Views: 11 Author: su Publish Time: 2018-12-12 Origin: Site
In general, high-performance concrete refers to concrete with high durability, high strength and high fluidity. The biggest difference between raw materials and ordinary concrete is that the high-performance water reducing agent and ultra-fine mineral admixture are the fifth concrete. The sixth essential component, their performance is the focus of the current concrete engineering and materials circles in various countries. High-performance water reducing agent, which belongs to organic chemical materials, including material type and property characteristics, raw material selection and synthesis process control, product molecular morphology structure and performance, to the physicochemical mechanism of water reducing agent in cement dispersion system, minus The influence of water agent on cement hydration performance and its application technology in concrete have yet to be systematically studied in theory and practical application. Japan is the most and most successful country for research and application of polycarboxylate water reducers, and has basically shifted from studying naphthalenes to polycarboxylates.
In Japan, various high-performance water reducers are collectively referred to as high-performance AE water reducers. The product has a high water-reducing rate and maintains the performance of concrete slump for a long time. It can achieve a certain amount of bleed air, which is quite wide. The amount of usage can be set freely within the range. According to the main components of the water-reducing agent, the high-performance water reducing agent can be classified into five categories: modified lignin, naphthalene, melamine, sulfamic acid, and polycarboxylic acid. The first four are mainly obtained by polycondensation of a monomer having a strong polar functional group by sulfonation condensation, and a polycarboxylic acid water reducing agent is mainly copolymerized by an unsaturated monomer under the action of an initiator, that is, a reactive group is required. The side link of the group is obtained by branching onto the main chain of the polymer. The molecular structure of the polycarboxylic acid type water reducing agent is comb-shaped, characterized by having a plurality of reactive groups in the main chain and having a relatively strong polarity; the side chain also has a hydrophilic active group, and the chain is long The number is large; the hydrophobic group has a shorter molecular segment and a smaller number. If the chemical structure of the polycarboxylic acid-based water reducing agent is represented by the following formula, the chemical formula of the actual representative is only a combination of some of them. In addition, from the perspective of the impact on cement hydration, there are two types of water-reducing agents: standard type and retarding type. For their use, there are also differences between ordinary, high-strength, ultra-high-strength and high-flow concrete.
High performance water reducing agents are generally compounded from one or several components. Most of the high-efficiency pumping agents in our country are compounded by several components such as high-efficiency water reducing agent, common water reducing agent, air entraining agent, retarder and thickener, which have high water reduction rate and certain Slug retention performance, similar to Japan's slow-setting high-performance AE water reducer for ordinary, high-strength concrete, is widely used in the production of C20 to C60 commercial concrete. Due to the large fluctuation of the composite admixture formula, the compatibility with different cements is poor. In addition, the technical level of each production enterprise varies greatly, and the high quality and correct application of the admixture products cannot be guaranteed. Adhesive adaptability often occurs in the project. The concrete is separated from the water, the retardation time is too long, the plastic shrinkage crack is more, and the durability is poor. China has not yet formulated a high-performance water reducer standard, and its technological development level is quite different from that of foreign developed countries.