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Preparation of calcium sulfoaluminate-belite cement from marble sludge waste
Construction and Building Materials 113 (2016) 764–772
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Preparation of calcium sulfoaluminate-belite cement from marble sludge waste E.A. El-Alfi, R.A. Gado ⇑ National Research Centre, Ceramics and Building Materials Department, 12311 Dokki, Cairo, Egypt
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
The recycling of waste material was
In this study, the feasibility of recycling marble sludge waste in the production of calcium sulfoaluminate-belite cement was investigated. 1: C4A3Š 2: β-C2S
1
3: CH 4: CaSO4 5: SiO2
2 1
1
1 1 2
1250 °C 1
1
Intensity (a.u)
successfully carried out leading to the production of less CO2 emission cement known as sulfoaluminatebelite cement. The influences of the cement raw mix composition and the different burning temperature were investigated to evaluate the reuse feasibility of marble sludge waste material in cement production. Calcium sulfoaluminate–belite cement, environmentally cement, can be produced by raw mix contains in weight percent 25% kaolin, 20% gypsum and 55% marble sludge waste at firing temperature 1200 °C.
1200 °C
2 1 2
1
1
2
1 2
3
5
1
10
20
4
13 2
3
30
1150 °C 1
2
40
1
50
2-Theta-scale
a r t i c l e
i n f o
Article history: Received 12 November 2015 Received in revised form 7 March 2016 Accepted 20 March 2016
Keywords: Marble sludge waste Environmentally cement Low-energy cement Sulfoaluminate–belite cement Ettringite
a b s t r a c t Marble sludge waste was used as a major cement raw material in sintering sulfoaluminate cement clinker successfully in the laboratory. The influences of raw mix composition as well as different burning temperatures were investigated. Starting materials and prepared cement were characterized through different techniques including; Fourier transform infrared spectroscopy (FTIR); X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that calcium sulfoaluminate–belite cement can be produced by burning a raw mixture contains in weight percent (25% kaolin, 20% gypsum and 55% marble sludge waste) at firing temperature ranging between 1200 and 1250 °C. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Abbreviations: C, CaO; S, SiO2; Š, SO3; A, Al2O3; F, Fe2O3; H, H2O. ⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (R.A. Gado). http://dx.doi.org/10.1016/j.conbuildmat.2016.03.103 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
Calcium sulfoaluminate–belite (CSAB) cement is promoted as a sustainable alternative to Portland cement (PC) because of lower energy consumption as well as reduction in CO2 emission during
E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
production. The calcium sulfoaluminate–belite cement phases can form and are stable at a temperature of approximately 1250 °C, which is lower than the temperature used for Portland cement production. Further, calcium sulfoaluminate–belite clinker is more friable and soft than Portland cement clinker, which reduces the energy needed for grinding process [1]. Calcium sulfoaluminate– belite cement principally utilizes Ye’elimite phase (C4A3Š), instead of tricalcium silicate (Alite, C3S) phase, as the primary early-age strength gaining phase and utilizes dicalcium silicate (Belite, b-C2S) phase to develop additional long-term strength. Ye’elimite phase (C4A3Š) has lower calcium oxide content than Portland cement phases, making it an attractive option for developing sustainable cement product [2]. Calcium sulfoaluminate– belite cement has shown rapid setting, high early strength, and shrinkage compensating properties due to the fast reacting of Ye’elimite phase (C4A3Š) and the expansive nature of ettringite [3]. In field practices, this kind of cement have been used mainly in precast concrete applications in cold environments and have shown good dimensional stability, low permeability, low alkalinity, good durability, and comparable compressive strength to Portland cement [4–7]. Raw mixes for calcium sulfoaluminate cement differ from those for Portland cement in that they contain a significant amount of sulfate. Therefore, the reactions and products are quite different from those normally found in Portland cement production [8]. The raw mix composition of this cement can be based on conventional raw materials (limestone, clay, bauxite and iron ores) but industrial by-products or wastes can be used as well [9,10] (for example fly ash, pyrite ash, galvanic sludge, metallurgical slags, phosphogypsum, etc. . ..). Furthermore, this new class of cement can be produced in existing installations using a conventional cement kiln system. Several types of industrial wastes can be used as raw materials to obtain the calcium sulfoaluminate (CSA) cement clinker. Wu et al. obtained a clinker of this cement from a mixture of municipal solid incineration wastes-limestone-bauxite-gypsum at 1250 °C, reaching more than 73.2 Mpa after 28 days of curing [11]. Li et al. [12] obtained cement by firing a mixture of fly ash, bauxite and calcium carbonate at 1300 °C. Li et al. [13] obtained the calcium sulfoaluminate (CSA) cement at a temperature as low as 1150 °C using fly ash and sludge as raw materials. Singh et al. [14,15] reported the formation of a ferric calcium sulfoaluminate cement from a mixture of calcium oxide, red mud and bauxite at 1250 °C, as well as using waste from a fertilizer industry, bauxite and iron mineral ore at 1250 °C. In general, these works showed the feasibility to obtain calcium sulfoaluminate (CSA) cement using many industrial wastes as raw materials. However, there is a great variety of industrial wastes that have the potential to be used as a source of the main components to fabricate this kind of cement [16]. Marble processing lines in the Egyptian factories produce huge amounts of marble wastes either solid or liquid (slurry, resulted from sawing the blocks to slabs and grinding and polishing processes). The random disposal of these wastes, estimated as one million tons yearly, in the areas near the factories (irrespective of their possible economic values) and with the increasing production cause severe environmental problems, such as land degradation, increase wastage of minerals, air pollution, water pollution, damage to flora and fauna as well as human resources displacement [17]. Recycling process of industrial by-products and waste materials coming from industrial manufacture activates have become an urgent problem for the near future. In the light of environmental protection standards which aiming to limit the accumulated of the industrial dump, the development of recycling techniques capable of exploiting the industrial wastes into new marketable products acquires an increasing importance for the industrial and environmental sectors.
765
In this study, the feasibility of reusing the marble sludge waste as starting materials in the preparation of sulfoaluminate-belite cement was evaluated. This work shows the feasibility of producing calcium sulfoaluminate-belite cement from a mixture of kaolin; marble sludge waste as a source of calcium carbonate (CaCO3) and gypsum (CaSO41/2H2O). The sintering temperature in the laboratory muffle furnace could be controlled by the temperature of 1150, 1200 and 1250 °C. The cement quality was investigated to evaluate the reuse feasibility of marble sludge waste material in cement production. 2. Materials and methods 2.1. Starting raw materials The raw materials used in this study were kaolin, marble sludge and gypsum. Kaolin material was supplied from the general company for ceramic & porcelain products (Sheeni); Marble sludge was collected from Shaq El Thoaban marble industrial zone; Egypt. The surface area of marble sludge waste was determined by using the method of N2 adsorption (BET) using automated gas sorption; model NOVA, Version 1.12 from the quantachrome. The measured surface area and specific gravity of marble sludge waste were 0.6695 m2/g and 2.67 respectively. Gypsum (hemihydrate, CaSO4 1/2H2O) was supplied from Gypsina company; Egypt. The main oxide compositions of starting raw materials chemically analyzed by X-ray fluorescence technique (Wavelength dispersive XRF; PANalytical) were reported in Table 1. The mineral composition phases of starting raw materials were identified by X-ray diffraction analysis technique using (XRD; X’Pert-PANalytical) diffractometer with Ni filter, with Cu Ka (k = 1.5406 Å) radiation at 40 kV, 30 mA at a scanning speed of 0.020°/s over the 2h range of 4–60°. FTIR spectra of starting raw materials were acquired using a JASCO FT/IR-6100. The IR spectra were recorded between 400 and 4000 cm1 with a resolution of 4 cm1 at room temperature. For preparing cement mixes, appropriate amounts of starting raw materials in predetermined wt.% proportions, as shown in Table 2, were taken and ball milled for 30 min using a top planetary ball mill (Fritsch planetary mono mill Pulverisette 6) for homogenization. The resultant powder samples with chemical oxides composition based on the XRF data of started materials, as shown in Table 3, were made into a thick paste using a low amount of water (5%) and moulded under a pressure of 50 Mpa into 5 5 cm cubes [18]. The cubes were dried overnight in a hot air oven at 100 °C and then fired in an electric laboratory muffle furnace (Lenton) at different firing temperatures (1150, 1200 and 1250 °C by a heating rate of 10 °C/ min) with sintering duration at the maximum temperature for 1 h in furnace for all cement clinker mixes. The theoretically expected calcium sulfoaluminate-belite cement phases were determined by adapting the Bogue method, shown in Table 4. The Bogue method is a technique used in the cement industry to estimate phase composition in Portland cement clinker from its chemical oxide composition. It was adapted for calcium sulfoaluminate-belite cement by assuming a phase assemblage of C4AF, C4A3Š, C2S, CŠ and C, as shown in the following equations (1)–(5) [1].
%C4 AF ¼ 3:043ð% Fe2 O3 Þ
ð1Þ
¼ 1:995ð%Al2 O3 Þ 1:273ð% Fe2 O3 Þ %C4 A3 S
ð2Þ
%C2 S ¼ 2:867ð% SiO2 Þ
ð3Þ
¼ 1:700ð% SO3 Þ 0:445ð% Al2 O3 Þ þ 0:284ð% Fe2 O3 Þ %CS
ð4Þ
%C ¼ 1:000ð% CaOÞ 1:867ð% SiO2 Þ 1:054ð% Fe2 O3 Þ 0:550ð% Al2 O3 Þ 0:700ð% SO3 Þ
ð5Þ
The synthesized clinkers were ground using a top planetary ball mill (Fritsch planetary mono mill Pulverisette 6) for 20 min to reach a Blaine fineness of 4500 (±100) m2/kg [19]. All the cement samples were submitted to characterization by different techniques in order to assess the reactants conversion and evaluate the phases formed on clinkering process at different temperatures [20].
