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Effects of CaO addition on lightweight aggregates produced from water reservoir sediment
Construction and Building Materials 25 (2011) 2997–3002
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effects of CaO addition on lightweight aggregates produced from water reservoir sediment Yi-Chong Liao, Chi-Yen Huang ⇑ Department of Resources Engineering, National Cheng Kung University, No. 1, University Road, East District, Tainan City 701, Taiwan, ROC
a r t i c l e
i n f o
Article history: Received 25 June 2010 Received in revised form 25 November 2010 Accepted 21 December 2010 Available online 20 January 2011 Keywords: LWA CaO C–S–H gel Bloating
a b s t r a c t Lightweight aggregates were produced from water reservoir sediment with various amounts of CaO at calcining temperatures of 1170 °C–1230 °C. It was found that C–S–H gel did not form with CaO addition. The bulk density and compressive strength of the lightweight aggregates meet the regulations for lightweight structural concrete. The properties of samples with 1% CaO by weight calcined at 1200 °C match those of a commercial product. Water adsorption and compressive strength decreased with increasing CaO addition since more of the glassy phase formed, which sealed pores and led to few connections between pores. Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved.
1. Introduction Water reservoir sediment in Taiwan precipitates with a mean amount of 14 million metric tons annually. According to a government report, the total amount of swept sediment in 2009 was 4.33 million metric tons. This huge amount of waste greatly shortens the usage life of water reservoirs and causes landfill problems. One solution is to use the sediment to manufacture lightweight aggregates (LWAs) which can be used to produce lightweight concrete for the construction of high-rise buildings. Many studies have focused on using recycled wastes, mostly ash, sludge, and mined residue, for manufacturing LWAs. The ash can be incinerated fly ash [1] or incinerated bottom ash [2–4], and the sludge can be industrial sludge [5–7] or sewage sludge [8,9]. The mined residue can be zeolitic rocks [10–14]. Some studies reported that LWAs can also be manufactured from a mixture of ash and sludge [15–17]. Chen et al. [1] mixed ash and reservoir sediment to manufacture LWAs and concluded that reservoir sediment is feasible for use due to its high content of glass-forming oxides and low level of flux oxides. Wei et al. [18] mixed reservoir sediment with various percentages of harbor sediment to produce LWAs which meet the criteria of a bulk density of particles of lower than 2.0 g/cm3 and water adsorption in the range of 2–20%. The European Union regulation UNIEN 13055-1 confines LWAs to have a unit weight of particles of lower than 2000 kg/m3 and a loose weight of lower than 1200 kg/m3.
⇑ Corresponding author. Tel.: +886 06 2757575x62832; fax: +886 06 2380421. E-mail address: [email protected] (C.-Y. Huang).
The low weight of LWAs is mostly due to their porous structure, which is produced by bloating during the heating process. Bloating is promoted when the chemical composition follows Riley’s diagram because the raw material includes ions which can form a glassy phase and gas is generated as the glassy phase forms [19]. Riley’s diagram includes SiO2, Al2O3, and flux materials such as Na2O, K2O, Fe2O3, FeO, MgO, and CaO. CaO can also promote a pozzolanic reaction since it reacts with H2O to form Ca(OH)2. Zhu et al. [20], Darvaz and Gunduz [21], and Turanli et al. [22] studied a pozzolanic reaction in which Ca(OH)2 reacted with SiO2 and Al2O3 in incinerated sewage sludge ash to form C–S–H and C–A–H gels. Mun [8] used sewage sludge to produce LWAs for nonstructural concrete and reported that CaO content affects the viscosity of raw materials at high temperatures. However, few studies have reported the effects of the amount of CaO used as the main flux oxide on the properties of LWAs produced from water reservoir sediment. In the present study, various amounts of CaO were added into water reservoir sediment to produce LWAs. The effect of CaO concentration on the physical properties of the LWAs was investigated.
2. Materials and methods The water reservoir sediment was obtained from Shihmen Reservoir in Taiwan. The sediment had a water content of 28% and an ignition loss of 5.57% with a d50 size of 8.49 lm. The chemical composition of the sediment was determined using an X-ray fluorescence spectrometer (XRF, Rigaku). The CaO powders (Shimakyo’s Pure Chemicals) were milled to pass through a No. 100 mesh. The sediment, without drying, was directly mixed with CaO powders, 1% and 5% by weight, by a small cement mixer, respectively. The mixture was then extruded by a vacuum extrusion machine. The extruded bar was cut into small lumps and
0950-0618/$ - see front matter Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.12.034
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pelletized into 10–20 mm spheres. These spheres were placed a laboratory-scale furnace and calcined for 30 min at a heating rate of 15 °C/min at 1170 °C, 1185 °C, 1200 °C, 1215 °C, and 1230 °C, respectively. When the air inside the furnace cooled to room temperature, the calcined LWAs were characterized using the following procedures. The mineral phases of the raw sediment and the modified sediment were measured by X-ray diffraction (XRD, Siemens D5000). The calcined LWAs were crushed and milled into powders to measure their mineral phases by XRD. The Archimedes method was employed to measure the bulk density and water adsorption after the LWAs were placed in boiling water for 24 h. The bulk density and water adsorption were calculated as follows [23]:
bulk density ¼ W D =ðW S W I Þ Water adsorptionð%Þ ¼ 100ðW S W D Þ=W D
SiO2 and Al2O3 in previous studies [20–22], respectively, no pozzolanic reaction was found in the modified sediment (1% and 5% CaO by weight) in the present study. The mineral phases were still quartz, albite, clinochlore, and muscovite. The relationship between the bulk density and water adsorption at various calcining temperatures is shown in Fig. 3a. The bulk density linearly decreased with increasing temperature. The decreasing trends of samples with 0% and 1% CaO by weight were similar. The bulk densities of samples with 0% and 1% CaO by weight ranged from 1.6 g/cm3 to 1.0 g/cm3 whereas that of the samples with 5% CaO by weight ranged from 2.0 g/cm3 to 1.1 g/ cm3. According to the European Union regulation EN-13055-1, the unit weight of LWAs should be lower than 2000 kg/m3. The
where WD is the dry weight of the calcined LWAs, WS is the 24 h saturated surfacedry weight, and WI is the immersed weight in water. The compressive strength was measured using a material testing system (MTS 810) with a cross head speed of 0.1 mm/s. The compressive strength of the calcined LWAs was calculated using [24,25]:
Compressive strength ¼ 2:8Pc =pX 2 where Pc is the fracture load and X is the diameter of the LWAs. Each recorded testing value was the mean of results from eight samples. The physical properties of LWAs calcined at 1200 °C and 1230 °C were compared to those of a commercial LWA, Leca Strutturale, which has been applied to the production of structural concrete [14]. Finally, an optical microscope and a scanning electron microscope (SEM) were used to observe the microstructure of the LWAs.
