As the twenty-first century dawns, mankind knows only too well that the modern scale and pace of development in different areas of manufacturing will have to be radically overhauled. Harmony and consensus of its economic needs must to be balanced against the needs of the environment around us.
The construction business is no exception. One of its main operations is the building materials industry (BMI) – whose technical level sets the benchmark for the growth of the entire construction industry.
In today’s Russia – and in fact all over the world – demanding environmental and economic conditions are prompting new methods for the production, manufacture and use of building materials in all possible spheres of application. Alongside this, particular care must be exercised in rational conservation of raw materials, the maximum possible use of locally-produced materials and by-products from different kinds of manufacturing, as well as a social, environmental and economic reorientation from producers towards market demands. It is vital to preserve and made good use of already-existing scientific and technical potential of the BMI industry, and its recognised schools and applications. One route to meeting these demanding challenges lies in the wider use of gypsum-based building materials. A pre-requisite for this is high-end processing of easily-obtained natural gypsum and waste materials which contain gypsum in gypsum binders – the ease of production for such products (particularly since it does not involve heat treatment), alongside their advanced properties (low heat and noise conduction, fire-resistance, high decorative and comfort qualities, environmentally friendly). Compilation and evaluation of both Russian and overseas feedback shows that in recent years in foreign markets the use of gypsum-based construction materials has grown considerably per unit mass of building projects (for example by 1.8 times in Japan, and by 2.5 times in the United States). The most popularly used applications of gypsum in construction are plasterboard, gypsum fiber board, and gypsum sheeting; small or medium-sized tiles, blocks, decorative, as finishing or acoustic material, and also in dry mortar and concrete mixes. These are typically used in buildings where the relative humidity is lower than 60%.
Turning now to Russia, the gypsum industry, just like the whole BMI business, is going through some difficult times. Companies in the industry, with very few exceptions, are in a run-down state, manufacturing is barely profitable, and the money made in the business is not sufficient to permit upgrading of obsolete equipment, far less to carry out any kinds of existing or upcoming R&D. This all means that gypsum-based materials are frequently low-quality. This is the cause of their neglect, and this leads on to a widespread drop in production. Market opportunities in recent years have been instead snapped up by foreign manufacturers, and the amount of over-priced and poor-quality goods on the market has added to the woes encountered by gypsum manufacturers.
Manufacturers, in trying to find a way out of the situation, have invested in technological equipment which isn’t suitable for the Russian market, and this leads inevitably to an inability to set up normal manufacturing. Yet even so, there is excellent Russian-developed technology, including much which is available for instant application. The most important of these developments have received Russian and international recognition, particularly research carried out by MGSU into the development of water-resistant gypsum binders which outstrip rival products produced abroad. These include:
Plaster-cement pozzolanic ( GTSPV ) – TU 21-31-62-89;
Composite gypsum binders ( GFP ) and water-resistant gypsum binders with low water needs ( VGVNV ) -TU 21-53-110-91.
These become especially durable if they are manufactured not from raw materials, but from gypsum-rich manufacturing by-products.
These developed binders, as opposed non-water-resistant binders, have universal properties which can be seen in their hydraulic hardening capabilities, their reduced tendency to creep, and their long-term durability. During the manufacture of these binders, the “Guidelines for the design, manufacture and use of products and designs made from concrete based on plaster-cement pozzolanic binders” and the “Guidelines for the production and use of wall masonry based on composite gypsum binders” should be followed. These guidelines, in their regulatory and technical requirements, open up new opportunities for the deployment of gypsum in the modern construction business. This is particularly so in outdoor structures (stone, blocks, panels) and in buildings which experience high humidity levels (partitions, plumbing and toilet facilities, ventilation facilities and panels) as well as in supporting structures.
Manufacturing concrete components using these binders doesn’t involve any heat processes. This recommends them for production of reinforced concrete sections at concrete factories, as the use of heat and humidity are entirely eliminated in the manufacturing process.
When discussing GFP and VGVNV, these kinds of binders are of particular benefit during monolithic structure building work, since they permit the concreting to be carried on at low temperatures without the use of the kind of special processes typically used when laying other kinds of concrete based on Portland cement. It ought to be noted that laying these kinds of cement work using this type of binder can be achieved in approximately a single day.