3. Results and discussions 3.1. Characterization of starting raw materials The results of X-ray diffraction (XRD) analysis of supplied starting raw materials as shown in Fig. 1 indicates that the kaolin shows the typical diffraction patterns of a well-crystallized layer lattice mineral of kaolinite with muscovite impurities as Illite mineral.
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Table 1 Chemical oxide composition of starting materials, wt.%.
Kaolin Gypsum Marble sludge
Al2O3
Fe2O3
CaO
Na2O
K2O
TiO2
MnO
MgO
SO3
BaO
LOIa
46.68 0.46 0.150
35.75 0.120 0.010
1.49 0.050 0.040
0.10 37.61 55.32
0.05 0.030 0.700
2.96 0.00 0.010
0.07 0.00 0.010
0.01 0.00 0.010
0.19 0.120 0.110
0.03 53.66 0.130
0.02 0.00 0.00
12.18 7.76 43.30
Loss on Ignition at 950 °C.
Kaolin
Gypsum
Marble sludge waste
A B C
25 20 15
20 20 20
55 60 65
Characteristic peaks for kaolinite (2h = 12.34, 20.34 and 24.87°), while peaks assigned to Illite mineral (2h = 9.11, 17.50 and 26.90°). The X-ray diffraction pattern of marble sludge waste as seen in Fig. 1 indicates that the marble sludge waste sample was mainly composed of calcite mineral (CaCO3) as confirmed by XRF analysis of marble sludge in Table 1. The XRD pattern also indicates that the presence of pure crystalline phase of gypsum (calcium sulfate hemihydrate, CaSO41/2H2O) without any impurity phases [21]. Infrared spectra (FTIR) of the starting raw materials (kaolin, marble sludge waste and gypsum) are given in Fig. 2. A typical spectrum of kaolin show bands, at 3640, 3455, 1610, 1035 and 700 cm1, the band observed at around 3640 cm1 has been ascribed to the inner hydroxyl while the bands observed at around the other characteristic bands in this region are generally ascribed to vibrations of the external hydroxyl. The absorption bands observed at 3455 cm1 and 1610 cm1 could be assigned to the OH vibrational mode of the hydroxyl molecule in water, which is observed in almost all the natural hydrous silicates. In the 1035 cm1 and 476 cm1 regions, main functional groups were Si–O and Al–OH. The doublet at 700 cm1 is due to Si–O–Si internal tetrahedral bridging bonds in SiO2 and OH deformation band [22]. The infrared spectrum of the marble sludge waste was characterized by three prominent absorption bands for calcite mineral at 1400, 850 and 700 cm1 and two minor peaks at 2500 and 2000 cm1, as shown in Fig. 2. The major absorption bands of carbonate spectra in the wavelength region have been attributed to the fundamental vibrations of the carbonate radical, CO-2 3 , and various bands have been assigned to correspond to the vibrations of the carbon and oxygen atoms along a crystallographic axial direction [23,24]. The broad bands at 3450 and 1610 cm1 corresponding to the vibrational mode of the hydroxyl molecule in water as well as peaks in range 2920 and 2850 cm1, which are attributed to the (tCH2) antisymmetric stretching vibration and symmetric stretching vibration (tCH2) of organic impurities in marble sludge waste [22]. The FTIR spectrum of the gypsum was shown in Fig. 2. There are main peaks in the gypsum FTIR spectrum for O–H bending vibration modes in the range 3600–3000 cm1, the in-plane O–H O
Phases
Phase calculated (wt.%) A
B
C
C4A3Š C2S C4AF CŠ C
22.30 43.60 1.58 18.62 3.76
18.05 35.44 1.31 19.85 14.41
13.71 27.11 1.03 21.13 25.31
K: Kaolin I: Illite C: Calcite G: Gypsum G G
G
G
GG
G
Gypsum
C
C K
I
C
C
C Marble sludge
K
I
10
20
I I
30
K, I
Mixes
Table 4 The theoretically expected calcium sulfoaluminate-belite cement phases adapting by the Bogue method [1].
K, I
Table 2 Prepared cement mixes from starting raw materials, wt.%.
Intensity (a.u)
a
SiO2
K
K
40
Kaolin
50
60
2-Theta-scale Fig. 1. X-ray diffraction pattern of starting raw materials.
bending vibrations in the range 1620 cml, and the bending vibration of the SO4 tetrahedron in the range 660–550 cml as well as S–O stretching vibration for sulfate group in the range 1140–1080 [25,26]. 3.2. Characterization of prepared cement samples 3.2.1. Fourier transform infrared spectroscopy (FTIR) The FTIR spectra of prepared cement samples (A, B and C) at different burning temperatures (1150, 1200 and 1250 °C) are illustrated in Figs. 3–5, respectively. Each prepared cement sample has
Table 3 Chemical oxide composition of prepared cement mixes.
a
Mixes/oxides
SiO2
Al2O3
Fe2O3
CaO
Na2O
K2O
TiO2
P2O3
MgO
SO3
F
LOIa
A B C
11.84 9.51 7.19
8.96 7.18 5.39
0.40 0.33 0.25
37.97 40.73 43.49
0.40 0.43 0.46
0.74 0.59 0.45
0.02 0.02 0.01
0.07 0.06 0.06
0.13 0.120 0.12
10.81 10.81 10.81
0.03 0.02 0.02
28.41 29.96 31.52
Loss on Ignition at 950 °C.
767
688 cm-1 520 cm-1
1417 cm-1
1157 cm-1 1122 cm-1 995-836 cm-1
1617 cm-1
2360 cm-1 3415 cm-1
4000
3000
2500
2000
1500
1000
690 cm-1 520 cm-1 690 cm-1 520 cm-1 414 cm-1
1160 cm-1 1122 cm-1 920-835 cm-1 1160 cm-1 1122 cm-1 925-835 cm-1
1617 cm-1
1617 cm-1 1417 cm-1
2360 cm-1
3420 cm-1
3500
1417 cm-1
2360 cm
-1
1150°C
3420 cm-1
Transmittance, T%
1200°C
500
Wavenumber, cm-1 Fig. 3. FTIR spectrum of cement samples (A) burned at different temperatures.
its own unique infrared spectrum bands. The infrared spectra of all prepared cement samples, shows the main absorption band and the identification of the functional group signals for calcium sulfoaluminate-belite cement which can be described as follow: ye’elimite phase (C4A3Š) has two absorption bands due to vibrational modes of sulfate [SO4]2 groups at 1100–1200 cm1 and a very intense absorption band due to silicate groups near to
2500
2000
1500
921-833 cm
640 cm-1 505 cm-1 650 cm-1 490 cm-1
1118 cm-1 1000 cm-1 880 cm-1 -1
1000
630 cm 490 cm-1
1157-1122 cm-1
1630,1615 cm-1 1417cm-1
2360 cm-1
3000
-1
3500
925-833 cm
4000
-1
1150°C
Fig. 2. FTIR spectrum of starting raw materials.
1250°C
1630,1615 cm-1 1417cm-1
3415 cm-1 3640 cm-1 3415 cm-1
Transmittance, T%
476 cm
500
1160-1122 cm-1
1000
675cm-1 -1
700 cm-1
1500
Wavenumber, cm-1
1630,1615 cm-1 1417cm-1
2000
1200°C
2360 cm-1
2500
2360 cm-1
660 cm-1-1 550 cm 850 cm
1400 cm 1035 cm
3000
700 cm-1
-1
1140 cm-1
1620 cm-1 -1
2500 cm-1
2920 cm-1 2850 cm-1
-1
3500
1250°C
3640 cm-1 3415 cm-1
4000
1610 cm-1
Kaolin
3455 cm-1
3455 cm-1
Marble sludge
3640 cm-1
Transmittance, T%
3600 cm-1 3455 cm-1
Gypsum
3000 cm-1
E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
500
Wavenumber, cm-1 Fig. 4. FTIR spectrum of cement samples (B) burned at different temperatures.
800–1000 cm1, the third band at 620 cm1 region is due to vibrational modes of [AlO4]5 tetrahedral as well as belite phase (b-C2S) the another calcium silicate phase, exhibits strong bands in the area 1000–800 cm1 with maximums at 990 and 840 cm1 due the stretching Si–O bond of the silicon tetrahedron and the bending vibration absorption band appear at lower frequencies 520 cm1 and a shoulder at 538 cm1. A broadened signal appears between 900 and 800 cm1, centered at 857 cm1. This feature is strongly asymmetrical which probably due to the result of the convolution of the two bands of belite phase (b-C2S), as a consequence of lower crystal perfection caused mainly by the presence of foreign ions in the lattice or because of the small particle size of minerals of calcium sulfoaluminate-belite cement. But it is also possible to highlight the presence of the three anhydrite bands at 677, 615, and 600 cm1, respectively [27]. Also, the presence of calcite (CaCO3) impurities was identified with IR absorption bands at 874 and 1424 cm1 [28]. In general, from the results of FTIR spectra of prepared cement samples (Figs. 3–5), as decreasing of kaolin percent in samples from A to C, the following differential notes are observed i) the intensity of calcium sulfoaluminate-belite cement main bands that appear in the range 400–1200 cm1 were remarkably decreased. ii) The intensity of the bands at 3640 cm1 and 1630 cm1 were increases indicating liberation of more Ca(OH)2 as a result of free unreacted lime hydration. iii) The strong asymmetric stretching Si–O band at 925 cm1 is decreased to low intensity indicates the low formation of belite phase (b-C2S). iv) the carbonate bands at 2360, 1420 and 875 cm1 are observed mainly due to the reactions of atmospheric CO2 with calcium hydroxide [29]. Furthermore, unreacted silica gives rise to its absorption band at 925 (Si–O–Si asymmetric stretching vibration) and unreacted lime
1
5: SiO2
2
2500
Wavenumber,
1250°C
1
Intensity (a.u)
675 cm-1
943-833 cm
2 1
12
2
4 5 3 13 2
12
1
1200°C
1 2
1000
3
675 cm
-1
925-835 cm
-1
1160-1122 cm-1
1427 cm
1500
2
-1
1159-1122 cm-1
1637,1617 cm-1 1469 cm-1 1630,1617 cm-1
2000
1
1
1
10
500
20
30
Fig. 5. FTIR spectrum of cement samples (C) burned at different temperatures.