3. Results The chemical compositions of sediment measured by XRF are shown in Table 1. The sediment is mainly SiO2 (61.4%), followed by Al2O3 (22.5%) and Fe2O3 (8.6%). The relationship of the chemical composition is plotted in Riley’s diagram in Fig. 1. The raw sediment corresponds to the bloating area in Riley’s diagram. The XRD pattern in Fig. 2 shows that the mineral phases of the raw sediment were quartz, albite, clinochlore, and muscovite. The mineral phases of the sediment modified with CaO, 1% and 5% by weight, respectively, were also measured before the sediment was calcined into LWAs. The mineral phases were found to be the same as those of the raw sediment. Ca(OH)2 was expected to form via the reaction of CaO with the water in the reservoir sediment. Although C–S–H gel and C–A–H gel formed via the reaction of Ca(OH)2 with
Fig. 2. Mineral phases of the raw sediment and the modified sediment.
Table 1 Chemical compositions of Shihmen reservoir sediment. Component
SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
K2O
Composition (wt.%)
61.4
22.7
8.6
0.7
2.0
1.3
3.4
Fig. 1. Relationship of chemical compositions in Riley’s diagram.
Fig. 3. Physical properties of LWAs calcined at various temperatures. (a) Bulk density and water adsorption, and (b) compressive strength.
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Y.-C. Liao, C.-Y. Huang / Construction and Building Materials 25 (2011) 2997–3002 Table 2 Properties of LWAs calcined at 1200 °C and 1230 °C compared with those of a commercial LWA. Lightweight aggregate
Bulk density (g/cm3) Water adsorption (%) Strength of particles (MPa) Strength/unit weight of particles
0 wt.%
1 wt.%
5 wt.%
Leca strutturale
1200 °C
1230 °C
1200 °C
1230 °C
1200 °C
1230 °C
1.29 9.14 6.47 5.02
1.09 20.24 5.58 5.12
1.33 3.24 6.27 4.71
0.96 11.15 3.45 3.59
1.55 2.79 5.07 3.27
1.12 1.89 1.91 1.71
1.3 >7 4.5 3.46
tion of LWAs. Water adsorption was independent of temperature for the samples with 5% CaO by weight. These results are different from those for ordinary LWAs, where water adsorption decreases with increasing bulk density and temperature. The compressive strength of LWAs calcined at various temperatures is shown in Fig. 3b. All compressive strengths were above 1.9 MPa. The compressive strength of the sample with 5% CaO by weight calcined at 1170 °C was higher than those of samples with 0% and 1% CaO by weight calcined at 1170 °C, but lower than those of samples with 0% and 1% CaO by weight calcined at above 1185 °C. Table 2 lists the physical properties of LWAs calcined at 1200 °C and 1230 °C and those of the commercial LWA. The table shows that the LWA with 1% CaO by weight calcined at 1200 °C was better than the commercial LWA, and that CaO addition reduced the ratio of strength to unit weight of particles. In previous studies [14], LWAs with a compressive strength of above 1 MPa were produced into structural concrete. This means that the LWAs obtained in this study can be applied to the production of structural concrete. The compressive strength decreased with increasing temperature and CaO addition. The mineral phases of LWAs without CaO addition after calcining are shown in Fig. 4a. The mineral phases were quartz, sillimanite, Fe2O3, ringwoodite, and corundum. The Fe2O3 phase was not the hematite phase. The mineral phases of the samples with 1% CaO by weight (see Fig. 4b) were the same as those for the samples with 0% CaO by weight. Quartz still existed in the LWAs but its crystallinity decreased with increasing temperature. These results show that the sillimanite phase increased and the ferrosilite phase disappeared at above 1185 °C. Fig. 4c shows the mineral phases of
Fig. 4. Mineral phases of LWAs with various amounts of CaO addition calcined at various temperatures. (a) 0 wt.%, (b) 1 wt.%, and (c) 5 wt.%.
aggregates produced in this study meet this regulation. The results show that bulk density increased with CaO addition. The water adsorption levels of samples with 0% and 1% CaO by weight increased with increasing calcining temperature. They had similar increasing trends although the water adsorption of the samples with 1% CaO by weight was lower than that of the samples without CaO. The trend of the samples with 5% CaO by weight was different from those of the samples with 0% and 1% CaO by weight. The water adsorption levels of the samples with 5% CaO by weight were all below 4%. Finally, CaO addition lowered the water adsorp-
Fig. 5. Optical photographs of sections of LWAs with various amounts of CaO addition. (a) 0 wt.%, (b) 1 wt.%, and (c) 5 wt.%.
