epoxy grouting material based on underwater cured epoxy resin, which has been applied in underwater fiberglass sleeve reinforcement technology. The fiberglass sleeve technology uses fiberglass sleeves as templates and uses underwater self compacting and curable epoxy resin grouting material to achieve effective bonding between the template and the concrete base. The method is simple and effective, which can avoid secondary corrosion damage and has good promotion and application value.
Preventing problems before they occur is a long and arduous task for science popularization
American scholars vividly describe the importance of protection for building durability using the "Five fold Law". The main connotation of this theory is that for every $1 saved in steel corrosion protection in new construction projects, an additional $5 protection fee is required when steel corrosion is discovered, an additional $25 maintenance fee is required when concrete cracks, and an additional $125 maintenance fee is required when severe damage occurs. This terrifying amplification effect has led governments around the world to invest heavily in research on the durability and reinforcement of reinforced concrete structures.
Heavy construction, light maintenance. At present, in terms of engineering construction, various departments and units in China have invested a lot of energy and material resources, but the daily maintenance level of the project is relatively low, and limited maintenance funds are often used for the repair and reinforcement of serious engineering problems, ignoring the importance of preventing problems before they occur and preventing them from happening.
For the corrosion protection of reinforced concrete, engineering personnel usually use coating anti-corrosion methods to isolate the concrete from corrosive media.
In recent years, engineering and scientific researchers have found that concrete is a porous and absorbent material. In environments where it comes into contact with foundations, rivers, and seawater, it cannot completely isolate concrete from water or corrosive media. The moisture in concrete cannot be eliminated under the influence of environmental temperature differences, leading to the detachment and detachment of the corrosion protection layer, ultimately resulting in the failure of the protection.
Breathable products that do not alter the appearance of concrete are considered a more ideal choice for concrete protection and are currently widely used in plain concrete protection engineering.
However, Wang Jian, Deputy General Manager of Zhongyan Technology, admitted that during the process of technology promotion, there have also been situations where "the paint can at least be seen, but this cannot be seen", which is a laughable situation. "The responsibility of researchers is not only to promote technological progress, but also to promote scientific popularization, which is a long and arduous task."
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Source: Xianji.com
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