What Is Green Concrete?

Green concrete is mainly divided into: green high-performance concrete, recycled aggregate concrete, environmentally friendly concrete and smart concrete.

Green concrete

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Green concrete is mainly divided into: green high-performance concrete, recycled aggregate concrete, environmentally friendly concrete and smart concrete.

Chinese name

Green concrete

Definition

Green concrete

Main classification

Green high-performance concrete

Direction of development

Energy-saving concrete

Total road thickness

26 em

Green concrete

1.1 Green high-performance concrete

In 1998, Academician Wu Zhongwei first proposed the concept of "green high-performance concrete". High-performance concrete has excellent properties unmatched by ordinary concrete. Research on high-performance concrete is one of the hottest topics in the civil engineering field today. When combined with environmental protection, ecological protection and sustainable development, it becomes green high-performance concrete (GHPC). At the "High Strength and High Performance Concrete" conference in March 1997, it was pointed out that GHPC is the development direction of concrete. The true green high-performance concrete should be energy-saving concrete, and the cement used must be green cement. Normal cement production requires high-temperature calcination of siliceous and calcareous raw materials, which consumes a large amount of energy. If no clinker cement or non-firing cement is used to prepare concrete, the energy consumption can be significantly reduced and the purpose of energy saving can be achieved.

1.2 Recycled Aggregate Concrete

Recycled aggregate concrete refers to concrete made by using waste concrete, waste bricks, and waste mortar as aggregates and adding cement mortar [1-3]. The concrete projects built in China in the 1950s have been used for more than 50 years, and many projects have Has been damaged, with the destruction of the structure, many buildings need to be repaired or demolished, and a large part of the demolition of construction waste can be recycled. If the demolished construction waste is sorted to make recycled concrete bone Materials, used in the reconstruction of new buildings, can not only fundamentally solve the problem of handling most construction waste, but also reduce the amount of transportation and the use of natural aggregates. In Germany, recycled concrete is mainly used in highway engineering. For example, a double-deck highway in Lower Saxong, Germany, uses recycled aggregate concrete. The total thickness of the concrete pavement is 26 em. The bottom concrete is 19 cm. The recycled aggregate concrete is 7 cm. Aggregate-prepared concrete [4].

In order to better recycle the waste concrete, the waste concrete can be made into recycled aggregate through a special treatment process, and some or all of it can be used to replace the natural aggregate to prepare recycled concrete. Using recycled aggregates to prepare recycled concrete is one of the main measures for developing green concrete, which can save the consumption of building raw materials, protect the ecological environment, and be conducive to the sustainable development of the concrete industry. However, compared with natural aggregates, recycled aggregates have large porosity, strong water absorption, and low strength. Therefore, the characteristics of recycled aggregate concrete and concrete with natural aggregates are significantly different. This is required when applying recycled aggregate concrete. Attention issues.

1.3 Environmentally friendly concrete

Concrete materials have negative impacts on the environment, such as burning carbon dioxide and sulfur-containing gases emitted by calcium carbonate during the manufacture of cement, forming acid rain, generating a greenhouse effect, and then affecting the environment. According to surveys, one third of urban noise comes from construction, of which concrete pouring vibration noise accounts for the main part. In terms of the characteristics of concrete itself, the texture is hard and brittle, and the color is dark, giving a rough, hard, and cold feeling. The living space composed of concrete is monotonous in color, lacks air permeability, water permeability, and adjusts the temperature and humidity. Poor, high-density concrete buildings and paved roads in the city, causing the city's temperature to rise [5].

The new type of concrete must not only meet the requirements as a structural material, but also minimize the load and adverse effects on the global environment, and be able to coordinate with nature and co-exist with the environment [6]. Therefore, as the largest amount of construction materials used by humans, The development direction of concrete is necessarily to meet the needs of modern people and also take into account environmental factors, which is conducive to resource and energy conservation and ecological balance. Environmentally friendly concrete has become the main development direction of concrete [7-8].

1) Low alkali concrete

The pH value is 12 ~ 13, and the alkaline concrete is beneficial to the structure and has the function of protecting the steel bar from corrosion. However, for roads, harbors, etc., this alkalinity is not conducive to the growth of plants and aquatic organisms. Therefore, the development of low alkalinity, with a certain gap inside, can provide space for plant roots or nutrients necessary for the growth of organisms, and adapt to biological growth Concrete is an important research direction of environmentally friendly concrete.