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Fig. 6. Microstructure observation of LWAs with various amounts of CaO addition. (a) 0 wt.%, (b) 1 wt.%, and (c) 5 wt.%.
the samples with 5% CaO by weight, which are different from those for samples with 0% and 1% CaO by weight. Quartz still existed, followed by anorthite, Fe2O3, and SiO2. The phases of Fe2O3 and SiO2 were in an oxide phase form rather than in a mineral form. The crystallinity of quartz decreased with increasing temperature, as in samples with 0% and 1% CaO by weight. In all XRD patterns, a small hill was found in the 2h range between 20° and 30°. The crystallinity of quartz decreased with temperature. Cross-sections of the LWAs with 0%, 1%, and 5% CaO by weight after calcining at various temperatures are shown in Fig. 5. The formations of pores in samples with 0% and 1% CaO by weight were similar, and much different from that for the samples with 5% CaO by weight. The pore distributions in samples with 0% and 1% CaO by weight were more uniform and the numbers of pores increased with increasing calcining temperature. In contrast, the pores in the samples with 5% CaO by weight had a random size which increased with calcining temperature. Some pores in the samples with 5% CaO by weight calcined at 1230 °C were larger than 4 mm, whereas the pores in samples with 0% and 1% CaO by weight were smaller than 2 mm. The surface inside pores in the
samples with 5% CaO by weight was glossy and smooth, as opposed to those in samples with 0% and 1% CaO by weight. The bottom of the samples with 5% CaO by weight was brown and red-bricked. The microstructure, observed by SEM, is shown in Fig. 6. The pores in samples with 0% and 1% CaO by weight were connected to each other. Pores larger than 0.4 mm were also found at a lower calcining temperature (1170 °C), whereas no pores larger than 0.4 mm were found in the samples with 5% CaO by weight. When the CaO addition was increased to 5% by weight, the surface inside pores became smooth and the small pores were unconnected. Cracks formed in the samples with 5% CaO by weight at the boundary between pores and the matrix.
4. Discussion CaO is considered a glass-forming oxide that can promote bloating behavior to form a porous structure and that can induce a pozzolanic reaction. In this study, a pozzolanic reaction was expected to develop with the addition of CaO. However, the XRD pattern of
Y.-C. Liao, C.-Y. Huang / Construction and Building Materials 25 (2011) 2997–3002
the modified sediment shows no C–S–H gel, C–A–H gel, portlandite phase, or lime phase; the mineral phases of the modified sediment are the same as those for the raw sediment (quartz, albite, muscovite, and clinochlore). This may be due to CaO reacting with carbonate ions within the water of sediment, since sediment is a kind of weathering product, with many carbonate compounds precipitating, resulting in CaO reacting with H2O and CO2 ions to 3 form amorphous CaCO3. This explains why no pozzolanic reaction occurred and why no lime phase or calcite phase was found in the XRD pattern. A comparison of the XRD pattern of the raw material with the data of chemical compositions indicates that iron ions mainly exist in the clinochlore structure due to the replacement of magnesium ions, and that sodium ions as well as potassium ions exist in the albite and muscovite structures. The albite and muscovite structures decomposed and transformed into other mineral phases when the temperature was increased to over 800 °C, which is how sillimanite, ringwoodite, corundum, ferrosilite, and iron oxide formed. Moreover, the increasing temperature also decreased the intensity of the quartz phase due to the quartz reacting and forming a glassy phase. This is confirmed by a small hill, indicating the existence of an amorphous structure, between 20° and 30° in the XRD patterns. Since high temperature leads to the transformation of mineral phases, the anorthite phase formed after calcining. With 5% CaO by weight, the number of calcium ions is sufficient to react with other phases from the decomposition of albite and muscovite to form anorthite. The phases that did not react with CaO, mainly chinochlore and muscovite, may make iron oxide and silicon oxide segregate into a pure compound state rather than a mineral state, like hematite and quartz. SEM photographs show that the increase of water adsorption with calcining temperature in samples with 0% and 1% CaO by weight is caused by pore connections. The samples without CaO had water adsorption of up to 20% and the samples with 1% CaO by weight had water adsorption of up to 11%. However, for the samples with 5% CaO by weight, the water adsorption levels were all below 4%. The increasing amount of CaO resulted in the formation of a glassy phase that sealed pores and prevented connections between pores. This explains why the water adsorption of samples with 5% CaO by weight is much lower than those of samples with 0% and 1% CaO by weight, in which calcining temperature promoted pore connections. However, pores in the samples with 5% CaO by weight initially began to form at 1215 °C. This means that CaO addition does not promote bloating as expected. It seems that CaO as a flux oxide is not good at promoting bloating but good at lowering water adsorption of LWAs by sealing pores. Although bulk density decreased with increasing calcining temperature and ranged from 2.0 g/cm3 to 1.0 g/cm3, water adsorption did not increase with increasing bulk density and calcining temperature. The water adsorption of the samples with 5% CaO by weight did not increase with decreasing bulk density. The results of compressive strength tests of LWAs also show that CaO addition weakens compressive strength. This may be caused by the excess amount of the glassy phase from CaO addition and by cracks that form between pores and the matrix. This explains why the samples with 5% CaO by weight are much weaker than samples with 0% and 1% CaO by weight; the compressive strength of the samples with 5% CaO by weight calcined at 1230 °C was only 1.91 MPa. Although the bulk densities of samples with 0% and 1% CaO by weight are lower than that of the samples with 5% CaO by weight, the compressive strengths are higher. This is very different from other LWAs, for which compressive strength decreases with decreasing bulk density. A comparison with a commercial LWA shows that the optimal CaO concentration is 1% by weight. At 1200 °C, the bulk density is close to that of the commercial product and the low water
