Introduction to the current situation and development of concrete technology?

The following is the current situation and development of concrete technology brought to you by Zhongda Consulting for reference.

Concrete is the largest contemporary man-made materials, but also the most important building materials. At present, the world's annual production of cement has more than 1.2 billion tons, China in the number of the first place, its production is about one-third of the world's total output. The annual use of concrete, although we have not seen accurate statistics, but if the cement production speculation, it is estimated that the annual use of concrete in our country can reach more than 600 million m3, the amount of work, social and economic significance of the great, is known to the ****. For the future development of China's needs, this paper is intended to be discussed in three areas.

1 ready-mixed concrete status and development

Concrete centralized mixing is a significant reform in the management of construction project production. Ready-mixed concrete application of the proportion of the size, marking the degree of industrialization of a country's concrete production. Foreign practice shows that the use of ready-mixed concrete, generally can improve the labor rate of 200% to 250%, saving cement 10% to 15%, reduce production costs by 5% or so, but also has to ensure quality, saving construction land, civilized construction and other aspects of superiority. The world's first ready-mixed concrete plant appeared in Germany, built in 1903, and later by the importance of each country, the rapid development. By the early 1980s, statistics show that in economically developed countries, the supply of ready-mixed concrete has reached 60% to 80% of all concrete production.

In our country, the concrete mixing plant was built in the early 80's in Shanghai, Changzhou, two cities. 20 years, due to the gradual expansion of the scale of construction, especially in Beijing and the southeast coastal areas of some of the rapid development of urban construction, the construction administrative departments at all levels to take a number of supportive policies and measures, so that the city of the production of ready-mixed concrete to 12% to 15% per year increase in the amplitude. The amount of ready-mixed concrete applied in cities such as Shanghai, Beijing, Guangzhou, Dalian, Changzhou and so on has reached more than 80% of the total amount of concrete used in the city, which is close to the level of economically developed countries. However, the development of ready-mixed concrete is unbalanced, as far as the whole country is concerned, the proportion of ready-mixed concrete in the amount of cast concrete is less than 30%, and some places even do not have ready-mixed concrete stations, compared with economically developed countries, China's ready-mixed concrete is still in its infancy. And China has built ready-mixed concrete station, mostly belong to the construction enterprise or enterprise group management, while the economic developed countries ready-mixed concrete has become an independent emerging industry, there are many professional companies specializing in the production and supply of ready-mixed concrete.

The rapid development of the ready-mixed concrete industry at the same time, but also exposed a number of issues that need attention. For example, the concrete pricing is unreasonable and the concrete supply and demand sides do not work closely together, the supply exceeds the demand and lead to lower prices to sell, and thus can not guarantee the quality of ready-mixed concrete. This vicious circle is not conducive to the long-term development of ready-mixed concrete.

In order to ensure the healthy development of ready-mixed concrete, we must pay attention to the following points:

1) Strengthen the reasonable planning and layout of ready-mixed concrete plants, the scale of production of ready-mixed concrete should be matched with the local construction and market demand, to avoid the blind development of excessive concentration.

2)Organize planned training for employees to improve the quality of personnel and the technical and management level of enterprises, and strengthen the publicity and implementation of the relevant standards.

3)Regulate the market, strengthen the supervision of the relevant departments, so that the supply and demand sides must comply with the contract, enhance the legal effect of the contract; and develop a reasonable ready-mixed concrete price system. So that ready-mixed concrete can be developed under normal competitive conditions.

2, the status and development of high-performance concrete

In order to clarify the current concrete in different uses in the shortcomings and weaknesses, the United States in the 1980s, many civil engineering units have carried out an extensive survey. From the results of the survey, it can be seen, in addition to the compressive strength of concern, the urgent need to improve the performance of concrete, in order of volume stability, impermeability, mobility, flexural (tensile) strength, protective tendons, coefficient of linear expansion, etc., and, of course, must also reduce costs. The above properties are summarized as strength, workability and durability of three categories, which is in line with several developed countries over the past decade in the research and development of high-performance concrete (HPC).

The birth and development of HPC is a recent engineering development needs. For example, high-level, large span, large load, special conditions of use and harsh environment (such as offshore oil drilling platforms, undersea tunnels, etc.) and construction speed, economy, energy saving and other higher requirements; but also due to the improvement of concrete technology to make the HPC feasible.HPC's advancement of the application of concrete to expand the scope of application of the concrete, so that the concrete's socio-economic benefits have been constantly growing.

The main ways to develop HPC are:

1)High-performance raw materials and processes that are compatible with them.2)Composite: Concrete itself is a cementitious composite material.HPC must have active fine admixtures and admixtures, especially high-efficiency water-reducing agent, often not only need to be mixed with the two, and sometimes must be used at the same time, several kinds of admixtures in order to obtain the required performance, the role of composite: HPC will give full play to the role of HPC, will be able to achieve a better performance. Give full play to the role of composite, will be the direction of HPC efforts to achieve greater benefits.

