Concrete superplasticizer: compatibility of superplasticizer and cement

The role of superplasticizer

As a superplasticizer, its fundamental role is to amplify the effect of water in concrete, so that it can improve the fluidity of concrete without increasing water consumption. As a cementing material, cement provides a gelation effect through a chemical reaction with water, so that the concrete can form a structure that meets the requirements. The superplasticizer does not react chemically with cement. So why do people come up with the concept of compatibility between cement and superplasticizer?

Superplasticizer is compatible with cement

People initially thought that superplasticizer were incompatible with cement, often when cement or concrete set abnormally. However, long before the invention of the superplasticizer for concrete, people were using Portland cement to prepare concrete. Inappropriate selection of cement raw materials and inappropriate raw material formulation may cause two types of abnormal condensation. One is called flashing, and the other is called false setting. The two types of coagulation have one thing in common, that is, cement or concrete will lose fluidity more than ten minutes after adding water. Flash condensation is accompanied by heat release, and the temperature rises sharply, but false condensation does not have this phenomenon. At the same time, these two kinds of abnormal coagulation are far from the conditions for testing concrete coagulation according to the penetration method. That is, when the penetration resistance is 3.5 MPa and 28 MPa, the initial and final setting states are reached, which is a kind of difference between water and silicate. The reaction has nothing to do with the abnormal reaction. The cement and sand are not cemented together due to the gelation reaction of cement and water, forming a real coagulation.

Why people think that superplasticizer are compatible with cement?

The cause of abnormal coagulation is often because the content of tricalcium aluminate in the clinker is too high, or the ratio between the added gypsum and tricalcium aluminate is inconsistent, or the temperature during cement grinding is too high, resulting in dehydration of dihydrate gypsum. It turns into hemihydrate gypsum. Hemihydrate gypsum reacts quickly when it meets water, causing the concrete to lose fluidity, or the mismatch of alkali and sulfur in the fresh concrete liquid causes the concrete to set abnormally, or the dihydrate gypsum is not used in the cement. The use of anhydrite with low solubility, etc., or the addition of triethanolamine (non-water reducing agent) as an early strength agent, can cause abnormal concrete condensation and other reasons. There are various reasons, but they are not caused by water reducing agents. The water-reducing agent has existed before it is used in concrete, and because of the water-reducing effect of the water-reducing agent, the water consumption in the concrete is reduced, which aggravates these problems and becomes extremely prominent. At first, it was a new type of material as a water-reducing agent, so people often misunderstood it as a water-reducing agent.

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