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adsorption is good for further processing. The ratio of strength to the unit weight of particles for the samples with 1% CaO by weight calcined at 1200 °C (4.71) is higher than that of the commercial product (3.46). 5. Conclusion The LWAs produced in this study meet the European Union regulation of the unit weight of LWAs being below 2000 kg/m3. They also satisfy the strength demand for structural concrete. The properties of samples with 1% CaO by weight calcined at 1200 °C achieve the performance of a commercial product. CaO addition does not promote the pozzolanic reaction and can lower water adsorption of LWAs, which is due to an excess amount of a glassy phase sealing pores; however, CaO addition weakens compressive strength. The decrease in bulk density with CaO addition of 0% and 1% by weight is caused by the numbers of pores rather than pore growth. Pore growth with increasing calcining temperature results in a decrease of bulk density with the addition of 5% CaO by weight. For samples with 5% CaO by weight, the mineral phases of LWAs were anorthite, quartz, Fe2O3, and SiO2, with Fe2O3 and SiO2 forming in a non-mineral state. References [1] Chen HJ, Wang SY, Tang CW. Reuse of incineration fly ashes and reaction ashes for manufacturing lightweight aggregate. Constr Build Mater 2010;24:46–55. [2] Cheeseman CR, Monteiro da Rocha S, Sollars C, Bethanis S, Boccaccini AR. Ceramic processing of incinerator bottom ash. Waste Manage 2003;23:907–16. [3] Cheeseman CR, Makinde A, Bethanis S. Properties of lightweight aggregate produced by rapid sintering of incinerator bottom ash. Resour Conserv Recycl 2005;43:147–62. [4] Anagostopoulos IM, Stivanakis VE. Utilization of lignite power generation residues for the production of lightweight aggregates. J Hazard Mater 2009;163:329–36. [5] Liaw CT, Chang HL, Hsu WC, Huang CR. A novel method to reuse paper sludge and co-generation ashes from paper mill. J Hazard Mater 1998;58:93–102. [6] Chang FC, Lo SL, Lee MY, Ko CH, Lin JD, Huang SC, et al. Leachability of metals from sludge-based artificial lightweight aggregate. J Hazard Mater 2007;14:98–105. [7] Laursen K, White TJ, Cresswell DJF, Wainwright PJ, Barton JR. Recycling of an industrial sludge and marine clay as light-weight aggregates. J Environ Manage 2006;80:208–13. [8] Mun KJ. Development and tests of lightweight aggregate using sewage sludge for nonstructural concrete. Constr Build Mater 2007;21:1583–8. [9] Wang X, Jin Y, Wang Z, Nie Y, Huang Q, Wang Q. Development of lightweight aggregate from dry sewage sludge and coal ash. Waste Manage 2009;29:1330–5. [10] Mueller A, Sokolova SN, Vereshagin VI. Characteristics of lightweight aggregates from primary and recycled raw materials. Constr Build Mater 2008;22:703–12. [11] de’Gennaro R, Cappelletti P, Cerri G, de’Gennaro M, Dondi M, Langella A. Zeolitic tuffs as raw materials for lightweight aggregates. Appl Clay Sci 2004;25:71–81. [12] de’Gennaro R, Cappelletti P, Cerri G, de’Gennaro M, Dondi M, Langella A. Neapolitan yellow tuff as raw material for lightweight aggregates in lightweight structural concrete production. Appl Clay Sci 2005;28:309–19. [13] de’Gennaro R, Cappelletti P, Cerri G, de’Gennaro M, Dondi M, Graziano SF, et al. Campanian Ignimbrite as raw material for lightweight aggregates. Appl Clay Sci 2007;37:115–26. [14] de’Gennaro R, Langella A, D’Amore M, Dondi M, Colella A, Cappelletti P, et al. Use of zeolite-rich rocks and waste materials for the production of structural lightweight concretes. Appl Clay Sci 2008;41:61–72. [15] Chiou IJ, Wang KS, Chen CH, Lin YT. Lightweight aggregate made from sewage sludge and incinerated ash. Waste Manage 2006;26:1453–61. [16] Huang SC, Chang FC, Lo SL, Lee MY, Wang CF, Lin JD. Production of lightweight aggregates from mining residues, heavy metal sludge, and incinerator fly ash. J Hazard Mater 2007;144:52–8. [17] González-Corrochano B, Alonso-Azcárate J, Rodas M. Characterization of lightweight aggregates manufactured from washing aggregate sludge and fly ash. Resour Conserv Recycl 2009;53:571–81. [18] Wei YL, Yang JC, Lin YY, Chuang SY, Wang HP. Recycling of harbor sediment as lightweight aggregate. Mar Pollut Bull 2008;57:867–72. [19] Riley CM. Relation of chemical process to the bloating clay. J Am Ceram Soc 1950;34:121–8. [20] Zhu WH, Yin YF, Jiang LH, Che LM. Study of micropore size distribution and its effect on the strength of silica fume cement phase. J Build Mater 2004;7:14–8.
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[21] Davraz M, Gunduz L. Engineering properties of amorphous silica as a new natural pozzolan for use in concrete. Cem Concr Res 2005;35:1251–61. [22] Turanli L, Uzal B, Bektas F. Effect of material characterization on the properties of blended cements containing high volumes of natural pozzolans. Cem Concr Res 2004;34:2277–82. [23] Neville AM. Properties of concrete. 4th ed. Harlow, Longman; 1994.
