Cement and Concrete Composites 95 (2019) 19–24

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Cement and Concrete Composites

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Reactivity and performance of dry granulation blast furnace slag cement T

∗∗ ∗
Junxiang Liu , Qingbo Yu , Zongliang Zuo, Fan Yang, Zhicheng Han, Qin Qin
School of Metallurgy, Northeastern University, Shenyang, Liaoning, 110819, PR China

A R T I C LE I N FO A B S T R A C T

Keywords: Dry granulation, as a new process for molten blast furnace slag treatment, is an attractive alternative to water
Blast furnace slag quenching. In this study, the performance of dry granulation slag in slag cement blends was investigated. The
Dry granulation results demonstrated that the early strength for dry granulation slag cement mortar was too low, which is less
Slag cement than 50% of the strength for the cement clinker. After 28 days, the compressive strength for dry granulation slag
Milling time
cement mortar containing 35 min-milled slag powder was higher than that for cement clinker. With a decrease in
Glass content
cement/slag ratio, the compressive strength for dry granulation slag cement mortar decreased, and then in-
creased, reaching 96.4% of the compressive strength for dry granulation slag cement mortar made with cement/
slag ratio of 2:1. Although the content of cement clinker decreased, there was enough Ca(OH)2 to activate dry
granulation slag particles to form compact CeSeH structure when the cement/slag ratio was 1.5:1.

1. Introduction fraction [3]. However, Douglas et al. [2] found that the compressive
strength did not increase necessarily with an increase in glass content at
Blast furnace slag, which is composed mainly of CaO, SiO2, Al2O3 a high level of glass content (> 88%). Wang et al. [13] found that the
and MgO, is the by-product of iron making. The molten slag is cooled reactivity of slag with particle size > 20 μm is greatly decreased, and
rapidly by water quenching, and it solidifies into a sand-like product the particles with fineness class < 5 μm played an important role during
containing high content of silica and alumina in an amorphous state hydration. Öner et al. found that the fineness of clinker played an im-
[1]. Because the finely ground water cooled slag has latent hydraulic portant role in compressive strength in early age [14]. In the study of
cementitious properties, it has been widely used as a supplementary Kumar et al. [15,16], the slag was activated using attrition milling for
cement material [2–5]. Due to environmental and energy considera- different lengths of time, ranging from 3 to 60 min. There was a rapid
tions, dry granulation for molten slag has recently received a con- decrease in particle size in first 5 min and it decreased slowly in particle
siderable amount of attention [6–8]. The glass content in slag particles, size after 5 min. In the SEM investigation, there were discrete slag
which are obtained from dry granulation process, is in the range from particles and gel fibers in hydrated slag corresponding to 3-min-milled
70% to 94% [9]. Hence, it is necessary to investigate the reactivity of slag at 28 days. And there were most compact structure, which corre-
dry granulation slag particles in slag cement blends. spond with high compressive strength, in hydrated slag corresponding
The activity of blast furnace slag is determined by chemical com- to 15- and 30-min-milled slag at 28 days.
position, glass content, and particle distribution of slag after milled. In the previous works, blast furnace slag, which was mixed with
Douglas et al. [2] investigated the compressive strength development cement clinker, was water quenching slag. But there were few literature
for two kinds of blast furnace slag, i.e. one from Canada and the other about reactivity and performance of dry granulation blast furnace slag.
from USA. And in their study, the compressive strengths were 36.2 MPa In the present study, the strength development of dry granulation blast
and 47.7 MPa respectively. Lea [10] found that the compressive furnace slag cement with different lengths of milling time and the ratio
strength for basic slag cement was greater than the compressive of clinker/slag was investigated. The structural evolution of slag cement
strength for acidic slag cement. According to European Standard ENV paste system was measured by X-ray diffraction (XRD) and Fourier
197–1:1992 and British Standards, the ratio of the mass of CaO plus Transform Infrared Spectroscopy (FTIR), and the microstructure de-
MgO to the mass of SiO2 must excess 1.0. And if not, the slag would be velopment was measured by Scanning Electronic Microscopy (SEM). All
hydraulically inactive [11,12]. Escalante et al. found that the slag with the information would provide a basis for the analysis of performance
97% glassy fraction was more reactive than the slag with 53.5% glassy of dry granulation slag cement.

