Granulated blast furnace slag has been used as an component of blast furnace cement for many years. The replacement of a certain clinker portion by blast furnace slag saves raw materials and thermal energy for pyroprocessing. Ingo Engeln from Polysius AG gives an overview of the Asian slag market and the use of Polysius' vertical roller mills in China and South Korea.

Granulated blast furnace slag, a by-product of pig iron production, has been used as an important component of blast furnace cement for many years, due to its latent hydraulic properties.

The replacement of a certain clinker portion by blast furnace slag does not only mean to save raw materials and thermal energy for pyroprocessing, but also provides for advantageous characteristics of the blast furnace cements:

• low heat of hydration helps to prevent cracks in the concrete due to temperature stresses,
• high resistance against sulphate attack,
• high resistance against alkali-aggregate reaction,
• high binding capacity of chlorides in blast furnace slag cement pastes,
• the low electrical conductivity of concrete made with blast furnace cement resulting in a positive effect on the corrosion protection of the concrete reinforcement.

In China, quality Ground Granulated Blastfurnace Slag (GGBS) (S95, blaine 4200-4500cm²/g) produced with vertical roller mills are being used to substitute clinker in conventional cement manufacturing as well as to partially replace OPC for ready-mixed concrete production, for which the percentage of GGBS usage is typically at 10-15% and 20-25% respectively. Such low percentage of GGBS in the mixing ratio, however, whilst achieving the purpose of saving some costs, is insufficient in enhancing concrete structural durability. A long journey remains ahead for the newly established slag grinding industry to reach the day when all the inherent qualities of GGBS and its superior characteristics over fly ash or other pozzolanic materials are fully appreciated.

This article touches on GGBS with blaine ranging 4200-4500cm²/g, complying with GB/T 18046 S95 and produced ideally with the state of the art equipment -vertical roller mills (VRM). Compared with GGBS produced by ball mills (BM), which is at typical blaine of 3800-4000cm²/g, VRM-produced GGBS is very much superior in terms of fineness, production efficiency, cost-effectiveness, product reactivity and its applications. Regardless of the chemical composition, significant differences between VRM GGBS and BM GGBS are with blaine fineness and particle size distribution (see Table 1 and Figure 1).

Eberhard Lang presents experimental data on high-performance concrete using blastfurnace slag cement. Durability, low heat of hydration and workability are notable features: superplasticisers and silica fume can be used to further modify concrete properties.

Results of investigations in laboratory scale as well as long experiences in practice indicate the special benefits of blastfurnace slag cements. These are, besides others, their comparatively low capillary porosity, their high resistance against sulphate attack, seawater or other aggressive attack, against alkali-aggregate reaction and to the diffusion of chlorides into the concrete. Recent research has also shown a high binding capacity of chlorides in blastfurnace slag cement pastes. A further aspect of importance for the corrosion protection of reinforcement is the comparatively low electrical conductivity of concrete made with blastfurnace slag cement. Due to their low heat of hydration, blastfurnace slag cements help to prevent cracks in concrete structures resulting from temperature stresses at early ages^.

This paper described researches to use some of these special properties in high performance concrete and shows some practical experiences.

China's iron and steel production continued to maintain a high growth in the first three quarters of 2005, though the price of steel products has been falling since April in the same year. It is estimated that China's annual steel output will soon reach 330Mt - enough to meet the market demand of 2010.

In the first three quarters of 2005 China produced 255.29Mt of crude steel, up 27.39% year on year; 239.2Mt of pig iron, up 30.98%; and 268.82Mt of rolled steel, up 25.82%. Of 268.82Mt of rolled steel, plate product accounted for 104.08Mt or 38.72% of the total, up 2.48% points year on year; and long product made up 137.82Mt or 51.27% of the total, down 2.61%. The change in the proportion of rolled steel reflects that the structural adjustment of rolled steel is developing toward the expected orientation. Despite fast growth of production, China still needs to import a large amount of high-class steel as quality of production is still low.

The introduction of slag cement has faced resistance in the Thai construction industry, mainly as a result of stubborn attitudes towards a new product. Nevertheless, Siam Cement believes it can change perceptions, and sees Thailand's expanding construction sector as fertile ground.

Thailand is one of the largest cement producers in southeast Asia and is an important supplier to the international market. Most of the Kingdom's production is of Portland cement though smaller quantities of speciality cements such as white cement, oil well cement, masonry cement and others are made as well.

One product that has been absent from the cement market is slag cement. Steel production in Thailand uses arc furnace technology and most of the slag waste produced locally is used for road construction.