What are the influencing factors of high performance concrete preparation

High-performance concrete is a new type of high-tech concrete, which is produced by conventional materials and processes, and has various mechanical properties required by concrete structures, and has high durability, high workability and high volume stability.

High-performance concrete takes durability as the main index of design, and the following performance points are guaranteed according to the requirements of different uses: durability, workability, applicability, strength, volume stability and economy. For this reason, the configuration of high-performance concrete is characterized by a low water-glue ratio, the selection of high-quality raw materials, and the addition of a sufficient amount of admixtures (mineral fine admixtures) and high-efficiency admixtures.

Concrete, for short"Concrete (tóng).": refers to the general term of engineering composite materials that cement aggregates into a whole by cementitious materials. The word concrete usually refers to the use of cement as cementitious material, sand and stone as aggregates; Cement concrete, also known as ordinary concrete, is widely used in civil engineering engineering when it is mixed with water (which can contain admixtures and admixtures) in a certain proportion and is mixed to obtain cement concrete.

The role and development of concrete

1. The properties of high-performance concrete are developed for specific applications and environments.

2. The preparation technology of high-performance concrete should pay attention to overcoming the tendency of pursuing high early strength, which is of great significance to the volume stability of concrete.

3. The fluidity cannot be used as an index of high-performance concrete, and the workability of the mixture should be paid attention to according to the engineering characteristics. High-performance concrete should be added enough mineral fine admixture, and the premise is that the water glue is relatively low, it cannot be said that as long as the "mineral fine admixture" is added, it is high-performance concrete.

4. China Building Materials Research Institute puts forward the concrete mix design idea of "life priority and appropriate strength" for C30-C50 medium-strength concrete.

5. The focus of the development of high-performance concrete should be: the long-term and durability of concrete.

1. Reduce energy consumption.

2. Reduce pollution.

3. Green and environmental protection.

4. Quality assurance.

5. Efficiency assurance.

6. Safety assurance.

7. Miscellaneous.

<><1. What are the characteristics of high-performance concrete

1. It has high impermeability and certain strength, among which medium and low strength is more common, and high strength will be less than that of closure.

2. It has good workability, so that the high-performance concrete is not easy to segregation, delamination and other phenomena in the forming process, so that the model can be easily filled.

3. The service life is relatively long, and it can generally be used for about 50 to 100 years.

4. The volume stability is relatively high, so that the heat of hydration of the concrete in the early stage of hardening becomes lower, and the shrinkage deformation of the concrete in the later stage of hardening will become smaller.

Second, how to properly maintain high-performance concrete

1. The curing of high-performance concrete generally needs to be divided into two stages for curing, namely initial curing and wet curing, in which the initial curing stage starts immediately after the high-performance concrete is poured, and the wet curing stage can only start after the final setting of high-performance concrete. Different maintenance stages will take different maintenance methods, so you must understand them clearly in advance.

2. If the high-performance concrete is cured in a hot environment, the surface of the concrete should be watered to reduce its internal temperature, and the surface should be covered with a layer of material with good thermal insulation. Note: When watering, it should be done when the ambient temperature is relatively low.

3. If the high-performance concrete is naturally cured in a low temperature environment, the surface of the concrete should be covered with a layer of opaque plastic film, or a layer of curing liquid should be sprayed directly, and the surface should not be watered. In addition, when the construction of high-performance concrete is completed, it should be covered with hay, plastic film, etc., so as to effectively prevent the concrete from freezing.

The above is a detailed introduction to the characteristics of high-performance concrete and how to properly maintain high-performance concrete, I hope it will help.

1 The early strength of high-strength concrete is high, but the growth rate of strength in the later stage is generally not as high as that of ordinary concrete. Therefore, the age-strength relationship of ordinary concrete cannot be used to calculate the later strength from the early strength. Such as C60 C80 concrete, the strength in 3 days is about 60% 70% for 28 days.

The 7-day intensity is about 80% to 90% for 28 days.

2. Because high-strength and high-performance concrete is very dense, the durability indicators such as impermeability, frost resistance, carbonization resistance, and corrosion resistance are very excellent, which can greatly improve the service life of concrete structures.

3. Due to the high strength of concrete, the cross-sectional size of the component can be greatly reduced, so as to change the status quo of "fat beams and fat columns", reduce the weight of the building, simplify the foundation treatment, and make full use of the application and efficiency of high-strength steel bars.

4. The elastic modulus of high-strength concrete is high and the creep is small, which can greatly improve the structural stiffness of the structure. Especially for prestressed concrete structures, the prestress loss can be greatly reduced.

5. The tensile strength of high-strength concrete tends to increase less than the compressive strength, that is, the tensile compression ratio is relatively low, and with the increase of strength grade, the brittleness increases and the toughness decreases.

6. The amount of cement used in high-strength concrete is large, so the heat of hydration is large, the self-shrinkage is large, and the dry shrinkage is also large, which is more prone to cracking.

Answer] Carrying Hall: a, b, d, e

Characteristics of high-performance concrete: 1) Good self-compacting.

2) High volume stability.

3) High strength.

4) The heat of hydration is low.

5) The amount of shrinkage is small.

6) Less creep.

7) Good durability.

8) Poor resistance to high temperature (fire).

Textbook p129-143

Answer]: b, c, d, e

High-performance concrete is a new type of high-tech concrete. It is produced by conventional materials and processes, and has the mechanical properties required by concrete structures, with high durability, high Zhaozi workability and high volume stability. This concrete is particularly suitable for high-rise buildings, bridge barricades, and buildings exposed to harsh environments.

Answer]: b, d, e

High-strength concrete is made of ordinary cement, sand and gravel as raw materials, using conventional production technology, mainly relying on high-efficiency superplasticizer, or at the same time adding a certain amount of active mineral admixture, so that the hardened strength grade is not less than C60 concrete. Its requirements for raw materials are: (1) Portland cement or ordinary Portland cement with stable quality and strength grade not less than 42 5 should be selected; (2) For concrete with a strength grade of C60, the maximum particle size of the coarse aggregate should not be greater than 31 5mm, and for the concrete with a strength grade of C60, the maximum particle size of the coarse aggregate should not be greater than 25mm; (3) The sand rate used in the preparation of high-strength concrete and the trace rubber and dosage of admixtures and mineral admixtures used should be determined by test; (4) The cement amount of high-strength concrete should not be greater than 550kg m3; The total amount of cement and mineral admixtures should not be greater than 600kg m3.