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Preparation of electrolytic manganese residue–ground granulated blastfurnace slag cement
Powder Technology 241 (2013) 12–18
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Preparation of electrolytic manganese residue–ground granulated blastfurnace slag cement Jia Wang, Bing Peng ⁎, Liyuan Chai, Qiang Zhang, Qin Liu School of Metallurgical Science and Engineering, Central South University, Changsha 410083, PR China
a r t i c l e
i n f o
Article history: Received 10 December 2012 Received in revised form 29 January 2013 Accepted 1 March 2013 Available online 13 March 2013 Keywords: Electrolytic manganese residue Cementitious materials Granulated blast furnace slag Chemical activation Mechanical activation
a b s t r a c t Electrolytic manganese residue (EMR) is added into ground granulated blastfurnace slag (GGBS) as an activator to prepare EMR–GGBS cement. The effects of chemical activation, mechanical activation, water-to-cement ratio and the curing process on the strength and setting properties of EMR–GGBS cement are investigated based on its slag activity index, setting time and compressive and flexural strength. The results show that EMR is an effective and efficient activator for GGBS. This composite activator excels in its purpose when mixed in an EMR/Ca(OH)2/ clinker at a weight ratio of 30:3:5. The cement strength exceeds that of Portland slag cement (P·S) 32.5 class, even reaching that of P·S 42.5 and 52.5 classes after adding 20–35% activator and over 5% clinker. It is necessary to ball-mill granulated blast furnace slag (GBFS) for 12 min or longer to achieve a high surface area, over 1.9688 m2/g, and clinker for 24–30 min to achieve a surface area of over 2.2699 m2/g, as well as to maintain the water-to-cement ratio between 0.45 and 0.64. The initial and final setting times of the cement are 180 min and 330 min, respectively, which is consistent with the desired times for applications of such cement. The cementitious material exhibits better performance after being cured at 30 °C for 24 h. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Portland cement is a building material that is widely used around the world. A significant amount of clay and limestone is consumed, and at least 1 ton of CO2, 0.74 kg of SO2, 120 kg of dust and other pollutants are discharged into the atmosphere to produce 1 ton of cement clinker [1]. Therefore, it is necessary to develop some new cementitious materials to replace the clinker [2,3]. Electrolytic manganese residue (EMR) is a solid waste found in filters after sulphuric acid leaching of manganese carbonate ore, MnO2 oxidative deferrisation and lime neutralisation. Approximately 6– 7 tons of residue is discharged into the environment per ton of electrolytic manganese product [4]. The accumulated amount of EMR during the past years is huge; EMR is a rarely recycled resource [5]. Use in the preparation of building materials for wall, subgrade and concrete [6–10] is one method of EMR reutilisation. EMR has the properties of both gypsum and hydraulic industrial solid wastes due to its main chemical components, CaSO4·2H2O, SiO2 and small amounts of Al2O3, Fe2O3, MnO2, etc. [11,12]. Its high moisture content, 20% to 30% water, and low activity of calcium sulphate, present in EMR as CaSO4·2H2O, makes it difficult to use in cementitious material production. Its other components, such as SiO2 and Al2O3, have low hydration rates. Therefore, EMR cannot be used as a chemical activator in cementitious
⁎ Corresponding author at: Central South University, PR China. Tel.: +86 731 88830577; fax: +86 731 88710171. E-mail address: [email protected] (B. Peng). 0032-5910/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.powtec.2013.03.003
materials until it is modified to promote the activity of its components and mixed with other appropriate auxiliary-activators [13]. Cement-making with EMR has mainly focused on Portland fly-ash cement and sulpho-aluminate cement. Li et al. [7] added 25% admixture, prepared by mixing 15% EMR treated at 300–850 °C with 85% fly-ash, into 75% 42.5 ordinary Portland cement (OPC) to make blended hydraulic cement. Hou et al. [8] prepared quasi-sulphoaluminate cementitious material by calcining large quantities of EMR together with limestone and kaolin at approximately 1200 °C. Studies of non-clinker or lessclinker ground granulated blastfurnace slag (GGBS) cement made with EMR as an activator are scarcely reported. GGBS is composed of glassystate minerals in a three-dimensional structure formed by active CaO, SiO2 and Al2O3. Kumar et al. [14] found that fibrous calcium silicate hydrates (C–S–H) and ettringite (AFt) were the predominant components of hardened GGBS cement paste based on a scanning electronic microscope (SEM) analysis. AFt is formed from the reaction of the active Al2O3 component in GGBS and a sulphate activator [15]. EMR is over 40% CaSO4; thus, combining EMR and GGBS should result in a successful cement. The studies of EMR utilisation in making cementitious materials have mostly centred on thermal modification of EMR and replacing gypsum with EMR as a retarder. Ke [9] treated EMR at 520–850 °C for Portland cement and noted that the strength of cement with less than 15% calcined EMR was the same as that of 52.5 OPC. Feng et al. [10] studied the feasibility of substituting EMR for gypsum in Portland cement with a maximum EMR content of 5%. These studies, however, ignore the effect of chemical and mechanical activation on the properties of cement. The successful activation of EMR sulphates on GGBS
J. Wang et al. / Powder Technology 241 (2013) 12–18
requires an alkalescent environment. On the one hand, the alkaline solution promotes dispersion and dissolution of GGBS [16]. On the other hand, the sulphates in EMR can react with the active Al2O3 in GGBS to make calcium sulphoaluminate hydrates in a Ca(OH)2 solution [17]. Mechanical milling not only can reduce particle size and increase its surface area but also can cause lattice defects to appear and induce crystalline transformations and non-crystallisation on the surface of particles [18,19]. In addition, during milling, chemical bonds such as Si–O, Al–O, O–H and Al–O–Si are broken, producing unsaturated bonds, free electrons and ions [20,21]. All of these factors increase the surface free energy of particles and promote material reactivity. In this work, the components and ratio of an EMR composite activator and the resultant effects on EMR–GGBS cement properties are studied. The composite activator studied is a mixture of EMR and auxiliary-activators (Ca(OH)2 and clinker). The EMR–GGBS cement used is composed of the EMR composite activator, GGBS and clinker as a strength regulator. The effect of chemical activation on the cement properties depends on the proportions of composite activator and GGBS. Then, the effects of milling method and time on the strength and setting properties are revealed. Separate grinding and intergrinding are two different milling methods for cement making. In separate grinding, the materials are milled separately and then mixed together. Its advantage is allowing for independent control over the degree to which raw material is ground, making it possible to fully activate every component's reactivity to obtain better cement properties [22]. The management for this process, however, is complicated. Thus, the intergrinding process, in which materials are first mixed and then milled together, is also studied as a comparison. Finally, the optimum water-to-cement ratio and curing process are determined, completing the EMR–GGBS cement preparation. Water has two functions during cement hydration [23]; one is to provide a liquid environment for hydration reactions, and the other is to guarantee fluidity of the cement paste. With adequate water in the mix, the degree and rate of cement hydration allows a sufficient amount of C–S–H gel to be created in the cement interior, thus increasing the cement strength [24]. With too much water in the mix, the volume of the reticular floccule, which is composed of hydration products, becomes far larger than that of the original water–cement system, causing superfluous water to separate out, and evaporate off the cement surface. This, in turn, makes the surface structure loose and produces voids among the cement particles, weakening the bonding capabilities of the slurry and reducing the strength of the material [25]. Curing time, temperature and humidity are 3 curing process parameters that greatly affect the properties of cement [26]. Thus, the effect of both the water-to-cement ratio and the curing conditions on strength is studied.
2. Materials and methods 2.1. Raw materials The EMR, granulated blast furnace slag (GBFS) and cement clinker were obtained from Xiangtan Electrolytic Manganese Dioxide Group Co. Ltd. (Hunan, China), Hunan Valin Xiangtan Steel Co. Ltd. (Hunan, China) and Hunan Pingtang Cement Plant (Hunan, China), respectively. The chemical compositions of the raw materials used in this experiment are given in Table 1. All grinding was performed using a planetary ball mill (Model: QM-3SP2, Nanjing NanDa Instrument Plant, China). Wet EMR was dried to a consistent weight of 80 °C in a vacuum drying oven and artificially broken until it passed through a 16 square mesh sieve. Broken EMR was ground for 18 min at 580 rpm using 2-mm-diameter steel balls with a ball-to-EMR weight ratio of 3.8. The pretreated EMR was measured to have a median size (D50) of 0.568 μm and a BET surface area of 13.14 m 2/g. Finally, the pretreated EMR was calcined at 350 °C in a muffle furnace for 1 h and cooled down naturally, creating modified EMR.