In recent years, a great deal of attention has been paid, both in Russia and internationally, to the opportunities for recycling gypsum-rich industrial waste by-products in the production process of a number of different gypsum binders. In Russia, this has gone on to involve the mechanical and chemical activation of components, which makes possible a significant release of energy in the particles of clinker and siliceous additive. This enables the swift formation of calcium hydrosulpho-aluminates and calcium hydroxide when the gypsum-rich binder compound is mixed with water during the early stages of hardening. The action of silica minerals is increased. This has the result that the hydration level of cement which contains GFP reaches its maximum in 90-120 days, while the concentration of Ð¡Ð°(ÐÐ)2 and quantity of aluminates is reduced to a level at which any danger of damage to the hydrosulphate aluminates or of a weakening in the material’s structure is eliminated. During the manufacture of an organic modifier, it is of primary importance to bear in mind the proportions to be used of the silica-containing compound, and of Portland cement. This proportion depends on the activity-level of the silica, and the kind and chemical composition of the cement being used. In turn, the activity-level of the silica additive similarly depends not so much on its origins, but on the degree of fineness to which it has been ground. During grinding, and most especially if there are surfactants present, the activity-level of silica particles increases – as is confirmed by the absorption rate of lime slurry which is produced in accordance with the TU 21-31-62-79. These results show that an increase in the specific surface area of the ground particles causes an increase in its activity in solution. Thus, if the specific surface areas of silicate granules and Portland cement and silicate conform to 300 and 500 m2/kg then the required proportion of silica to Portland cement is exactly 1.5. If the specific surface area of the silicate granules is increased to 712 m2/kg then the proportion drops to exactly 1:1.
Experience shows that the silicate material is extremely resistant to intense levels of pulverising – so that obtaining silicate granules with a specific surface area higher than 300 m2/kg can only be achieved with disproportionate time and energy resources, and thus makes its use unviable economically. Combining the crushed granules with other analogous materials to achieve a more intensive binding of the calcium hydroxide can be achieved by adding a small quantity of microsilicate – an industrial by-product in ferrosilicon production – in a proportion of between 5% and 15% of the volume of Portland cement, dependent on the initial activity-level of the chemical additives and the chemical make-up of the Portland.
The effectiveness of the microsilicate (MS) can be seen in the reduced concentrations of calcium oxide in solution after 28 days, down to 0.31 to 0.33 gr/litre. This would be typical for formulations containing a satisfactory amount of ADM that characterises high activity. This means that adding MS, which has a specific surface area of between 1800 and 2200 m2/kg can provide the essential corrective factor to provide stable hardening in gypsum – cement/silicate – water systems.
Pulverised fuel ash can be reduced to a fine powder far more easily than silicate granulate, and its binding activity level is notably higher. When using normal Portland cement and fuel ash crushed to a fineness of 900 m2/kg, the ratio required of Ash to Cement is 1.5. If both of these components are are ground for a similar period (ten minutes) then their specific surface area will be exactly equal to – cement 550, and ash 1312 m2/kg. When using this level of grinding, the required proportion of the components drops to 1:1.
The results of determining the activity-level of finely-ground grit and waste glass by-products show the weak level of binding these additives have with calcium oxide – quite separately from the specific surface areas of these additives and the Portland cement. These means that these additives need to be used in GFP alongside microsilicates. It follows, therefore, that complex silica-based additives has a synergetic effect, and the microsilicates in it can be considered to be the component that guarantees the long-lasting durability of the products made with it. The presence in complex silica-based additives of super-plasticisers or other kinds of surfactants moves them up into the category of organic mineral modifiers. They contribute to an intensified mechanical activation while shortening the duration time of the activation process. The resulting GMM not only gives the gypsum binder hydraulic properties, but also regulates the other binder properties in a desirable direction too. Examples include slowing the setting time, lowering average density, boosting strength under tension or pressure, impact resistance, burst instability, and other factors. Production of GMM could be organised on a centralised basis – for example, at plants which produce dry building material mixes. Thanks to these universal modifiers, the GMM capabilities of composite gypsum binders and available through their application acquire a whole new range of possibilities which are more typically characteristic of Portland cement. However, they continue to have the same primary benefits of gypsum binders – rapid setting and hardening. Alongside this GFP also has low demands on water – thus opening up opportunities for manufacturing which does not involve any heat treatment processes.
The Strommashina plant in Samara, Russia, strives to meet the challenge of creating new manufacturing equipment for producing building materials, with a heightened awareness of the need to safeguard the environment, and establish harm-free manufacturing. For many decades Strommashina has been perfecting the production of the technology for grinding and crushing equipment; kilns and drying units; agglomerators; separators; mixers; and pelletisers. When equipment made by Strommashina is incorporated into a production facility, it can achieve new increased output targets in all types of building materials – and most particularly, the company’s range of equipment for producing gypsum binders enjoys great popular success.