Mechanical properties of slag based geopolymer 1. Compressive strength

The mechanical test was carried out by Compression Testing Machine at the age of 7 days. The compression testing machine was used to determine the maximum load of the 20x20x20 mm cubes. The effect of grinding on the strength was measured on specimen with 6 grinding time (0, 1, 3, 5, 10, 20 minutes) with 5 probe specimens (30 pieces). The compressive strength results based on the measurements of geopolymer cube. The maximum forces were used to calculate the compressive strength of the geopolymer cubes.

σ=_𝐴^𝐹 σ=Compressive strength (MPa)

F=Maximum applied force (N) A= Surface area (mm²)-400mm²

(1) 2.4.2. Body density of the geopolymer concrete

The density of various geopolymer concrete specimens was determined before crushing. The density was determined using the equation of:

The Figure 2. illustrates the results of the particle size analysis. The particle size distribution shows that the coarser particles above 100 µm can slightly change their size after 10 minutes grinding, and the amount of them not really decrease. The coarsest particle size sharply decrease only after 20 minutes grinding. After 20 minutes there is a strong particle size reduction in the finer fraction too. There is a significant change in the finer fraction even 1 minute grinding, because not only the grinding ceramic balls serve as a grinding media, but the coarser particles too. For 10 minutes grinding the stress intensity was not enough to break coarse particles only to break the smaller ones. Based on the particle size distribution the stirred media mill produced fine fraction (below 1 µm) and coarser particles at the same time, showing wider particle size distribution curve. For better understanding of particle size distribution, the characteristic particle size diameter x80 and x50 were plotted as a function of grinding time (Figure 3). It can be seen that slight changes of the median particle size (x ) and x till 10 minutes and after 20 minutes grinding sharp decrease

occurred in both x50 and x80. The increasing grinding time in stirred media mill resulted in increase in product fineness. Beside the significant increase of submicron particles, coarser particles are presented in the product, in considerable amount even after 10 min grinding time.

a) b)

FIGURE 2. PARTICLE SIZE DISTRIBUTION AND VOLUME RATIO OF THE RAW AND GROUND SLAG

FIGURE 3. CHARACTERISTIC PARTICLE SIZES OF THE GROUND SLAG DEPENDING ON THE GRINDING TIME

The specific surface area generated by grinding of the slag in the stirred media mill is described as a function of specific grinding energy. The higher the grinding energy, the higher the specific surface area. The highest specific surface area can be achieved by stirred media mill with specific surface area of 23489.47 cm²/g after 20 minutes grinding and using 60 Wh specific energy input. The finest median particle size achieved by the stirred media mill is 3.5 μm after 20 minutes grinding. The particles ground in stirred media mill may be aggregated after 3 minutes grinding time and the aggregates are destroyed only after 20 minutes grinding.

The specific surface area well correlated with the particle size distribution. After 1 minute only a small increase can be observed in the specific surface results from the slightly increasing amount of finer (smaller than 1µm) fraction. The sharp increase can be seen after 20 minutes grinding due to the large amount of fine fraction. To reach higher specific surface area more specific grinding energy is necessary. Grinding can decrease the particle size and increase the specific surface area.

The results of particle size reduction can be seen on the scanning electron microscopy pictures (Figure 4).

The original angular grains become more rounded with grinding time, and the particles become finer with 20 minutes grinding with some bigger particles. These investigations well correlate with the results of particle size analyses.

FIGURE 4. THE EFFECT OF GRINDING ON THE PARTICLE SIZE AND SHAPE

3.2. Mechanical properties

To determine the effect of mechanical activation on geopolymer compressive strength the most important parameter is the specific surface area on which the reaction with alkali activating solution can be completed.

