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Fabrication of hollow microspheres filled fly ash geopolymer composites with excellent strength and low density
Materials Letters 161 (2015) 451–454
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Fabrication of hollow microspheres filled fly ash geopolymer composites with excellent strength and low density Ning-Ning Shao, Ze Liu n, Yuan-Yi Xu, Fan-Long Kong, Dong-Min Wang School of Chemical and Environmental Engineering, China University of Mining & Technology, Beijing 100083, China
art ic l e i nf o
a b s t r a c t
Article history: Received 5 July 2015 Received in revised form 21 August 2015 Accepted 1 September 2015 Available online 6 September 2015
Novel high-strength lightweight inorganic nonmetal material (INM) was initially fabricated by the filling of hollow microspheres in fly ash geopolymers in this study. The optimal properties in relation to compressive strength versus density of prepared samples were noted to be (14 MPa versus 580 Kg/m3), (17.9 MPa versus 641 Kg/m3), and (22.1 MPa versus 782 Kg/m3). Such excellent properties were similar to that of high-performance foam ceramics, but with no calcination process in the present work. The excellent performance was demonstrated to result from the high degree of geopolymerization and excellent filling properties of employed hollow microspheres in geopolymer matrix. & 2015 Elsevier B.V. All rights reserved.
Keywords: Composite materials Microstructure High-strength Lightweight Geopolymer
1. Introduction Out of the consideration of safety, energy-saving, and environmental protection of building constructions, lightweight inorganic nonmetal materials (INMs) with high-strength have attracted a great attention worldwide. Normally, strength is proportional to density, which has proposed a challenging difficulty to researchers. Though, some INMs simultaneously possessing low density and high-strength have been successfully synthesized, it is hard to achieve the high performance with low energy consumption of fabrication. A summarization of INMs with low bulk density ( o1000 Kg/m3) and relative high compressive strength (4 5 MPa) from previous reports is shown in Fig. 1a [1–14]. Geopolymers are a class of inorganic polymer materials with Si–O–Si and Si–O–Al bonds in a highly cross linked amorphous network [15]. It has been a research hotspot in recent years due to its excellent fire resistance, thermal stability, relative high strength, and low shrinkage. Moreover, geopolymers can generally perform 80% or greater reduction in CO2 footprint and 60% less energy consumption when compared with the manufacturing of ordinary Portland cement (OPC) [16]. Hollow microsphere is another increasingly popular engineering material that is usually used as a kind of reinforced material filled in matrix. By enclosing the porosity in the thin wall of hollow microspheres, the reinforced materials would achieve low density and without large reduction in mechanical properties [17]. n
Corresponding author. E-mail address: [email protected] (Z. Liu).
http://dx.doi.org/10.1016/j.matlet.2015.09.016 0167-577X/& 2015 Elsevier B.V. All rights reserved.
Based on the understanding of high-strength lightweight INMs, this study focused on the fabrication of such materials by hollow microspheres filling fly ash based geopolymer composites.
2. Experimental The aluminosilicate materials used in this study was ultra-fined circulating fluidized bed combustion fly ash (CFA) with mean particle size of 4.6 μm, and its chemical composition in terms of main oxides were 42.0% SiO2, 34.2% Al2O3, 11.0% CaO, and 2.84% Fe2O3. The hollow microspheres were S38HS hollow glass bubbles (HGB) supplied by 3 M company. Water glass (WG, molar ratio SiO2/Na2O¼ 3.2) and sodium hydroxide solutions (denoted as NH (aq)) with concentrations of 4, 6, 8, 10, and 12 M were employed as the activator for the geopolymer synthesis. The HGB was designed to successively replace 30, 40, and 50 wt% CFA to make mixed drier. Then, WG (mass ratio WG/CFA ¼0.93) and NH(aq) in certain concentration were added in the mixed drier to make uniform slurry. Subsequently, the slurry was cast into cubic molds (40 40 160 mm3 for each mold) and cured at 60 °C for 24 h. After demolding, the samples were exposed in ambient temperature for additional 28d curing. Moreover, pure foamed geopolymer (HGB dosage was 0) in three different density levels activated by the corresponding optimal activator for the HGB filled CFA based geopolymers was later synthesized as the blank control samples. All the prepared samples were marked as Cx–Dy (x and y were Arabic numbers), where C and the following x means concentration of NH(aq), D and the y indicated the dosage of HGB.
