Explain the influencing factors and performance indicators of concrete admixtures

Non-concrete admixtures are widely used in concrete production. With the continuous advancement of technology in the construction industry, people’s requirements for cement concrete are getting higher and higher. This is reflected in the fact that it not only requires concrete to have early strength, adjustable setting, large fluidity, high durability, light weight, etc., but also requires easy molding, low preparation cost, simple maintenance, etc. In order to meet people’s needs, concrete admixtures were born.

Concrete admixture product quality inspection measures the composition, performance and quality stability of a certain admixture to determine whether it meets the specified physical requirements. , chemical performance indicators. Such as appearance, active substance content, solubility, specific gravity, pH value of aqueous solution, chloride ion content, salt content, sugar content, foaming property, surface tension, and whether there is corrosion of steel bars, etc. The performance test of admixtures mixed into cement slurry (also called clean slurry) is used to check the performance indicators that admixtures should meet when adapting to different types of cement. Its measurement items include slurry fluidity, setting time, exothermic changes in hydration heat, stability, settlement test, etc. Concrete admixtures are mixed into concrete for adaptability testing, that is, the concrete mixed with admixtures is compared with the benchmark concrete to test the water reduction rate, bleeding rate, air content, setting time, and slump of the new concrete. Loss, check the compressive strength, impermeability, frost resistance, shrinkage, creep and corrosion of steel bars after hardening of the concrete. The quality control indicators that these test projects should meet (including benchmark concrete) and the quality requirements for test materials

Concrete admixtures The application of polycarboxylic high-performance water-reducing agents has developed rapidly in recent years, and has accelerated With the development of new technologies in concrete building construction, polycarboxylate high-performance water-reducing agents should also be able to reduce the amount of cement used. Generally, cement can be saved by about 10% to 15%. This means how much can this project save on the amount of cement? The emergence of polycarboxylate high-performance water-reducing agent brings energy saving to resources and reduces environmental pollution caused by clinker burning. It plays an important role. . The concrete admixture polycarboxylic acid high-performance water-reducing agent is a surfactant whose molecular structure is a carboxyl-containing graft copolymer. It has a high and relatively long-lasting water-reducing effect in concrete. Dozens of surfactants with the above molecular structure characteristics can be found in domestic and foreign literature, including: maleic acid (ester) graft copolymer, acrylate graft copolymer, terminal sulfonic acid group-containing graft copolymer substances, unsaturated polyether graft copolymers, etc. All such copolymers form a “comb-like” or “dendritic” branched chain structure. The difference is the length of the main chain and branched chains, stiffness, shape, polarity, etc.

There are many factors that affect the strength of concrete admixtures. From the internal factors, they mainly include cement strength, water-cement ratio and aggregate quality. Cement strength and water-cement ratio: The strength of concrete mainly comes from the bonding strength between cement stone and aggregate. The higher the strength of the cement, the higher the strength of the cement stone itself and the bonding strength with the aggregate, and the higher the strength of the concrete. Tests have proven that the strength of concrete is directly proportional to that of cement. The theoretical water requirement for complete hydration of cement is about 23% of the cement weight. However, when actually mixing concrete, in order to obtain good workability, the water-cement ratio is approximately 0.40–0.65. After the excess water evaporates, Concrete admixture pores are left inside the concrete, and the greater the water-cement ratio, the larger the pores left, which reduces the effective pressure-bearing area and reduces the strength of the concrete. On the other hand, when excess water encounters coarse aggregate during its migration within the concrete, due to the obstruction of the coarse aggregate, water tends to accumulate at the bottom and form blisters, which greatly weakens the bonding strength between the mortar and the aggregate. Reduce the strength of concrete. Therefore, when the cement strength and other conditions are the same, the smaller the water-cement ratio, the higher the concrete strength

The pouring construction of concrete admixture pumped concrete has many features compared with the pouring construction of ordinary concrete. Advantages (such as saving manpower, material resources, shortening the construction period, etc.), and the one-way cost increase is not much. Therefore, in recent years, high-rise building concrete construction has widely used pumped concrete pouring. The extensive use of pumped concrete has promoted the development of commercial concrete. Technology The progress has provided guarantee for the preparation and construction of pumped concrete. Concrete admixtures However, pumped concrete generally has the characteristics of large slump, which to a certain extent increases the difficulty of concrete quality control. In particular, the segregation and sinking of concrete are very common, seriously affecting the apparent performance of concrete. and structural functions. Therefore, how to effectively solve the segregation problem of concrete is an important issue that needs to be studied in the current development of pumped concrete.

Concrete admixture high-performance water-reducing agent is researched and developed through molecular design and assembly technology, controlled water-reducing agent release type heteropoly acid water reducing agent PC-L100H. Different cement slurry and concrete tests, The results show that PC-L100H has released characteristics and excellent performance in slow working environment. Concrete admixtures have developed very rapidly since the application of polycarboxylate water-reducing admixtures was launched in China. In particular, polyacid high-efficiency water-reducing agents have been designated as special concrete admixtures for railway engineering, but they have also greatly promoted the popularity and application of heteropolyacid high-efficiency water reducing agents. Compared with traditional water reducing agents, polycarboxylate water reducing agents have many advantages, such as high water reducing rate and good adaptability.properties, etc. In the actual engineering application process, the existing polycarboxylate water-reducing agent shows certain problems, mainly due to the fluctuation of raw materials in concrete quality, and the working performance of concrete will show obvious fluctuations, especially A slump loss. The current methods to solve the problem are mainly to adjust the proportion, increase the dosage of polycarboxylate water-reducing agent or use it slowly, but these measures or operations are very complicated, increase the cost, or easily cause accidents.

</p