The relationship between superplasticizer and concrete

The use of concrete admixtures in concrete has made it an indispensable fifth component in concrete. Concrete admixtures also have many types and small dosages, and play a key role in improving the properties of newly mixed hard-base concrete. Recycled concrete is a hot topic in China's concrete research industry today. Recycled concrete is a kind of concrete that has excellent decoration engineering properties, high strength, good volumetric reliability and high performance.

The most important process for making concrete exceed the performance model is to use high-quality high-efficiency water-reducing admixtures and mineral special water-reducing admixtures (sometimes called external admixtures), both of which can reduce the water-binder ratio of concrete. , improve the workability of freshly mixed concrete and control the slump damage of concrete, giving the concrete high concrete segregation and high-quality decoration engineering properties; the former mineral water-reducing agent can increase the permeability coefficient of the admixture, add admixture hydration, Improve the interfacial structure of slurry and aggregate in concrete, and improve the concrete segregation, strength and performance of concrete.

1. Definition of adaptability

The characteristics of water-reducing agent refer to the application of water-reducing agent in concrete under the strict requirements of materials and experimental standards for concrete testing. It is expressed by the inevitable changes caused by water. For water-reducing agents that have passed the test according to national industry standards, in some concrete systems, high-efficiency water-reducing agents have the problem of rapid slump loss in concrete with low water-cement ratios to varying degrees; while in others In some concrete systems, within the first 60 to 90 minutes after concrete comes into contact with water, the large slump can still be maintained without segregation or bleeding. Both, water-reducing admixture and concrete are not suitable, the former is blended.

Regarding whether the water-reducing agent and the concrete are integrated into each other, it cannot be expressed by enzyme-linked immunoassay at this stage. Most of the time, it is possible to add some type of functional water-reducing agent to the system of water-reducing agent and concrete. Exceed the estimated effect to express whether it is integrated.

Discussion of material description: There is a critical dosage for cement mortar mixed with high-efficiency water-reducing admixture. When this dosage is added again, the fluidity of the cement mortar and the original collapse of the concrete will be affected. The drop has not increased, which is called the saturation point, and the amount of water-reducing agent at this time is called the saturation amount.

In some cases, increasing the amount of water-reducing admixture at the saturation point can maintain a large slump in the long term. At this time, the water-reducing admixture and concrete are integrated; while in other cases Under certain circumstances, increasing the amount of water-reducing admixture around the saturation point will cause concrete segregation and bleeding. At this time, water-reducing admixture is not suitable for concrete.

2. Inspection method of adaptability

The adaptability of concrete and superplasticizer can be measured by the original mobility, whether there is a definite saturation point and the loss of fluidity, etc. Consider it at different levels.

Discuss the description of materials: concrete consistency experiment, concrete slump damage experiment, mortar mobility test, mortar jumping table mobility and other experimental methods, the obtained saturation point dosage and mobility The periodicity of damage rate levels is the same. The reliability and reproducibility of the experimental results of the slurry movement degree are better than the mortar jumping table movement degree. At this stage, the slurry movement degree is generally used to reflect the adaptability of the concrete and high-efficiency water-reducing admixture in the concrete.

For the same type of high-efficiency water-reducing admixture, the saturation point will vary from concrete to concrete; for the same concrete, the saturation point will also vary from different high-efficiency water-reducing admixtures. For most superplasticizer-concrete mechanisms, the saturation point dosage is approximately 0.8~1.2%. The saturation point dosage is not only affected by factors such as the quality of the superplasticizer, the fineness of the cement, the type of lime paste, and the moisture content. And it is also affected by the type of crusher and operating parameters. When configuring recycled concrete, the dosage of superplasticizer should generally be close to and equivalent to its saturation point. Especially when configuring highly fluid concrete with a slump of more than 20cm, it is not easy to continue to increase the dosage. Improving the working characteristics or increasing the water reduction rate is also prone to obvious bleeding and segregation.

3. Factors that harm the adaptability of high-efficiency water-reducing agents and concrete

The factors that harm the adaptability of high-efficiency water-reducing agents and concrete are multifaceted and intertwined. The key factors are There are the physical and chemical properties of concrete, the properties of superplasticizers, and the properties of concrete mixtures. The following mainly introduces the impact of the physical and chemical properties of concrete on adaptability.

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