13
Table 1 Chemical compositions of used raw materials (wt.%). Material
Loss
SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
MnO
EMR Blast furnace slag Cement clinker
5.45 0.09 0.38
30.60 32.15 22.13
6.83 16.82 5.41
7.19 0.97 3.62
17.10 37.94 66.33
0.94 8.76 0.68
24.50 2.56 0.5
5.45 0.34 –
The GBFS and clink were dried and broken following the same procedure used for EMR and then milled for 30 min with balls-toGBFS and balls-to-clinker weight ratios of 3.8 and 3.4, respectively. The pretreated GBFS was measured to have a D50 of 5.67 μm and a surface area of 4.6677 m 2/g. The pretreated clinker was measured to have a D50 of 16.42 μm and a surface area of 2.2699 m 2/g. 2.2. Chemical activation The modified EMR, CP Ca(OH)2 and pretreated clinker were mixed according to an L16(4 5) orthogonal table (see Table 2) to prepare the composite activator EMR mixture. The mixture was then added into pretreated GBFS in a 3:7 mixture to slag weight ratio, creating GGBS modified by EMR. Finally, the 7-day activity index (A7) and 28-day activity index (A28) of the modified GGBS were measured to evaluate the effectiveness of EMR mixture excitation on GGBS to determine the optimal composite activator ratio. The pretreated GBFS, EMR mixture in a 30:3:5 EMR/Ca(OH)2/clinker weight ratio and pretreated clinker were mixed according to Table 3 to obtain EMR–GGBS cement. Then, the setting time and compressive and flexural strength of this cement were measured to evaluate the effect of chemical activation in the EMR mixture on GGBS cement to determine the optimal proportion for the composite activator. Different percentages of pretreated clinker, a 13% EMR mixture and pretreated GBFS were mixed to obtain EMR– GGBS cement. The compressive and flexural strength of these mixtures were measured to evaluate the impact of clinker on the strength of GGBS cement and to determine the optimal clinker content.
Table 2 Orthogonal experiment for the ratio of EMR mixture. No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Influence factors
Activity index
A
Ca(OH)2
B
Clinker
C
EMR
A7
A28
1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4
3 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
2 4 6 8 2 4 6 8 2 4 6 8 2 4 6 8
1 2 3 4 2 1 4 3 3 4 1 2 4 3 2 1
15 20 25 30 20 15 30 25 25 30 15 20 30 25 20 15
83 98 89 96 68 74 91 71 71 91 72 80 103 79 76 77
64 89 82 81 74 73 97 65 76 85 72 83 75 70 77 78
Influence factors
A: Ca(OH)2
B: Clinker
Activity index
A7
A28
A7
A28
A7
A28
∑(1) ∑(2) ∑(3) ∑(4) ∑(1)/4 ∑(2)/4 ∑(3)/4 ∑(4)/4 R
366 304 314 335 91.5 76 78.5 83.75 15.5
326 309 316 300 81.5 77.25 79 75 6.5
325 342 328 324 81.25 85.5 82 81 4.5
289 317 328 307 72.25 79.25 82 76.75 9.75
306 322 310 381 76.5 80.5 77.5 95.25 18.75
287 323 293 338 71.75 80.75 73.25 84.5 12.75
C: EMR
J. Wang et al. / Powder Technology 241 (2013) 12–18
3. Results and discussion
No.
Admixture (wt.%)
Slag (wt.%)
Clinker (wt.%)
Initial setting time (min)
Final setting time (min)
1 2 3 4 5 6 7 8
5 10 15 20 25 30 35 40
65 60 55 50 45 40 35 30
30 30 30 30 30 30 30 30
75 90 130 200 190 185 190 175
105 165 230 330 355 350 315 320
2.3. Mechanical activation The GBFS and clinker were artificially broken to pass through a 16 square mesh sieve and then milled for 6 min, 12 min, 18 min, 24 min or 30 min at 580 rpm using 2-mm-diameter steel balls at a balls-toGBFS weight ratio of 3.8 and a balls-to-clinker ratio of 3.4. Finally, 50% milled GBFS and 30% pretreated clinker were mixed with a 20% EMR mixture prepared at a 30:3:5 EMR/Ca(OH)2/clinker weight ratio to obtain EMR–GGBS cement, and 30% milled clinker and 50% pretreated GBFS were combined with 20% of the EMR mixture described previously. The setting time, compressive and flexural strength of the resultant material were measured to evaluate the functionality of the mechanical activation provided by the separate grinding process for slag cement to determine optimal GBFS and clinker milling times. The dried EMR, GBFS and clinker were artificially broken to pass through a 16 square mesh sieve. Then, the broken EMR was treated at 350 °C in a muffle furnace for 1 h, cooled naturally and mixed with CP Ca(OH)2 and pretreated clinker in a 30:3:5 EMR/ Ca(OH)2/clinker weight ratio to create an EMR mixture. Finally a 20% EMR mixture, 50% broken GBFS and 30% broken clinker were first mixed and then milled together, following the same milling procedure described above, using a ball-to-material weight ratio of 3.4 to create EMR–GGBS cement. The setting time and compressive and flexural strength were measured to evaluate the mechanical activation performance in slag cement prepared using the intergrinding process in comparison with that in separate ground cement. 2.4. Water-to-cement ratio and curing process A sample of 20% composite activator prepared in a weight ratio of 30:3:5 EMR/Ca(OH)2/clinker, 50% pretreated GBFS and 30% pretreated clinker were mixed to make EMR–GGBS cement mortar samples with water-to-cement ratios of 0.45, 0.50, 0.55, 0.60 and 0.65 and then cured under 4 different conditions according to Table 3. The compressive and flexural strength of the resulting material were measured to evaluate the effect of the water-to-cement ratio and the curing process on the strength of cement in order to determine the optimal parameters. 2.5. Characterisation and evaluation of cement properties The A7 and A28 of modified GGBS were measured according to China National Cement Standardization Technical Committee (NCSTC) standard method GB/T18046-2008 [27]. The compressive and flexural strength of the cements were measured according to ISO 679-1989 [28]. The setting time of the cements were measured according to ISO 9597-2008 [29]. An Instron3369 (USA) universal material testing machine was used to measure the compressive and flexural strength. An ASAP 2010 volumetric adsorption analyser produced by Micromeritics Instrument Corp. was used to measure the BET surface area. An LS601 laser diffraction size analyser produced by Zhuhai Omec Instruments Corp. was used to measure particle size.
3.1. Ratio of the components of the EMR composite activator The values used for every composite activator component were based on our early exploratory single ingredient experiments [1]. The results of A7 and A28 are presented in Table 2. The optimal class group for A7 is A1B2C4, and its Ca(OH)2/clinker/EMR weight ratio is 3:4:30. The optimal class group for A28 is A1B3C4, with a Ca(OH)2/clinker/ EMR weight ratio of 3:6:30. Based on an A7 ranged analysis in the orthogonal table, the three ingredients in order of importance are EMR, Ca(OH)2 and clinker. Based on A28, the order of importance is EMR, clinker and Ca(OH)2. This indicates that EMR is the most important activator. Ca(OH)2 acts as a stronger activator of the early activity of GGBS than clinker, but clinker is a stronger activator of the late activity of GGBS than is Ca(OH)2. The final optimal weight ratio of Ca(OH)2/ cement/clinker EMR is determined to be 3:5:30 to guarantee good early and late excitation of the EMR mixture on GGBS. 3.2. Content of EMR mixture in cement The setting times of EMR–GGBS cements containing varied quantities of an EMR mixture are given in Table 3. The data show that the setting time is at first prolonged and then shortened with increased mixture content. The primary component of the mixture is EMR, which is mainly composed of gypsum. The gypsum reacts with the active Al2O3 in GGBS to quickly create AFt at the beginning of hydration when the mixture content is below 20–25%. This causes the cement particles to be encased by a thin AFt layer, preventing the hydration of active silicate and prolonging the initial and final setting times from 75 min to 200 min and from 105 min to 355 min, respectively. When the mixture content is over 20–25%, more AFt is created and grows as acicular crystals that overlap among the cement particles to form a reticular structure. This makes the slurry set normally so that the initial and final setting times are shortened to 175 min and 315 min, respectively. Although the setting time of all samples complies fully with international standards, initial setting times of approximately 3 h and final setting times of approximately 5–6 h are preferable for EMR–GGBS cement applications. Thus, a 20–40% mixture is selected as the optimal range of proportions. The strengths of cements containing varied quantities of EMR mixture are shown in Fig. 1. The compressive and flexure strengths first increase and then decline with increasing EMR mixture content. The SiO2 and Al2O3 in GGBS and clinker are fully activated when combined with adequate quantities of mixture, thus elevating the degree of hydration, which in turn strengthens the cement paste once it has hardened. The total quantity of GGBS and clinker present, however, decreases detrimentally as the mixture quantity becomes excessive, 50
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0
45
28dFS 40 35 30
28dCS
25 20
3dCS
15 10
3dFS 0
5
5 10
15
20
25
30
35
40
EMR Mixture Content (wt%) Fig. 1. Effect of EMR mixture content on cement strength.
45
Comperssive Strength (MPa)
Table 3 Effect of EMR mixture content on cement setting time.
Flexural Strength (MPa)
14
28dFS
28dCS
3dFS
3dCS 20
0
40
60
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
15
57.5 55.0 52.5 50.0 47.5 45.0 42.5 40.0 37.5 35.0 32.5 30.0 27.5 25.0 22.5 20.0 17.5 15.0 12.5 10.0 7.5
28dFS
28dCS
3dFS
3dCS 5
80
10
Clinker Content (wt%)
15
20
25
30
Comperssive Strength (MPa)
57.5 55.0 52.5 50.0 47.5 45.0 42.5 40.0 37.5 35.0 32.5 30.0 27.5 25.0 22.5 20.0 17.5 15.0 12.5 10.0
Flexural Strength (MPa)
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Comperssive Strength (MPa)
Flexural Strength (MPa)
J. Wang et al. / Powder Technology 241 (2013) 12–18
GBFS Milling Time (min)
Fig. 2. Effect of clinker content on cement strength.
