Views: 21 Author: su Publish Time: 2018-11-28 Origin: Site
In recent years, polycarboxylate water reducers have gradually moved from experimentation to practice. More and more scholars' attention and scientific research have provided many references for the development of this field. Today's polycarboxylate superplasticizers control the fluidity of concrete mixes and control fluidity losses by controlling the concentration of long and short side chains in the polymer. However, most of the superplasticizers are naphthalene. Because of its relatively low slump loss during use, it is unable to meet the relevant technical requirements, and because of the instability of the composite product, it has an effect on the hardening and durability of the concrete. This weakness is a key factor in inhibiting its development. The sulfamic acid system has a monocyclic aromatic hydrocarbon type structural characteristic. Due to its high water reduction rate, good slump and convenient construction, it is the focus of discussion with the polycarboxylic acid system.
At present, most of the concrete mixing stations are located in the edge areas of the city, so that there is a long distance between concrete production and pouring, which will lead to concrete loss and reduce its pumping function. Causes the same slump loss, including entry materials and weather. Among them, the functions of raw materials are mostly derived from cement, pellet grading, and water reducing agents. Adding a water reducing agent can make the concrete have the advantages of small water-to-gel ratio, less water consumption per unilateral, and less cement. Among them, the polycarboxylate water reducing agent has high water reduction rate and good water retention performance, which can be the future development goal of the industry.
When the general water reducing agent is adsorbed by the cement particles, it becomes a rigid chain form, and the steric effect cannot be exhibited, and the damage phenomenon cannot be solved. The polycarboxylic acid-based hydroxyl group and the sulfonic acid group anion have an electric repulsion. It has been found that the polypotassium potential of the polycarboxylic acid is not more than that of the naphthalene, and the dispersion effect is better than that of the naphthalene. Further, the ether bond in the polycarboxylic acid and the water molecule are combined to form a hydrogen bond to form a protective film which has a dispersing effect and at the same time stabilizes the cement particles. According to the effect theory, the length of the side chain is proportional to the dispersion effect. For ordinary concrete mix ratios, the long side chain bond polymer does not exhibit a large water reduction effect. The polycarboxylic acid polymer relies on the electric repulsion between the negative ions and the three-dimensional effect of the side chain. From this point of view, changing the weight between each functional group of the polymer backbone, the length of the main side chain, and the number of connections, after the balance of the structure, can improve the efficiency of water reduction and slump. Polycarboxylate superplasticizer, which adsorbs cement particles, because it has ether bonds, constitutes a relatively thick protective film, making the cement stable. Different types of water reducing agents work differently. The naphthalene is adsorbed onto the surface of the cement particles, causing electrostatic force between the cement particles. Then the product covers the surface, which weakens the electrostatic force, and the polycarboxylate superplasticizer adheres to On cement, it leads to stronger space resistance between cement particles, so it has higher water reduction performance. In addition, the polycarboxylic acid molecule is a chain structure, and a long side chain is connected to the main chain. When the hydration product covers the surface of the cement particle, the cement particles remain dispersed, so that the naphthalene type water reducing agent is Polycarboxylates can cause less slump loss in concrete. However, polycarboxylates are more sensitive, subtle changes in raw material components, and deterioration in raw material quality have a significant impact on their use.
In foreign countries, the water reducing agent has experienced a long history of development. Through the copolymerization of olefins and unsaturated carboxylic acids, Japan has developed new water reducing agents, which are characterized by low added amount, high water reducing effect, and low slump loss. Compared with the previous two generations, it makes up for the lack of stability and poor protection. At the same time, it can be used to equip high-flow, self-compacting concrete, known as the third-generation water reducer. Subsequently, some developed countries in the West gradually shifted their research priorities and gradually transitioned to polycarboxylic acids.
In the concrete construction, a certain amount of polycarboxylic acid admixture is added, which makes the contractor reduce the cost of concrete by nearly 20% in actual engineering, and has considerable economic benefits. As a water reducing agent for formulating concrete, polyhydroxy acids are a key factor in improving the performance of concrete. The incorporation of polycarboxylic acids allows the slump to meet regulatory requirements. In addition, it also makes the construction quick and worthy of extensive application in the construction of anti-seepage concrete. However, for polycarboxylate water-reducing agents with other special functions, such as water-reducing agents with anti-mud function, research on this aspect is relatively rare. It is not ideal for the dispersion properties of cement. In subsequent studies, we can introduce some new functional groups to improve the corresponding dispersion performance. On the other hand, for example, for clay and its principle of action, the mechanism of action against mud-reducing agents and clay, etc., more systematic research is needed to provide a theoretical basis for practical engineering.