- Email: [email protected]
Reactivity and performance of dry granulation blast furnace slag cement
Cement and Concrete Composites 95 (2019) 19–24
Contents lists available at ScienceDirect
Cement and Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp
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: Blast furnace slag Dry granulation Slag cement Milling time Glass content
Dry granulation, as a new process for molten blast furnace slag treatment, is an attractive alternative to water quenching. In this study, the performance of dry granulation slag in slag cement blends was investigated. The results demonstrated that the early strength for dry granulation slag cement mortar was too low, which is less than 50% of the strength for the cement clinker. After 28 days, the compressive strength for dry granulation slag cement mortar containing 35 min-milled slag powder was higher than that for cement clinker. With a decrease in cement/slag ratio, the compressive strength for dry granulation slag cement mortar decreased, and then increased, 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 Blast furnace slag, which is composed mainly of CaO, SiO2, Al2O3 and MgO, is the by-product of iron making. The molten slag is cooled rapidly by water quenching, and it solidifies into a sand-like product containing high content of silica and alumina in an amorphous state [1]. Because the finely ground water cooled slag has latent hydraulic cementitious properties, it has been widely used as a supplementary cement material [2–5]. Due to environmental and energy considerations, dry granulation for molten slag has recently received a considerable amount of attention [6–8]. The glass content in slag particles, which are obtained from dry granulation process, is in the range from 70% to 94% [9]. Hence, it is necessary to investigate the reactivity of dry granulation slag particles in slag cement blends. The activity of blast furnace slag is determined by chemical composition, glass content, and particle distribution of slag after milled. Douglas et al. [2] investigated the compressive strength development for two kinds of blast furnace slag, i.e. one from Canada and the other from USA. And in their study, the compressive strengths were 36.2 MPa and 47.7 MPa respectively. Lea [10] found that the compressive strength for basic slag cement was greater than the compressive strength for acidic slag cement. According to European Standard ENV 197–1:1992 and British Standards, the ratio of the mass of CaO plus MgO to the mass of SiO2 must excess 1.0. And if not, the slag would be hydraulically inactive [11,12]. Escalante et al. found that the slag with 97% glassy fraction was more reactive than the slag with 53.5% glassy
∗
fraction [3]. However, Douglas et al. [2] found that the compressive strength did not increase necessarily with an increase in glass content at a high level of glass content (> 88%). Wang et al. [13] found that the reactivity of slag with particle size > 20 μm is greatly decreased, and the particles with fineness class < 5 μm played an important role during hydration. Öner et al. found that the fineness of clinker played an important role in compressive strength in early age [14]. In the study of Kumar et al. [15,16], the slag was activated using attrition milling for different lengths of time, ranging from 3 to 60 min. There was a rapid decrease in particle size in first 5 min and it decreased slowly in particle size after 5 min. In the SEM investigation, there were discrete slag particles and gel fibers in hydrated slag corresponding to 3-min-milled slag at 28 days. And there were most compact structure, which correspond with high compressive strength, in hydrated slag corresponding to 15- and 30-min-milled slag at 28 days. In the previous works, blast furnace slag, which was mixed with cement clinker, was water quenching slag. But there were few literature about reactivity and performance of dry granulation blast furnace slag. In the present study, the strength development of dry granulation blast furnace slag cement with different lengths of milling time and the ratio of clinker/slag was investigated. The structural evolution of slag cement paste system was measured by X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR), and the microstructure development was measured by Scanning Electronic Microscopy (SEM). All the information would provide a basis for the analysis of performance 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: [email protected] (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.
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
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 temperature 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 [(CaO + MgO + Al2O3)/SiO2], was 1.76, and blast furnace slag contains less lime than cement clinker. The dry granulation slag were ground using ball milling, and then, the slag powder were mixed with clinker. Fig. 2 shows particle size distributions for cement clinker and dry granulation slag with different milling time, which were determined by using a laser diffraction particle size analyzer. The particle size distribution for dry granulation slag with 20-min-milled was about 36% of the particles finer than 20 μm and about 42% coarser than 40 μm. With an increase in milling time, the particle size distribution for dry granulation slag with 35-min-milled was about 50% of the particles finer than 20 μm and about 22% coarser than 40 μm. In this work, two cement paste systems were investigated: 100% cement clinker, which was used as a reference sample, and blended slag cements containing dry granulation slag with different milling time and replacement levels.
