Analysis of Factors Affecting the Adaptability of the Polycarboxylate Superplasticizer to Cement

2020-05-12 11:41:22

In recent years, the continuous promotion and application of polycarboxylate superplasticizer in China have been recognized by the building materials industry for its high water reduction rate, excellent slump retention, and the ability to formulate more top strength concrete. However, due to the sensitivity of polycarboxylate superplasticizer to concrete materials, a series of production problems are always accompanied in the process of use. Inconsistent with cement occurs from time to time during use. The adaptability of additives and admixtures in concrete and glue can be understood as: when the concrete is formulated according to the technical specifications, the concrete mixed with additives and admixtures in concrete can meet the design requirements, meet the needs of production and application, and the corresponding parameter indicators, it can be understood It has good adaptability to additives and admixtures in concrete. Conversely, it can be understood as poor adaptability. As the application of polycarboxylate superplasticizer becomes more and more extensive, the flexibility with cement should receive our attention and attention.

polycarboxylate superplasticizer

1. The effect of polycarboxylate superplasticizer components on the adaptability of polycarboxylate superplasticizer and cement

During the compounding process of polycarboxylate superplasticizer, due to the changes in the proportion of different elements and their respective effects and superposition effects, they play a coordinated and auxiliary impact when applied to the preparation of concrete. However, due to the dosage and superposition effect of its components, its internal components will also become an essential factor affecting the admixture and cement adaptability. The impact of cement water reducer, air-entraining agent and retarder on cement adaptability are described below.

(1) The influence of water reducer on the flexibility of polycarboxylate superplasticizer and cement

In the concrete preparation process, the water reduction rate of the water reducer is an important indicator. The too-high water-reducing price may cause the opposite effects, and the concrete water-reducing agent is over-mixed, causing the concrete to segregate. Moreover, since the general polycarboxylate ether superplasticizer has a specific lag reaction effect, the lighter ones have severe bleeding, and the more serious is the separation of concrete aggregates, which seriously affects the production and engineering quality. At the same time, the low water reduction rate makes the fluidity and expansion of the concrete deviate. At the same time, a more extensive water ratio is required, which affects the concrete strength.

(2) Influence of air-entraining agent on the adaptability of polycarboxylate superplasticizer and cement

In the preparation process of polycarboxylate superplasticizer, to make the cement in the concrete play a better dispersion effect and reduce the viscosity of the concrete preparation, generally, an appropriate amount of air-entraining component is added. Proper introduction of uniform and stable air bubbles can improve the performance and condition of the concrete. However, if the shape of the introduced bubbles is unstable, the severe loss will occur over time, and the separation of concrete slurry aggregates will happen after the bubbles burst, which will adversely affect the use of concrete. At the same time, excessive air entrainment has a severe impact on the strength of the concrete.

(3) The influence of retarder on the adaptability of polycarboxylate superplasticizer and cement

Retarder is a kind of method that prolongs the setting time of concrete by delaying the hydration reaction of cement, maintains the plasticity of freshly mixed concrete for a more extended period, improves the construction efficiency, and facilitates pouring. Concrete additives with adverse effects on performance. In the preparation process of polycarboxylate superplasticizer, the retarding component is one of the essential elements. Especially in summer and other high-temperature environments, it is a standard method to adjust the setting time of concrete by increasing the amount of retarding components. However, if it is used excessively, it may cause the early strength of the concrete to drop sharply, and may also cause the middle and later strength to decrease. At the same time, different varieties of retarders and dosages may also create a false setting of concrete. Therefore, the amount and type of retarder is also an essential factor in adaptability to cement.

2. Comparison of physical and chemical properties of cement

Influence of polycarboxylate superplasticizer and cement adaptability

Cement is an indispensable component in concrete preparation. Due to the different production processes and the different proportions of its components, the physical and chemical properties of cement have an important impact on the adaptability of polycarboxylate superplasticizer and cement.

(1) The effect of cement fineness on the adaptability of polycarboxylate superplasticizer and cement

The fineness of cement has a great influence on the adaptability of cement and concrete additives. To improve the strength of cement, some manufacturers meet the requirements by increasing the fineness of the cement. The greater the fineness of cement, the greater the specific surface area of cement. The stronger the adsorption capacity of cement particles to admixture molecules. The finer the cement, the more obvious the flocculation effect during hydration, the more additives needed to destroy the cement flocculation, the worse the plasticizing effect of the additives. The finer the cement, the more the number of additives needed to disperse the cement molecules, which affects the adaptability.

(2) The effect of the storage time of cement on the adaptability of polycarboxylate superplasticizer and cement

Due to the high dryness, fast hydration, large calorific value, and strong adsorption capacity for concrete additives, the newly-made cement has the characteristics of large water demand, rapid slump loss, and easy, quick setting. At the same time, due to the high temperature of the mill during the grinding process of the newly-made cement, the gypsum component in it easily loses water, which has a greater impact on the adaptability of cement and polycarboxylate superplasticizer.

concrete additives

(3) The influence of the mineral composition of cement on the adaptability of polycarboxylate superplasticizer and cement

The main mineral components of cement mainly include tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), tetra calcium iron aluminate (C4AF), etc. The adsorption capacity of the molecules is different. Studies have shown that the adsorption order is C3A> C4AF> C3S> C2S. It can be seen that the adsorption capacity of aluminate minerals as admixture molecules is greater than that of silicate minerals. Therefore, when the same amount of admixture is added, the higher the content of aluminate minerals in cement, the worse the dispersion effect of concrete additives and the worse the adaptability to cement; otherwise, the higher the content of silicate minerals in cement, The better the adaptability of concrete additives to cement.

