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The issue on the disposal of water treatment plant (WTP) sludge has been raised in recent years. Recycling technology has been considered as an alternative method to solve the disposal problem. The purpose of this study was to investigate the feasibility of recycling WTP sludge as an alternative raw material in AAC production. Mechanical, physical and mineralogical analyses were performed to determine the influence of WTP sludge replacement on the AAC products. Different water-to-solid ratios were studied to examine the performance of WTP sludge-containing AAC. Pre-treatments of WTP sludge with the calcination processes were examined to improve the final properties of AAC product.

The experimental results showed WTP sludge had a high moisture content of 65.7wt.% and a LOI of 16.5wt.%. The main chemical compositions of WTP sludge were SiO2, Al2O3, and Fe2O3. WTP sludge contains some phases, such as quartz, hematite and albite. It was observed that WTP sludge contained high amount of organic matters.

The addition of WTP sludge was shown favorable to the tobermorite formation. The tobermorite formation can be enhanced if the C/S ratio was adjusted because tobermorite formation was very sensitive to the C/S ratio. The compressive strength development in AAC product was shown mainly due to the formation of tobermorite and filling of the formed tobermorite in space between raw materials. The replacement ratios of WTP sludge at 5-25% was favorable to compressive strength development. However excessive replacement ratios of WTP sludge inhibited the tobermorite formation thus having significant effects on the reduction of compressive strength.

The experimental results showed that NaOH(aq) had significant effects to decrease the compressive strength of AAC. The addition of alkali in the form of NaOH(aq)caused significant reduction in density and compressive strengths of AAC due to the less dense microstructures. Neutralization reactions by Na ions caused higher volume expansion and swelling hydration products. In a high alkali concentration, similar minerals patterns were formed. However, less pore formed and non-uniform hydration products were found, which caused the reduction in compressive strength. Hydrogarnet was formed phase in AAC with Al/(Si+Al) ratio higher than 0.04. The amount of hydrogarnet increased with increasing of Al/(Si+Al) ratio. The hydrogarnet formation in AAC specimens leads to decreasing of the density followed by reducing the compressive strength.

Lastly, the strength developments in AAC products depend on the density of AAC, the formation of tobermorite and filling of the formed tobermorite in space between particles of AAC specimens. The results showed that The WTP sludge can substitute primary raw materials for AAC production. It is suggested that recycling WTP sludge for production of AAC can reduce consumption of natural resources thus solve the problem of waste disposal.

The calcination process at temperature 900°C for 30 minutes is recommended to reduce organic matters in WTP sludge and to transform silica into amorphous silica that lead to the increase silica reactivity. Activator of Na2CO3 was effective in the transformation into amorphous silica. However, the additions of Na2CO3 tend to increasing Na+ concentration in WTP sludge ashes. Using WTP sludge ash in the AAC production can obtain lighter products, which also have the higher compressive strength. The highest performance factor value was obtained due to the increase of formed tobermorite and the enhancements pore filling degree.

Al-Wakeel, Ei & El-Korashy, Sa (1996), "Reaction mechanism of the hydrothermally treated CaO-SiO2-Al2O3 and CaO-SiO2-Al2O3-CaSO4 systems". Journal of materials science, 31, 1909-1913.
Albayrak, M., Yörükoğlu, A., Karahan, S., Atlıhan, S., Yılmaz Aruntaş, H. & Girgin, İ. (2007), "Influence of zeolite additive on properties of autoclaved aerated concrete". Building and environment, 42, 3161-3165.
Alp, A & Aydin, Ao (1998), "Effect of alkaline additives on the thermal properties of bauxite". Journal of thermal analysis and calorimetry, 53, 141-149.
Arabi, N. & Jauberthie, R. (2012), "Calcium Silicate Materials: Substitution of Hydrated Lime by Ground Granulated Blast Furnace Slag in Autoclaving Conditions". Journal of Materials in Civil Engineering, 24, 1230-1236.