Fig. 2. Particle size distribution of cement clinker and dry granulation slag.
firstly cured in a fog room at 20 °C and at 95% relative humidity for 24 h, and then demoulded and placed in water bath at 20 °C until testing ages. The hydration of cement phases was studied by XRD technique. XRD analysis was performed on X-ray diffractometer system (X’ Pert Pro) using Cu Kα radiation running at 40 kV and 40 mA and a scan rate of 7° 2θ/min between 10° and 80° 2θ. Fourier Transform Infrared Spectroscopy (Agilent Cary 660 FTIR) was used for structural characterization of slag cement paste. The sample pellets were prepared by compressing 2 mg of sample powder with 190 mg of KBr under 30 MPa force for 1 min. The spectra were recorded in the range of 500–4000 cm−1 with 2 cm−1 resolution and 32 scans each time. Microstructural characterization of the samples was done using SEM (ZEISS Ultra Plus). For compressive strength determination, the cement mortar was 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 24 h, the samples were demoulded and cured in water at 20 °C for 3, 7 and 28 days respectively.
2.2. Methods 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 cement clinker. Samples
CaO
SiO2
Al2O3
MgO
TiO2
TFe
S
K
Blast furnace slag Cement clinker
41.21 62.82
34.38 21.40
11.05 5.33
8.22 3.24
0.35 0.25
0.52 2.12
1.02 –
0.38 0.72
3.1. Effect of milling time Fig. 3 shows the compressive strengths development for dry granulation slag cement mortar and cement clinker mortar after hydration. 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 20
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
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 increase in milling time, the specific surface area of slag particles become large, and much more network structures of amorphous phase are destroyed 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 and 0.263 nm in the hydration of dry granulation slag cement with 35min-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 much more OH− ions participating in the corrosion of protective film of dry granulation slag particles. In theory, there should be much more CeSeH phases in the pores in dry granulation slag cement paste. However, there was weak peaks of CeSeH phases at 0.303 nm, 0.288 nm and 0.182 nm. In Fig. 4(b), it was clear that a broad and high peak near 970 cm−1 was due to the stretching of SieO bonds representing the CeSeH gel. And there was a high intensity peak in dry granulation slag cement with 35-min-milled slag. Combined with XRD patterns, it indicated the formation of crystalline and amorphous CeSeH in the dry granulation slag cement paste system [20–23]. It was probably that the partial formed CeSeH phase was in amorphous phase at around d∼0.303 nm. Fig. 5 shows typical SEM micrographs for dry granulation slag cement after hydration. After 28 day of hydration, the honeycomb structure of CeSeH phase also can be observed, which will continue to grow up to connect with each other after hydration. The CH phases were detectable in the form of thin-plate hexagonal crystals, which were embedded in the compact materials. The CH phases also can offer OH− ions to activate dry granulation slag particles in the later hydration stage. There was a certain amount of honeycomb structure of CeSeH phase in dry granulation slag cement paste containing 20-minmilled slag, which resulted in the lower compressive strength than that for dry granulation slag cement paste with 35-min-milled slag. Due to mechanical activation, the network structure of small diameter dry
Fig. 3. Compressive strength of slag cement with different milling time after hydration.
lower than the compressive strength for cement clinker mortar. The early strengths for dry granulation slag cement mortar were approximately 50% of the strengths for cement clinker mortar at 1 day and 3 days, which were similar with the results of Bougara et al. [18]. At 7 days and 28 days, the compressive strengths for dry granulation slag cement mortar were higher than 50% of the strengths for cement clinker mortar. It indicated that dry granulation slag began to contribute to the compressive strength of slag cement mortar after 3 days. In all the hydration time, the compressive strengths for dry granulation slag cement mortar containing 50% 35-min-milled slag always were higher than the compressive strengths for slag cement mortar containing 50% 20-min-milled. At 28 days, the compressive strength for dry granulation slag cement mortar made with 35-min-milled slag always was higher than the compressive strength for cement clinker mortar. In the structure of dry granulation slag with high content of amorphous phase, some calcium ions are coated by silicate network, i.e. SiO4 tetrahedron or the structure of ≡SieOeCaeOeSi≡. The silicate network is regarded as protective film on the surface of slag particles to avoid corrosion by water [19]. In the slag cement blend system, Ca (OH)2, as one production of cement clinker hydration, can release OH− into water. As strong polarity ion, OH− ions can accelerate the corrosion of protective film and the network structure collapse with it moving toward the core of slag particles. The Ca2+ ions and SiO42−
Fig. 4. XRD patterns and FTIR spectra of slag cement with different milling time after 28 days. 21
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
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 35min-milled dry granulation slag cement paste was more compact. On the contrary, there were much more pores in 20-min-milled dry granulation 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 granulation slag cement mortars with various cement/slag ratios. It was observed that the compressive strengths for dry granulation slag cement mortar became low with a decrease in cement/slag ratio after 7 days hydration. After 28 days in the experiments, the compressive strengths for dry granulation slag cement mortar with cement/slag ratio of 2:1 was highest. The compressive strengths for dry granulation slag cement mortar became low, and then increased slightly as a decrease in cement/slag ratio. With the low content of cement clinker in slag cement, there was much dry granulation slag particles un-activated and they were embedded between CeSeH and Ca(OH)2 phase. As an increase in hydration time, more and more dry granulation slag particles were activated by Ca(OH)2. The low Ca/Si ratio CeSeH phase generated and they are filled in the pores in the slag cement mortar to form compact structure [15,24]. Meanwhile, the CeSeH phase enclosed the frameworks of dry granulation slag particles after corrosion by OH− ions.