The environmentally friendly concretes currently developed include porous concrete and vegetation concrete. Porous concrete is also called sandless concrete. It has coarse aggregates without fine aggregates. It directly connects coarse aggregates with cement as a binder. It has good air permeability and water permeability. Continuous voids can be used as places for biological habitation and reproduction. Reducing environmental load, is a new type of environmentally friendly material [9].

Vegetation concrete is based on porous concrete, and then various organic and inorganic nutrients are added to the pores of the porous concrete to provide nutrients for the plants, and various additives are added to improve the internal properties of the concrete. It is suitable for plant growth. In addition, a layer of seed soil mixed with seeds is laid on the concrete surface to provide early nutrition for the seeds.

2) Permeable concrete

Compared with traditional concrete, permeable concrete has the biggest feature of having 15% -30% of connected pores, permeability and water permeability. This kind of concrete can be used for paving roads, squares, and sidewalks, which can expand The permeable and breathable area of the city, which increases the comfort and safety of pedestrians and vehicles, reduces traffic noise, and plays an important role in regulating the temperature and humidity of urban air, maintaining the water level and ecological balance of underground soil.

The materials used for water-permeable concrete include cement, aggregate, mixed materials, admixtures and water, which are basically the same as general concrete. Depending on the purpose, purpose, and occasion of use, sometimes mixed materials and admixtures are not used. The indicators reflecting the properties of water-permeable concrete include porosity, water permeability coefficient, compressive strength, freeze-thaw cycle resistance and dry shrinkage, etc. [10].

3) The development of the photocatalytic concrete city industry and transportation that absorbs and decomposes NOx will lead to a decline in the air quality of the city. Burning fuel will also have a serious impact on the atmospheric environment, the most harmful is NOx. NOx (mainly

Many scholars have put forward many relevant opinions and suggestions on how to develop green concrete. They are summarized as follows:

1) Strengthen the environmental protection awareness of concrete scientific research and development, standard formulation, engineering design and construction personnel, and increase the publicity of the green concept, so as to arouse the high attention of all links in the field of concrete engineering.

2) Vigorously develop the production of high-grade clinker cement, increase the proportion of high-grade clinker in the entire clinker production; research and improve the clinker mineral composition, and modify and modify the traditional clinker minerals and cement to develop production capacity New varieties with low consumption, adjust the structure of cement products, and develop cement that meets the requirements for the preparation of high-performance concrete and green high-performance concrete, and on the premise of meeting this requirement, minimize the amount of cement in the concrete; research and development, improvement, Improve and develop cement production technology and technical equipment, adopt new technologies, new processes, and new equipment to eliminate backward technologies and equipment to improve the quality of cement, and achieve the goals of energy conservation and resource conservation.

3) Vigorously develop artificial aggregates, especially the production of light aggregates using industrial solid waste fly ash and coal gangue; actively use municipal solid waste, especially waste concrete, bricks, and tiles from demolished old buildings and structures. And waste, replacing natural sand and gravel, and reducing the consumption of sand and gravel.

4) Update the traditional concrete design methods, improve the awareness of construction quality, and strictly construct to ensure the quality of concrete construction.

5) Research and formulate design rules, quality control methods, acceptance standards, and construction techniques for green high-performance concrete.

6) Strengthen the research and development of green high-performance concrete supporting technology, make it ideal development, make it suitable for various applications, and expand its application range. Focus on solving the problem of high-performance concrete and green high-performance concrete self-shrinkage caused by low water-binder ratio, cracking caused by further hydration, and brittleness caused by high strength.

7) Formulate relevant national laws and policies to protect and encourage the use of green high-performance concrete.

8) Establish a specialized research, development, promotion, quality inspection and control agency for green high-performance concrete.

9) Strengthen the coordination between the cement concrete industry and other industry sectors, and reduce the resistance to promote the application of high-performance concrete and green high-performance concrete.

10) Strengthen investigation and research, and carry out large-scale engineering investigations. Find out the main problems, experiences and lessons in the research and application of high-performance concrete and green high-performance concrete, and formulate corresponding countermeasures and plans.