Aroni, In S 1993. Autoclaved aerated concrete: properties, testing and design: RILEM recommended practice: RILEM Technical Committees 78-MCA and 51-ALC, CRC PressI Llc.
Bayuseno, Ap, Schmahl, Ww & Müllejans, T. (2009), "Hydrothermal processing of MSWI Fly Ash-towards new stable minerals and fixation of heavy metals". Journal of hazardous materials, 167, 250-259.
Bulteel, D., Garcia-Diaz, E., Vernet, C. & Zanni, H. (2002), "Alkali–silica reaction: a method to quantify the reaction degree". Cement and concrete research, 32, 1199-1206.
Chen, H.X., Ma, X. & Dai, H.J. (2010), "Reuse of water purification sludge as raw material in cement production". Cement and Concrete Composites, 32, 436-439.
Coleman, N.J. & Brassington, D.S. (2003), "Synthesis of Al-substituted 11 Å tobermorite from newsprint recycling residue: a feasibility study". Materials research bulletin, 38, 485-497.
Connan, H., Klimesch, D., Ray, A. & Thomas, P. (2006), "Thermal characterisation of autoclaved cement made with alumina-silica rich industrialwaste". Journal of thermal analysis and calorimetry, 84, 521-525.
Connan, H., Ray, A., Thomas, P. & Guerbois, J.P. (2007), "Effect of autoclaving temperature on calcium silicate-based building products containing clay-brick waste". Journal of thermal analysis and calorimetry, 88, 115-119.
Hartmann, A. & Buhl, J.C. (2012), "Reaction Behavior of Autoclaved Aerated Concrete and Sodium Aluminate at Mild Alkaline and Acid Hydrothermal Conditions: Model for AAC Recycling". Journal of Materials in Civil Engineering, 24, 441-450.
Hauser, A., Eggenberger, U. & Mumenthaler, T. (1999), "Fly ash from cellulose industry as secondary raw material in autoclaved aerated concrete". Cement and concrete research, 29, 297-302.
Hillier, S & Lumsdon, Dg (2008), "Distinguishing opaline silica from cristobalite in bentonites: a practical procedure and perspective based on NaOH dissolution". Clay Minerals, 43, 477-486.
Holt, Erika & Raivio, Paula (2005), "Use of gasification residues in aerated autoclaved concrete". Cement and concrete research, 35, 796-802.
Houston, J, Maxwell, Robert S & Carroll, S (2009), "Transformation of meta-stable calcium silicate hydrates to tobermorite: reaction kinetics and molecular structure from XRD and NMR spectroscopy". Geochemical transactions, 10, 1.
Huang, X., Ni, W., Cui, W., Wang, Z. & Zhu, L. (2012), "Preparation of autoclaved aerated concrete using copper tailings and blast furnace slag". Construction and Building Materials, 27, 1-5.
Isu, N., Maenami, H. & Ishida, Eh (2004), "Hydrothermally Solidified Water Purification Sludge with High Specific Surface Area". J. Ceram. Soc. Japan, Suppl, 112, S1364-1351.1367.
Isu, N., Teramura, S., Ishida, H. & Mitsuda, T. (1994), "Mechanical Property Evolution during Autoclaving Process of Aerated Concrete Using Slag: II, Fracture Toughness and Microstructure". Journal of the American Ceramic Society, 77, 2093-2096.
Jenkins, Ron & Snyder, Robert L (1996), "Diffraction Theory". Introduction to X-ray Powder Diffractometry, Volume 138, 47-95.
Jing, Z., Jin, F., Hashida, T., Yamasaki, N. & Ishida, E.H. (2008a), "Influence of additions of coal fly ash and quartz on hydrothermal solidification of blast furnace slag". Cement and Concrete Research, 38, 976-982.
Jing, Z., Jin, F., Hashida, T., Yamasaki, N. & Ishida, E.H. (2008b), "Influence of tobermorite formation on mechanical properties of hydrothermally solidified blast furnace slag". Journal of Materials Science, 43, 2356-2361.