Silica is a material that dissolves easily in strong alkaline solution at high pH, and play an important role in the condensation process (Lingard et al. 2012). Based on that fact, the mechanical activation effect improved the dissolution of SiO2 and Al2O3 as grinding can increase the amount of fine particles that can be easily dissolved, and transforms to hard geopolymer. In this investigation 6M NaOH was used for alkali solution and mixed with the ground material. Figure 5. shows the relationship between grinding time and compressive strength. The vitrified slag ground for 20 minutes showed the highest specific surface area and compressive strength. The alkali solution can easily reach the finer particles due to the high specific surface, and results in high compressive strength. The effect of grinding on the compressive strength is found to be followed an increasing trend of the power function, with R²⁼ 0.9. The relationship between compressive strength and particle density shows decreasing trend.

The differences in the body density of the geopolymer may be derived from the pores and voids that formed due to the not suitable compaction, caused by the rapid setting time. With increasing grinding time most of the particles possess similar grain size, and the pores between them will be empty.

FIGURE 5. THE EFFECT OF GRINDING ON THE COMPRESSIVE STRENGTH AND BODY DENSITY

4. Conclusion

As geopolymer is a relatively new type of binder material in recent years therefore it is important to collect a great amount of knowledge about the topic and ensure the fulfilment of expectations of the geopolymer technology. The slag based geopolymer like other geopolymer require heat curing in order to accelerate the geopolymerisation process. As the alkali activation of the aluminosilicate materials is the first step of the geopolymerisation process, the strength of the geopolymer concrete is highly depend on the concentration of the alkaline solution which determine the rate of dissolution. The compressive strength usually increases with increasing molarity of NaOH, but the high amount of Ca²⁺ ions can react with OH^- to form Ca(OH)2

and precipitate. This process lower the alkalinity that may inhibit the dissolution of aluminosilicate particles. The amount of sodium hydroxide solution and its concentration is the most important factor in the geopolymerisation process, as the hydroxide ions dissolves the aluminosilicate. The addition of alkali silicate increase the available silica content. The early hardening of the geopolymer concrete can be a problem in the sample preparation stage as there is no time to adequately compact the fresh geopolymer sample into sample holder. The inadequate compaction cause larger pores and voids in the geopolymer concrete. The time of setting in the case of slag was less than 5 minutes. The surface of the geopolymer is covered with white encrusting. It may be sodium bicarbonate which forms when there is in excess amount of NaOH that can react with the slag particles (Davidovits 2011). The sodium hydroxide migrates up to the surface of the geopolymer during drying and reacts with the atmospheric CO2. Promising slag based geopolymer concrete compressive strength up to 21.5 MPa were obtained. Further research should be carried out to ensure a longer setting time as the rapid setting of the geopolymer makes difficult the casting of moulds. More knowledge of the mechanical parameters such as flexural strength, elastic modulus should be carried out.

5. Acknowledgement

The described work/article was carried out as part of the „Sustainable Raw Material Management Thematic Network – RING 2017”, EFOP-3.6.2-16-2017-00010 project in the framework of the Széchenyi 2020

Program. The realization of this project is supported by the European Union, co-financed by the European Social Fund.

6. References

Bondar, D., Lynsdale, C.J., Milestone, N.B., Hassani, N., Ramezanianpour, A.A. (2011), Engineering Properties of Alkali-Activated Natural Pozzolan Concrete. ACI Materials Journal, 108(1).

Cheng, T.W., Chiu, J.P., (2003), Fire-resistant geopolymer produced by granulated blast furnace slag, Minerals Engineering 16 205–21

Davidovits, J., (2011), Geopolymer chemistry and applications. France: Geopolymer Institute

Kumar, S., Kumar, R., Mehrotra, S.P.J (2010), Influence of granulated blast furnace slag on the reaction, structure and properties of fly ash based geopolymer, Material Science 45: 607

Kumar S., Mucsi G., Kristály F., Pekker P., Mechanical activation of fly ash and its influence on micro and nano-structural behaviour of resulting geopolymers, Advanced Powder Technology, 28 (3), 2017 Lindgård, J., Andiç-Çakır, Ö., Fernandes, I., Rønning, T.F., Thomas, M.D. (2012), Alkali–silica Reactions (ASR): Literature Review on Parameters Influencing Laboratory Performance Testing. Cement and Concrete Research, 42(2)

Lloyd, N., and Rangan, B., (2010), Geopolymer Concrete with Fly Ash. Paper presented at Second International Conference on Sustainable Construction Materials and Technologies.

