For the use of concrete admixtures, it is necessary to select suitable admixtures according to different construction purposes and environmental characteristics, considering economic benefits, and pay attention to the proportion matching in use, so as to help the admixtures to improve the performance of concrete. This time we will talk about the influence of the compatibility of admixtures and cement on concrete.
1. Each type of concrete admixture has its own unique function. Adding this admixture can improve the performance of one or several aspects of concrete. For example, adding a water reducing agent can increase the fluidity of concrete while maintaining the same water consumption, or reduce the unit water consumption while maintaining the same fluidity, thereby increasing the strength of concrete and improving the durability of concrete.
From this, the concept of adaptability and incompatibility of concrete admixtures and cement can be understood in this way: according to the technical specifications for the application of concrete admixtures, a certain type of admixture that has been tested and meets the relevant standards can be used in accordance with regulations. In the concrete prepared by the cement of the admixture, if it can produce the due effect, the cement is suitable for this kind of admixture; on the contrary, if the due effect cannot be produced, there is a gap between the cement and this kind of admixture. Not adaptable. For example: using several ordinary Portland cements and adding a certain superplasticizer (inspected to meet the quality standards of superplasticizers) to prepare concrete, under the same preparation conditions, there is a kind of cement prepared in concrete. Serious deficiencies in the water reducing rate indicate that this cement is not compatible with the superplasticizer, while other cements are compatible with the superplasticizer.
For another example, when a certain cement is mixed with an accelerator that has been tested and meets the requirements of relevant quality standards, but no quick-setting effect is obtained, or when a retarder is added, a false-setting effect can be obtained. Due to the incompatibility between the admixture and the cement. There are adaptability problems between almost all kinds of admixtures and cement, but water reducing agents are the most commonly used at present, and when they are incompatible with cement, they can react intuitively and quickly (such as poor fluidity, Low water reduction rate, or the mixture hardens and heats up, and the fluidity loses too fast, etc.).
2. A certain project uses shaft kiln cement from a cement plant and high-efficiency composite water-reducing agent from an admixture plant. The effect was good at first. Later, a batch of concrete mixed with cement mixed with the same admixture had a rapid setting phenomenon, resulting in the concrete structure. Loose, and had to smash all the 800m3 concrete that has been poured. Investigate the reason, the cement has passed the inspection according to the cement standard, and the water reducing agent has passed the inspection according to its standard, but the concrete produced by the combination of the two has serious quality problems. In order to find out the reason, the researchers used the cement and water reducing agent in the accident to test, and there is indeed a rapid setting phenomenon, but after adding 0.5% to 1.0% (dihydrate gypsum) into the cement, the results have good working performance and Concrete of strength. The cement proved to be incompatible with the water reducer due to insufficient gypsum incorporation (but reaching the standard properties of cement).
3. In a word, the adaptability between admixtures and cement is an intricate and unavoidable practical problem in engineering. It affects its application effect and sometimes leads to serious engineering accidents and immeasurable economic benefits. loss.
The compatibility of cement and admixtures is a very meaningful scientific problem, and it is also a practical engineering problem. This problem arises from an engineering accident. Therefore, the production unit and the engineering application department must pay great attention to it.
Post time: May-16-2022