Hence, the compressive strengths for dry granulation slag cement mortar became high. The compressive strength for dry granulation slag cement mortar 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. It is mean that the dry granulation slag cement containing 60% of dry granulation slag and 40% of cement clinker can reach a high compressive strength and can be used to build industrial construction. Fig. 7 shows XRD patterns of slag cement with various cement/slag ratios after 28 days. The variation in characteristic peaks of CH phases at 0.491 nm, 0.311 nm, 0.263 nm 0.193 nm and 0.180 nm can be detected. During slag cement hydration, CH phase, generating from the hydration of cement clinker, was consumed due to reaction with slag particles. There was a decrease in characteristic peaks of CH phases at
22
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
Fig. 8. Typical SEM micrographs for dry granulation slag cement with different cement/slag ratio after 28 days.
than that for cement clinker mortar after 28 days. 3.When the cement/slag ratio was 1:1.5, the CH phase was also sufficient to activate dry granulation slag particles, and the compact structure materials formed.
0.311 nm and 0.180 nm with a decrease in cement/slag ratio. It was mean that the mount of CH phases decreased in the dry granulation slag cement paste. Meanwhile, there was an increase in characteristic peak of CeSeH and C2S phases at 0.303 nm with a decrease in cement/slag 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 dry granulation slag particles were activated by sufficient Ca(OH)2 at 28 days, though the content of cement clinker decreased. And more CeSeH phase generated in dry granulation slag cement mortar. Fig. 8 shows typical SEM micrographs for dry granulation slag cement with various cement/slag ratios after 28 days hydration. It was clear that there was much thin-plate CH phase generated when the cement/slag ratio was 2:1. And some pores formed in CH phase and CeSeH phase. In dry granulation slag cement with cement/slag ratio of 1.5:1, the honeycomb structure CeSeH phase also can be observed, which reduced the compressive strength for dry granulation slag cement. When cement/slag ratio was 1:1, the CeSeH phase generated in the space between the adjacent CH phase. Hence, the structure of CH phase became compact. With an increase in the content of dry granulation slag, reaching 60%, the compact CeSeH phase formed. The CH phase, generated from cement clinker, was enough to activate dry granulation slag particles in dry granulation slag cement with 40% content of cement clinker.