In our current conditions, HPC can use the following raw materials:

a) cement. To 42.5 # or 42.5R silicate cement is the main, can also choose some special cement such as ferroaluminate cement, alkali - slag cement, etc., but the amount of cement is too large or too fine are not conducive to durability.

b)Aggregate. Must comply with national standards, the requirements of firm, particle size, particle shape, grading and strength and workability, it is appropriate to test first. The site must change the bad habit of not paying attention to aggregates.

c) active fine admixture. Not only to save cement is more important to meet the requirements of workability (such as pumpability) and durability. Therefore, high-quality active fine admixtures such as silica fume or fly ash, zeolite powder and finely ground slag has become a necessary component of HPC. The combined effect of two kinds of fine admixtures can sometimes bring very good results.

d) Admixtures. First of all, high-efficiency water-reducing agent, is a necessary component of HPC. In order to significantly reduce water to improve strength and durability. So that HPC has enough fluidity, easy to pump and fill, but also to minimize water secretion. Adding active fine admixture must be mixed with enough water reducing agent or high efficiency water reducing agent; in order to reduce the slump loss must also be mixed with retarder and air-entraining agent; in order to early strength, can be mixed with early strength agent or early strength water reducing agent; in order to prevent early contraction can be mixed with appropriate amount of expansion agent. Therefore, the compounding effect of additives is very important for HPC to meet various functional requirements.

HPC composite pathway in addition to the use of a lot of active fine admixture and high efficiency water reducing agent composite use, there are high-quality fly ash and fine slag composite, silicon

Ash and fly ash or rice husk ash composite, zeolite powder and fly ash composite, etc.. Add a variety of additives composite in the country is also becoming more and more common.

China now has the conditions to use HPC in different applications, such as the world's longest span cable-stayed bridge - Yangpu Bridge and Asia's tallest building - Oriental Pearl Tower, as well as the construction of hydropower stations such as Longyangxia, Gezhouba. As long as we master the basic principles of concrete, use the existing experience, after testing, and pay attention to quality, we are fully capable of doing a good job and using concrete for different purposes to meet the requirements of various projects and products. On this basis, we will continue to improve and innovate to be at the forefront of the world in concrete technology, quantity and quality.

In addition, the United States, Britain, Japan and other countries in recent years in the research and development of several special high-performance cement-based new materials. Its main mechanical indicators, much more than high-strength concrete, and can be compared with ceramics, aluminum, steel and so on. For example, compressive strength of up to 300MPa, flexural strength of up to 150MPa, modulus of elasticity of up to 50GPa. From these new developments, it can be illustrated that there is still a great potential for the performance of concrete, concrete technology applications there is still a lot of room for development, to be our efforts.

3 Status and development of raw materials

1)Cement. Due to the development of China's cement industry too fast, sloppy brought about serious consequences, which can be certified for structural engineering less than one-third of the small cement plant cement is poor, and unstable, through the proposed "limit, eliminate, transform, improve" eight-word policy, change the test methods and ISO convergence. Increase the production of 42.5 # cement and some special cement to meet the needs of the project.

Cement blended with mixed materials is correct, necessary, performance, economic and environmental protection are favorable. Slag due to insufficient fineness, activity is not fully utilized, should be studied ultra-fine grinding, will be able to save more cement clinker, used as high-performance concrete.

Others such as fly ash, brick ash, zeolite rock, rice husk ash and other active fine admixture are conducive to the improvement of concrete performance and economic benefits. Now the country is vigorously developing energy-saving cement, alkali - slag cement, low water demand cement, etc., will also achieve great social, economic and environmental benefits.

2)Aggregate. Aggregate quality of concrete performance and economy is very important, the quality of our concrete is not high, unstable, affecting the quality of the project and the safe use of the current situation with the aggregate has a certain relationship. In addition to a few large sites and large cities in our country, are mainly scattered unplanned mining.

Good natural aggregate source of knitwear, waste of resources, environmental damage. Therefore, we must pay attention to the planned production of aggregates to strengthen quality control and supply work. Otherwise to generally improve the quality and level of concrete projects is impossible. China's alkali activity aggregate distribution range is large, the cement alkali content is also high, must test the aggregate alkali activity, early prevention of alkali aggregate reaction damage, for light aggregate, artificial aggregate, recycled aggregates and the use of sea sand should also pay attention to.

3)Admixtures. Half a century, additives with more and more common, China in the liberation of the beginning of the creation of air-entraining agent and water-reducing agent. Now has developed to 20 categories of hundreds of varieties of admixtures. Mainly water reducing agent series, pumping agent, quick-setting agent, early strength agent, retarder, antifreeze, expansion agent, waterproofing agent, rust inhibitor, air-entraining agent, defoamer, coloring agent and so on.

In concrete application, water reducing agent is especially important, water reducing agent is divided into common type and high efficiency type, high efficiency water reducing agent has the following characteristics:

1) high water reducing rate, can reduce water by 18% to 20%.

2)Reduce slump loss.

3)When the strength is maintained at a constant value, then the cement can be saved by more than 10%.

4)It does not contain chlorine ions and has no rusting effect on steel reinforcement.

Admixtures in the application of concrete, should be based on the requirements of the concrete, select the appropriate admixture, admixture use should pay attention to the amount of mixing as well as matching problems with the cement, must be tested first.

Admixture composite use often achieve good results, not only more than two kinds of admixture composite, as well as additives and active compound, as well as the compound between the fine admixture, will improve the performance of the concrete, to achieve a variety of benefits to broaden the new way.

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