1. Loesche has developed a new method for producing ultra-fine blast furnace slag using a cyclone separation system. The method produces blast furnace slag with a typical fineness of 4,500-6,500 Blaine in a vertical roller mill, then separates the ultra-fine particles above 10,000 Blaine in cyclones. 2. Tests of the cyclone separation system showed it could produce 10-20% of material above 10,000 Blaine fineness from the mill product. The remaining "grit" material had fineness suitable for normal blast furnace slag uses. Concrete tests with the ultra-fine slag showed significantly higher early strength compared to normal slag fineness.

1. LOESCHE METHOD FOR MANUFACTURING
ULTRA-FINE BLAST FURNACE SLAG
Dr. Holger Wulfert, Dr. Winfried Ruhkamp, Andre Bätz, Paul Erwerth
Material Tests: Prof. Ludwig, Bauhaus University, Weimar, FIB
Blast furnace slag grain with reaction seam of CSH phases (taken by B. Möser, Bauhaus University, Weimar, FIB)

2. 2
1. Initial situation
Due to the high CO2
emissions that are associat-
ed with the production of Portland cement clinker,
a central objective of the cement manufacturer
is to reduce the clinker proportion by using
composite materials. One of the most important
composite materials is blast furnace slag. The
amounts of blast furnace slag that accumulate
are used almost exclusively today as a composite
material in cement or a concrete additive in
concrete. The usual fineness range of the blast
furnace slag is between 3,500 and 6,000 Blaine.
To be able to exploit the performance potential of
blast furnace slag fully, material producers have
expressed again and again the wish for a suitable
preparation technique for creating the finest blast
furnace slag.
Ultra-fine blast furnace slag could reduce one of
the main weaknesses of cements containing blast
furnace slag, that being too little early strength for
many applications (Diagram 1).
As is already apparent today, the ultra-fine blast
furnace slag could be used for many different
specialised products.
Until now extremely finely ground blast furnace
slag (> 10,000 Blaine) has been produced in
ball mills (mostly in batch operation) in a very
energy-intensive way. Generating such a high
degree of fineness requires an enormous amount
of energy. The consequent high cost of the corre-
sponding products has so far prevented a great-
er market penetration, with the result being that
binder systems based on the finest blast furnace
slag have so far only been used in niche areas.
Against the backdrop of the situation described
above, Loesche has developed a more energy-
efficient production of the finest blast furnace slag.
The concept includes initially manufacturing a blast
furnace slag of typical fineness (4,500-6,500 Blaine)
on a vertical roller mill, from which the finest blast
furnace slag is separated in an extremely effective
and economical manner. This low-cost production
of the finest blast furnace slag will enable a wider
market access for the corresponding products.
2. Tests for attaining ultra-fine BFS on pilot scale
Blast furnace slag produced in large-scale
Loesche grinding plants usually has finenesses
between 3500 and 6000 Blaine, max. 7000 Blaine.
Investigations on grinding products from an
industrial vertical roller mill showed that, depend-
ing on the fineness, grinding products contain
ultrafine material components with degrees
of fineness of >10,000 Blaine, in the range of
approx. 10 to 20 %.
A way has been found to be able to use known
and tested equipment and technologies to at-
tain the ultra-fine content without significantly
increasing the specific power consumption.
For this, the product is drawn out of the product
silo and fed into a separate plant in order to attain
the ultra-fine product.
As a core part of this type of technology, a
specialised cyclone is used for the finest dust.
The basic structure of such a system is illustrated
in a simplified flowchart in figure 1.
GBFS-mortar mix 50% / 50% with CEM I 52,5 R
0
10
20
30
40
50
60
70
80
90
100
86.9
36.5
77.8
20.1
65.0
42.5
BFS with 5,000 Bl.
38.2
19.6
61.7
BFS with 3,600 Bl. BFS with 17,000 Bl.
2 d 7 d 28 d
Compressivestrength[MPa]
Diagram 1: Compressive
strength development as a
function of BFS-fineness

3. 3
It is known that the fineness of a final product
determines the geometric dimensions of the cy-
clone to be used. Because of the relatively small
dimensions, generating larger amounts of the
product requires working with a larger number of
cyclones, which are consolidated into so-called
multi-cyclone batteries.
In the first experimental tests, the following points
were the focus:
• Proof of the general operational capability and
control capability of the multi-cyclone facility
regarding the achievable fineness and the fine
material yield.
• The use of a disperser, which transfers the
grinding material from the grinding plant’s silo
back into a gas/solid matter suspension with-
out any agglomerates forming.
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Feed silo
Supply
Multicyclone system Filter
9147 9397 9362
Feed to cyclone:
Blaine
cm²/g 6000 5000 4500
Feed to cyclone:
P50
µm 6.0 6.8 8.5
Portion of ultra
fine material
% 18 14 10
Ultra fine mat. cm²/g 12000 11000 12000
Fines: P50 µm 2.1 2.2 2.1
Grit: Blaine cm²/g 4650 4050 3650
Grit: P50 µm 7.0 8.2 11.4
Table 1: Proportion of ultra-fine material and “grit” at different degrees of fineness in feed
Figure 1: LOESCHE Cyclone-plant for producing of ultrafine materials
Disperser
Fan
Ultra fine
Grit