Acknowledgement This research was supposed by The National Key Research and Development Program of China (2017YFB0603603), The Fundamental Research Funds for the Central Universities (N162504008), The National Natural Science Foundation of China (51304048, 51704071), The National Postdoctoral Program for Innovative Talents (BX201600028), The China Postdoctoral Science Foundation (2017M621148). References [1] D.M. Sadek, Effect of cooling technique of blast furnace slag on the thermal behavior of solid cement bricks, J. Clean. Prod. 79 (2014) 134–141. [2] E. Douglas, A. Elola, V. Mohan Malhotra, Characterization of ground granulated blast-furnace slags and fly ashes and their hydration in Portland cement blends, Cem. Concr. Aggregates 12 (1990) 38–46. [3] J.I. Escalante, L.Y. Gomez, K.K. Johal, Reactivity of blast-furnace slag in Portland cement blends hydrated under different conditions, Cement Concr. Res. 31 (2001) 1403–1409. [4] H. Savastano Jr., P.G. Warden, R.S.P. Coutts, Ground iron blast furnace slag as a matrix for cellulose-cement materials, Cement Concr. Compos. 23 (2001) 389–397. [5] N.R. Rakhimova, R.Z. Rakhimov, Characterisation of ground hydrated Portland cement-based mortar as an additive to alkali-activated slag cement, Cement Concr. Compos. 57 (2015) 55–63. [6] M. Barati, S. Esfahani, T.A. Utigard, Energy recovery from high temperature slags, Energy 36 (2011) 5440–5449. [7] Y.Q. Sun, Z.T. Zhang, L.L. Liu, X.D. Wang, Heat recovery from high temperature slags: a review of chemical methods, Energies 8 (2015) 1917–1935. [8] J.X. Liu, Q.B. Yu, Z.L. Zuo, W.J. Duan, Z.C. Han, Q. Qin, F. Yang, Experimental investigation on molten slag granulation for waste heat recovery from various
4. Conclusions 1.The dry granulation slag particles can be used as a supplementary cement material, and the maximum replacement reach 60%. 2. Due to mechanical activation, the specific area of dry granulation slag particles became large, which was beneficial to destroy the glass network structure. Hence, the compressive strength for dry granulation slag cement mortar with 35-min-milled slag was higher 23
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
[17] J.X. Liu, Q.B. Yu, W.J. Duan, Q. Qin, Experimental investigation on ligament formation for molten slag granulation, Appl. Therm. Eng. 73 (2014) 888–893. [18] A. Bougara, C. Lynsdale, N.B. Milestone, Reactivity and performance of blastfurnace slags of differing origin, Cement Concr. Compos. 32 (2010) 319–324. [19] Y. Luan, T. Ishida, T. Nawa, T. Sagawa, Enhanced model and simulation of hydration process of blast furnace slag in blended cement, J. Adv. Concr. Technol. 10 (2012) 1–13. [20] S. Nasrazadani, T. Springfield, Application of Fourier transform infrared spectroscopy in cement Alkali quantification, Mater. Struct. 47 (2014) 1607–1615. [21] R. Ylmén, U. Jäglid, Britt-Marie Steenari, I. Panas, Early hydration and setting of Portland cement monitored by IR, SEM and vicat techniques, Cement Concr. Res. 39 (2009) 433–439. [22] R. Ylmén, U. Jäglid, Carbonation of Portland cement studied by diffuse reflection Fourier transform infrared spectroscopy, Int. J. Concrete Struct. Mater. 7 (2013) 119–125. [23] H.K. Choudhary, A.V. Anupama, R. Kumar, M.E. Panzi, S. Matteppanavar, N.S. Baburao, B. Sahoo, Observation of phase transformations in cement during hydration, Coustr. Building Mater. 101 (2015) 122–129. [24] R. Taylor, I.G. Richardson, R.M.D. Brydson, Composition and microstructure of 20year-old ordinary Portland cement-ground granulated blast-furnace slag blends containing 0 to 100% slag, Cement Concr. Res. 40 (2010) 971–983.
metallurgical slags, Appl. Therm. Eng. 103 (2016) 1112–1118. [9] J.X. Liu, Q.B. Yu, W.J. Duan, Q. Qin, Experimental investigation of glass content of blast furnace slag by dry granulation, Environ. Prog. Sustain. Energy 34 (2015) 485–491. [10] F.M. Lea, The Chemistry of Cement and Concrete, third ed., Edward Arnold, London, 1970, pp. 727–730. [11] A.M. Neville, Properties of Concrete, fourth ed., ELBS Publication, Addison-Wesley Longman Limited, Essex, UK, 1996, p. 80. [12] S.C. Pal, A. Mukherjee, S.R. Pathak, Investigation of hydraulic activity of ground granulated blast furnace slag in concrete, Cement Concr. Res. 33 (2003) 1481–1486. [13] P.Z. Wang, R. Trettin, V. Rudert, Effect of fineness and particle size distribution of granulated blast-furnace slag on the hydraulic reactivity in cement systems, Adv. Cement Res. 17 (2005) 161–166. [14] M. Öner, K. Erdoğdu, A. Günlü, Effect of components fineness on strength of blast furnace slag cement, Cement Concr. Res. 33 (2003) 463–469. [15] S. Kumar, R. Kumar, A. Bandopadhyay, T.C. Alex, B.R. Kumar, S.K. Das, S.P. Mehrotra, Mechanical activation of granulated blast furnace slag and its effect on the properties and structure of portland slag cement, Cement Concr. Compos. 30 (2008) 679–685. [16] R. Kumar, S. Kumar, S. Badjena, S.P. Mehrotra, Hydration of mechanically activated granulated blast furnace slag, Metall. Mater. Trans. B 36B (2005) 873–883.
