Fields of application of blast-furnace and converter slag

Chemical composition of the slag: CaO - 40-45%; SiO2 - 32 - 36%; A12O3 - 11-17%.

After grinding of metallurgical slag and extraction of iron from them by dry magnetic separation, aggregate /gravel/ is obtained that has excellent chemical and physical and mechanical properties and has different fields of application in industry and agriculture such as:

1. Production of concrete - The blast-furnace slag is used as aggregate for making concrete /slag gravel for concrete and construction/. Concretes with aggregate of blast-furnace slag are lighter, have good fire-resistance /withstand up to 600°C/ and are considerably cheaper. The best results for concrete are obtained when the ratio between slag and river sand is 1:1. Lightweight structural concretes for facade elements have apparent density of 1900 kg/m3 and compressive strength of 30 MPa, at 350 kg/m3 cement. 

2. The blast-furnace slag - is an excellent material for ground-mechanical works such as making foundation pillows for roads, embankments, flooring, street pavements, pavement for railways and others.

The slag has very good drainage properties and is insensitive to water. Their modulus of elasticity retains constant values in different seasons and weather conditions, which is very important for the hydrothermal mode of roadways. The modulus of elasticity, defined by a compression plate, is 200 MPa, which is far greater than the requirements for such a purpose, and over time it is increased to 300 MPa. It was found that the recovery of the loaded slag pillow is performed simultaneously with the unloading. 

The high modulus of elasticity makes it possible to reduce the thickness of the base in road and street pavements, as reflected by the respective economic effect. The blast-furnace slag has an advantage in the performance of embankments at greater height /12 - 15 m/ and in bad earth-fill and hydrogeological conditions in the ground massif, which the road embankment lies on and there is a risk of landslides. 

Moreover, the modulus of elasticity of the slag is several times larger than that of the fine-grained cohesive soils and natural coarse aggregate. It should be known that not only soils,but also natural coarse aggregate contains clay, and therefore when there is an increase in their water content, the modulus of elasticity is significantly reduced and in many cases falls below 30 MPa, which is considered a minimum value for this purpose. When using slag, smaller embankments can be made, with steeper slopes compared to those designed with natural coarse aggregate and fine-grained soils. Thus, the volume of embankment can be significantly reduced. For this purpose, the slag may be transported over longer distances. Thus, the raw-material source of construction is expanded. 

Reshitsa falls within one of the worst regions in terms of climate conditions. The natural coarse aggregate and breakstone material are with poor thermotechnical indicators and migration of water into the ground base is significant. This gives to the soils in the base unfavourable consistence, which corresponds to small bearing capacity. The use of slag solves these problems because it eliminates the danger of frost, allows to work with one kind of material for making the base and the base to be performed by only one technology of laying and compaction, which in turn provides faster construction (to be compacted better, the layers should have a thickness of up to 0.4 m, and the most effective and therefore the most economical compaction is obtained for 12 strokes of the machine).

3. Asphalt construction - the experience in many countries shows that non-granular blast-furnace slag may have application in asphalt construction. The slag may be used as a mineral material in the production of mixtures for the implementation of the basic and binder layers of roads and streets, adding a little more bitumen (1.4 - 1.6 %), due to the higher porosity. 

There is no significant difference in the technology of laying of asphalt mixtures with natural stone materials and with crushed blast-furnace slag /even with slag the compaction work for mixtures is greater/.

Experiments made with blast-furnace slag have confirmed the excellent bearing capacity of the roadway. 

It is recommended that asphalt bases use fractions of non-granular blast-furnace slag for the purposes of asphalt construction.

4. Slag flour - experience has shown that the blast-furnace slag can be used for obtaining slag flour, which is an excellent substitute for the stone powder used in asphalt construction in significant quantities.

5. Slag wool - the slag wool is used for thermal and sound insulation in construction and industry up to +600 degrees Celsius.

6. Construction ceramics - laboratory articles have shown that non-granular slag can be used as a raw material in obtaining ceramic mass, baked at 1000 degrees Celsius. As an advantage it is pointed out the opportunity for the articles to be removed from the furnace at a high temperature without risk of cracking. These articles have high strength, low water absorption, high frost resistance and thermal resistance. By a certain variation in the composition of the furnace charge cladding tiles, floor tiles, glazed tiles, stoneware pipes, acid-resistant products, etc. can be produced.

7. Use in agriculture - blast-furnace slag with higher content of CaO is of interest for agriculture to neutralize acidic soils and increase yields.

8. Cement concretes - Converter slag is a suitable material for the preparation of fractions for aggregate for cement concretes to class C25/30 inclusive, and probably for higher brands, without increasing the amount of cement. The introduction of a certain quantity of ash from thermal power plants in the concrete mixture will have a positive effect on the plasticity of the mixture and the strength properties of the hardened concrete. Furthermore, the kinetics of the strength development in the period 28-90 days, in the concretes with slag, is better expressed in comparison to the concretes with stone materials.