[24] Li Y, Wu D, Zhang J, Chang L, Fang Z, Shi Y. Measurement and statistics of single pellet mechanical strength of differently shaped catalysts. Powder Technol 2000;113:176–84. [25] Yashima S, Kanda Y, Sano S. Relationship between particle size and fracture energy or impact velocity required to fracture as estimated from single particle crushing. Powder Technol 1987;51:277–82.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effects of CaO addition on lightweight aggregates produced from water reservoir sediment Yi-Chong Liao, Chi-Yen Huang ⇑ Department of Resources Engineering, National Cheng Kung University, No. 1, University Road, East District, Tainan City 701, Taiwan, ROC
a r t i c l e
i n f o
Article history: Received 25 June 2010 Received in revised form 25 November 2010 Accepted 21 December 2010 Available online 20 January 2011 Keywords: LWA CaO C–S–H gel Bloating
a b s t r a c t Lightweight aggregates were produced from water reservoir sediment with various amounts of CaO at calcining temperatures of 1170 °C–1230 °C. It was found that C–S–H gel did not form with CaO addition. The bulk density and compressive strength of the lightweight aggregates meet the regulations for lightweight structural concrete. The properties of samples with 1% CaO by weight calcined at 1200 °C match those of a commercial product. Water adsorption and compressive strength decreased with increasing CaO addition since more of the glassy phase formed, which sealed pores and led to few connections between pores. Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved.
1. Introduction Water reservoir sediment in Taiwan precipitates with a mean amount of 14 million metric tons annually. According to a government report, the total amount of swept sediment in 2009 was 4.33 million metric tons. This huge amount of waste greatly shortens the usage life of water reservoirs and causes landfill problems. One solution is to use the sediment to manufacture lightweight aggregates (LWAs) which can be used to produce lightweight concrete for the construction of high-rise buildings. Many studies have focused on using recycled wastes, mostly ash, sludge, and mined residue, for manufacturing LWAs. The ash can be incinerated fly ash [1] or incinerated bottom ash [2–4], and the sludge can be industrial sludge [5–7] or sewage sludge [8,9]. The mined residue can be zeolitic rocks [10–14]. Some studies reported that LWAs can also be manufactured from a mixture of ash and sludge [15–17]. Chen et al. [1] mixed ash and reservoir sediment to manufacture LWAs and concluded that reservoir sediment is feasible for use due to its high content of glass-forming oxides and low level of flux oxides. Wei et al. [18] mixed reservoir sediment with various percentages of harbor sediment to produce LWAs which meet the criteria of a bulk density of particles of lower than 2.0 g/cm3 and water adsorption in the range of 2–20%. The European Union regulation UNIEN 13055-1 confines LWAs to have a unit weight of particles of lower than 2000 kg/m3 and a loose weight of lower than 1200 kg/m3.
⇑ Corresponding author. Tel.: +886 06 2757575x62832; fax: +886 06 2380421. E-mail address: [email protected] (C.-Y. Huang).
The low weight of LWAs is mostly due to their porous structure, which is produced by bloating during the heating process. Bloating is promoted when the chemical composition follows Riley’s diagram because the raw material includes ions which can form a glassy phase and gas is generated as the glassy phase forms [19]. Riley’s diagram includes SiO2, Al2O3, and flux materials such as Na2O, K2O, Fe2O3, FeO, MgO, and CaO. CaO can also promote a pozzolanic reaction since it reacts with H2O to form Ca(OH)2. Zhu et al. [20], Darvaz and Gunduz [21], and Turanli et al. [22] studied a pozzolanic reaction in which Ca(OH)2 reacted with SiO2 and Al2O3 in incinerated sewage sludge ash to form C–S–H and C–A–H gels. Mun [8] used sewage sludge to produce LWAs for nonstructural concrete and reported that CaO content affects the viscosity of raw materials at high temperatures. However, few studies have reported the effects of the amount of CaO used as the main flux oxide on the properties of LWAs produced from water reservoir sediment. In the present study, various amounts of CaO were added into water reservoir sediment to produce LWAs. The effect of CaO concentration on the physical properties of the LWAs was investigated.