24
Contents lists available at ScienceDirect
Cement and Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp
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: Blast furnace slag Dry granulation Slag cement Milling time Glass content
Dry granulation, as a new process for molten blast furnace slag treatment, is an attractive alternative to water quenching. In this study, the performance of dry granulation slag in slag cement blends was investigated. The results demonstrated that the early strength for dry granulation slag cement mortar was too low, which is less than 50% of the strength for the cement clinker. After 28 days, the compressive strength for dry granulation slag cement mortar containing 35 min-milled slag powder was higher than that for cement clinker. With a decrease in cement/slag ratio, the compressive strength for dry granulation slag cement mortar decreased, and then increased, 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 Blast furnace slag, which is composed mainly of CaO, SiO2, Al2O3 and MgO, is the by-product of iron making. The molten slag is cooled rapidly by water quenching, and it solidifies into a sand-like product containing high content of silica and alumina in an amorphous state [1]. Because the finely ground water cooled slag has latent hydraulic cementitious properties, it has been widely used as a supplementary cement material [2–5]. Due to environmental and energy considerations, dry granulation for molten slag has recently received a considerable amount of attention [6–8]. The glass content in slag particles, which are obtained from dry granulation process, is in the range from 70% to 94% [9]. Hence, it is necessary to investigate the reactivity of dry granulation slag particles in slag cement blends. The activity of blast furnace slag is determined by chemical composition, glass content, and particle distribution of slag after milled. Douglas et al. [2] investigated the compressive strength development for two kinds of blast furnace slag, i.e. one from Canada and the other from USA. And in their study, the compressive strengths were 36.2 MPa and 47.7 MPa respectively. Lea [10] found that the compressive strength for basic slag cement was greater than the compressive strength for acidic slag cement. According to European Standard ENV 197–1:1992 and British Standards, the ratio of the mass of CaO plus MgO to the mass of SiO2 must excess 1.0. And if not, the slag would be hydraulically inactive [11,12]. Escalante et al. found that the slag with 97% glassy fraction was more reactive than the slag with 53.5% glassy
∗
fraction [3]. However, Douglas et al. [2] found that the compressive strength did not increase necessarily with an increase in glass content at a high level of glass content (> 88%). Wang et al. [13] found that the reactivity of slag with particle size > 20 μm is greatly decreased, and the particles with fineness class < 5 μm played an important role during hydration. Öner et al. found that the fineness of clinker played an important role in compressive strength in early age [14]. In the study of Kumar et al. [15,16], the slag was activated using attrition milling for different lengths of time, ranging from 3 to 60 min. There was a rapid decrease in particle size in first 5 min and it decreased slowly in particle size after 5 min. In the SEM investigation, there were discrete slag particles and gel fibers in hydrated slag corresponding to 3-min-milled slag at 28 days. And there were most compact structure, which correspond with high compressive strength, in hydrated slag corresponding to 15- and 30-min-milled slag at 28 days. In the previous works, blast furnace slag, which was mixed with cement clinker, was water quenching slag. But there were few literature about reactivity and performance of dry granulation blast furnace slag. In the present study, the strength development of dry granulation blast furnace slag cement with different lengths of milling time and the ratio of clinker/slag was investigated. The structural evolution of slag cement paste system was measured by X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR), and the microstructure development was measured by Scanning Electronic Microscopy (SEM). All the information would provide a basis for the analysis of performance 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: [email protected] (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.
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
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 temperature 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 [(CaO + MgO + Al2O3)/SiO2], was 1.76, and blast furnace slag contains less lime than cement clinker. The dry granulation slag were ground using ball milling, and then, the slag powder were mixed with clinker. Fig. 2 shows particle size distributions for cement clinker and dry granulation slag with different milling time, which were determined by using a laser diffraction particle size analyzer. The particle size distribution for dry granulation slag with 20-min-milled was about 36% of the particles finer than 20 μm and about 42% coarser than 40 μm. With an increase in milling time, the particle size distribution for dry granulation slag with 35-min-milled was about 50% of the particles finer than 20 μm and about 22% coarser than 40 μm. In this work, two cement paste systems were investigated: 100% cement clinker, which was used as a reference sample, and blended slag cements containing dry granulation slag with different milling time and replacement levels.