Fig. 3. Effect of GBFS milling time on cement strength.
leading to a decrease in silicate and aluminate levels and strength. Thus, it is determined that the cement strength exceeds that of the Portland slag cement (P·S) 32.5 and P·S 42.5 classes according to China NCSTC standard GB175-2007 [30] when the mixture content is maintained between 5 and 35% and between 18 and 24%, respectively.
3.3. Content of clinker in cement The clinker is not only used as an auxiliary-activator in the EMR mixture but is also added into EMR–GGBS cement as an auxiliarymaterial to regulate the strength. The strengths of cements containing varied quantities of clinker are shown in Fig. 2. It is seen that the cement strength exceeds that of the P·S 32.5, P·S 42.5 and P·S 52.5 classes when the clinker content is over 5%, 31% and 68%, respectively.
3.4. Milling time of GBFS The cement setting time, BET surface area and D50 of GBFS milled for different amounts of time are listed in Table 4. The particle size decreases from 44.69 μm to 5.67 μm, while the surface area increases from 1.3522 m 2/g to 4.6677 m 2/g with prolonged milling time. The initial and final setting times are 240 min and 370 min, respectively, when the GBFS is milled for 6 min and constant at approximately 185 min and 330 min, respectively, after the material is milled for over 12 min. The strengths of cements made with GBFS milled for different lengths of time are presented in Fig. 3. It is implied that the cement strength exceeds that of the P·S 32.5 and P·S 42.5 classes when the material is milled for longer than 8 min for surface areas over 1.5577 m 2/g and 24 min for surface areas over 3.5128 m 2/g, respectively. Mechanical ball milling reduces the GBFS particle size, increases its surface area and promotes reactivity. This causes the GGBS to participate more in the hydration reaction so that the cement setting time decreases and the strength increases for prolonged milling times. Table 4 Effect of GBFS milling time on cement setting time.
3.5. Milling time of clinker The cement setting time, BET surface area and D50 of clinker milled for different amounts of time are presented in Table 5. The clinker particle size decreases from 35.22 μm to 12.09 μm with prolonged milling time in the beginning, leading to an increase in surface area from 1.3595 m 2/g to 2.7941 m 2/g, while the initial and final setting time decreased from 260 min to 180 min and from 465 min to 335 min, respectively. The reduction of clinker particle size by mechanical ball milling promotes reactivity, thus accelerating the hydration of silicate and aluminate and reducing the setting time. Excessively prolonged milling, however, causes the clinker particles to bond and agglomerate. The D50 increases to 16.42 μm and the surface area decreases to 2.7941 m 2/g if milling exceeds 24 min, while the initial and final setting times remain constant at approximately 175 min and 335 min, respectively. The effect of milling time on the strength of cement with added clinker is shown in Fig. 4. It is seen that the strength initially increases and then, after a milling time of 24 min, decreases slightly, which agrees with the analysis of the effect of milling time on clinker particle size and reactivity described above. The cement strength exceeds that of the P·S 32.5 and P·S 42.5 classes when milled for longer than 6 min for surface areas greater than 1.3595 m 2/g and when milled for 18–22 min for surface areas greater than 2.2914 m2/g, respectively. 3.6. Influence of the intergrinding process on cement properties The setting time, BET surface area and D50 of cement materials prepared by intergrinding are presented in Table 6. The process for mixed materials can be considered to have 3 stages. First, due to mechanical grinding with steel balls, the particle size decreases and the surface area increases very quickly when the material is milled for less than 12 min. The transformation rate decreases once the particles have been ground to 28.34 μm, which occurs in the 12–18 min milling-time range, and the surface area decreases from 1.8431 m 2/g to 1.8085 m 2/g due to agglomeration of some of the mixed materials. Table 5 Effect of clinker milling time on cement setting time.
No.
Ball milling time (min)
D50 (μm)
BET surface area (m2/g)
Initial setting time (min)
Final setting time (min)
No.
Ball milling time (min)
D50 (μm)
BET surface area (m2/g)
Initial setting time (min)
Final setting time (min)
1 2 3 4 5
6 12 18 24 30
44.69 23.39 13.02 8.84 5.67
1.3522 1.9688 3.0176 3.5128 4.6677
240 190 190 180 190
370 335 320 325 345
1 2 3 4 5
6 12 18 24 30
35.22 22.90 17.52 12.09 16.42
1.3595 1.7466 2.2914 2.7941 2.2699
260 230 235 180 170
465 450 400 335 335
6.5
28dFS
6.0 5.5 5.0 4.5 4.0 3.5
3dFS
3.0 2.5
3dCS
2.0
5
10
15
20
25
7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
30
The ratio of water to cement is set between 0.45 and 0.65 in accordance with previous exploratory experiments. The strengths of cements prepared in different ratios are shown in Fig. 6. The 3 d compressive strength first increases and then decreases, while the 3 d flexure strength decreases gradually. The effect of this ratio on 28 d strength, however, is not obvious. The maximum achieved flexure is 6.7 MPa for a ratio of 0.5, and the maximum compressive strength is 47.3 MPa for a ratio of 0.55. The cement strength exceeds that of the P·S 32.5 and P·S 42.5 classes for ratios of 0.45–0.64 and 0.45–0.55, respectively.
Table 6 Effect of intergrinding on cement setting time.
3 4 5
6 12 18 24 30
42.05 28.34 25.31 17.38 11.94
40 35
28dCS
30 25 20 15
3dFS
10 5
3dCS 10
0
15
20
25
30
BET surface area (m2/g)
Initial setting time (min)
Final setting time (min)
0.8214 1.8361 1.8054 2.4669 2.9402
265 220 210 190 130
395 365 335 310 260
3.8. Curing process The strength of cement cured under different conditions is listed in Table 7. The strength growth in sample 1# is faster during 1 d to 7 d. A comparison of 1 d and 3 d strengths for samples 1# and 2# indicates that higher curing temperatures accelerate hydration, promote a greater degree of hydration and have a significant effect on early strength. The strength of sample 4# is slightly lower than that of sample 1# due to excessive water on the surface. Comparing the strength of samples 1# and 3# illustrates that wetness levels that meet the requirements of the slow hydration process are critical for achieving late strength. The curing process of sample 1# is determined to be the optimal balance between low energy consumption and high cement strength. 4. Conclusions EMR is the primary determinant of chemical activation of GGBS in a composite activator. Ca(OH)2 is a stronger activator in early GGBS activity, and clinker is stronger in late activity. The best composite activator properties are achieved with a 30:3:5 EMR/Ca(OH)2/clinker weight ratio. The cement strength exceeds that of the P·S 32.5 class and even reaches that of the P·S 42.5 and 52.5 classes when the cement is prepared following the optimised mixture parameters: 20–35% activator and over 5% clinker. The separate grinding process is better than the intergrinding process because the strength of the cement prepared by the former can exceed that of P·S 42.5, while 7.0
50
28dFS 45
6.5
Flexural Strength (MPa)
3.7. Ratio of water to cement
1
45
Fig. 5. Effect of intergrinding on cement strength.
Finally, after 18 min of milling, the transformation rate increases again due to attrition of particles with similar sizes. The reduction in particle size and the resultant increase in surface area accelerates the hydration of mixed materials and the formation of hydration products, thus the setting time decreases with prolonged milling. A 24–26 min milling time is most suitable for application in cement production. Although the process and management of intergrinding is simpler than that of separate grinding, a broad distribution of particles sizes, which is the result of differing grindabilities of the raw materials, is easily created during the intergrinding process. High-hardness materials tend to remain as larger particles, while softer materials become smaller particles after intergrinding. The surface area of EMR (see the literature [1]) is larger than that of GBFS and clinker after being milled for the same amount of time, indicating that the clinker and GBFS are harder to grind than EMR. This has a significant effect on the strength of cement treated by intergrinding process (see Fig. 5). The 3 d strength merely reaches that of the P·S 32.5 class when the material is milled for over 27 min. The 28 d strength exceeds that of the P·S 32.5 and P·S 42.5 classes after milling for over 16 min and 22 min, respectively. Therefore, the early strength of cement treated by intergrinding is lower than that of cement treated by separate grinding.
D50 (μm)
50
Intergrinding Milling Time (min)
Fig. 4. Effect of clinker milling time on cement strength.
Ball milling time (min)
55
28dFS
5
Clinker Milling Time (min)
No.
60
6.0
28dCS
40
5.5
35
5.0
30 25
4.5
3dFS 20
4.0 3.5
15
3dCS
10
3.0 0.45
0.50
0.55
0.60
0.65
Water-to-Cement Ratio Fig. 6. Effect of the water-to-cement ratio on cement strength.
Comperssive Strength (MPa)
7.0
Flexural Strength (MPa)
46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12
28dCS
Comperssive Strength (MPa)
7.5
Flexural Strength (MPa)
J. Wang et al. / Powder Technology 241 (2013) 12–18
Comperssive Strength (MPa)
16
J. Wang et al. / Powder Technology 241 (2013) 12–18
17
Table 7 Effect of curing process on cement strength. No.
