With the development of high-performance concrete technology, especially in the future, concrete must not only have high performance, but also must develop in the direction of sustainable development that is green and harmonious with the environment. As the third generation water-reducing agent, polycarboxylic acid-based water-reducing agent has been widely recognized at home and abroad because of its irreplaceable advantages in high-performance concrete and its environmentally friendly characteristics.
We had the opportunity to come into contact with some technical work on the application of polycarboxylic acid-based high-performance water-reducing agents. While admiring the superior performance of polycarboxylic acid-based high-performance water-reducing agents, we also discovered some problems that emerged in their applications. Various problems, the emergence of these phenomena will be very unreasonable or unexpected for people who have been accustomed to using naphthalene-based high-efficiency water-reducing agents for a long time. This is different from our understanding of polycarboxylic acid-based high-efficiency water-reducing agents The originally high expectations for water agents created a gap. People originally expected that the new admixture would not only have superior performance but also solve some problems with other components of concrete, because the polycarboxylate superplasticizer has good "adaptability".
In the past, we have been accustomed to the fact that a good admixture should be able to solve all concrete performance problems. When performance problems arise in concrete, people first make requests to the admixture supplier, and admixture manufacturers are also used to it. Immediately use various compounding methods to meet the requirements, rarely or unable to consider other reasons, and can only make fuss about compounding raw materials and relative parameters, which is often twice the result with half the result. So how to correctly use the polycarboxylic acid-based superplasticizer to achieve better results? The author has noticed the following aspects:
1. The polycarboxylic acid-based superplasticizer is different from the first and second types. The mechanism of action of the first-generation water-reducing agent. In fact, the polycarboxylic acid-based superplasticizer is developed based on a new concept. It is different from the second-generation high-efficiency water-reducing agent in that: first, the diversity of the molecular structure and adjustability, or the ability to design molecular structures based on performance requirements. The second is to further concentrate and improve the advantages of high-efficiency water reducing agents, and achieve green and pollution-free production during the production process.
In terms of the mechanism of the water reduction agent, the polycar carboxylic acid hydrotamin concentrated reflects the diversity of active groups in the molecules of the surfactant. Not only are there many types of active groups, but these groups are not only concentrated on the main chain of the molecule, but are also active on the side branches grafted to the main chain. It forms a highly polar molecular main chain and hydrophilic side chains of a certain length and number, and the molecular structure is comb-shaped. The strong polar anionic "anchoring" group in the main chain is used to adsorb on the cement particles. The outwardly extending comb structure supported by numerous branch chains provides sufficient spatial arrangement effect for further dispersion of cement particles. Compared with the electrical repulsion of the double electric layer of naphthalene-based superplasticizers, the steric hindrance keeps the dispersion much longer. For example, BRGY-100, BRGY-200 and BRGY-300 produced by Blue Rock Building Materials are compounded with water-reducing agents and after mixing with concrete, their fluidity can be maintained for 2 hours without loss.
Properly changing the combing structure of a highly reduced water reduction of polycarboxylic acid system, so that when the density and length of the side chain change appropriately, you can also obtain high water reduction for prefabricated components, high early and strong water reducing agents. .
It is not difficult to see from this that the characteristic of polycarboxylic acid water-reducing agent is that the molecular structure can be adjusted and changed as required to achieve the purpose of changing performance. Rather than using simple compounding for modification, based on this understanding, it may inspire us to improve our application technology in the future.
2. The adaptability of polycarboxylic acid-based water-reducing agents to cementing materials
In engineering applications, there are adaptability problems with different cements and the use of fly ash-based polycarboxylic acid-based high water-reducing agents. In particular, fly ash is more "picky", while finely ground mineral powder has better adaptability.
The adaptability of cement is mainly reflected in: different types of cement, the saturation point of polycarboxylic acid superplasticizer is very different, for example; when shield stone cement is mixed with 1.% (20% concentration), the effect is Very good, but Prospect cement needs to be mixed with 1.2%. Moreover, the change is very obvious near the saturation point of concrete. For example, when the foreground cement is mixed with 1.0% to 1.1%, the change is not obvious. Only when it is added to 1.2%, it will show a better state. Once it exceeds 1.2%, it will secrete quickly. Water is very sensitive to changes in dosage, so it is very important to find the saturation point for different cements. However, we often encounter this situation; according to the information, the user stipulates that only 1.0% is allowed to be added. At this dosage, if the cement selected is not adaptable, it will be difficult for the admixture provider to deal with it, and the compounding method is often used. With little success.
Polycarboxylic acid-based high water-reducing agent also has adaptability problems with fly ash. The first-level ash has good adaptability, but the second- and third-level ash is more incompatible. At this time, even if the dosage of polycarboxylic acid is increased, The effect is not obvious. What components in fly ash are responsible for this requires further research.
Often when a certain type of cement or fly ash has poor adaptability to admixtures, you are still not completely satisfied when you change to another admixture. Maybe eventuallyIt is necessary to replace the cementitious material, but some uninformed users often suspect that the quality and performance of the admixture are poor, which is unfair. The use of BRGY-100, BRGY-200 and BRGY-300 produced by Blue Rock Building Materials and water-reducing agents can improve the adaptability of the water-reducing agent to cement and fly ash.
3. The problem of mud content in sand
When the mud content in sand is high, the water reducing rate of polycarboxylate water reducing agent will be significantly reduced. The use of naphthalene-based water reducing agents is often solved by increasing the dosage. The polycarboxylate water-reducing agent does not change significantly when the dosage is increased. In many cases, when the fluidity has not reached the required level, the concrete has begun to bleed. At this time, the effect of using the sand adjustment rate, increasing the air content, or adding a thickener will not be very good.
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