∗
Corresponding author. P.O, Box327, Northeastern University, No11, Lane 3, Wenhua Road, Heping District, Shenyang, Liaoning, PR China.
∗∗
Corresponding author. P.O, Box327, Northeastern University, No11, Lane 3, Wenhua Road, Heping District, Shenyang, Liaoning, PR China.
E-mail address: Yuqb@mail.neu.edu.cn (Q. Yu).

https://doi.org/10.1016/j.cemconcomp.2018.10.008
Received 14 July 2016; Received in revised form 10 September 2018; Accepted 11 October 2018
Available online 13 October 2018
0958-9465/ © 2018 Elsevier Ltd. All rights reserved.
J. Liu et al. Cement and Concrete Composites 95 (2019) 19–24

Fig. 1. Dry granulation for molten slag and slag particles.

2. Materials and methods

2.1. Materials

In this method, the granulated blast furnace slag samples are dry
granulation slag. Fig. 1 shows the dry granulation for molten blast
furnace slag and slag particles. In the process for dry granulation, the
molten blast furnace slag was poured into the rotary cup with a high
rotating speed. Under the action of centrifugal force, the liquid slag
releasing from the edge of rotary cup was granulated to small spherical
droplets. The slag droplets are cooled and freeze in the flight [8,9,17].
The minimum diameter of spherical particles was 0.5 mm and the
maximum diameter was 4.3 mm. In the experiment, the initial tem-
perature of molten slag was 1460 °C, and the volume flow rate of
molten slag was controlled at 23.4 cm3 s−1. The diameter of the rotary
cup was 130 mm, with a rotating speed of 1000 rpm. The main chemical
components (mass percent, %) of blast furnace slag and cement clinker
are shown in Table 1. Basicity of slag, defined as Fig. 2. Particle size distribution of cement clinker and dry granulation slag.
[(CaO + MgO + Al2O3)/SiO2], was 1.76, and blast furnace slag con-
tains less lime than cement clinker. firstly cured in a fog room at 20 °C and at 95% relative humidity for
The dry granulation slag were ground using ball milling, and then, 24 h, and then demoulded and placed in water bath at 20 °C until
the slag powder were mixed with clinker. Fig. 2 shows particle size testing ages. The hydration of cement phases was studied by XRD
distributions for cement clinker and dry granulation slag with different technique. XRD analysis was performed on X-ray diffractometer system
milling time, which were determined by using a laser diffraction par- (X’ Pert Pro) using Cu Kα radiation running at 40 kV and 40 mA and a
ticle size analyzer. The particle size distribution for dry granulation slag scan rate of 7° 2θ/min between 10° and 80° 2θ. Fourier Transform
with 20-min-milled was about 36% of the particles finer than 20 μm and Infrared Spectroscopy (Agilent Cary 660 FTIR) was used for structural
about 42% coarser than 40 μm. With an increase in milling time, the characterization of slag cement paste. The sample pellets were prepared
particle size distribution for dry granulation slag with 35-min-milled by compressing 2 mg of sample powder with 190 mg of KBr under
was about 50% of the particles finer than 20 μm and about 22% coarser 30 MPa force for 1 min. The spectra were recorded in the range of
than 40 μm. 500–4000 cm−1 with 2 cm−1 resolution and 32 scans each time.
In this work, two cement paste systems were investigated: 100% Microstructural characterization of the samples was done using SEM
cement clinker, which was used as a reference sample, and blended slag (ZEISS Ultra Plus).
cements containing dry granulation slag with different milling time and For compressive strength determination, the cement mortar was
replacement levels. prepared in 40 × 40 × 160 mm with a cement/water ratio of 2:1 and a
cement/aggregate ratio of 1:3. As before, the cement mortar samples
were cured in a fog room at 20 °C and at 95% relative humidity. After
2.2. Methods
24 h, the samples were demoulded and cured in water at 20 °C for 3, 7
and 28 days respectively.
The cement clinker and blended slag cement were cast in 20 mm
cube moulds with a cement/water ratio of 2:1. These samples were
3. Results and discussion
Table 1
The main chemical components (mass percent, %) of blast furnace slag and
3.1. Effect of milling time
cement clinker.
Samples CaO SiO2 Al2O3 MgO TiO2 TFe S K Fig. 3 shows the compressive strengths development for dry gran-
ulation slag cement mortar and cement clinker mortar after hydration.
Blast furnace slag 41.21 34.38 11.05 8.22 0.35 0.52 1.02 0.38
Cement clinker 62.82 21.40 5.33 3.24 0.25 2.12 – 0.72 It was observed that the compressive strengths for dry granulation slag
cement mortar containing 50% slag, at 1 day, 3 days and 7 days, were

