Polycarboxylate performance model water-reducing agent is a new type of water-reducing agent that has many outstanding advantages, but its functional principle is not completely clear at this stage. The following are some of the opinions listed:
(1) Polycarboxylic acid polymers have an obvious retarding effect on concrete, mainly because the carboxyl group is used as a retarding component, and R-COO~ forms a complex with Ca2+ ionization function to reduce Ca2+ in the liquid. Ionization solubility slows down the production of Ca(OH)2 crystals, reduces the production of C-H-S glue, and slows down the hydration of concrete.
(2) Carboxyl (-COOH), hydroxyl (-OH), amine (-NH2), polyoxyalkyl (-O-R)n and other chemical properties that are highly sensitive to water are the key to industrial companies Through amphoteric ion functions such as adsorption, refinement, moisture, and lubrication, it provides refinement and circulation properties to concrete particles, and by reducing the friction between concrete particles and reducing the free energy between concrete particles and water interfaces, freshly mixed concrete can be improved of workability. At the same time, polycarboxylic acid compounds are adsorbed on the surface of concrete particles, and the carboxylate ions make the concrete particles carry negative charges, which in turn causes an inductive electric conflict between the concrete particles and refines the concrete particles, thereby inhibiting the excitation tendency of the cement mortar ( DLVO methodology), expand the contact area between concrete particles and water, so that the concrete is fully hydrated. During the process of spreading concrete particles, the mineral acid water that excites the body lock tail is released, improving workability and reducing the mixing water flow.
(3) The steric blocking function of the polycarboxylic acid ion chain (i.e. immediate conflict). Polycarboxylic acid molecules are adsorbed on the surface of concrete particles in a “comb-like” manner, forming an adsorption layer on the surface of the glue material. When the polymer ion adsorption layers are close to each other and intersect, a mathematical structure is formed between the polymer ion chains. The spatial blocking function prevents the excitation of concrete particles, which is an important reason why carboxylic acid superplasticizers have stronger refining potential than other mechanisms.
(4) The principle of maintaining the refinement of polycarboxylic acid superplasticizer can be known from the relationship between the elapsed time after cement mortar mixing and the Zeta potential difference. Under normal circumstances, the slump damage of concrete using naphthalene series and sodium thiocyanate series high-efficiency superplasticizer after 60 minutes is significantly higher than that of concrete containing polycarboxylic acid-based performance model superplasticizer. The key to this is that the former is different from the adsorption modeling of concrete objects. The inertial force of the nanomaterial adsorption layer between concrete objects is the immediate induced electric repulsion, and the change in Zeta potential difference is small.
When discussing the principle of its effect on concrete refinement, it was found that the ionization repulsion expressed only by the DLVO methodology often differs greatly from the experimental results. The experimental results of Uchikawa and Anaka showed that the steric hindrance effect can fully express the refining effect of polycarboxylic acid-type water-reducing agent on concrete, that is, the nanomaterials are adsorbed on the surface of concrete particles, and they flex and stretch into the liquid-containing support. The chains create steric hindrance so that objects cannot come close to each other, thus making the concrete particles refined and stable. This principle is now widely accepted. Many people in Kihoa studied the isothermal adsorption of concrete by polymers with similar ionic qualities and different branch chain lengths and pointed out that polymers with long branch chains have low potential differences and high steric repulsion, so after adsorption, they have Concrete refinement properties are very good, but object refinement reliability is not. The author believes that if the branch chain is too long, it will cause the surface branch chains between the refined objects to become entangled with each other, which will in turn lead to the excitation of the object.
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