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Fig. 1. (a) Summary of high-strength lightweight INMs; (b) test strength versus density of different experimental batches.
Specimens test and characterization: a CS200 universal strength testing apparatus (50 KN capacity, Ningbo Weiheng, China) was used to determine the flexural strength and compressive strength. The stress loading rate was kept at a low speed of 12 cm/min, and final strength calculation was according to the China standard GB/T 17671-1999. The microstructure of the samples was determined using a scanning electron microscope (JEOL JSM-7001F, Japan). A Nicolet iS10 FTIR spectrometer (Thermo Scientific, USA) was employed for the collection of the FTIR data, using KBr pressed disk method. Moreover, X-ray diffraction (XRD) patterns were recorded using an X'TRA high-performance powder X-ray diffractometer (Smartlab 9000, Japan) with Cu Kα radiation generated at 40 mA and 40 kV.
3. Results and discussion A summarization of high-strength lightweight (o1000 Kg/m3, 45 MPa) INMs from previous works as well as the results from this study are shown in Fig. 1a. Obviously, foam ceramics behave the far more outstanding strength-density properties than the other INMs of previous studies, but the high manufacturing cost significantly limited its structural applications. However, the prepared samples in this study were found to show almost similar properties with the foam ceramics and higher strength than the other INMs. The strength versus density as well as HGB dosage and NH(aq) concentration are shown in Fig. 1b. It is observed that both the
Fig. 2. (a) FTIR spectra and (b) XRD patterns of geopolymers activated by different NH(aq).
compressive strength and flexural strength increased with the increase of NH(aq) concentration until to 10 M. For the 12 M NH(aq), all activated samples were found to show severe cracking and no strength could be detected, so was the C10–D50. For the samples activated with NH(aq) of same concentration, both the density and strength basically declined with the increase of HGB dosages. From the comprehensive consideration of strength versus density properties, the optimal sample batches in different HGB dosages are C8–D50, C8– D40, and C10–D30 respectively, in relation to (compressive strength, flexural strength, density) of (14 MPa, 2.43 MPa, 580 Kg/m3), (17.9 MPa, 2.83 MPa, 641 Kg/m3), and (22.1 MPa, 3.5 MPa, 782 Kg/m3), respectively. Additionally, comparing the HGB filled geopolymer composites with the control samples (see Fig. 1b), it is indicated that the HGB played a key role for the excellent performance of the former. Fig. 2a shows the FTIR spectra of different NH(aq) activated geopolymer composite samples. It has been demonstrated that the strong peaks in the range of 1020–1060 cm 1 are attributed to the asymmetric stretching vibration of Si–O–T (T ¼Si or Al), which is the main charateristics of N–A–S–H gels [18]. The band in this study becomes sharper and gradually shift to lower frequencies with the increase of NH(aq) concentrations to 10 M, indicating more amorphous N–A–S–H gels formed [18]. However, the 12 M NH(aq) activated samples shows much weaker and broader Si–O– T peak, which may be due to the excessive hydroxyl groups in 12 M NH(aq) would inversely restrain the formation of Si–O–T
N.-N. Shao et al. / Materials Letters 161 (2015) 451–454
453
Fig. 3. SEM of HGB filled geopolymer composites.
