Dry building mixtures – current situation and technology perspectives in Russia

According to the state standards GOST 31189-2003 “Dry building mixtures. Classification”, dry building mixtures are mixtures of dry components containing binding agents, filling materials, modifying additives, which are manufactured using industrial methods (Figs. 1 and 2). As opposed to mortar and concrete mixtures ready for use, dry mixtures are delivered to construction sites in a dry form, and mixed with water directly before use. During its utilization cycle, the dry building mixture goes through three different states:

– dry mixture;

– mortar (concrete mix), mixed with water and ready for use;

– mortar (concrete) – hardened state.

In some countries, two-component compositions are widely used. Such compositions consist of a packaged dry mixture and a tempering agent that may contain one or several liquid additives, for example, polymer dispersion, plasticizer, bishofite for magnesial mixtures, etc. The volume of consumption of dry building mixtures and two-component compositions depends on the region and climatic conditions. The consumption of two-component compositions in regions with a hot climate is higher than in countries with a moderate climate (Fig. 3). This is why dry mixtures have the greater perspectives for conditions in Russia.

Limestone-based plaster mixtures have been known for over eight thousand years, and gypsum-based building mixtures were used in Babylon more than six thousand years ago. It is known that building mixtures based on pozzolanic hydraulically hardened binding materials (such as powdered volcanic ash) were used about three thousand years ago. The use of additives to improve the technical and technological parameters of building mixtures, such as egg white, ashes, soap, etc., began as far back as in the ancient world and the middles ages. Starting from the middle of the 19^th century, the active application of Portland cement for the production of building mixtures began. The first patent on manufacturing and application of dry building mortar was published in Europe in 1893. Development of the production technology of dry building mixtures passed through several stages. In the first stage, the mixtures were manufactured on site (or near the site) from raw materials (binding and filling) previously delivered to the construction site. These mixtures featured a minimal modification rate. In the next stage, thanks to the development of transportation methods and equipment for the manufacture of mixtures, and ready for use mixtures centrally produced at mortar- and concrete-mixing station and plants, became the most widespread. The transition to centralized delivery of mixtures contributed considerably to an improvement in quality, to an immense increase in the production volumes of modified mixtures and the rate of their modification, as well as to a reduction in the costs.

The production of mixtures developed actively starting in the 1960s, thanks to the development of binder chemistry, the creation of efficient dry additives and improvements in the production and processing of mixtures. In principle, the introduction of dry building mixtures technology facilitated the development of new compositions for thin layers of 0.5-6 mm, which made it possible to increase the quality of plaster, facings, masonry and other applications. By the use of dry mixtures in thin layers the productivity increased by 1.5–5 times, while materials consumption reduced by 3–10 times, compared with traditional methods of work in which ready for use mixtures are applied. The high efficiency of dry building mixture applications for thin-layer technologies created the potential for the establishment and fast growth of dry building mixtures as a separate branch of the construction industry.

An important factor for the further development of dry building mixtures production in the world is the implementation of mechanical operations for dry building mixtures processing including a system for bunker transportation of mixtures (bulk), systems for the automatic mixing with water (tempering), and the mechanized feeding of mortar mixtures to an application site. The introduction of mechanical operations into the processing of dry building mixtures increased the volume of consumption of dry plaster mixtures by 600 % in Germany in the period from 1960 to 1995. In addition, the number of employees dealing with plasterwork was reduced by 25 %, which means an increase in labour productivity of 800 % [3].

Currently, the production of dry building mixtures is a high-powered branch of the construction industry. There are about 1000 large plants manufacturing dry building mixtures worldwide, and production technologies are ranked among the most high-tech, with a high level of labour productivity, mechanical operations and automation (Figs. 4–6). The calculated annual volume of dry building mixtures production amounts to about 90-100 million t. The production of dry building mixtures is developing dynamically, production volume increases on average by 1 to 3 % per year, companies are merging, two-component mixtures are being replaced by dry building mixtures, the share of mechanized processing is increasing , the range of products is expanding, performance indicators are improving and manufacturing technologies are progressing.

The first modern plants manufacturing dry building mixtures were built in Russia during the Soviet years. However, the range of mixtures manufactured by those plants was usually limited to mortar and concrete mixtures of simple composition, which reduced the efficiency of the operation of the plants and, therefore, hindered the development of dry building mixtures production as a whole. Limitation of the mixtures range was caused by the need to purchase some expensive additives used for the manufacturing of dry mixtures abroad (such as redispersible polymer powders, cellulose ethers, etc.), which was impossible under the conditions of currency reserves deficit.