gives rise to its absorption bands at 3640, 1630 and 1450– 1500 cm1 (vibrations of OH group and Ca–O stretching vibration). Calcite arising from partial carbonation of unreacted lime gives its absorption bands at 2360, 1420, 840, and 700 cm1. The belite phase (b-C2S) gives rise to the following absorption bands: three maxima at 950, and 840 cm1 (Si–O asymmetric stretching modes), medium intensity band at 430 cm1 (Si–O bending mode), and a strong band at 530 cm1 (Si–O–Si out of plane bending mode) [30]. On the other hand, as clinker temperatures increase from 1150 to 1250 °C leads to i) shifting the main bands of calcium sulfoaluminate-belite cement that appear in the range of 400–1200 cm1 to a little higher frequencies as a result of more polymerization [31]; ii) decreasing in the intensity of the bands corresponding to Portlandite Ca (OH)2 at 3630 cm1 and 1630 cm1. The band assignments are in good agreement with those reported in the previous studies [27–31]. 3.2.2. X-ray diffraction analysis (XRD) The XRD pattern of prepared cement samples (A, B and C) were shown in Figs. 6–8, respectively. The XRD pattern of prepared cement sample (A) as illustrated in Fig. 6, shows that the ye’elimite phase (C4A3Š, 2h = 23.66, 33.82 and 41.69°) was the major phase in the clinker product with belite phase (b-C2S, 2h = 32.16, 34.20 and 41.17°), unreacted silica (SiO2, 2h = 20.86, 26.64 and 50.15°) as minor phases in clinker samples burned at 1150 °C. The appearance of the main diffraction intensity for the belite phase (b-C2S, 2h = 32.16°) in the cement sample (A) which fired at 1150 °C confirming that the formation of this phase starts at lower firing temperature within the range of 1000 °C [32]. On the contrary, the intensity of the ye’elimite phase (C4A3Š) enhanced as firing temperature increasing to 1250 °C. XRD pattern shows that the characteristic peak of unreacted silica (SiO2) is gradually
40
1150°C
1
50
60
2-Theta-scale
cm-1
Fig. 6. XRD pattern of cement samples (A) at different temperatures.
1: C4A3Š 2: β-C2S 3: CH 4: CaSO4 5: SiO2
2 4
1 4
2
1 2
2, 3 4
3 5
1250°C
2
1 2
Intensity (a.u)
3000
1 1
-1
2360 cm-1 2360 cm-1 3640 cm-1 3415 cm-1
1150°C
3500
675 cm-1
3640 cm-1 3415 cm-1
1200°C
4000
2: β-C2S 3: CH 4: CaSO4
1
3640 cm-1 3419 cm-1
Transmittance, T%
1250°C
1: C4A3Š
1120 cm-1 1000 cm-1 880 cm-1
1637,1617 cm-1 1427 cm-1
E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
2360 cm-1
768
2, 3
3 45
3
2
3
° 4 1200 C
12
2 2, 3 14
4
3
3 1
3
5
5
10
20
30
2 1
40
24
1150°C 5
50
60
2-Theta-scale Fig. 7. XRD pattern of cement samples (B) at different temperatures.
E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
1: C4A3Š 2: β-C2S 4
3: CH 4: CaSO4 5: SiO2
1
2, 3 4, 2 4
1250°C
12
Intensity (a.u)
2, 3
3
1
4, 2
4
4
3
1 2
2
4 1200°C
4, 2
1 4
2, 3
3 3
1
2 24 1150°C
4
10
20
30
40
50
60
769
temperature. A decrease in the intensity of the following phases C4A3Š and b-C2S content was observed with an increase in the percent of CaO sourced from marble sludge waste as well as decreasing in kaolin percent. Thus, the crystalline phase C4A3Š in the doped samples became less abundant compared to the cement samples A and B burned at the sample temperatures. The anhydrite calcium sulfate (CaSO4) was detected in cement samples B and C until burning temperature at 1250 °C, which indicated that the reaction to form C4A3Š was still not complete at these high temperatures, which mainly due to a deficiency in acidic oxides content in their raw mix. Finally, the X-ray diffraction analysis results of different cement samples (A, B and C) in this study indicates that the characteristic peaks of the ye’elimite phase (C4A3Š) are gradually weakened in the cement samples A, B and C, respectively. This is mainly due to the reduction in kaolin percent in their mixes. According to Xray diffraction analysis results, the optimum burning temperature for the formation of calcium sulfoaluminate-belite cement was found to be (1250 °C) for the raw mix sample containing in weight percent 25% kaolin, 20% gypsum and 55% marble sludge waste. The formation of the ye’elimite phase (C4A3Š) in this study is in agreement with previous reports which indicated the formation of the ye’elimite phase at 1200–1250 °C by using other industrial byproduct wastes [33]. From the above experiments, it was shown that the calcium sulfoaluminate-belite cement could be synthesized between 1200 °C and 1250 °C. The high amounts of C4A3Š and b-C2S in cement indicates the high durability and rapid hardening of calcium sulfoaluminate cement [34]. The XRD results confirm all results obtain from different used techniques in this study.
2-Theta-scale 4. Characterization of hardened cement samples Fig. 8. XRD pattern of cement samples (C) at different temperatures.
weakened in prepared cement samples as the firing temperature increases, which indicates the more consuming of acidic oxides from raw kaolin for more formation of calcium sulfoaluminatebelite cement. The XRD show that the appearance of Portlandite (CH, 2h = 18.04, 28.69 and 34.11°) in the sample (A) burned at 1150 °C which mainly due to the presence of uncombined calcium oxide in the sample. The XRD pattern of prepared cement sample (B) fired at different temperatures (1150, 1200 and 1250 °C) are shown in Fig. 7. The data show that, the appearance of Portlandite (CH, 2h = 18.04, 28.69 and 34.11°), unreacted silica (SiO2, 2h = 20.86, 26.64 and 50.15°) and anhydrite calcium sulfate (CaSO4, 2h = 25.44, 31.34 and 40.79°) with belite (b-C2S) and ye’elimite phase (C4A3Š). It can be also noticed that the cement sample (B) fired at 1150 and 1250 °C shows the higher intensity of Portlandite and anhydrite calcium sulfate (CaSO4) than those fired at 1200 °C. This probably due to decomposition of calcium sulfoaluminate phases at a higher temperature (1250 °C) and incomplete reaction at 1150 °C which reflects on calcium sulfoaluminate-belite cement main phases as illustrated in Fig. 7. The XRD results of the cement sample (B) show that the optimum temperature was 1200 °C due to less Portlandite (CH) phase peaks as well as less anhydrite calcium sulfate (CaSO4) phase peaks. The XRD pattern of the cement sample (C) burned at different firing temperatures (1150, 1200 and 1250 °C) are shown in Fig. 8. The results of the cement sample (C) fired at 1150 °C show the essentially following mineralogical composition phases C4A3Š, b-C2S, CH and anhydrite calcium sulfate (CaSO4). It can be also noticed that cement sample (C) fired at 1250 °C shows the higher intensity of Portlandite phase (CH) and anhydrite calcium sulfate phase (CaSO4) as well as the lower intensity of C4A3Š and b-C2S phases than cement samples (B and C) fired at the same
The specimens of prepared sulfoaluminate-belite cement paste (w/c ratio = 0.50) were cured for 28 days, then they were characterized by determining their physico-mechanical properties [35,36]. The results were based on the average of three cube samples. The physico-mechanical properties of the hardened cement specimens cured at room temperature are illustrated in Table 5. As indicated from results, the highest compressive strength values (within the range of 36 Mpa) were recorded to cement samples (A) which burned at 1200 and 1250 °C, respectively. It was observed that hardened cubes of cement samples (C) which burned at 1200 and 1250 °C respectively were self-cracked and deteriorated during the curing period. The dimensional instability mainly has been linked to the high free lime content in hardened samples. The large amounts of free lime may cause expansion, strength loss and crack of the hardened paste, due to a delayed hydration of free calcium oxide (hard burned) to produce calcium hydroxide, which takes place topo-chemically and usually associated with an increase in matrix volume. Thus, excessive amounts of free calcium oxide in clinker must be avoided [37]. After the mechanical testing, a fractured hardened paste of highly compressive strength sample (A-1200 °C) was chosen, crushed by hand with a metallic mortar. The ground powder was characterized by different used techniques as well as morphology investigation by scanning electron microscope (SEM) attached with EDX Unit (Energy dispersive X-ray analyses), with accelerating voltage 30 K.V., (JEOL Ltd., Japan). 4.1. X-ray diffraction analysis (XRD) The XRD pattern of hardened sample cured for 28 days in comparison with its anhydrous sample (A-1200 °C) is illustrated in Fig. 9. The main hydration products were ettringite phase (C3A3CŠ32H2O, 2h = 11.49, 19.92 and 28.91°), low sulfate calcium sulfoaluminate hydrate (monosulfate C3ACŠ12H2O, 2h = 9.92,