1# 2# 3# 4#
Curing condition
Cured Cured Cured Cured
Flexural strength/MPa
at 30 °C in a curing box for 24 h and then demoulded and sequentially cured in a curing box at 30 °C at 60 °C in a curing box for 24 h and then demoulded and sequentially cured in a curing box at 30 °C in a room for 24 h and then demoulded and sequentially cured in a room at 30 °C in a curing box for 24 h and then demoulded and sequentially cured in water at 30 °C
that of the later merely reaches the strength of P·S 32.5. It is necessary to ball-mill GBFS for 12 min or longer to ensure that the surface area is greater than 1.9688 m2/g, and the clinker must be ball-milled for 24–30 min for a surface area of over 2.2699 m 2/g. In addition, the water-to-cement ratio must be 0.45–0.64. The initial and final setting times of such a cement are approximately 180 min and 330 min, respectively, which is preferred for EMR–GGBS cement applications. The cement's early strength benefits from a higher curing temperature, and wetness promotes the development of late strength. The cement exhibits better performance if it is cured at 30 °C in a curing box for 24 h and then demoulded and sequentially cured in curing box at 30 °C. Acknowledgement The authors acknowledge the National High Technology Research and Development Program of China (2010AA065205) and the Key Project of Science and Technology of Hunan Province (2008FJ1013) for their financial support of this study. References [1] J. Wang, B. Peng, L. Chai, Q. Zhang, Q. Liu, Study on cementing material making with electrolytic manganese residue, 3rd International Symposium on HighTemperature Metallurgical Processing—TMS 2012 Annual Meeting and Exhibition, Minerals, Metals and Materials Society, 2012, pp. 461–471. [2] G.R. Lomboy, K. Wang, J. Quan, J. Zhuo, Properties of cementitious materials in their dry state and their influences on viscosity of the cementitious pastes, Powder Technology 229 (2012) 104–111. [3] A.K.H. Kwan, J.J. Chen, Adding fly ash microsphere to improve packing density, flowability and strength of cement paste, Powder Technology 234 (2013) 19–25. [4] K. Hagelstein, Globally sustainable manganese metal production and use, Journal of Environmental Management 90 (12) (2009) 3736–3740. [5] N. Duan, W. Fan, Z. Changbo, Analysis of pollution materials generated from electrolytic manganese industries, Resources, Conservation and Recycling 54 (8) (2010) 506–511. [6] Q. Jueshi, H. Pengkun, W. Zhi, Crystallization characteristic of glass-ceramic made from electrolytic manganese residue, Journal of Wuhan University of Technology —Materials Science Edition 27 (1) (2012) 45–49. [7] T.P. Li, H.L. Xie, H.X. Mei, Experimental study of calcinated electrolysis manganese residue and fly ash complex admixture, Bulletin of the Chinese Ceramic Society 26 (3) (2007) 567–592. [8] P. Hou, J. Qian, Z. Wang, Production of quasi-sulphoaluminate cementitious materials with electrolytic manganese residue, Cement and Concrete Composites 34 (2) (2012) 248–254. [9] G.J. Ke, Hydration mechanism of binding material made of burnt manganesecement, Journal of Central-South Institute of Technology 11 (2) (1997) 8–13. [10] Y. Feng, Y.X. Chen, F. Liu, Studies on replacement of gypsum by manganese slag as retarder in cement manufacture, Modern Chemical Industry 26 (2) (2006) 57–60. [11] B. Du, Z. Ru, C. Zhou, Analysis of physical–chemical characteristics for electrolytic manganese residues, in: J.H. Li, H.L. Hu (Eds.), 5th International Conference on Waste Management and Technology Beijing, PR China, 2010, pp. 505–508. [12] C. Tao, M. Li, Z. Liu, Composition and recovery method for electrolytic manganese residue, Journal of Central South University of Technology 16 (1) (2009) 309–312. [13] M. Sahmaran, H.A. Christianto, I.Q. Yaman, The effect of chemical admixtures and mineral additives on the properties of self-compacting mortars, Cement and Concrete Composites 28 (2006) 432–440. [14] S. Kumar, R. Kumar, B. A., 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 and Concrete Composites 30 (2008) 679–685. [15] J. Pourchez, Current understanding of cellulose ethers impact on the hydration of C3A and C3A-sulphate systems, Cement and Concrete Research 39 (8) (2009) 664–669. [16] S. Aydin, B. Baradan, Mechanical and microstructural properties of heat cured alkali-activated slag mortars, Materials and Design 35 (2012) 374–383. [17] N. Bhanumathidas, N. Kalidas, Dual role of gypsum: set retarder and strength accelerator, Indian Concrete Journal 78 (3) (2004) 170–173.
Compressive strength/MPa
1d
3d
7d
28 d
1d
3d
7d
28 d
2.59 6.44 – –
4.0 7.34 3.22 3.62
7.79 8.0 – –
8.35 8.66 4.37 7.52
3.2 8.7 – –
19 25.5 13.2 18.4
35.9 35.2 – –
45 47 26.8 43.7
[18] I.B. Celik, The effects of particle size distribution and surface area upon cement strength development, Powder Technology 188 (3) (2009) 272–276. [19] H. Binici, O. Aksogan, I.H. Cagatay, M. Tokyay, E. Emsen, The effect of particle size distribution on the properties of blended cements incorporating GGBFS and natural pozzolan (NP), Powder Technology 177 (3) (2007) 140–147. [20] S. Aydin, Ç. Karatay, B. Baradan, The effect of grinding process on mechanical properties and alkali-silica reaction resistance of fly ash incorporated cement mortars, Powder Technology 197 (1–2) (2010) 68–72. [21] Y.M. Zhang, T.J. Napier-Munn, Effects of particle size distribution, surface area and chemical composition on Portland cement strength, Powder Technology 83 (1995) 245–252. [22] M. Oner, K. Erdogdu, A. Gunlu, Effect of components fineness on strength of blast furnace slag cement, Cement and Concrete Research 33 (2001) 463–469. [23] J.P. Bigas, J.L. Gallias, Single-drop agglomeration of fine mineral admixtures for concrete and water requirement of pastes, Powder Technology 130 (1–3) (2003) 110–115. [24] A. Carpinteri, R. Brighenti, Fracture behaviour of plain and fiber-reinforced concrete with different water content under mixed mode loading, Materials and Design 31 (4) (2010) 2032–2042. [25] M. Nematzadeh, M. Naghipour, Compressing fresh concrete technique and the effect of excess water content on physical–mechanical properties of compressed concrete, Materials and Design 37 (2012) 256–267. [26] H. Zhao, W. Sun, X. Wu, B. Gao, Effect of initial water-curing period and curing condition on the properties of self-compacting concrete, Materials and Design 35 (2012) 194–200. [27] NCSTC, GB/T18046-2008 Ground Granulated Blast Furnace Slag Used for Cement and Concrete, China Standards Press, Bei Jing, 2008. [28] ISO 679, Methods of Testing Cements—Determination of Strength, 1989. [29] ISO 9597, Cement-Test Methods—Determination of Setting Time and Soundness, 2008. [30] NCSTC, GB175-2007 Common Portland Cement, China Standards Press, Bei Jing, 2007.
Jia Wang, born in 1982, received his B.S. degree in 2004 and an M.S. degree in 2007 in environmental engineering from Central South University (CSU), Changsha, China. He is now a Ph.D. candidate in the School of Metallurgical Science and Engineering of CSU, majoring in metallurgical environmental engineering. He has been actively involved in the recycling and utilisation of industrial and municipal solid waste, the preparation of photocatalysis antibacterial materials, smelting and environmental protection process design. He has published 8 papers as the first author, holds 4 patents and is a nationally registered environmental protection engineer.
Bing Peng was born in 1956. After receiving his Ph.D. degree in metallurgical engineering from CSU, he joined the faculty of the Department of Environmental Engineering of CSU, where he continues as professor, doctoral tutor and vice director. His major research interests have been directed towards the cleaning of production, environment protection, recycling and utilisation of solid waste in smelting plants. He has published more than 130 papers, applied for 26 patents and is a well-known expert in this field.
Liyuan Chai was born in 1966. After receiving his Ph.D. degree in metallurgical engineering from CSU, he joined the faculty in the School of Metallurgical Science and Engineering of CSU, where he continues as professor, doctoral tutor, academic leader and vice president. His major research interests have been the treatment, recycling and utilisation of pollutants produced in heavy metal smelting plants. He has published more than 200 papers, applied for 38 patents and is a famous expert in this field.
18
J. Wang et al. / Powder Technology 241 (2013) 12–18 Qiang Zhang was born in 1982 and received his M.S. degree in 2011 in environmental engineering from CSU. He is now a Ph.D. candidate in the Chinese Academy of Sciences, majoring in environmental engineering. He has been actively involved in the utilisation of industrial solid waste to prepare cement. He has published 2 papers as the first author and holds 2 patents.
Qin Liu was born in 1989 and received her B.S. degree in 2010 in environmental engineering from CSU. She is now an M.S. candidate in the Environmental Engineering Research Institute of CSU. She has been actively involved in the preparation of photocatalysis cementitious materials. She has published 1 paper as the first author.
