Today’s polycarboxylate based superplasticizer
polycarboxylate based superplasticizer, today, are the most effective industrial plasticizers of all water-reducing substances known to building science. The main advantage of polycarboxylate based superplasticizer is their inherent dual effect on cement systems. This is achieved due to the combined steric and electrostatic effects.
The main advantages of polycarboxylate based superplasticizer are: high strength characteristics; good appearance of the product; high water reduction, saving of cement; low dosage (0.2-1% by weight of cement). They are environmentally friendly products, harmless to the environment and humans.
polycarboxylate based superplasticizer are classified as comb polymers (macromolecules consisting of a flexible main chain with side chains sewn to it). The main chain of a polycarboxylate based superplasticizer molecule usually performs two functions: polycarboxylate based superplasticizer molecules are adsorbed by side chains on solid particles and are capable of further intermolecular interaction.
We have synthesized water-soluble surface-active oligomers based on methacrylic acid and polyoxypolyhydroxymethylmethacrylate containing from 10 to 35 polyoxyethylene units in the side chain. The molar content of methacrylic acid varied from 60 to 80%. The conditions for the synthesis of such oligomers have been worked out, their composition has been determined, and its compliance with the loading recipe has been shown. Solubility in water and surface activity of the synthesized oligomers have been studied. The dependence of the surface activity on the composition of the oligomer, as well as on the chain length of the polyoxyethylene radical, has been established.
The synthesized polycarboxylate oligomers were tested when they were used as superplasticizers in the production of concrete. It has been established that the use of such surface-active oligomers makes it possible to obtain self-compacting concrete mixtures that are not inferior in their properties to concrete mixtures made using special plasticizers from leading construction companies.
In recent years, highly effective polycarboxylate based superplasticizer have been increasingly used in construction practice in the manufacture of new generation concretes. They are intensively studied by many leading companies that already produce on an industrial scale a number of similar additives, which have received the commercial name “hyperplasticizers”, since the real possibilities of reducing the water-cement ratio (up to 40%) and thinning the concrete mix are much higher than those of traditional polymethylenenaphthalenesulfonates (PNS). ) and polymethylenemelaminesulfonates (PMS). The molecular design for the creation of highly effective water-soluble carbon-chain polycarboxylate based superplasticizer is based on such a chemical modification of carboxyl-containing polymers, which makes it possible to introduce long side oligoalkylene oxide chains into these macromolecules through the formation of the corresponding ester or amide groups. This provides practically unlimited possibilities for controlling the chemical and physical behavior of polymers and their interaction with cement particles by changing the length of the main and side chains, electric charges, side chain density, and free functional groups. Numerous similar carbon-chain polymers are described in the literature, which are called “comb-shaped” because of the shape of the macromolecule.
In particular, these polycarboxylate based superplasticizer have acquired a special role in the manufacture of self-compacting (SCC) and self-levelling (SLC) concrete mixtures, reactive powder concretes (RPC), which open a very promising new stage in concrete technology. Actually, only with the advent of polycarboxylate based superplasticizer did the widespread production and use of these modified concretes become real. As a rule, acrylates and methyl methacrylates serve as the basis for carbon chain polymers. For the first time, these additives were obtained in the early 80s and quickly gained a prominent place in the market. The structure of their molecule is shown in the figure.