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Table 5 The physico-mechanical properties of the hardened cement samples cured up to 28 days. Properties
Mixes A
Bulk density [g/cm3] Apparent porosity [%] Compressive strength [Mpa]
B 1200 °C
1250 °C
1150 °C
1200 °C
1250 °C
1150 °C
1200 °C
1250 °C
1.88 16.70 27
1.90 15.20 36
1.90 14.85 35
1.83 19.54 15.7
1.84 17.95 18.45
1.86 17.03 22.11
1.80 24.53 9.86
– – –
– – –
Hydrated sample (Age : 28 Days) 3: Ettringite 4: Monosulphate 5: CSH 4, 5 3 4 6: CH 43 3
3
6 6
35
6 4 3
5 43
Intensity (a.u)
1: C4A3Š
1
2: β-C2S
C
1150 °C
Dry cement (A-1200°C) 2
12
Spectroscopic methods are commonly used to study the chemistry of cement hydration. The chemical environment of the vibrations band of the dry cement bonds changes as hydration occurs. The sample will absorb some of the light at wavelengths that are characteristic of its chemical composition. In the present work, the hydration of calcium sulfoaluminate-belite cement has been observed by means of infrared spectroscopy. Infrared spectra (FTIR) of the hydrated sample in a comparison with its anhydrous sample are given in Fig. 10. This spectrum corresponds to the difference between that acquired after 28 days of hydration, and the spectrum of dry cement. From the results in Fig. 10, we observe significant changes in the spectrum of dry cement sample due to hydration process. As hydration progresses at 28 days, there is a broad feature forming with its center at 3450 and 1630 cm1 caused by the bending vibration of irregularly bound water [45–47]. The broadband at 3450 cm1 is intensified with hydration, indicating that the increase of hydrated products associated with water. The peaks at 3640 and 1630 cm1 correspond to the inner hydroxyl group in Portlandite Ca (OH)2 which is formed as silicate phases in the cement dissolve
1 2
Hydrated sample (Age : 28 Days)
20
30
40
50
2-Theta-scale
Transmittance, T%
19.90 and 22.28°) calcium silicate hydrate phase (CSH, 2h = 28.58, 29.06 and 31.58°) and Portlandite Ca (OH)2 (CH, 2h = 18.10, 28.72 and 34.17°). The ettringite deficiency in the hardened sample mainly due to the absence of additional gypsum added upon hydration process. The ye’elimite phase is used or activated with an addition of calcium sulfate, either as gypsum or anhydrite [38]. Furthermore, it is possible to modify the hydration process of calcium sulfoaluminate cement not only by its composition but also by the selection of different quantities or sources of calcium sulfate [39]. Hence, the amount of added calcium sulfate strongly modifies the ettringite formation and the water demand to complete full hydration [40,41]. In addition, the amount of ettringite is affected by the reactivity of calcium sulfate (solubility and dissolution rate) at early ages [40]. Hence, the selection of the sulfate source is a key issue to achieve the desired properties. Furthermore, depending on the other phases present in calcium sulfoaluminate cement, other hydration products may occur such as CSH gels, stratlingite, katoite, monocarboaluminate or hydrogarnet [42–44]. Hence, further studies on the chemistry of hydration for prepared calcium sulfoaluminate-belite cement will be required.
3640 cm-1 3455-3420 cm-1
Fig. 9. XRD pattern of hardened cement sample (A).
1150 cm-1 995cm-1 875 cm-1
10
1630 cm-1 1420 cm-1
2360 cm-1
1
4.2. Fourier transform infrared spectroscopy (FTIR)
Dry cement (A-1200°C)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber, cm-1 Fig. 10. FTIR spectrum of hydrated cement sample (A) in comparison with its anhydrous sample burned at 1200 °C.
E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
for forming calcium silicate hydrate (CSH) phases upon hydration process. Characteristic sulfate absorption bands are found in the range 1150 cm1 due to the vibration of the SO2 4 group in sulfates [48]. The asymmetric stretching Si–O band is shifted to high frequencies centered at 995 cm1 with hydration indicates that the formation of calcium silicate hydrate (CSH) [49]. These diphump features are taken to reflect the dissolution of belite phase (b-C2S) and simultaneously the polymerization of silica [50–52] to form calcium silicate hydrate (CSH). The decrease and increase in intensities of the out-of-plane and in-plane Si-O bending vibrations are occurring in significant changes with hydration. The carbonates peaks at 2360, 1420 and 875 cm1 are observed due to the reactions of atmospheric CO2 with Portlandite Ca (OH)2 [39]. 4.3. Scanning electron microscopy (SEM)
771
phases in the voids after 28 days of hydration. The belite phase is observed to remain much less hydrated during this period. After 28 days of hydration, amounts of Portlandite Ca (OH)2 and calcium silicate hydrate (CSH) were observed on SEM micrographs, indicating b-C2S hydration has taken place which already confirmed from XRD results. It is expected that the ye’elimite phase (C4A3Š) would be completely hydrated much before 28 days of hydration. The combination of XRD and SEM analysis indicates that calcium sulfoaluminate phase hydrates produce ettringite phase (C3A3CŠ32H2O) as well as low sulfate calcium sulfoaluminate hydrate (monosulfate C3ACŠ12H2O) while belite (b-C2S) phase hydrates to produce the calcium silicate hydrate (CSH) that fills porosity of specimen, and results in a dense structure.
5. Conclusion
Scanning electron microscope was used to analyze the morphology of the fracture surface of the hardened sample specimens cured at 28 days. SEM investigations can help us to get a better understanding of the morphologies of the sample. The microstructural examinations of the phase distribution of the hardened sample specimens (A, w/c ratio = 0.50) are shown in Fig. 11. The selected micrographs of the fracture transversal section of hardened sample (A) after curing time show the presence of a large amount of short rod-like crystals in the hardening paste as illustrated in Fig. 11. EDX measurements data show the presence of Ca, S, O, Si, Al and this result combined with XRD measurements reveal that the ettringite phase (C3A3CŠ32H2O) presence in the hydrated sample as the main phase of hydration process [53]. The SEM micrograph shows the presence of sponge-like sulfoaluminate phases in the whole matrix and needle-like ettringite
In this study, the feasibility of recycling the marble sludge waste as starting materials in the production of calcium sulfoaluminate-belite cement was investigated. The prepared cement samples were subjected to furnace sintering at temperatures of 1150, 1200 and 1250 °C for the same holding time (1 h). Different techniques were performed for mineralogical examination of the obtained samples. The following conclusions were reached under the experimental observations of this study: 1. It is possible to recycle the marble sludge waste in the synthesis of calcium sulfoaluminate-belite cement. 2. Calcium sulfoaluminate–belite cement, environmentally cement, can be produced by raw mix contains in weight percent 25% kaolin, 20% gypsum and 55% marble sludge waste.
Fig. 11. SEM of hydrated cement sample (A) with EDX analysis.
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3. As the firing temperature of the prepared cement samples increases between 1150 and 1250 °C, the calcium sulfoaluminate-belite cement phases enhanced. 4. The prepared cement sample (A) gives the best burn ability with the maximum sulfoaluminate-belite phases at 1250 °C, as well as good mechanical properties upon hydration process than that other prepared cement samples (B and C).
