As we all know: the birth of water-reducing agents heralds a new level in the construction industry. Although the adaptability of water-reducing agents to cement is better than other water-reducing agents, it has been found in actual engineering applications that water-reducing agents There are still adaptability problems with cement.
In recent years, research work related to water-reducing agents has mainly focused on the following aspects: 1. Research on synthesis processes and optimization of composition and molecular structure, so as to Further improve the water-reducing performance and fluidity retention ability of the polymer; 2. Research on the relationship between molecular structure and performance, as well as the mechanism of action of this new high-performance water-reducing agent; 3. Research on application technology; 4. Mother liquor series Chemicalization and research on the compounding properties of different mother liquors. Although the adaptability of water-reducing agents to cement is better than other water-reducing agents, it has been found in actual engineering applications that there are still adaptability problems between water-reducing agents and cement. Not much research has been done on the adaptability of raw materials. Engineering practice has proven that this is an important factor restricting the popularization and application of water-reducing agents.
When used with other cements, the fluidity may be lost rapidly; moreover, when the same water-reducing agent is used in different cements, its fluidity and retention properties are also different. Below we analyze the impact of concrete raw materials on the adaptability of water-reducing agents from the following aspects.
Water-reducing agents have different dispersion and fluidity-maintaining abilities for different cements. They should be used as water-reducing agents with good fluidity and fluidity-maintaining capabilities for certain cements, and for other cements. , it may cause rapid loss of liquidity. In addition to cement, other concrete raw materials also have adaptability problems with polycarboxylic water-reducing agents. The test found that the fluidity of cement slurry mixed with high-performance water-reducing agents remained basically unchanged within 2 hours, while the concrete using the same raw materials had The fluidity of the fresh mix is almost completely lost within half an hour. There is a huge contrast between the fluidity results of the cement slurry using the same materials and the fluidity results of the new concrete mixture, which fully demonstrates that other raw materials in the concrete also have a great impact on the application performance of the superplasticizer.
Most of the organic admixtures added to cement slurry show affinity to cement particles or cement splash particles, which leads to significant adsorption. The charged organic molecules interact with the particle surface through electrostatic forces (particles The surface charge and the ionic group of the admixture molecule). In addition to the chemical reaction between the cement phase and the admixture, the adsorbed compounds will change the surface properties of the cement particles and thus affect its interaction with the liquid phase and other cement particles. In addition to the interaction between the cement slurry and the admixture interface, the adsorbed substances will also change the surface properties of the cement particles to affect their chemical interactions with the liquid phase and with other cement particles. Typical adsorbent anionic surfactants and adsorbates will transfer a net negative electrostatic charge to the particle surface, causing mutual repulsion between adjacent cement particle surfaces and conducive to enhanced dispersion.
Compared with traditional high-efficiency water-reducing agents, water-reducing agents have the following outstanding advantages: (1) It has very high dispersion performance at low dosage, high water-reducing rate, and obvious Enhancement effect; (2) The fluidity of concrete remains excellent; (3) Small shrinkage, low alkali content, and moderate air entrainment; (4) The molecular structure is highly designable; (5) Environmentally friendly; (6) Adaptability better.
The water-reducing agent has a water-reducing effect, mainly due to the anionic effect created by the carboxyl group on the main chain and the steric hindrance produced by the neutral long side chain containing polyoxyethylene. Most of the main chains of high-performance water reducing agents are grafted with various active groups, such as carboxyl groups with a certain length, polyoxyethylene chains, sulfonic acid groups, -COOH and -SO3Na, which can produce dispersion and flow effects on cement particles. sexual groups. The high-performance water-reducing agent is generally adsorbed between the layers of cement particles in a comb-like manner. First, due to its steric hindrance, the cement particles are dispersed among themselves and reduce their aggregation. In addition, because the EO side chain of the water-reducing agent molecule is relatively long, it can still stretch between the surfaces of the organic mineral particles. Therefore, the hydration reaction of cement has a relatively small impact on the water-reducing agent molecules, allowing it to maintain its good performance for a long time. The dispersion effect allows concrete to reduce slump loss.
A large number of tests and engineering practices have shown that the mud in the sand and gravel raw materials has a nearly fatal impact on the water-reducing agent. Due to the layered structure of the clay, it has strong adsorption to the water-reducing agent, resulting in The content of effective water-reducing agent in the cement slurry is greatly reduced. This impact is mainly reflected in the impact on the workability of fresh concrete, as well as the impact on the later strength and structural stability of the structure. Admixtures such as fly ash and mineral powder also have a significant impact on the application performance of the water-reducing agent.
Since the raw material conditions and application environment in actual concrete projects are far more complex than laboratory research, there are still many related application technologies that need to be continuously studied and discussed in the current application process, especially water-reducing admixtures. New issues such as the adaptability of concrete, sensitivity to water consumption, and delayed bleeding still need to be systematically studied. In addition, it is the application technology of high-performance water-reducing agent in ordinary commercial concrete.In order to improve the performance and economy, it is also necessary to develop suitable polymers for the slump maintenance problem of small slump concrete. In order to maximize the performance of water-reducing admixtures in engineering applications, promote the application of water-reducing admixtures in engineering projects, and ensure the quality of concrete construction and structural safety, it is necessary to conduct in-depth research on the application performance of water-reducing admixtures in concrete raw materials. The influence of concrete raw materials on the application performance of water-reducing agent is found out. </p
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