bond [19]. The geopolymerization degree revealed by the Si–O–T peak is well in agreement with the test strength results (Fig. 1b). In addition, the weak peak around 1431 cm 1, which is only obviously viewed in 12 M NH(aq) activated samples, is ascribed to the stretching vibration of O–C–O bond [20], indicating the excessive alkalinity of 12 M NH(aq) for the geopolymerization. The XRD patterns of different NH(aq) activated geopolymer samples were shown in Fig. 2b. It is noted that the geopolymer composites included quartz as the major crystalline phase, calcite and hematite in small quantity were also detected. According to previous study [21], the broad hump around 20–40° was the characteristic peak of amorphous N–A–S–H gels, and the peak area reflect the geopolymeric reaction degree. It is obvious that the 10 M NH(aq) activated specimens possesses highest reaction degree, then is 8 M NH(aq), NH(aq) with 4, 6, and 12 M concentrations came in the last, which is well in agreement with the strength and FTIR test results. Fig. 3 focused on the fracture surface of HGB filled geopolymer samples. It is viewed from Fig. 3a that the hollow microspheres were well dispersed in geopolymer matrix. Fig. 3b–d shows the morphology of internal walls of residual holes. It is noted that the remained HGB shells tightly adhered to the geopolymer matrix, basically with no gaps could be observed, revealing an important reason of the high strength of the materials. Additionally, as shown in Fig. 3d, the HGB possesses very thin walls (about 0.2 μm), implying large cavity volume of the hollow microspheres, which is the essential reason of the lightweight property of the materials. The geopolymer matrix (see Fig. 3c–e) is recognized to be made up of countless nanosized particles tightly adhered to each other. These nanosized particles were demonstrated to be the main geopolymerization product: N–A–S–H gels, which is associated with the dissolution of CFA particles in high alkaline solution and the formation of geopolymer gels [22]. The existence of numerous nanosized N–A–S–H gel particles indicated the high degree of geopolymerization, which may be another important reason of the high strength of geopolymer samples in this study. In addition, the smooth surface of the HGB shell in Fig. 3e indicate the excellent alkali resistance of HGB.
4. Conclusions Novel high-strength lightweight INM was initially fabricated by the filling of hollow microspheres in fly ash based geopolymers in this study. The prepared samples exhibit excellent strength to density properties. This excellent performance is associated with the mainly two reasons: (1) the high degree of geopolymerization; (2) excellent filling property of HGB microspheres, with basically no gaps could be observed between HGB microspheres and geopolymer gels.
Acknowledgment This work was financially supported by the Fundamental Research Funds for the Central Universities of China (Nos. 2009KH09 and 2009QH02).
References [1] X. Chen, A. Lu, G. Qu, Preparation and characterization of foam ceramics from red mud and fly ash using sodium silicate as foaming agent, Ceram. Int. 39 (2013) 1923–1929. [2] A. Strachota, M. Černý, Z. Chlup, K. Rodzeń, K. Depa, M. Halasová, J. Schweigstillová, Preparation of finely macroporous SiOC foams with high mechanical properties and with hierarchical porosity via pyrolysis of a siloxane/epoxide composite, Ceram. Int. 41 (2015) 8402–8410. [3] L.Y. Yin, X.G. Zhou, J.S. Yu, H.L. Wang, S. Zhao, Z. Luo, B. Yang, New consolidation process inspired from making steamed bread to prepare Si3N4 foams by protein foaming method, J. Eur. Ceram. Soc. 33 (2013) 1387–1392. [4] X. Chen, Y. Yan, Y. Liu, Z. Hu, Utilization of circulating fluidized bed fly ash for the preparation of foam concrete, Constr. Build. Mater. 54 (2014) 137–146. [5] E.P. Kearsley, P.J. Wainwright, The effect of high fly ash content on the compressive strength of foamed concrete, Cem. Concr. Res. 31 (2001) 105–112. [6] K.H. Yang, K.H. Lee, Tests on high-performance aerated concrete with a lower density, Constr. Build. Mater. 74 (2015) 109–117. [7] A. Just, B. Middendorf, Microstructure of high-strength foam concrete, Mater. Charact. 60 (2009) 741–748. [8] P. Hlaváček, V. Šmilauer, F. Škvára, L. Kopecký, R. Šulc, Inorganic foams made from alkali-activated fly ash: mechanical, chemical and physical properties, J. Eur. Ceram. Soc. 35 (2) (2015) 703–709.
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[9] K. Pimraksa, P. Chindaprasirt, A. Rungchet, K. Sagoe-Crentsil, T. Sato, Lightweight geopolymer made of highly porous siliceous materials with various Na2O/Al2O3 and SiO2/Al2O3 ratios, Mater. Sci. Eng. A 528 (2011) 6616–6623. [10] R.A. Aguilar, O.B. Díaz, J.I.E. García, Lightweight concretes of activated metakaolin-fly ash binders, with blast furnace slag aggregates, Constr. Build. Mater. 24 (2010) 1166–1175. [11] T.Y. Li, Preparation of water-resistant lightweight gypsum panel with high strength (Ph.D. dissertation), Zhejiang University, China, 2013. [12] H.C. Wu, P. Sun, New building materials from fly ash-based lightweight inorganic polymer, Constr. Build. Mater. 21 (2007) 211–217. [13] Y. Zaetang, A. Wongsa, V. Sata, P. Chindaprasirt, Use of lightweight aggregates in pervious concrete, Constr. Build. Mater. 48 (2013) 585–591. [14] Z. Wu, L. Sun, P. Wan, J. Li, Z. Hu, J. Wang, In situ foam-gelcasting fabrication and properties of highly porous γ-Y2Si2O7 ceramic with multiple pore structures, Scr. Mater. 103 (2015) 6–9. [15] J.L. Provis, J.S.J. van Deventer, Geopolymerisation kinetics. 1. In situ energy dispersive X-ray diffractometry, Chem. Eng. Sci. 62 (2007) 2309–2317. [16] K. Komnitsas, D. Zaharaki, Geopolymerisation: a review and prospects for the minerals industry, Miner. Eng. 20 (2007) 1261–1277.