At the beginning of the 1990s, as the market economy was developing in the Russian Federation, a market for dry building mixtures was also forming. Wide-scale introduction of modified dry mixtures into construction practice in Russia began in the middle of 1990s. Within a relatively short period of time, dry mixtures have become an integral part of modern construction:

– several hundred production facilities for dry building mixtures have been built;

– the share of modern complete plants including those with large production capacity (over 100 000 t/a) is being increased;

– mechanical methods for processing dry mixtures at construction sites are being developed;

– production of nearly all types of dry building mixtures used in worldwide construction practice has been launched;

– a domestic raw material base for the production of dry mixtures is gradually being formed.

– Thus, the production of dry building mixtures both in Russia, and in the whole world, is now a separate dynamically developing branch of the construction industry, despite a relatively short development history.

 At present, 12 types of dry mixtures for different applications are manufactured (Fig. 7). The most widespread are plaster, masonry and facing mixtures, the consumption volume of which considerably exceeds the volume of consumption of other types of mixtures (Fig. 8). The advantages of dry mixtures in comparison with ready for use mixtures can be frequently found in the scientific literature and in reports by experts. In our opinion, a direct comparison of these mixtures is difficult, because they have been designed for special applications, respectively. At the same time, when construction is widespread, and large amounts of building mixtures are applied, the use of concrete and mortar mixtures is usually without competition thanks to significantly lower costs. Dry mixtures are frequently just effective additions for various construction processes in which mixtures ready for use are exploited. For example, these are the use of dry mixtures for repairs to technological defects of concrete and reinforced concrete structures, levelling surfaces of concrete floors, etc. This is why it is more reasonable to consider the fields of application of building mixtures of different types.

As opposed to mixtures ready for use, the application of dry building mixtures makes it possible to carry out the work both with thick layers (according to traditional technology), and thin
layers, when the layer thickness is from 0.5 to 6 mm. The application of dry mixtures is most efficient when used for thin layers.

The technology of the manufacture of dry building mixtures makes it possible to obtain mixtures with optimal granulometric composition of filling materials and aggregates, with precise dosage of the mixture components (without taking into consideration an error caused by the humidity of the raw materials and the concentration of liquid additives, which take place when ready for use mixtures are being prepared). As a result, the higher quality of dry mixtures and mortars or the concrete manufactured from them, compared with traditional mixtures, is ensured. Apart from this, there is an opportunity to obtain mixtures with unique physical and mechanical properties. For instance, these are super-high-strength concrete and mortar, super abrasion-resistant coverings, insulation materials, mixtures with non-constant granulometric composition, etc.

As opposed to mixtures ready for use, there are no technological limitations for the distance of transportation for dry mixtures. Dry building mixtures can be stored at a construction site for long periods (up to 1 year), without this changing their properties significantly, and they can be used in small portions when required. This enables the reduction of transportation costs, and also the quantity of waste when work is carried out. Transportation and storage of dry mixtures can be carried out at temperatures both above and below 0ºC, which is very important in the northern regions of the Russian Federation.

The high mobility of dry building mixtures makes construction technology more optimal, portions of the mixtures can be applied when necessary, and work can be carried out at a long distance from a manufacturing base. This is why dry mixtures are widely used for transportation construction.

The high efficiency of the use of dry building mixtures is reached when it is necessary to apply rapid setting mortars (concrete) and rapid setting mortar (concrete) mixtures. In this case centralized delivery of ready-for-use mixtures is limited due to the short setting time. Concrete mixtures for underwater concreting, with limited setting time, can be taken as an example. In Europe, over 0.5 million tons of mixtures of this type are manufactured annually.

The factors that limit the application of dry building mixtures, are their higher cost compared with ready-for-use mixtures, because of a need for drying and fillers screening, use of dry additives only, which are more expensive than water additives, as well as the necessary costs for packaging. The higher cost of dry mixtures limits their applications, especially when volumes are high. However, the higher cost of dry mixtures is compensated by high labour productivity and the lower materials consumption rate of technologies based on the application of dry ­building mixtures, especially when the mechanization rate is high.