Acknowledgments The authors would like to thanks, Dr. M. Rashwan for providing marble sludge waste material as well as their valuable help. The authors wish to gratefully acknowledge the help and support of National research centre (NRC) – Egypt; Science and Technology Development Fund (STDF) – Egypt; Institut Français d’Egypte (IFE) and Laboratoire national de métrologie et d’essais (LNE), France. References [1] Irvin A. Chen, Maria C.G. Juenger, Incorporation of coal combustion residuals into calcium sulfoaluminate-belite cement clinkers, Cement Concr. Compos. 34 (2012) 893–902. [2] Irvin A. Chen, Craig W. Hargis, Maria C.G. Juenger, Understanding expansion in calcium sulfoaluminate–belite cements, Cem. Concr. Res. 42 (2012) 51–60. [3] F.P. Glasser, L. Zhang, High-performance cement matrices based on calcium sulfoaluminate–belite compositions, Cem. Concr. Res. 31 (2001) 1881–1886. [4] L. Zhang, F.P. Glasser, New concretes based on calcium sulfoaluminate cement, in: R.K. Dhir, T.D. Dyer (Eds.), Modern Concrete Materials: Binders, Additions and Admixtures, Thomas Telford, London, 1999, pp. 261–274. [5] K. Quillin, Performance of belite–sulfoaluminate cements, Cem. Concr. Res. 31 (2001) 1341–1349. [6] V. Zivica, I. Janotka, Chemical resistance of sulfoaluminate belite cement based materials, Build. Res. J. 47 (1999) 117–134. [7] N. Sherman, J. Beretka, L. Santoro, G.L. Valenti, Long-term behaviour of hydraulic binders based on calcium sulfoaluminate and calcium sulfosilicate, Cem. Concr. Res. 25 (1995) 113–126. [8] Ivan Janotka, Udovit Krajei, Subhash C. Mojumdar, Performance of sulphoaluminate-belite cement with high C4A3Š content, in: Ceramics – Silikáty 51 (2) (2007) 74–81. [9] J. Berekta et al., Hydraulic behaviour of calcium sulfoaluminate-based cement derived from industrial process waste, Cem. Concr. Res. 26 (1993) 1673–1682. [10] S. Sahu, J. Majling, Preparation of sulfoaluminate belite cement from fly ash, Cem. Concr. Res. 24 (1994) 1065–1072. [11] K. Wu, H. Shi, X. Guo, Utilization of municipal solid waste incineration fly ash for sulfoaluminate cement clinker production, in: Waste Manage. 31 (9–10) (2011) 2001–2008. [12] J. Li, H. Ma, H. Zhao, Preparation of sulphoaluminate-alite composite mineralogical phase cement clinker from high alumina fly ash, Key Eng. Mater. 334–335 (2007) 421–424. [13] H. Li, D.K. Agrawal, J. Cheng, M.R. Silsbee, Microwave sintering of sulphoaluminate cement with utility wastes, Cem. Concr. Res. 31 (9) (2001) 1257–1261. [14] M. Singh, S.N. Upadhayay, P.M. Prasad, Preparation of iron rich cements using red mud, Cem. Concr. Res. 27 (7) (1997) 1037–1046. [15] M. Singh, P.C. Kapur, Pradip, Preparation of calcium sulphoaluminate cement using fertiliser plant wastes, in: J. Hazard. Mater. 157 (1) (2008) 106–113. [16] M. Gallardo, J.M. Almanza, D.A. Cortés, J.C. Escobedo, J.I. Escalante-García, Synthesis and mechanical properties of a calcium sulphoaluminate cement made of industrial wastes, in: Materiales de Construcción 64 (315) (2014). [17] A.O. Mashaly, B.N. Shalaby, M.A. El-Hefnawi, Characterization of the marble sludge of the Shaq El Thoaban Industrial Zone, Egypt and its compatibility for various recycling applications, Aust. J. Basic Appl. Sci. 6 (3) (2012) 153–161. [18] Maneesh Singh, P.C. Kapur, Pradip, Preparation of calcium sulphoaluminate cement using fertiliser plant wastes, in: J. Hazard. Mater. 157 (2008) 106–113. [19] Frank Bullerjahn, Dirk Schmitt, Mohsen Ben Haha, Effect of raw mix design and of clinkering process on the formation and mineralogical composition of (ternesite) belite calcium sulphoaluminate ferrite clinker, Cem. Concr. Res. 59 (2014) 87–95. [20] Milena Marroccoli, Maria Lucia Pace, Antonio Telesca, Gian Lorenzo Valenti, Synthesis of calcium sulfoaluminate cements from Al2O3-rich by-products from aluminium manufacture, 2010. ISBN: 9781450714907. [21] Joint Commission on Powder Diffraction Standards – International Centre for Diffraction Data, http://www.icdd.com, 2003. [22] M.F. Zawrah, R.M. Khattab, E.M. Saad, R.A. Gado, Effect of surfactant types and their concentration on the structural characteristics of nanoclay, in: Spectrochim. Acta Part A: Mol. Biomol. Spectrosc. 122 (2014) 616–623.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Preparation of calcium sulfoaluminate-belite cement from marble sludge waste E.A. El-Alfi, R.A. Gado ⇑ National Research Centre, Ceramics and Building Materials Department, 12311 Dokki, Cairo, Egypt
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
The recycling of waste material was
In this study, the feasibility of recycling marble sludge waste in the production of calcium sulfoaluminate-belite cement was investigated. 1: C4A3Š 2: β-C2S
1
3: CH 4: CaSO4 5: SiO2
2 1
1
1 1 2
1250 °C 1
1
Intensity (a.u)
successfully carried out leading to the production of less CO2 emission cement known as sulfoaluminatebelite cement. The influences of the cement raw mix composition and the different burning temperature were investigated to evaluate the reuse feasibility of marble sludge waste material in cement production. Calcium sulfoaluminate–belite cement, environmentally cement, can be produced by raw mix contains in weight percent 25% kaolin, 20% gypsum and 55% marble sludge waste at firing temperature 1200 °C.
1200 °C
2 1 2
1
1
2
1 2
3
5
1
10
20
4
13 2
3
30
1150 °C 1
2
40
1
50
2-Theta-scale
a r t i c l e
i n f o
Article history: Received 12 November 2015 Received in revised form 7 March 2016 Accepted 20 March 2016
Keywords: Marble sludge waste Environmentally cement Low-energy cement Sulfoaluminate–belite cement Ettringite
a b s t r a c t Marble sludge waste was used as a major cement raw material in sintering sulfoaluminate cement clinker successfully in the laboratory. The influences of raw mix composition as well as different burning temperatures were investigated. Starting materials and prepared cement were characterized through different techniques including; Fourier transform infrared spectroscopy (FTIR); X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that calcium sulfoaluminate–belite cement can be produced by burning a raw mixture contains in weight percent (25% kaolin, 20% gypsum and 55% marble sludge waste) at firing temperature ranging between 1200 and 1250 °C. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Abbreviations: C, CaO; S, SiO2; Š, SO3; A, Al2O3; F, Fe2O3; H, H2O. ⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (R.A. Gado). http://dx.doi.org/10.1016/j.conbuildmat.2016.03.103 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
Calcium sulfoaluminate–belite (CSAB) cement is promoted as a sustainable alternative to Portland cement (PC) because of lower energy consumption as well as reduction in CO2 emission during
E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
production. The calcium sulfoaluminate–belite cement phases can form and are stable at a temperature of approximately 1250 °C, which is lower than the temperature used for Portland cement production. Further, calcium sulfoaluminate–belite clinker is more friable and soft than Portland cement clinker, which reduces the energy needed for grinding process [1]. Calcium sulfoaluminate– belite cement principally utilizes Ye’elimite phase (C4A3Š), instead of tricalcium silicate (Alite, C3S) phase, as the primary early-age strength gaining phase and utilizes dicalcium silicate (Belite, b-C2S) phase to develop additional long-term strength. Ye’elimite phase (C4A3Š) has lower calcium oxide content than Portland cement phases, making it an attractive option for developing sustainable cement product [2]. Calcium sulfoaluminate– belite cement has shown rapid setting, high early strength, and shrinkage compensating properties due to the fast reacting of Ye’elimite phase (C4A3Š) and the expansive nature of ettringite [3]. In field practices, this kind of cement have been used mainly in precast concrete applications in cold environments and have shown good dimensional stability, low permeability, low alkalinity, good durability, and comparable compressive strength to Portland cement [4–7]. Raw mixes for calcium sulfoaluminate cement differ from those for Portland cement in that they contain a significant amount of sulfate. Therefore, the reactions and products are quite different from those normally found in Portland cement production [8]. The raw mix composition of this cement can be based on conventional raw materials (limestone, clay, bauxite and iron ores) but industrial by-products or wastes can be used as well [9,10] (for example fly ash, pyrite ash, galvanic sludge, metallurgical slags, phosphogypsum, etc. . ..). Furthermore, this new class of cement can be produced in existing installations using a conventional cement kiln system. Several types of industrial wastes can be used as raw materials to obtain the calcium sulfoaluminate (CSA) cement clinker. Wu et al. obtained a clinker of this cement from a mixture of municipal solid incineration wastes-limestone-bauxite-gypsum at 1250 °C, reaching more than 73.2 Mpa after 28 days of curing [11]. Li et al. [12] obtained cement by firing a mixture of fly ash, bauxite and calcium carbonate at 1300 °C. Li et al. [13] obtained the calcium sulfoaluminate (CSA) cement at a temperature as low as 1150 °C using fly ash and sludge as raw materials. Singh et al. [14,15] reported the formation of a ferric calcium sulfoaluminate cement from a mixture of calcium oxide, red mud and bauxite at 1250 °C, as well as using waste from a fertilizer industry, bauxite and iron mineral ore at 1250 °C. In general, these works showed the feasibility to obtain calcium sulfoaluminate (CSA) cement using many industrial wastes as raw materials. However, there is a great variety of industrial wastes that have the potential to be used as a source of the main components to fabricate this kind of cement [16]. Marble processing lines in the Egyptian factories produce huge amounts of marble wastes either solid or liquid (slurry, resulted from sawing the blocks to slabs and grinding and polishing processes). The random disposal of these wastes, estimated as one million tons yearly, in the areas near the factories (irrespective of their possible economic values) and with the increasing production cause severe environmental problems, such as land degradation, increase wastage of minerals, air pollution, water pollution, damage to flora and fauna as well as human resources displacement [17]. Recycling process of industrial by-products and waste materials coming from industrial manufacture activates have become an urgent problem for the near future. In the light of environmental protection standards which aiming to limit the accumulated of the industrial dump, the development of recycling techniques capable of exploiting the industrial wastes into new marketable products acquires an increasing importance for the industrial and environmental sectors.