[17] P.K. Rohatgi, N. Gupta, B.F. Schultz, D.D. Luong, The synthesis, compressive properties, and applications of metal matrix syntactic foams, JOM 63 (2011) 36–42. [18] D. Panias, I.P. Giannopoulou, T. Perraki, Effect of synthesis parameters on the mechanical properties of fly ash-based geopolymers, Coll. Surf. A 301 (2007) 246–254. [19] V.D. Glukhovsky, Ancient, modern and future concretes, in: Proceedings of the First International Conference on Alkaline Cements and Concretes. Kiev, Ukraine, 1994, pp. 1–9. [20] M. Criado, A. Palomo, A. Fernández-Jiménez, Alkali activation of fly ashes. Part 1: Effect of curing conditions on the carbonation of the reaction products, Fuel 84 (2005) 2048–2054. [21] X. Guo, H. Shi, W.A. Dick, Compressive strength and microstructural characteristics of class C fly ash geopolymer, Cem. Concr. Compos. 32 (2010) 142–147. [22] E. Álvarez-Ayuso, X. Querol, F. Plana, A. Alastuey, N. Moreno, M. Izquierdo, M. Barra, Environmental, physical and structural characterisation of geopolymer matrixes synthesised from coal (co-) combustion fly ashes, J. Hazard. Mater. 154 (2008) 175–183.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Fabrication of hollow microspheres filled fly ash geopolymer composites with excellent strength and low density Ning-Ning Shao, Ze Liu n, Yuan-Yi Xu, Fan-Long Kong, Dong-Min Wang School of Chemical and Environmental Engineering, China University of Mining & Technology, Beijing 100083, China
art ic l e i nf o
a b s t r a c t
Article history: Received 5 July 2015 Received in revised form 21 August 2015 Accepted 1 September 2015 Available online 6 September 2015
Novel high-strength lightweight inorganic nonmetal material (INM) was initially fabricated by the filling of hollow microspheres in fly ash geopolymers in this study. The optimal properties in relation to compressive strength versus density of prepared samples were noted to be (14 MPa versus 580 Kg/m3), (17.9 MPa versus 641 Kg/m3), and (22.1 MPa versus 782 Kg/m3). Such excellent properties were similar to that of high-performance foam ceramics, but with no calcination process in the present work. The excellent performance was demonstrated to result from the high degree of geopolymerization and excellent filling properties of employed hollow microspheres in geopolymer matrix. & 2015 Elsevier B.V. All rights reserved.
Keywords: Composite materials Microstructure High-strength Lightweight Geopolymer
1. Introduction Out of the consideration of safety, energy-saving, and environmental protection of building constructions, lightweight inorganic nonmetal materials (INMs) with high-strength have attracted a great attention worldwide. Normally, strength is proportional to density, which has proposed a challenging difficulty to researchers. Though, some INMs simultaneously possessing low density and high-strength have been successfully synthesized, it is hard to achieve the high performance with low energy consumption of fabrication. A summarization of INMs with low bulk density ( o1000 Kg/m3) and relative high compressive strength (4 5 MPa) from previous reports is shown in Fig. 1a [1–14]. Geopolymers are a class of inorganic polymer materials with Si–O–Si and Si–O–Al bonds in a highly cross linked amorphous network [15]. It has been a research hotspot in recent years due to its excellent fire resistance, thermal stability, relative high strength, and low shrinkage. Moreover, geopolymers can generally perform 80% or greater reduction in CO2 footprint and 60% less energy consumption when compared with the manufacturing of ordinary Portland cement (OPC) [16]. Hollow microsphere is another increasingly popular engineering material that is usually used as a kind of reinforced material filled in matrix. By enclosing the porosity in the thin wall of hollow microspheres, the reinforced materials would achieve low density and without large reduction in mechanical properties [17]. n
Corresponding author. E-mail address: [email protected] (Z. Liu).
http://dx.doi.org/10.1016/j.matlet.2015.09.016 0167-577X/& 2015 Elsevier B.V. All rights reserved.