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Powder Technology journal homepage: www.elsevier.com/locate/powtec
Preparation of electrolytic manganese residue–ground granulated blastfurnace slag cement Jia Wang, Bing Peng ⁎, Liyuan Chai, Qiang Zhang, Qin Liu School of Metallurgical Science and Engineering, Central South University, Changsha 410083, PR China
a r t i c l e
i n f o
Article history: Received 10 December 2012 Received in revised form 29 January 2013 Accepted 1 March 2013 Available online 13 March 2013 Keywords: Electrolytic manganese residue Cementitious materials Granulated blast furnace slag Chemical activation Mechanical activation
a b s t r a c t Electrolytic manganese residue (EMR) is added into ground granulated blastfurnace slag (GGBS) as an activator to prepare EMR–GGBS cement. The effects of chemical activation, mechanical activation, water-to-cement ratio and the curing process on the strength and setting properties of EMR–GGBS cement are investigated based on its slag activity index, setting time and compressive and flexural strength. The results show that EMR is an effective and efficient activator for GGBS. This composite activator excels in its purpose when mixed in an EMR/Ca(OH)2/ clinker at a weight ratio of 30:3:5. The cement strength exceeds that of Portland slag cement (P·S) 32.5 class, even reaching that of P·S 42.5 and 52.5 classes after adding 20–35% activator and over 5% clinker. It is necessary to ball-mill granulated blast furnace slag (GBFS) for 12 min or longer to achieve a high surface area, over 1.9688 m2/g, and clinker for 24–30 min to achieve a surface area of over 2.2699 m2/g, as well as to maintain the water-to-cement ratio between 0.45 and 0.64. The initial and final setting times of the cement are 180 min and 330 min, respectively, which is consistent with the desired times for applications of such cement. The cementitious material exhibits better performance after being cured at 30 °C for 24 h. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Portland cement is a building material that is widely used around the world. A significant amount of clay and limestone is consumed, and at least 1 ton of CO2, 0.74 kg of SO2, 120 kg of dust and other pollutants are discharged into the atmosphere to produce 1 ton of cement clinker [1]. Therefore, it is necessary to develop some new cementitious materials to replace the clinker [2,3]. Electrolytic manganese residue (EMR) is a solid waste found in filters after sulphuric acid leaching of manganese carbonate ore, MnO2 oxidative deferrisation and lime neutralisation. Approximately 6– 7 tons of residue is discharged into the environment per ton of electrolytic manganese product [4]. The accumulated amount of EMR during the past years is huge; EMR is a rarely recycled resource [5]. Use in the preparation of building materials for wall, subgrade and concrete [6–10] is one method of EMR reutilisation. EMR has the properties of both gypsum and hydraulic industrial solid wastes due to its main chemical components, CaSO4·2H2O, SiO2 and small amounts of Al2O3, Fe2O3, MnO2, etc. [11,12]. Its high moisture content, 20% to 30% water, and low activity of calcium sulphate, present in EMR as CaSO4·2H2O, makes it difficult to use in cementitious material production. Its other components, such as SiO2 and Al2O3, have low hydration rates. Therefore, EMR cannot be used as a chemical activator in cementitious
⁎ Corresponding author at: Central South University, PR China. Tel.: +86 731 88830577; fax: +86 731 88710171. E-mail address: [email protected] (B. Peng). 0032-5910/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.powtec.2013.03.003
materials until it is modified to promote the activity of its components and mixed with other appropriate auxiliary-activators [13]. Cement-making with EMR has mainly focused on Portland fly-ash cement and sulpho-aluminate cement. Li et al. [7] added 25% admixture, prepared by mixing 15% EMR treated at 300–850 °C with 85% fly-ash, into 75% 42.5 ordinary Portland cement (OPC) to make blended hydraulic cement. Hou et al. [8] prepared quasi-sulphoaluminate cementitious material by calcining large quantities of EMR together with limestone and kaolin at approximately 1200 °C. Studies of non-clinker or lessclinker ground granulated blastfurnace slag (GGBS) cement made with EMR as an activator are scarcely reported. GGBS is composed of glassystate minerals in a three-dimensional structure formed by active CaO, SiO2 and Al2O3. Kumar et al. [14] found that fibrous calcium silicate hydrates (C–S–H) and ettringite (AFt) were the predominant components of hardened GGBS cement paste based on a scanning electronic microscope (SEM) analysis. AFt is formed from the reaction of the active Al2O3 component in GGBS and a sulphate activator [15]. EMR is over 40% CaSO4; thus, combining EMR and GGBS should result in a successful cement. The studies of EMR utilisation in making cementitious materials have mostly centred on thermal modification of EMR and replacing gypsum with EMR as a retarder. Ke [9] treated EMR at 520–850 °C for Portland cement and noted that the strength of cement with less than 15% calcined EMR was the same as that of 52.5 OPC. Feng et al. [10] studied the feasibility of substituting EMR for gypsum in Portland cement with a maximum EMR content of 5%. These studies, however, ignore the effect of chemical and mechanical activation on the properties of cement. The successful activation of EMR sulphates on GGBS
J. Wang et al. / Powder Technology 241 (2013) 12–18
requires an alkalescent environment. On the one hand, the alkaline solution promotes dispersion and dissolution of GGBS [16]. On the other hand, the sulphates in EMR can react with the active Al2O3 in GGBS to make calcium sulphoaluminate hydrates in a Ca(OH)2 solution [17]. Mechanical milling not only can reduce particle size and increase its surface area but also can cause lattice defects to appear and induce crystalline transformations and non-crystallisation on the surface of particles [18,19]. In addition, during milling, chemical bonds such as Si–O, Al–O, O–H and Al–O–Si are broken, producing unsaturated bonds, free electrons and ions [20,21]. All of these factors increase the surface free energy of particles and promote material reactivity. In this work, the components and ratio of an EMR composite activator and the resultant effects on EMR–GGBS cement properties are studied. The composite activator studied is a mixture of EMR and auxiliary-activators (Ca(OH)2 and clinker). The EMR–GGBS cement used is composed of the EMR composite activator, GGBS and clinker as a strength regulator. The effect of chemical activation on the cement properties depends on the proportions of composite activator and GGBS. Then, the effects of milling method and time on the strength and setting properties are revealed. Separate grinding and intergrinding are two different milling methods for cement making. In separate grinding, the materials are milled separately and then mixed together. Its advantage is allowing for independent control over the degree to which raw material is ground, making it possible to fully activate every component's reactivity to obtain better cement properties [22]. The management for this process, however, is complicated. Thus, the intergrinding process, in which materials are first mixed and then milled together, is also studied as a comparison. Finally, the optimum water-to-cement ratio and curing process are determined, completing the EMR–GGBS cement preparation. Water has two functions during cement hydration [23]; one is to provide a liquid environment for hydration reactions, and the other is to guarantee fluidity of the cement paste. With adequate water in the mix, the degree and rate of cement hydration allows a sufficient amount of C–S–H gel to be created in the cement interior, thus increasing the cement strength [24]. With too much water in the mix, the volume of the reticular floccule, which is composed of hydration products, becomes far larger than that of the original water–cement system, causing superfluous water to separate out, and evaporate off the cement surface. This, in turn, makes the surface structure loose and produces voids among the cement particles, weakening the bonding capabilities of the slurry and reducing the strength of the material [25]. Curing time, temperature and humidity are 3 curing process parameters that greatly affect the properties of cement [26]. Thus, the effect of both the water-to-cement ratio and the curing conditions on strength is studied.
2. Materials and methods 2.1. Raw materials The EMR, granulated blast furnace slag (GBFS) and cement clinker were obtained from Xiangtan Electrolytic Manganese Dioxide Group Co. Ltd. (Hunan, China), Hunan Valin Xiangtan Steel Co. Ltd. (Hunan, China) and Hunan Pingtang Cement Plant (Hunan, China), respectively. The chemical compositions of the raw materials used in this experiment are given in Table 1. All grinding was performed using a planetary ball mill (Model: QM-3SP2, Nanjing NanDa Instrument Plant, China). Wet EMR was dried to a consistent weight of 80 °C in a vacuum drying oven and artificially broken until it passed through a 16 square mesh sieve. Broken EMR was ground for 18 min at 580 rpm using 2-mm-diameter steel balls with a ball-to-EMR weight ratio of 3.8. The pretreated EMR was measured to have a median size (D50) of 0.568 μm and a BET surface area of 13.14 m 2/g. Finally, the pretreated EMR was calcined at 350 °C in a muffle furnace for 1 h and cooled down naturally, creating modified EMR.
