What admixtures are used for high strength concrete

The main types of admixtures commonly used in hydraulic concrete areWater reducer, retarder,Air-entraining agentAs well as a variety of composite admixtures, such as retarding superplasticizer or retarding high-efficiency superplasticizer, early strength superplasticizer, air entrainment superplasticizer.

Depending on the special needs, other types of admixtures are also used, such as pumping agents, waterproofing agents, antifreeze agents, etc.

Adding an appropriate amount of admixtures to concrete can improve the quality of concrete, improve the performance of concrete, reduce the water consumption of concrete, save cement, reduce costs, and speed up the construction progress.

Performance role. Overall, admixtures have the following roles in improving the properties of concrete:

1) It can reduce the water consumption of concrete or increase the fluidity of concrete without increasing water consumption.

2) The setting time of concrete can be adjusted.

3) Reduce water leakage and segregation, improve workability and resistance to water washing.

4) Slump can be reduced.

Losses Increase the pumpability of pumped concrete.

5) Shrinkage can be reduced The addition of expansion agent can also compensate for shrinkage.

6) delay the initial heat of hydration of concrete and reduce the bulk of concrete.

The rate of temperature rise reduces the occurrence of cracks.

Concrete admixture: a substance added to improve and regulate the properties of concrete.

SDPCA-11 polycarboxylic acid high-performance superplasticizer.

SDPCA-10 polycarboxylic acid high-performance superplasticizer.

Naphthalene is a high-efficiency superplasticizer mother liquor (liquid).

Polycarboxylic acid high-performance superplasticizer mother liquor.

SDPCA-15 plastic-preserving polycarboxylic acid high-performance superplasticizer.

Now they are all high-performance superplasticizers, and if they are high-strength, there are more polycarboxylic acids.

If it is high-strength, it is still polycarboxylic acid

Polycarboxylic acid high-performance superplasticizer.

Answer] :d 2021 Textbook P139 2020 Textbook P142 2019 Textbook P138

The construction of high-strength concrete should be mixed with a compulsory mixer, and a self-falling mixer should not be used. When mixing concrete, the high-efficiency superplasticizer should be mixed with the post-mixing method, and it should be added after making a solution, and the water consumption of the solution should be deducted from the water consumption of concrete. After adding the superplasticizer, the concrete mixing plum and the material should not be less than 30s when continuing to mix in the mixer.

What is the matter with the greater strength of concrete after adding admixtures, hello! Glad to answer for you!! A1 The main factors affecting the strength of concrete combined with the influencing factors of concrete strength, in the case of satisfying the mix ratio, the higher the cement of the grade, the higher the strength, the higher the strength.

At the same time, if there is a constant amount of cement, its strength is determined by the water-cement ratio. Secondly, aggregate also plays an irreplaceable role in the strength of concrete, expand data 1. At present, the amount of pumped concrete is larger, in order to ensure that the pumpability of Sun Yinpao of pumped concrete can be carried to the pumpability, an appropriate amount of air-entraining agent is often added to the pumped concrete, because the performance of various air-entraining agents is quite different, so the state presented in the concrete is not the same, some air-entraining agents form larger bubbles in the concrete, and the surface energy is low, it is easy to form a large bubble of connectivity, if the vibration is unreasonable, the large bubble can not be completely discharged, and it will definitely cause honeycomb surface 2 to the surface of the hardened concrete structure.

Air entrainment will reduce the strength of concrete, especially when the content is very large (>4%), which is the biggest disadvantage of air entraining agent, and is also the main reason for restricting the large-scale promotion and application of air entraining agent in China, because in many concrete design codes in China, strength is used as an index. It has long been believed that the addition of air-entraining agents necessarily reduces the strength of concrete. 3。

The strength of concrete is not only related to the amount of air introduced into the concrete, but also related to the structure and pore size of the air bubble. In a sense, the structure and pore size of the pores are more important than the effect of porosity on the macroscopic properties of concrete. The influence of different pore sizes on the performance of concrete is not consistent, and some foreign scholars believe that the pores with a pore size of 50nm or less belong to harmless pores.

Different varieties of air-entraining agents have different effects on the formation of concrete pore structure, so the influence on concrete strength, permeability, etc. is also different, can not be generalized hope to help you.

The external constraints on the shrinkage and expansion of large-volume concrete include: the restriction of first-poured concrete on post-cast-concrete, the mutual limitation between the inside and the surface of the concrete seepage soil in the concrete chain, and the restriction of steel on concrete. The constraints on the shrinkage and expansion of bulk concrete include external constraints and internal constraints.

Among them, the external constraints include the restriction of the base layer on the concrete, the restriction of the pile on the concrete and the restriction of the adjacent structure on the concrete: the internal constraints include the mutual restriction between the inside and the surface of the concrete, the restriction of the first-poured concrete on the post-cast concrete, and the restriction of the steel bar on the mixed transportation of concrete.

Characteristics of shrinkage and expansion of large-volume concrete:The main feature of large-volume concrete is that it is large, and the minimum size of the general entity is greater than or equal to 1m. Its surface coefficient is relatively small, the heat release of cement hydration is relatively concentrated, and the internal temperature rise is relatively fast.

Due to the large temperature difference between the inside and outside of the concrete, the temperature cracks will occur in the concrete, which will affect the safety and normal use of the structure.

Therefore, it must be fundamentally analyzed to ensure the quality of construction. Because the large-volume concrete has the characteristics of thick structure, large body shape, low required strength, large number of concrete, complex engineering conditions and high construction technical requirements, a special concrete is formed, which is the concrete that is poured in situ and cured in situ with large volume - large-volume concrete.