Jing, Z., Jin, F., Hashida, T., Yamasaki, N. & Ishida, H. (2007a), "Hydrothermal solidification of blast furnace slag by formation of tobermorite". Journal of materials science, 42, 8236-8241.
Jing, Z., Matsuoka, N., Jin, F., Hashida, T. & Yamasaki, N. (2007b), "Municipal incineration bottom ash treatment using hydrothermal solidification". Waste management, 27, 287-293.
Jing, Z., Ran, X., Jin, F. & Ishida, E.H. (2010), "Hydrothermal solidification of municipal solid waste incineration bottom ash with slag addition". Waste management, 30, 1521-1527.
Jozefaciuk, G, Muranyi, A & Alekseeva, T (2002), "Effect of extreme acid and alkali treatment on soil variable charge". Geoderma, 109, 225-243.
Kalousek, G.L. (2006), "Crystal chemistry of hydrous calcium silicates: I, Substitution of aluminum in lattice of tobermorite". Journal of the American Ceramic Society, 40, 74-80.
Karakurt, C., Kurama, H. & Topçu, İ.B. (2010), "Utilization of natural zeolite in aerated concrete production". Cement and Concrete Composites, 32, 1-8.
Khatib, Jm & Wild, S (1996), "Pore size distribution of metakaolin paste". Cement and Concrete Research, 26, 1545-1553.
Khursheed, Anjam 2011. Scanning electron microscope optics and spectrometers, World Scientific Publishing Company.
Kim, Jong-Wan & Lee, Hae-Geon (2001), "Thermal and carbothermic decomposition of Na2CO3 and Li2CO3". Metallurgical and Materials Transactions B, 32, 17-24.
Klimesch, D.S., Ray, A. & Guerbois, J.P. (2002), "Differential scanning calorimetry evaluation of autoclaved cement based building materials made with construction and demolition waste". Thermochimica acta, 389, 195-198.
Klimesch, Ds & Ray, A. (1998a), "Effects of quartz particle size on hydrogarnet formation during autoclaving at 180° c in the CaO-Al2O3-SiO2-H2O system". Cement and concrete research, 28, 1309-1316.
Klimesch, Ds & Ray, A. (1998b), "Hydrogarnet formation during autoclaving at 180° C in unstirred metakaolin-lime-quartz slurries". Cement and concrete research, 28, 1109-1117.
Kosminski, Adam 2001. Reactions between sodium and silicon minerals during gasification of low-rank coal, University of Adelaide, Department of Chemical Engineering.
Kuo, Yi-Ming, Wang, Jian-Wen, Chao, How-Ran, Wang, Chih-Ta & Chang-Chien, Guo-Ping (2008), "Effect of cooling rate and basicity during vitrification of fly ash: Part 2. On the chemical stability and acid resistance of slags". Journal of hazardous materials, 152, 554-562.
Kurama, H., Topçu, İ.B. & Karakurt, C. (2009), "Properties of the autoclaved aerated concrete produced from coal bottom ash". Journal of materials processing technology, 209, 767-773.
Letterman, Raymond D 1999. Water quality and treatment: a handbook of community water supplies, McGraw-hill New York.
Maenami, Hiroki, Watanabe, Osamu, Ishida, Hideki & Mitsuda, Takeshi (2000), "Hydrothermal solidification of kaolinite–quartz–lime mixtures". Journal of the American Ceramic Society, 83, 1739-1744.
Matsui, K., Kikuma, J., Tsunashima, M., Ishikawa, T., Matsuno, S., Ogawa, A. & Sato, M. (2011), "In situ time-resolved X-ray diffraction of tobermorite formation in autoclaved aerated concrete: Influence of silica source reactivity and Al addition". Cement and Concrete Research, 41, 510-519.
Meller, N., Kyritsis, K. & Hall, C. (2009), "The mineralogy of the CaO–Al2O3–SiO2–H2O (CASH) hydroceramic system from 200 to 350° C". Cement and Concrete Research, 39, 45-53.