13
Table 1 Chemical compositions of used raw materials (wt.%). Material
Loss
SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
MnO
EMR Blast furnace slag Cement clinker
5.45 0.09 0.38
30.60 32.15 22.13
6.83 16.82 5.41
7.19 0.97 3.62
17.10 37.94 66.33
0.94 8.76 0.68
24.50 2.56 0.5
5.45 0.34 –
The GBFS and clink were dried and broken following the same procedure used for EMR and then milled for 30 min with balls-toGBFS and balls-to-clinker weight ratios of 3.8 and 3.4, respectively. The pretreated GBFS was measured to have a D50 of 5.67 μm and a surface area of 4.6677 m 2/g. The pretreated clinker was measured to have a D50 of 16.42 μm and a surface area of 2.2699 m 2/g. 2.2. Chemical activation The modified EMR, CP Ca(OH)2 and pretreated clinker were mixed according to an L16(4 5) orthogonal table (see Table 2) to prepare the composite activator EMR mixture. The mixture was then added into pretreated GBFS in a 3:7 mixture to slag weight ratio, creating GGBS modified by EMR. Finally, the 7-day activity index (A7) and 28-day activity index (A28) of the modified GGBS were measured to evaluate the effectiveness of EMR mixture excitation on GGBS to determine the optimal composite activator ratio. The pretreated GBFS, EMR mixture in a 30:3:5 EMR/Ca(OH)2/clinker weight ratio and pretreated clinker were mixed according to Table 3 to obtain EMR–GGBS cement. Then, the setting time and compressive and flexural strength of this cement were measured to evaluate the effect of chemical activation in the EMR mixture on GGBS cement to determine the optimal proportion for the composite activator. Different percentages of pretreated clinker, a 13% EMR mixture and pretreated GBFS were mixed to obtain EMR– GGBS cement. The compressive and flexural strength of these mixtures were measured to evaluate the impact of clinker on the strength of GGBS cement and to determine the optimal clinker content.
Table 2 Orthogonal experiment for the ratio of EMR mixture. No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Influence factors
Activity index
A
Ca(OH)2
B
Clinker
C
EMR
A7
A28
1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4
3 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
2 4 6 8 2 4 6 8 2 4 6 8 2 4 6 8
1 2 3 4 2 1 4 3 3 4 1 2 4 3 2 1
15 20 25 30 20 15 30 25 25 30 15 20 30 25 20 15
83 98 89 96 68 74 91 71 71 91 72 80 103 79 76 77
64 89 82 81 74 73 97 65 76 85 72 83 75 70 77 78
Influence factors
A: Ca(OH)2
B: Clinker
Activity index
A7
A28
A7
A28
A7
A28
∑(1) ∑(2) ∑(3) ∑(4) ∑(1)/4 ∑(2)/4 ∑(3)/4 ∑(4)/4 R
366 304 314 335 91.5 76 78.5 83.75 15.5
326 309 316 300 81.5 77.25 79 75 6.5
325 342 328 324 81.25 85.5 82 81 4.5
289 317 328 307 72.25 79.25 82 76.75 9.75
306 322 310 381 76.5 80.5 77.5 95.25 18.75
287 323 293 338 71.75 80.75 73.25 84.5 12.75
C: EMR
J. Wang et al. / Powder Technology 241 (2013) 12–18
3. Results and discussion
No.
Admixture (wt.%)
Slag (wt.%)
Clinker (wt.%)
Initial setting time (min)
Final setting time (min)
1 2 3 4 5 6 7 8
5 10 15 20 25 30 35 40
65 60 55 50 45 40 35 30
30 30 30 30 30 30 30 30
75 90 130 200 190 185 190 175
105 165 230 330 355 350 315 320
2.3. Mechanical activation The GBFS and clinker were artificially broken to pass through a 16 square mesh sieve and then milled for 6 min, 12 min, 18 min, 24 min or 30 min at 580 rpm using 2-mm-diameter steel balls at a balls-toGBFS weight ratio of 3.8 and a balls-to-clinker ratio of 3.4. Finally, 50% milled GBFS and 30% pretreated clinker were mixed with a 20% EMR mixture prepared at a 30:3:5 EMR/Ca(OH)2/clinker weight ratio to obtain EMR–GGBS cement, and 30% milled clinker and 50% pretreated GBFS were combined with 20% of the EMR mixture described previously. The setting time, compressive and flexural strength of the resultant material were measured to evaluate the functionality of the mechanical activation provided by the separate grinding process for slag cement to determine optimal GBFS and clinker milling times. The dried EMR, GBFS and clinker were artificially broken to pass through a 16 square mesh sieve. Then, the broken EMR was treated at 350 °C in a muffle furnace for 1 h, cooled naturally and mixed with CP Ca(OH)2 and pretreated clinker in a 30:3:5 EMR/ Ca(OH)2/clinker weight ratio to create an EMR mixture. Finally a 20% EMR mixture, 50% broken GBFS and 30% broken clinker were first mixed and then milled together, following the same milling procedure described above, using a ball-to-material weight ratio of 3.4 to create EMR–GGBS cement. The setting time and compressive and flexural strength were measured to evaluate the mechanical activation performance in slag cement prepared using the intergrinding process in comparison with that in separate ground cement. 2.4. Water-to-cement ratio and curing process A sample of 20% composite activator prepared in a weight ratio of 30:3:5 EMR/Ca(OH)2/clinker, 50% pretreated GBFS and 30% pretreated clinker were mixed to make EMR–GGBS cement mortar samples with water-to-cement ratios of 0.45, 0.50, 0.55, 0.60 and 0.65 and then cured under 4 different conditions according to Table 3. The compressive and flexural strength of the resulting material were measured to evaluate the effect of the water-to-cement ratio and the curing process on the strength of cement in order to determine the optimal parameters. 2.5. Characterisation and evaluation of cement properties The A7 and A28 of modified GGBS were measured according to China National Cement Standardization Technical Committee (NCSTC) standard method GB/T18046-2008 [27]. The compressive and flexural strength of the cements were measured according to ISO 679-1989 [28]. The setting time of the cements were measured according to ISO 9597-2008 [29]. An Instron3369 (USA) universal material testing machine was used to measure the compressive and flexural strength. An ASAP 2010 volumetric adsorption analyser produced by Micromeritics Instrument Corp. was used to measure the BET surface area. An LS601 laser diffraction size analyser produced by Zhuhai Omec Instruments Corp. was used to measure particle size.
3.1. Ratio of the components of the EMR composite activator The values used for every composite activator component were based on our early exploratory single ingredient experiments [1]. The results of A7 and A28 are presented in Table 2. The optimal class group for A7 is A1B2C4, and its Ca(OH)2/clinker/EMR weight ratio is 3:4:30. The optimal class group for A28 is A1B3C4, with a Ca(OH)2/clinker/ EMR weight ratio of 3:6:30. Based on an A7 ranged analysis in the orthogonal table, the three ingredients in order of importance are EMR, Ca(OH)2 and clinker. Based on A28, the order of importance is EMR, clinker and Ca(OH)2. This indicates that EMR is the most important activator. Ca(OH)2 acts as a stronger activator of the early activity of GGBS than clinker, but clinker is a stronger activator of the late activity of GGBS than is Ca(OH)2. The final optimal weight ratio of Ca(OH)2/ cement/clinker EMR is determined to be 3:5:30 to guarantee good early and late excitation of the EMR mixture on GGBS. 3.2. Content of EMR mixture in cement The setting times of EMR–GGBS cements containing varied quantities of an EMR mixture are given in Table 3. The data show that the setting time is at first prolonged and then shortened with increased mixture content. The primary component of the mixture is EMR, which is mainly composed of gypsum. The gypsum reacts with the active Al2O3 in GGBS to quickly create AFt at the beginning of hydration when the mixture content is below 20–25%. This causes the cement particles to be encased by a thin AFt layer, preventing the hydration of active silicate and prolonging the initial and final setting times from 75 min to 200 min and from 105 min to 355 min, respectively. When the mixture content is over 20–25%, more AFt is created and grows as acicular crystals that overlap among the cement particles to form a reticular structure. This makes the slurry set normally so that the initial and final setting times are shortened to 175 min and 315 min, respectively. Although the setting time of all samples complies fully with international standards, initial setting times of approximately 3 h and final setting times of approximately 5–6 h are preferable for EMR–GGBS cement applications. Thus, a 20–40% mixture is selected as the optimal range of proportions. The strengths of cements containing varied quantities of EMR mixture are shown in Fig. 1. The compressive and flexure strengths first increase and then decline with increasing EMR mixture content. The SiO2 and Al2O3 in GGBS and clinker are fully activated when combined with adequate quantities of mixture, thus elevating the degree of hydration, which in turn strengthens the cement paste once it has hardened. The total quantity of GGBS and clinker present, however, decreases detrimentally as the mixture quantity becomes excessive, 50
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0
45
28dFS 40 35 30
28dCS
25 20
3dCS
15 10
3dFS 0
5
5 10
15
20
25
30
35
40
EMR Mixture Content (wt%) Fig. 1. Effect of EMR mixture content on cement strength.
45
Comperssive Strength (MPa)
Table 3 Effect of EMR mixture content on cement setting time.
Flexural Strength (MPa)
14
28dFS
28dCS
3dFS
3dCS 20
0
40
60
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
15
57.5 55.0 52.5 50.0 47.5 45.0 42.5 40.0 37.5 35.0 32.5 30.0 27.5 25.0 22.5 20.0 17.5 15.0 12.5 10.0 7.5
28dFS
28dCS
3dFS
3dCS 5
80
10
Clinker Content (wt%)
15
20
25
30
Comperssive Strength (MPa)
57.5 55.0 52.5 50.0 47.5 45.0 42.5 40.0 37.5 35.0 32.5 30.0 27.5 25.0 22.5 20.0 17.5 15.0 12.5 10.0
Flexural Strength (MPa)
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Comperssive Strength (MPa)
Flexural Strength (MPa)
J. Wang et al. / Powder Technology 241 (2013) 12–18
GBFS Milling Time (min)
Fig. 2. Effect of clinker content on cement strength.