Fig. 2. Particle size distribution of cement clinker and dry granulation slag.
firstly cured in a fog room at 20 °C and at 95% relative humidity for 24 h, and then demoulded and placed in water bath at 20 °C until testing ages. The hydration of cement phases was studied by XRD technique. XRD analysis was performed on X-ray diffractometer system (X’ Pert Pro) using Cu Kα radiation running at 40 kV and 40 mA and a scan rate of 7° 2θ/min between 10° and 80° 2θ. Fourier Transform Infrared Spectroscopy (Agilent Cary 660 FTIR) was used for structural characterization of slag cement paste. The sample pellets were prepared by compressing 2 mg of sample powder with 190 mg of KBr under 30 MPa force for 1 min. The spectra were recorded in the range of 500–4000 cm−1 with 2 cm−1 resolution and 32 scans each time. Microstructural characterization of the samples was done using SEM (ZEISS Ultra Plus). For compressive strength determination, the cement mortar was 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 24 h, the samples were demoulded and cured in water at 20 °C for 3, 7 and 28 days respectively.
2.2. Methods 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 cement clinker. Samples
CaO
SiO2
Al2O3
MgO
TiO2
TFe
S
K
Blast furnace slag Cement clinker
41.21 62.82
34.38 21.40
11.05 5.33
8.22 3.24
0.35 0.25
0.52 2.12
1.02 –
0.38 0.72
3.1. Effect of milling time Fig. 3 shows the compressive strengths development for dry granulation slag cement mortar and cement clinker mortar after hydration. 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 20
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
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 increase in milling time, the specific surface area of slag particles become large, and much more network structures of amorphous phase are destroyed 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 and 0.263 nm in the hydration of dry granulation slag cement with 35min-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 much more OH− ions participating in the corrosion of protective film of dry granulation slag particles. In theory, there should be much more CeSeH phases in the pores in dry granulation slag cement paste. However, there was weak peaks of CeSeH phases at 0.303 nm, 0.288 nm and 0.182 nm. In Fig. 4(b), it was clear that a broad and high peak near 970 cm−1 was due to the stretching of SieO bonds representing the CeSeH gel. And there was a high intensity peak in dry granulation slag cement with 35-min-milled slag. Combined with XRD patterns, it indicated the formation of crystalline and amorphous CeSeH in the dry granulation slag cement paste system [20–23]. It was probably that the partial formed CeSeH phase was in amorphous phase at around d∼0.303 nm. Fig. 5 shows typical SEM micrographs for dry granulation slag cement after hydration. After 28 day of hydration, the honeycomb structure of CeSeH phase also can be observed, which will continue to grow up to connect with each other after hydration. The CH phases were detectable in the form of thin-plate hexagonal crystals, which were embedded in the compact materials. The CH phases also can offer OH− ions to activate dry granulation slag particles in the later hydration stage. There was a certain amount of honeycomb structure of CeSeH phase in dry granulation slag cement paste containing 20-minmilled slag, which resulted in the lower compressive strength than that for dry granulation slag cement paste with 35-min-milled slag. Due to mechanical activation, the network structure of small diameter dry
Fig. 3. Compressive strength of slag cement with different milling time after hydration.
lower than the compressive strength for cement clinker mortar. The early strengths for dry granulation slag cement mortar were approximately 50% of the strengths for cement clinker mortar at 1 day and 3 days, which were similar with the results of Bougara et al. [18]. At 7 days and 28 days, the compressive strengths for dry granulation slag cement mortar were higher than 50% of the strengths for cement clinker mortar. It indicated that dry granulation slag began to contribute to the compressive strength of slag cement mortar after 3 days. In all the hydration time, the compressive strengths for dry granulation slag cement mortar containing 50% 35-min-milled slag always were higher than the compressive strengths for slag cement mortar containing 50% 20-min-milled. At 28 days, the compressive strength for dry granulation slag cement mortar made with 35-min-milled slag always was higher than the compressive strength for cement clinker mortar. In the structure of dry granulation slag with high content of amorphous phase, some calcium ions are coated by silicate network, i.e. SiO4 tetrahedron or the structure of ≡SieOeCaeOeSi≡. The silicate network is regarded as protective film on the surface of slag particles to avoid corrosion by water [19]. In the slag cement blend system, Ca (OH)2, as one production of cement clinker hydration, can release OH− into water. As strong polarity ion, OH− ions can accelerate the corrosion of protective film and the network structure collapse with it moving toward the core of slag particles. The Ca2+ ions and SiO42−
Fig. 4. XRD patterns and FTIR spectra of slag cement with different milling time after 28 days. 21
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
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 35min-milled dry granulation slag cement paste was more compact. On the contrary, there were much more pores in 20-min-milled dry granulation 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 granulation slag cement mortars with various cement/slag ratios. It was observed that the compressive strengths for dry granulation slag cement mortar became low with a decrease in cement/slag ratio after 7 days hydration. After 28 days in the experiments, the compressive strengths for dry granulation slag cement mortar with cement/slag ratio of 2:1 was highest. The compressive strengths for dry granulation slag cement mortar became low, and then increased slightly as a decrease in cement/slag ratio. With the low content of cement clinker in slag cement, there was much dry granulation slag particles un-activated and they were embedded between CeSeH and Ca(OH)2 phase. As an increase in hydration time, more and more dry granulation slag particles were activated by Ca(OH)2. The low Ca/Si ratio CeSeH phase generated and they are filled in the pores in the slag cement mortar to form compact structure [15,24]. Meanwhile, the CeSeH phase enclosed the frameworks of dry granulation slag particles after corrosion by OH− ions.