Mitsuda, Takeshi, Sasaki, Kaori & Ishida, Hideki (1992), "Phase evolution during autoclaving process of aerated concrete". Journal of the American Ceramic Society, 75, 1858-1863.
Monteiro, Sn, Alexandre, J, Margem, Ji, Sánchez, R & Vieira, Cmf (2008), "Incorporation of sludge waste from water treatment plant into red ceramic". Construction and Building Materials, 22, 1281-1287.
Mostafa, Ny (2005), "Influence of air-cooled slag on physicochemical properties of autoclaved aerated concrete". Cement and concrete research, 35, 1349-1357.
Narayanan, N. & Ramamurthy, K. (2000a), "Microstructural investigations on aerated concrete". Cement and concrete research, 30, 457-464.
Narayanan, N. & Ramamurthy, K. (2000b), "Structure and properties of aerated concrete: a review". Cement and Concrete Composites, 22, 321-329.
Pera, Jean & Amrouz, Achène (1998), "Development of highly reactive metakaolin from paper sludge". Advanced Cement Based Materials, 7, 49-56.
Rodríguez, N.H., Ramírez, S.M., Varela, Mt, Guillem, M., Puig, J., Larrotcha, E. & Flores, J. (2010), "Re-use of drinking water treatment plant (DWTP) sludge: Characterization and technological behaviour of cement mortars with atomized sludge additions". Cement and Concrete Research, 40, 778-786.
Şahin, Remzi, Demirboğa, Ramazan, Uysal, Habib & Gül, Rüstem (2003), "The effects of different cement dosages, slumps and pumice aggregate ratios on the compressive strength and densities of concrete". Cement and concrete research, 33, 1245-1249.
Shan, C., Jing, Z., Pan, L., Zhou, L., Pan, X. & Lu, L. (2011), "Hydrothermal solidification of municipal solid waste incineration fly ash". Research on Chemical Intermediates, 37, 551-565.
Shvarzman, Akovler, Kovler, K, Grader, Gs & Shter, Ge (2003), "The effect of dehydroxylation/amorphization degree on pozzolanic activity of kaolinite". Cement and Concrete Research, 33, 405-416.
Skoog, Douglas A, Holler, F James & Nieman, Timothy A (1998), "Principles of instrumental analysis".
Smaoui, N, Bérubé, Ma, Fournier, Benoit, Bissonnette, B & Durand, B (2005), "Effects of alkali addition on the mechanical properties and durability of concrete". Cement and Concrete Research, 35, 203-212.
Spence, Roger D & Shi, Caijun 2004. Stabilization and solidification of hazardous, radioactive, and mixed wastes, CRC press.
Steudel, A, Batenburg, Lf, Fischer, Hr, Weidler, Pg & Emmerich, K (2009), "Alteration of swelling clay minerals by acid activation". Applied Clay Science, 44, 105-115.
Taylor, Harry Fw 1997. Cement chemistry, Thomas Telford Services Ltd.
Urhan, S. (1987), "Alkali silica and pozzolanic reactions in concrete. Part 1: Interpretation of published results and an hypothesis concerning the mechanism". Cement and concrete research, 17, 141-152.
Wang, Kejin, Shah, Surendra P & Mishulovich, Alexander (2004), "Effects of curing temperature and NaOH addition on hydration and strength development of clinker-free CKD-fly ash binders". Cement and concrete research, 34, 299-309.
Watanabe, O., Kitamura, K., Maenami, H. & Ishida, H. (2001), "Hydrothermal treatment of a silica sand complex with lime". Journal of the American Ceramic Society, 84, 2318-2322.
Webb, Paul A (2001), "An introduction to the physical characterization of materials by mercury intrusion porosimetry with emphasis on reduction and presentation of experimental data". Micromeritics Instrument Corp, Norcross, Georgia.
Wittmann, Folker H 1992. Advances in autoclaved aerated concrete, AA Balkema.