Fig. 3. Effect of GBFS milling time on cement strength.
leading to a decrease in silicate and aluminate levels and strength. Thus, it is determined that the cement strength exceeds that of the Portland slag cement (P·S) 32.5 and P·S 42.5 classes according to China NCSTC standard GB175-2007 [30] when the mixture content is maintained between 5 and 35% and between 18 and 24%, respectively.
3.3. Content of clinker in cement The clinker is not only used as an auxiliary-activator in the EMR mixture but is also added into EMR–GGBS cement as an auxiliarymaterial to regulate the strength. The strengths of cements containing varied quantities of clinker are shown in Fig. 2. It is seen that the cement strength exceeds that of the P·S 32.5, P·S 42.5 and P·S 52.5 classes when the clinker content is over 5%, 31% and 68%, respectively.
3.4. Milling time of GBFS The cement setting time, BET surface area and D50 of GBFS milled for different amounts of time are listed in Table 4. The particle size decreases from 44.69 μm to 5.67 μm, while the surface area increases from 1.3522 m 2/g to 4.6677 m 2/g with prolonged milling time. The initial and final setting times are 240 min and 370 min, respectively, when the GBFS is milled for 6 min and constant at approximately 185 min and 330 min, respectively, after the material is milled for over 12 min. The strengths of cements made with GBFS milled for different lengths of time are presented in Fig. 3. It is implied that the cement strength exceeds that of the P·S 32.5 and P·S 42.5 classes when the material is milled for longer than 8 min for surface areas over 1.5577 m 2/g and 24 min for surface areas over 3.5128 m 2/g, respectively. Mechanical ball milling reduces the GBFS particle size, increases its surface area and promotes reactivity. This causes the GGBS to participate more in the hydration reaction so that the cement setting time decreases and the strength increases for prolonged milling times. Table 4 Effect of GBFS milling time on cement setting time.
3.5. Milling time of clinker The cement setting time, BET surface area and D50 of clinker milled for different amounts of time are presented in Table 5. The clinker particle size decreases from 35.22 μm to 12.09 μm with prolonged milling time in the beginning, leading to an increase in surface area from 1.3595 m 2/g to 2.7941 m 2/g, while the initial and final setting time decreased from 260 min to 180 min and from 465 min to 335 min, respectively. The reduction of clinker particle size by mechanical ball milling promotes reactivity, thus accelerating the hydration of silicate and aluminate and reducing the setting time. Excessively prolonged milling, however, causes the clinker particles to bond and agglomerate. The D50 increases to 16.42 μm and the surface area decreases to 2.7941 m 2/g if milling exceeds 24 min, while the initial and final setting times remain constant at approximately 175 min and 335 min, respectively. The effect of milling time on the strength of cement with added clinker is shown in Fig. 4. It is seen that the strength initially increases and then, after a milling time of 24 min, decreases slightly, which agrees with the analysis of the effect of milling time on clinker particle size and reactivity described above. The cement strength exceeds that of the P·S 32.5 and P·S 42.5 classes when milled for longer than 6 min for surface areas greater than 1.3595 m 2/g and when milled for 18–22 min for surface areas greater than 2.2914 m2/g, respectively. 3.6. Influence of the intergrinding process on cement properties The setting time, BET surface area and D50 of cement materials prepared by intergrinding are presented in Table 6. The process for mixed materials can be considered to have 3 stages. First, due to mechanical grinding with steel balls, the particle size decreases and the surface area increases very quickly when the material is milled for less than 12 min. The transformation rate decreases once the particles have been ground to 28.34 μm, which occurs in the 12–18 min milling-time range, and the surface area decreases from 1.8431 m 2/g to 1.8085 m 2/g due to agglomeration of some of the mixed materials. Table 5 Effect of clinker milling time on cement setting time.
No.
Ball milling time (min)
D50 (μm)
BET surface area (m2/g)
Initial setting time (min)
Final setting time (min)
No.
Ball milling time (min)
D50 (μm)
BET surface area (m2/g)
Initial setting time (min)
Final setting time (min)
1 2 3 4 5
6 12 18 24 30
44.69 23.39 13.02 8.84 5.67
1.3522 1.9688 3.0176 3.5128 4.6677
240 190 190 180 190
370 335 320 325 345
1 2 3 4 5
6 12 18 24 30
35.22 22.90 17.52 12.09 16.42
1.3595 1.7466 2.2914 2.7941 2.2699
260 230 235 180 170
465 450 400 335 335
6.5
28dFS
6.0 5.5 5.0 4.5 4.0 3.5
3dFS
3.0 2.5
3dCS
2.0
5
10
15
20
25
7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
30
The ratio of water to cement is set between 0.45 and 0.65 in accordance with previous exploratory experiments. The strengths of cements prepared in different ratios are shown in Fig. 6. The 3 d compressive strength first increases and then decreases, while the 3 d flexure strength decreases gradually. The effect of this ratio on 28 d strength, however, is not obvious. The maximum achieved flexure is 6.7 MPa for a ratio of 0.5, and the maximum compressive strength is 47.3 MPa for a ratio of 0.55. The cement strength exceeds that of the P·S 32.5 and P·S 42.5 classes for ratios of 0.45–0.64 and 0.45–0.55, respectively.
Table 6 Effect of intergrinding on cement setting time.
3 4 5
6 12 18 24 30
42.05 28.34 25.31 17.38 11.94
40 35
28dCS
30 25 20 15
3dFS
10 5
3dCS 10
0
15
20
25
30
BET surface area (m2/g)
Initial setting time (min)
Final setting time (min)
0.8214 1.8361 1.8054 2.4669 2.9402
265 220 210 190 130
395 365 335 310 260
3.8. Curing process The strength of cement cured under different conditions is listed in Table 7. The strength growth in sample 1# is faster during 1 d to 7 d. A comparison of 1 d and 3 d strengths for samples 1# and 2# indicates that higher curing temperatures accelerate hydration, promote a greater degree of hydration and have a significant effect on early strength. The strength of sample 4# is slightly lower than that of sample 1# due to excessive water on the surface. Comparing the strength of samples 1# and 3# illustrates that wetness levels that meet the requirements of the slow hydration process are critical for achieving late strength. The curing process of sample 1# is determined to be the optimal balance between low energy consumption and high cement strength. 4. Conclusions EMR is the primary determinant of chemical activation of GGBS in a composite activator. Ca(OH)2 is a stronger activator in early GGBS activity, and clinker is stronger in late activity. The best composite activator properties are achieved with a 30:3:5 EMR/Ca(OH)2/clinker weight ratio. The cement strength exceeds that of the P·S 32.5 class and even reaches that of the P·S 42.5 and 52.5 classes when the cement is prepared following the optimised mixture parameters: 20–35% activator and over 5% clinker. The separate grinding process is better than the intergrinding process because the strength of the cement prepared by the former can exceed that of P·S 42.5, while 7.0
50
28dFS 45
6.5
Flexural Strength (MPa)
3.7. Ratio of water to cement
1
45
Fig. 5. Effect of intergrinding on cement strength.
Finally, after 18 min of milling, the transformation rate increases again due to attrition of particles with similar sizes. The reduction in particle size and the resultant increase in surface area accelerates the hydration of mixed materials and the formation of hydration products, thus the setting time decreases with prolonged milling. A 24–26 min milling time is most suitable for application in cement production. Although the process and management of intergrinding is simpler than that of separate grinding, a broad distribution of particles sizes, which is the result of differing grindabilities of the raw materials, is easily created during the intergrinding process. High-hardness materials tend to remain as larger particles, while softer materials become smaller particles after intergrinding. The surface area of EMR (see the literature [1]) is larger than that of GBFS and clinker after being milled for the same amount of time, indicating that the clinker and GBFS are harder to grind than EMR. This has a significant effect on the strength of cement treated by intergrinding process (see Fig. 5). The 3 d strength merely reaches that of the P·S 32.5 class when the material is milled for over 27 min. The 28 d strength exceeds that of the P·S 32.5 and P·S 42.5 classes after milling for over 16 min and 22 min, respectively. Therefore, the early strength of cement treated by intergrinding is lower than that of cement treated by separate grinding.
D50 (μm)
50
Intergrinding Milling Time (min)
Fig. 4. Effect of clinker milling time on cement strength.
Ball milling time (min)
55
28dFS
5
Clinker Milling Time (min)
No.
60
6.0
28dCS
40
5.5
35
5.0
30 25
4.5
3dFS 20
4.0 3.5
15
3dCS
10
3.0 0.45
0.50
0.55
0.60
0.65
Water-to-Cement Ratio Fig. 6. Effect of the water-to-cement ratio on cement strength.
Comperssive Strength (MPa)
7.0
Flexural Strength (MPa)
46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12
28dCS
Comperssive Strength (MPa)
7.5
Flexural Strength (MPa)
J. Wang et al. / Powder Technology 241 (2013) 12–18
Comperssive Strength (MPa)
16
J. Wang et al. / Powder Technology 241 (2013) 12–18
17
Table 7 Effect of curing process on cement strength. No.