Hence, the compressive strengths for dry granulation slag cement mortar became high. The compressive strength for dry granulation slag cement mortar 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. It is mean that the dry granulation slag cement containing 60% of dry granulation slag and 40% of cement clinker can reach a high compressive strength and can be used to build industrial construction. Fig. 7 shows XRD patterns of slag cement with various cement/slag ratios after 28 days. The variation in characteristic peaks of CH phases at 0.491 nm, 0.311 nm, 0.263 nm 0.193 nm and 0.180 nm can be detected. During slag cement hydration, CH phase, generating from the hydration of cement clinker, was consumed due to reaction with slag particles. There was a decrease in characteristic peaks of CH phases at
22
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
Fig. 8. Typical SEM micrographs for dry granulation slag cement with different cement/slag ratio after 28 days.
than that for cement clinker mortar after 28 days. 3.When the cement/slag ratio was 1:1.5, the CH phase was also sufficient to activate dry granulation slag particles, and the compact structure materials formed.
0.311 nm and 0.180 nm with a decrease in cement/slag ratio. It was mean that the mount of CH phases decreased in the dry granulation slag cement paste. Meanwhile, there was an increase in characteristic peak of CeSeH and C2S phases at 0.303 nm with a decrease in cement/slag 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 dry granulation slag particles were activated by sufficient Ca(OH)2 at 28 days, though the content of cement clinker decreased. And more CeSeH phase generated in dry granulation slag cement mortar. Fig. 8 shows typical SEM micrographs for dry granulation slag cement with various cement/slag ratios after 28 days hydration. It was clear that there was much thin-plate CH phase generated when the cement/slag ratio was 2:1. And some pores formed in CH phase and CeSeH phase. In dry granulation slag cement with cement/slag ratio of 1.5:1, the honeycomb structure CeSeH phase also can be observed, which reduced the compressive strength for dry granulation slag cement. When cement/slag ratio was 1:1, the CeSeH phase generated in the space between the adjacent CH phase. Hence, the structure of CH phase became compact. With an increase in the content of dry granulation slag, reaching 60%, the compact CeSeH phase formed. The CH phase, generated from cement clinker, was enough to activate dry granulation slag particles in dry granulation slag cement with 40% content of cement clinker.
Acknowledgement This research was supposed by The National Key Research and Development Program of China (2017YFB0603603), The Fundamental Research Funds for the Central Universities (N162504008), The National Natural Science Foundation of China (51304048, 51704071), The National Postdoctoral Program for Innovative Talents (BX201600028), The China Postdoctoral Science Foundation (2017M621148). References [1] D.M. Sadek, Effect of cooling technique of blast furnace slag on the thermal behavior of solid cement bricks, J. Clean. Prod. 79 (2014) 134–141. [2] E. Douglas, A. Elola, V. Mohan Malhotra, Characterization of ground granulated blast-furnace slags and fly ashes and their hydration in Portland cement blends, Cem. Concr. Aggregates 12 (1990) 38–46. [3] J.I. Escalante, L.Y. Gomez, K.K. Johal, Reactivity of blast-furnace slag in Portland cement blends hydrated under different conditions, Cement Concr. Res. 31 (2001) 1403–1409. [4] H. Savastano Jr., P.G. Warden, R.S.P. Coutts, Ground iron blast furnace slag as a matrix for cellulose-cement materials, Cement Concr. Compos. 23 (2001) 389–397. [5] N.R. Rakhimova, R.Z. Rakhimov, Characterisation of ground hydrated Portland cement-based mortar as an additive to alkali-activated slag cement, Cement Concr. Compos. 57 (2015) 55–63. [6] M. Barati, S. Esfahani, T.A. Utigard, Energy recovery from high temperature slags, Energy 36 (2011) 5440–5449. [7] Y.Q. Sun, Z.T. Zhang, L.L. Liu, X.D. Wang, Heat recovery from high temperature slags: a review of chemical methods, Energies 8 (2015) 1917–1935. [8] J.X. Liu, Q.B. Yu, Z.L. Zuo, W.J. Duan, Z.C. Han, Q. Qin, F. Yang, Experimental investigation on molten slag granulation for waste heat recovery from various
4. Conclusions 1.The dry granulation slag particles can be used as a supplementary cement material, and the maximum replacement reach 60%. 2. Due to mechanical activation, the specific area of dry granulation slag particles became large, which was beneficial to destroy the glass network structure. Hence, the compressive strength for dry granulation slag cement mortar with 35-min-milled slag was higher 23
