The use of concrete admixtures is a major advancement in concrete technology, which can improve the quality and performance of concrete, increase the construction speed and quality of the project, save cement and energy, and have significant economic and social benefits. The application of polycarboxylate water-reducing agent has made concrete technology a breakthrough development.
The alkali content, sodium sulfate and chloride ion content of the polycarboxylic acid water reducer are very low, and it will not pollute the natural environment during the production process. The preparation of concrete with high fluidity and low slump loss is realized because of the application of polycarboxylic acid water-reducing agent. The performance of polycarboxylic acid can be optimized by designing the molecular structure of polycarboxylic acid, so that it has the characteristics of "intelligent". Due to the molecular structure characteristics, it has many advantages: wide adaptability of cement, high water reduction rate, good slump retention performance, excellent plasticizing effect, strong plasticity of molecular structure, multiple synthesis technologies, and great potential for high performance, so it is also called Superplasticizer.
1 Development of water reducing agent
The first generation water-reducing agent lignosulfonate is one of the main by-products of the paper industry. It is a surfactant and has a certain ability to disperse cement particles.
The second-generation naphthalene-based water-reducing agent is also an anionic surfactant, which can play the role of electrostatic repulsion and steric repulsion between cement particles, prevent direct contact with each other, play a role of lubrication, and strengthen the cement slurry The fluidity of the body.
The molecules of the third-generation polycarboxylic acid water reducer have a comb-like structure, with more active groups on the main chain and side chains, and sulfonic acid groups, carboxylic acid groups and hydroxyl groups are attached to the main chain. On the side chain are longer polyalkoxy groups. Various groups have different effects on the dispersibility of cement particles. Thiopropionic acid is a new type of cement admixture—polycarboxylic acid water-reducing agent, which is mainly used to control molecular weight in the production of polycarboxylic acid water-reducing agent. It is a high-performance modifier, which greatly improves the water-reduction rate and slump retention of concrete. performance.
2 The application of polycarboxylic acid water reducer makes concrete high performance
2.1 Ultra-high-strength concrete
2.2 High durability concrete
2.3 Self-compacting concrete
2.4 Fair-faced concrete
3 Problems and solutions of polycarboxylic acid water reducer in practical application
At present, the application of polycarboxylic acid water reducing agent has been relatively common, but there are still many problems in practical application. Due to economic benefits, the current choice of water reducing agent can only blindly pursue high water reducing rate and low price. Therefore, the most commonly used polycarboxylic acid water-reducing agent is to directly mix some auxiliary materials with high-reducible water-reducing mother liquor synthesized at normal temperature, or to mix some auxiliary materials with a certain amount of high-reducible water-reducing mother liquor synthesized at room temperature and a certain amount of slump-preserving mother liquor. However, the functional mother liquor with better performance, which uses high-quality raw materials, molecular structure design, and advanced technology, cannot be used on a large scale due to its high price or low water reduction rate. In addition, in the past two years, due to the national environmental protection policy regulation, the supply of sand and gravel is tight, the price is rising, and the quality cannot be guaranteed. Even the quality of cement fluctuates from time to time. This has led to some problems in actual engineering applications, and even There is a sound that polycarboxylic acid water reducers are not as good as naphthalene and aliphatic water reducers.
Polycarboxylic acid water reducer has many excellent properties, which is unmatched by other series of water reducers. Due to the wide application of polycarboxylic acid water reducer, concrete technology has been developed by leaps and bounds. Although there are still some problems in practical applications, there are a series of corresponding mature methods that can be solved.