2. Materials and methods The water reservoir sediment was obtained from Shihmen Reservoir in Taiwan. The sediment had a water content of 28% and an ignition loss of 5.57% with a d50 size of 8.49 lm. The chemical composition of the sediment was determined using an X-ray fluorescence spectrometer (XRF, Rigaku). The CaO powders (Shimakyo’s Pure Chemicals) were milled to pass through a No. 100 mesh. The sediment, without drying, was directly mixed with CaO powders, 1% and 5% by weight, by a small cement mixer, respectively. The mixture was then extruded by a vacuum extrusion machine. The extruded bar was cut into small lumps and
0950-0618/$ - see front matter Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.12.034
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Y.-C. Liao, C.-Y. Huang / Construction and Building Materials 25 (2011) 2997–3002
pelletized into 10–20 mm spheres. These spheres were placed a laboratory-scale furnace and calcined for 30 min at a heating rate of 15 °C/min at 1170 °C, 1185 °C, 1200 °C, 1215 °C, and 1230 °C, respectively. When the air inside the furnace cooled to room temperature, the calcined LWAs were characterized using the following procedures. The mineral phases of the raw sediment and the modified sediment were measured by X-ray diffraction (XRD, Siemens D5000). The calcined LWAs were crushed and milled into powders to measure their mineral phases by XRD. The Archimedes method was employed to measure the bulk density and water adsorption after the LWAs were placed in boiling water for 24 h. The bulk density and water adsorption were calculated as follows [23]:
bulk density ¼ W D =ðW S W I Þ Water adsorptionð%Þ ¼ 100ðW S W D Þ=W D
SiO2 and Al2O3 in previous studies [20–22], respectively, no pozzolanic reaction was found in the modified sediment (1% and 5% CaO by weight) in the present study. The mineral phases were still quartz, albite, clinochlore, and muscovite. The relationship between the bulk density and water adsorption at various calcining temperatures is shown in Fig. 3a. The bulk density linearly decreased with increasing temperature. The decreasing trends of samples with 0% and 1% CaO by weight were similar. The bulk densities of samples with 0% and 1% CaO by weight ranged from 1.6 g/cm3 to 1.0 g/cm3 whereas that of the samples with 5% CaO by weight ranged from 2.0 g/cm3 to 1.1 g/ cm3. According to the European Union regulation EN-13055-1, the unit weight of LWAs should be lower than 2000 kg/m3. The
where WD is the dry weight of the calcined LWAs, WS is the 24 h saturated surfacedry weight, and WI is the immersed weight in water. The compressive strength was measured using a material testing system (MTS 810) with a cross head speed of 0.1 mm/s. The compressive strength of the calcined LWAs was calculated using [24,25]:
Compressive strength ¼ 2:8Pc =pX 2 where Pc is the fracture load and X is the diameter of the LWAs. Each recorded testing value was the mean of results from eight samples. The physical properties of LWAs calcined at 1200 °C and 1230 °C were compared to those of a commercial LWA, Leca Strutturale, which has been applied to the production of structural concrete [14]. Finally, an optical microscope and a scanning electron microscope (SEM) were used to observe the microstructure of the LWAs.
3. Results The chemical compositions of sediment measured by XRF are shown in Table 1. The sediment is mainly SiO2 (61.4%), followed by Al2O3 (22.5%) and Fe2O3 (8.6%). The relationship of the chemical composition is plotted in Riley’s diagram in Fig. 1. The raw sediment corresponds to the bloating area in Riley’s diagram. The XRD pattern in Fig. 2 shows that the mineral phases of the raw sediment were quartz, albite, clinochlore, and muscovite. The mineral phases of the sediment modified with CaO, 1% and 5% by weight, respectively, were also measured before the sediment was calcined into LWAs. The mineral phases were found to be the same as those of the raw sediment. Ca(OH)2 was expected to form via the reaction of CaO with the water in the reservoir sediment. Although C–S–H gel and C–A–H gel formed via the reaction of Ca(OH)2 with
Fig. 2. Mineral phases of the raw sediment and the modified sediment.
Table 1 Chemical compositions of Shihmen reservoir sediment. Component
SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
K2O
Composition (wt.%)
61.4
22.7
8.6
0.7
2.0
1.3
3.4
Fig. 1. Relationship of chemical compositions in Riley’s diagram.
Fig. 3. Physical properties of LWAs calcined at various temperatures. (a) Bulk density and water adsorption, and (b) compressive strength.
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Y.-C. Liao, C.-Y. Huang / Construction and Building Materials 25 (2011) 2997–3002 Table 2 Properties of LWAs calcined at 1200 °C and 1230 °C compared with those of a commercial LWA. Lightweight aggregate
Bulk density (g/cm3) Water adsorption (%) Strength of particles (MPa) Strength/unit weight of particles
0 wt.%
1 wt.%
5 wt.%
Leca strutturale
1200 °C
1230 °C
1200 °C
1230 °C
1200 °C
1230 °C
1.29 9.14 6.47 5.02
1.09 20.24 5.58 5.12
1.33 3.24 6.27 4.71
0.96 11.15 3.45 3.59
1.55 2.79 5.07 3.27
1.12 1.89 1.91 1.71
1.3 >7 4.5 3.46
tion of LWAs. Water adsorption was independent of temperature for the samples with 5% CaO by weight. These results are different from those for ordinary LWAs, where water adsorption decreases with increasing bulk density and temperature. The compressive strength of LWAs calcined at various temperatures is shown in Fig. 3b. All compressive strengths were above 1.9 MPa. The compressive strength of the sample with 5% CaO by weight calcined at 1170 °C was higher than those of samples with 0% and 1% CaO by weight calcined at 1170 °C, but lower than those of samples with 0% and 1% CaO by weight calcined at above 1185 °C. Table 2 lists the physical properties of LWAs calcined at 1200 °C and 1230 °C and those of the commercial LWA. The table shows that the LWA with 1% CaO by weight calcined at 1200 °C was better than the commercial LWA, and that CaO addition reduced the ratio of strength to unit weight of particles. In previous studies [14], LWAs with a compressive strength of above 1 MPa were produced into structural concrete. This means that the LWAs obtained in this study can be applied to the production of structural concrete. The compressive strength decreased with increasing temperature and CaO addition. The mineral phases of LWAs without CaO addition after calcining are shown in Fig. 4a. The mineral phases were quartz, sillimanite, Fe2O3, ringwoodite, and corundum. The Fe2O3 phase was not the hematite phase. The mineral phases of the samples with 1% CaO by weight (see Fig. 4b) were the same as those for the samples with 0% CaO by weight. Quartz still existed in the LWAs but its crystallinity decreased with increasing temperature. These results show that the sillimanite phase increased and the ferrosilite phase disappeared at above 1185 °C. Fig. 4c shows the mineral phases of
Fig. 4. Mineral phases of LWAs with various amounts of CaO addition calcined at various temperatures. (a) 0 wt.%, (b) 1 wt.%, and (c) 5 wt.%.
aggregates produced in this study meet this regulation. The results show that bulk density increased with CaO addition. The water adsorption levels of samples with 0% and 1% CaO by weight increased with increasing calcining temperature. They had similar increasing trends although the water adsorption of the samples with 1% CaO by weight was lower than that of the samples without CaO. The trend of the samples with 5% CaO by weight was different from those of the samples with 0% and 1% CaO by weight. The water adsorption levels of the samples with 5% CaO by weight were all below 4%. Finally, CaO addition lowered the water adsorp-
Fig. 5. Optical photographs of sections of LWAs with various amounts of CaO addition. (a) 0 wt.%, (b) 1 wt.%, and (c) 5 wt.%.