1# 2# 3# 4#
Curing condition
Cured Cured Cured Cured
Flexural strength/MPa
at 30 °C in a curing box for 24 h and then demoulded and sequentially cured in a curing box at 30 °C at 60 °C in a curing box for 24 h and then demoulded and sequentially cured in a curing box at 30 °C in a room for 24 h and then demoulded and sequentially cured in a room at 30 °C in a curing box for 24 h and then demoulded and sequentially cured in water at 30 °C
that of the later merely reaches the strength of P·S 32.5. It is necessary to ball-mill GBFS for 12 min or longer to ensure that the surface area is greater than 1.9688 m2/g, and the clinker must be ball-milled for 24–30 min for a surface area of over 2.2699 m 2/g. In addition, the water-to-cement ratio must be 0.45–0.64. The initial and final setting times of such a cement are approximately 180 min and 330 min, respectively, which is preferred for EMR–GGBS cement applications. The cement's early strength benefits from a higher curing temperature, and wetness promotes the development of late strength. The cement exhibits better performance if it is cured at 30 °C in a curing box for 24 h and then demoulded and sequentially cured in curing box at 30 °C. Acknowledgement The authors acknowledge the National High Technology Research and Development Program of China (2010AA065205) and the Key Project of Science and Technology of Hunan Province (2008FJ1013) for their financial support of this study. References [1] J. Wang, B. Peng, L. Chai, Q. Zhang, Q. Liu, Study on cementing material making with electrolytic manganese residue, 3rd International Symposium on HighTemperature Metallurgical Processing—TMS 2012 Annual Meeting and Exhibition, Minerals, Metals and Materials Society, 2012, pp. 461–471. [2] G.R. Lomboy, K. Wang, J. Quan, J. Zhuo, Properties of cementitious materials in their dry state and their influences on viscosity of the cementitious pastes, Powder Technology 229 (2012) 104–111. [3] A.K.H. Kwan, J.J. Chen, Adding fly ash microsphere to improve packing density, flowability and strength of cement paste, Powder Technology 234 (2013) 19–25. [4] K. Hagelstein, Globally sustainable manganese metal production and use, Journal of Environmental Management 90 (12) (2009) 3736–3740. [5] N. Duan, W. Fan, Z. Changbo, Analysis of pollution materials generated from electrolytic manganese industries, Resources, Conservation and Recycling 54 (8) (2010) 506–511. [6] Q. Jueshi, H. Pengkun, W. Zhi, Crystallization characteristic of glass-ceramic made from electrolytic manganese residue, Journal of Wuhan University of Technology —Materials Science Edition 27 (1) (2012) 45–49. [7] T.P. Li, H.L. Xie, H.X. Mei, Experimental study of calcinated electrolysis manganese residue and fly ash complex admixture, Bulletin of the Chinese Ceramic Society 26 (3) (2007) 567–592. [8] P. Hou, J. Qian, Z. Wang, Production of quasi-sulphoaluminate cementitious materials with electrolytic manganese residue, Cement and Concrete Composites 34 (2) (2012) 248–254. [9] G.J. Ke, Hydration mechanism of binding material made of burnt manganesecement, Journal of Central-South Institute of Technology 11 (2) (1997) 8–13. [10] Y. Feng, Y.X. Chen, F. Liu, Studies on replacement of gypsum by manganese slag as retarder in cement manufacture, Modern Chemical Industry 26 (2) (2006) 57–60. [11] B. Du, Z. Ru, C. Zhou, Analysis of physical–chemical characteristics for electrolytic manganese residues, in: J.H. Li, H.L. Hu (Eds.), 5th International Conference on Waste Management and Technology Beijing, PR China, 2010, pp. 505–508. [12] C. Tao, M. Li, Z. Liu, Composition and recovery method for electrolytic manganese residue, Journal of Central South University of Technology 16 (1) (2009) 309–312. [13] M. Sahmaran, H.A. Christianto, I.Q. Yaman, The effect of chemical admixtures and mineral additives on the properties of self-compacting mortars, Cement and Concrete Composites 28 (2006) 432–440. [14] S. Kumar, R. Kumar, B. A., 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 and Concrete Composites 30 (2008) 679–685. [15] J. Pourchez, Current understanding of cellulose ethers impact on the hydration of C3A and C3A-sulphate systems, Cement and Concrete Research 39 (8) (2009) 664–669. [16] S. Aydin, B. Baradan, Mechanical and microstructural properties of heat cured alkali-activated slag mortars, Materials and Design 35 (2012) 374–383. [17] N. Bhanumathidas, N. Kalidas, Dual role of gypsum: set retarder and strength accelerator, Indian Concrete Journal 78 (3) (2004) 170–173.
Compressive strength/MPa
1d
3d
7d
28 d
1d
3d
7d
28 d
2.59 6.44 – –
4.0 7.34 3.22 3.62
7.79 8.0 – –
8.35 8.66 4.37 7.52
3.2 8.7 – –
19 25.5 13.2 18.4
35.9 35.2 – –
45 47 26.8 43.7
[18] I.B. Celik, The effects of particle size distribution and surface area upon cement strength development, Powder Technology 188 (3) (2009) 272–276. [19] H. Binici, O. Aksogan, I.H. Cagatay, M. Tokyay, E. Emsen, The effect of particle size distribution on the properties of blended cements incorporating GGBFS and natural pozzolan (NP), Powder Technology 177 (3) (2007) 140–147. [20] S. Aydin, Ç. Karatay, B. Baradan, The effect of grinding process on mechanical properties and alkali-silica reaction resistance of fly ash incorporated cement mortars, Powder Technology 197 (1–2) (2010) 68–72. [21] Y.M. Zhang, T.J. Napier-Munn, Effects of particle size distribution, surface area and chemical composition on Portland cement strength, Powder Technology 83 (1995) 245–252. [22] M. Oner, K. Erdogdu, A. Gunlu, Effect of components fineness on strength of blast furnace slag cement, Cement and Concrete Research 33 (2001) 463–469. [23] J.P. Bigas, J.L. Gallias, Single-drop agglomeration of fine mineral admixtures for concrete and water requirement of pastes, Powder Technology 130 (1–3) (2003) 110–115. [24] A. Carpinteri, R. Brighenti, Fracture behaviour of plain and fiber-reinforced concrete with different water content under mixed mode loading, Materials and Design 31 (4) (2010) 2032–2042. [25] M. Nematzadeh, M. Naghipour, Compressing fresh concrete technique and the effect of excess water content on physical–mechanical properties of compressed concrete, Materials and Design 37 (2012) 256–267. [26] H. Zhao, W. Sun, X. Wu, B. Gao, Effect of initial water-curing period and curing condition on the properties of self-compacting concrete, Materials and Design 35 (2012) 194–200. [27] NCSTC, GB/T18046-2008 Ground Granulated Blast Furnace Slag Used for Cement and Concrete, China Standards Press, Bei Jing, 2008. [28] ISO 679, Methods of Testing Cements—Determination of Strength, 1989. [29] ISO 9597, Cement-Test Methods—Determination of Setting Time and Soundness, 2008. [30] NCSTC, GB175-2007 Common Portland Cement, China Standards Press, Bei Jing, 2007.
Jia Wang, born in 1982, received his B.S. degree in 2004 and an M.S. degree in 2007 in environmental engineering from Central South University (CSU), Changsha, China. He is now a Ph.D. candidate in the School of Metallurgical Science and Engineering of CSU, majoring in metallurgical environmental engineering. He has been actively involved in the recycling and utilisation of industrial and municipal solid waste, the preparation of photocatalysis antibacterial materials, smelting and environmental protection process design. He has published 8 papers as the first author, holds 4 patents and is a nationally registered environmental protection engineer.
Bing Peng was born in 1956. After receiving his Ph.D. degree in metallurgical engineering from CSU, he joined the faculty of the Department of Environmental Engineering of CSU, where he continues as professor, doctoral tutor and vice director. His major research interests have been directed towards the cleaning of production, environment protection, recycling and utilisation of solid waste in smelting plants. He has published more than 130 papers, applied for 26 patents and is a well-known expert in this field.
Liyuan Chai was born in 1966. After receiving his Ph.D. degree in metallurgical engineering from CSU, he joined the faculty in the School of Metallurgical Science and Engineering of CSU, where he continues as professor, doctoral tutor, academic leader and vice president. His major research interests have been the treatment, recycling and utilisation of pollutants produced in heavy metal smelting plants. He has published more than 200 papers, applied for 38 patents and is a famous expert in this field.
18
J. Wang et al. / Powder Technology 241 (2013) 12–18 Qiang Zhang was born in 1982 and received his M.S. degree in 2011 in environmental engineering from CSU. He is now a Ph.D. candidate in the Chinese Academy of Sciences, majoring in environmental engineering. He has been actively involved in the utilisation of industrial solid waste to prepare cement. He has published 2 papers as the first author and holds 2 patents.
Qin Liu was born in 1989 and received her B.S. degree in 2010 in environmental engineering from CSU. She is now an M.S. candidate in the Environmental Engineering Research Institute of CSU. She has been actively involved in the preparation of photocatalysis cementitious materials. She has published 1 paper as the first author.