4. 4
0
10
20
30
40
50
60
70
80
90
100
The gas/solid matter mixture is transported
through the plant with the suction of a fan.
The grinding product with a selectable fineness,
between 4500 and 6500 Blaine wherever possible,
is stored in a bin and supplied to a disperser facil-
ity via a rotary gate and speed-controlled screw
conveyor.
From here the gas/solid matter mixture reaches
the multicyclone.
The ultra-fine material leaves the cyclones via the
immersion tube and is transported to the filter.
The material from the lower stream of the mul-
ti-cyclone apparatus, called “grit”, has a fineness
in the range of conventional blast furnace slag
and can be used as such (Tab.1 and 2).
Feed to cyclone: Blaine cm²/g 5000 4500
Feed to cyclone: P50 µm 6.8 8.5
Portion of ultra fine material % 14 9 10 5.5
Ultra fine mat.: Blaine cm²/g 11000 16000 12000 17000
Ultra fine mat.: P50 µm 2.2 1.7 2.1 1.6
Grit: Blaine cm²/g 4050 3950 3650 3850
Grit: P50 µm 8.2 8.3 11.4 10.7
Table 2: Manufacturing of various ultra-fine material at equal fineness of the feeding material
Diagram 2: Compressive strengths of blended cements with blast furnace slag from a Loesche blast furnace slag grinding plant
36.0
6.5
15.1
Curing time [d]
32.4
43.1
20.2
45.1
53.1
55.8
2 d 7 d 28 d
1.00 CEM
0.50 BFS meal with 4000 BLAINE
0.70 BFS meal with 4000 BLAINE
Compressivestrength(N/mm2
)/normprisms
Development of compressive strength compared
to CEM I 42,5 R (1.00) and mixtures with 50 and 70
Ma.-% BFS meal
(12,600 Blaine)

5. 5
3. Cycloning results and material tests of the
ultra-fine blast furnace slag
In the Loesche test center many grinding and
cycloning tests have been carried out with many
different types of blast furnace slag over the past
year.
The throughput of the cycloning plant’s fine material
is 20 to 80 kg/h.
The greater the fineness of the feed material (grind-
ing material), the higher the proportion of ultra-fine
material. The higher the proportion of ultra-fine ma-
terial, the lower its fineness. These correlations are
shown in tables 1 and 2.
The degrees of fineness are stated in Blaine.
The authors are aware that the stated values may
contain errors, since the Blaine procedure for high
degrees of fineness no longer produces any exact
values. Thus the given values have a purely indic-
ative value.
For these degrees of fineness it is common to
characterise the material with P50 values that have
been determined by laser granulometry with a
CILAS device.
Of course the user is immediately faced with the
question of how the “remaining blast furnace slag”
proportion can be used.
Tables 1 and 2 show paired values:
• Fineness of the ultra-fine material and
• of the remaining “grit”.
The degrees of fineness of the “grit” vary within the
ranges of commonly used blast furnace slags.
This makes it clear that there is no waste product
and the grit can be used completely normally as a
composite material.
Diagrams 2 and 3 show compressive strengths
of blended cements with typical degrees of blast
furnace slag fineness (4000 Blaine) and of ultra-fine
blast furnace slag (12600 Blaine), attained from the
4000 Blaine material, that has been produced in a
blast furnace slag grinding plant with a Loesche mill.
With technology of this type, the binder industry in
question is made able to produce ultra-fine blast
furnace slag in a cost-efficient way.
If prices are significantly below those of the prod-
ucts currently available on the market, a dynamic
development of the demand in various applications
is to be expected.
The first manufacturing pilot plant is expected to go
into operation in 2018.
Diagram 3: Compressive strengths of blended cements with ultra-fine blast furnace slag, attained from
a grinding product from a blast furnace slag production plant
0
10
20
30
40
50
60
70
80
90
100
36.0
30.5
33.2
Curing time [d]
59.7
43.1
63.6
78.8
53.1
69.2
2 d 7 d 28 d
1.00 CEM
0.30 BFS meal 12600 Blaine
0.50 BFS meal 12600 Blaine
0.70 BFS meal 12600 Blaine
25.0
58.9
73.5
Compressivestrength(N/mm2
)/normprisms
Development of compressive strength
compared to CEM I 42,5 R (1.00) and
mixtures with 30, 50 and 70 Ma.-% BFS
meal (12,600 Blaine)

6. 6
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Figure 2: Integrating a cycloning system into a Loesche blast furnace slag grinding plant

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8. LOESCHE GmbH
Hansaallee 243
D-40549 Duesseldorf, Germany
Tel. +49 - 211 - 5353 - 0
Fax +49 - 211 - 5353 - 500
Email loesche@loesche.de
www.loesche.com