A water-reducing agent that can drastically reduce the flow of mixing water under the same standard as the slump of the product concrete is called a high-efficiency water-reducing agent. High-efficiency water-reducing admixtures have a significant refining effect on concrete, which can further improve the fluidity of concrete mixtures and the slump of finished concrete. At the same time, they can significantly reduce water demand and significantly improve the workability of concrete. This article focuses on the impact of high-efficiency superplasticizer on the structure of hardened cement stone and the principle of superplasticizer function.
High-efficiency water reducing agent is suitable for components and cast-in-place rigid components in various manufacturing and industrial buildings, municipal administration, road networks, seaports, water conservancy and other construction projects. Reinforced concrete; suitable for high-strength, ultra-wide-strength and medium-strength concrete, as well as concrete with required early strength, moderate cold resistance, and large flowability; suitable for component goods concrete components in the steam curing process; suitable for making various composites The water reducing and improving component of the water reducing agent (i.e. masterbatch).
1. The effect of high-efficiency water reducing agent on freshly mixed soil
1.1 Water reduction effect.
(1) After mixing high-efficiency water-reducing admixture into concrete, the water-cement ratio can be significantly reduced while maintaining fluidity. The water reduction rate of high-efficiency water-reducing agents reaches 10% to 25%, while the water-reducing rate of general water-reducing agents is 5% to 15%, hence the name of high-efficiency water-reducing agents. The main reason for the water-reducing effect is the adsorption and refinement effect of the concrete on the water-reducing agent.
(2) Concrete will form some flocculation-like structure during the water mixing and initial hardening process. There are many reasons for the flocculation structure. It may be because the concrete minerals (C3A, C4AF, C3S, C2S) often have different charges during the hydration process, which causes the charges between men and women to interact and flocculate; it may also be because the concrete The thermal transport of particles in the liquid collides, adsorbs, and moves each other at some edges and corners to form a flocculated structure; it is also like the van der Waals electromagnetic force between objects and the early stage of dissolution and hydration reaction. Will cause flocculation. In this flocculated structure, a lot of mixing water is encapsulated, thereby reducing the water flow required for concrete hydration and reducing the workability of fresh concrete. In order to maintain the required workability of freshly mixed concrete at the construction site, the amount of water required during mixing must be relatively increased, which will promote the formation of excessive permeability in the cement stone structure, thus seriously affecting the performance of the hard-base concrete. A series of mathematical and physical properties, if this unnecessary water can be discharged, the water required for mixing concrete can be greatly reduced. By adding appropriate water-reducing agents in the process of making concrete, it can have very good properties. This kind of effect.
(3) Discussion shows that after adding water-reducing agent, the hydrophobic groups of the water-reducing agent are directionally adsorbed on the surface of concrete particles, and the hydrophilic groups tend to be saturated. The solution constitutes a single-ion or multiple-ion adsorption membrane.
(4) Because of the directional adsorption of surfactant ions, the surface of concrete particles contains the same marked charge. Therefore, under the effect of electrical repulsion, not only The water mechanism of the concrete is placed in a relatively stable floating state (the potential difference between the electric double layer is increased), and the flocculated structure formed by the concrete in the early stage of water release is refined and disintegrated, so that the acidic water stimulated by the flocculated body is discharged, thereby achieving reduction reduction. water destination.
1.2 Efficacy of plastic products.
(1) After adding water-reducing agent to concrete, the fluidity can be improved while maintaining the water-cement ratio without changing. Ordinary water-reducing agents can increase the slump of freshly mixed concrete by about 10cm while maintaining the concrete dosage unchanged. High-efficiency water-reducing agents can produce concrete with a slump of more than 25cm.
(2) In addition to the previously mentioned effects of adsorption and refinement, the functions of plastic products also have moistening and lubrication effects.
Moisture effect: After the concrete is mixed with water, the surface of the particles will be moistened by water. The moisture will have a great impact on the properties of the newly mixed soil. When this kind of spreading When the moist ecology is completed, the total amount of surface free energy reduction can be calculated by the equation proposed by Glbbs.
(4) Lubricating effect: The chemical hydrophilic groups in the water-reducing agent are directionally adsorbed on the surface of concrete particles and can easily hydrogen bond with oxygen molecules. way to associate. The inertial force of this hydrogen bond association may exceed the ionic electromagnetic force between oxygen molecules and concrete particles. When the concrete particles absorb any water-reducing agent, relying on the association effect of hydrogen bonds between R-SO3θ and oxygen molecules, plus the hydrogen bond association between oxygen molecules, a stable layer of petroleum ether is produced on the surface of the concrete particles. This film has a permanent protective effect, preventing direct contact between concrete particles and acting as a lubrication between particles.
(5) The addition of water-reducing agent is accompanied by the introduction of a sufficient amount of bubbles (even if it is a non-air-entraining water-reducing agent, small bubbles will be introduced. Measure the bubbles).
This kind of abrasive bubbles is surrounded by an ion membrane that is directionally adsorbed by the water-reducing agent, and contains the same charge as the concrete particle adsorption membrane, so the vapor The electrical repulsion between the bubbles and the concrete particles also leads to the refinement of the concrete particles, thus increasing the drag potential between the concrete particles (such as ball bearing function). This kind ofThe effect is more significant for concrete mixed with air-entraining water-reducing agent.
(6) Due to the adsorption and refinement effects, moistening effects and moisturizing effects of the water-reducing agent, the mixture can be easily mixed with a small amount of water. The soil is mixed evenly, thereby improving the workability of freshly mixed soil.
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