Based on the understanding of high-strength lightweight INMs, this study focused on the fabrication of such materials by hollow microspheres filling fly ash based geopolymer composites.
2. Experimental The aluminosilicate materials used in this study was ultra-fined circulating fluidized bed combustion fly ash (CFA) with mean particle size of 4.6 μm, and its chemical composition in terms of main oxides were 42.0% SiO2, 34.2% Al2O3, 11.0% CaO, and 2.84% Fe2O3. The hollow microspheres were S38HS hollow glass bubbles (HGB) supplied by 3 M company. Water glass (WG, molar ratio SiO2/Na2O¼ 3.2) and sodium hydroxide solutions (denoted as NH (aq)) with concentrations of 4, 6, 8, 10, and 12 M were employed as the activator for the geopolymer synthesis. The HGB was designed to successively replace 30, 40, and 50 wt% CFA to make mixed drier. Then, WG (mass ratio WG/CFA ¼0.93) and NH(aq) in certain concentration were added in the mixed drier to make uniform slurry. Subsequently, the slurry was cast into cubic molds (40 40 160 mm3 for each mold) and cured at 60 °C for 24 h. After demolding, the samples were exposed in ambient temperature for additional 28d curing. Moreover, pure foamed geopolymer (HGB dosage was 0) in three different density levels activated by the corresponding optimal activator for the HGB filled CFA based geopolymers was later synthesized as the blank control samples. All the prepared samples were marked as Cx–Dy (x and y were Arabic numbers), where C and the following x means concentration of NH(aq), D and the y indicated the dosage of HGB.
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N.-N. Shao et al. / Materials Letters 161 (2015) 451–454
Fig. 1. (a) Summary of high-strength lightweight INMs; (b) test strength versus density of different experimental batches.
Specimens test and characterization: a CS200 universal strength testing apparatus (50 KN capacity, Ningbo Weiheng, China) was used to determine the flexural strength and compressive strength. The stress loading rate was kept at a low speed of 12 cm/min, and final strength calculation was according to the China standard GB/T 17671-1999. The microstructure of the samples was determined using a scanning electron microscope (JEOL JSM-7001F, Japan). A Nicolet iS10 FTIR spectrometer (Thermo Scientific, USA) was employed for the collection of the FTIR data, using KBr pressed disk method. Moreover, X-ray diffraction (XRD) patterns were recorded using an X'TRA high-performance powder X-ray diffractometer (Smartlab 9000, Japan) with Cu Kα radiation generated at 40 mA and 40 kV.
3. Results and discussion A summarization of high-strength lightweight (o1000 Kg/m3, 45 MPa) INMs from previous works as well as the results from this study are shown in Fig. 1a. Obviously, foam ceramics behave the far more outstanding strength-density properties than the other INMs of previous studies, but the high manufacturing cost significantly limited its structural applications. However, the prepared samples in this study were found to show almost similar properties with the foam ceramics and higher strength than the other INMs. The strength versus density as well as HGB dosage and NH(aq) concentration are shown in Fig. 1b. It is observed that both the
Fig. 2. (a) FTIR spectra and (b) XRD patterns of geopolymers activated by different NH(aq).
