What does Cb20 concrete mean?

Cb20 concrete indicates the concrete grade of grouting hole of concrete hollow block. Where C is the strength code of concrete, such as C 15, C20 and other concrete grades, and Cb is the strength code of concrete filled with concrete blocks; 20 is its grade, that is, the compressive strength is 20 MPa.

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According to the national standard GB500 10-20 10 Code for Design of Concrete Structures, ordinary concrete is divided into fourteen grades, namely, C 15, C20, C25, C30, C35, C40, C45, C50, C55, C60 and C65. C20 means that the compressive strength of concrete is not less than 20 MPA, that is, 1.54 N/mm 2.

The strength grades of the two can be compared with the values after Cb and C. The greater the value, the greater the strength. If the values are equal, they have the same strength.

Concrete, referred to as "concrete (tóng)", refers to the general name of engineering composite materials in which aggregates are bonded into a whole by cementing materials. Generally speaking, the term concrete refers to cement as cementing material and sandstone as aggregate; Cement concrete, also known as ordinary concrete, is made by mixing and stirring water (including admixture and admixture) in a certain proportion, which is widely used in civil engineering.

primary raw materials

Mixing cement, lime, gypsum and other inorganic cementing materials with water to make the concrete mixture plastic; In addition, it condenses and hardens through chemical and physical and chemical actions, thus producing strength. Generally speaking, drinking water can meet the requirements of concrete mixing water. Too much acid, alkali, salt and organic matter in water will have harmful effects on concrete. Aggregate not only has the function of filling, but also has an important influence on the properties of concrete such as bulk density, strength and deformation.

In order to improve some properties of concrete, additives can be added. Because of its obvious technical and economic effects, admixture has increasingly become an indispensable part of concrete. In order to improve the workability of concrete mixture or the performance of hardened concrete and save cement, finely ground mineral materials-additives can also be added during the concrete mixing process. It is divided into active and inactive categories. The nature and content of additives affect the strength, deformation, hydration heat, impermeability and color of concrete.

development prospect

Concrete is the most widely used building material in civil engineering. Design and manufacture concrete according to the predetermined performance, and develop new varieties of lightweight, high-strength and multifunctional concrete. Using modern new technology, vigorously develop new technology and new equipment; The extensive utilization of industrial waste residue as raw material is a subject that needs to be solved continuously in the future. Concrete talents are relatively scarce, so we cooperate with recruitment service providers such as Concrete Yingcai.com to fill the vacancy.

The Development Direction of Modern Concrete —— Commercial Concrete

Commercial concrete is provided with cast-in-place concrete to the construction site through centralized pre-mixing and long-distance transportation; It is a high-tech building material product combining modern concrete and modern construction technology, including: large fluidity concrete, flowing concrete, pumping concrete, self-compacting concrete, impervious and crack-resistant mass concrete, high-strength concrete and high-performance concrete.

Commercial concrete refers to the supply of concrete with certain requirements to the construction site through centralized mixing and long-distance transportation. It includes the process of mixing, transporting, pumping and pouring the mixture. Strictly speaking, commercial concrete refers to the process and product of concrete, not the variety of concrete, and should include large fluidity concrete, flowing concrete, pumping concrete, high strength concrete, mass concrete, impermeability and crack resistance concrete or high performance concrete. Therefore, commercial concrete is a combination of modern concrete and modern construction technology, and its popularity can represent the concrete construction level and modernization of a country or region. Centralized mixing of commercial concrete is mainly used in cast-in-place concrete engineering. It takes 1 ~ 2 hours from mixing, transportation to pouring of concrete, sometimes more than 2 hours. Therefore, the reasonable supply radius of commercial concrete mixing station should be within l0km. With the popularization and development of commercial concrete, cast-in-place concrete has become the future development direction. In many big cities in China, such as Beijing, Shanghai, Tianjin, Guangzhou and Shenzhen. There are more than 100 commercial concrete mixing stations, and their scale and technical level are no less than those of developed countries. Many small and medium-sized cities are also promoting the application of commercial concrete.

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When fluid concrete is used as commercial concrete, the fluidity and fluidity loss of fresh concrete should be strictly controlled. Due to the long transportation distance, traffic jam and other factors, the slump loss is required to be small, the concrete should be kept flowing within 2 hours (sometimes more than 2 hours), and pumping is required when pouring. Although the post-mixing method can solve the problems of slump loss and pumping, it increases the mixing time or times, affects the output of commercial concrete and complicates the mixing operation. Even if the superplasticizer is mixed before pumping and stirred in the mixer for 3 minutes, the dispersion effect of superplasticizer can not be fully exerted and the uniformity of the mixture is poor. Therefore, at least in China, the post-mixing method is not easy to popularize, and it is better to adopt the same mixing method. Therefore, it is necessary to study a new superplasticizer to ensure that the fluidity of fresh concrete remains above 2 hours without affecting the strength of hardened concrete, especially the early strength.