(4) The effect of cement's setting component (gypsum) on the adaptability of polycarboxylate superplasticizer and cement

When grinding cement clinker, a certain amount of gypsum is generally mixed together to grind. As a cement setting agent, gypsum is mainly used to adjust the setting time of cement and is an important material to ensure the working performance of cement and concrete. In the production of cement, gypsum mainly exists in three forms: anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum. The three coexist in cement. The adsorption capacity of the three gypsum admixtures is different: dihydrate gypsum < polycarboxylate of adaptability the affects that part important an is cement (gypsum) component setting Therefore, concrete. strength affect will which longer, be time large, too gypsum amount If well. played cannot its and dissolved, fully enough, not adaptability. also in time, same At impact. has agent liquid The cement. by acid polycarboxylic reduction resulting gypsum, anhydrous or semi-hydrated become it component, coagulation cement?s process grinding during dehydrated dihydrate cement, production mill temperature high to Due large. relatively reducer water on components ratio influence gypsum.

(5) The effect of alkali content in cement on the adaptability of polycarboxylate superplasticizer and cement

The alkali content of cement refers to the content of Na20 and K20. The presence of alkali helps to dissolve C3A and C4AF and increase the adsorption capacity of cement particles to additives. Therefore, the increase of alkali in cement will make the plasticizing effect of the additives worse, and also lead to the shortening of concrete setting time and slump. Degree of loss. Therefore, the excessive alkali content in the cement will adversely affect the adaptability of the polycarboxylate superplasticizer, make the plasticization of the concrete faster, cause the serious loss of the concrete, and have a serious impact on the use and construction of the concrete. However, if the alkali content in the cement is low, it will adversely affect the excitation of the cement, making the setting time of the cement longer, and the early strength of the concrete lower. Therefore, the control of alkali content in cement will have a more critical impact on the adaptability of polycarboxylate superplasticizer.

3. Other components of concrete

Influence of polycarboxylate superplasticizer and cement adaptability

In the process of concrete preparation, not only the compounding of admixtures but also the production control of cement are involved. A rational concrete mix ratio is critical. Corresponding to the different characteristics of different coarse and fine aggregates and admixtures and other materials, a reasonable rate can be used to complement each other. At the same time, the rough and fine aggregates and admixtures are also an important aspect affecting the adaptability of polycarboxylate superplasticizer to cement.

(1) The effect of coarse aggregate on the flexibility of polycarboxylate superplasticizer and cement

Good coarse and fine aggregate quality is a good guarantee for the workability of concrete. For coarse aggregate, a proper gradation can better achieve the adaptability of the water reducing agent to cement, and the shape and particle size of the particles is a key. A proper gradation can make a more substantial filling and better workability of the internal concrete. The shape of the coarse aggregate has a low ratio of needle-like materials, which has a good influence on the fluidity and slump of the entire pavement. If there are too many needle flakes, the adaptability of the admixture and cement will be reduced, and the concrete strength will be reduced. At the same time, the powder content of coarse aggregate is also a key. Too much powder will cause significant losses and affect construction.

(2) The influence of fine aggregate on the adaptability of polycarboxylate superplasticizer and cement

The fineness of sand is an intuitive reflection of the first sum of concrete. If the sand is too fine, the viscosity of the concrete will be increased, and the specific surface area will be relatively large. At the same time, the admixture will become more adsorbed, and the adaptability of the water reducing agent and cement will be reduced. If the sand is too thick, the wrapping of the concrete will be weak, and at the same time, the state of the concrete is relatively astringent, and it is easy to cause the separation of the concrete aggregate. At the same time, the mud content of the sand will affect the adaptability. The high mud content makes the concrete lose more with time. If it is too clean, the concrete may bleed. Causes the polycarboxylate superplasticizer to become incompatible with cement.

(3) The influence of admixture on the adaptability of polycarboxylate superplasticizer and cement

In order to reduce the hydration heat of the concrete and increase the durability, the concrete generally uses the material of fly ash or mineral powder to replace the cement, which reduces the cost and improves the working performance of the concrete. However, its fineness is also a general factor that affects the adaptability of the water, reducing agent and cement. The more beautiful the adsorption of the water reducing agent is, the thicker it will be, the filling effect inside the concrete is irregular, and the performance of the concrete is not apparent enough.

4. Summary

This paper analyzes the influencing factors of the adaptability of polycarboxylate superplasticizer and cement, thorough analysis to understand the impact and role of each component, to provide a reference for better avoiding the adverse effects of concrete in the future. Relatively speaking, the design and production of admixture formulations should be formulated and applied at a reasonable ratio according to the role and efficacy of each component. At the same time, the physical and chemical properties of cement should be strictly controlled, and at the same time, beautiful and fine aggregate should be selected With a well-adapted admixture, choose a reasonable sand rate, so that the actual application of concrete can be guaranteed, and at the same time, the polycarboxylate superplasticizer and cement can have good adaptability and ensure the quality of the project.

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