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J. Liu et al. Cement and Concrete Composites 95 (2019) 19–24

ions detach from the silicate network. And then, the CeSeH phase
generate in interstitial solution. They are filled in the pores of slag
particles to enhance the strength of slag cement mortar. With an in-
crease in milling time, the specific surface area of slag particles become
large, and much more network structures of amorphous phase are de-
stroyed by mechanical force. Hence, it is easy for OH− ions to reach the
core of slag particles and more and more Ca2+ ions and SiO42− ions
generate in interstitial solution. This is why the compressive strength
for dry granulation slag cement mortar with 35-min-milled slag always
was higher than that for slag cement mortar with 20-min-milled slag in
all the hydration stage.
Fig. 4 shows XRD patterns and FTIR spectra of slag cement with
different lengths of milling time after 28 days. It indicated the presence
of alite (C3S), belite (C2S), portlandite (CH) and tobermorite (CeSeH)
phase. In the progress of hydration, C3S and C2S were consumed, and
they resulted in the formation of CeSeH and CH phase. In contrast to
dry granulation slag cement containing 20-min-milled slag, there was a
significant decrease in the peak of C3S at 0.268 nm and C2S at 0.268 nm
Fig. 3. Compressive strength of slag cement with different milling time after
and 0.263 nm in the hydration of dry granulation slag cement with 35-
hydration. min-milled slag. According to the reaction of C3S and C2S, there should
be much more CeSeH and CH phase generating. However, there was a
significant decrease in the peak of CH at 0.263 nm. It indicated that
lower than the compressive strength for cement clinker mortar. The
much more OH− ions participating in the corrosion of protective film of
early strengths for dry granulation slag cement mortar were approxi-
dry granulation slag particles. In theory, there should be much more
mately 50% of the strengths for cement clinker mortar at 1 day and 3
CeSeH phases in the pores in dry granulation slag cement paste.
days, which were similar with the results of Bougara et al. [18]. At 7
However, there was weak peaks of CeSeH phases at 0.303 nm,
days and 28 days, the compressive strengths for dry granulation slag
0.288 nm and 0.182 nm. In Fig. 4(b), it was clear that a broad and high
cement mortar were higher than 50% of the strengths for cement
peak near 970 cm−1 was due to the stretching of SieO bonds re-
clinker mortar. It indicated that dry granulation slag began to con-
presenting the CeSeH gel. And there was a high intensity peak in dry
tribute to the compressive strength of slag cement mortar after 3 days.
granulation slag cement with 35-min-milled slag. Combined with XRD
In all the hydration time, the compressive strengths for dry granulation
patterns, it indicated the formation of crystalline and amorphous
slag cement mortar containing 50% 35-min-milled slag always were
CeSeH in the dry granulation slag cement paste system [20–23]. It was
higher than the compressive strengths for slag cement mortar con-
probably that the partial formed CeSeH phase was in amorphous phase
taining 50% 20-min-milled. At 28 days, the compressive strength for
at around d∼0.303 nm.
dry granulation slag cement mortar made with 35-min-milled slag al-
Fig. 5 shows typical SEM micrographs for dry granulation slag ce-
ways was higher than the compressive strength for cement clinker
ment after hydration. After 28 day of hydration, the honeycomb
mortar.
structure of CeSeH phase also can be observed, which will continue to
In the structure of dry granulation slag with high content of amor-
grow up to connect with each other after hydration. The CH phases
phous phase, some calcium ions are coated by silicate network, i.e. SiO4
were detectable in the form of thin-plate hexagonal crystals, which
tetrahedron or the structure of ≡SieOeCaeOeSi≡. The silicate net-
were embedded in the compact materials. The CH phases also can offer
work is regarded as protective film on the surface of slag particles to
OH− ions to activate dry granulation slag particles in the later hydra-
avoid corrosion by water [19]. In the slag cement blend system, Ca
tion stage. There was a certain amount of honeycomb structure of
(OH)2, as one production of cement clinker hydration, can release OH−
CeSeH phase in dry granulation slag cement paste containing 20-min-
into water. As strong polarity ion, OH− ions can accelerate the corro-
milled slag, which resulted in the lower compressive strength than that
sion of protective film and the network structure collapse with it
for dry granulation slag cement paste with 35-min-milled slag. Due to
moving toward the core of slag particles. The Ca2+ ions and SiO42−
mechanical activation, the network structure of small diameter dry

Fig. 4. XRD patterns and FTIR spectra of slag cement with different milling time after 28 days.