In a number of cases, dry mixtures have higher workability and mobility, compared with ready-for-use mixtures. The most efficient fields of application of dry mixtures are thin-layer technologies, materials with higher requirements for quality and special properties, as well as when construction sites are located at a distance from the manufacturing base, under conditions of consumption of mixtures by portion, for quick-setting and fast-hardening mixtures, and others.

Three groups of materials are used for the production of dry building mixtures: binding agents, fillers and/or aggregates, modifying additives (Table 1). Regarding the type of binding agents, dry mixtures are divided into simple and complex mixtures.Simple binding materials are divided, respectively, into cement, lime, magnesium and polymers. Complex binding materials containing several simple binding agents are also used in the production of dry building mixtures. Here, the content of each agent should not be less than 20 % (Fig. 4). Most widespread are mixtures based on cement-and-limestone binding materials, used for the preparation of plaster mixtures, expansible binding materials based on Portland cement and alumina cement, and others.

The type of binding material used for the preparation of dry mixture, determines the majority of performance parameters of mortars (concrete) in particular the water and frost resisting properties, the hygienic properties, etc. Therefore, there is a range of specific features for the selection of binding materials. For example, in dry mixtures, for which stricter requirements for adhesion to a surface are set (plaster, facing, repair, installation, hydro-insulation, etc.), plain Portland cements of 50 MPa activity are the most effective, which makes it possible to reduce the consumption of polymer additives and, respectively, the cost of the dry mixture. In other mixtures, the choice of the type of Portland cement is defined in a similar way to that for mortar and ready-for use concrete mixtures.

In contrast to premixed mortar and concrete mixes, polymer binding agents, such as water-soluble polymers (for example, cellulose ether) and redispersible polymer powders or polymer dispersions can be used as binding materials.

Recently, dry mixtures on the basis of magnesian binding materials usually used for floor construction have been actively produced and advertised. From our point of view, application of dry mixtures on the basis of magnesian binding materials with tempering agent (bishofite) containing chlorine is extremely dangerous. This is connected with the presence of chlorides, which may lead to corrosion of reinforcing elements in re­inforced concrete structures, onto which magnesian mixtures are applied. The use of magnesian mixtures requires the development of special measures to ensure the safety and reliability of the utilization of buildings and constructions. These requirements should be included in the Building Materials Safety Regulations, which are currently in the process of approval by the State Duma of the Russian Federation.

The type, granulometric composition, and quality of fillers/aggregates have a considerable influence on practically all parameters of mortar (concrete) mixtures, and mortars (concrete). Normally, screened fillers and aggregates are used in the technology for the production of dry mixtures. This is concerned with the use of dry sand and fillers, the screening of which is technically uncomplicated. Apart from this, the selection of an optimal fraction composition guarantees a reduction in the consumption of modifying additives, and in some cases, an increase in the stability of their performance. For example, during nearly ten years of the application of plasticizing additives on the basis of polycarboxylate ethers by various producers, for the production of dry mixtures by Alit, no malfunction was registered as a result of their adsorption on fine fractions or clay admixtures in fillers that can be found in the manufacture of premixed concrete.

Dry mixtures are divided into concrete, mortar, and disperse mixtures, depending on the maximum fineness of the fillers/aggregates. Disperse mixtures are used for thin layers (0.5–6 mm) which, in their turn, can be divided onto coarse-, ­
small- and finely dispersed mixtures. A certain minimal thickness of the working layer corresponds to each type of mixture (Table 2).

A modern technology for dry building mixtures is based on the application of modifying additives for various purposes. The development and implementation of additives on the basis of cellulose ethers, polymer dispersions and redispersible polymer powders enabled the creation of dry mixture compositions for work with thin layers. The further technical development in the production of dry mixtures also depends, to a considerable extent, on the development of technologies for the production of new additives, and for the improvement of existing additives. The main types of additives used in the production of dry mixtures are shown in Table 3.

In order to illustrate the progress in the development of modifying additives, we can take the example of water-retaining additives on the basis of cellulose ethers. Initially, methylcellulose, that has a range of limitations for use, was applied as an additive. The application of methylcellulose with mixed esterification, i.e. methyl-hydroxipropylcellulose and methylhydroxiethylcellulose, led to a considerable increase in the water solubility, the temperature of solubility and the gel formation. In order to improve the thixotropic properties of mixtures, the producers of additives started to modify cellulose ethers with thixotropic additives, such as amylum ethers, poly-acrylonitrile, etc. Further development was connected with compensation of strength speed generation reduction of mortars (concrete), when cellulose ethers are introduced. For this, additives with a high rate of replacement have been developed. A new technology for the production of cellulose ethers with an even lower inhibiting effect has become the next step in this direction.