765
In this study, the feasibility of reusing the marble sludge waste as starting materials in the preparation of sulfoaluminate-belite cement was evaluated. This work shows the feasibility of producing calcium sulfoaluminate-belite cement from a mixture of kaolin; marble sludge waste as a source of calcium carbonate (CaCO3) and gypsum (CaSO41/2H2O). The sintering temperature in the laboratory muffle furnace could be controlled by the temperature of 1150, 1200 and 1250 °C. The cement quality was investigated to evaluate the reuse feasibility of marble sludge waste material in cement production. 2. Materials and methods 2.1. Starting raw materials The raw materials used in this study were kaolin, marble sludge and gypsum. Kaolin material was supplied from the general company for ceramic & porcelain products (Sheeni); Marble sludge was collected from Shaq El Thoaban marble industrial zone; Egypt. The surface area of marble sludge waste was determined by using the method of N2 adsorption (BET) using automated gas sorption; model NOVA, Version 1.12 from the quantachrome. The measured surface area and specific gravity of marble sludge waste were 0.6695 m2/g and 2.67 respectively. Gypsum (hemihydrate, CaSO4 1/2H2O) was supplied from Gypsina company; Egypt. The main oxide compositions of starting raw materials chemically analyzed by X-ray fluorescence technique (Wavelength dispersive XRF; PANalytical) were reported in Table 1. The mineral composition phases of starting raw materials were identified by X-ray diffraction analysis technique using (XRD; X’Pert-PANalytical) diffractometer with Ni filter, with Cu Ka (k = 1.5406 Å) radiation at 40 kV, 30 mA at a scanning speed of 0.020°/s over the 2h range of 4–60°. FTIR spectra of starting raw materials were acquired using a JASCO FT/IR-6100. The IR spectra were recorded between 400 and 4000 cm1 with a resolution of 4 cm1 at room temperature. For preparing cement mixes, appropriate amounts of starting raw materials in predetermined wt.% proportions, as shown in Table 2, were taken and ball milled for 30 min using a top planetary ball mill (Fritsch planetary mono mill Pulverisette 6) for homogenization. The resultant powder samples with chemical oxides composition based on the XRF data of started materials, as shown in Table 3, were made into a thick paste using a low amount of water (5%) and moulded under a pressure of 50 Mpa into 5 5 cm cubes [18]. The cubes were dried overnight in a hot air oven at 100 °C and then fired in an electric laboratory muffle furnace (Lenton) at different firing temperatures (1150, 1200 and 1250 °C by a heating rate of 10 °C/ min) with sintering duration at the maximum temperature for 1 h in furnace for all cement clinker mixes. The theoretically expected calcium sulfoaluminate-belite cement phases were determined by adapting the Bogue method, shown in Table 4. The Bogue method is a technique used in the cement industry to estimate phase composition in Portland cement clinker from its chemical oxide composition. It was adapted for calcium sulfoaluminate-belite cement by assuming a phase assemblage of C4AF, C4A3Š, C2S, CŠ and C, as shown in the following equations (1)–(5) [1].
%C4 AF ¼ 3:043ð% Fe2 O3 Þ
ð1Þ
¼ 1:995ð%Al2 O3 Þ 1:273ð% Fe2 O3 Þ %C4 A3 S
ð2Þ
%C2 S ¼ 2:867ð% SiO2 Þ
ð3Þ
¼ 1:700ð% SO3 Þ 0:445ð% Al2 O3 Þ þ 0:284ð% Fe2 O3 Þ %CS
ð4Þ
%C ¼ 1:000ð% CaOÞ 1:867ð% SiO2 Þ 1:054ð% Fe2 O3 Þ 0:550ð% Al2 O3 Þ 0:700ð% SO3 Þ
ð5Þ
The synthesized clinkers were ground using a top planetary ball mill (Fritsch planetary mono mill Pulverisette 6) for 20 min to reach a Blaine fineness of 4500 (±100) m2/kg [19]. All the cement samples were submitted to characterization by different techniques in order to assess the reactants conversion and evaluate the phases formed on clinkering process at different temperatures [20].
3. Results and discussions 3.1. Characterization of starting raw materials The results of X-ray diffraction (XRD) analysis of supplied starting raw materials as shown in Fig. 1 indicates that the kaolin shows the typical diffraction patterns of a well-crystallized layer lattice mineral of kaolinite with muscovite impurities as Illite mineral.
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Table 1 Chemical oxide composition of starting materials, wt.%.
Kaolin Gypsum Marble sludge
Al2O3
Fe2O3
CaO
Na2O
K2O
TiO2
MnO
MgO
SO3
BaO
LOIa
46.68 0.46 0.150
35.75 0.120 0.010
1.49 0.050 0.040
0.10 37.61 55.32
0.05 0.030 0.700
2.96 0.00 0.010
0.07 0.00 0.010
0.01 0.00 0.010
0.19 0.120 0.110
0.03 53.66 0.130
0.02 0.00 0.00
12.18 7.76 43.30
Loss on Ignition at 950 °C.
Kaolin
Gypsum
Marble sludge waste
A B C
25 20 15
20 20 20
55 60 65
Characteristic peaks for kaolinite (2h = 12.34, 20.34 and 24.87°), while peaks assigned to Illite mineral (2h = 9.11, 17.50 and 26.90°). The X-ray diffraction pattern of marble sludge waste as seen in Fig. 1 indicates that the marble sludge waste sample was mainly composed of calcite mineral (CaCO3) as confirmed by XRF analysis of marble sludge in Table 1. The XRD pattern also indicates that the presence of pure crystalline phase of gypsum (calcium sulfate hemihydrate, CaSO41/2H2O) without any impurity phases [21]. Infrared spectra (FTIR) of the starting raw materials (kaolin, marble sludge waste and gypsum) are given in Fig. 2. A typical spectrum of kaolin show bands, at 3640, 3455, 1610, 1035 and 700 cm1, the band observed at around 3640 cm1 has been ascribed to the inner hydroxyl while the bands observed at around the other characteristic bands in this region are generally ascribed to vibrations of the external hydroxyl. The absorption bands observed at 3455 cm1 and 1610 cm1 could be assigned to the OH vibrational mode of the hydroxyl molecule in water, which is observed in almost all the natural hydrous silicates. In the 1035 cm1 and 476 cm1 regions, main functional groups were Si–O and Al–OH. The doublet at 700 cm1 is due to Si–O–Si internal tetrahedral bridging bonds in SiO2 and OH deformation band [22]. The infrared spectrum of the marble sludge waste was characterized by three prominent absorption bands for calcite mineral at 1400, 850 and 700 cm1 and two minor peaks at 2500 and 2000 cm1, as shown in Fig. 2. The major absorption bands of carbonate spectra in the wavelength region have been attributed to the fundamental vibrations of the carbonate radical, CO-2 3 , and various bands have been assigned to correspond to the vibrations of the carbon and oxygen atoms along a crystallographic axial direction [23,24]. The broad bands at 3450 and 1610 cm1 corresponding to the vibrational mode of the hydroxyl molecule in water as well as peaks in range 2920 and 2850 cm1, which are attributed to the (tCH2) antisymmetric stretching vibration and symmetric stretching vibration (tCH2) of organic impurities in marble sludge waste [22]. The FTIR spectrum of the gypsum was shown in Fig. 2. There are main peaks in the gypsum FTIR spectrum for O–H bending vibration modes in the range 3600–3000 cm1, the in-plane O–H O
Phases
Phase calculated (wt.%) A
B
C
C4A3Š C2S C4AF CŠ C
22.30 43.60 1.58 18.62 3.76
18.05 35.44 1.31 19.85 14.41
13.71 27.11 1.03 21.13 25.31
K: Kaolin I: Illite C: Calcite G: Gypsum G G
G
G
GG
G
Gypsum
C
C K
I
C
C
C Marble sludge
K
I
10
20
I I
30
K, I
Mixes
Table 4 The theoretically expected calcium sulfoaluminate-belite cement phases adapting by the Bogue method [1].
K, I
Table 2 Prepared cement mixes from starting raw materials, wt.%.
Intensity (a.u)
a
SiO2
K
K
40
Kaolin
50
60
2-Theta-scale Fig. 1. X-ray diffraction pattern of starting raw materials.
bending vibrations in the range 1620 cml, and the bending vibration of the SO4 tetrahedron in the range 660–550 cml as well as S–O stretching vibration for sulfate group in the range 1140–1080 [25,26]. 3.2. Characterization of prepared cement samples 3.2.1. Fourier transform infrared spectroscopy (FTIR) The FTIR spectra of prepared cement samples (A, B and C) at different burning temperatures (1150, 1200 and 1250 °C) are illustrated in Figs. 3–5, respectively. Each prepared cement sample has
Table 3 Chemical oxide composition of prepared cement mixes.
a
Mixes/oxides
SiO2
Al2O3
Fe2O3
CaO
Na2O
K2O
TiO2
P2O3
MgO
SO3
F
LOIa
A B C
11.84 9.51 7.19
8.96 7.18 5.39
0.40 0.33 0.25
37.97 40.73 43.49
0.40 0.43 0.46
0.74 0.59 0.45
0.02 0.02 0.01
0.07 0.06 0.06
0.13 0.120 0.12
10.81 10.81 10.81
0.03 0.02 0.02
28.41 29.96 31.52
Loss on Ignition at 950 °C.
767
688 cm-1 520 cm-1
1417 cm-1
1157 cm-1 1122 cm-1 995-836 cm-1
1617 cm-1
2360 cm-1 3415 cm-1
4000
3000
2500
2000
1500
1000
690 cm-1 520 cm-1 690 cm-1 520 cm-1 414 cm-1
1160 cm-1 1122 cm-1 920-835 cm-1 1160 cm-1 1122 cm-1 925-835 cm-1
1617 cm-1
1617 cm-1 1417 cm-1
2360 cm-1
3420 cm-1
3500
1417 cm-1
2360 cm
-1
1150°C
3420 cm-1
Transmittance, T%
1200°C
500
Wavenumber, cm-1 Fig. 3. FTIR spectrum of cement samples (A) burned at different temperatures.
its own unique infrared spectrum bands. The infrared spectra of all prepared cement samples, shows the main absorption band and the identification of the functional group signals for calcium sulfoaluminate-belite cement which can be described as follow: ye’elimite phase (C4A3Š) has two absorption bands due to vibrational modes of sulfate [SO4]2 groups at 1100–1200 cm1 and a very intense absorption band due to silicate groups near to
2500
2000
1500
921-833 cm
640 cm-1 505 cm-1 650 cm-1 490 cm-1
1118 cm-1 1000 cm-1 880 cm-1 -1
1000
630 cm 490 cm-1
1157-1122 cm-1
1630,1615 cm-1 1417cm-1
2360 cm-1
3000
-1
3500
925-833 cm
4000
-1
1150°C
Fig. 2. FTIR spectrum of starting raw materials.