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J. Liu et al. Cement and Concrete Composites 95 (2019) 19–24

Fig. 5. Typical SEM micrographs for dry granulation slag cement with different milling time after 28 days.

Fig. 6. Variation in compressive strength of slag cement with different cement/

slag ratio.

granulation slag particles was destroyed by OH− ions completely. The

CeSeH phase generated and grew up, and they were filled between the
frameworks of dry granulation slag particles. Hence, the structure of 35-
min-milled dry granulation slag cement paste was more compact. On
the contrary, there were much more pores in 20-min-milled dry gran-
ulation slag cement paste, which were caused by the unreacted slag
particles.

3.2. Effect of cement/slag ratio Fig. 7. XRD patterns of slag cement with different cement/slag ratio after 28
days.
Fig. 6 shows the compressive strengths development for dry gran-
ulation slag cement mortars with various cement/slag ratios. It was Hence, the compressive strengths for dry granulation slag cement
observed that the compressive strengths for dry granulation slag cement mortar became high.
mortar became low with a decrease in cement/slag ratio after 7 days The compressive strength for dry granulation slag cement mortar
hydration. After 28 days in the experiments, the compressive strengths with cement/slag ratio of 1:1.5 was 96.4% of the compressive strength
for dry granulation slag cement mortar with cement/slag ratio of 2:1 for dry granulation slag cement mortar with cement/slag ratio of 2:1. It
was highest. The compressive strengths for dry granulation slag cement is mean that the dry granulation slag cement containing 60% of dry
mortar became low, and then increased slightly as a decrease in ce- granulation slag and 40% of cement clinker can reach a high com-
ment/slag ratio. With the low content of cement clinker in slag cement, pressive strength and can be used to build industrial construction.
there was much dry granulation slag particles un-activated and they Fig. 7 shows XRD patterns of slag cement with various cement/slag
were embedded between CeSeH and Ca(OH)2 phase. As an increase in ratios after 28 days. The variation in characteristic peaks of CH phases
hydration time, more and more dry granulation slag particles were at 0.491 nm, 0.311 nm, 0.263 nm 0.193 nm and 0.180 nm can be de-
activated by Ca(OH)2. The low Ca/Si ratio CeSeH phase generated and tected. During slag cement hydration, CH phase, generating from the
they are filled in the pores in the slag cement mortar to form compact hydration of cement clinker, was consumed due to reaction with slag
structure [15,24]. Meanwhile, the CeSeH phase enclosed the frame- particles. There was a decrease in characteristic peaks of CH phases at
works of dry granulation slag particles after corrosion by OH− ions.

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J. Liu et al. Cement and Concrete Composites 95 (2019) 19–24

Fig. 8. Typical SEM micrographs for dry granulation slag cement with different cement/slag ratio after 28 days.

0.311 nm and 0.180 nm with a decrease in cement/slag ratio. It was than that for cement clinker mortar after 28 days.
mean that the mount of CH phases decreased in the dry granulation slag 3.When the cement/slag ratio was 1:1.5, the CH phase was also
cement paste. Meanwhile, there was an increase in characteristic peak sufficient to activate dry granulation slag particles, and the compact
of CeSeH and C2S phases at 0.303 nm with a decrease in cement/slag structure materials formed.
ratio. As a matter of fact, C2S was consumed in the hydration of cement
clinker, and the mount of C2S phases decreased. It indicated that many Acknowledgement
dry granulation slag particles were activated by sufficient Ca(OH)2 at
28 days, though the content of cement clinker decreased. And more This research was supposed by The National Key Research and
CeSeH phase generated in dry granulation slag cement mortar. Development Program of China (2017YFB0603603), The Fundamental
Fig. 8 shows typical SEM micrographs for dry granulation slag ce- Research Funds for the Central Universities (N162504008), The
ment with various cement/slag ratios after 28 days hydration. It was National Natural Science Foundation of China (51304048, 51704071),
clear that there was much thin-plate CH phase generated when the The National Postdoctoral Program for Innovative Talents
cement/slag ratio was 2:1. And some pores formed in CH phase and (BX201600028), The China Postdoctoral Science Foundation
CeSeH phase. In dry granulation slag cement with cement/slag ratio of (2017M621148).
1.5:1, the honeycomb structure CeSeH phase also can be observed,
which reduced the compressive strength for dry granulation slag ce- References
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