compressive strength and flexural strength increased with the increase of NH(aq) concentration until to 10 M. For the 12 M NH(aq), all activated samples were found to show severe cracking and no strength could be detected, so was the C10–D50. For the samples activated with NH(aq) of same concentration, both the density and strength basically declined with the increase of HGB dosages. From the comprehensive consideration of strength versus density properties, the optimal sample batches in different HGB dosages are C8–D50, C8– D40, and C10–D30 respectively, in relation to (compressive strength, flexural strength, density) of (14 MPa, 2.43 MPa, 580 Kg/m3), (17.9 MPa, 2.83 MPa, 641 Kg/m3), and (22.1 MPa, 3.5 MPa, 782 Kg/m3), respectively. Additionally, comparing the HGB filled geopolymer composites with the control samples (see Fig. 1b), it is indicated that the HGB played a key role for the excellent performance of the former. Fig. 2a shows the FTIR spectra of different NH(aq) activated geopolymer composite samples. It has been demonstrated that the strong peaks in the range of 1020–1060 cm 1 are attributed to the asymmetric stretching vibration of Si–O–T (T ¼Si or Al), which is the main charateristics of N–A–S–H gels [18]. The band in this study becomes sharper and gradually shift to lower frequencies with the increase of NH(aq) concentrations to 10 M, indicating more amorphous N–A–S–H gels formed [18]. However, the 12 M NH(aq) activated samples shows much weaker and broader Si–O– T peak, which may be due to the excessive hydroxyl groups in 12 M NH(aq) would inversely restrain the formation of Si–O–T
N.-N. Shao et al. / Materials Letters 161 (2015) 451–454
453
Fig. 3. SEM of HGB filled geopolymer composites.
bond [19]. The geopolymerization degree revealed by the Si–O–T peak is well in agreement with the test strength results (Fig. 1b). In addition, the weak peak around 1431 cm 1, which is only obviously viewed in 12 M NH(aq) activated samples, is ascribed to the stretching vibration of O–C–O bond [20], indicating the excessive alkalinity of 12 M NH(aq) for the geopolymerization. The XRD patterns of different NH(aq) activated geopolymer samples were shown in Fig. 2b. It is noted that the geopolymer composites included quartz as the major crystalline phase, calcite and hematite in small quantity were also detected. According to previous study [21], the broad hump around 20–40° was the characteristic peak of amorphous N–A–S–H gels, and the peak area reflect the geopolymeric reaction degree. It is obvious that the 10 M NH(aq) activated specimens possesses highest reaction degree, then is 8 M NH(aq), NH(aq) with 4, 6, and 12 M concentrations came in the last, which is well in agreement with the strength and FTIR test results. Fig. 3 focused on the fracture surface of HGB filled geopolymer samples. It is viewed from Fig. 3a that the hollow microspheres were well dispersed in geopolymer matrix. Fig. 3b–d shows the morphology of internal walls of residual holes. It is noted that the remained HGB shells tightly adhered to the geopolymer matrix, basically with no gaps could be observed, revealing an important reason of the high strength of the materials. Additionally, as shown in Fig. 3d, the HGB possesses very thin walls (about 0.2 μm), implying large cavity volume of the hollow microspheres, which is the essential reason of the lightweight property of the materials. The geopolymer matrix (see Fig. 3c–e) is recognized to be made up of countless nanosized particles tightly adhered to each other. These nanosized particles were demonstrated to be the main geopolymerization product: N–A–S–H gels, which is associated with the dissolution of CFA particles in high alkaline solution and the formation of geopolymer gels [22]. The existence of numerous nanosized N–A–S–H gel particles indicated the high degree of geopolymerization, which may be another important reason of the high strength of geopolymer samples in this study. In addition, the smooth surface of the HGB shell in Fig. 3e indicate the excellent alkali resistance of HGB.
4. Conclusions Novel high-strength lightweight INM was initially fabricated by the filling of hollow microspheres in fly ash based geopolymers in this study. The prepared samples exhibit excellent strength to density properties. This excellent performance is associated with the mainly two reasons: (1) the high degree of geopolymerization; (2) excellent filling property of HGB microspheres, with basically no gaps could be observed between HGB microspheres and geopolymer gels.
Acknowledgment This work was financially supported by the Fundamental Research Funds for the Central Universities of China (Nos. 2009KH09 and 2009QH02).