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Fig. 6. Microstructure observation of LWAs with various amounts of CaO addition. (a) 0 wt.%, (b) 1 wt.%, and (c) 5 wt.%.
the samples with 5% CaO by weight, which are different from those for samples with 0% and 1% CaO by weight. Quartz still existed, followed by anorthite, Fe2O3, and SiO2. The phases of Fe2O3 and SiO2 were in an oxide phase form rather than in a mineral form. The crystallinity of quartz decreased with increasing temperature, as in samples with 0% and 1% CaO by weight. In all XRD patterns, a small hill was found in the 2h range between 20° and 30°. The crystallinity of quartz decreased with temperature. Cross-sections of the LWAs with 0%, 1%, and 5% CaO by weight after calcining at various temperatures are shown in Fig. 5. The formations of pores in samples with 0% and 1% CaO by weight were similar, and much different from that for the samples with 5% CaO by weight. The pore distributions in samples with 0% and 1% CaO by weight were more uniform and the numbers of pores increased with increasing calcining temperature. In contrast, the pores in the samples with 5% CaO by weight had a random size which increased with calcining temperature. Some pores in the samples with 5% CaO by weight calcined at 1230 °C were larger than 4 mm, whereas the pores in samples with 0% and 1% CaO by weight were smaller than 2 mm. The surface inside pores in the
samples with 5% CaO by weight was glossy and smooth, as opposed to those in samples with 0% and 1% CaO by weight. The bottom of the samples with 5% CaO by weight was brown and red-bricked. The microstructure, observed by SEM, is shown in Fig. 6. The pores in samples with 0% and 1% CaO by weight were connected to each other. Pores larger than 0.4 mm were also found at a lower calcining temperature (1170 °C), whereas no pores larger than 0.4 mm were found in the samples with 5% CaO by weight. When the CaO addition was increased to 5% by weight, the surface inside pores became smooth and the small pores were unconnected. Cracks formed in the samples with 5% CaO by weight at the boundary between pores and the matrix.
4. Discussion CaO is considered a glass-forming oxide that can promote bloating behavior to form a porous structure and that can induce a pozzolanic reaction. In this study, a pozzolanic reaction was expected to develop with the addition of CaO. However, the XRD pattern of
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the modified sediment shows no C–S–H gel, C–A–H gel, portlandite phase, or lime phase; the mineral phases of the modified sediment are the same as those for the raw sediment (quartz, albite, muscovite, and clinochlore). This may be due to CaO reacting with carbonate ions within the water of sediment, since sediment is a kind of weathering product, with many carbonate compounds precipitating, resulting in CaO reacting with H2O and CO2 ions to 3 form amorphous CaCO3. This explains why no pozzolanic reaction occurred and why no lime phase or calcite phase was found in the XRD pattern. A comparison of the XRD pattern of the raw material with the data of chemical compositions indicates that iron ions mainly exist in the clinochlore structure due to the replacement of magnesium ions, and that sodium ions as well as potassium ions exist in the albite and muscovite structures. The albite and muscovite structures decomposed and transformed into other mineral phases when the temperature was increased to over 800 °C, which is how sillimanite, ringwoodite, corundum, ferrosilite, and iron oxide formed. Moreover, the increasing temperature also decreased the intensity of the quartz phase due to the quartz reacting and forming a glassy phase. This is confirmed by a small hill, indicating the existence of an amorphous structure, between 20° and 30° in the XRD patterns. Since high temperature leads to the transformation of mineral phases, the anorthite phase formed after calcining. With 5% CaO by weight, the number of calcium ions is sufficient to react with other phases from the decomposition of albite and muscovite to form anorthite. The phases that did not react with CaO, mainly chinochlore and muscovite, may make iron oxide and silicon oxide segregate into a pure compound state rather than a mineral state, like hematite and quartz. SEM photographs show that the increase of water adsorption with calcining temperature in samples with 0% and 1% CaO by weight is caused by pore connections. The samples without CaO had water adsorption of up to 20% and the samples with 1% CaO by weight had water adsorption of up to 11%. However, for the samples with 5% CaO by weight, the water adsorption levels were all below 4%. The increasing amount of CaO resulted in the formation of a glassy phase that sealed pores and prevented connections between pores. This explains why the water adsorption of samples with 5% CaO by weight is much lower than those of samples with 0% and 1% CaO by weight, in which calcining temperature promoted pore connections. However, pores in the samples with 5% CaO by weight initially began to form at 1215 °C. This means that CaO addition does not promote bloating as expected. It seems that CaO as a flux oxide is not good at promoting bloating but good at lowering water adsorption of LWAs by sealing pores. Although bulk density decreased with increasing calcining temperature and ranged from 2.0 g/cm3 to 1.0 g/cm3, water adsorption did not increase with increasing bulk density and calcining temperature. The water adsorption of