1250°C
1630,1615 cm-1 1417cm-1
3415 cm-1 3640 cm-1 3415 cm-1
Transmittance, T%
476 cm
500
1160-1122 cm-1
1000
675cm-1 -1
700 cm-1
1500
Wavenumber, cm-1
1630,1615 cm-1 1417cm-1
2000
1200°C
2360 cm-1
2500
2360 cm-1
660 cm-1-1 550 cm 850 cm
1400 cm 1035 cm
3000
700 cm-1
-1
1140 cm-1
1620 cm-1 -1
2500 cm-1
2920 cm-1 2850 cm-1
-1
3500
1250°C
3640 cm-1 3415 cm-1
4000
1610 cm-1
Kaolin
3455 cm-1
3455 cm-1
Marble sludge
3640 cm-1
Transmittance, T%
3600 cm-1 3455 cm-1
Gypsum
3000 cm-1
E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
500
Wavenumber, cm-1 Fig. 4. FTIR spectrum of cement samples (B) burned at different temperatures.
800–1000 cm1, the third band at 620 cm1 region is due to vibrational modes of [AlO4]5 tetrahedral as well as belite phase (b-C2S) the another calcium silicate phase, exhibits strong bands in the area 1000–800 cm1 with maximums at 990 and 840 cm1 due the stretching Si–O bond of the silicon tetrahedron and the bending vibration absorption band appear at lower frequencies 520 cm1 and a shoulder at 538 cm1. A broadened signal appears between 900 and 800 cm1, centered at 857 cm1. This feature is strongly asymmetrical which probably due to the result of the convolution of the two bands of belite phase (b-C2S), as a consequence of lower crystal perfection caused mainly by the presence of foreign ions in the lattice or because of the small particle size of minerals of calcium sulfoaluminate-belite cement. But it is also possible to highlight the presence of the three anhydrite bands at 677, 615, and 600 cm1, respectively [27]. Also, the presence of calcite (CaCO3) impurities was identified with IR absorption bands at 874 and 1424 cm1 [28]. In general, from the results of FTIR spectra of prepared cement samples (Figs. 3–5), as decreasing of kaolin percent in samples from A to C, the following differential notes are observed i) the intensity of calcium sulfoaluminate-belite cement main bands that appear in the range 400–1200 cm1 were remarkably decreased. ii) The intensity of the bands at 3640 cm1 and 1630 cm1 were increases indicating liberation of more Ca(OH)2 as a result of free unreacted lime hydration. iii) The strong asymmetric stretching Si–O band at 925 cm1 is decreased to low intensity indicates the low formation of belite phase (b-C2S). iv) the carbonate bands at 2360, 1420 and 875 cm1 are observed mainly due to the reactions of atmospheric CO2 with calcium hydroxide [29]. Furthermore, unreacted silica gives rise to its absorption band at 925 (Si–O–Si asymmetric stretching vibration) and unreacted lime
1
5: SiO2
2
2500
Wavenumber,
1250°C
1
Intensity (a.u)
675 cm-1
943-833 cm
2 1
12
2
4 5 3 13 2
12
1
1200°C
1 2
1000
3
675 cm
-1
925-835 cm
-1
1160-1122 cm-1
1427 cm
1500
2
-1
1159-1122 cm-1
1637,1617 cm-1 1469 cm-1 1630,1617 cm-1
2000
1
1
1
10
500
20
30
Fig. 5. FTIR spectrum of cement samples (C) burned at different temperatures.
gives rise to its absorption bands at 3640, 1630 and 1450– 1500 cm1 (vibrations of OH group and Ca–O stretching vibration). Calcite arising from partial carbonation of unreacted lime gives its absorption bands at 2360, 1420, 840, and 700 cm1. The belite phase (b-C2S) gives rise to the following absorption bands: three maxima at 950, and 840 cm1 (Si–O asymmetric stretching modes), medium intensity band at 430 cm1 (Si–O bending mode), and a strong band at 530 cm1 (Si–O–Si out of plane bending mode) [30]. On the other hand, as clinker temperatures increase from 1150 to 1250 °C leads to i) shifting the main bands of calcium sulfoaluminate-belite cement that appear in the range of 400–1200 cm1 to a little higher frequencies as a result of more polymerization [31]; ii) decreasing in the intensity of the bands corresponding to Portlandite Ca (OH)2 at 3630 cm1 and 1630 cm1. The band assignments are in good agreement with those reported in the previous studies [27–31]. 3.2.2. X-ray diffraction analysis (XRD) The XRD pattern of prepared cement samples (A, B and C) were shown in Figs. 6–8, respectively. The XRD pattern of prepared cement sample (A) as illustrated in Fig. 6, shows that the ye’elimite phase (C4A3Š, 2h = 23.66, 33.82 and 41.69°) was the major phase in the clinker product with belite phase (b-C2S, 2h = 32.16, 34.20 and 41.17°), unreacted silica (SiO2, 2h = 20.86, 26.64 and 50.15°) as minor phases in clinker samples burned at 1150 °C. The appearance of the main diffraction intensity for the belite phase (b-C2S, 2h = 32.16°) in the cement sample (A) which fired at 1150 °C confirming that the formation of this phase starts at lower firing temperature within the range of 1000 °C [32]. On the contrary, the intensity of the ye’elimite phase (C4A3Š) enhanced as firing temperature increasing to 1250 °C. XRD pattern shows that the characteristic peak of unreacted silica (SiO2) is gradually
40
1150°C
1
50
60
2-Theta-scale
cm-1
Fig. 6. XRD pattern of cement samples (A) at different temperatures.
1: C4A3Š 2: β-C2S 3: CH 4: CaSO4 5: SiO2
2 4
1 4
2
1 2
2, 3 4
3 5
1250°C
2
1 2
Intensity (a.u)
3000
1 1
-1
2360 cm-1 2360 cm-1 3640 cm-1 3415 cm-1
1150°C
3500
675 cm-1
3640 cm-1 3415 cm-1
1200°C
4000
2: β-C2S 3: CH 4: CaSO4
1
3640 cm-1 3419 cm-1
Transmittance, T%
1250°C
1: C4A3Š
1120 cm-1 1000 cm-1 880 cm-1
1637,1617 cm-1 1427 cm-1
E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
2360 cm-1
768
2, 3
3 45
3
2
3
° 4 1200 C
12
2 2, 3 14
4
3
3 1
3
5
5
10
20
30
2 1
40
24
1150°C 5
50
60
2-Theta-scale Fig. 7. XRD pattern of cement samples (B) at different temperatures.
E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
1: C4A3Š 2: β-C2S 4
3: CH 4: CaSO4 5: SiO2
1
2, 3 4, 2 4
1250°C
12
Intensity (a.u)
2, 3
3
1
4, 2
4
4
3
1 2
2
4 1200°C
4, 2
1 4
2, 3
3 3
1
2 24 1150°C
4
10
20
30
40
50
60
769
temperature. A decrease in the intensity of the following phases C4A3Š and b-C2S content was observed with an increase in the percent of CaO sourced from marble sludge waste as well as decreasing in kaolin percent. Thus, the crystalline phase C4A3Š in the doped samples became less abundant compared to the cement samples A and B burned at the sample temperatures. The anhydrite calcium sulfate (CaSO4) was detected in cement samples B and C until burning temperature at 1250 °C, which indicated that the reaction to form C4A3Š was still not complete at these high temperatures, which mainly due to a deficiency in acidic oxides content in their raw mix. Finally, the X-ray diffraction analysis results of different cement samples (A, B and C) in this study indicates that the characteristic peaks of the ye’elimite phase (C4A3Š) are gradually weakened in the cement samples A, B and C, respectively. This is mainly due to the reduction in kaolin percent in their mixes. According to Xray diffraction analysis results, the optimum burning temperature for the formation of calcium sulfoaluminate-belite cement was found to be (1250 °C) for the raw mix sample containing in weight percent 25% kaolin, 20% gypsum and 55% marble sludge waste. The formation of the ye’elimite phase (C4A3Š) in this study is in agreement with previous reports which indicated the formation of the ye’elimite phase at 1200–1250 °C by using other industrial byproduct wastes [33]. From the above experiments, it was shown that the calcium sulfoaluminate-belite cement could be synthesized between 1200 °C and 1250 °C. The high amounts of C4A3Š and b-C2S in cement indicates the high durability and rapid hardening of calcium sulfoaluminate cement [34]. The XRD results confirm all results obtain from different used techniques in this study.
2-Theta-scale 4. Characterization of hardened cement samples Fig. 8. XRD pattern of cement samples (C) at different temperatures.