Cement and Concrete Composites 95 (2019) 19–24
J. Liu et al.
[17] J.X. Liu, Q.B. Yu, W.J. Duan, Q. Qin, Experimental investigation on ligament formation for molten slag granulation, Appl. Therm. Eng. 73 (2014) 888–893. [18] A. Bougara, C. Lynsdale, N.B. Milestone, Reactivity and performance of blastfurnace slags of differing origin, Cement Concr. Compos. 32 (2010) 319–324. [19] Y. Luan, T. Ishida, T. Nawa, T. Sagawa, Enhanced model and simulation of hydration process of blast furnace slag in blended cement, J. Adv. Concr. Technol. 10 (2012) 1–13. [20] S. Nasrazadani, T. Springfield, Application of Fourier transform infrared spectroscopy in cement Alkali quantification, Mater. Struct. 47 (2014) 1607–1615. [21] R. Ylmén, U. Jäglid, Britt-Marie Steenari, I. Panas, Early hydration and setting of Portland cement monitored by IR, SEM and vicat techniques, Cement Concr. Res. 39 (2009) 433–439. [22] R. Ylmén, U. Jäglid, Carbonation of Portland cement studied by diffuse reflection Fourier transform infrared spectroscopy, Int. J. Concrete Struct. Mater. 7 (2013) 119–125. [23] H.K. Choudhary, A.V. Anupama, R. Kumar, M.E. Panzi, S. Matteppanavar, N.S. Baburao, B. Sahoo, Observation of phase transformations in cement during hydration, Coustr. Building Mater. 101 (2015) 122–129. [24] R. Taylor, I.G. Richardson, R.M.D. Brydson, Composition and microstructure of 20year-old ordinary Portland cement-ground granulated blast-furnace slag blends containing 0 to 100% slag, Cement Concr. Res. 40 (2010) 971–983.
metallurgical slags, Appl. Therm. Eng. 103 (2016) 1112–1118. [9] J.X. Liu, Q.B. Yu, W.J. Duan, Q. Qin, Experimental investigation of glass content of blast furnace slag by dry granulation, Environ. Prog. Sustain. Energy 34 (2015) 485–491. [10] F.M. Lea, The Chemistry of Cement and Concrete, third ed., Edward Arnold, London, 1970, pp. 727–730. [11] A.M. Neville, Properties of Concrete, fourth ed., ELBS Publication, Addison-Wesley Longman Limited, Essex, UK, 1996, p. 80. [12] S.C. Pal, A. Mukherjee, S.R. Pathak, Investigation of hydraulic activity of ground granulated blast furnace slag in concrete, Cement Concr. Res. 33 (2003) 1481–1486. [13] P.Z. Wang, R. Trettin, V. Rudert, Effect of fineness and particle size distribution of granulated blast-furnace slag on the hydraulic reactivity in cement systems, Adv. Cement Res. 17 (2005) 161–166. [14] M. Öner, K. Erdoğdu, A. Günlü, Effect of components fineness on strength of blast furnace slag cement, Cement Concr. Res. 33 (2003) 463–469. [15] S. Kumar, R. Kumar, A. Bandopadhyay, T.C. Alex, B.R. Kumar, S.K. Das, S.P. Mehrotra, Mechanical activation of granulated blast furnace slag and its effect on the properties and structure of portland slag cement, Cement Concr. Compos. 30 (2008) 679–685. [16] R. Kumar, S. Kumar, S. Badjena, S.P. Mehrotra, Hydration of mechanically activated granulated blast furnace slag, Metall. Mater. Trans. B 36B (2005) 873–883.
24