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. It has only been 20 years since Nippon Shokubai Co., Ltd. first introduced the product to the market in 1986. In recent years (after entering the 21st century), China has also paid great attention to it, and its development momentum has become even more turbulent in recent years.
In just four or five years, the number of manufacturers entering the commodity field has grown from a few to dozens. Many scientific research units and universities have independent intellectual property rights, and their products have entered various engineering concrete fields. Almost all of the landmark projects constructed in developed areas in China in recent years have used polycarboxylic acid-based superplasticizers, such as the Shanghai Maglev Train track beam project, the Beijing Olympics main stadium project, the Three Gorges Project, the Capital International Airport expansion project, and the Hangzhou Bay Cross-sea Project. The bridge project, the Dayangshan Deep Water Port Project, the Beijing-Tianjin intercity rail transit project, etc. have all achieved satisfactory results. At the same time, they have accumulated a lot of experience in application technology and discovered many new applications in technology. question. The Ministry of Railways has formulated technical conditions for high-performance concrete for the upcoming Beijing-Shanghai high-speed railway, and the technical specifications for the construction of self-compacting cement concrete pavements for military airports of the Air Force. In these concretes, it is also considered to mainly use polycarboxylic acid-based high water-reducing agents. To this end, relevant experimental research work has been carried out since 2006.
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 various problems that arise in some applications. , 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 original understanding of polycarboxylic acid-based high-efficiency water-reducing agents. High expectations create gaps. 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 that a good admixture should be able to solve all concrete performance problems. When concrete performance problems arise, 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 polycarboxylic acid-based high water-reducing agents. In particular, fly ash is more "picky", while finely ground mineral powder has better adaptability.
&To reduce the cost, different admixtures are often used for simple compounding. This compounding can often achieve the effect of 1+1>2, which is usually called the super-stack effect. Currently, water-reducing agents other than polycarboxylic acid-based water-reducing agents are rarely used alone. In the past two or three decades, my country's admixture compounding technology should be said to be internationally leading. In the subconscious mind of many manufacturers and users, any concrete performance requirements can be solved using compounding technology. This actually creates a dependence on admixtures. Whether it is a problem that should be solved by admixtures or poor concrete performance due to changes or even deterioration of raw materials, you can raise it with the admixture supplier and let them solve it.
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