the samples with 5% CaO by weight did not increase with decreasing bulk density. The results of compressive strength tests of LWAs also show that CaO addition weakens compressive strength. This may be caused by the excess amount of the glassy phase from CaO addition and by cracks that form between pores and the matrix. This explains why the samples with 5% CaO by weight are much weaker than samples with 0% and 1% CaO by weight; the compressive strength of the samples with 5% CaO by weight calcined at 1230 °C was only 1.91 MPa. Although the bulk densities of samples with 0% and 1% CaO by weight are lower than that of the samples with 5% CaO by weight, the compressive strengths are higher. This is very different from other LWAs, for which compressive strength decreases with decreasing bulk density. A comparison with a commercial LWA shows that the optimal CaO concentration is 1% by weight. At 1200 °C, the bulk density is close to that of the commercial product and the low water
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adsorption is good for further processing. The ratio of strength to the unit weight of particles for the samples with 1% CaO by weight calcined at 1200 °C (4.71) is higher than that of the commercial product (3.46). 5. Conclusion The LWAs produced in this study meet the European Union regulation of the unit weight of LWAs being below 2000 kg/m3. They also satisfy the strength demand for structural concrete. The properties of samples with 1% CaO by weight calcined at 1200 °C achieve the performance of a commercial product. CaO addition does not promote the pozzolanic reaction and can lower water adsorption of LWAs, which is due to an excess amount of a glassy phase sealing pores; however, CaO addition weakens compressive strength. The decrease in bulk density with CaO addition of 0% and 1% by weight is caused by the numbers of pores rather than pore growth. Pore growth with increasing calcining temperature results in a decrease of bulk density with the addition of 5% CaO by weight. For samples with 5% CaO by weight, the mineral phases of LWAs were anorthite, quartz, Fe2O3, and SiO2, with Fe2O3 and SiO2 forming in a non-mineral state. References [1] Chen HJ, Wang SY, Tang CW. Reuse of incineration fly ashes and reaction ashes for manufacturing lightweight aggregate. Constr Build Mater 2010;24:46–55. [2] Cheeseman CR, Monteiro da Rocha S, Sollars C, Bethanis S, Boccaccini AR. Ceramic processing of incinerator bottom ash. Waste Manage 2003;23:907–16. [3] Cheeseman CR, Makinde A, Bethanis S. Properties of lightweight aggregate produced by rapid sintering of incinerator bottom ash. Resour Conserv Recycl 2005;43:147–62. [4] Anagostopoulos IM, Stivanakis VE. Utilization of lignite power generation residues for the production of lightweight aggregates. J Hazard Mater 2009;163:329–36. [5] Liaw CT, Chang HL, Hsu WC, Huang CR. A novel method to reuse paper sludge and co-generation ashes from paper mill. J Hazard Mater 1998;58:93–102. [6] Chang FC, Lo SL, Lee MY, Ko CH, Lin JD, Huang SC, et al. Leachability of metals from sludge-based artificial lightweight aggregate. J Hazard Mater 2007;14:98–105. [7] Laursen K, White TJ, Cresswell DJF, Wainwright PJ, Barton JR. Recycling of an industrial sludge and marine clay as light-weight aggregates. J Environ Manage 2006;80:208–13. [8] Mun KJ. Development and tests of lightweight aggregate using sewage sludge for nonstructural concrete. Constr Build Mater 2007;21:1583–8. [9] Wang X, Jin Y, Wang Z, Nie Y, Huang Q, Wang Q. Development of lightweight aggregate from dry sewage sludge and coal ash. Waste Manage 2009;29:1330–5. [10] Mueller A, Sokolova SN, Vereshagin VI. Characteristics of lightweight aggregates from primary and recycled raw materials. Constr Build Mater 2008;22:703–12. [11] de’Gennaro R, Cappelletti P, Cerri G, de’Gennaro M, Dondi M, Langella A. Zeolitic tuffs as raw materials for lightweight aggregates. Appl Clay Sci 2004;25:71–81. [12] de’Gennaro R, Cappelletti P, Cerri G, de’Gennaro M, Dondi M, Langella A. Neapolitan yellow tuff as raw material for lightweight aggregates in lightweight structural concrete production. Appl Clay Sci 2005;28:309–19. [13] de’Gennaro R, Cappelletti P, Cerri G, de’Gennaro M, Dondi M, Graziano SF, et al. Campanian Ignimbrite as raw material for lightweight aggregates. Appl Clay Sci 2007;37:115–26. [14] de’Gennaro R, Langella A, D’Amore M, Dondi M, Colella A, Cappelletti P, et al. Use of zeolite-rich rocks and waste materials for the production of structural lightweight concretes. Appl Clay Sci 2008;41:61–72. [15] Chiou IJ, Wang KS, Chen CH, Lin YT. Lightweight aggregate made from sewage sludge and incinerated ash. Waste Manage 2006;26:1453–61. [16] Huang SC, Chang FC, Lo SL, Lee MY, Wang CF, Lin JD. Production of lightweight aggregates from mining residues, heavy metal sludge, and incinerator fly ash. J Hazard Mater 2007;144:52–8. [17] González-Corrochano B, Alonso-Azcárate J, Rodas M. Characterization of lightweight aggregates manufactured from washing aggregate sludge and fly ash. Resour Conserv Recycl 2009;53:571–81. [18] Wei YL, Yang JC, Lin YY, Chuang SY, Wang HP. Recycling of harbor sediment as lightweight aggregate. Mar Pollut Bull 2008;57:867–72. [19] Riley CM. Relation of chemical process to the bloating clay. J Am Ceram Soc 1950;34:121–8. [20] Zhu WH, Yin YF, Jiang LH, Che LM. Study of micropore size distribution and its effect on the strength of silica fume cement phase. J Build Mater 2004;7:14–8.
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