The further development in the production of dry building mixtures in the world will depend on two global factors, namely macroeconomic and technological factors. From the macroeconomics point of view, the highest increase in the production volume of dry building mixtures can be expected in the developing counties, such as China, India, Russia, Brazil, and others, due to the growth in consumption. Taking into account the global forecast that the middle class will increase by 1 billion people by the year 2020–2025, the global volume of production could grow by 20–30 million tons of dry mixtures. Apart from this, the consumption and, respectively, the production of dry mixtures will gradually increase in the economically developed counties. It is expected that the growth rate in those countries will remain at a pre-crisis level, on average, 2 % per year.

In the Russian Federation, the production of dry mixtures will develop with a higher growth rate, compared with other countries, due to the following factors:

1. A high potential for the increase of construction volumes in Russia. Today, Russia lags behind the economically developed countries by a factor of 2–2.5 times. In addition, there is a major shortage of residential space in the country.

2. An insufficient standard in the use of mechanical processing of dry mixtures at construction sites. At present, all conditions are in existance for Russia to reach the level of the developed countries in this direction in the near future.

3. A lot of work will be required for the heating of buildings including the installation of insulation systems. There is no doubt that there will be significant investments in this sector in the near future, with the purpose of increasing the energy efficiency of the utility services, and to solve environmental problems.

4. The absence of a domestic base for the production of a majority of additives with the required quality and range leads to the use of expensive imported additives. However, the situation is gradually changing. According to our forecast, the volume of dry additives production in the Russian Federation should considerably increase during the next 5 to 7 years, which will cause a reduction in the cost of dry building mixtures and, respectively, an increase in their consumption volume, especially in mixtures for mass application.

The development of the technology, production and application of dry mixtures depends, to a considerable extent, on the progress in improving the existing additives and developing new types of additives. A technology for extremely high strength self-compacting dry building mixtures can be taken as an example. The development of these mixtures is based upon a kind of “resonance” effect observed with an increase in cement strength due to introduction of complex of chemical additives, which was discovered by the ASTC “Alit”. The efficiency of additives‘ combined simultaneous introducing considerably exceeds the summary efficiency on strength increase achieved by introducing same additives separately. As a result, we managed to obtain mortars formed under molding technology, with the strength of 120–150 MPa (data given for industrially manufactured mixtures, on the basis of ordinary Portland cement M500 D0). With this strength, high fracture resistance is formed, which makes it possible to produce articles of complicated shape with high crack resistance. As a result, it becomes possible to reduce material consumption when arranging building structures and manufacturing products with a complicated shape, including those for machine building, shipbuilding, etc.

The research into and adaptation of dry mixture technologies for low temperature conditions is an important technological problem for Russia. Above all, this relates to the workability and efficiency of polymer additives at temperatures below 0 °C, as well as to the formation of reliable adhesion contact with a surface under such conditions. The solution of this problem would make it possible to reduce the dependence on seasonal specifics when working with dry mixtures. The perspectives for the application of dry mixtures are in the direction of carcass composite materials. They consist of grains of fillers, fastened with adhesive composition. As a result, a material with a honey-comb structure is formed. Thin-layer adhesive compositions are widely used in the technology of dry mixtures, for example, mixtures for sanitizing plaster, decorative structural coverings, etc. Using a porous filler (expanded clay, foam polystyrene granules, etc.) for grains leads to efficient heat insulating materials.Heat insulation is the most urgent task in the current situation of energy shortage.

 The research carried out by ASTC “Alit” demonstrates that the advantage of carcass composite materials on the basis of dry mixtures is that the resulting material has a good quality and workability. Taking into account that heat insulating materials are consumed in large amounts by the construction and industrial sectors, this tendency makes it possible to increase the volume of production of dry building mixtures and create heat insulating systems consisting of dry mixtures only. Thus, despite its relatively short development period, the production and technology of dry mixtures have become a significant branch of the building materials industry, with an annual turnover of over 40 billion US$. During the coming decades, a considerable increase in the production volume of dry mixtures is expected, due to market growth and the expansion of the dry mixture product range.