How to break the concrete slump loss quickly? Large slump often causes some construction accidents. As a project, we must strictly prevent this problem from occurring. How can we solve this problem? What solutions are there =
(1) Post-mixing method of water-reducing agent
That is, mixing sand, stone, cement and water Then add water reducing agent. This method has a significant effect on suppressing slump loss. The main reason is that after cement meets water, C3A and C4AF in the cement can quickly generate ettringite in an environment with gypsum. C3A and C4AF are significantly reduced in the system. At this time, water-reducing agents are added and are absorbed and consumed by C3A and C4AF. The amount of water-reducing agent is significantly reduced. A large amount of water-reducing agent can be relatively fully adsorbed by C3s and C3S. The electrokinetic potential of cement particles is significantly increased and remains relatively stable for a certain period of time, which directly reflects the good workability of concrete. , the slump loss is small, and this method is simple and easy to apply. However, this method has certain limitations, and the use of soil has certain limitations.
(2) Adjust concrete admixtures
Use high molecular weight water-reducing agents in combination with an appropriate amount of water-retaining components to increase the amount of water in the concrete without increasing water consumption. The free water content can alleviate slump loss. However, this method can easily lead to increased concrete costs. The water-reducing agent is made into granules with different particle sizes and different dissolution rates through physical methods, and is mixed into fresh concrete to form different hydration gradients in the cement hydration system. It can be replenished at any time due to the consumption of C3A and C4AF. The water reducing agent in the system always maintains the water reducing agent in the critical micelle state, so that there is no or very little loss in slump. You can also make a shell on the surface of the water-reducing agent that can slowly dissolve in alkaline solution and have different dissolution rates, thereby controlling the concentration of the water-reducing agent in the cement slurry and achieving the purpose of inhibiting collapse. You can also choose appropriate active ingredients containing polar groups to react chemically with the water-reducing agent, continuously and slowly release the dispersant into the water-cement system, control the dissolution rate of the water-reducing agent and maintain a certain concentration, so that the cement particles A certain electrokinetic potential is always maintained to achieve the purpose of suppressing collapse.
(3) Reduce the temperature of the concrete leaving the machine
The higher the temperature of the concrete, the faster the hydration rate of the cement, the shorter the time for the cement particles to maintain a certain electrokinetic potential, and the free The greater the proportion of water that becomes bound water. Therefore, the higher the temperature of fresh concrete, the faster the collapse; the lower the temperature, the slower the collapse. Generally speaking, for every 10°C increase in temperature, the slump loss increases by 10% to 40%. Therefore, the temperature of various raw materials should be lowered to inhibit collapse.
(4) Method of adding retarder
The theories of retarder’s effect on cement retardation include adsorption theory, complex salt generation theory, precipitation theory and controlling the growth of hydroxide crystals theory. Most organic retarder are surface active, they adsorb at the solid-liquid interface and change the surface properties of solid particles, that is, hydrophilicity. Due to adsorption, the hydroxyl groups in their molecules hinder the cement hydration process on the surface of cement particles, shielding the crystals from contact with each other, and changing the structure formation process. Another view of the retarding mechanism is that the retarder is adsorbed on Ca(OH)2: soil, inhibiting its continued growth. The growth of ca(OH)2: will stop before reaching a certain degree of supersaturation. This theory focuses on the adsorption of retarder on ca(OH)2 soil, rather than on the adsorption of hydration product soil. However, studies have shown that simply inhibiting or changing the growth and state of ca(OH)2 is not enough to cause retardation, but what is more important is the adsorption of the retarder on the hydrated C3S soil. The organic retarder slows down the hydration of C3A in the cement and selectively exchanges it with the water-reducing agent adsorbed on the Al2O3 surface. The exchanged water-reducing agent significantly increases the concentration of the water-reducing agent in the solution, which is C3A, C2s Adsorption provides sufficient water reducing agent, effectively suppressing slump loss.
In short, there are many factors that affect the slump loss of concrete. The fundamental reason is that different mineral components in cement have different adsorption capacities for water-reducing agents. Cement with high C3A and C4AF content is prone to large collapse problems. Post-mixing method, retardant mixing method, lowering the temperature of out-of-machine concrete, adjusting concrete admixtures, etc.</p
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