Mucsi, G., Csöke, B., (2012): Power plant fly ash as valuable raw material. Geosci and Eng 2012 1, 223-236

Mucsi, G., Szabó, R., Rácz, Á., Kristály, F., Kumar, S., (2019): Combined utilization of red mud and mechanically activated fly ash in geopolymers. Rudarsko-Geolosko-Naftni Zbornik 2019 34 (1), 27-36 Palomo, A., Grutzeck, M.W. & Blanco, M.T., (1999), Alkali-Activated Fly Ashes: A Cement for the Future.

Cement and Concrete Research, 29(8)

Provis, J.L., Van Deventer, J.S.J., (2009), Geopolymers: Structure, processing, properties and industrial applications. Woodhead Cambridge, UK

Sakkas, Κ., Nomikos, P., Sofianos, A., Panias, D., (2013), Slag based geopolymer for passive fire protection of tunnels World Tunnel Congress 2013 Geneva Underground – the way to the future! G.

Anagnostou & H. Ehrbar 2013 Taylor & Francis Group, London

Xu, H., Van Deventer, J.S.J., (2000), The Geopolymerisation of Alumino-Silicate Minerals. International Journal of Mineral Processing, 59(3).

III. RING – Sustainable Raw Material Management Thematic Network – RING 2017

1 Soproni Egyetem, Faipari Géptani Intézet 4. Bajcsy Zs. str. Sopron 9400 Hungary

suzanna.kornfeld@gmail.com

Abstract: Market relations nowadays require reduced price and improved quality of products that is only possible the providers increase their efficiency. A key to achieving this is the adequate process-oriented alignment and control of company processes as well as their co-ordination and execution in order to ensure sustainability. In logistics there are plenty of opportunities for innovation that enable any compa-ny to streamline their operation, increase their competitiveness and as a result their ability to generate more profit. With the help of existing and new methods the processes of companies can be examined, and the critical points of operation detected. These sources of error must be revealed in line with the compa-ny’s overall strategy and then optimized, eliminated or reduced to the lowest possible minimum. However, it is not only sources of error that must be examined and detected but also less efficient activities and the individual elements of the system.

Key words: sustainability, efficiency, innovation, competitiveness, quality

1. Introduction

Technological development has already affected the economy and the labour market many times over the course of time and there is still a chance of it happening again. Climate change, existing environmental problems, diminishing resources whose availability is scarce, the lack of professionals, and the altered labour market require all economic operators to take a different approach. All the above effects force businesses to introduce a sustainable and more responsible attitude from an environmental point of view.

The unpredictability of the market, its increasing dynamism, the available and more and more ‘disturbing’

product selection, and the complexity of the situations deriving from it, cause businesses to face bigger and bigger challenges. While gaining a competitive edge, a bigger market share, and reducing costs, sus-tainable operation must be achieved by customer satisfaction without quality being impaired. (Emerson, 1999). Due to the constant demand for development and investment, businesses must make bigger and bigger efforts to achieve a bigger market share and generate more profit long-term and with permanent growth. Profit generation clearly shows that the main goal of companies is to make money (Goldratt E. M.

2004). Therefore, money is obviously the most efficient tool in the world, in the economy and in industry not only as a value measurement but also a means of payment (Antonioni P. 2011). The special character-istics of our financial systems generate environmental and social conflicts within the concept of sustaina-bility (Arnsperger 2015).

This is why due to the complexity of effects arising in the above market conditions, certain individual, economic and ecological goals must be taken into consideration so that businesses can to react to the complex challenges of our century in time, fast, and in a flexible way, through innovative strategies and a sustainable corporate governance approach. These challenges constantly make it difficult for companies to stay competitive and successful and make it harder for them to adjust with minimum effort. The avoid-ance of negative effects and the achievement of economic gains motivate companies to implement