References [1] X. Chen, A. Lu, G. Qu, Preparation and characterization of foam ceramics from red mud and fly ash using sodium silicate as foaming agent, Ceram. Int. 39 (2013) 1923–1929. [2] A. Strachota, M. Černý, Z. Chlup, K. Rodzeń, K. Depa, M. Halasová, J. Schweigstillová, Preparation of finely macroporous SiOC foams with high mechanical properties and with hierarchical porosity via pyrolysis of a siloxane/epoxide composite, Ceram. Int. 41 (2015) 8402–8410. [3] L.Y. Yin, X.G. Zhou, J.S. Yu, H.L. Wang, S. Zhao, Z. Luo, B. Yang, New consolidation process inspired from making steamed bread to prepare Si3N4 foams by protein foaming method, J. Eur. Ceram. Soc. 33 (2013) 1387–1392. [4] X. Chen, Y. Yan, Y. Liu, Z. Hu, Utilization of circulating fluidized bed fly ash for the preparation of foam concrete, Constr. Build. Mater. 54 (2014) 137–146. [5] E.P. Kearsley, P.J. Wainwright, The effect of high fly ash content on the compressive strength of foamed concrete, Cem. Concr. Res. 31 (2001) 105–112. [6] K.H. Yang, K.H. Lee, Tests on high-performance aerated concrete with a lower density, Constr. Build. Mater. 74 (2015) 109–117. [7] A. Just, B. Middendorf, Microstructure of high-strength foam concrete, Mater. Charact. 60 (2009) 741–748. [8] P. Hlaváček, V. Šmilauer, F. Škvára, L. Kopecký, R. Šulc, Inorganic foams made from alkali-activated fly ash: mechanical, chemical and physical properties, J. Eur. Ceram. Soc. 35 (2) (2015) 703–709.
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N.-N. Shao et al. / Materials Letters 161 (2015) 451–454
[9] K. Pimraksa, P. Chindaprasirt, A. Rungchet, K. Sagoe-Crentsil, T. Sato, Lightweight geopolymer made of highly porous siliceous materials with various Na2O/Al2O3 and SiO2/Al2O3 ratios, Mater. Sci. Eng. A 528 (2011) 6616–6623. [10] R.A. Aguilar, O.B. Díaz, J.I.E. García, Lightweight concretes of activated metakaolin-fly ash binders, with blast furnace slag aggregates, Constr. Build. Mater. 24 (2010) 1166–1175. [11] T.Y. Li, Preparation of water-resistant lightweight gypsum panel with high strength (Ph.D. dissertation), Zhejiang University, China, 2013. [12] H.C. Wu, P. Sun, New building materials from fly ash-based lightweight inorganic polymer, Constr. Build. Mater. 21 (2007) 211–217. [13] Y. Zaetang, A. Wongsa, V. Sata, P. Chindaprasirt, Use of lightweight aggregates in pervious concrete, Constr. Build. Mater. 48 (2013) 585–591. [14] Z. Wu, L. Sun, P. Wan, J. Li, Z. Hu, J. Wang, In situ foam-gelcasting fabrication and properties of highly porous γ-Y2Si2O7 ceramic with multiple pore structures, Scr. Mater. 103 (2015) 6–9. [15] J.L. Provis, J.S.J. van Deventer, Geopolymerisation kinetics. 1. In situ energy dispersive X-ray diffractometry, Chem. Eng. Sci. 62 (2007) 2309–2317. [16] K. Komnitsas, D. Zaharaki, Geopolymerisation: a review and prospects for the minerals industry, Miner. Eng. 20 (2007) 1261–1277.
[17] P.K. Rohatgi, N. Gupta, B.F. Schultz, D.D. Luong, The synthesis, compressive properties, and applications of metal matrix syntactic foams, JOM 63 (2011) 36–42. [18] D. Panias, I.P. Giannopoulou, T. Perraki, Effect of synthesis parameters on the mechanical properties of fly ash-based geopolymers, Coll. Surf. A 301 (2007) 246–254. [19] V.D. Glukhovsky, Ancient, modern and future concretes, in: Proceedings of the First International Conference on Alkaline Cements and Concretes. Kiev, Ukraine, 1994, pp. 1–9. [20] M. Criado, A. Palomo, A. Fernández-Jiménez, Alkali activation of fly ashes. Part 1: Effect of curing conditions on the carbonation of the reaction products, Fuel 84 (2005) 2048–2054. [21] X. Guo, H. Shi, W.A. Dick, Compressive strength and microstructural characteristics of class C fly ash geopolymer, Cem. Concr. Compos. 32 (2010) 142–147. [22] E. Álvarez-Ayuso, X. Querol, F. Plana, A. Alastuey, N. Moreno, M. Izquierdo, M. Barra, Environmental, physical and structural characterisation of geopolymer matrixes synthesised from coal (co-) combustion fly ashes, J. Hazard. Mater. 154 (2008) 175–183.