A. Pustovgar on the difficulty of selecting the composition of the CCC

As part of the expert round table held by the magazine "Dry Building Mixes", we listened to the report of the head of the scientific and educational innovation center of MGSU, Dean of the Faculty of Thermal Power Plants, Professor, Candidate of Technical Sciences Andrey Pustovgar, which, in our opinion, is of particular interest to all market participants.

First of all, Professor A. Pustovgar noted that the current situation on the Russian CCC market indicates that certain regions of Russia are very interested in expanding production, which was directly expressed by the leaders of the Moscow Region, Nizhny Novgorod Region, Tatarstan and other regions that do not have raw materials for cement production.

According to A. Pustovgar, the use of gypsum-based mixtures is due to a number of positive properties that only this group of binders has:

• complete absence of shrinkage deformations,
• fast strength gain,
• excellent thermal insulation and sound insulation properties,
• high fire resistance.

And given that CCC is mainly used for interior work, high environmental friendliness and vapor permeability are added to these qualities.

The professor emphasized the special relevance and prospects of the widespread use of gypsum binders in the decoration and construction of structures specifically for Russia:

• Russia has half of all explored gypsum deposits in the world,
• the cost of production of gypsum-based construction mix is 5 times lower than the cost of cement production,
• energy consumption for the production of a ton of gypsum mix is 6 times lower than for the production of a ton of cement,
• the use of gypsum construction mixes (concretes and mortars) accelerates the production of construction works several times (relative to the use of cement-based mixes).

Materials based on modified gypsum binders have the speed of strength gain and all the sanitary and hygienic properties of ordinary gypsum, but at the same time they have better strength characteristics and greater water resistance. This combination is not only excellent for interior decoration of premises with specific operating modes, but also allows you to use compositions based on modified gypsum binders for the construction of load-bearing or enclosing structures in structures of various purposes and different storeys. In addition, the use of such mixtures increases the energy saving of buildings, reduces the construction time, reduces the cost of construction, increases the turnover of formwork, and allows the widespread use of mechanized construction technologies without involving heavy construction equipment.

A. Pustovgar noted that while most enterprises producing dry building mixes easily cope with the problem of selecting a complex of modifying additives, the choice of specific brands of these additives is often fraught with difficulties and, as a rule, becomes the intellectual capital of the enterprise.

To illustrate this statement, the professor devoted the rest of his presentation to highlighting one of these difficulties that arises when developing the composition of a mixture for mechanized application.

The most important indicator of the quality of the CCC of machine application is the time of maintaining working properties, which is achieved by the correct selection of the brand of cellulose ether and other rheological additives.

The machine-applied solution must acquire the required properties immediately after mixing with water and retain them for at least two hours. These properties include rheological characteristics that ensure its pumpability, performing application operations, pruning, leveling, and glossing.

In this case, the choice of specific brands of modifying additives, according to A. Pustovgar, is influenced by such factors as the nature of the dynamic effect on the mixture, depending on the type of pumping equipment; the type, amount and specific surface area of the binder; the amount, granulometric composition and particle shape of the aggregate used; the type and amount of modifying additives themselves; thixotropic properties and cohesive strength of the mortar.

The rheology of mortars always depends on their structure, on the nature of the processes of setting and hardening as a result of hydration of binders. With the correct and accurate selection of modifying additives, the course of these processes can be controlled within a fairly wide range, which ultimately allows us to obtain a CCC with all the necessary properties. But making such a selection is not an easy task, especially for the average domestic CCC manufacturing enterprise, which often does not have all the necessary technologies.

Source: Dry Building Mixes Magazine