weakened in prepared cement samples as the firing temperature increases, which indicates the more consuming of acidic oxides from raw kaolin for more formation of calcium sulfoaluminatebelite cement. The XRD show that the appearance of Portlandite (CH, 2h = 18.04, 28.69 and 34.11°) in the sample (A) burned at 1150 °C which mainly due to the presence of uncombined calcium oxide in the sample. The XRD pattern of prepared cement sample (B) fired at different temperatures (1150, 1200 and 1250 °C) are shown in Fig. 7. The data show that, the appearance of Portlandite (CH, 2h = 18.04, 28.69 and 34.11°), unreacted silica (SiO2, 2h = 20.86, 26.64 and 50.15°) and anhydrite calcium sulfate (CaSO4, 2h = 25.44, 31.34 and 40.79°) with belite (b-C2S) and ye’elimite phase (C4A3Š). It can be also noticed that the cement sample (B) fired at 1150 and 1250 °C shows the higher intensity of Portlandite and anhydrite calcium sulfate (CaSO4) than those fired at 1200 °C. This probably due to decomposition of calcium sulfoaluminate phases at a higher temperature (1250 °C) and incomplete reaction at 1150 °C which reflects on calcium sulfoaluminate-belite cement main phases as illustrated in Fig. 7. The XRD results of the cement sample (B) show that the optimum temperature was 1200 °C due to less Portlandite (CH) phase peaks as well as less anhydrite calcium sulfate (CaSO4) phase peaks. The XRD pattern of the cement sample (C) burned at different firing temperatures (1150, 1200 and 1250 °C) are shown in Fig. 8. The results of the cement sample (C) fired at 1150 °C show the essentially following mineralogical composition phases C4A3Š, b-C2S, CH and anhydrite calcium sulfate (CaSO4). It can be also noticed that cement sample (C) fired at 1250 °C shows the higher intensity of Portlandite phase (CH) and anhydrite calcium sulfate phase (CaSO4) as well as the lower intensity of C4A3Š and b-C2S phases than cement samples (B and C) fired at the same
The specimens of prepared sulfoaluminate-belite cement paste (w/c ratio = 0.50) were cured for 28 days, then they were characterized by determining their physico-mechanical properties [35,36]. The results were based on the average of three cube samples. The physico-mechanical properties of the hardened cement specimens cured at room temperature are illustrated in Table 5. As indicated from results, the highest compressive strength values (within the range of 36 Mpa) were recorded to cement samples (A) which burned at 1200 and 1250 °C, respectively. It was observed that hardened cubes of cement samples (C) which burned at 1200 and 1250 °C respectively were self-cracked and deteriorated during the curing period. The dimensional instability mainly has been linked to the high free lime content in hardened samples. The large amounts of free lime may cause expansion, strength loss and crack of the hardened paste, due to a delayed hydration of free calcium oxide (hard burned) to produce calcium hydroxide, which takes place topo-chemically and usually associated with an increase in matrix volume. Thus, excessive amounts of free calcium oxide in clinker must be avoided [37]. After the mechanical testing, a fractured hardened paste of highly compressive strength sample (A-1200 °C) was chosen, crushed by hand with a metallic mortar. The ground powder was characterized by different used techniques as well as morphology investigation by scanning electron microscope (SEM) attached with EDX Unit (Energy dispersive X-ray analyses), with accelerating voltage 30 K.V., (JEOL Ltd., Japan). 4.1. X-ray diffraction analysis (XRD) The XRD pattern of hardened sample cured for 28 days in comparison with its anhydrous sample (A-1200 °C) is illustrated in Fig. 9. The main hydration products were ettringite phase (C3A3CŠ32H2O, 2h = 11.49, 19.92 and 28.91°), low sulfate calcium sulfoaluminate hydrate (monosulfate C3ACŠ12H2O, 2h = 9.92,
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E.A. El-Alfi, R.A. Gado / Construction and Building Materials 113 (2016) 764–772
Table 5 The physico-mechanical properties of the hardened cement samples cured up to 28 days. Properties
Mixes A
Bulk density [g/cm3] Apparent porosity [%] Compressive strength [Mpa]
B 1200 °C
1250 °C
1150 °C
1200 °C
1250 °C
1150 °C
1200 °C
1250 °C
1.88 16.70 27
1.90 15.20 36
1.90 14.85 35
1.83 19.54 15.7
1.84 17.95 18.45
1.86 17.03 22.11
1.80 24.53 9.86
– – –
– – –
Hydrated sample (Age : 28 Days) 3: Ettringite 4: Monosulphate 5: CSH 4, 5 3 4 6: CH 43 3
3
6 6
35
6 4 3
5 43
Intensity (a.u)
1: C4A3Š
1
2: β-C2S
C
1150 °C
Dry cement (A-1200°C) 2
12
Spectroscopic methods are commonly used to study the chemistry of cement hydration. The chemical environment of the vibrations band of the dry cement bonds changes as hydration occurs. The sample will absorb some of the light at wavelengths that are characteristic of its chemical composition. In the present work, the hydration of calcium sulfoaluminate-belite cement has been observed by means of infrared spectroscopy. Infrared spectra (FTIR) of the hydrated sample in a comparison with its anhydrous sample are given in Fig. 10. This spectrum corresponds to the difference between that acquired after 28 days of hydration, and the spectrum of dry cement. From the results in Fig. 10, we observe significant changes in the spectrum of dry cement sample due to hydration process. As hydration progresses at 28 days, there is a broad feature forming with its center at 3450 and 1630 cm1 caused by the bending vibration of irregularly bound water [45–47]. The broadband at 3450 cm1 is intensified with hydration, indicating that the increase of hydrated products associated with water. The peaks at 3640 and 1630 cm1 correspond to the inner hydroxyl group in Portlandite Ca (OH)2 which is formed as silicate phases in the cement dissolve
1 2
Hydrated sample (Age : 28 Days)
20
30
40
50
2-Theta-scale
Transmittance, T%
19.90 and 22.28°) calcium silicate hydrate phase (CSH, 2h = 28.58, 29.06 and 31.58°) and Portlandite Ca (OH)2 (CH, 2h = 18.10, 28.72 and 34.17°). The ettringite deficiency in the hardened sample mainly due to the absence of additional gypsum added upon hydration process. The ye’elimite phase is used or activated with an addition of calcium sulfate, either as gypsum or anhydrite [38]. Furthermore, it is possible to modify the hydration process of calcium sulfoaluminate cement not only by its composition but also by the selection of different quantities or sources of calcium sulfate [39]. Hence, the amount of added calcium sulfate strongly modifies the ettringite formation and the water demand to complete full hydration [40,41]. In addition, the amount of ettringite is affected by the reactivity of calcium sulfate (solubility and dissolution rate) at early ages [40]. Hence, the selection of the sulfate source is a key issue to achieve the desired properties. Furthermore, depending on the other phases present in calcium sulfoaluminate cement, other hydration products may occur such as CSH gels, stratlingite, katoite, monocarboaluminate or hydrogarnet [42–44]. Hence, further studies on the chemistry of hydration for prepared calcium sulfoaluminate-belite cement will be required.
3640 cm-1 3455-3420 cm-1
Fig. 9. XRD pattern of hardened cement sample (A).
1150 cm-1 995cm-1 875 cm-1
10
1630 cm-1 1420 cm-1
2360 cm-1
1
4.2. Fourier transform infrared spectroscopy (FTIR)
Dry cement (A-1200°C)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber, cm-1 Fig. 10. FTIR spectrum of hydrated cement sample (A) in comparison with its anhydrous sample burned at 1200 °C.
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for forming calcium silicate hydrate (CSH) phases upon hydration process. Characteristic sulfate absorption bands are found in the range 1150 cm1 due to the vibration of the SO2 4 group in sulfates [48]. The asymmetric stretching Si–O band is shifted to high frequencies centered at 995 cm1 with hydration indicates that the formation of calcium silicate hydrate (CSH) [49]. These diphump features are taken to reflect the dissolution of belite phase (b-C2S) and simultaneously the polymerization of silica [50–52] to form calcium silicate hydrate (CSH). The decrease and increase in intensities of the out-of-plane and in-plane Si-O bending vibrations are occurring in significant changes with hydration. The carbonates peaks at 2360, 1420 and 875 cm1 are observed due to the reactions of atmospheric CO2 with Portlandite Ca (OH)2 [39]. 4.3. Scanning electron microscopy (SEM)
771
phases in the voids after 28 days of hydration. The belite phase is observed to remain much less hydrated during this period. After 28 days of hydration, amounts of Portlandite Ca (OH)2 and calcium silicate hydrate (CSH) were observed on SEM micrographs, indicating b-C2S hydration has taken place which already confirmed from XRD results. It is expected that the ye’elimite phase (C4A3Š) would be completely hydrated much before 28 days of hydration. The combination of XRD and SEM analysis indicates that calcium sulfoaluminate phase hydrates produce ettringite phase (C3A3CŠ32H2O) as well as low sulfate calcium sulfoaluminate hydrate (monosulfate C3ACŠ12H2O) while belite (b-C2S) phase hydrates to produce the calcium silicate hydrate (CSH) that fills porosity of specimen, and results in a dense structure.
5. Conclusion
Scanning electron microscope was used to analyze the morphology of the fracture surface of the hardened sample specimens cured at 28 days. SEM investigations can help us to get a better understanding of the morphologies of the sample. The microstructural examinations of the phase distribution of the hardened sample specimens (A, w/c ratio = 0.50) are shown in Fig. 11. The selected micrographs of the fracture transversal section of hardened sample (A) after curing time show the presence of a large amount of short rod-like crystals in the hardening paste as illustrated in Fig. 11. EDX measurements data show the presence of Ca, S, O, Si, Al and this result combined with XRD measurements reveal that the ettringite phase (C3A3CŠ32H2O) presence in the hydrated sample as the main phase of hydration process [53]. The SEM micrograph shows the presence of sponge-like sulfoaluminate phases in the whole matrix and needle-like ettringite
In this study, the feasibility of recycling the marble sludge waste as starting materials in the production of calcium sulfoaluminate-belite cement was investigated. The prepared cement samples were subjected to furnace sintering at temperatures of 1150, 1200 and 1250 °C for the same holding time (1 h). Different techniques were performed for mineralogical examination of the obtained samples. The following conclusions were reached under the experimental observations of this study: 1. It is possible to recycle the marble sludge waste in the synthesis of calcium sulfoaluminate-belite cement. 2. Calcium sulfoaluminate–belite cement, environmentally cement, can be produced by raw mix contains in weight percent 25% kaolin, 20% gypsum and 55% marble sludge waste.
Fig. 11. SEM of hydrated cement sample (A) with EDX analysis.
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3. As the firing temperature of the prepared cement samples increases between 1150 and 1250 °C, the calcium sulfoaluminate-belite cement phases enhanced. 4. The prepared cement sample (A) gives the best burn ability with the maximum sulfoaluminate-belite phases at 1250 °C, as well as good mechanical properties upon hydration process than that other prepared cement samples (B and C).
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