Research foundation and current situation
In view of the commonly used traditional concrete accelerator always has one or another deficiencies, many concrete science and technology workers are committed to the research and development of new concrete accelerator.So far, although the research is not very mature, but some results are encouraging.The main research direction and ideas include the following aspects:
1.Development of concrete accelerator of calcium salt
Calcium salts can reduce the PH value of C3S-H2O system, thus accelerating the hydration of C3S, which in turn accelerates the hydration and hardening of cement.Calcium salts that have this effect and do not contain chloride ions, sodium and potassium ions include calcium nitrate, calcium formate and calcium bromide.Calcium formate is the best substitute for calcium chloride.Calcium nitrate also has a good early strength effect on Portland cement, but the effect of Portland cement mixed with mixed materials is weak, but I believe that with the deepening of research, calcium salt will be one of the new concrete accelerator better development varieties.
2.Further study on the effect of new generation of organic and inorganic compounds on concrete accelerator
At present, there are a lot of concrete accelerator which are composed of organic matter, sulfate or chlorine salts. Although the concrete accelerator and a series of other effects of improving concrete performance have been improved to some extent, the adverse effect of traditional early strength agents on concrete has not been changed.The organic matter series concrete accelerator itself does not have the damage to the concrete flaw, as concrete accelerator application in the concrete main question is how to strengthen the anticipated early strength function.At present, many experts believe that the main research can still be carried out along the direction of organic compound and inorganic compound, but the selection of inorganic compound needs to be further studied.In addition, there is another solid alcohol-amine organic concrete accelerator, which is easier to compound with inorganic concrete accelerator, so it can obtain better early-strength effect.
3.Study on the properties and effects of high-priced cation with concrete accelerator function
Most of the cement hydration products are c-s-h gels, which are obtained by the hydration of C3S and C2S.Since the high-priced cation has compression effect on the diffusion double electric layer of C-S-H colloidal particles, it can accelerate the condensation of C-S-H colloidal particles, thus reducing their concentration in liquid phase, accelerating the hydration reaction of C3S and C2S, and accelerating the hardening process of cement and concrete.For example, Al3+ is a kind of high-priced cation with the above effects, which can accelerate the hydration reaction of C3S and C2S and promote the hardening process of cement and concrete.There are many similar high-priced cations, once the formation of composite concrete accelerator products, it will be a good direction of development of concrete accelerator.
4.Application practice of embryo material as concrete accelerator
The crystallization process is a process of energy reduction, so theoretically it should be spontaneous.However, in fact, when the crystal precipitates from the liquid phase, it needs to break through an energy barrier.This energy barrier makes it difficult for crystals to precipitate spontaneously, which is why supersaturated solutions exist.A very small amount of the same crystal in the supersaturated solution can make the solution precipitate rapidly.If the crystalline embryo material is added in the process of cement hydration, the energy barrier of hydration product precipitation can be reduced and the precipitation rate can be accelerated.The increase of precipitation rate can lead to the decrease of the concentration of hydration products in the liquid phase.The effect of embryo material has also been noticed and studied by concrete scientists investigate.The test results show that adding 2% ground cement in concrete can increase the early strength of concrete by 10%-15%, and the later strength has no bad influence.It should be pointed out that the best results are obtained by mixing concrete with the same kind of cement used to mix concrete.
Research and development prospects
Known from the analysis of the above, chlorine salt and sodium (potassium) concrete accelerator make the itself disadvantages of research and development without chloride and sodium (potassium) concrete accelerator is imperative, though workers have noticed many concrete chlorine salt and sodium (potassium) is the disadvantage of concrete accelerator and has been working on the new development of concrete accelerator, but the strong adaptability, good effect, and low cost without chloride and sodium (potassium) early strength agent is not yet finalize the design product.Therefore, the research, development and application of chlorine-free and sodium (potassium) concrete early-strength agents attract more attention of concrete construction and scientific research workers.